CN107732974B - Low-voltage photovoltaic power generation system and method thereof - Google Patents

Low-voltage photovoltaic power generation system and method thereof Download PDF

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CN107732974B
CN107732974B CN201711204935.1A CN201711204935A CN107732974B CN 107732974 B CN107732974 B CN 107732974B CN 201711204935 A CN201711204935 A CN 201711204935A CN 107732974 B CN107732974 B CN 107732974B
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bus
particle
voltage
grid
current
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CN107732974A (en
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陈思哲
张宏
张桂东
叶远茂
章云
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Guangdong University of Technology
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Guangdong University of Technology
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    • H02J3/385—
    • 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
    • H02J3/32—Arrangements for balancing of the load in a network by storage of energy using batteries with converting means
    • 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
    • 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)
  • Control Of Electrical Variables (AREA)
  • Inverter Devices (AREA)

Abstract

The invention discloses a low-voltage photovoltaic power generation system and a method thereof, wherein the low-voltage photovoltaic power generation system comprises a plurality of photovoltaic units and a plurality of DC-DC converters which are arranged in one-to-one correspondence with the photovoltaic units; a first capacitor is respectively connected between the positive output end and the negative output end of each DC-DC converter in parallel; the input ends of the DC-DC converters are connected with an energy storage device; the output end of the grid-connected inverter is connected with an alternating current power grid; the series current compensator and the second capacitor are respectively connected in parallel between the positive input end and the negative input end of the grid-connected inverter; a plurality of first local controllers correspondingly connected with the control ends of the DC-DC converters respectively; a second local controller connected to the control terminal of the series current compensator; the third local controller is connected with the control end of the grid-connected inverter; and a central controller. The DC-DC converter has low voltage withstand level, reduces cost, can avoid active power fluctuation of an input alternating current power grid caused by illumination fluctuation, and has high power grid stability.

Description

Low-voltage photovoltaic power generation system and method thereof
Technical Field
The invention relates to the technical field of photovoltaic power generation, in particular to a low-voltage photovoltaic power generation system and a method thereof.
Background
In a photovoltaic power generation system, due to uneven illumination, one way commonly adopted at present is to configure a DC/DC converter and a controller for each photovoltaic unit, so that each photovoltaic unit becomes an independent photovoltaic module, and a plurality of photovoltaic modules are connected to a direct current bus and connected to an alternating current power grid through a grid-connected inverter. Referring to fig. 1, fig. 1 is a schematic structural diagram of a photovoltaic power generation system provided in the prior art; because each photovoltaic unit is provided with an independent DC/DC converter and a maximum power point tracking control algorithm, each photovoltaic unit can be operated at the maximum power point, the efficiency of the photovoltaic unit is exerted to the maximum extent, and the photovoltaic unit has high capabilities of resisting local shadow and component electrical parameter mismatch.
However, in the above method, since each DC/DC converter is directly connected to the DC bus, the withstand voltage level of all DC/DC converters must be higher than the DC bus voltage, resulting in a significant increase in the cost of the photovoltaic power generation system. In the method, each photovoltaic unit is not connected in series, but is connected with the direct current bus independently, so that each photovoltaic unit works at the maximum power point, but the fluctuation of illumination still causes the fluctuation of the active power input by each photovoltaic module into the alternating current power grid, and the stability of the power grid is affected; the photovoltaic power generation system cannot participate in the response of the demand side, and economic benefit is affected.
Therefore, how to provide a low-voltage photovoltaic power generation system with high stability and low cost and a method thereof are problems that a person skilled in the art needs to solve at present.
Disclosure of Invention
The invention aims to provide a low-voltage photovoltaic power generation system and a method thereof, wherein the DC-DC converter has low voltage withstand level, reduces cost, can avoid active power fluctuation of an input alternating current power grid caused by illumination fluctuation, and has high power grid stability.
In order to solve the above technical problems, the present invention provides a low-voltage photovoltaic power generation system, comprising:
a plurality of photovoltaic units and a plurality of DC-DC converters which are arranged in one-to-one correspondence with the photovoltaic units; the negative output ends of the photovoltaic units are connected with the negative input ends of the grid-connected inverter, the positive output ends of the photovoltaic units are respectively connected with the negative output ends of the corresponding DC-DC converters, and the positive output ends of the DC-DC converters are connected with the positive input ends of the grid-connected inverter; a first capacitor is respectively connected between the positive output end and the negative output end of each DC-DC converter in parallel; the input end of each DC-DC converter is connected with an energy storage device;
the DC-DC converter is used for selectively controlling the first capacitor to charge the energy storage device or controlling the energy storage device to discharge the first capacitor so as to provide compensation voltage for a photovoltaic unit connected with the first capacitor;
The output end of the grid-connected inverter is connected with an alternating current power grid;
the energy storage device;
the series current compensator is respectively connected in parallel between the positive input end and the negative input end of the grid-connected inverter, and the second capacitor is connected in parallel between the positive input end and the negative input end of the grid-connected inverter; the input end of the series current compensator is connected with the energy storage device; the series current compensator is used for carrying out current compensation on the grid-connected inverter so as to ensure that the active power of the grid-connected inverter is constant in time sharing;
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 a driving pulse signal according to the current voltage of the corresponding photovoltaic unit at the maximum power point and the preset bus voltage 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 bus voltage;
the second local controller is connected with the control end of the series current compensator and is used for generating driving pulses to control the output current of the series current compensator;
the third local controller is connected with the control end of the grid-connected inverter and is used for generating driving pulses to control the direct-current bus voltage of the input end of the grid-connected inverter;
The input end of the central controller is respectively connected with the output ends of the first local controller, the second local controller and the third local controller, and the output end of the central controller is respectively connected with the input ends of the second local controller and the third local controller; the central controller is used for calculating given values of direct current bus voltage of the grid-connected inverter and given values of direct current bus current of the series current compensator in the future n time periods, and sending the given values to the third local controller and the second local controller respectively for control.
