CN115528667A - Direct-current micro-grid cluster control system and multi-stage cooperative control method thereof - Google Patents
Direct-current micro-grid cluster control system and multi-stage cooperative control method thereof Download PDFInfo
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- H—ELECTRICITY
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- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
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- H02J2300/20—The dispersed energy generation being of renewable origin
- H02J2300/22—The renewable source being solar energy
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Abstract
The invention discloses a direct current micro-grid cluster control system and a multi-stage cooperative control method thereof, wherein the method comprises the following steps: selecting one electrical unit from each direct current microgrid as a main unit; when the communication condition of the master unit is triggered, the master units among the direct current micro grids perform communication, and the communication of the slave units in the direct current micro grids is synchronously triggered; and the supply and demand balance of the direct-current microgrid cluster is achieved by carrying out hierarchical cooperative control by utilizing information communicated among the main units, the main units and the slave units. The invention adopts a master-slave distributed coordination control mechanism, so that the master unit and the slave unit can jointly compensate power/current sharing mismatch and SOC imbalance of the energy storage unit in the direct current microgrid, the coordination between the master units can realize power/current distribution and SOC balance of the energy storage unit of the whole cluster system, and the reliability of the system is improved.
Description
Technical Field
The invention belongs to the technical field of direct current micro-grids, and particularly relates to a direct current micro-grid cluster, a multi-stage cooperative control method of the direct current micro-grid cluster and a control system.
Background
The direct-current micro-grid is a micro-grid formed by direct current, is an important component of a future intelligent power distribution and utilization system, and has important significance for promoting energy conservation and emission reduction and realizing sustainable development of energy. Compared with an alternating-current microgrid, the direct-current microgrid can more efficiently and reliably receive distributed renewable energy power generation systems such as wind and light, energy storage units, electric vehicles and other direct-current power loads.
The existing direct current micro-grid has the following defects in the topological structure and the control method:
(1) The direct-current micro-grid is an effective method capable of absorbing new energy and improving the utilization rate of the new energy, but the new energy has the characteristics of non-schedulability, random fluctuation and reverse peak regulation; meanwhile, the comprehensive load also has random fluctuation and instability; the uncertainty of the operation scheduling of the direct-current micro-grid system is increased by the two methods, and the stable operation of various working conditions is difficult to guarantee by the existing control method;
(2) The cooperative control problem on the demand side is multi-energy, multi-mode, multi-level, multi-target and non-linear, and the existing optimization method cannot balance the contradiction among control targets and cannot ensure the coordination among different components;
(3) Most of new energy is distributed, the larger the information sharing span among the components is, the existing coordination control optimization method cannot ensure the global property and accuracy of information acquisition, and the convergence speed is relatively slow.
Disclosure of Invention
In view of this, the present invention provides a dc microgrid cluster control system and a multi-stage cooperative control method thereof, which ensure that each unit in a cluster works coordinately and stably, achieve power/current distribution and energy storage SOC (state of charge) balance of the whole cluster system, and improve reliability of the system.
In order to solve the technical problems, the technical scheme of the invention is to provide a direct current microgrid cluster which comprises a plurality of direct current microgrids, wherein each direct current microgrid comprises a plurality of electric units, and each electric unit is an energy storage unit or a photovoltaic unit; the electric units in each direct current microgrid are provided with only one main unit at the same time, and the rest are slave units; the direct current microgrid can only communicate with the master unit, and the master unit and the slave unit in the direct current microgrid as well as the slave unit and the slave unit can communicate with each other.
The invention also provides a multistage cooperative control method of the direct current microgrid cluster, which is applied to the direct current microgrid cluster and comprises the following steps:
selecting one electrical unit from each direct current microgrid as a main unit;
when the communication condition of the master unit is triggered, the master units among the direct current micro grids communicate, and the communication of the slave units in the direct current micro grids is synchronously triggered;
and the supply and demand balance of the direct-current microgrid cluster is achieved by carrying out hierarchical cooperative control by utilizing information communicated among the main units, the main units and the slave units.
As an improvement, the method for selecting one electrical unit from each dc microgrid as a main unit includes:
all the electric units in the direct current microgrid are initialized to be slave units, and the slave units can receive heartbeat signals from the master units;
when a slave unit receives the heartbeat signal of the main unit and times out, the slave unit is used as a competitor to initiate voting;
the contestants vote themselves after updating the numbers of the contestants in due periods, and initiate voting invitations to other slave units in the direct current microgrid, wherein the voting invitations are accompanied by numbers of the contestants in due periods;
the contestants count the votes obtained by themselves, if the number of the votes obtained exceeds half, the contestants are taken as main units, and the voting is finished;
if the contestant receives the heartbeat signal from the master unit during the time the vote is initiated, the vote is stopped and the master unit is re-used as the slave unit.
As a further improvement, the slave unit casts votes to the first candidate initiating a voting invitation to itself; if the tenure number of the candidate is smaller than the tenure number of the candidate, refusing voting; if the candidate finally selects the master unit, the own tenure number is updated to the tenure number of the candidate.
As another further improvement, the expiration number is monotonically increasing; if the random number of the main unit is smaller than that of any other electric unit, the main unit updates the random number to the maximum random number value in the direct current microgrid and takes the random number as a slave unit again; and if the slave unit deadline number is smaller than the deadline number of any other electric unit, the slave unit updates the deadline number to the maximum deadline number value in the direct current microgrid.
As an improvement, the communication trigger condition of the master unit is:
；
wherein,
；
in the formula,
the deviation between the voltage observed value and the voltage reference value is obtained;
for the moment of triggering
And of the previous moment
A deviation of (a);
modulo a relationship matrix between the master units; b k Is the weight between the main cell and the voltage reference value; l is 0 Represents a laplace matrix; b is 0 Representing a weight matrix between the main cells and the voltage reference values,
；
and
are adjustment coefficients within a specified range.
As an improvement, the hierarchical cooperative control method comprises a photovoltaic unit control method and an energy storage unit control method;
the photovoltaic control method comprises a photovoltaic main unit control strategy and a photovoltaic slave unit control strategy;
the energy storage unit control method comprises an energy storage main unit control strategy and an energy storage slave unit control strategy.
As an improvement, the photovoltaic slave control strategy comprises:
carrying out PI control on the difference between the reference value of the inner ring control current and the output current of the photovoltaic slave unit;
carrying out pulse width modulation on the result of PI control;
controlling the duty ratio of the pulse width modulation result to obtain a control signal, and controlling the output voltage of the photovoltaic slave unit through the control signal;
when no energy storage unit participates in the same direct current microgrid, the method for obtaining the reference value of the inner loop control current comprises the following steps:
inputting the droop control coefficient and the output current of the photovoltaic slave unit, the droop control coefficient and the output current of the photovoltaic master unit corresponding to the photovoltaic slave unit into a photovoltaic slave unit current control function to obtain a current state quantity;
inputting the voltage observed value of the photovoltaic slave unit and the voltage observed value of the photovoltaic master unit corresponding to the photovoltaic slave unit into a photovoltaic slave unit voltage control function to obtain a voltage state quantity;
integrating the current state quantity and the voltage state quantity;
and (3) performing the operation: the integrated result + (voltage observed value of the photovoltaic master unit corresponding to the photovoltaic slave unit-voltage observed value of the photovoltaic slave unit) -droop control output value;
performing PI control on the calculated result to obtain an inner loop control current reference value;
when energy storage units participate in the same direct-current microgrid, the method for obtaining the reference value of the inner-loop control current comprises the following steps:
carrying out maximum power point tracking control on the output voltage and the output current of the photovoltaic slave unit to obtain an outer ring control voltage reference value;
and PI control is carried out on the difference between the outer ring control voltage reference value and the output voltage of the photovoltaic slave unit to obtain an inner ring control current reference value.
As an improvement, the photovoltaic slave unit voltage control function is
Wherein k represents a direct-current microgrid k in the direct-current microgrid cluster; i represents a photovoltaic slave unit i in the direct current microgrid k;
is a voltage state quantity;
deriving the voltage observation;
is a voltage regulation factor;
the connection relation between the photovoltaic slave unit i and the photovoltaic slave unit j is 1 if the photovoltaic slave unit i and the photovoltaic slave unit j are connected, otherwise, the connection relation is 0;
is a voltage observation;
the voltage observed value of the photovoltaic slave unit j in the direct-current micro-grid k is obtained;
for the weight of the relationship between master and slave units, if the slave unit has access to the master unit
Is 1, otherwise is 0;
the voltage observed value of the photovoltaic main unit in the direct current micro-grid k is obtained;
the photovoltaic slave unit current control function is
Wherein k represents a direct-current microgrid k in the direct-current microgrid cluster; i represents a photovoltaic slave unit i in the direct current microgrid k;
is a current state quantity;
a current regulation factor;
the connection relation between the photovoltaic slave unit i and the photovoltaic slave unit j is shown;
in order to control the droop control coefficient,
to output a current;
for the droop control coefficient of the photovoltaic slave unit j in the direct current microgrid k,
the output current of the photovoltaic slave unit j in the direct current microgrid k is;
the droop control coefficient of the photovoltaic main unit in the direct current microgrid k is obtained;
and (4) outputting current of the photovoltaic main unit in the direct current microgrid k.
As an improvement, the photovoltaic master unit control strategy comprises:
performing PI control on the difference between the reference value of the inner ring control current and the output current of the photovoltaic main unit;
carrying out pulse width modulation on the result of PI control;
controlling the duty ratio of the pulse width modulation result to obtain a control signal, and controlling the output voltage of the photovoltaic main unit through the control signal;
when no energy storage unit participates in the same direct current microgrid, the method for obtaining the reference value of the inner loop control current comprises the following steps:
inputting droop control coefficients and output currents of other photovoltaic main units in the cluster into a current control function of the photovoltaic main units to obtain current state quantities;
inputting voltage observed values of other photovoltaic main units and voltage reference values of the photovoltaic main units in the cluster into a photovoltaic slave unit voltage control function to obtain voltage state quantities;
integrating the sum of the current state quantity and the voltage state quantity;
and (3) performing the operation: voltage reference value of the photovoltaic main cell + (result of integration-droop control output value) -port voltage of the photovoltaic main cell;
performing PI control on the calculated result to obtain an inner loop control current reference value;
when energy storage units participate in the same direct-current microgrid, the method for obtaining the reference value of the inner-loop control current comprises the following steps:
carrying out maximum power point tracking control on the output voltage and the output current of the photovoltaic main unit to obtain an outer ring control voltage reference value;
and PI control is carried out on the difference between the reference value of the outer ring control voltage and the output voltage of the photovoltaic main unit to obtain the reference value of the inner ring control current.
