CN107834590B - Photovoltaic power generation high-voltage direct current transmission device and method thereof - Google Patents

Photovoltaic power generation high-voltage direct current transmission device and method thereof Download PDF

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CN107834590B
CN107834590B CN201711204933.2A CN201711204933A CN107834590B CN 107834590 B CN107834590 B CN 107834590B CN 201711204933 A CN201711204933 A CN 201711204933A CN 107834590 B CN107834590 B CN 107834590B
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voltage
particle
current
power
grid
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CN107834590A (en
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陈思哲
王镇浩
叶远茂
张桂东
章云
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Guangdong University of Technology
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Guangdong University of Technology
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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
    • H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
    • 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
    • H02J3/383—
    • 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
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/56—Power conversion systems, e.g. maximum power point trackers
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E70/00—Other energy conversion or management systems reducing GHG emissions
    • Y02E70/30—Systems combining energy storage with energy generation of non-fossil origin

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Photovoltaic Devices (AREA)
  • Control Of Electrical Variables (AREA)
  • Charge And Discharge Circuits For Batteries Or The Like (AREA)
  • Supply And Distribution Of Alternating Current (AREA)

Abstract

The invention discloses a photovoltaic power generation high-voltage direct current power transmission device and a method thereof, wherein the device comprises a plurality of photovoltaic units which are mutually connected in series, and a circuit after being connected in series is connected with the input end of a high-voltage grid-connected inverter; the output end of the high-voltage grid-connected inverter is connected with an alternating current power grid; the input ends of the plurality of DC-DC converters are respectively connected with the output ends of the photovoltaic units in a one-to-one correspondence manner, and the plurality of energy storage units are respectively connected with the output ends of the DC-DC converters in a one-to-one correspondence manner; the first local controllers are respectively connected with the control ends of the DC-DC converters in a one-to-one correspondence manner and are used for enabling the photovoltaic units to respectively operate at the respective maximum power points under the preset high-voltage bus current; the second local controller is connected with the control end of the high-voltage grid-connected inverter; and a central controller. The DC-DC converter is not directly connected with the high-voltage direct current bus, so that the cost is reduced, the power generation efficiency is improved, and the generation of hot spots is avoided as much as possible.

Description

Photovoltaic power generation high-voltage direct current transmission device and method thereof
Technical Field
The invention relates to the technical field of photovoltaic power generation, in particular to a photovoltaic power generation high-voltage direct current transmission device and a method thereof.
Background
New energy is an important component of energy supply systems. The large-scale development of new energy has become an important way for many countries to advance the core content of energy transformation and to cope with climate change. The low-voltage distribution network has limited admitting capability for new energy, so that the direct access to the high-voltage distribution network becomes a necessary trend of large-scale new energy grid-connected power generation. Because the output voltage of a single photovoltaic unit is low, in order to realize high-voltage grid connection, the voltage level of a photovoltaic power generation system is usually required to be improved by adopting a mode of connecting photovoltaic units in series.
At present, DC-DC converters are connected in parallel to two ends of a photovoltaic unit, and referring to fig. 1, fig. 1 is a schematic structural diagram of a photovoltaic power generation system provided in the prior art. Under the condition of uniform illumination, the DC-DC converter does not work, when partial shadow occurs, the DC-DC module only needs to keep the current flowing through each series photovoltaic unit consistent, so that most of power generated by the whole photovoltaic system can be transmitted to a power grid, the power generation efficiency can be effectively improved, and meanwhile, the phenomenon of multimodal output power characteristics is avoided.
However, in this method, since the DC-DC converter is directly connected to the high-voltage direct-current bus, all DC-DC converters must have a higher withstand voltage level than the high-voltage direct-current bus voltage, which results in a significant increase in the cost of the photovoltaic power generation system. Because the cost is too high, a parallel DC-DC converter cannot be configured for each photovoltaic unit, and then the currents of a plurality of series photovoltaic units controlled by the same DC-DC converter are equal, the problems that the photovoltaic units cannot work from the maximum power point, the power generation efficiency is low, hot spots are generated, damage is caused to the photovoltaic units and the like are faced under the condition of partial shadow.
Therefore, how to provide a photovoltaic power generation high-voltage direct current transmission device with low cost and high power generation efficiency and a method thereof is a problem that needs to be solved by those skilled in the art at present.
Disclosure of Invention
The invention aims to provide a photovoltaic power generation high-voltage direct current transmission device and a method thereof, wherein a DC-DC converter is not directly connected with a high-voltage direct current bus, so that the cost is reduced, the power generation efficiency is improved, and the generation of hot spots is avoided as much as possible.