Preferably, the photovoltaic system further comprises a plurality of voltage detection devices which are respectively connected with the photovoltaic units in a one-to-one correspondence manner, wherein the voltage detection devices are used for detecting the voltages of the corresponding photovoltaic units and sending the voltages to the corresponding first local controllers, and the output ends of the voltage detection devices are connected with the input ends of the corresponding first local controllers.
Preferably, the intelligent energy storage device further comprises an electric quantity detection device, wherein the input end of the electric quantity detection device is connected with the energy storage device, and the output end of the electric quantity detection device is connected with the central controller.
To solve the above technical problem, the present invention further provides a low-voltage photovoltaic power generation method, based on the system described in any one of the above, the method includes:
the first local controller acquires the voltage of the photovoltaic unit at the maximum power point in real time;
generating a first driving pulse signal according to the voltage of the maximum power point and a preset bus voltage, and sending the first driving pulse signal to a DC-DC converter, so that the DC-DC converter controls a first capacitor to provide a compensation voltage with a specific magnitude, the photovoltaic unit operates at the maximum power point of the photovoltaic unit, and the sum of the voltage generated by the photovoltaic unit and the compensation voltage provided by the DC-DC converter is equal to the preset bus voltage;
the DC-DC converter converts the current output by the corresponding photovoltaic unit into direct current and inputs the direct current into the grid-connected inverter;
a second local controller connected with the series current compensator generates a second driving pulse signal, and controls the series current compensator to perform current compensation on the grid-connected inverter so that the active power output by the grid-connected inverter is constant in time sharing;
and a third local controller connected with the grid-connected inverter generates a third driving pulse signal to control the grid-connected inverter to convert the direct current into alternating current and input the alternating current into an alternating current power grid.
Preferably, the process of generating the first driving pulse signal by the first local controller includes:
obtaining a preset compensation voltage given value according to the deviation between the given value of the direct current bus voltage and the voltage of the corresponding photovoltaic unit at the maximum power point obtained in real time;
PI control is carried out on deviation between a preset compensation voltage given value and a first capacitance voltage obtained in real time, so that the duty ratio of the DC-DC converter is obtained;
and carrying out pulse width modulation on the duty ratio of the DC-DC converter to obtain a first driving pulse signal, and sending the first driving pulse signal to the DC-DC converter for control.
Preferably, the process of generating the second driving pulse signal by the second local controller connected to the series current compensator includes:
PI control is carried out on deviation between a given value of direct current bus current and an actual measurement value of direct current bus current at the input end of the grid-connected inverter, so that the duty ratio of the series current compensator is obtained;
and performing pulse width modulation on the duty ratio of the series current compensator to obtain a second driving pulse signal, and sending the second driving pulse signal to the series current compensator for control.
Preferably, the process of generating the third driving pulse signal by the third local controller connected with the grid-connected inverter includes:
PI control is carried out on the deviation between a given value of the DC bus voltage at the input end of the grid-connected inverter and an actual measurement value of the DC bus voltage, and d-axis control voltage is generated;
PI control is carried out on the deviation between a given value of reactive power of the AC power grid input by the grid-connected inverter and an actual measurement value of reactive power of the AC power grid input by the 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 third driving pulse signal is obtained and is sent to the grid-connected inverter for control.
Preferably, the method for acquiring the given value of the dc bus voltage and the given value of the dc bus current includes:
step S1: randomly initializing the speed and position of a particle swarm as the speed and position of a first period of each particle in the power rated range of the DC-DC converter and the 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)＝[U bus (1,k),U bus (2,k),…,U bus (n,k),I bus (1,k),I bus (2,k),…,I bus (n,k)] T ，k＝1,2,…,z
U bus (i, k) is a given value of the dc bus voltage at the input of the grid-connected inverter at the i-th moment of the kth particle; i bus (i, k) is a given value of the direct current bus current of the input end of the 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 a penalty function generated by subtracting the residual electric quantity of the energy storage device from the total electric charge profit of n time periods in the future when any time period exceeds an 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 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 uniform along withMechanically distributing rand;
step S4: checking the particles obtained in the step S3, and limiting the particles to respective rated values if the given value of the DC bus voltage or the given value of the DC bus current 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 surplus electric quantity of the energy storage device exceeding 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 ＝[U bus (1),U bus (2),…,U bus (n),I bus (1),I bus (2),…,I bus (n)] T
u in global historical best position to be obtained bus (1),U bus (2),…,U bus (n) I in a global historical optimum position to be obtained as a given value of the DC bus voltage for n time periods in the future bus (1),I bus (2),…,I bus (n) as a given value of the dc bus current for n time periods in the future, respectively, the third local controller and the second local controller are assigned correspondingly.