As an improvement, the photovoltaic main unit voltage control function is
Wherein k represents a direct-current microgrid k in the direct-current microgrid cluster; 0 represents a photovoltaic main unit in the direct current microgrid k;
is a voltage state quantity;
deriving the voltage observation;
is a voltage regulation factor;
the connection relation between the main unit of the direct current microgrid k and the photovoltaic main unit of the direct current microgrid l is 1 if the connection exists, or 0 if the connection does not exist;
is a voltage observation;
voltage observed values of photovoltaic main units of other direct current micro-grids l in the cluster are obtained;
for weighting the relationship between the main cells and the voltage reference value, if the main cells have access to the voltage reference value
Is 1, otherwise is 0;
is a voltage reference value;
the photovoltaic main unit current control function is
Wherein k represents a direct-current microgrid k in the direct-current microgrid cluster; 0 represents a photovoltaic main unit in the direct current microgrid k;
is a current state quantity;
is a current regulation factor;
the connection relation between the main unit of the direct current microgrid k and the main unit of the direct current microgrid l is 1 if the connection exists, or 0 if the connection does not exist;
is a droop control coefficient;
is an output current;
a droop control coefficient for another photovoltaic main unit in the cluster;
is the output current of another photovoltaic main unit in the cluster.
As an improvement, the control strategy of the energy storage slave unit is as follows:
when the energy storage slave unit participates in the direct-current microgrid, PI control is carried out on the difference between the reference value of the inner-loop control current and the output current of the energy storage slave unit;
carrying out pulse width modulation on the result of PI control;
controlling the duty ratio of the pulse width modulation result to obtain a control signal, and controlling the output voltage of the energy storage slave unit through the control signal;
the method for obtaining the reference value of the inner loop control current comprises the following steps:
inputting voltage observed values of the energy storage main units in the same direct-current microgrid and voltage observed values of other energy storage slave units in the same direct-current microgrid into a voltage control function of the energy storage slave units to obtain voltage state quantities;
inputting state variables of other energy storage slave units in the same direct-current microgrid and state variables of an energy storage master unit in the same direct-current microgrid into a power control function of the energy storage slave units to obtain power state quantities;
integrating the sum of the voltage state quantity and the power state quantity;
and (3) carrying out operation: the result of the integration + (voltage observation-droop control output-port voltage value);
and performing PI control on the calculated result to obtain an inner loop control current reference value.
As an improvement, the energy storage slave unit voltage control function is
Wherein k represents a direct-current microgrid k in the direct-current microgrid cluster; i represents an energy storage slave unit i in the direct current micro-grid k;
is a voltage state quantity;
deriving a voltage observation;
is a voltage regulation factor;
the connection relation between the energy storage slave unit i and the energy storage slave unit j is 1 if the energy storage slave unit i and the energy storage slave unit j are connected, otherwise, the connection relation is 0;
is a voltage observation;
the voltage observed value of the energy storage slave unit j in the direct current micro-grid k is obtained;
as a weight of the relationship between the master and slave units, if accessible
Is 1, otherwise is 0;
the voltage observed value of the energy storage main unit in the direct current microgrid k is obtained;
the energy storage slave unit power control function is
Wherein k represents a direct-current microgrid k in the direct-current microgrid cluster; i represents an energy storage slave unit i in the direct current micro-grid k;
is a power state quantity;
is a power control coefficient;
the connection relation between the energy storage slave unit i and the energy storage slave unit j is 1 if the energy storage slave unit i and the energy storage slave unit j are connected, otherwise, the connection relation is 0;
is a state variable;
the state variable of the energy storage slave unit j in the direct current micro-grid k is obtained;
for the weight of the relationship between master and slave units, if the slave unit has access to the master unit
Is 1, otherwise is 0;
is the state variable of the energy storage main unit in the direct current micro-grid k.
As an improvement, the control strategy of the energy storage main unit is as follows:
when the energy storage main unit participates in the direct-current microgrid, PI control is carried out on the difference between the reference value of the inner-loop control current and the output current of the energy storage main unit;
carrying out pulse width modulation on the result of PI control;
controlling the duty ratio of the pulse width modulation result to obtain a control signal, and controlling the output voltage of the energy storage slave unit through the control signal;
the method for obtaining the reference value of the inner loop control current comprises the following steps:
inputting the voltage reference value of the energy storage main unit and the voltage observation values of the energy storage main units of other direct current micro-grids in the cluster into a voltage control function of the energy storage main unit to obtain a voltage state quantity;
inputting state variables of energy storage main units of other direct current micro-grids in the cluster into a power control function of the energy storage main unit to obtain power state quantities;
integrating the sum of the voltage state quantity and the power state quantity;
and (3) carrying out operation: the result of the integration + (voltage reference-port voltage value-droop control output value);
and performing PI control on the calculated result to obtain an inner loop control current reference value.
As an improvement, the energy storage main unit voltage control function is
Wherein k represents a direct-current microgrid k in the direct-current microgrid cluster; 0 represents an energy storage main unit in the direct current microgrid k;
is a voltage state quantity;
deriving the voltage observation;
is a voltage regulation factor;
the connection relation between the main unit of the direct current microgrid k and the main unit of the direct current microgrid l is 1 if the connection exists, or 0 if the connection does not exist;
is a voltage observation;
voltage observed values of the light energy storage main units of other direct current micro-grids l in the cluster are obtained;
for weighting the relationship between the main cells and the voltage reference value, if the main cells have access to the voltage reference value
Is 1, otherwise is 0;
is a voltage reference value;
the energy storage main unit power control function is
Wherein k represents a direct-current microgrid k in the direct-current microgrid cluster; 0 represents an energy storage main unit in the direct current microgrid k;
is a power state quantity;
is a power control coefficient;
the connection relation between the main unit of the direct current microgrid k and the main unit of the direct current microgrid l is 1 if the connection exists, or 0 if the connection does not exist;
is a state variable;
another direct current in the clusterState variables of the energy storage master unit of the microgrid l.
As an improvement, the calculation formula of the state variable is
Wherein k represents a direct-current microgrid k in the direct-current microgrid cluster; i represents an energy storage unit i in the direct current microgrid k;
is the output power of the energy storage unit;
the lower limit value of the SOC when the energy storage unit discharges;
the upper limit value of the SOC when the energy storage unit discharges;
and the nominal capacity of the energy storage unit i in the direct current micro-grid k.
As an improvement, the observed value of the voltage of the slave unit is calculated by the formula
Wherein k represents a direct-current microgrid k in the direct-current microgrid cluster; i represents a photovoltaic slave unit or an energy storage slave unit i in the direct current microgrid k;
is a voltage observation;
is the port voltage value;
the connection relation between the photovoltaic slave unit i and the photovoltaic slave unit j or between the energy storage slave unit i and the energy storage slave unit j is 1 if the photovoltaic slave unit i and the energy storage slave unit j are connected, otherwise, the connection relation is 0;
and (3) voltage observed values of the photovoltaic slave unit j or the energy storage slave unit j in the direct-current microgrid K.
As an improvement, the observed value of the voltage of the main unit is calculated by the formula
Wherein k represents a direct-current microgrid k in the direct-current microgrid cluster; 0 represents a photovoltaic main unit or an energy storage main unit in the direct current microgrid k;
is a voltage observation;
is the port voltage value;
the connection relationship between the main unit of the direct current microgrid k and the main unit of the direct current microgrid l is 1 if the connection is present, or 0 if the connection is not present;
and (4) obtaining voltage observed values of the photovoltaic main units of other direct current micro-grids l in the cluster.
The invention also provides a multi-stage cooperative control system of the direct current microgrid cluster, which is applied to the direct current microgrid cluster and is characterized by comprising the following components in parts by weight:
the election module is used for selecting one electric unit from each direct current microgrid as a main unit;
a communication trigger module for triggering the communication of the main unit, when the communication condition of the main unit is triggered, the main unit between the DC micro-grids performs communication, and the DC micro-gridsThe communication of the slave units within is synchronously triggered; the communication trigger conditions of the master unit are:
；
wherein,
；
in the formula,
the deviation between the voltage observed value and the voltage reference value is obtained;
for the moment of triggering
And of the previous moment
A deviation of (a);
modulo a relationship matrix between the master units; b k Is the weight between the master cell and the voltage reference; l is 0 Represents a laplace matrix; b is 0 Representing a weight matrix between the main cells and the voltage reference values,
；
and
the adjustment coefficient is within a specified range;
the cooperative control module is used for performing hierarchical cooperative control by utilizing information communicated among the main units, the main units and the slave units to achieve the balance of supply and demand of the direct-current microgrid cluster, and comprises a photovoltaic unit control module and an energy storage unit control module;
the photovoltaic unit control module comprises a photovoltaic main unit control module and a photovoltaic slave unit control module;
the energy storage unit control module comprises an energy storage main unit control module and an energy storage slave unit control module.
As an improvement, the photovoltaic slave unit control module is used for carrying out PI control on the difference between an inner ring control current reference value and the output current of the photovoltaic slave unit;
carrying out pulse width modulation on the result of PI control;
controlling the duty ratio of the pulse width modulation result to obtain a control signal, and controlling the output voltage of the photovoltaic slave unit through the control signal;
when no energy storage unit participates in the same direct current microgrid, the method for obtaining the reference value of the inner loop control current comprises the following steps:
inputting the droop control coefficient and the output current of the photovoltaic slave unit, the droop control coefficient and the output current of the photovoltaic master unit corresponding to the photovoltaic slave unit into a current control function of the photovoltaic slave unit to obtain a current state quantity;
inputting the voltage observed value of the photovoltaic slave unit and the voltage observed value of the photovoltaic master unit corresponding to the photovoltaic slave unit into a photovoltaic slave unit voltage control function to obtain a voltage state quantity;
integrating the current state quantity and the voltage state quantity;
and (3) carrying out operation: the integrated result + (voltage observed value of the photovoltaic master unit corresponding to the photovoltaic slave unit-voltage observed value of the photovoltaic slave unit) -droop control output value;
performing PI control on the result after the operation to obtain an inner loop control current reference value;
when energy storage units participate in the same direct-current microgrid, the method for obtaining the reference value of the inner-loop control current comprises the following steps:
carrying out maximum power point tracking control on the output voltage and the output current of the photovoltaic slave unit to obtain an outer ring control voltage reference value;
and performing PI control on the difference between the outer ring control voltage reference value and the output voltage of the photovoltaic slave unit to obtain an inner ring control current reference value.
As an improvement, the photovoltaic main unit control module is used for performing PI control on the difference between an inner ring control current reference value and the output current of the photovoltaic main unit;
carrying out pulse width modulation on the result of PI control;
controlling the duty ratio of the pulse width modulation result to obtain a control signal, and controlling the output voltage of the photovoltaic main unit through the control signal;
when no energy storage unit participates in the same direct current microgrid, the method for obtaining the reference value of the inner loop control current comprises the following steps:
inputting droop control coefficients and output currents of other photovoltaic main units in the cluster into a current control function of the photovoltaic main units to obtain current state quantities;
inputting voltage observed values of other photovoltaic main units and voltage reference values of the photovoltaic main units in the cluster into a photovoltaic slave unit voltage control function to obtain voltage state quantities;
integrating the sum of the current state quantity and the voltage state quantity;
and (3) performing the operation: voltage reference value of the photovoltaic main cell + (result of integration-droop control output value) -port voltage of the photovoltaic main cell;
performing PI control on the calculated result to obtain an inner loop control current reference value;
when energy storage units participate in the same direct-current microgrid, the method for obtaining the reference value of the inner-loop control current comprises the following steps:
carrying out maximum power point tracking control on the output voltage and the output current of the photovoltaic main unit to obtain an outer ring control voltage reference value;
and performing PI control on the difference between the outer ring control voltage reference value and the output voltage of the photovoltaic main unit to obtain an inner ring control current reference value.
