Optical storage system and reactive power coordination control method

Abstract

The embodiment of the invention provides an optical storage system and a reactive power coordination control method. The optical storage system comprises a power grid controller, at least one PCS and at least one inverter. The direct current side of each inverter is connected to the corresponding photovoltaic module, the direct current side of each PCS is connected to the corresponding energy storage module, and the PCS, the alternating current sides of the inverters and the load are electrically connected at the PCC; the power grid controller reduces reactive power output of the PCS and increases reactive power output of the inverters based on the active power and apparent power of each inverter and PCS state information, so that the total reduction amount of the reactive power of the PCS is equal to the total increase amount of the reactive power of the inverters; the PCS state information comprises the reactive power of each PCS, or the reactive power of any PCS and the total number of the PCS. On the basis, the inverter bears the reactive power demand, the problem that the reactive power output capacity of the PCS is limited is solved, the reactive power demand is determined on the basis of the reactive power output of the PCS, and the problem that the inverter is difficult to bear reactive power accurately is solved.

Description

Technical Field

[0001] The present application relates to the technical field of photovoltaic power generation, and particularly to a photovoltaic energy storage system and a reactive power coordination control method. Background Art

[0002] When the power grid operates in island mode, a power conversion system (PCS) is used to construct the grid voltage and provide the reactive power required for transient voltage support and secondary voltage regulation under load disturbances. However, the reactive power output capacity of the PCS is restricted by the charge and discharge state of the battery, and the output reactive power is less.

[0003] On the other hand, the active power output of the photovoltaic inverter will be lower than the rated capacity of the photovoltaic inverter for a long time every day. Therefore, the inverter has the potential to provide reactive power for the power grid.

[0004] However, it is difficult to accurately obtain the specific reactive power demand of local loads in the power grid, and it is difficult to determine the reactive power borne by the inverter according to the reactive power demand; in addition, if there is a need to control the PCS not to output reactive power, affected by the line impedance, it is difficult for the PCS implementing the virtual synchronous generator (VSG) control algorithm to ensure that the reactive power output is zero. If the reactive power output of the PCS is forcibly reduced to zero, the voltage at the point of common coupling (PCC) is likely to have a large static error, affecting the stable operation of the system.

[0005] Therefore, how to control the inverter to bear the reactive power demand of the system and reduce the reactive power output by the PCS is a technical problem to be solved urgently at present. Summary of the Invention

[0006] A photovoltaic energy storage system and a reactive power coordination control method provided by an embodiment of the present application are used to solve the problems of limited reactive power output capacity of the PCS and the difficulty for the inverter to accurately provide reactive power.

[0007] In a first aspect, the present application provides a photovoltaic energy storage system, which includes a grid controller, at least one energy storage converter PCS, and at least one inverter; the DC side of each inverter is connected to the corresponding photovoltaic module, the DC side of each PCS is connected to the corresponding energy storage component, and the AC side of each PCS, the AC side of each inverter, and at least one load are electrically connected at a point of common coupling PCC; the grid controller is configured to reduce the reactive power output of each PCS to the PCC and increase the reactive power output of each inverter based on the active power and apparent power of each inverter and the PCS status information; wherein, the sum of the reduced output amounts of the reactive power of each PCS is equal to the sum of the increased output amounts of the reactive power of each inverter; the PCS status information includes the reactive power of each PCS, or the PCS status information includes the reactive power of any one PCS and the total number of PCSs.

[0008] Based on the technical solution in this design, the grid controller can obtain the ability of each inverter to bear reactive power according to the active power and apparent power of each inverter, and the grid controller can obtain the total reactive power output of the PCSs in the photovoltaic energy storage system based on the PCS status information and use this as the reactive power demand of the load; further, when the reactive power demand of the load remains unchanged, the grid controller can increase the reactive power output of the inverter and reduce the reactive power output of the PCS based on the ability of each inverter to bear reactive power and the reactive power demand of the load, thereby solving the problems of limited reactive power output capacity of the PCS and the inability of the inverter to accurately provide reactive power.

