CN115313446A - Micro-grid power balance control method - Google Patents
Micro-grid power balance control method Download PDFInfo
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- CN115313446A CN115313446A CN202211083611.8A CN202211083611A CN115313446A CN 115313446 A CN115313446 A CN 115313446A CN 202211083611 A CN202211083611 A CN 202211083611A CN 115313446 A CN115313446 A CN 115313446A
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/28—Arrangements for balancing of the load in a network by storage of energy
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/388—Islanding, i.e. disconnection of local power supply from the network
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J9/00—Circuit arrangements for emergency or stand-by power supply, e.g. for emergency lighting
- H02J9/04—Circuit arrangements for emergency or stand-by power supply, e.g. for emergency lighting in which the distribution system is disconnected from the normal source and connected to a standby source
- H02J9/06—Circuit arrangements for emergency or stand-by power supply, e.g. for emergency lighting in which the distribution system is disconnected from the normal source and connected to a standby source with automatic change-over, e.g. UPS systems
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Abstract
The invention relates to the technical field of microgrid stability control and discloses a microgrid power balance control method. According to the micro-grid power balance control method, smooth switching between isolated network and grid connection can be realized, the problem of power supply interruption when the grid connection state is switched to the isolated network is solved, and guarantee is provided for the micro-grid to run in various stable states and transient states.
Description
Technical Field
The invention relates to the technical field of microgrid stability control, in particular to a microgrid power balance control method.
Background
The stable operation of the microgrid is the premise of safe and reliable operation of the microgrid and benefit exertion. The micro-grid can fully exert the benefits only by realizing grid connection and stable isolated grid, fast isolation and seamless switching and really realizing plug and play of the micro-grid. Due to the common characteristics of low overload capacity, small inertia or no inertia of the distributed power generation power supply of the microgrid and the problems of sudden change of the load in the microgrid and the like, the system of the microgrid is easy to oscillate and even collapse, and the development and application of the microgrid are severely restricted. In order to improve the situation, energy storage equipment is usually used in the existing microgrid structure to maintain the stability of the transient state of the system, and voltage and frequency support is provided for the microgrid when necessary, but a mature control method which only takes the energy storage equipment as a control object and can meet the requirement of stable operation of the microgrid in various operation modes does not exist at present;
in order to overcome the above drawbacks of the prior art, an object of the present invention is to provide a microgrid power balance control method.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides the following technical scheme: a microgrid power balance control method is characterized in that energy storage equipment is connected into a microgrid through a bidirectional inverter, when the microgrid operates in an isolated network, a V-f control mode is adopted, the energy storage equipment provides voltage source support for a micro power source in the microgrid and provides power support according to output of the micro power source and load change, and the specific working mode is as follows:
(1) When the output power of the micro power supply is equal to the power required by the load, the output of the energy storage device is approximately zero, and the power required by the load is completely supplied by the micro power supply;
(2) When the output power of the micro power supply is larger than the power required by the load, the energy storage equipment is controlled to be charged, and the redundant power of the micro power supply after meeting the load is absorbed;
(3) And when the output power of the micro power supply is smaller than the power required by the load, controlling the energy storage equipment to discharge to supplement the insufficient output power of the micro power supply.
Preferably, in the operating mode (1), the modulation ratio ma of the bidirectional inverter is kept unchanged; in the working mode (2), the modulation ratio ma of the bidirectional inverter is reduced along with the increase of the direct-current voltage in the continuous charging process; in the operation mode (3), the modulation ratio ma of the bidirectional inverter increases as the discharge-sustaining direct-current voltage decreases.
Preferably, the micro power supply is referenced to the voltage and frequency output of the bi-directional inverter.