As an improvement, the energy storage slave unit control module is used for performing PI control on the difference between the reference value of the inner ring control current and the output current of the energy storage slave unit when the energy storage slave unit participates in the direct current microgrid;
carrying out pulse width modulation on the result of PI control;
controlling the duty ratio of the pulse width modulation result to obtain a control signal, and controlling the output voltage of the energy storage slave unit through the control signal;
the method for obtaining the reference value of the inner loop control current comprises the following steps:
inputting voltage observed values of the energy storage main units in the same direct-current microgrid and voltage observed values of other energy storage slave units in the same direct-current microgrid into a voltage control function of the energy storage slave units to obtain voltage state quantities;
inputting state variables of other energy storage slave units in the same direct current microgrid and state variables of an energy storage master unit in the same direct current microgrid into a power control function of the energy storage slave units to obtain power state quantities;
integrating the sum of the voltage state quantity and the power state quantity;
and (3) performing the operation: the result of integration + (voltage observation-droop control output-port voltage value);
and performing PI control on the calculated result to obtain an inner loop control current reference value.
As an improvement, the energy storage main unit control module is used for performing PI control on the difference between an inner ring control current reference value and the output current of the energy storage main unit when the energy storage main unit participates in the direct current microgrid;
carrying out pulse width modulation on the result of PI control;
controlling the duty ratio of the pulse width modulation result to obtain a control signal, and controlling the output voltage of the energy storage slave unit through the control signal;
the method for obtaining the reference value of the inner loop control current comprises the following steps:
inputting the voltage reference value of the energy storage main unit and the voltage observation values of the energy storage main units of other direct current micro-grids in the cluster into a voltage control function of the energy storage main unit to obtain a voltage state quantity;
inputting state variables of energy storage main units of other direct current micro-grids in the cluster into a power control function of the energy storage main units to obtain power state quantities;
integrating the sum of the voltage state quantity and the power state quantity;
and (3) carrying out operation: the result of the integration + (voltage reference-port voltage value-droop control output value);
and performing PI control on the calculated result to obtain an inner loop control current reference value.
The invention has the advantages that:
the invention introduces a distributed organization type P system (DTPS), and provides a master-slave type three-level control structure for coordination control of a direct current micro-grid cluster. The novel DTPS design method enables the direct-current microgrid cluster to be easily mapped to the DTPS. In order to efficiently select one master unit for each microgrid, a distributed election algorithm is developed. When the master unit fails, a new master unit can be reselected in time, so that single-point failure caused by a single master unit in the traditional strategy is avoided, and different communication topologies can be adapted. In addition, aiming at the problem of communication failure caused by large communication traffic between DC-MGs, a distributed communication triggering method based on DTPS is designed. The master-slave distributed coordination control mechanism can enable the master unit and the slave unit to jointly compensate power/current sharing mismatch and SOC imbalance of the energy storage unit in the direct-current micro-grid, coordination between the master unit and the slave unit can achieve power/current distribution and SOC balance of the whole cluster system, and reliability of the system is improved. The DTPS-based hierarchical coordination control strategy can coordinate ordered and efficient transmission of information under different working conditions, so that supply and demand balance is met, the stability of the voltage of a common bus is effectively guaranteed, and the communication pressure is relieved.
Drawings
Fig. 1 is a schematic diagram of a dc microgrid cluster structure in the present invention, wherein L denotes a master unit, and F denotes a slave unit.
FIG. 2 is a flow chart of the present invention.
Fig. 3a and 3b are schematic diagrams of control strategies of the photovoltaic slave units and the photovoltaic master units.
Fig. 4a and 4b are schematic control strategies of the energy storage slave unit and the energy storage master unit.
Fig. 5 is a schematic structural diagram of a control system according to the present invention.
Fig. 6 is a schematic diagram of a microgrid cluster constructed as a result of verification.
Fig. 7a direct bus voltage under the strategy mentioned and the conventional strategy in scenario a.
Fig. 7b photovoltaic cell output current under the strategy presented in scenario a and the conventional strategy.
Fig. 7c communication trigger time in scenario a.
Dc bus voltage under the strategy presented in scenario B of fig. 8a and the conventional strategy.
Fig. 8B illustrates the state of charge of the energy storage unit under the proposed and conventional strategy in scenario B.
Fig. 8c scenario B communication trigger time.
Detailed Description
In order that those skilled in the art will better understand the technical solutions of the present invention, the present invention will be further described in detail with reference to the following embodiments.
The direct-current micro-grid cluster refers to a plurality of direct-current micro-grids of different power supply main bodies in a certain area, and the direct-current micro-grid cluster can be formed by further expanding the direct-current micro-grid. When the internal power of the direct current microgrid is excessive, power can be injected into adjacent nodes; when there is a power deficit internally, the power provided by the neighboring nodes may be absorbed. The voltage difference between the nodes can be realized by energy management scheduling and control of the DC bus voltage.
The existing micro-grid cluster generally adopts three control modes of centralized control, decentralized control and distributed control.
1. The centralized control connects the supply and demand sides through the central controller and the communication network, and the coordination function that can be achieved includes: two/three level regulation of dc voltage, power flow control, and interactive control objectives including changing operating modes, maximizing efficiency and minimizing operating costs, etc. For the small direct current micro-grid, each unit can be directly controlled by a central controller, and high bandwidth communication is carried out by adopting a master-slave control method; for larger-scale dc micro-grids, a central controller needs to be incorporated into the hierarchical control structure to improve system reliability.
The disadvantages are that:
(1) There is a single point of failure, if the central controller or any critical communication link fails, the corresponding control objective may not be achieved;
(2) For important control units, redundant communication systems need to be installed to reduce the likelihood of failure, which increases economic costs;
(3) The central controller has large calculation amount and is easy to cause insufficient communication channels and blockage.
2. The distributed control method is realized by only a local controller to coordinate the performance of a plurality of control units in the direct current microgrid.
The disadvantages are that:
(1) The lack of information from other adjacent control units is limited by the inherent performance of the control units, and the expandability is very limited;
(2) The accuracy of the voltage sensor can affect the effectiveness and reliability based on the common bus voltage signal at all times.
3. The distributed control uses a consistency algorithm and injects the protocol into each local controller to realize information interaction of adjacent control units. Therefore, variables in any controller are adjusted according to values of neighbors of the controller, information perception equivalent to that of a central controller in centralized control is achieved, the problem of single-point faults is avoided, limitation of system observation information is made up, and the aims of output current sharing, voltage recovery, overall efficiency improvement, SOC balance and the like are achieved.
The disadvantages are that:
the performance analysis such as convergence speed and stability margin has high complexity, especially in non-ideal environment characterized by communication delay and measurement error.
In order to solve the above problem in the control manner, as shown in fig. 1, firstly, the present invention provides a dc microgrid cluster, which includes a plurality of dc microgrids, wherein the dc microgrid includes a plurality of electrical units, and the electrical units are energy storage units or photovoltaic units; the electric units in each direct current microgrid are provided with only one main unit at the same time, and the rest are slave units; the direct current microgrid can be communicated with each other only by the master unit, and the master unit and the slave unit in the direct current microgrid as well as the slave unit and the slave unit can be communicated with each other. It is noted that the above-mentioned communication rules are implemented by a physical communication network, whereas the topological relation between two electrical units is implemented by corresponding communication rules.
The direct current microgrid cluster is constructed according to a distributed organization type P system (DTPS), which is one of membrane computing models having a network type topological structure. The TPS consists of a number of units, which are arranged individually in one environment. Each cell contains one or more objects or variables. Typically, an environment has some objects or variables. In the present invention, the TPS used is an evolved communication organisation type P system. Distributed organization type P systems (DTPS) are an extension of the organization Type P Systems (TPS). The DTPS consists of multiple TPS, each of which is a subsystem thereof.
According to the characteristics of each electric unit of the distributed direct-current micro-grid cluster, different distributed organization units are designed, and the organization units are physically connected through a communication network. Therefore, the direct-current microgrid cluster forms a three-level distributed coordination control network between an electric unit per se, a direct-current microgrid interior and a direct-current microgrid, and coordination among a plurality of subnetworks in the direct-current microgrid cluster can be realized.
Based on the dc microgrid cluster having the communication rule and the topology structure, the present invention further provides a multi-level cooperative control method for a dc microgrid cluster, which is applied to the dc microgrid cluster, and as shown in fig. 2, the specific steps include:
s1 selects one electrical unit from each dc microgrid as a master unit.
In order to efficiently select one electric unit in the direct current microgrid as a main unit of the direct current microgrid to be responsible for communication among the direct current microgrids, the invention provides a distributed election mechanism which can quickly select the main unit within an allowable range for coordination control. The mechanism can avoid the problem of single-point failure of a single main unit and reduce communication pressure; at the same time, it allows any electrical unit (photovoltaic unit or energy storage unit) in the dc microgrid cluster that maintains the bus voltage stable to act as a master unit or a slave unit at any switching moment to meet the plug and play requirement. The method comprises the following specific steps:
s11, all the electric units in the direct current microgrid are initialized to be slave units, and the slave units can receive heartbeat signals from the master units.
An electrical unit in a dc microgrid may have three states during election of the main unit: master unit, contestants, slave units. All electrical units within the network need to be initialized as slaves before the first election. The master unit may periodically send a heartbeat signal to all slave units within the network, which the slave units may receive.
And S12, when the master unit heartbeat signal received by a certain slave unit is overtime, the slave unit is used as a competitor to initiate voting.
Each electrical unit has a voting timer, and the time-out of the heartbeat signal means that the interval between two heartbeat signals received by the slave unit exceeds a threshold value, which indicates that the master unit in the network is disconnected or does not have the master unit at all. It is then necessary to race out a master unit as soon as possible for piggybacking communications with other dc micro grids. And the slave unit receiving the heartbeat signal time-out enters an election state to initiate a vote.
And S13, the contestants vote themselves after updating own election numbers, and initiate voting invitations to other slave units in the direct current microgrid, wherein the voting invitations are accompanied with the election numbers of the contestants.
The tenure number is the number used to meter the iterations of the master unit, and each time a vote is initiated, a new tenure number is updated. The expiration number is preferably monotonically increasing, e.g., first, second, third, etc.
After becoming an election, the voting invitations can be sent to other slave units in the network.
Before a new master unit does not elect, the slave unit can cast votes to only the first candidate initiating the voting invitation to the slave unit, so that repeated voting is avoided; in addition, if the tenure number of the candidate is smaller than the tenure number of the candidate, the voting is refused; if the candidate finally selects the master unit, the own tenure number is updated to the tenure number of the candidate.
S14, the contestants count the votes obtained by the contestants, if the number of the votes is more than half, the contestants are taken as a main unit, and the voting is finished;
s15, if the contestant receives the heartbeat signal of the master unit during the voting initiation, stopping the voting and acting as the slave unit again.
The heartbeat signal of the master unit is re-received during the voting period, indicating that the previous master unit has recovered or that a new master unit has elected. This time should avoid wasting resources even if voting is stopped.