In order to solve the technical problems, the invention provides a photovoltaic power generation high-voltage direct current transmission device, which comprises:
the photovoltaic units are connected in series, and the positive end and the negative end of the circuit after the photovoltaic units are connected in series are respectively connected with the input end of the high-voltage grid-connected inverter through corresponding high-voltage direct-current transmission lines;
the output end of the high-voltage grid-connected inverter is connected with an alternating current power grid;
the input ends of the plurality of DC-DC converters are respectively connected with the output ends of the photovoltaic units in a one-to-one correspondence manner, and the plurality of energy storage units are respectively connected with the output ends of the DC-DC converters in a one-to-one correspondence manner; the DC-DC converter is used for controlling the energy storage unit connected with the DC-DC converter to provide compensation current for the photovoltaic unit connected with the DC-DC converter;
a plurality of first local controllers which are respectively connected with the control ends of the DC-DC converters in a one-to-one correspondence manner; the first local controller is used for generating pulse driving signals according to the current of the photovoltaic unit corresponding to the first local controller at the maximum power point and the preset high-voltage bus current to control the output of the DC-DC converter, so that each photovoltaic unit respectively operates at the respective maximum power point under the preset high-voltage bus current;
the second local controller is connected with the control end of the high-voltage grid-connected inverter and is used for generating driving pulses to control the output of the high-voltage grid-connected inverter;
the input end of the central controller is connected with the output ends of the first local controller and the second local controller respectively, and the output end of the central controller is connected with the input end of the second local controller; the central controller is used for calculating the active power given value of the high-voltage grid-connected inverter in the n time periods in the future and sending the active power given value to the second local controller for control.
Preferably, the photovoltaic power generation system further comprises a plurality of current detection devices which are respectively connected with the photovoltaic units in a one-to-one correspondence manner, wherein the current detection devices are used for detecting the currents of the corresponding photovoltaic units and sending the currents to the corresponding first local controllers, and the output ends of the current detection devices are connected with the input ends of the corresponding first local controllers.
Preferably, the electric quantity detecting device is further included, the input end of the electric quantity detecting device is connected with the energy storage unit, and the output end of the electric quantity detecting device is connected with the central controller.
In order to solve the technical problem, the invention also provides a photovoltaic power generation high-voltage direct current transmission method, which comprises the following steps of:
the first local controller acquires the current of the photovoltaic unit at the maximum power point in real time;
generating a first pulse driving signal according to the current of the maximum power point and a preset high-voltage bus current, and sending the first pulse driving signal to a DC-DC converter, so that the DC-DC converter controls an energy storage unit to provide a compensation current with a specific size to the photovoltaic unit, the photovoltaic unit operates at the maximum power point of the photovoltaic unit, and the sum of the current generated by the photovoltaic unit and the compensation current provided by the DC-DC converter is equal to the preset high-voltage bus current;
and inputting the direct current in the high-voltage direct current transmission line into a high-voltage grid-connected inverter, and generating a second driving pulse signal by a second local controller to control the high-voltage grid-connected inverter to convert the direct current in the high-voltage direct current transmission line into alternating current and input the alternating current into an alternating current power grid.
Preferably, the method for generating the first pulse driving signal by the first local controller includes:
PI control is carried out on deviation between a preset compensation current given value and current of a corresponding photovoltaic unit at a maximum power point obtained in real time to generate the duty ratio of the DC-DC converter;
and carrying out pulse width modulation on the duty ratio to obtain a first pulse driving signal, and sending the first pulse driving signal to the DC-DC converter for control.
Preferably, the method for generating the second pulse driving signal by the second local controller includes:
PI control is carried out on the deviation between a given value of the active power of the input alternating current power grid of the high-voltage grid-connected inverter and an actual measurement value of the active power of the input alternating current power grid of the high-voltage grid-connected inverter, and d-axis control voltage is generated;
PI control is carried out on the deviation between a given value of reactive power of the alternating current power grid input by the high-voltage grid-connected inverter and an actual measurement value of reactive power of the alternating current power grid input by the high-voltage grid-connected inverter, and q-axis control voltage is generated;
and after the d-axis control voltage and the q-axis control voltage are subjected to rotation/static conversion and space vector pulse width modulation, a second pulse driving signal is obtained and is sent to the high-voltage grid-connected inverter for control.
Preferably, the method for acquiring the given value of the active power of the input alternating current power grid of the high-voltage grid-connected inverter comprises the following steps:
and obtaining and calculating the active power set value of the high-voltage grid-connected inverter in the future n time periods according to the current residual electric quantity of each energy storage unit, the real-time electricity prices in the future n time periods, and the average output power and average output voltage of the photovoltaic unit corresponding to the illumination and temperature prediction results in the future n time periods.