[0009] In a possible design, the grid controller is configured to: control the reactive power output of each inverter respectively based on the product of the power generation weight coefficient of each inverter and the reactive power reference quantity; wherein, the power generation weight coefficient of each inverter is the ratio of the reactive power margin of each inverter to the total reactive power margin, the reactive power margin of each inverter is obtained based on the active power and apparent power of each inverter, and the total reactive power margin is the sum of the reactive power margins of each inverter; the reactive power reference quantity is obtained based on the PCS status information.

[0010] Based on the technical solution in this design, the grid controller can calculate the reactive power that each inverter can output according to the active power and apparent power of each inverter, which represents the reactive power margin of the inverter; further, the grid controller can calculate the total reactive power margin of all the inverters according to the reactive power margin of each inverter; further, the grid controller can calculate the proportion of the reactive power output of each inverter, that is, the power generation weight coefficient, based on the reactive power margin and the total reactive power margin of each inverter; finally, the grid controller can calculate the magnitude of the reactive power that each inverter needs to bear based on the product of the power generation weight coefficient of each inverter and the reactive power reference quantity, and control the reactive power output of each inverter based on this.

[0011] In a possible design, the reactive power reference quantity is the sum of the deviation powers of each PCS; wherein, the deviation power is the difference between the preset target reactive power and the reactive power of the PCS; or the reactive power reference quantity is the sum of the deviation powers obtained by proportional-integral operation of each PCS; or the reactive power reference quantity is the sum of the reactive powers after low-pass filtering of each PCS and the deviation powers obtained by proportional-integral operation of each PCS.

[0012] It can be understood that, under the condition of a stable load, the sum of the reactive powers output by each PCS can be approximately regarded as the reactive power demand of the load.

[0013] Based on the technical solution of this design, the grid controller can calculate the total amount of reactive power output by the PCS cluster to be adjusted according to the difference between the reactive power output by each PCS and the preset target reactive power, that is, the reactive power reference quantity; further, the grid controller combines the reactive power share that the inverter can bear to obtain the reactive power output reference value of each inverter, and adjusts the reactive power output of the inverter according to the reactive power output reference value of each inverter.

[0014] In addition, if extremely fast operation speed and low algorithm architecture design difficulty are considered, the reactive power reference quantity can be directly calculated based on the sum of the deviation powers of each PCS; if both operation speed and calculation accuracy are considered, the reactive power reference quantity can be calculated based on the sum of the deviation powers after proportional-integral of each PCS. In this way, the reactive power output of the inverter can be accurately controlled through the proportional-integral loop; if the calculation is considered to be as accurate as possible, the reactive power reference quantity can be calculated based on the sum of the reactive powers after low-pass filtering of each PCS and the deviation powers after proportional-integral of each PCS. In this way, the low-pass filtering can filter out high-frequency noise, avoid too large jumps in the reactive power reference value output by the grid controller to the inverter, and at the same time, the reactive power output of the inverter and the PCS can be accurately controlled through the proportional-integral loop.

[0015] In a possible design, the reactive power reference quantity is the product of the deviation power of any one PCS and the total number of PCSs; wherein, the deviation power is the difference between the preset target reactive power and the reactive power of the PCS; or the reactive power reference quantity is the product of the deviation power obtained by proportional-integral operation of any one PCS and the total number of PCSs; or the reactive power reference quantity is the product of the first parameter and the total number of PCSs; wherein, the first parameter is the sum of the reactive power after low-pass filtering of any one PCS and the deviation power obtained by its proportional-integral operation.

[0016] It can be understood that, under the condition of a stable load, the sum of the reactive powers output by each PCS can be approximately regarded as the reactive power demand of the load.

[0017] Based on the technical solution of this design, the grid controller approximately calculates the total amount of reactive power output to be adjusted for the PCS cluster, that is, the reactive power reference quantity, according to the difference between the reactive power output by any one PCS and the preset target reactive power, and the total number of PCSs in the system. Furthermore, in combination with the reactive power ratio that the inverter can undertake, the reference value of the reactive power output of each inverter is obtained, and the reactive power output of the inverter is adjusted according to the reference value of the reactive power output of each inverter.