In addition, if the random number of the main unit is smaller than the random number of any other electric unit, the main unit updates the random number to the maximum random number value in the direct current microgrid and is used as the slave unit again. The main unit with a smaller duty cycle than the other electrical units is selected because a new main unit is already selected during a fault or disconnection, and therefore needs to be timely relocated to avoid confusion.
And if the slave unit deadline number is smaller than the deadline number of any other electric unit, the slave unit updates the deadline number to the maximum deadline number value in the direct current microgrid. The slave unit expiration number is smaller than the expiration numbers of the other electrical units, which indicates that a new master unit has been generated during the period of the failed line, and the information should be updated in time.
Due to the distributed election mechanism, the topological structure of the whole direct current microgrid cluster is also dynamically changed. Distributed election algorithms allow any electrical unit in each dc microgrid to act as a master or slave at any time (communication topology change, master failure or service decommissioning) in the uppermost communication network, such as: when the master unit fails, a new master unit can be elected in time, so that single-point failure caused by a single master unit in the traditional strategy can be avoided, and different communication topologies can be adapted.
To describe the topological relationships, two relationship matrices are defined as follows:
1. when the master unit and the slave unit have the above existing relationship for voting and receiving heartbeat information, the same exists in the communication topology, and the information exchange is performed after the event triggering condition is met (which will be described in detail later). To describe the relationship of master and slave, a matrix of N × N, a = a (k) = a (a), is defined ij ) To represent the adjacent matrix in the network DC micro-grid k, if there is a connection between the control unit i and the control unit j, the corresponding element a is made ij Is 1, otherwise is 0;
2. in the case that a plurality of direct current micro-grids form a cluster, the communication inside the cluster is shown above, the communication between the clusters is only between the main units of each cluster, and in order to describe the relationship between the main units and the main units, an N is defined k *N l A = a (a) of the matrix kl ) To represent the adjacency matrix of the clusters in the dc microgrid cluster, if there is a connection between the master unit k and the master unit l, let the corresponding element a kl Is 1, otherwise is 0.
And S2, when the communication condition of the master unit is triggered, the master units among the direct current micro grids perform communication, and the communication of the slave units in the direct current micro grids is synchronously triggered.
In order to reduce system overhead, communication between electrical units is not always performed, and a certain trigger condition needs to be met to start communication.
The main reason why the electrical units need to communicate for cooperative control is that bus voltage drops when the system is unstable, so that a voltage observation function needs to be designed, and the voltage state of the main unit is represented as follows:
wherein k represents a direct-current microgrid k in the direct-current microgrid cluster, and 0 represents a main unit in the direct-current microgrid k;
is a voltage state quantity;
is a voltage regulation factor;
the connection relationship between the main unit of the direct current microgrid k and the main unit of the direct current microgrid l is 1 if the connection is present, or 0 if the connection is not present;
is a voltage observation;
is a voltage observation of the master unit of the dc microgrid l;
the last trigger time;
the last trigger time of the main unit of the direct current micro-grid l is obtained;
weighting the relationship between the main cells and the voltage reference if the main cells have access to the voltage reference
Is 1, otherwise is 0;
is a voltage reference value.
Defining the local observed voltage deviation as:
，
for the voltage deviation at the time t,
the observed value of the voltage at the time t,
is a voltage reference value. The voltage observer observation voltage inconsistency based on the distributed scheme can be expressed as:
wherein k represents a direct-current microgrid k in the direct-current microgrid cluster, and 0 represents a main unit in the direct-current microgrid k;
the voltage deviation derivation result at the moment t;
is a voltage regulation factor;
voltage deviation of last trigger time;
the voltage deviation is the last trigger time of the main unit of the direct current micro-grid l;
weighting the relationship between the main cells and the voltage reference if the main cells have access to the voltage reference
Is 1, otherwise is 0.
Defining the voltage deviation at the moment of triggering
Deviation from last time voltage
The deviation of (a) is:
the following can be obtained:
wherein,
in order to be a laplacian matrix,
the weight matrix between the master cell and the voltage reference is the same as above for the remaining letters.
Based on the above derivation, the present invention therefore provides a communication triggering mechanism, where the communication triggering conditions of the master unit are:
；
wherein,
；
in the formula,
the deviation between the voltage observed value and the voltage reference value is obtained;
for the moment of triggering
And of the previous moment
A deviation of (a);
modulo a relationship matrix between the master units; b k Is the weight between the master cell and the voltage reference; l is a radical of an alcohol 0 Represents a laplace matrix; b 0 Representing a weight matrix between the main cells and the voltage reference values,
；
and
is the adjustment coefficient within the designated range.
When the system is in a stable state, no communication is carried out among the main units, the main-slave units and the slave units, and the communication is maintained by the local controller; when the local control voltage observer of the main unit observes that the voltages of the direct current buses are inconsistent, namely the distributed communication triggering conditions are met, information interaction between the main units of the corresponding direct current microgrid cluster is triggered, and meanwhile, information interaction between the slave units in the middle layer communication network is sequentially triggered. Thus, it relieves the large traffic required for cluster communication, reducing the need for real-time information transmission.
The communication alternating current information comprises observation voltage, droop coefficient and resistance.
And S3, hierarchical cooperative control is performed by utilizing information communicated among the main units, the main units and the slave units to achieve the supply and demand balance of the direct-current microgrid cluster.
Based on the communication and topological structure of the direct current microgrid cluster, the invention provides a three-level coordination control framework for the direct current microgrid cluster: the first-stage electric unit, the interior of the second-stage direct-current microgrid and the third-stage direct-current microgrid.
In the first-level control, local control is realized for each photovoltaic unit or energy storage unit in the direct-current microgrid cluster.
For photovoltaic cells, its own control includes two modes: a Maximum Power Point Tracking (MPPT) operation mode and a DROOP (DROOP) control mode. When the photovoltaic needs to maintain the bus voltage stable, namely the energy storage unit quits operation at the moment, and the photovoltaic unit works in a droop control mode. And when the energy storage mode participates in operation, the photovoltaic unit works in the MPPT control mode.
For the energy storage unit, when the energy storage unit participates in the stabilization of the bus voltage, droop control is also adopted to realize local current sharing.
When the droop control is performed, the output voltage of each electrical unit can be expressed as
Wherein k represents a direct-current microgrid k in the direct-current microgrid cluster, and i represents an electric unit in the direct-current microgrid k;
is the voltage at the end of the line,
for the voltage reference value after the secondary control
In order to control the droop control coefficient,
to output a current.
In the second-level and third-level control, a photovoltaic unit control method and an energy storage unit control method are specifically included;
the photovoltaic control method comprises a photovoltaic main unit control strategy and a photovoltaic slave unit control strategy; each photovoltaic unit has two control modes, and when the MPPT control mode is selected, the system is kept the stability of direct current busbar voltage by the energy storage unit. When the constant voltage control mode is selected, the master-slave control layer is required to perform the cooperative control. After distributed election, if the system meets a distributed information exchange triggering condition, information exchange between the photovoltaic main unit and the adjacent photovoltaic main unit of the direct current microgrid and between the photovoltaic main unit and the slave units of the direct current microgrid in the direct current microgrid is triggered.
The energy storage unit control method comprises an energy storage main unit control strategy and an energy storage slave unit control strategy. Each energy storage unit has two states: and the master-slave control mode is operated and quit operation is carried out. Similarly, after the uppermost-layer distributed election, if the system meets the distributed information exchange triggering condition, information exchange between the energy storage main unit and the adjacent direct-current microgrid energy storage main unit in the direct-current microgrid and between the direct-current microgrid energy storage main unit and the slave units of the direct-current microgrid is triggered. Meanwhile, the energy storage leader can also access a voltage reference value.
Since voltage regulation and current sharing accuracy cannot be achieved in the direct current MG, there is a trade-off between accurate voltage regulation and equalizing current. However, for a multi-microgrid distributed system, when each distributed electrical unit performs power distribution according to its own capacity, it cannot be guaranteed that the output voltage of each microgrid control unit is regulated to a rated value. A compromise is therefore taken to adjust the average value of the voltage observed by the electrical unit to an acceptable range. In order to achieve the purpose, the invention designs a two-layer voltage observer, and the observer of each electric unit can receive the voltage observed value of the adjacent control unit and update the own observed result:
first, the voltage observed value calculation formula of the slave unit
Wherein k represents a direct-current microgrid k in the direct-current microgrid cluster; i represents a photovoltaic slave unit or an energy storage slave unit i in the direct current micro-grid k;
is a voltage observation;
is the port voltage value;
the connection relation between the photovoltaic slave unit i and the photovoltaic slave unit j or between the energy storage slave unit i and the energy storage slave unit j is 1 if the photovoltaic slave unit i and the energy storage slave unit j are connected, otherwise, the connection relation is 0;
and (3) observing the voltage of the photovoltaic slave unit j or the energy storage slave unit j in the direct current microgrid K.
Second, voltage observed value calculation formula of main unit
Wherein k represents a direct-current microgrid k in the direct-current microgrid cluster; 0 represents a photovoltaic main unit or an energy storage main unit in the direct current microgrid k;
is a voltage observation;
is the port voltage value;
the connection relationship between the main unit of the direct current microgrid k and the main unit of the direct current microgrid l is 1 if the connection is present, or 0 if the connection is not present;
and (4) obtaining voltage observed values of the photovoltaic main units of other direct current micro-grids l in the cluster.
Based on the superiority of the direct current microgrid cluster communication network, the intercommunication of the slave units in each direct current microgrid and the intercommunication of the master units among the direct current microgrids can be ensured. Then, all the master units and slave units can make the respective output voltages gradually consistent through the voltage observers:
the photovoltaic slave unit control strategy, the photovoltaic master unit control strategy, the energy storage slave unit control strategy and the energy storage master unit control strategy are introduced one by one.
As shown in fig. 3a, a control flow of the photovoltaic slave unit is shown. The control strategy of the photovoltaic slave unit specifically comprises:
s311 referring the inner loop control current
With the photovoltaic slave unit outputting current
The difference of (a) is subjected to PI control.
Wherein the inner loop controls the current reference value
The acquisition method of (2) is related to the control mode of the photovoltaic slave unit.
When no energy storage unit participates in the same direct-current microgrid, the inner ring controls the current reference value
The obtaining method comprises the following steps:
(1) Controlling the droop of the photovoltaic slave unit
And output current
And the droop control coefficient of the photovoltaic main unit corresponding to the photovoltaic slave unit
And output current
Input photovoltaic slave unit current control function obtains current state quantity
(ii) a The photovoltaic slave unit current control function is
Wherein k represents a direct-current microgrid k in the direct-current microgrid cluster; i represents a photovoltaic slave unit i in the direct current microgrid k;
is a current state quantity;
a current regulation factor;
the connection relationship between the slave units in the DC micro-grid k is realized if possibleBy connecting
Is 1, otherwise is 0;
in order to control the droop control coefficient,
is an output current;
for the droop control coefficient of the photovoltaic slave unit j in the direct current microgrid k,
the output current of the photovoltaic slave unit j in the direct current microgrid k is;
the droop control coefficient of the photovoltaic main unit in the direct current microgrid k is obtained;
and (4) outputting current of the photovoltaic main unit in the direct current microgrid k.