Preferably, the method for calculating the active power set value of the high-voltage grid-connected inverter in the future n time periods according to the current remaining power of each energy storage unit, the real-time electricity prices in the future n time periods, and the average output power and average output voltage of the photovoltaic unit corresponding to the illumination and temperature prediction results in the future n time periods specifically includes:
step S1: randomly initializing the speed and position of a particle group as the speed and position of the first period of each particle within the power rated range of the DC-DC converter and the high-voltage grid-connected inverter; the population of particles consists of z particles, each of which has a position in multidimensional space expressed as a vector of the form:
x(k)＝[P(1,k),P(2,k),…,P(n,k)] T ，k＝1,2,…,z
p (i, k) is the active power given value of the high-voltage grid-connected inverter at the ith moment of the kth particle;
step S2: calculating an initialization fitness value of each particle; the fitness value is equal to the total electric charge profit of n time periods in the future minus a penalty function generated by the residual electric quantity of each energy storage unit exceeding an allowable range in any time period; taking the position of the first period of each particle as the initial historical optimal position of each particle, selecting the particle with the largest fitness from the particle groups of the first period, and taking the particle with the largest fitness as the initial global historical optimal position of the particle groups;
step S3: calculating the speed of each particle in the period according to the speed of the last period of each particle, the distance between the position of each particle in the last period and the historical optimal position of the particle, and the distance between the position of each particle in the last period and the current global historical optimal position, and calculating the position of each particle in the period according to the position of each particle in the last period and the speed of each particle in the period, wherein the calculation formula is as follows:
v t+1 (k) V, the speed of the particle present period t (k) X is the velocity of the last cycle of the particle t+1 (k) For the position of the particle's own period, x t (k) P being the position of the last period of the particle lb (k) For the historical best position of the period on the particle, P gb (k) For a global historical optimal position for a period over the population of particles,c 1 、c 2 is constant, r 1 And r 2 Is uniformly and randomly distributed rand;
step S4: checking the particles obtained in the step S3, and limiting the current of the DC-DC converter or the power of the high-voltage grid-connected inverter to respective rated values if the current or the power exceeds a corresponding preset rated range;
step S5: calculating the fitness value of each particle in the period, wherein the fitness value is equal to the total electric charge profit of n time periods in the future minus a penalty function generated by the fact that the residual electric quantity of each energy storage unit exceeds an allowable range in any time period; comparing the fitness value of each particle in the period with the fitness value of the self historical optimal position, and selecting the historical optimal position with a larger fitness value as the corresponding particle; comparing the fitness value of each particle in the period with the fitness value of the global historical optimal position, and selecting the position with the largest fitness value as the global historical optimal position;
step S6: judging whether a preset termination condition is met, and returning to the step S3 if the preset termination condition is not met; if the preset termination condition is reached, the global historical optimal position can be obtained as follows:
p gb ＝[P(1),P(2),…,P(n)] T
p (1), P (2), …, P (n) in the obtained global historical optimum position are given to the second local controller as the active power given value of the high-voltage grid-connected inverter for the future n periods.
Preferably, the preset termination condition is that an increment of the fitness value of the global historical optimal position is smaller than a preset threshold value or reaches the maximum iteration number.
Preferably, the process of calculating the active power given value of the high-voltage grid-connected inverter for n time periods in the future includes constraint conditions, wherein the constraint conditions include:
the residual electric quantity of any energy storage unit is in a preset percentage range of the rated capacity of the energy storage unit;
the current of the high-voltage direct-current transmission line is equal to the sum of the current generated by any photovoltaic unit and the compensation current provided by the corresponding DC-DC converter;
the output power of any one of the DC-DC converters is not greater than the rated value of the power of the DC-DC converter;
the output power of the high-voltage grid-connected inverter cannot exceed the rated value of the self power.
The invention provides a photovoltaic power generation high-voltage direct current transmission device and a method thereof. Therefore, the voltage withstand level of the DC-DC converter is higher than that of the photovoltaic units, and the voltage withstand level of the DC-DC converter is N times of that of the photovoltaic units and N is the number of the photovoltaic units according to the principle of series voltage division.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required in the prior art and the embodiments will be briefly described below, and it is apparent that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 is a schematic structural diagram of a photovoltaic power generation system provided in the prior art;
fig. 2 is a schematic structural diagram of a photovoltaic power generation high-voltage direct current transmission device provided by the invention;
fig. 3 is a flowchart of a process of a photovoltaic power generation high-voltage direct current transmission method provided by the invention.
Detailed Description
The invention provides a photovoltaic power generation high-voltage direct current transmission device and a method thereof, wherein a DC-DC converter is not directly connected with a high-voltage direct current bus, so that the cost is reduced, the power generation efficiency is improved, and the generation of hot spots is avoided as much as possible.