[0018] In addition, if considering the operation speed and the design difficulty of the algorithm architecture, the reactive power reference quantity can be directly calculated based on the product of the deviation power of any one PCS and the total number of PCSs; if considering both the operation speed and the calculation accuracy, the reactive power reference quantity can be calculated based on the product of the deviation power after proportional-integral of any one PCS and the total number of PCSs. In this way, the reactive power output of the inverter can be accurately controlled through the proportional-integral loop; if considering the calculation to be as accurate as possible, the sum of the reactive power after low-pass filtering of any one PCS and the deviation power after proportional-integral is multiplied by the total number of PCSs to calculate the reactive power reference quantity. In this way, low-pass filtering can filter out high-frequency noise, avoid too large jumps in the reactive power reference values output by the grid controller to the inverter and the PCS, and at the same time, the reactive power output of the inverter can be accurately controlled through proportional-integral control.

[0019] In a possible design, the grid controller is further configured to: in response to the PCC voltage not being within the preset voltage range, based on the PCC voltage and the preset common reference voltage, output the internal potential reference adjustment quantity to each PCS controller respectively; wherein, the preset voltage range is obtained based on the common reference voltage; each PCS includes a PCS controller and a power conversion circuit, and each PCS controller is configured to: adjust the output voltage of the power conversion circuit based on the internal potential reference quantity and the frequency reference quantity to adjust the PCC voltage to within the preset voltage range; wherein, the internal potential reference quantity is obtained based on the reactive power of the PCS and the internal potential reference adjustment quantity, and the frequency reference quantity is obtained based on the active power of the PCS.

[0020] Since the PCC voltage may change after adjusting the reactive power output of the inverter and the PCS, the controller provided with the virtual synchronous control module will automatically output reactive power to support the PCC voltage to return to within the preset voltage range. For example, after adjusting the reactive power output of the PCS to zero, the PCC voltage drops, resulting in a rapid increase in the reactive power output by the PCS. Therefore, the ideal adjustment result is that after the inverter undertakes part or all of the reactive power, the PCC voltage can quickly return to the preset common reference voltage to avoid changes in the reactive power output by the PCS.

[0021] Based on the technical solution in this design, when the PCC voltage deviates from the preset voltage range, the grid controller adjusts the internal electromotive force of the PCS to regulate its own port voltage; since the PCS port voltage is the difference between the internal electromotive force of the PCS and the voltage drop across the virtual impedance, and the PCC voltage is the sum of the voltage drops across each PCS port and the impedance of the line from the PCS to the PCC, therefore, the grid controller can quickly restore the PCC voltage to the preset voltage range by adjusting the internal electromotive force of the PCS, thereby avoiding changes in the reactive power output by the PCS.

[0022] In a possible design, the internal electromotive force reference adjustment amount is obtained by proportional-integral operation on the common voltage deviation value; where the common voltage deviation value is the difference between the common reference voltage and the PCC voltage.

[0023] It can be understood that the internal electromotive force reference adjustment amount obtained by proportional-integral can accurately adjust the PCC voltage to the common reference voltage.

[0024] In a possible design, if the PCC voltage is greater than or equal to the maximum value of the preset voltage range, the internal electromotive force reference adjustment amount is obtained by proportional-integral operation on the second parameter; where the maximum value of the preset voltage range is the sum of the common reference voltage and the first threshold, and the second parameter is the difference between the maximum value of the preset voltage range and the PCC voltage; if the PCC voltage is less than or equal to the minimum value of the preset voltage range, the internal electromotive force reference adjustment amount is obtained by proportional-integral operation on the third parameter; where the minimum value of the preset voltage range is the difference between the common reference voltage and the second threshold, and the third parameter is the difference between the minimum value of the preset voltage range and the PCC voltage.

[0025] It can be understood that if the PCC voltage is too large, that is, greater than or equal to the maximum value of the preset voltage range, then the difference between the maximum value of the preset voltage range and the PCC voltage needs to be proportional-integrated to obtain the internal electromotive force reference adjustment amount; if the PCC voltage is moderate, that is, within the preset voltage range, then there is no need to adjust the PCC voltage; if the PCC voltage is small, that is, less than or equal to the minimum value of the preset voltage range, then the difference between the minimum value of the preset voltage range and the PCC voltage needs to be proportional-integrated to obtain the internal electromotive force reference adjustment amount.