(2) Observing the voltage of the photovoltaic slave unit
And the voltage observed value of the photovoltaic main unit corresponding to the photovoltaic slave unit
Input photovoltaic slave cell voltage control function to obtain voltage state quantity
(ii) a The photovoltaic slave unit voltage control function is
Wherein k represents a direct-current microgrid k in the direct-current microgrid cluster; i represents a photovoltaic slave unit i in the direct current microgrid k;
is a voltage state quantity;
deriving the voltage observation;
is a voltage regulation factor;
the connection relation between the photovoltaic slave unit i and the photovoltaic slave unit j is 1 if the photovoltaic slave unit i and the photovoltaic slave unit j are connected, otherwise, the connection relation is 0;
is a voltage observation;
the voltage observed value of the photovoltaic slave unit j in the direct-current micro-grid k is obtained;
for the weight of the relationship between master and slave units, if the slave unit has access to the master unit
Is 1, otherwise is 0;
the voltage observed value of the photovoltaic main unit in the direct current micro-grid k is obtained;
(3) Current state quantity
And voltage state quantity
Performing integration;
(4) And (3) carrying out operation: integrated result + (voltage observed value of photovoltaic master cell corresponding to photovoltaic slave cell)
-voltage observations of the photovoltaic slave unit
) -a droop control output value;
(5) PI control is carried out on the result after the operation to obtain an inner loop control current reference value
；
When an energy storage unit participates in the same direct-current micro-grid, the photovoltaic slave unit is controlled in an MPPT mode, and the inner ring controls a current reference value
The obtaining method comprises the following steps:
(1) The output voltage of the photovoltaic slave unit
And output current
Maximum power point tracking control is carried out to obtain an outer ring control voltage reference value
；
(2) Control the voltage reference value of the outer loop
With the output voltage of the photovoltaic slave unit
Performing PI control on the difference to obtain an inner loop control current reference value
。
S312, performing pulse width modulation on the result of the PI control;
s313, duty ratio control is carried out on the pulse width modulation result to obtain a control signal, and the output voltage of the photovoltaic slave unit is controlled through the control signal.
As shown in fig. 3b, a control flow of the photovoltaic main unit is demonstrated. The control strategy of the photovoltaic main unit specifically comprises:
s321 converting the inner loop control current reference value
And the output current of the photovoltaic main unit
The difference of (a) is subjected to PI control.
Also, the inner loop controls the current reference value
The acquisition method of (2) is related to the control mode of the photovoltaic slave unit.
When no energy storage unit participates in the same direct-current microgrid, the inner ring controls the current reference value
The obtaining method comprises the following steps:
(1) Droop control coefficients for other photovoltaic main units in a cluster
Output current of the power supply
Inputting a current control function of a photovoltaic main unit to obtain a current state quantity
(ii) a The photovoltaic main unit current control function is
Wherein k represents a direct-current microgrid k in the direct-current microgrid cluster; 0 represents a photovoltaic main unit in the direct current microgrid k;
is a current state quantity;
is a current regulation factor;
the connection relation between the main unit of the direct current microgrid k and the main unit of the direct current microgrid l is 1 if the connection exists, or 0 if the connection does not exist;
is a droop control coefficient;
is an output current;
a droop control coefficient for another photovoltaic main unit in the cluster;
is the output current of another photovoltaic main unit in the cluster.
(2) Observing the voltage of other photovoltaic main units in the cluster
Voltage reference value of the photovoltaic main unit
Input photovoltaic slave cell voltage control function to obtain voltage state quantity
(ii) a The photovoltaic main unit voltage control function is
Wherein k represents a direct-current microgrid k in the direct-current microgrid cluster; 0 represents a photovoltaic main unit in the direct current microgrid k;
is a voltage state quantity;
deriving the voltage observation;
is a voltage regulation factor;
the connection relation between the main unit of the direct current microgrid k and the photovoltaic main unit of the direct current microgrid l is 1 if the connection exists, or 0 if the connection does not exist;
is a voltage observed value;
voltage observed values of the photovoltaic main units of other direct current micro-grids l in the cluster are obtained;
for weighting the relationship between the main cells and the voltage reference value, if the main cells have access to the voltage reference value
Is 1, otherwise is 0;
is a voltage reference value;
(3) Current state quantity
And voltage state quantity
The sum of (1) is integrated;
(4) And (3) carrying out operation: voltage reference value of the photovoltaic main unit
+ (result of integration-droop control output value) -Port Voltage of the photovoltaic Main Unit
；
(5) Performing PI control on the calculated result to obtain an inner loop control current reference value
；
When the energy storage units participate in the same direct-current micro-grid, the photovoltaic main power supply is controlled in an MPPT mode, and the inner ring controls the current reference value
The obtaining method comprises the following steps:
(1) The output voltage of the photovoltaic main unit
And output current
Maximum power point tracking control is carried out to obtain an outer ring control voltage reference value
；
(2) Control the voltage reference value of the outer loop
And the output voltage of the photovoltaic main unit
Performing PI control on the difference to obtain an inner loop control current reference value
。
S322 pulse width modulation is carried out on the result of PI control;
s323, controlling the duty ratio of the pulse width modulation result to obtain a control signal, and controlling the output voltage of the photovoltaic main unit through the control signal;
as shown in fig. 4a, the control flow of the energy storage slave unit is shown. The control strategy of the energy storage slave unit specifically comprises the following steps:
s331, when the energy storage slave unit participates in the direct current microgrid, controlling the current reference value of the inner ring
With the stored energy slave unit outputting current
Performing PI control on the difference;
the energy storage slave unit does not participate in the direct-current microgrid during overcharge or overdischarge, and the inner ring of the energy storage slave unit controls the current reference value
The obtaining method comprises the following steps:
(1) Observing the voltage of the energy storage main units in the same direct current microgrid
And voltage observation values of other energy storage slave units in the same direct current microgrid
Input energy storage obtains voltage state quantity from unit voltage control function
(ii) a The energy storage slave unit voltage control function is
Wherein k represents a direct-current microgrid k in the direct-current microgrid cluster; i represents an energy storage slave unit i in the direct current microgrid k;
is a voltage state quantity;
deriving the voltage observation;
is a voltage regulation factor;
the connection relation between the energy storage slave unit i and the energy storage slave unit j is 1 if the energy storage slave unit i and the energy storage slave unit j are connected, otherwise, the connection relation is 0;
is a voltage observation;
the voltage observed value of the energy storage slave unit j in the direct current micro-grid k is obtained;
for the weight of the relationship between master and slave units, if the slave unit has access to the master unit
Is 1, otherwise is0；
The voltage observed value of an energy storage main unit in the direct current micro-grid k is obtained;
(2) State variables of other energy storage slave units in the same direct current micro-grid
And state variable of energy storage main unit in same direct current micro-grid
Input energy storage obtains power state quantity from unit power control function
(ii) a The energy storage slave unit power control function is
Wherein k represents a direct-current microgrid k in the direct-current microgrid cluster; i represents an energy storage slave unit i in the direct current micro-grid k;
is a power state quantity;
is a power control coefficient;
the connection relation between the energy storage slave unit i and the energy storage slave unit j is 1 if the energy storage slave unit i and the energy storage slave unit j are connected, otherwise, the connection relation is 0;
is a state variable;
slave unit for storing energy in direct current micro-grid kA state variable of j;
for the weight of the relationship between master and slave units, if the slave unit has access to the master unit
Is 1, otherwise is 0;
is the state variable of the energy storage main unit in the direct current micro-grid k.
For the energy storage units, the overall service life is affected by overcharge and overdischarge, so that the energy storage units are required to be kept at a relatively average consistent level, and therefore, a power control function needs to be designed for the energy storage units. Wherein the state variable is calculated by
Wherein k represents a direct-current microgrid k in the direct-current microgrid cluster; i represents an energy storage unit i in the direct current microgrid k;
for the output power of the energy storage unit
The lower limit value of the SOC when the energy storage unit discharges;
the upper limit value of the SOC when the energy storage unit discharges;
and the nominal capacity of the energy storage unit i in the direct current micro-grid.
The state variables of the energy storage master unit and the energy storage slave unit are calculated identically.
(3) Voltage state quantity
And power state quantity
The sum of (1) is integrated;
(4) And (3) carrying out operation: result of integration + (Voltage observed value)
-droop control output value-port voltage value
）；
(5) Performing PI control on the calculated result to obtain an inner loop control current reference value
。
S332, performing pulse width modulation on the result of the PI control;
and S333, carrying out duty ratio control on the pulse width modulation result to obtain a control signal, and controlling the output voltage of the energy storage slave unit through the control signal.
As shown in fig. 4b, the control flow of the energy storage main unit is shown. The control strategy of the energy storage main unit is as follows:
s341, when the energy storage main unit participates in the direct-current microgrid, the inner ring is controlled to control the current reference value
And the output current of the energy storage main unit
The difference of (a) is subjected to PI control.
The inner loop controls the current reference value
The obtaining method comprises the following steps:
(1) Reference voltage of the energy storage main unit
And voltage observation values of energy storage main units of other direct current micro-grids in the cluster
Obtaining voltage state quantity by inputting voltage control function of energy storage main unit
(ii) a The energy storage main unit voltage control function is
Wherein k represents a direct-current microgrid k in the direct-current microgrid cluster; 0 represents an energy storage main unit in the direct current microgrid k;
is a voltage state quantity;
deriving a voltage observation;
is a voltage regulation factor;
the connection relation between the main unit of the direct current microgrid k and the main unit of the direct current microgrid l is 1 if the connection exists, or 0 if the connection does not exist;
is a voltage observation;
voltage observed values of the light energy storage main units of other direct current micro-grids l in the cluster are obtained;
for weighting the relationship between the main cells and the voltage reference value, if the main cells have access to the voltage reference value
Is 1, otherwise is 0;
is a voltage reference value;
(2) State variable of energy storage main unit of other direct current micro-grids in cluster
Input energy storage main unit power control function to obtain power state quantity
(ii) a The energy storage main unit power control function is
Wherein k represents a direct-current microgrid k in the direct-current microgrid cluster; 0 represents an energy storage main unit in the direct current microgrid k;
is a power state quantity;
is a power control coefficient;
the connection relation between the main unit of the direct current microgrid k and the main unit of the direct current microgrid l is 1 if the connection exists, or 0 if the connection does not exist;
is a state variable;
and (3) state variables of energy storage main units of another direct current micro-grid l in the cluster.
The state variable is obtained by the same control strategy as the energy storage slave unit, and the details are not repeated here.
(3) Voltage state quantity
And power state quantity
The sum of (1) is integrated;
(4) And (3) carrying out operation: result of integration + (Voltage reference value)
-port voltage value
-droop control output value);
(5) Performing PI control on the calculated result to obtain an inner loop control current reference value
。
S342, carrying out pulse width modulation on the result of PI control;
and S343, duty ratio control is carried out on the pulse width modulation result to obtain a control signal, and the output voltage of the energy storage slave unit is controlled through the control signal.