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments of the present invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The invention provides a photovoltaic power generation high-voltage direct current transmission device, which is shown in fig. 2, wherein fig. 2 is a schematic structural diagram of the photovoltaic power generation high-voltage direct current transmission device; the device comprises:
the photovoltaic units 1 are connected in series, and the positive end and the negative end of a circuit after the photovoltaic units 1 are connected in series are respectively connected with the input end of the high-voltage grid-connected inverter 5 through corresponding high-voltage direct-current transmission lines;
the output end of the high-voltage grid-connected inverter 5 is connected with an alternating current power grid;
the input ends of the plurality of DC-DC converters 2 are respectively connected with the output ends of the photovoltaic units 1 in a one-to-one correspondence manner, and the plurality of energy storage units 3 are respectively connected with the output ends of the DC-DC converters 2 in a one-to-one correspondence manner; the DC-DC converter 2 is used for controlling the energy storage unit 3 connected with the DC-DC converter to provide compensation current for the photovoltaic unit 1 connected with the DC-DC converter;
a plurality of first local controllers 4 respectively connected with the control ends of the DC-DC converters 2 in a one-to-one correspondence manner; the first local controller 4 is configured to generate a pulse driving signal according to a current of the corresponding photovoltaic unit 1 at a maximum power point and a preset high-voltage bus current to control output of the DC-DC converter 2, so that each photovoltaic unit 1 operates at the respective maximum power point under the preset high-voltage bus current;
the second local controller 6 is connected with the control end of the high-voltage grid-connected inverter 5 and is used for generating driving pulses to control the output of the high-voltage grid-connected inverter 5;
the input end of the central controller 7 is respectively connected with the output ends of the first local controller 4 and the second local controller 6, and the output end of the central controller 7 is connected with the input end of the second local controller 6; the central controller 7 is used for calculating the set value of the active power of the high-voltage grid-connected inverter 5 in the next n time periods and sending the set value to the second local controller 6 for control.
Preferably, the device further comprises a plurality of current detection devices which are respectively connected with the photovoltaic units 1 in a one-to-one correspondence manner, wherein the current detection devices are used for detecting the current of the corresponding photovoltaic units 1 and sending the current to the corresponding first local controllers 4, and the output ends of the current detection devices are connected with the input ends of the corresponding first local controllers 4.
It should be noted that, after receiving the measured value of the current of the photovoltaic unit 1 sent by the current detection device, the first local controller 4 compares the measured value with a preset current threshold value stored in the first local controller 4 in advance, generates a corresponding driving pulse signal according to the compared difference value, and sends the driving pulse signal to the DC-DC converter 2 to control the corresponding energy storage unit 3 to charge or discharge, so as to provide a compensation current with a corresponding magnitude for the photovoltaic unit 1.
The current detection device may be an ammeter or a current transformer, but may be any other device, which is not limited in the present invention.
Preferably, the device further comprises an electric quantity detection device, wherein the input end of the electric quantity detection device is connected with the energy storage unit 3, and the output end of the electric quantity detection device is connected with the central controller 7.
After receiving the remaining power of the energy storage unit 3 sent by the power detection device, the central controller 7 calculates the set value of the active power of the high-voltage grid-connected inverter 5 in the n future time periods according to the current remaining power of each energy storage unit 3 in the whole device, the real-time power price in the n future time periods, and the average output power and average output voltage of the photovoltaic unit 1 corresponding to the illumination and temperature prediction results in the n future time periods, with the aim of maximizing the electric charge gain of the whole photovoltaic power generation system.
The invention provides a photovoltaic power generation high-voltage direct current transmission device, wherein two ends of each photovoltaic unit are connected with a DC-DC converter in parallel, and two ends of each DC-DC converter are connected with an energy storage unit in parallel. Therefore, the voltage withstand level of the DC-DC converter is higher than that of the photovoltaic units, and the voltage withstand level of the DC-DC converter is N times of that of the photovoltaic units and N is the number of the photovoltaic units according to the principle of series voltage division.
The invention also provides a photovoltaic power generation high-voltage direct current transmission method, which is based on the device of any one of the above, and is shown in fig. 3, and fig. 3 is a flow chart of a process of the photovoltaic power generation high-voltage direct current transmission method. The method comprises the following steps:
step s101: the first local controller acquires the current of the photovoltaic unit at the maximum power point in real time;
step s102: generating a first pulse driving signal according to the current of the maximum power point and a preset high-voltage bus current, and sending the first pulse driving signal to the DC-DC converter, so that the DC-DC converter controls the energy storage unit to provide a compensating current with a specific size to the photovoltaic unit, the photovoltaic unit operates at the maximum power point of the photovoltaic unit, and the sum of the current generated by the photovoltaic unit and the compensating current provided by the DC-DC converter is equal to the preset high-voltage bus current;
step s103: and inputting the direct current in the high-voltage direct current transmission line into a high-voltage grid-connected inverter, and generating a second driving pulse signal by a second local controller to control the high-voltage grid-connected inverter to convert the direct current in the high-voltage direct current transmission line into alternating current and input the alternating current into an alternating current power grid. Wherein the process of step s102 includes:
PI control is carried out on deviation between a preset compensation current given value and current of a corresponding photovoltaic unit at a maximum power point obtained in real time to generate the duty ratio of the DC-DC converter;
and carrying out pulse width modulation on the duty ratio to obtain a first pulse driving signal, and sending the first pulse driving signal to the DC-DC converter for control.