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 grid-connected inverter for n time periods in the future includes a constraint condition, and the constraint condition includes:
the residual electric quantity of the energy storage device is in a preset percentage range of the rated capacity of the energy storage device;
the voltage of the direct current bus is equal to the sum of the voltage generated by any photovoltaic unit and the compensation voltage provided by the corresponding DC-DC converter;
The direct current bus current is equal to the sum of the currents output by the series current compensator and all the DC-DC converters;
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 dc bus voltage, the dc bus current and the current of the series current compensator cannot exceed their own preset nominal values. Series current compensator series series current compensator series current series current compensator series current compensator
The invention provides a low-voltage photovoltaic power generation system and a method thereof, wherein the low-voltage photovoltaic power generation system comprises a plurality of photovoltaic units and DC-DC converters which are connected in series in one-to-one correspondence with the photovoltaic units, a series circuit is connected in parallel with two ends of a grid-connected inverter, the output end of each DC-DC converter is connected in parallel with a first capacitor, the input end of each DC-DC converter is connected with an energy storage device, and the two ends of the grid-connected inverter are also connected in parallel with a series current compensator and a second capacitor. According to the invention, each DC-DC converter can control the corresponding first capacitor to provide corresponding compensation voltage for the corresponding photovoltaic unit, so that each photovoltaic unit can work at the maximum power point, and the DC-DC converter is not directly connected with the DC bus, and the DC bus voltage is borne by the DC-DC converter and the photovoltaic units connected in series with the DC-DC converter, so that the withstand voltage value of the DC-DC converter is smaller than the DC bus voltage, and the system cost is reduced. And because of the existence of the series current compensator, even if the current output by each photovoltaic series branch fluctuates, the current compensation can be performed on the current, the constant active power of the current compensator is ensured, and the stability of the power grid is good.
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 low-voltage photovoltaic power generation system provided by the invention;
fig. 3 is a flowchart of a process of a low-voltage photovoltaic power generation method provided by the invention.
Detailed Description
The core of the invention is to provide a low-voltage photovoltaic power generation system and a method thereof, the DC-DC converter has low voltage withstand level, the cost is reduced, the fluctuation of active power input into an alternating current power grid caused by illumination fluctuation can be avoided, and the stability of the power grid is high.
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 low-voltage photovoltaic power generation system, which is shown in FIG. 2, and FIG. 2 is a schematic structural diagram of the low-voltage photovoltaic power generation system; the system comprises:
a plurality of photovoltaic units 1 and a plurality of DC-DC converters 2 which are arranged in one-to-one correspondence with the photovoltaic units 1; the negative output ends of the photovoltaic units 1 are connected with the negative input ends of the grid-connected inverter 6, the positive output ends of the photovoltaic units 1 are respectively connected with the negative output ends of the corresponding DC-DC converters 2, and the positive output ends of the DC-DC converters 2 are connected with the positive input ends of the grid-connected inverter 6; a first capacitor is respectively connected between the positive output end and the negative output end of each DC-DC converter 2 in parallel; the input ends of the DC-DC converters 2 are connected with an energy storage device 3;
the DC-DC converter 2 is used for selectively controlling the first capacitor to charge the energy storage device 3 or controlling the energy storage device 3 to discharge the first capacitor so as to provide compensation voltage for the photovoltaic unit 1 connected with the first capacitor;
the output end of the grid-connected inverter 6 is connected with an alternating current power grid;
an energy storage device 3;
a series current compensator 5 and a second capacitor respectively connected in parallel between the positive and negative input ends of the grid-connected inverter 6; the input end of the series current compensator 5 is connected with the energy storage device 3; the series current compensator 5 is used for carrying out current compensation on the grid-connected inverter 6 to ensure that the active power of the grid-connected inverter 6 is constant in time sharing;
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 driving pulse signal according to a voltage of the corresponding photovoltaic unit 1 at a current maximum power point and a preset bus voltage to control output of the DC-DC converter 2, so that each photovoltaic unit 1 operates at the corresponding maximum power point under the preset bus voltage;
the second local controller 7 is connected with the control end of the series current compensator of the grid-connected inverter 6 and is used for generating driving pulses to control the output current of the series current compensator of the grid-connected inverter 6;
the third local controller 8 is connected with the control end of the grid-connected inverter 6 and is used for generating a driving pulse to control the direct current bus voltage of the input end of the grid-connected inverter 6;
the input end of the central controller 9 is respectively connected with the output ends of the first local controller 4, the second local controller 7 and the third local controller 8, and the output end of the central controller 9 is respectively connected with the input ends of the second local controller 7 and the third local controller 8; the central controller 9 is used for calculating the given value of the direct current bus voltage of the grid-connected inverter 6 and the given value of the direct current bus current of the series current compensator in the future n time periods, and respectively and correspondingly transmitting the given value of the direct current bus voltage and the given value of the series current compensator to the third local controller 8 and the second local controller 7 for control.
It can be understood that each photovoltaic unit 1 and the corresponding DC-DC converter 2 are connected in series to form a photovoltaic series branch circuit which is connected into the positive and negative input ends of the grid-connected inverter 6; therefore, the DC bus voltage is commonly born by the DC/DC converter 2 and the photovoltaic unit 1, and the withstand voltage value of the DC/DC converter 2 is smaller than the DC bus voltage, so that the system cost can be reduced.