As shown in fig. 5, the present invention further provides a multi-stage cooperative control system for a dc microgrid cluster, which is applied to the dc microgrid cluster and includes:
the election module is used for selecting one electric unit from each direct current microgrid as a main unit;
a communication trigger module for triggering the communication of the master unit, when the communication condition of the master unit is triggered, the master unit between the DC micro-grids communicates, and the communication of the slave units in the DC micro-grid is communicated with the master unitTriggering; the communication trigger conditions of the master unit are as follows:
；
wherein,
；
in the formula,
the deviation between the voltage observed value and the voltage reference value is obtained;
for the moment of triggering
And of the previous moment
A deviation of (a);
modulo a relationship matrix between the master units; b k Is the weight between the main cell and the voltage reference value; l is 0 Represents a laplace matrix; b 0 Representing a weight matrix between the main cells and the voltage reference values,
；
and
are adjustment coefficients within a specified range.
The cooperative control module is used for performing hierarchical cooperative control by utilizing information communicated among the main units, the main units and the slave units to achieve the balance of supply and demand of the direct-current microgrid cluster, and comprises a photovoltaic unit control module and an energy storage unit control module;
the photovoltaic unit control module comprises a photovoltaic main unit control module and a photovoltaic slave unit control module;
the energy storage unit control module comprises an energy storage main unit control module and an energy storage slave unit control module.
The photovoltaic slave unit control module is used for carrying out PI control on the difference between the reference value of the inner ring control current and the output current of the photovoltaic slave unit;
carrying out pulse width modulation on the result of PI control;
controlling the duty ratio of the pulse width modulation result to obtain a control signal, and controlling the output voltage of the photovoltaic slave unit through the control signal;
when no energy storage unit participates in the same direct current microgrid, the method for obtaining the reference value of the inner loop control current comprises the following steps:
inputting the droop control coefficient and the output current of the photovoltaic slave unit, the droop control coefficient and the output current of the photovoltaic master unit corresponding to the photovoltaic slave unit into a current control function of the photovoltaic slave unit to obtain a current state quantity;
inputting the voltage observed value of the photovoltaic slave unit and the voltage observed value of the photovoltaic master unit corresponding to the photovoltaic slave unit into a photovoltaic slave unit voltage control function to obtain a voltage state quantity;
integrating the current state quantity and the voltage state quantity;
and (3) carrying out operation: the integrated result + (voltage observed value of the photovoltaic master unit corresponding to the photovoltaic slave unit-voltage observed value of the photovoltaic slave unit) -droop control output value;
performing PI control on the result after the operation to obtain an inner loop control current reference value;
when energy storage units participate in the same direct-current microgrid, the method for obtaining the reference value of the inner-loop control current comprises the following steps:
carrying out maximum power point tracking control on the output voltage and the output current of the photovoltaic slave unit to obtain an outer ring control voltage reference value;
and PI control is carried out on the difference between the outer ring control voltage reference value and the output voltage of the photovoltaic slave unit to obtain an inner ring control current reference value.
The photovoltaic main unit control module is used for carrying out PI control on the difference between the reference value of the inner ring control current and the output current of the photovoltaic main unit;
carrying out pulse width modulation on the result of PI control;
controlling the duty ratio of the pulse width modulation result to obtain a control signal, and controlling the output voltage of the photovoltaic main unit through the control signal;
when no energy storage unit participates in the same direct current microgrid, the method for obtaining the reference value of the inner loop control current comprises the following steps:
inputting droop control coefficients and output currents of other photovoltaic main units in the cluster into a current control function of the photovoltaic main units to obtain current state quantities;
inputting voltage observed values of other photovoltaic main units in the cluster and voltage reference values of the photovoltaic main units into a photovoltaic slave unit voltage control function to obtain voltage state quantities;
integrating the sum of the current state quantity and the voltage state quantity;
and (3) carrying out operation: voltage reference of the photovoltaic main cell + (result of integration-droop control output value) -port voltage of the photovoltaic main cell;
performing PI control on the calculated result to obtain an inner loop control current reference value;
when energy storage units participate in the same direct-current microgrid, the method for obtaining the reference value of the inner-loop control current comprises the following steps:
carrying out maximum power point tracking control on the output voltage and the output current of the photovoltaic main unit to obtain an outer ring control voltage reference value;
and performing PI control on the difference between the outer ring control voltage reference value and the output voltage of the photovoltaic main unit to obtain an inner ring control current reference value.
The energy storage slave unit control module is used for carrying out PI control on the difference between the reference value of the inner ring control current and the output current of the energy storage slave unit when the energy storage slave unit participates in the direct-current microgrid;
carrying out pulse width modulation on the result of PI control;
controlling the duty ratio of the pulse width modulation result to obtain a control signal, and controlling the output voltage of the energy storage slave unit through the control signal;
the method for obtaining the reference value of the inner loop control current comprises the following steps:
inputting voltage observed values of the energy storage main units in the same direct-current microgrid and voltage observed values of other energy storage slave units in the same direct-current microgrid into a voltage control function of the energy storage slave units to obtain voltage state quantities;
inputting state variables of other energy storage slave units in the same direct current microgrid and state variables of an energy storage master unit in the same direct current microgrid into a power control function of the energy storage slave units to obtain power state quantities;
integrating the sum of the voltage state quantity and the power state quantity;
and (3) carrying out operation: the result of integration + (voltage observation-droop control output-port voltage value);
and performing PI control on the calculated result to obtain an inner loop control current reference value.
The energy storage main unit control module is used for carrying out PI control on the difference between the reference value of the inner ring control current and the output current of the energy storage main unit when the energy storage main unit participates in the direct-current microgrid;
carrying out pulse width modulation on the result of PI control;
controlling the duty ratio of the pulse width modulation result to obtain a control signal, and controlling the output voltage of the energy storage slave unit through the control signal;
the method for obtaining the reference value of the inner loop control current comprises the following steps:
inputting the voltage reference value of the energy storage main unit and the voltage observation values of the energy storage main units of other direct current micro-grids in the cluster into a voltage control function of the energy storage main unit to obtain a voltage state quantity;
inputting state variables of energy storage main units of other direct current micro-grids in the cluster into a power control function of the energy storage main units to obtain power state quantities;
integrating the sum of the voltage state quantity and the power state quantity;
and (3) performing the operation: the result of the integration + (voltage reference-port voltage value-droop control output value);
and performing PI control on the calculated result to obtain an inner loop control current reference value.
In order to verify the feasibility of the invention, a direct current microgrid cluster system as shown in fig. 6 is built in MATLAB/Simulink, and the basic physical topology of the system comprises a cluster formed by two direct current microgrids MG1 and MG2, wherein PV represents a photovoltaic unit and BES represents an energy storage unit.
A. Load fluctuation under independent photovoltaic system
In the scenario a, it is set that all energy storage units are disconnected from operation due to the fact that the upper limit or the lower limit of the SOC is reached or due to troubleshooting and the like, and distributed election is triggered at this time. And in each sub-network, the photovoltaic units select photovoltaic main units according to a distributed election algorithm, and the rest photovoltaic units are slave unit states. If the observed voltage of the photovoltaic main unit in the MG1 meets the triggering condition due to load fluctuation, triggering the photovoltaic main unit to access the observed voltage and current of the photovoltaic main unit in the adjacent MG2 and accessing the reference value of the bus voltage
. Meanwhile, the photovoltaic slave unit in the MG1 is triggered to access the observed voltage and current of the photovoltaic master unit, and to access the observed voltage and current of the adjacent photovoltaic slave unit.
Setting the initial load of the system to be 7.2kW, selecting PV1,1 in MG1 and PV2,3 in MG2 as main units by the system, and enabling the two units to exchange information and to be capable of exchanging informationAccessing voltage reference values
. In this case, 25% of the present load is increased at 5s and 33% of the present load is decreased at 10s, the simulation results of the dc bus voltage fluctuation and the photovoltaic unit output current under the proposed strategy and the conventional strategy are shown in fig. 7a and 7b, and the distributed communication trigger time is shown in fig. 7 c.
B. Load fluctuation under optical storage system
In a scene B, the photovoltaic unit and the energy storage unit run together in the system, the photovoltaic unit is in an MPPT mode, and the energy storage unit is communicated with each other through a master-slave three-layer control framework to stabilize the voltage of a direct current bus. In the optical storage hybrid sub-network, the energy storage units select energy storage main units according to a distributed election algorithm, and the rest energy storage units are in slave unit states. If the energy storage in the MG1 meets the triggering condition due to load fluctuation when the cell observation voltage meets the triggering condition, the cell observation voltage is triggered to access the observation voltage and the state variable of the energy storage main unit in the adjacent MG2, and the bus voltage reference value is accessed
. Meanwhile, the energy storage slave unit in the MG1 is triggered to access the observed voltage and the state variable of the energy storage master unit and access the observed voltage and the state variable of the adjacent energy storage slave unit.
Setting an initial load of 28.9kW and a total photovoltaic power of 20kW, wherein the energy supplied by the photovoltaic unit cannot meet the load requirement, and the energy storage unit is in a discharge state; when t =90s, the load power is reduced to 5.8kW, the photovoltaic unit is over-powered and absorbed by the energy storage unit, and the energy storage unit is changed from a discharge state to a charge state. Simulation results of the voltage fluctuation of the direct current bus and the state of charge of the energy storage unit under the strategy and the traditional strategy are shown in the figures 8a and 8b, and the distributed communication triggering time is shown in the figure 8 c.
Through a master-slave distributed coordination control strategy, the elected master unit can bring the slave unit to make up for power/current sharing mismatch in the sub-network and SOC imbalance of the energy storage unit; meanwhile, the coordination among the main units can also realize the power/current distribution and energy storage SOC balance of the whole cluster system, and the reliability of the system is improved. The master-slave coordination control can realize orderly and efficient transmission of cooperative information under different operation conditions, so that the supply and demand balance is met, the stability of the voltage of the public bus is effectively ensured, and the plug and play requirements of the system are met.
The above is only a preferred embodiment of the present invention, and it should be noted that the above preferred embodiment should not be considered as limiting the present invention, and the protection scope of the present invention should be subject to the scope defined by the claims. It will be apparent to those skilled in the art that various modifications and adaptations can be made without departing from the spirit and scope of the invention, and these modifications and adaptations should be considered within the scope of the invention.
Claims (23)
1. The utility model provides a little electric wire netting cluster of direct current, includes a plurality of little electric wire netting of direct current, its characterized in that: the direct-current micro-grid comprises a plurality of electric units, and the electric units are energy storage units or photovoltaic units; each electric unit in each direct-current microgrid is provided with only one main unit at the same time, and the rest are slave units; the direct current microgrid can only communicate with the master unit, and the master unit and the slave unit in the direct current microgrid as well as the slave unit and the slave unit can communicate with each other.
2. A multi-stage cooperative control method of a direct current microgrid cluster, which is applied to the direct current microgrid cluster of claim 1, and is characterized by comprising the following steps:
selecting one electrical unit from each direct current microgrid as a main unit;
when the communication condition of the master unit is triggered, the master units among the direct current micro grids communicate, and the communication of the slave units in the direct current micro grids is synchronously triggered;
and the supply and demand balance of the direct-current microgrid cluster is achieved by carrying out hierarchical cooperative control by utilizing information communicated among the main units, the main units and the slave units.