It can be understood that the high-voltage DC bus current is determined by the active power input to the ac grid by the high-voltage grid-connected inverter, however, the photoelectric conversion current Impp corresponding to the maximum power point of each series photovoltaic unit is different under the uneven illumination, so the control objective of the DC-DC converter is to make each photovoltaic unit operate at the respective maximum power point under the same high-voltage DC bus current by adjusting the compensation current Icomp. Specifically, the DC-DC converter adopts a current closed-loop control method, and the output compensation current Icomp of the DC-DC converter is controlled to follow the preset compensation current set value to change.
It is further known that the preset compensation current set point is generated by a disturbance observation method, and the purpose of the preset compensation current set point is to enable the photovoltaic unit connected in parallel with the DC-DC converter corresponding to the preset compensation current set point to operate at the current corresponding to the maximum power point. The specific implementation method comprises the following steps: applying disturbance by adjusting and outputting a preset compensation current given value, detecting the change of the output power of the photovoltaic unit connected in parallel with the disturbance, and if the output power of the photovoltaic unit is increased after the disturbance, indicating that the disturbance can improve the output power of the photovoltaic unit, and continuously adjusting and outputting the preset compensation current given value in the same direction next time; otherwise, if the output power of the photovoltaic unit is reduced after the disturbance, the disturbance is unfavorable for improving the output power of the photovoltaic unit, and the preset compensation current given value is regulated and output in the opposite direction next time.
In addition, the method for generating the second pulse driving signal by the second local controller comprises the following steps:
PI control is carried out on the deviation between a given value of the active power of the input alternating current power grid of the high-voltage grid-connected inverter and an actual measurement value of the active power of the input alternating current power grid of the high-voltage grid-connected inverter, and d-axis control voltage is generated;
PI control is carried out on the deviation between a given value of reactive power of the alternating current power grid input by the high-voltage grid-connected inverter and an actual measurement value of reactive power of the alternating current power grid input by the high-voltage grid-connected inverter, and q-axis control voltage is generated;
and (3) performing rotation/static conversion and space vector pulse width modulation (SVPWN, space Vector Pulse Width Modulation) on the d-axis control voltage and the q-axis control voltage to obtain a second pulse driving signal, and transmitting the second pulse driving signal to the high-voltage grid-connected inverter for control.
It can be understood that the high-voltage grid-connected inverter adopts a vector control method based on grid voltage orientation, and is used for realizing closed-loop control of active power and reactive power of an input alternating-current power grid, so that the active power of the input alternating-current power grid is constant in time sharing. The set active power value of the high-voltage grid-connected inverter input alternating current power grid is calculated and generated by a method, and the set reactive power value is set to be zero.
The method for acquiring the given value of the active power of the input alternating current power grid of the high-voltage grid-connected inverter comprises the following steps:
and obtaining and calculating the active power set value of the high-voltage grid-connected inverter of the n time periods in the future according to the current residual electric quantity of each energy storage unit, the real-time electricity prices of the n time periods in the future and the average output power and average output voltage of the photovoltaic unit corresponding to the illumination and temperature prediction results of the n time periods in the future.
It can be understood that, it is to be noted that, the particle swarm optimization algorithm is adopted to calculate the active power set value of the high-voltage grid-connected inverter of n time periods in the future, so as to maximize the economic benefit of the whole photovoltaic power generation system, and the economic benefit of the whole photovoltaic power generation system can be calculated according to the following formula:
wherein, define i=1, 2,..n is the serial number of unit time period, j=1, 2,..m is the serial number of series module, and a series module includes a photovoltaic unit, a DC-DC converter and an energy storage unit, and P (i) is the active power given value of the high-voltage grid-connected inverter of the i-th period, and Pri (i) is the electricity price of the i-th period, Δt is the time length of unit time period.