Preferably, the system further comprises a plurality of voltage detection devices which are respectively connected with the photovoltaic units 1 in a one-to-one correspondence manner, wherein the voltage detection devices are used for detecting the voltages of the corresponding photovoltaic units 1 and sending the voltages to the corresponding first local controllers 4, and the output ends of the voltage detection devices are connected with the input ends of the corresponding first local controllers 4.
The voltage detection device may be a voltmeter, a voltage sensor, or the like, and the present invention is not particularly limited thereto.
Preferably, the system further comprises an electric quantity detection device, wherein an input end of the electric quantity detection device is connected with the energy storage device 3, and an output end of the electric quantity detection device is connected with the central controller 9.
The electric quantity detection device can be an electric quantity sensor, and of course, the electric quantity detection device can also be other devices capable of detecting electric quantity, and the invention is not limited to the type of the electric quantity sensor.
The invention provides a low-voltage photovoltaic power generation system which comprises a plurality of photovoltaic units and DC-DC converters which are connected in series and are in one-to-one correspondence with the photovoltaic units, wherein a series circuit is connected in parallel with two ends of a grid-connected inverter, the output end of each DC-DC converter is connected in parallel with a first capacitor, the input end of each DC-DC converter is connected with an energy storage device, and the two ends of the grid-connected inverter are also connected with a series current compensator and a second capacitor in parallel. According to the invention, each DC-DC converter can control the corresponding first capacitor to provide corresponding compensation current for the corresponding photovoltaic unit, so that each photovoltaic unit can work at the maximum power point, and the DC-DC converter is not directly connected with the DC bus, and the DC bus voltage is borne by the DC-DC converter and the photovoltaic units connected in series with the DC-DC converter, so that the withstand voltage value of the DC-DC converter is smaller than the DC bus voltage, and the system cost is reduced. And because of the existence of the series current compensator, even if the current output by each photovoltaic series branch fluctuates, the current compensation can be performed on the current, the constant active power of the current compensator is ensured, and the stability of the power grid is good.
The invention also provides a low-voltage photovoltaic power generation method, which is characterized in that based on the system, referring to fig. 3, fig. 3 is a flow chart of a process of the low-voltage photovoltaic power generation method. The method comprises the following steps:
Step s101: the first local controller 4 acquires the voltage of the photovoltaic unit 1 at the maximum power point in real time;
step s102: the first local controller 4 generates a first driving pulse signal according to the voltage of the maximum power point and the preset bus voltage and sends the first driving pulse signal to the DC-DC converter 2, so that the DC-DC converter 2 controls the first capacitor to provide a compensation voltage with a specific magnitude, the photovoltaic unit 1 operates at the maximum power point of the photovoltaic unit 1, and the sum of the voltage generated by the photovoltaic unit 1 and the compensation voltage provided by the DC-DC converter 2 is equal to the preset bus voltage;
step s103: the DC-DC converter 2 converts the current output by the corresponding photovoltaic unit 1 into direct current and inputs the direct current into the grid-connected inverter 6;
step s104: the second local controller 7 connected with the series current compensator 5 generates a second driving pulse signal and controls the series current compensator 5 to perform current compensation on the grid-connected inverter 6 so that the active power output by the grid-connected inverter 6 is constant in time sharing;
step s105: the third local controller 8 connected to the grid-connected inverter 6 generates a third driving pulse signal, controls the grid-connected inverter 6 to convert the direct current into alternating current, and inputs the alternating current into an alternating current power grid.
It can be understood that, under uneven illumination, the voltages corresponding to the maximum power points of the parallel photovoltaic units 1 are different, so that the control objective of the DC/DC converter 2 is to adjust the output voltages of the parallel photovoltaic units 1 so that the parallel photovoltaic units 1 can respectively operate at the respective maximum power points under the DC bus voltage.
The DC/DC converter 2 adopts a voltage closed-loop control method to control the output voltage to change along with the preset compensation voltage set value. The process of generating the first driving pulse signal by the first local controller 4 includes:
obtaining a preset compensation voltage given value according to the deviation between the given value of the direct current bus voltage and the voltage of the corresponding photovoltaic unit 1 at the maximum power point obtained in real time;
PI control is carried out on deviation between a preset compensation voltage given value and the first capacitor voltage photovoltaic unit 1 acquired in real time, so that the duty ratio of the DC-DC converter 2 is obtained;
the duty ratio of the DC-DC converter 2 is pulse width modulated to obtain a first driving pulse signal, and the first driving pulse signal is sent to the DC-DC converter 2 for control.
In addition, the preset compensation voltage set value of the DC/DC converter 2 is generated by a disturbance observation method, and the purpose of the preset compensation voltage set value is to make the photovoltaic unit 1 connected in series with the preset compensation voltage set value operate at the voltage corresponding to the maximum power point. The specific implementation method comprises the following steps: applying disturbance by adjusting a preset compensation voltage set value, detecting the change of the output power of the photovoltaic unit 1 connected in series with the disturbance, and if the output power of the photovoltaic unit 1 is increased after the disturbance, indicating that the disturbance can improve the output power of the photovoltaic unit 1, and continuously adjusting the preset compensation voltage set value in the same direction next time; on the contrary, if the output power of the photovoltaic unit 1 is reduced after the disturbance, the disturbance is unfavorable for improving the output power of the photovoltaic unit 1, and the preset compensation voltage given value is regulated and output in the opposite direction next time.