Preferably, the power frequency sine wave is discretized to obtain sine wave data of a plurality of discrete time points in a power frequency period, a sine table array sin [ n ] composed of the sine wave data is formed, a corresponding rectangular pulse sequence is formed according to the sine table array to replace a power frequency sine wave required by V-f control to be used as a modulation wave, a switch point number nf corresponding to the sine table in the power frequency period is obtained through the relationship between the switch frequency and the power frequency, and a rectangular pulse used for modulation is selected according to the moving step length of the sine table pointer when the power frequency sine wave is realized by taking the multiple of the total number n and nf of elements of the sine table array.
Preferably, when the microgrid is connected to the power grid, a PQ decoupling control mode is adopted, power change is quickly tracked, and meanwhile, the change of active power or reactive power is independently controlled.
Preferably, firstly, the reactive power is adjusted to zero, then the active power is independently controlled, the fluctuation of the power of the micro power source is stabilized, the exchange power between the micro grid and the public power grid is controllable, and the specific working mode is as follows:
(1) When the difference between the output power of the micro power source and the consumed power of the load fluctuates in the positive direction, the energy storage equipment is controlled to be charged, and redundant power is absorbed;
(2) And when the difference value between the output power of the micro power supply and the consumed power of the load fluctuates in a negative direction, the energy storage equipment is controlled to discharge, and the power shortage of the load is met.
Preferably, the power frequency sine wave is discretized to obtain sine wave data of a plurality of discrete time points in a power frequency cycle, a sine table array sin [ m ] composed of the sine wave data is formed, a corresponding rectangular pulse sequence is formed according to the sine table array to replace the power frequency sine wave required by a voltage feedforward part in PQ decoupling control to serve as a modulation wave, the number mf of switch points corresponding to the sine table in the power frequency cycle is obtained through the relation between the switch frequency and the power frequency, and rectangular pulses for modulation are selected by the step length of the movement of a pointer of the sine table when the total number m of elements of the sine table and the multiple of mf of the sine table are used for realizing the power frequency sine wave.
Preferably, when the isolated network/grid-connected dual mode is switched, one or more of voltage, frequency, phase and power of another operation mode are firstly tracked and corrected in the current operation mode, and then the other operation mode is switched after the requirement is met.
Preferably, when the microgrid is switched from an isolated network mode to a grid-connected mode, a V-f control mode is adopted to track the voltage and the phase in the grid-connected mode during isolated network, and after grid connection, the control mode is converted into a PQ decoupling control mode;
when the microgrid is switched from a grid-connected mode to an isolated grid mode, the method is divided into a planned mode and an unplanned mode: (1) planned grid connection: before grid connection, the exchange power of the microgrid and the public power grid is adjusted to zero by switching loads or limiting the output of the micro power supply, and after grid connection, the control mode is switched to a V-f control mode; (2) non-planned grid connection: and the control mode is directly converted into a V-f control mode, the energy storage device is controlled to output or absorb power if the exchange power is within the capacity allowable range of the energy storage device in the switching process, and the load is quickly cut off or the output of the micro power source is limited if the exchange power exceeds the capacity allowable range of the energy storage device.
Preferably, if the SOC of the energy storage device does not meet the minimum set threshold requirement, a constant large current is first used to forcibly charge the energy storage device, and when the SOC reaches the set threshold, a constant voltage small current is then used to charge the energy storage device.
Compared with the prior art, the invention has the following beneficial effects: in the process of pulse width modulation in the isolated network operation mode and the grid-connected operation mode, the sine table array is used as a reference adjusting wave, and a switching link is established for mutual switching between the isolated network operation mode and the grid-connected operation mode, so that the energy storage equipment can track and correct the voltage, the frequency and other related quantities in another operation mode when operating in any one mode, and conditions are created for seamless smooth switching.
Due to the fact that a link for switching between grid connection and isolated network is found, the problem of power supply interruption caused when the micro-grid is converted from a grid connection state to an isolated network state is well solved, and a user can provide a seamless and stable power supply for a load under the condition that other power supplies of the micro-grid are in failure (including power failure of the power grid).