Further, it can be further known that the method for calculating the active power given value of the high-voltage grid-connected inverter of the next n time periods specifically includes:
step S1: randomly initializing the speed and the position of a particle swarm as the speed and the position of a first period of each particle in the power rated range of the DC-DC converter and the high-voltage grid-connected inverter; the particle group consists of z particles, each particle position in the multidimensional space being represented as a vector of the form:
x(k)＝[P(1,k),P(2,k),…,P(n,k)] T ，k＝1,2,…,z
p (i, k) is the active power given value of the high-voltage grid-connected inverter of the kth particle at the ith moment;
step S2: calculating an initialization fitness value of each particle; the fitness value is equal to the penalty function generated by subtracting the residual electric quantity of each energy storage unit from the total electric charge profit of n time periods in the future when any time period exceeds the allowable range; taking the position of the first period of each particle as the initial historical optimal position of each particle, selecting the particle with the largest fitness from the particle group of the first period, and taking the particle as the initial global historical optimal position of the particle group;
it should be noted that, the fitness value of each particle in the particle swarm is calculated according to the following formula:
wherein K is a weight coefficient of a penalty function, PEN (i, j, K) is a penalty function generated by the fact that the residual electric quantity of a jth energy storage unit of kth particles in an ith unit time period exceeds an allowable range, and the penalty function is calculated as follows:
first, let theWherein U is pv (i, j) is the voltage of the jth photovoltaic unit in the ith period; p (P) pv (i, j) is the output power of the jth photovoltaic unit during the ith period;
then, let E s (i+1,j,k)＝E s (i,j,k)+P s (i,j,k)Δt；
Finally, let the
Wherein E is s (i, j, k) is the remaining power of the kth particle in the jth energy storage unit in the ith unit time period; p (P) s (i, j, k) is the output power of the jth energy storage unit of the kth particle in the ith unit time period;
step S3: the speed of each particle in the period is calculated according to the speed of each particle in the period, the distance between the position of each particle in the period and the historical optimal position of the particle, and the distance between the position of each particle in the period and the current global historical optimal position, and the position of each particle in the period is calculated according to the position of each particle in the period and the speed of each particle in the period, wherein the calculation formula is as follows:
v t+1 (k) For the speed of the particle's own period, v t (k) Is the speed of the last period of the particle, x t+1 (k) For the position of the particle's own period, x t (k) Is the position of the last period of the particle, P lb (k) For the historical optimum position of the last period of the particle, P gb (k) Is the global historical best position for a period on a particle swarm,c 1 、c 2 is constant, r 1 And r 2 Is uniformly and randomly distributed rand;
step S4: checking the particles obtained in the step S3, and limiting the current of the DC-DC converter or the power of the high-voltage grid-connected inverter to respective rated values if the current or the power of the high-voltage grid-connected inverter exceeds the corresponding preset rated range;
step S5: calculating the fitness value of each particle in the period, wherein the fitness value is equal to the total electric charge profit of n time periods in the future minus a penalty function generated by the surplus electric quantity of each energy storage unit exceeding the allowable range in any time period; comparing the fitness value of each particle in the period with the fitness value of the historical optimal position of the particle, and selecting the historical optimal position with larger fitness value as the corresponding particle; comparing the fitness value of each particle in the period with the fitness value of the global history optimal position, and selecting the position with the largest fitness value as the global history optimal position;
step S6: judging whether a preset termination condition is met, and if the preset termination condition is not met, returning to the step S3; if the preset termination condition is reached, the global history optimal position can be obtained as follows:
p gb ＝[P(1),P(2),…,P(n)] T
p (1), P (2), …, P (n) in the obtained global history optimal position are given to the second local controller as active power given values of the high-voltage grid-connected inverter of n time periods in the future.
Preferably, the preset termination condition is that an increment of the fitness value of the global history optimal position is smaller than a preset threshold or reaches a maximum number of iterations.
It should be noted that, for example, when the maximum number of iterations reaches 10, the calculation is terminated. Of course, the present invention is not limited to a specific numerical value of the maximum iteration number, nor to a specific content of the preset termination condition.
Preferably, the process of calculating the active power given value of the high-voltage grid-connected inverter of n time periods in the future comprises the constraint condition, wherein the constraint condition comprises:
the residual electric quantity of any energy storage unit is in a preset percentage range of the rated capacity of the energy storage unit; the preset percentage range here may be 20% to 80%, although the invention is not limited thereto, namely:
20％E sN ≤E s (i,j)+P s (i,j)Δt≤80％E sN ，i＝1,2,...,n，j＝1,2,...,m
wherein E is sN For rated capacity of energy-storage unit E s (i, j) is the remaining power of the jth energy storage unit, P s (i, j) is the output power of the jth DC/DC converter in the ith period.
The current of the high-voltage direct-current transmission line is equal to the sum of the current generated by any photovoltaic unit and the compensation current provided by the corresponding DC-DC converter; namely:
wherein I is bus (i) Representing the bus current for the i-th period.
The output power of any DC-DC converter is not greater than the rated value of the power of the DC-DC converter; namely:
wherein I is comp (i, j, k) is the output current of the jth DC-DC converter at the ith time in the kth particle. I sN Is the rated current of the DC-DC converter.
The output power of the high-voltage grid-connected inverter cannot exceed the rated value of the self power, namely:
|P(i)|≤P N ，i＝1,2,...,n
wherein P is N Is the rated power of the high-voltage grid-connected inverter.
Before the active power set value of the high-voltage grid-connected inverter of n time periods in the future is calculated by using a particle swarm optimization algorithm, 2 n-by-m-dimensional matrix vectors are defined to be respectively used for the electricity price and the active power of the high-voltage grid-connected inverter.
Pri＝[Pri(1),Pri(2),…,Pri(n)] T ，P＝[P(1),P(2),…,P(n)] T
Where Pri represents the electricity price for n time periods in the future and P represents the active power of the high voltage grid-tie inverter.
Defining 4 n multiplied by m dimensional matrixes for describing the residual capacity of the energy storage unit, the charge and discharge power of the energy storage unit, the output power of the photovoltaic unit and the output voltage of the photovoltaic unit as follows:
wherein E is s Representing the residual electric quantity of the energy storage unit; p (P) s Representing the charge and discharge power of the energy storage unit; p (P) pv Representing the output power of the photovoltaic unit; u (U) pv Representing the photovoltaic cell output voltage.