In another embodiment, the process of generating the second driving pulse signal by the second local controller 7 connected to the series current compensator 5 includes:
PI control is carried out on deviation between a given value of direct current bus current and an actual measurement value of direct current bus current at the input end of the grid-connected inverter 6, so that the duty ratio of the series current compensator 5 is obtained;
the duty ratio of the series current compensator 5 is subjected to pulse width modulation to obtain a second driving pulse signal, and the second driving pulse signal is sent to the series current compensator 5 for control.
It can be understood that the series current compensator 5 adopts a direct current bus current closed-loop control method to control the direct current bus current to track a given value, so that the active power output by the grid-connected inverter 6 is constant in time sharing.
In another embodiment, the process of generating the third driving pulse signal by the third local controller connected to the grid-connected inverter 6 includes:
PI control is carried out on the deviation between a given value of the DC bus voltage at the input end of the grid-connected inverter 6 and an actual measurement value of the DC bus voltage, and d-axis control voltage is generated;
PI control is carried out on the deviation between a given value of reactive power of the AC power grid input by the grid-connected inverter 6 and an actual measurement value of reactive power of the AC power grid input by the grid-connected inverter 6, 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 third driving pulse signal is obtained and is sent to the grid-connected inverter 6 for control.
It can be understood that the grid-connected inverter 6 adopts a vector control method based on grid voltage orientation, and is used for realizing closed-loop control on the voltage of the direct-current bus and output reactive power, so that the voltage of the direct-current bus tracks a given value, and the photovoltaic power generation system works in a unit power factor. Wherein the reactive power setpoint is set to zero.
In summary, each DC/DC converter 2 adjusts its own output voltage to make the photovoltaic unit 1 connected in series with it operate at the voltage corresponding to the maximum power point; the grid-connected inverter 6 controls the direct current bus voltage to be constant in time sharing, and the series current compensator 5 controls the direct current bus current to be constant in time sharing, so that the output power of the whole photovoltaic power generation system is constant in time sharing.
Specifically, the method for acquiring the given value of the DC bus voltage and the given value of the DC bus current comprises the following steps:
calculating the given value of the voltage of the direct current bus and the given value of the current bus current of the n time periods in the future according to the current residual capacity of the energy storage device 3 in the whole device, the real-time electricity price of the n time periods in the future, and the average output voltage and the average output power of the photovoltaic scheme source corresponding to the illumination and temperature prediction results of the n time periods in the future, and taking the electric charge gain maximization of the whole photovoltaic power generation system as a target.
It should be noted that, the particle swarm optimization algorithm is adopted to calculate the given value of the voltage of the direct current bus and the given value of the current of the direct current bus in the 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:
where i=1, 2,..n is the number of the unit time period, j=1, 2,..m is the number of the series module, one series module comprising one photovoltaic unit 1, one DC-DC converter 2, one first capacitor, one first local controller 4,U bus (i) For the given value of the voltage of the direct current bus in the ith period, I bus (i) A given value of the direct current bus current in the ith period; pri (i) is the electricity price of the ith period, and Δt is the time length of the unit period.
It is further known that the specific process of obtaining the given value of the dc bus voltage and the given value of the dc bus current is as follows:
step S1: randomly initializing the speed and position of a particle swarm as the speed and position of a first period of each particle within the power rated range of the DC-DC converter 2 and the grid-connected inverter 6; the particle group consists of z particles, each particle position in the multidimensional space being represented as a vector of the form:
x(k)＝[U bus (1,k),U bus (2,k),…,U bus (n,k),I bus (1,k),I bus (2,k),…,I bus (n,k)] T ，k＝1,2,…,z
U bus (i, k) is a given value of the dc bus voltage of the input terminal of the grid-connected inverter 6 at the i-th moment by the kth particle; i bus (i, k) is the DC bus current of the input end of the grid-connected inverter 6 at the ith moment of the kth particleIs set at a given value of (2);
step S2: calculating an initialization fitness value of each particle; the fitness value is equal to the penalty function generated by subtracting the surplus electric quantity of the energy storage device 3 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 the weight coefficient of the penalty function, PEN (i, j, K) is the penalty function generated by the fact that the residual electric quantity of the jth energy storage device 3 exceeds the allowable range in the ith unit time period, and the penalty function is calculated as follows:
first, let the
Then, let E s (i+1,k)＝E s (i,k)+P s (i,k)Δt；
Finally, let the
Wherein U is mpp (i, j) is the output voltage of the jth photovoltaic unit 1 at the ith moment; i (I, j) is the output current of the jth photovoltaic unit 1 at the ith moment; e (E) s (i, k) is the current residual capacity of the energy storage device 3 at the i-th moment in the kth particle; p (P) s (i, k) is the output power of the energy storage device 3 at the i-th moment in the kth particle;
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 particles to respective rated values if the given value of the direct current bus voltage or the given value of the direct current bus current of the DC-DC converter 2 grid-connected inverter 6 exceeds a corresponding preset rated range;
Wherein, the allowable range of the DC bus voltage and the DC bus current is as follows
U bus (i,k)≤U busN ，|I bus (i,k)|≤I busN ，i＝1,2,...,n，k＝1,2,…,z
The allowable current range of the series current compensator 5 is as follows:
the output voltage allowable range of the DC/DC converter 2 is as follows:
|U(i,j,k)|＝|U bus (i,k)-U mpp (i,j)|≤U N ，i＝1,2,...,n，j＝1,2,...,m，k＝1,2,…,z
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 the energy storage device 3 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 ＝[U bus (1),U bus (2),…,U bus (n),I bus (1),I bus (2),…,I bus (n)] T
u in global historical best position to be obtained bus (1),U bus (2),…,U bus (n) I in the global historical optimum position to be obtained as a given value of DC bus voltage for n time periods in the future bus (1),I bus (2),…,I bus (n) as given values of the direct current bus currents of n time periods in the future, respectively, the second local controller 7 and the third local controller 8 are assigned to the grid-connected inverter 6, respectively.