Drawings
Other features, objects and advantages of the present application will become more apparent upon reading of the following detailed description of non-limiting embodiments thereof, made with reference to the accompanying drawings in which:
FIG. 1 is a schematic diagram of the charging operation of the energy storage device of the present invention;
FIG. 2 is a schematic diagram of the discharge operating state of the energy storage device of the present invention;
FIG. 3 is a schematic block diagram of the V-f control in isolated grid mode of the present invention;
FIG. 4 is a PQ decoupling control principle block diagram based on sine table reference in the grid-connected mode of the invention;
fig. 5 is a control flow block diagram of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. The drawings are only for purposes of illustration and are not intended to be limiting, certain elements of the drawings may be omitted, enlarged or reduced to better illustrate the embodiments of the present invention, and do not represent the size of the actual product, and it is understood that some well-known structures, elements and descriptions thereof in the drawings may be omitted for persons skilled in the art.
Referring to fig. 1 to 5, in a method for controlling power balance of a microgrid, an energy storage device is connected to the microgrid through a bidirectional inverter, and when the microgrid operates in an isolated grid, a V-f control mode is adopted, the energy storage device provides a voltage source support for a micro power source in the microgrid, and provides a power support according to output of the micro power source and load change, and the specific working mode is as follows:
(1) When the output power of the micro power supply is equal to the power required by the load, the output of the energy storage device is approximately zero, and the power required by the load is completely supplied by the micro power supply;
(2) When the output power of the micro power supply is larger than the power required by the load, the energy storage equipment is controlled to be charged, and the surplus power of the micro power supply after the load is met is absorbed;
(3) And when the output power of the micro power supply is smaller than the power required by the load, controlling the energy storage device to discharge to supplement the insufficient output power of the micro power supply.
In the working mode (1), the modulation ratio ma of the bidirectional inverter is kept unchanged; in the working mode (2), the modulation ratio ma of the bidirectional inverter is reduced along with the increase of the direct-current voltage in the continuous charging process; in the operation mode (3), the modulation ratio ma of the bidirectional inverter increases as the discharge-sustaining direct-current voltage decreases.
Wherein the micro power supply takes the voltage and frequency output of the bidirectional inverter as a reference.
The method comprises the steps of discretizing a power frequency sine wave to obtain sine wave data of a plurality of discrete time points in a power frequency cycle, forming a sine table array sin [ n ] composed of the sine wave data, forming a corresponding rectangular pulse sequence according to the sine table array to replace a power frequency sine wave required by V-f control to serve as a modulation wave, obtaining the number nf of switch points corresponding to the sine table in the power frequency cycle through the relation between the switch frequency and the power frequency, and selecting a rectangular pulse for modulation for the moving step length of a pointer of the sine table when the power frequency sine wave is realized by using the multiple of the total number n and nf of elements of the sine table array.
When the microgrid is connected to the power grid, a PQ decoupling control mode is adopted, power change is quickly tracked, and meanwhile, the change of active power or reactive power is independently controlled.
Wherein, turn reactive power to zero earlier, independent control active power again stabilizes little power fluctuation, makes exchange power controllable between microgrid and public power grid, and concrete working method is:
(1) When the difference between the output power of the micro power source and the consumed power of the load fluctuates in the positive direction, the energy storage equipment is controlled to be charged, and redundant power is absorbed;
(2) And when the difference value between the output power of the micro power supply and the consumed power of the load fluctuates in a negative direction, the energy storage equipment is controlled to discharge, and the power shortage of the load is met.
The method comprises the steps of discretizing a power frequency sine wave to obtain sine wave data of a plurality of discrete time points in a power frequency cycle, forming a sine table array sin [ m ] composed of the sine wave data, forming a corresponding rectangular pulse sequence according to the sine table array to replace the power frequency sine wave required by a voltage feedforward part in PQ decoupling control to serve as a modulation wave, obtaining the number mf of switch points corresponding to the sine table in the power frequency cycle through the relation between the switch frequency and the power frequency, and selecting rectangular pulses for modulation by using the moving step length of the pointer of the sine table when the total number m of elements of the sine table and the multiple of the mf of the sine table are used for realizing power frequency sine wave.