3. The multi-stage cooperative control method for the direct current microgrid cluster according to claim 2, wherein the method for selecting one electrical unit from each direct current microgrid as a main unit comprises:
all the electric units in the direct current microgrid are initialized to be slave units, and the slave units can receive heartbeat signals from the master unit;
when a slave unit receives the heartbeat signal of the main unit and times out, the slave unit is used as a competitor to initiate voting;
the contestants vote themselves after updating own vacation numbers, and initiate voting invitations to other slave units in the direct current microgrid, wherein the voting invitations are accompanied with the contestant vacation numbers;
the contestants count the votes obtained by themselves, if the number of the votes obtained exceeds half, the contestants are taken as main units, and the voting is finished;
if the contestant receives the heartbeat signal from the master unit during the time the vote is initiated, the vote is stopped and the master unit is re-used as the slave unit.
4. The multi-stage cooperative control method for the direct-current microgrid cluster as recited in claim 3, characterized in that: the slave unit casts votes to a first candidate initiating a voting invitation to the slave unit; if the tenure number of the candidate is smaller than the tenure number of the candidate, refusing voting; if the candidate is finally elected as the master unit, the master unit updates its own tenure number to the candidate tenure number.
5. The multi-stage cooperative control method for the direct-current microgrid cluster as recited in claim 3, characterized in that: the number of the expiration date is monotonically increased; if the random number of the main unit is smaller than the random number of any other electric unit, the main unit updates the random number to the maximum random number value in the direct current microgrid and takes the random number as a slave unit again; and if the slave unit dead time number is smaller than the dead time number of any other electric unit, the slave unit updates the dead time number to the maximum dead time number value in the direct current microgrid.
6. According to claim2, the multi-stage cooperative control method of the dc microgrid cluster is characterized in that the communication triggering conditions of the master unit are as follows:
；
wherein,
；
in the formula,
the deviation between the voltage observed value and the voltage reference value is obtained;
for the moment of triggering
And of the previous moment
A deviation of (a);
modulo a relationship matrix between the master units; b k Is a main unit andweights between voltage reference values; l is a radical of an alcohol 0 Represents a laplace matrix; b 0 Representing a weight matrix between the main cells and the voltage reference values,
；
and
are adjustment coefficients within a specified range.
7. The multi-stage cooperative control method for the direct-current microgrid cluster is characterized in that the hierarchical cooperative control method comprises a photovoltaic unit control method and an energy storage unit control method;
the photovoltaic unit control method comprises a photovoltaic main unit control strategy and a photovoltaic slave unit control strategy;
the energy storage unit control method comprises an energy storage main unit control strategy and an energy storage slave unit control strategy.
8. The method according to claim 7, wherein the photovoltaic slave unit control strategy comprises:
performing PI control on the difference between the reference value of the inner ring control current and the output current of the photovoltaic slave unit;
carrying out pulse width modulation on the result of PI control;
controlling the duty ratio of the pulse width modulation result to obtain a control signal, and controlling the output voltage of the photovoltaic slave unit through the control signal;
when no energy storage unit participates in the same direct current microgrid, the method for obtaining the reference value of the inner loop control current comprises the following steps:
inputting the droop control coefficient and the output current of the photovoltaic slave unit, the droop control coefficient and the output current of the photovoltaic master unit corresponding to the photovoltaic slave unit into a photovoltaic slave unit current control function to obtain a current state quantity;
inputting the voltage observed value of the photovoltaic slave unit and the voltage observed value of the photovoltaic master unit corresponding to the photovoltaic slave unit into a photovoltaic slave unit voltage control function to obtain a voltage state quantity;
integrating the current state quantity and the voltage state quantity;
and (3) carrying out operation: the integrated result + (voltage observed value of the photovoltaic master unit corresponding to the photovoltaic slave unit-voltage observed value of the photovoltaic slave unit) -droop control output value;
performing PI control on the result after the operation to obtain an inner loop control current reference value;
when energy storage units participate in the same direct-current microgrid, the method for obtaining the reference value of the inner-loop control current comprises the following steps:
carrying out maximum power point tracking control on the output voltage and the output current of the photovoltaic slave unit to obtain an outer ring control voltage reference value;
and PI control is carried out on the difference between the outer ring control voltage reference value and the output voltage of the photovoltaic slave unit to obtain an inner ring control current reference value.
9. The multi-stage cooperative control method for the direct-current microgrid cluster as recited in claim 8, characterized in that:
the photovoltaic slave unit voltage control function is
Wherein k represents a direct-current microgrid k in the direct-current microgrid cluster; i represents a photovoltaic slave unit i in the direct current microgrid k;
is a voltage state quantity;
deriving the voltage observation;
is a voltage regulation factor;
the connection relation between the photovoltaic slave unit i and the photovoltaic slave unit j is 1 if the photovoltaic slave unit i and the photovoltaic slave unit j are connected, otherwise, the connection relation is 0;
is a voltage observation;
the voltage observed value of the photovoltaic slave unit j in the direct-current micro-grid k is obtained;
for the weight of the relationship between master and slave units, if the slave unit has access to the master unit
Is 1, otherwise is 0;
the voltage observed value of the photovoltaic main unit in the direct current micro-grid k is obtained;
the photovoltaic slave unit current control function is
Wherein k represents a direct-current microgrid k in the direct-current microgrid cluster; i represents a photovoltaic slave unit i in the direct current microgrid k;
is a current state quantity;
a current regulation factor;
the relation between the photovoltaic slave unit i and the photovoltaic slave unit j is 1 if the connection is made, otherwise, the relation is 0;
in order to control the droop control coefficient,
to output a current;
is the droop control coefficient of the photovoltaic slave unit j in the direct current micro-grid k,
the output current of the photovoltaic slave unit j in the direct current micro-grid k is obtained;
the droop control coefficient of the photovoltaic main unit in the direct current microgrid k is obtained;
and (4) outputting current of the photovoltaic main unit in the direct current microgrid k.
10. The method of claim 7, wherein the photovoltaic master unit control strategy comprises:
performing PI control on the difference between the reference value of the inner ring control current and the output current of the photovoltaic main unit;
carrying out pulse width modulation on the result of PI control;
controlling the duty ratio of the pulse width modulation result to obtain a control signal, and controlling the output voltage of the photovoltaic main unit through the control signal;
when no energy storage unit participates in the same direct current microgrid, the method for obtaining the reference value of the inner loop control current comprises the following steps:
inputting droop control coefficients and output currents of other photovoltaic main units in the cluster into a current control function of the photovoltaic main units to obtain current state quantities;
inputting voltage observed values of other photovoltaic main units in the cluster and voltage reference values of the photovoltaic main units into a photovoltaic slave unit voltage control function to obtain voltage state quantities;
integrating the sum of the current state quantity and the voltage state quantity;
and (3) carrying out operation: voltage reference of the photovoltaic main cell + (result of integration-droop control output value) -port voltage of the photovoltaic main cell;
performing PI control on the calculated result to obtain an inner loop control current reference value;
when energy storage units participate in the same direct-current microgrid, the method for obtaining the reference value of the inner-loop control current comprises the following steps:
carrying out maximum power point tracking control on the output voltage and the output current of the photovoltaic main unit to obtain an outer ring control voltage reference value;
and performing PI control on the difference between the outer ring control voltage reference value and the output voltage of the photovoltaic main unit to obtain an inner ring control current reference value.
11. The multi-stage cooperative control method for the direct-current microgrid cluster as recited in claim 10, characterized in that:
the photovoltaic main unit voltage control function is
Wherein k represents a direct-current microgrid k in the direct-current microgrid cluster; 0 represents a photovoltaic main unit in the direct current microgrid k;
is a voltage state quantity;
deriving the voltage observation;
is a voltage regulation factor;
the connection relation between the main unit of the direct current microgrid k and the photovoltaic main unit of the direct current microgrid l is 1 if the connection exists, or 0 if the connection does not exist;
is a voltage observation;
voltage observed values of photovoltaic main units of other direct current micro-grids l in the cluster are obtained;
for weighting the relationship between the main cells and the voltage reference value, if the main cells have access to the voltage reference value
Is 1, otherwise is 0;
is a voltage reference value;
the photovoltaic main unit current control function is
Wherein k represents direct current in the direct current microgrid clusterA microgrid k;0 represents a photovoltaic main unit in the direct current microgrid k;
is a current state quantity;
a current regulation factor;
the connection relation between the main unit of the direct current microgrid k and the main unit of the direct current microgrid l is 1 if the connection exists, or 0 if the connection does not exist;
is a droop control coefficient;
to output a current;
a droop control coefficient for another photovoltaic main unit in the cluster;
is the output current of another photovoltaic main unit in the cluster.
12. The method according to claim 7, wherein the control strategy of the energy storage slave unit is:
when the energy storage slave unit participates in the direct-current microgrid, PI control is carried out on the difference between the reference value of the inner-loop control current and the output current of the energy storage slave unit;
carrying out pulse width modulation on the result of PI control;
controlling the duty ratio of the pulse width modulation result to obtain a control signal, and controlling the output voltage of the energy storage slave unit through the control signal;
the method for obtaining the reference value of the inner loop control current comprises the following steps:
inputting voltage observed values of the energy storage main units in the same direct-current microgrid and voltage observed values of other energy storage slave units in the same direct-current microgrid into a voltage control function of the energy storage slave units to obtain voltage state quantities;
inputting state variables of other energy storage slave units in the same direct current microgrid and state variables of an energy storage master unit in the same direct current microgrid into a power control function of the energy storage slave units to obtain power state quantities;
integrating the sum of the voltage state quantity and the power state quantity;
and (3) performing the operation: the result of integration + (voltage observation-droop control output-port voltage value);
and performing PI control on the calculated result to obtain an inner loop control current reference value.
13. The multi-stage cooperative control method of the direct-current microgrid cluster as recited in claim 12, characterized in that:
the energy storage slave unit voltage control function is
Wherein k represents a direct-current microgrid k in the direct-current microgrid cluster; i represents an energy storage slave unit i in the direct current microgrid k;
is a voltage state quantity;
deriving a voltage observation;
is a voltage regulation factor;
the connection relation between the energy storage slave unit i and the energy storage slave unit j is 1 if the energy storage slave unit i and the energy storage slave unit j are connected, otherwise, the connection relation is 0;
is a voltage observation;
the voltage observed value of the energy storage slave unit j in the direct current micro-grid k is obtained;
as a weight of the relationship between the master and slave units, if the slave unit has access to the master unit
Is 1, otherwise is 0;
the voltage observed value of an energy storage main unit in the direct current micro-grid k is obtained;
the energy storage slave unit power control function is
Wherein k represents a direct-current microgrid k in the direct-current microgrid cluster; i represents an energy storage slave unit i in the direct current micro-grid k;
is a power state quantity;
is a power control coefficient;
the connection relation between the energy storage slave unit i and the energy storage slave unit j is 1 if the energy storage slave unit i and the energy storage slave unit j are connected, otherwise, the connection relation is 0;
is a state variable;
the state variable of the energy storage slave unit j in the direct current micro-grid k is obtained;
for the weight of the relationship between master and slave units, if the slave unit has access to the master unit
Is 1, otherwise is 0;
is the state variable of the energy storage main unit in the direct current micro-grid k.