[0026] In a possible design, the internal electromotive force reference quantity is the sum of the fourth parameter of the PCS, the internal electromotive force reference adjustment amount, and the preset first standard internal electromotive force. The fourth parameter of the PCS is obtained by the PCS controller performing virtual synchronous control on the reactive power of the PCS and the preset reactive power reference; the frequency reference quantity is the sum of the fifth parameter of the PCS and the preset first standard frequency. The fifth parameter of the PCS is obtained by the PCS controller performing virtual synchronous control on the active power of the PCS and the preset active power reference.

[0027] The PCS controller can adopt the VSG control strategy to perform virtual synchronous control on the active power of the PCS and the preset active reference power to obtain the fourth parameter of the PCS, and superimpose the fourth parameter of the PCS on the internal potential reference adjustment amount and the preset first standard internal potential to obtain the internal potential reference quantity; in addition, the PCS controller can adopt the VSG control strategy to perform virtual synchronous control on the active power of the PCS and the preset active reference power to obtain the fifth parameter, and superimpose the fourth parameter of the PCS on the first standard frequency to obtain the frequency reference quantity; further, the PCS controller can generate a pulse width modulation signal according to the internal potential reference quantity and the frequency reference quantity to adjust the output voltage of the power conversion circuit, so as to further make the PCC voltage return to the preset voltage range.

[0028] In a possible design, the internal potential reference quantity is the sum of the sixth parameter of the PCS and the preset second standard internal potential. The sixth parameter is obtained by the PCS controller performing virtual synchronous control on the drooping reactive power of the PCS and the reactive power output by the PCS. The drooping reactive power of the PCS is obtained by the PCS controller performing drooping control on the difference between the target output voltage and the output voltage of the PCS based on the preset reactive-voltage drooping coefficient. The target output voltage is the sum of the standard output voltage of the PCS and the internal potential reference adjustment amount; the frequency reference quantity is the sum of the seventh parameter of the PCS and the preset second standard frequency. The seventh parameter is obtained by the PCS controller performing virtual synchronous control on the drooping active power of the PCS and the active power of the PCS. The drooping active power of the PCS is obtained by the PCS controller performing drooping control on the difference between the second standard frequency and the output frequency of the PCS based on the preset active-frequency drooping coefficient.

[0029] Based on the technical solution in this design, the PCS controller configured with the primary frequency modulation / voltage regulation circuit can obtain the target output voltage based on the sum of the standard output voltage of the PCS and the internal potential reference adjustment amount; perform drooping control on the difference between the target output voltage and the output voltage of the PCS based on the preset reactive-voltage drooping coefficient to obtain the drooping reactive power of the PCS; further, the PCS controller can adopt the VSG control strategy to perform virtual synchronous control on the drooping reactive power of the PCS and the reactive power output by the PCS, output the sixth parameter of the PCS, and obtain the internal potential reference quantity based on the sum of the sixth parameter and the preset second standard internal potential;

[0030] In addition, the PCS controller configured with the primary frequency modulation / voltage regulation circuit can perform drooping control on the difference between the preset second standard frequency and the output frequency of the PCS based on the preset active-frequency drooping coefficient to obtain the drooping active power of the PCS; and perform virtual synchronous control on the drooping active power of the PCS and the active power of the PCS to obtain the seventh parameter of the PCS; further, the PCS controller obtains the frequency reference quantity based on the sum of the seventh parameter and the second standard frequency.

[0031] Therefore, the PCS controller can generate a pulse width modulation signal according to the internal potential reference quantity and the frequency reference quantity to adjust the output voltage of the power conversion circuit, thereby enabling the PCC voltage to return to the preset voltage range.

[0032] In a second aspect, the present application further provides a reactive power coordination control method applied to a photovoltaic energy storage system. The photovoltaic energy storage system includes at least one PCS and at least one inverter; the DC side of each inverter is connected to the corresponding photovoltaic module, the DC side of each PCS is connected to the corresponding energy storage component, and the AC side of each PCS, the AC side of each inverter, and at least one load are electrically connected at the PCC; the reactive power coordination control method includes: based on the active power and apparent power of each inverter and the PCS status information, reducing the reactive power output of each PCS to the PCC and increasing the reactive power output of each inverter; wherein, the sum of the reduced output amounts of the reactive power of each PCS is equal to the sum of the increased output amounts of the reactive power of each inverter; the PCS status information includes the reactive power of each PCS, or the PCS status information includes the reactive power of any one PCS and the total number of PCSs.