When the isolated network/grid-connected dual mode is switched, one or more of voltage, frequency, phase and power of another operation mode are firstly tracked and corrected in the current operation mode, and then the other operation mode is switched after the requirements are met.
When the microgrid is switched from an isolated network mode to a grid-connected mode, tracking voltage and phase in the grid-connected mode by adopting a V-f control mode in the isolated network mode, and converting the control mode into a PQ decoupling control mode after grid connection;
when the microgrid is switched from a grid-connected mode to an isolated grid mode, the method is divided into a planned mode and an unplanned mode: (1) planned grid connection: before grid connection, the exchange power of the microgrid and the public power grid is adjusted to zero by switching loads or limiting the output of the micro power supply, and after grid connection, the control mode is switched to a V-f control mode; (2) non-planned grid connection: and the control mode is directly converted into a V-f control mode, the energy storage equipment is controlled to output or absorb power if the exchange power is within the capacity allowable range of the energy storage equipment in the switching process, and the load is quickly cut off or the output of the micro power supply is limited if the exchange power exceeds the capacity allowable range of the energy storage equipment.
If the SOC of the energy storage equipment cannot meet the minimum set threshold requirement, the energy storage equipment is forcibly charged by adopting constant large current, and when the SOC reaches the set threshold, the energy storage equipment is charged by using constant voltage small current.
The invention provides a micro-grid power balance control method which can be used for controlling energy storage equipment in a micro-grid isolated network and grid-connected operation mode and in the process of converting isolated network to grid-connected and grid-connected to isolated network. The energy storage equipment is connected into the microgrid through a bidirectional inverter, and the connection between the microgrid and the public power grid is realized through a PCC (common connection point between the microgrid and the public power grid) switch. The following is a detailed content of the control method, and a flowchart of the control method can be seen in fig. 5.
1. V-f control in isolated network mode:
under the condition of power grid failure or under the condition of no grid connection, the energy storage equipment provides voltage source support for micro power sources such as photovoltaic power sources in the micro grid by adjusting the bidirectional inverter, and simultaneously provides power support according to the output of the micro power sources and load change.
There are three operating conditions in isolated network mode: 1) When the output power of the photovoltaic power supply and the power required by the load are equal, the load power is completely supplied by the photovoltaic power supply, and the output power of the energy storage device is approximately zero (namely equal to zero or very close to zero); 2) When the output of the photovoltaic power supply is greater than the power required by the load, the output of the photovoltaic power supply provides redundant power to the energy storage device after the load is met, at the moment, the bidirectional inverter works in a rectification state, and the energy storage device works in a charging state (as shown in fig. 1); 3) When the output of the photovoltaic power supply is smaller than the power required by the load, the bidirectional inverter works in an inversion state, and the energy storage device works in a discharge state (as shown in fig. 2), if the discharge does not meet the load requirement, part of the load is disconnected under the control of the central controller). In isolated grid mode of operation, the photovoltaic power source is referenced to the voltage and frequency output by the bi-directional inverter to maintain its normal operation.
If the energy storage device cannot meet the power requirement of the load after charging and discharging, the upper-level controller coordinates to change the output of the micro power supply in the microgrid or change the load size to realize the stable operation of the microgrid, and the content is out of the scope of the invention.
In the first operating situation, the inverter modulation ratio ma remains constant, in the second operating situation the inverter modulation ratio ma decreases as the continuous charging dc voltage increases, and in the third operating situation the inverter modulation ratio ma increases as the continuous discharging dc voltage decreases.