14. The method according to claim 7, wherein the control strategy of the energy storage master unit is:
when the energy storage main unit participates in the direct-current microgrid, PI control is carried out on the difference between the reference value of the inner-loop control current and the output current of the energy storage main unit;
carrying out pulse width modulation on the result of PI control;
controlling the duty ratio of the pulse width modulation result to obtain a control signal, and controlling the output voltage of the energy storage slave unit through the control signal;
the method for obtaining the reference value of the inner loop control current comprises the following steps:
inputting the voltage reference value of the energy storage main unit and the voltage observation values of the energy storage main units of other direct current micro-grids in the cluster into a voltage control function of the energy storage main unit to obtain a voltage state quantity;
inputting state variables of energy storage main units of other direct current micro-grids in the cluster into a power control function of the energy storage main unit to obtain power state quantities;
integrating the sum of the voltage state quantity and the power state quantity;
and (3) carrying out operation: the result of integration + (voltage reference value-port voltage value-droop control output value);
and performing PI control on the calculated result to obtain an inner loop control current reference value.
15. The multi-stage cooperative control method for the direct-current microgrid cluster as recited in claim 14, characterized in that:
the energy storage main unit voltage control function is
Wherein k represents a direct-current microgrid k in the direct-current microgrid cluster; 0 represents an energy storage main unit in the direct current microgrid k;
is a voltage state quantity;
deriving the voltage observation;
is a voltage regulation factor;
the connection relation between the main unit of the direct current microgrid k and the main unit of the direct current microgrid l is 1 if the connection exists, or 0 if the connection does not exist;
is a voltage observation;
voltage observed values of the light energy storage main units of other direct current micro-grids l in the cluster are obtained;
for weighting the relationship between the main cells and the voltage reference value, if the main cells have access to the voltage reference value
Is 1, otherwise is 0;
is a voltage reference value;
the energy storage main unit power control function is
Wherein k represents a direct-current microgrid k in the direct-current microgrid cluster; 0 represents an energy storage main unit in the direct current microgrid k;
is a power state quantity;
is a power control coefficient;
the connection relation between the main unit of the direct current microgrid k and the main unit of the direct current microgrid l is 1 if the connection exists, or 0 if the connection does not exist;
is a state variable;
and (3) state variables of the energy storage main unit of another direct current micro-grid l in the cluster.
16. The multi-stage cooperative control method for the direct current microgrid cluster as recited in any one of claims 12 or 14, characterized in that: the calculation formula of the state variable is
Wherein k represents a direct-current microgrid k in the direct-current microgrid cluster; i represents an energy storage unit i in the direct current microgrid k;
is the output power of the energy storage unit;
the lower limit value of the SOC when the energy storage unit discharges;
the upper limit value of the SOC when the energy storage unit discharges;
the nominal capacity of the energy storage unit i in the direct current micro-grid k.
17. The multi-stage cooperative control method for the direct current microgrid cluster as recited in any one of claims 8 or 12, characterized in that:
the observed value of the voltage of the slave unit is calculated by the formula
Wherein k represents direct current micro-electricity in a direct current micro-grid clusterA net k; i represents a photovoltaic slave unit or an energy storage slave unit i in the direct current micro-grid k;
is a voltage observation;
is the port voltage value;
the connection relation between the photovoltaic slave unit i and the photovoltaic slave unit j or between the energy storage slave unit i and the energy storage slave unit j is 1 if the photovoltaic slave unit i and the energy storage slave unit j are connected, otherwise, the connection relation is 0;
and (3) voltage observed values of the photovoltaic slave unit j or the energy storage slave unit j in the direct-current microgrid K.
18. The multi-stage cooperative control method for the direct current microgrid cluster as recited in any one of claims 10 or 14, characterized in that:
the observed value of the voltage of the main unit is calculated by the formula
Wherein k represents a direct-current microgrid k in the direct-current microgrid cluster; 0 represents a photovoltaic main unit or an energy storage main unit in the direct current microgrid k;
is a voltage observed value;
is the port voltage value;
the connection relationship between the main unit of the direct current microgrid k and the main unit of the direct current microgrid l is 1 if the connection is present, or 0 if the connection is not present;
and (4) obtaining voltage observed values of the photovoltaic main units of other direct current micro-grids l in the cluster.
19. A multi-stage cooperative control system of a DC microgrid cluster, which is applied to the DC microgrid cluster of claim 1, and is characterized by comprising:
the election module is used for selecting one electric unit from each direct current microgrid as a main unit;
the communication triggering module is used for triggering the communication of the main unit, when the communication condition of the main unit is triggered, the main unit among the direct current micro grids carries out communication, and the communication of the slave units in the direct current micro grids is synchronously triggered; the communication trigger conditions of the master unit are as follows:
；
wherein,
；
in the formula,
the deviation between the voltage observed value and the voltage reference value is obtained;
for the moment of triggering
And of the previous moment
A deviation of (a);
modulo a relationship matrix between the master units; b k Is the weight between the main cell and the voltage reference value; l is a radical of an alcohol 0 Represents a laplace matrix; b is 0 Representing a weight matrix between the main cells and the voltage reference values,
；
and
the adjustment coefficient is within a specified range;
the cooperative control module is used for performing hierarchical cooperative control by utilizing information communicated among the main units, the main units and the slave units to achieve the balance of supply and demand of the direct-current microgrid cluster, and comprises a photovoltaic unit control module and an energy storage unit control module;
the photovoltaic unit control module comprises a photovoltaic main unit control module and a photovoltaic slave unit control module;
the energy storage unit control module comprises an energy storage main unit control module and an energy storage slave unit control module.
20. The multi-stage cooperative control system of the dc microgrid cluster of claim 19, characterized in that:
the photovoltaic slave unit control module is used for carrying out PI control on the difference between the reference value of the inner ring control current and the output current of the photovoltaic slave unit;
carrying out pulse width modulation on the result of PI control;
controlling the duty ratio of the pulse width modulation result to obtain a control signal, and controlling the output voltage of the photovoltaic slave unit through the control signal;
when no energy storage unit participates in the same direct current microgrid, the method for obtaining the reference value of the inner loop control current comprises the following steps:
inputting the droop control coefficient and the output current of the photovoltaic slave unit, the droop control coefficient and the output current of the photovoltaic master unit corresponding to the photovoltaic slave unit into a current control function of the photovoltaic slave unit to obtain a current state quantity;
inputting the voltage observed value of the photovoltaic slave unit and the voltage observed value of the photovoltaic master unit corresponding to the photovoltaic slave unit into a photovoltaic slave unit voltage control function to obtain a voltage state quantity;
integrating the current state quantity and the voltage state quantity;
and (3) carrying out operation: the integrated result + (voltage observed value of the photovoltaic master unit corresponding to the photovoltaic slave unit-voltage observed value of the photovoltaic slave unit) -droop control output value;
performing PI control on the calculated result to obtain an inner loop control current reference value;
when energy storage units participate in the same direct-current microgrid, the method for obtaining the reference value of the inner-loop control current comprises the following steps:
carrying out maximum power point tracking control on the output voltage and the output current of the photovoltaic slave unit to obtain an outer ring control voltage reference value;
and PI control is carried out on the difference between the outer ring control voltage reference value and the output voltage of the photovoltaic slave unit to obtain an inner ring control current reference value.
21. The multi-stage cooperative control system of the dc microgrid cluster of claim 19, characterized in that:
the photovoltaic main unit control module is used for carrying out PI control on the difference between the reference value of the inner ring control current and the output current of the photovoltaic main unit;
carrying out pulse width modulation on the result of PI control;
controlling the duty ratio of the pulse width modulation result to obtain a control signal, and controlling the output voltage of the photovoltaic main unit through the control signal;
when no energy storage unit participates in the same direct current microgrid, the method for obtaining the reference value of the inner loop control current comprises the following steps:
inputting droop control coefficients and output currents of other photovoltaic main units in the cluster into a current control function of the photovoltaic main units to obtain current state quantities;
inputting voltage observed values of other photovoltaic main units in the cluster and voltage reference values of the photovoltaic main units into a photovoltaic slave unit voltage control function to obtain voltage state quantities;
integrating the sum of the current state quantity and the voltage state quantity;
and (3) carrying out operation: voltage reference value of the photovoltaic main cell + (result of integration-droop control output value) -port voltage of the photovoltaic main cell;
performing PI control on the calculated result to obtain an inner loop control current reference value;
when energy storage units participate in the same direct-current microgrid, the method for obtaining the reference value of the inner-loop control current comprises the following steps:
carrying out maximum power point tracking control on the output voltage and the output current of the photovoltaic main unit to obtain an outer ring control voltage reference value;
and performing PI control on the difference between the outer ring control voltage reference value and the output voltage of the photovoltaic main unit to obtain an inner ring control current reference value.
22. The multi-stage cooperative control system of the dc microgrid cluster of claim 19, characterized in that:
the energy storage slave unit control module is used for carrying out PI control on the difference between the reference value of the inner ring control current and the output current of the energy storage slave unit when the energy storage slave unit participates in the direct-current microgrid;
carrying out pulse width modulation on the result of PI control;
controlling the duty ratio of the pulse width modulation result to obtain a control signal, and controlling the output voltage of the energy storage slave unit through the control signal;
the method for obtaining the reference value of the inner loop control current comprises the following steps:
inputting voltage observed values of the energy storage main units in the same direct-current microgrid and voltage observed values of other energy storage slave units in the same direct-current microgrid into a voltage control function of the energy storage slave units to obtain voltage state quantities;
inputting state variables of other energy storage slave units in the same direct current microgrid and state variables of an energy storage master unit in the same direct current microgrid into a power control function of the energy storage slave units to obtain power state quantities;
integrating the sum of the voltage state quantity and the power state quantity;
and (3) carrying out operation: the result of integration + (voltage observation-droop control output-port voltage value);
and performing PI control on the calculated result to obtain an inner loop control current reference value.
23. The multi-stage cooperative control system of the dc microgrid cluster of claim 19, characterized in that:
the energy storage main unit control module is used for carrying out PI control on the difference between the reference value of the inner ring control current and the output current of the energy storage main unit when the energy storage main unit participates in the direct-current microgrid;
carrying out pulse width modulation on the result of PI control;
controlling the duty ratio of the pulse width modulation result to obtain a control signal, and controlling the output voltage of the energy storage slave unit through the control signal;
the method for obtaining the reference value of the inner loop control current comprises the following steps:
inputting the voltage reference value of the energy storage main unit and the voltage observation values of the energy storage main units of other direct current micro-grids in the cluster into a voltage control function of the energy storage main unit to obtain a voltage state quantity;
inputting state variables of energy storage main units of other direct current micro-grids in the cluster into a power control function of the energy storage main unit to obtain power state quantities;
integrating the sum of the voltage state quantity and the power state quantity;
and (3) performing the operation: the result of integration + (voltage reference value-port voltage value-droop control output value);
and performing PI control on the calculated result to obtain an inner loop control current reference value.
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