The preset termination condition is that the increment of the fitness value of the global history optimal position is smaller than a preset threshold value or the maximum iteration number is reached.
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 grid-connected inverter 6 for n time periods in the future includes constraints including:
the remaining power of the energy storage device 3 is within a preset percentage range of the rated capacity of the energy storage device 3; the preset percentage range here may be 20% to 80%, although the invention is not limited thereto, namely:
20％E sN ≤E s (i)+P s (i)Δt≤80％E sN ，i＝1,2,...,n
wherein E is sN For the rated capacity of the energy-storage means 3, E s (i) For the residual capacity of the energy storage unit in the ith period, P s (i) The expression of the output power of the energy storage unit in the ith period is as follows:
wherein I is s (i) For the output current of the series current compensator 5 at the i-th period, U mpp (I, j) is the output voltage of the jth photovoltaic unit 1 in the ith period, and I (I, j) is the output current of the jth photovoltaic unit 1 in the ith period.
The voltage of the direct current bus is equal to the sum of the voltage generated by any photovoltaic unit 1 and the compensation voltage provided by the corresponding DC-DC converter 2; namely:
U bus (i)＝U(i,j)+U mpp (i,j)，i＝1,2,...,n，j＝1,2,...,m
Wherein U is bus (i) The DC bus voltage in the i-th period is represented, and U (i, j) represents the output voltage of the j-th DC/DC converter 2 in the i-th period.
The direct current bus current is equal to the sum of the currents output by the series current compensator 5 and all the DC-DC converters 2; namely:
the output power of any one DC-DC converter 2 is not greater than the rated value of the power of the DC-DC converter itself; namely:
|U(i,j)|≤U N ，i＝1,2,...,n，j＝1,2,...,m
wherein U is N Is the rated voltage of the DC/DC converter 2.
The dc bus voltage, the dc bus current and the current of the series current compensator 5 cannot exceed their preset nominal values; namely:
U bus (i)≤U busN ，|I bus (i)|≤I busN ，|I s (i)|≤I sN ，i＝1,2,...,n
wherein U is busN For DC bus voltage rating, I busN For DC bus current rating, I sN For the series current compensator 5 current rating.
Before the particle swarm optimization algorithm is used to calculate the given value of the voltage and the given value of the current of the direct current bus in n time periods in the future, 5 n-dimensional vectors are required to be defined and are respectively used for describing electricity price, direct current bus voltage, direct current bus current, current of the series current compensator 5 and residual electric quantity of the energy storage device 3; 2 n x m dimensional matrix vectors are defined to describe the output voltage and current of the photovoltaic unit 1, respectively.
Wherein the 5 n-dimensional vectors are as follows:
Pri＝[Pri(1),Pri(2),…,Pri(n)] T ；
U bus ＝[U bus (1),U bus (2),…,U bus (n)] T ；
I bus ＝[I bus (1),I bus (2),…,I bus (n)] T ；
I s ＝[I s (1),I s (2),…,I s (n)] T ；
E s ＝[E s (1),E s (2),…,E s (n)] T
wherein Pri represents electricity prices of n time periods in the future, U bus Representing a DC bus voltage; i bus Indicating the current of a direct current bus, I s Representing the series current compensator 5 current, E s Representing the remaining power of the energy storage device 3;
the 2 n x m dimensional matrices are as follows:
wherein U is mpp The output voltage of the photovoltaic unit 1 is represented, and I represents the output current of the photovoltaic unit 1.
The invention provides a low-voltage photovoltaic power generation method, which comprises a plurality of photovoltaic units and DC-DC converters which are connected in series and are in one-to-one correspondence with the photovoltaic units, wherein a series circuit is connected in parallel with two ends of a grid-connected inverter, the output end of each DC-DC converter is connected in parallel with a first capacitor, the input end of each DC-DC converter is connected with an energy storage device, and the two ends of the grid-connected inverter are also connected in parallel with a series current compensator and a second capacitor. According to the invention, each DC-DC converter can control the corresponding first capacitor to provide corresponding compensation current for the corresponding photovoltaic unit, so that each photovoltaic unit can work at the maximum power point, and the DC-DC converter is not directly connected with the DC bus, and the DC bus voltage is borne by the DC-DC converter and the photovoltaic units connected in series with the DC-DC converter, so that the withstand voltage value of the DC-DC converter is smaller than the DC bus voltage, and the system cost is reduced. And because of the existence of the series current compensator, even if the current output by each photovoltaic series branch fluctuates, the current compensation can be performed on the current, the constant active power of the current compensator is ensured, and the stability of the power grid is good.