Under the isolated network operation mode, V-f control needs a power frequency sine wave as a modulation wave, and the method for forming the modulation wave comprises the following steps: discretizing a power frequency sine wave (preferably a power frequency sine wave with the amplitude of 1) to obtain sine wave data of a plurality of (n) discrete time points in a power frequency cycle, forming a sine table array sin [ n ] consisting of the sine wave data as a reference, forming a rectangular pulse sequence corresponding to the power frequency sine wave data at each discrete time point according to the sine table array to replace the power frequency sine wave required by V-f control at each discrete time point as a modulation wave, obtaining the number nf of switching points corresponding to a power frequency cycle sine table (namely a switching frequency value taking one power frequency cycle as a unit) according to the relationship between the switching frequency and the power frequency, selecting a rectangular pulse for modulation by taking the multiple of the total number n and nf of the elements of the sine table as the step length of the movement of a pointer of the sine table when the power frequency sine wave is realized, thereby selecting a plurality of matrix pulses (matrix pulse subsequences) corresponding to the time points of the switching signals from the matrix pulse sequences, and comparing the modulation waves with the switching signals and modulating and outputting the sine waves (including the same phase) according with the sine waves (comprising the same phase).
Taking phase A as an example for analysis, the period of the triangular carrier wave corresponds to a period count value Coignr, the conduction pulse time of phase A corresponds to a pulse count Councipa, the number of points of phase A in the sine table array is nA, councipa =0.5 × Coignr (1 + ma sin [ nA ]), and the modulation waves of phase B and phase C can also be obtained by performing corresponding point shifting operations on the sine table array. The V-f control schematic block diagram is shown in fig. 3.
When the microgrid operates in an isolated network, the bidirectional inverter operates in a V-f control mode, a current array pointer sin _ pointer in a sine array changes according to a certain step length to realize power frequency modulation waves, and the phase locking angle theta is updated by using an angle corresponding to the sin _ pointer.
2. PQ decoupling control in a grid-connected mode:
the control method during grid-connected operation mainly aims to stabilize power grid power fluctuation caused by access of a photovoltaic power supply and the like with random fluctuation under the influence of weather factors to a power grid, and finally realizes controllability and stability of power exchange between the micro-grid and a public power grid, or realizes power following of the micro-grid.
Since the photovoltaic power supply mainly generates active power, the active power is the main power of the exchange power fluctuation caused by grid-connected operation. When active power fluctuation is compensated, reactive power may need to be adjusted to zero, so that when the microgrid is connected to the power grid, an active and reactive decoupling control method is adopted to quickly track power change, and meanwhile, the bidirectional inverter can be independently controlled to output active or reactive change.
The PQ decoupling control needs to transform variables in a three-symmetric stationary coordinate system into variables in a synchronous rotating coordinate system with grid fundamental wave voltage as a reference through coordinate transformation (namely, the variables are transformed into d-q coordinates through park transformation), and after the transformation, a fundamental wave alternating current sinusoidal variable is transformed into a direct current variable in the synchronous rotating coordinate system. Wherein the q-axis current is related to the reactive power and the d-axis current is related to the active component, the conversion achieving the decoupling of the active power and the reactive power.
The specific control mode is as follows: when the difference value between the output power of the micro power source and the consumed power of the load fluctuates in the positive direction (namely fluctuates towards the direction that the difference value is larger than zero), the energy storage equipment is controlled to be charged, and redundant power is absorbed; (1) And when the difference value between the output power of the micro power source and the consumed power of the load fluctuates in a negative direction (namely fluctuates towards a direction that the difference value is less than zero), controlling the energy storage equipment to discharge so as to meet the power shortage of the load. The control mode can keep the stability and controllability of the exchange power between the microgrid and the public power grid.