The invention provides a photovoltaic power generation high-voltage direct current transmission method, wherein two ends of each photovoltaic unit are connected with a DC-DC converter in parallel, and two ends of each DC-DC converter are connected with an energy storage unit in parallel. Therefore, the voltage withstand level of the DC-DC converter is higher than that of the photovoltaic units, and the voltage withstand level of the DC-DC converter is N times of that of the photovoltaic units and N is the number of the photovoltaic units according to the principle of series voltage division.
The above embodiments are only preferred embodiments of the present invention, and the above embodiments may be arbitrarily combined, and the combined embodiments are also within the scope of the present invention. It should be noted that other modifications and variations to the present invention can be envisioned by those of ordinary skill in the art without departing from the spirit and scope of the present invention.
In the present specification, each embodiment is described in a progressive manner, and each embodiment is mainly described in a different point from other embodiments, and identical and similar parts between the embodiments are all enough to refer to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant points refer to the description of the method section.
It should also be noted that in this specification, 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. Moreover, 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. Without further limitation, an element defined by the phrase "comprising one … …" does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises the element.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (10)

1. A photovoltaic power generation high voltage direct current transmission device, comprising:
the photovoltaic units are connected in series, and the positive end and the negative end of the circuit after the photovoltaic units are connected in series are respectively connected with the input end of the high-voltage grid-connected inverter through corresponding high-voltage direct-current transmission lines;
the output end of the high-voltage grid-connected inverter is connected with an alternating current power grid;
the input ends of the plurality of DC-DC converters are respectively connected with the output ends of the photovoltaic units in a one-to-one correspondence manner, and the plurality of energy storage units are respectively connected with the output ends of the DC-DC converters in a one-to-one correspondence manner; the DC-DC converter is used for controlling the energy storage unit connected with the DC-DC converter to provide compensation current for the photovoltaic unit connected with the DC-DC converter;
a plurality of first local controllers which are respectively connected with the control ends of the DC-DC converters in a one-to-one correspondence manner; the first local controller is used for generating pulse driving signals according to the current of the photovoltaic unit corresponding to the first local controller at the maximum power point and the preset high-voltage bus current to control the output of the DC-DC converter, so that each photovoltaic unit respectively operates at the respective maximum power point under the preset high-voltage bus current;
the second local controller is connected with the control end of the high-voltage grid-connected inverter and is used for generating driving pulses to control the output of the high-voltage grid-connected inverter;
the input end of the central controller is connected with the output ends of the first local controller and the second local controller respectively, and the output end of the central controller is connected with the input end of the second local controller; the central controller is used for calculating the active power given value of the high-voltage grid-connected inverter in the n time periods in the future and sending the active power given value to the second local controller for control.
2. The device according to claim 1, further comprising a plurality of current detection devices respectively connected to each of the photovoltaic units in a one-to-one correspondence, wherein the current detection devices are configured to detect currents of the corresponding photovoltaic units and send the currents to the corresponding first local controllers, and output ends of the current detection devices are connected to input ends of the corresponding first local controllers.
3. The device of claim 2, further comprising an electrical quantity detection device, wherein an input of the electrical quantity detection device is connected to the energy storage unit, and an output of the electrical quantity detection device is connected to the central controller.
4. A photovoltaic power generation hvdc transmission method, characterized in that it comprises, based on the device according to any one of claims 1 to 3:
the first local controller acquires the current of the photovoltaic unit at the maximum power point in real time;
generating a first pulse driving signal according to the current of the maximum power point and a preset high-voltage bus current, and sending the first pulse driving signal to a DC-DC converter, so that the DC-DC converter controls an energy storage unit to provide a compensation current with a specific size to the photovoltaic unit, the photovoltaic unit operates at the maximum power point of the photovoltaic unit, and the sum of the current generated by the photovoltaic unit and the compensation current provided by the DC-DC converter is equal to the preset high-voltage bus current;
and inputting the direct current in the high-voltage direct current transmission line into a high-voltage grid-connected inverter, and generating a second driving pulse signal by a second local controller to control the high-voltage grid-connected inverter to convert the direct current in the high-voltage direct current transmission line into alternating current and input the alternating current into an alternating current power grid.
5. The method of claim 4, wherein the first local controller generates the first pulsed drive signal by:
PI control is carried out on deviation between a preset compensation current given value and current of a corresponding photovoltaic unit at a maximum power point obtained in real time to generate the duty ratio of the DC-DC converter;
and carrying out pulse width modulation on the duty ratio to obtain a first pulse driving signal, and sending the first pulse driving signal to the DC-DC converter for control.