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 (6)

1. A low voltage photovoltaic power generation system, comprising:
a plurality of photovoltaic units and a plurality of DC-DC converters which are arranged in one-to-one correspondence with the photovoltaic units; the negative output ends of the photovoltaic units are connected with the negative input ends of the grid-connected inverter, the positive output ends of the photovoltaic units are respectively connected with the negative output ends of the corresponding DC-DC converters, and the positive output ends of the DC-DC converters are connected with the positive input ends of the grid-connected inverter; a first capacitor is respectively connected between the positive output end and the negative output end of each DC-DC converter in parallel; the input end of each DC-DC converter is connected with an energy storage device;
The DC-DC converter is used for selectively controlling the first capacitor to charge the energy storage device or controlling the energy storage device to discharge the first capacitor so as to provide compensation voltage for a photovoltaic unit connected with the first capacitor;
the output end of the grid-connected inverter is connected with an alternating current power grid;
the energy storage device;
the series current compensator is respectively connected in parallel between the positive input end and the negative input end of the grid-connected inverter, and the second capacitor is connected in parallel between the positive input end and the negative input end of the grid-connected inverter; the input end of the series current compensator is connected with the energy storage device; the series current compensator is used for carrying out current compensation on the grid-connected inverter so as to ensure that the active power of the grid-connected inverter is constant in time sharing;
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 a first driving pulse signal according to the current voltage of the corresponding photovoltaic unit at the maximum power point and the preset bus voltage 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 bus voltage;
The second local controller is connected with the control end of the series current compensator and is used for generating a second driving pulse signal to control the output current of the series current compensator;
the third local controller is connected with the control end of the grid-connected inverter and is used for generating a third driving pulse signal to control the direct current bus voltage of the input end of the grid-connected inverter;
the input end of the central controller is respectively connected with the output ends of the first local controller, the second local controller and the third local controller, and the output end of the central controller is respectively connected with the input ends of the second local controller and the third local controller; the central controller is used for calculating given values of direct current bus voltage of the grid-connected inverter and given values of direct current bus current of the series current compensator in n time periods in the future, and respectively and correspondingly transmitting the given values to the third local controller and the second local controller for control;
the process of generating the second driving pulse signal by the second local controller connected with the series current compensator includes:
PI control is carried out on deviation between a given value of direct current bus current and an actual measurement value of direct current bus current at the input end of the grid-connected inverter, so that the duty ratio of the series current compensator is obtained;
Pulse width modulation is carried out on the duty ratio of the series current compensator to obtain the second driving pulse signal, and the second driving pulse signal is sent to the series current compensator for control;
the process of generating the third driving pulse signal by the third local controller connected with the grid-connected inverter comprises the following steps:
PI control is carried out on the deviation between a given value of the DC bus voltage at the input end of the grid-connected inverter and an actual measurement value of the DC bus voltage, and d-axis control voltage is generated;
PI control is carried out on the deviation between a given value of reactive power of the AC power grid input by the grid-connected inverter and an actual measurement value of reactive power of the AC power grid input by the grid-connected inverter, and q-axis control voltage is generated;
the d-axis control voltage and the q-axis control voltage are subjected to rotation/static conversion and space vector pulse width modulation, and then the third driving pulse signal is obtained and sent to the grid-connected inverter for control;
the method for acquiring the given value of the DC bus voltage and the given value of the DC bus current comprises the following steps:
step S1: randomly initializing the speed and position of a particle swarm as the speed and position of a first period of each particle in the power rated range of the DC-DC converter and the 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)＝[U bus (1,k),U bus (2,k),…,U bus (n,k),I bus (1,k),I bus (2,k),…,I bus (n,k)] T ，k＝1,2,…,z
U bus (i, k) is a given value of the dc bus voltage at the input of the grid-connected inverter at the i-th moment of the kth particle; i bus (i, k) is a given value of the direct current bus current of the input end of the grid-connected inverter at the ith moment of the kth particle; where i is a sequence number of a unit time period, i=1, 2, … …, n;
step S2: calculating an initialization fitness value of each particle; the fitness value is equal to a penalty function generated by subtracting the residual electric quantity of the energy storage device from the total electric charge profit of n time periods in the future when any time period exceeds an 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 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 Currently for the particle swarmThe global history of the best locations is used,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 particles to respective rated values if the given value of the DC bus voltage or the given value of the DC bus current 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 surplus electric quantity of the energy storage device exceeding 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 ＝[U bus (1),U bus (2),,U bus (n),I bus (1),I bus (2),,I bus (n)] T
u in global historical best position to be obtained bus (1),U bus (2),,U bus (n) I in a global historical optimum position to be obtained as a given value of the DC bus voltage for n time periods in the future bus (1),I bus (2),,I bus (n) as a given value of the dc bus current for n time periods in the future, respectively, the third local controller and the second local controller are assigned correspondingly.
2. The system according to claim 1, further comprising a plurality of voltage detection devices respectively connected to each of the photovoltaic units in a one-to-one correspondence, wherein the voltage detection devices are configured to detect voltages of the corresponding photovoltaic units and send the voltages to the corresponding first local controllers, and output ends of the voltage detection devices are connected to input ends of the corresponding first local controllers.
3. The system of claim 2, further comprising an electrical quantity detection device, an input of the electrical quantity detection device being connected to the energy storage device, an output of the electrical quantity detection device being connected to the central controller.