Similar to the isolated network mode, in the grid-connected mode, a voltage feedforward part in PQ decoupling control also needs a power frequency sine wave as a modulation wave, and the forming method of the modulation wave in the invention is the same as that of the modulation wave in V-f control, and comprises the following steps: discretizing a power frequency sine wave (preferably a power frequency sine wave with the amplitude of 1 for convenience of operation), obtaining sine wave data of a plurality of discrete time points in a power frequency period, forming a sine table array sin [ m ] consisting of the sine wave data, forming a corresponding rectangular pulse sequence according to the sine table array to replace the power frequency sine wave required by a voltage feedforward part in PQ decoupling control as a modulation wave, obtaining the number mf of switching points corresponding to the sine table in the power frequency period through the relationship between the switching frequency and the power frequency, and selecting the rectangular pulse for modulation by taking the multiple of the total number m and mf of the elements of the sine table (namely the value of the switching frequency taking one power frequency period as a unit) as the step length of the movement of a pointer of the sine table when the power frequency sine wave is realized. m and n are integers greater than 1, and may be the same or different. The PQ decoupling control schematic block diagram is shown in fig. 4, where Pref is a given active power, qref is a given reactive power, iidref is an active current, iiqref is a reactive current, ea, eb, and ec are grid voltages, iia, iib, and iic are inverter output currents, udc is an inverter dc-side voltage, udcref is an inverter dc-voltage reference, k is a transformation ratio of a transformer, w0 is a synchronous rotation angular frequency, ma is a modulation ratio, uma, umb, and umc are modulation waves for PQ decoupling control, uiabc is a three-phase voltage of a filter capacitor of a bidirectional inverter, and uiabcref is a three-phase voltage reference of a filter capacitor of the bidirectional inverter.
When the bidirectional inverter works in a grid-connected mode, a phase-locked angle theta changes along with the phase of a grid voltage, a reference modulation wave is realized by using a phase-locked angle corresponding to a current array pointer sin _ pointer of a pointer sin _ pointer PQ in a sine table array and a corresponding angle, the modulation wave obtained by a PQ decoupling current loop is superposed on the reference modulation wave generated by a sine table, an output modulation wave controlled by PQ decoupling can be obtained, and the power tracking of the grid-connected mode is realized.
In the two modes, the generated sine table array is used as a reference modulation wave, so that the energy storage system can track and correct the related quantities such as voltage, frequency, phase, power and the like of another operation mode when operating in any one mode, the sine table array serves as a link for mode switching, conditions are created for seamless and smooth switching between the two modes, and the problem that the reference of voltage, frequency and the like is difficult to give when the mode switching is performed in a conventional method is solved.
3. The control method for converting isolated network into grid connection comprises the following steps:
firstly, a V-f control mode is adopted to control a bidirectional inverter as a voltage source, voltage and phase under a grid-connected mode are tracked, and after grid connection, the control mode is converted into a PQ decoupling control mode.
4. The control method for converting grid connection into isolated network comprises the following steps:
(1) Converting planned grid connection into isolated grid connection:
the central main control system is required to issue an instruction, the switching power of the PCC points is adjusted to be zero by measures such as switching loads or limiting photovoltaic source output, the PCC points are controlled to be switched off rapidly (the process is controlled by the central controller), and the control method is converted into a V-f control mode and is switched to isolated network operation.
(2) Converting unplanned grid connection into isolated grid connection:
and (2) performing non-planned grid connection, namely, the PCC loses the power supply of the power grid due to sudden power failure of the PCC or power grid failure, and the like, wherein the control method is directly converted into a V-f control mode, the exchange power of the PCC during the switching process is supplied or absorbed by the energy storage equipment within the allowable range of the capacity of the energy storage equipment, and if the exchange power exceeds the capacity range of the PCC, measures such as load shedding or limitation of the output of the photovoltaic power supply and the like must be rapidly taken, so that the bidirectional inverter can stably operate.