6. The method of claim 5, wherein the second local controller generates a second pulsed drive signal comprising:
PI control is carried out on the deviation between a given value of the active power of the input alternating current power grid of the high-voltage grid-connected inverter and an actual measurement value of the active power of the input alternating current power grid of the high-voltage grid-connected inverter, and d-axis control voltage is generated;
PI control is carried out on the deviation between a given value of reactive power of the alternating current power grid input by the high-voltage grid-connected inverter and an actual measurement value of reactive power of the alternating current power grid input by the high-voltage grid-connected inverter, and q-axis control voltage is generated;
and after the d-axis control voltage and the q-axis control voltage are subjected to rotation/static conversion and space vector pulse width modulation, a second pulse driving signal is obtained and is sent to the high-voltage grid-connected inverter for control.
7. The method according to claim 6, wherein the method for obtaining the given value of the active power of the input ac power grid of the high-voltage grid-connected inverter comprises:
and obtaining and calculating the active power set value of the high-voltage grid-connected inverter in the future n time periods according to the current residual electric quantity of each energy storage unit, the real-time electricity prices in the future n time periods, and the average output power and average output voltage of the photovoltaic unit corresponding to the illumination and temperature prediction results in the future n time periods.
8. The method according to claim 7, wherein the method for calculating the active power set value of the high-voltage grid-connected inverter for the future n time periods according to the current remaining power of each energy storage unit, the real-time electricity prices for the future n time periods, and the average output power and average output voltage of the photovoltaic units corresponding to the illumination and temperature prediction results for the future n time periods specifically includes:
step S1: randomly initializing the speed and position of a particle group as the speed and position of the first period of each particle within the power rated range of the DC-DC converter and the high-voltage grid-connected inverter; the population of particles consists of z particles, each of which has a position in multidimensional space expressed as a vector of the form:
x(k)＝[P(1,k),P(2,k),…,P(n,k)] T ，k＝1,2,…,z
p (i, k) is the active power given value of the high-voltage grid-connected inverter at the ith moment of the kth particle;
step S2: calculating an initialization fitness value of each particle; the fitness value is equal to the total electric charge profit of n time periods in the future minus a penalty function generated by the residual electric quantity of each energy storage unit exceeding an allowable range in any time period; taking the position of the first period of each particle as the initial historical optimal position of each particle, selecting the particle with the largest fitness from the particle groups of the first period, and taking the particle with the largest fitness as the initial global historical optimal position of the particle groups;
step S3: calculating the speed of each particle in the period according to the speed of the last period of each particle, the distance between the position of each particle in the last period and the historical optimal position of the particle, and the distance between the position of each particle in the last period and the current global historical optimal position, and calculating the position of each particle in the period according to the position of each particle in the last period and the speed of each particle in the period, wherein the calculation formula is as follows:
v t+1 (k) V, the speed of the particle present period t (k) X is the velocity of the last cycle of the particle t+1 (k) For the position of the particle's own period, x t (k) P being the position of the last period of the particle lb (k) For the historical best position of the period on the particle, P gb (k) For a global historical optimal position for a period over the population of particles,c 1 、c 2 is constant, r 1 And r 2 Is uniformly and randomly distributed rand;
step S4: checking the particles obtained in the step S3, and limiting the current of the DC-DC converter or the power of the high-voltage grid-connected inverter to respective rated values if the current or the power exceeds a corresponding preset rated range;
step S5: calculating the fitness value of each particle in the period, wherein the fitness value is equal to the total electric charge profit of n time periods in the future minus a penalty function generated by the fact that the residual electric quantity of each energy storage unit exceeds an allowable range in any time period; comparing the fitness value of each particle in the period with the fitness value of the self historical optimal position, and selecting the historical optimal position with a larger fitness value as the corresponding particle; comparing the fitness value of each particle in the period with the fitness value of the global historical optimal position, and selecting the position with the largest fitness value as the global historical optimal position;
step S6: judging whether a preset termination condition is met, and returning to the step S3 if the preset termination condition is not met; if the preset termination condition is reached, the global historical optimal position can be obtained as follows:
p gb ＝[P(1),P(2),…,P(n)] T
p (1), P (2), …, P (n) in the obtained global historical optimum position are given to the second local controller as the active power given value of the high-voltage grid-connected inverter for the future n periods.
9. The method of claim 8, wherein the preset termination condition is that an increment of an fitness value of the global historical best position is less than a preset threshold or a maximum number of iterations is reached.
10. The method of claim 8, wherein the process of calculating the active power setpoint for the high voltage grid-tie inverter for n time periods in the future comprises constraints comprising:
the residual electric quantity of any energy storage unit is in a preset percentage range of the rated capacity of the energy storage unit;
the current of the high-voltage direct-current transmission line is equal to the sum of the current generated by any photovoltaic unit and the compensation current provided by the corresponding DC-DC converter;
the output power of any one of the DC-DC converters is not greater than the rated value of the power of the DC-DC converter;
the output power of the high-voltage grid-connected inverter cannot exceed the rated value of the self power.
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