[0033] Based on the technical solution in the present design, the grid controller can obtain the reactive power bearing capacity of each inverter according to the active power and apparent power of each inverter, and the grid controller can obtain the total reactive power output of the PCSs in the photovoltaic energy storage system according to the PCS status information and use this as the reactive power demand of the load; further, when the reactive power demand of the load does not change, the grid controller can increase the reactive power output of the inverter and reduce the reactive power output of the PCS based on the reactive power bearing capacity of each inverter and the reactive power demand of the load, thereby solving the problems of limited reactive power output capacity of the PCS and the inability of the inverter to accurately provide reactive power.

[0034] In a possible design, based on the active power and apparent power of each inverter and the PCS status information, reducing the reactive power output of each PCS to the PCC and increasing the reactive power output of each inverter includes: controlling the reactive power output of each inverter respectively based on the product of the power generation weight coefficient of each inverter and the reactive power reference quantity; wherein, the power generation weight coefficient of each inverter is the ratio of the reactive power margin of each inverter to the total reactive power margin, the reactive power margin of each inverter is obtained based on the active power and apparent power of each inverter, and the total reactive power margin is the sum of the reactive power margins of each inverter; the reactive power reference quantity is obtained based on the PCS status information.

[0035] Based on the technical solution in this design, the grid controller can calculate the reactive power that each inverter can output according to the active power and apparent power of each inverter, which represents the reactive power margin of the inverter; further, the grid controller can calculate the total reactive power margin of all inverters according to the reactive power margin of each inverter; further, the grid controller can calculate the proportion of reactive power output of each inverter, that is, the power generation weight coefficient, based on the reactive power margin and the total reactive power margin of each inverter; finally, the grid controller can calculate the magnitude of the reactive power that each inverter needs to bear based on the product of the power generation weight coefficient of each inverter and the reactive power reference quantity, and control each inverter to output reactive power based on this.

[0036] In a possible design, the reactive power reference quantity is the sum of the deviation powers of each PCS; where the deviation power is the difference between the preset target reactive power and the reactive power of the PCS; or the reactive power reference quantity is the sum of the deviation powers obtained by proportional-integral operation of each PCS; or the reactive power reference quantity is the sum of the reactive powers after low-pass filtering of each PCS and the deviation powers obtained by proportional-integral operation of each PCS.

[0037] It can be understood that when the load is stable, the sum of the reactive powers output by each PCS can be approximately regarded as the reactive power demand of the load.

[0038] Based on the technical solution of this design, the grid controller can calculate the total amount of reactive power for adjusting the output of the PCS cluster according to the difference between the reactive power output by each PCS and the preset target reactive power, that is, the reactive power reference quantity; further, the grid controller can obtain the reactive power output reference value of each inverter by combining the reactive power share that the inverter can bear, and adjust the reactive power output of the inverter according to the reactive power output reference value of each inverter.

[0039] In addition, if extremely fast operation speed and low algorithm architecture design difficulty are considered, the reactive power reference quantity can be directly calculated based on the sum of the deviation powers of each PCS; if both operation speed and calculation accuracy are considered, the reactive power reference quantity can be calculated based on the sum of the deviation powers after proportional-integral of each PCS. In this way, the reactive power output of the inverter can be accurately controlled through the proportional-integral loop; if as accurate calculation as possible is considered, the reactive power reference quantity can be calculated based on the sum of the reactive powers after low-pass filtering of each PCS and the deviation powers after proportional-integral of each PCS. In this way, low-pass filtering can filter out high-frequency noise, avoid too large jumps in the reactive power reference value output by the grid controller to the inverter, and at the same time, the reactive power output of the inverter and PCS can be accurately controlled through the proportional-integral loop.

[0040] In a possible design, the reactive power reference quantity is the product of the deviation power of any one PCS and the total number of PCSs; wherein, the deviation power is the difference between the preset target reactive power and the reactive power of the PCS; or the reactive power reference quantity is the product of the deviation power obtained after proportional-integral operation of any one PCS and the total number of PCSs; or the reactive power reference quantity is the product of a first parameter and the total number of PCSs; wherein, the first parameter is the sum of the reactive power of any one PCS after low-pass filtering and the deviation power obtained after its proportional-integral operation.