In order to show the control method more intuitively, the control process of isolated network, grid connection, isolated network to grid connection and grid connection to isolated network is explained from the array level of the sine table:
when the microgrid operates in an isolated network, the bidirectional inverter operates in a V-f control mode, a current array pointer sin _ pointer in a sine array changes according to a certain step length to realize power frequency modulation waves, and an angle corresponding to the sin _ pointer is used for updating a phase locking angle theta;
when the microgrid is connected to the power grid, the bidirectional inverter operates in a PQ decoupling control mode, a phase-locked angle theta changes along with the phase change of the grid voltage, a reference modulation wave is realized by using the phase-locked angle corresponding to a current array pointer sin _ pointer of a pointer sin _ pointer PQ in a sine table array and a corresponding angle, the modulation wave obtained by a PQ decoupling current loop is superposed on the reference modulation wave generated by the sine table, an output modulation wave of PQ decoupling control can be obtained, and the power tracking of a grid-connected mode is realized;
when the isolated network is switched to the grid connection, a phase locking angle theta is changed along with the voltage phase of the power grid, a pointer sin _ pointerPQ of a sine table array corresponding to the theta is calculated, the current array pointer sin _ pointerPQ is used for tracking the sin _ pointerPQ, a bidirectional inverter runs in a V-f voltage source mode in the process, a modulation wave generates the change depending on the sin _ pointerPQ, when the two pointers are equal, a PCC point is controlled to be closed quickly, the mode is switched to the grid connection running mode, a reference modulation wave depends on the change of the sin _ pointerPQ (sin _ pointerPQ and sin _ pointerPQ are kept equal), and after the stable running, the modulation wave generated by a PQ decoupling current loop is superposed on the reference modulation wave according to a power instruction, so that the power tracking control is realized;
when the grid connection operation is required to be switched to the isolated network operation, the phase locking angle theta keeps a switching period corresponding to the sin _ pointer at the switching moment (the sin _ pointer and the sin _ pointer PQ are still equal at the moment), the sin _ pointer does not track the sin _ pointer PQ any more, the reference modulation wave does not depend on the change of the sin _ pointer PQ, the PCC point can be controlled to be rapidly switched off at the moment, and the microgrid is in an isolated network state. And the sin _ pointer changes according to the pointer value at the switching moment and a certain step length to realize a new reference modulation wave and change the new reference modulation wave into a V-f controlled isolated network operation mode.
No matter whether the isolated network, the grid connection or the switching process between the isolated network and the grid connection possibly involve charging and discharging adjustment of the energy storage equipment, the residual capacity (SOC) of the energy storage equipment needs to be judged due to protection of the energy storage equipment, if the SOC of the energy storage equipment cannot meet the minimum set threshold value requirement, the energy storage equipment is forcibly charged by adopting constant large current, and after the SOC reaches the set threshold value, the constant voltage small current is used for charging the energy storage equipment.
In the present invention, "a is equal to B" and "a and B are equal to" include not only that a and B are mathematically equal but also that a falls within a range including B and having upper and lower limits.
Those not described in detail in this specification are within the skill of the art.
It is noted that, in this document, relational terms such as first and second, and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.
Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.
Claims (10)
1. A microgrid power balance control method is characterized in that energy storage equipment is connected into a microgrid through a bidirectional inverter, when the microgrid operates in an isolated network, a V-f control mode is adopted, the energy storage equipment provides voltage source support for a micro power source in the microgrid and provides power support according to output of the micro power source and load change, and the specific working mode is as follows:
(1) When the output power of the micro power supply is equal to the power required by the load, the output of the energy storage device is approximately zero, and the power required by the load is completely supplied by the micro power supply;
(2) When the output power of the micro power supply is larger than the power required by the load, the energy storage equipment is controlled to be charged, and the redundant power of the micro power supply after meeting the load is absorbed;
(3) And when the output power of the micro power supply is smaller than the power required by the load, controlling the energy storage device to discharge to supplement the insufficient output power of the micro power supply.
2. The microgrid power balance control method of claim 1, characterized in that: in the working mode (1), the modulation ratio ma of the bidirectional inverter is kept unchanged; in the working mode (2), the modulation ratio ma of the bidirectional inverter is reduced along with the increase of the direct-current voltage in the continuous charging process; in the operation mode (3), the modulation ratio ma of the bidirectional inverter increases as the discharge-sustaining direct-current voltage decreases.