4. The low-voltage photovoltaic power generation method is characterized by being applied to a low-voltage photovoltaic power generation system provided with a plurality of DC-DC converters, grid-connected inverters, a first capacitor, an energy storage device, a first local controller, a second local controller and a third local controller, wherein the DC-DC converters are arranged in one-to-one correspondence with photovoltaic units, and the method comprises the following steps:
the first local controller acquires the voltage of the photovoltaic unit at the maximum power point in real time;
generating a first driving pulse signal according to the voltage of the maximum power point and a preset bus voltage, and sending the first driving pulse signal to a DC-DC converter, so that the DC-DC converter controls a first capacitor to provide a compensation voltage with a specific magnitude, the photovoltaic unit operates at the maximum power point of the photovoltaic unit, and the sum of the voltage generated by the photovoltaic unit and the compensation voltage provided by the DC-DC converter is equal to the preset bus voltage;
the DC-DC converter converts the current output by the corresponding photovoltaic unit into direct current and inputs the direct current into the grid-connected inverter;
a second local controller connected with the series current compensator generates a second driving pulse signal, and controls the series current compensator to perform current compensation on the grid-connected inverter so that the active power output by the grid-connected inverter is constant in time sharing;
A third local controller connected with the grid-connected inverter generates a third driving pulse signal to control the grid-connected inverter to convert the direct current into alternating current and input the alternating current into an alternating current power grid;
the process of generating the first driving pulse signal by the first local controller comprises the following steps:
obtaining a preset compensation voltage given value according to the deviation between the given value of the direct current bus voltage and the voltage of the corresponding photovoltaic unit at the maximum power point obtained in real time;
PI control is carried out on deviation between a preset compensation voltage given value and a first capacitance voltage obtained in real time, so that the duty ratio of the DC-DC converter is obtained;
pulse width modulation is carried out on the duty ratio of the DC-DC converter to obtain a first driving pulse signal, and the first driving pulse signal is sent to the DC-DC converter for control;
the process of generating a second driving pulse signal by a second local controller connected with the series current compensator includes:
PI control is carried out on deviation between a given value of direct current bus current and an actual measurement value of direct current bus current at the input end of the grid-connected inverter, so that the duty ratio of the series current compensator is obtained;
pulse width modulation is carried out on the duty ratio of the series current compensator to obtain a second driving pulse signal, and the second driving pulse signal is sent to the series current compensator for control;
The process of generating a third driving pulse signal by the third local controller connected with the grid-connected inverter comprises the following steps:
PI control is carried out on the deviation between a given value of the DC bus voltage at the input end of the grid-connected inverter and an actual measurement value of the DC bus voltage, and d-axis control voltage is generated;
PI control is carried out on the deviation between a given value of reactive power of the AC power grid input by the grid-connected inverter and an actual measurement value of reactive power of the AC power grid input by the grid-connected inverter, and q-axis control voltage is generated;
the d-axis control voltage and the q-axis control voltage are subjected to rotation/static conversion and space vector pulse width modulation, and then a third driving pulse signal is obtained and sent to the grid-connected inverter for control;
the method for acquiring the given value of the DC bus voltage and the given value of the DC bus current comprises the following steps:
step S1: randomly initializing the speed and position of a particle swarm as the speed and position of a first period of each particle in the power rated range of the DC-DC converter and the 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)＝[U bus (1,k),U bus (2,k),…,U bus (n,k),I bus (1,k),I bus (2,k),…,I bus (n,k)] T ，k＝1,2,…,z
U bus (i, k) is a given value of the dc bus voltage at the input of the grid-connected inverter at the i-th moment of the kth particle; i bus (i, k) is a given value of the direct current bus current of the input end of the grid-connected inverter at the ith moment of the kth particle; where i is a sequence number of a unit time period, i=1, 2, … …, n;
step S2: calculating an initialization fitness value of each particle; the fitness value is equal to a penalty function generated by subtracting the residual electric quantity of the energy storage device from the total electric charge profit of n time periods in the future when any time period exceeds an 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 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 For the current global historical best position of 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 particles to respective rated values if the given value of the DC bus voltage or the given value of the DC bus current 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 surplus electric quantity of the energy storage device exceeding 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 ＝[U bus (1),U bus (2),…,U bus (n),I bus (1),I bus (2),…,I bus (n)] T
global history to be obtained is the mostU in good position bus (1),U bus (2),,U bus (n) I in a global historical optimum position to be obtained as a given value of the DC bus voltage for n time periods in the future bus (1),I bus (2),,I bus (n) as a given value of the dc bus current for n time periods in the future, respectively, the third local controller and the second local controller are assigned correspondingly.
5. The method of claim 4, 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.
6. The method of claim 4, wherein the process of calculating the active power setpoint for the grid-tied inverter for n time periods in the future comprises constraints comprising:
the residual electric quantity of the energy storage device is in a preset percentage range of the rated capacity of the energy storage device;
the voltage of the direct current bus is equal to the sum of the voltage generated by any photovoltaic unit and the compensation voltage provided by the corresponding DC-DC converter;
The direct current bus current is equal to the sum of the currents output by the series current compensator and all the DC-DC converters;
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 dc bus voltage, the dc bus current and the current of the series current compensator cannot exceed their own preset nominal values.
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