[0041] It can be understood that, when the load is stable, the sum of the reactive powers output by each PCS can be approximately regarded as the reactive power demand of the load.

[0042] Based on the technical solution of this design, the grid controller approximately calculates the total amount of reactive power output by the PCS cluster to be adjusted, that is, the reactive power reference quantity, according to the difference between the reactive power output by any one PCS and the preset target reactive power, and the total number of PCSs in the system. Furthermore, the reference value of the reactive power output of each inverter is obtained by combining the reactive power ratio that the inverter can bear, and the reactive power output of the inverter is adjusted according to the reference value of the reactive power output of each inverter.

[0043] In addition, if the operation speed and the design difficulty of the algorithm architecture are considered, the reactive power reference quantity can be directly calculated based on the product of the deviation power of any one PCS and the total number of PCSs; if the operation speed and the calculation accuracy are considered, the reactive power reference quantity can be calculated based on the product of the deviation power after proportional-integral of any one PCS and the total number of PCSs. In this way, the reactive power output of the inverter can be accurately controlled through the proportional-integral loop; if the calculation is required to be as accurate as possible, the sum of the reactive power of any one PCS after low-pass filtering and the deviation power after proportional-integral is multiplied by the total number of PCSs to calculate the reactive power reference quantity. In this way, the low-pass filtering can filter out high-frequency noise, avoid too large jumps in the reactive power reference values output by the grid controller to the inverter and the PCS, and at the same time, the reactive power output of the inverter can be accurately controlled through proportional-integral control.

[0044] In a possible design, the reactive power coordination control method further includes: in response to the PCC voltage not being within the preset voltage range, respectively outputting an internal potential reference adjustment quantity to each PCS controller based on the PCC voltage and the preset common reference voltage; wherein, the preset voltage range is obtained based on the common reference voltage; adjusting the output voltage of the power conversion circuit based on the internal potential reference quantity and the frequency reference quantity to adjust the PCC voltage to within the preset voltage range; wherein, the internal potential reference quantity is obtained based on the reactive power of the PCS and the internal potential reference adjustment quantity, and the frequency reference quantity is obtained based on the active power of the PCS.

[0045] Since the PCC voltage may change after adjusting the reactive power output of the inverter and PCS, the controller with a virtual synchronous control module will automatically output reactive power to support the recovery of the PCC voltage to the preset voltage range. For example, after adjusting the reactive power output of the PCS to zero, the PCC voltage drops, resulting in a rapid increase in the reactive power output of the PCS. Therefore, the ideal adjustment result is that after the inverter undertakes part or all of the reactive power, the PCC voltage can quickly recover to the preset common reference voltage to avoid changes in the reactive power output of the PCS.

[0046] Based on the technical solution in this design, when the PCC voltage deviates from the preset voltage range, the grid controller adjusts the internal electromotive force of the PCS to regulate its own port voltage; since the PCS port voltage is the difference between the internal electromotive force of the PCS and the voltage drop on the virtual impedance, and the PCC voltage is the sum of the voltage differences between each PCS port voltage and the voltage drop on the impedance of the line from the PCS to the PCC, therefore, the grid controller can quickly recover the PCC voltage to the preset voltage range by adjusting the internal electromotive force of the PCS, thereby avoiding changes in the reactive power output of the PCS.

[0047] In a possible design, the internal electromotive force reference adjustment amount is obtained by proportional-integral operation on the common voltage deviation value; where the common voltage deviation value is the difference between the common reference voltage and the PCC voltage.

[0048] It can be understood that the internal electromotive force reference adjustment amount obtained by proportional-integral can accurately adjust the PCC voltage to the common reference voltage.

[0049] In a possible design, if the PCC voltage is greater than or equal to the maximum value of the preset voltage range, the internal electromotive force reference adjustment amount is obtained by proportional-integral operation on the second parameter; where the maximum value of the preset voltage range is the sum of the common reference voltage and the first threshold, and the second parameter is the difference between the maximum value of the preset voltage range and the PCC voltage; if the PCC voltage is less than or equal to the minimum value of the preset voltage range, the internal electromotive force reference adjustment amount is obtained by proportional-integral operation on the third parameter; where the minimum value of the preset voltage range is the difference between the common reference voltage and the second threshold, and the third parameter is the difference between the minimum value of the preset voltage range and the PCC voltage.