3. The microgrid power balance control method of claim 1, characterized in that: the micro power supply is referenced to the voltage and frequency output of the bi-directional inverter.
4. The microgrid power balance control method of claim 1, characterized in that: discretizing a power frequency sine wave to obtain sine wave data of a plurality of discrete time points in a power frequency cycle, forming a sine table array sin [ n ] composed of the sine wave data, forming a corresponding rectangular pulse sequence according to the sine table array to replace a power frequency sine wave required by V-f control to serve as a modulation wave, obtaining the number nf of switch points corresponding to the sine table in the power frequency cycle through the relationship between the switching frequency and the power frequency, and selecting a rectangular pulse for modulation by taking the multiple of the total number n and nf of the elements of the sine table as the moving step length of a pointer of the sine table during the implementation of the power frequency sine wave.
5. The microgrid power balance control method of claim 1, characterized in that: when the microgrid is connected to the power grid, a PQ decoupling control mode is adopted, power change is quickly tracked, and meanwhile, the change of active power or reactive power is independently controlled.
6. The microgrid power balance control method of claim 5, wherein the microgrid power balance control method comprises the following steps: firstly, adjusting reactive power to zero, then independently controlling active power, stabilizing the power fluctuation of a micro power source, and enabling the exchange power between the micro grid and a public power grid to be controllable, wherein the specific working mode is as follows:
(1) When the difference between the output power of the micro power source and the consumed power of the load fluctuates in the positive direction, the energy storage equipment is controlled to be charged, and redundant power is absorbed;
(2) And when the difference value between the output power of the micro power supply and the consumed power of the load fluctuates negatively, the energy storage equipment is controlled to discharge, and the power shortage of the load is met.
7. The microgrid power balance control method of claim 6, wherein the microgrid power balance control method comprises the following steps: discretizing a power frequency sine wave to obtain sine wave data of a plurality of discrete time points in a power frequency cycle, forming a sine table array sin [ m ] composed of the sine wave data, forming a corresponding rectangular pulse sequence according to the sine table array to replace a power frequency sine wave required by a voltage feedforward part in PQ decoupling control as a modulation wave, obtaining the number mf of switching points corresponding to the sine table in the power frequency cycle through the relationship between the switching frequency and the power frequency, and selecting a rectangular pulse for modulation by using the moving step length of the pointer of the sine table when the power frequency sine wave is realized by using the multiple of the total number m and mf of the elements of the sine table.
8. The microgrid power balance control method of claim 1, characterized in that: when the isolated network/grid-connected dual mode mutual switching is carried out, one or more of voltage, frequency, phase and power of another operation mode are firstly tracked and corrected in the current operation mode, and then the operation mode is switched to the other operation mode after the requirements are met.
9. The microgrid power balance control method of claim 1, characterized in that: when the microgrid is switched from an isolated grid mode to a grid-connected mode, tracking the voltage and the phase in the grid-connected mode by adopting a V-f control mode during the isolated grid, and converting the control mode into a PQ decoupling control mode after grid connection;
when the microgrid is switched from a grid-connected mode to an isolated grid mode, the method is divided into a planned mode and an unplanned mode: (1) planned grid connection: before grid connection, the exchange power of the microgrid and the public power grid is adjusted to zero by switching loads or limiting the output of the micro power supply, and after grid connection, the control mode is switched to a V-f control mode; (2) non-planned grid connection: and the control mode is directly converted into a V-f control mode, the energy storage device is controlled to output or absorb power if the exchange power is within the capacity allowable range of the energy storage device in the switching process, and the load is quickly cut off or the output of the micro power source is limited if the exchange power exceeds the capacity allowable range of the energy storage device.
10. The microgrid power balance control method of claim 1, characterized in that: if the SOC of the energy storage equipment cannot meet the minimum set threshold requirement, the energy storage equipment is forcibly charged by adopting constant large current, and when the SOC reaches the set threshold, the energy storage equipment is charged by adopting constant voltage small current.
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