[0050] It can be understood that if the PCC voltage is too large, that is, greater than or equal to the maximum value of the preset voltage range, then the difference between the maximum value of the preset voltage range and the PCC voltage needs to be proportional-integrated to obtain the internal electromotive force reference adjustment amount; if the PCC voltage is moderate, that is, within the preset voltage range, then there is no need to adjust the PCC voltage; if the PCC voltage is small, that is, less than or equal to the minimum value of the preset voltage range, then the difference between the minimum value of the preset voltage range and the PCC voltage needs to be proportional-integrated to obtain the internal electromotive force reference adjustment amount.

[0051] In a possible design, the internal potential reference quantity is obtained based on the reactive power of the PCS and the internal potential reference adjustment quantity, including: performing virtual synchronous control on the reactive power of the PCS and a preset reactive reference power to obtain a fourth parameter of the PCS; obtaining the internal potential reference quantity based on the sum of the fourth parameter of the PCS, the internal potential reference adjustment quantity, and a preset first standard internal potential; the frequency reference quantity is obtained based on the active power of the PCS, including: performing virtual synchronous control on the active power of the PCS and a preset active reference power to obtain a fifth parameter of the PCS; obtaining the frequency reference quantity based on the sum of the fifth parameter of the PCS and a preset first standard frequency.

[0052] The PCS controller can adopt the VSG control strategy to perform virtual synchronous control on the active power of the PCS and a preset active reference power to obtain a fourth parameter of the PCS, and superimpose the fourth parameter of the PCS on the internal potential reference adjustment quantity and a preset first standard internal potential to obtain the internal potential reference quantity; in addition, the PCS controller can adopt the VSG control strategy to perform virtual synchronous control on the active power of the PCS and a preset active reference power to obtain a fifth parameter, and superimpose the fourth parameter of the PCS on the first standard frequency to obtain the frequency reference quantity; further, the PCS controller can generate a pulse width modulation signal according to the internal potential reference quantity and the frequency reference quantity to adjust the output voltage of the power conversion circuit, so as to further make the PCC voltage return to the preset voltage range.

[0053] In a possible design, the internal potential reference quantity is obtained based on the reactive power of the PCS and the internal potential reference adjustment quantity, including: obtaining a target output voltage based on the sum of the standard output voltage of the PCS and the internal potential reference adjustment quantity; performing droop control on the difference between the target output voltage and the output voltage of the PCS based on a preset reactive-voltage droop coefficient to obtain the droop reactive power of the PCS; performing virtual synchronous control on the droop reactive power of the PCS and the reactive power output by the PCS to obtain a sixth parameter of the PCS; obtaining the internal potential reference quantity based on the sum of the sixth parameter and a preset second standard internal potential; the frequency reference quantity is obtained based on the active power of the PCS, including: performing droop control on the difference between a preset second standard frequency and the output frequency of the PCS based on a preset active-frequency droop coefficient to obtain the droop active power of the PCS; performing virtual synchronous control on the droop active power of the PCS and the active power of the PCS to obtain a seventh parameter of the PCS; obtaining the frequency reference quantity based on the sum of the seventh parameter and the second standard frequency.

[0054] Based on the technical solution in this design, the PCS controller configured with a primary frequency modulation / voltage regulation circuit can obtain the target output voltage based on the sum of the standard output voltage of the PCS and the internal potential reference adjustment amount; perform droop control on the difference between the target output voltage and the output voltage of the PCS based on the preset reactive-voltage droop coefficient to obtain the droop reactive power of the PCS; further, the PCS controller can perform virtual synchronous control on the droop reactive power of the PCS and the reactive power output by the PCS by using the VSG control strategy, output the sixth parameter of the PCS, and obtain the internal potential reference amount based on the sum of the sixth parameter and the preset second standard internal potential;

[0055] In addition, the PCS controller configured with a primary frequency modulation / voltage regulation circuit can perform droop control on the difference between the preset second standard frequency and the output frequency of the PCS based on the preset active-frequency droop coefficient to obtain the droop active power of the PCS; and perform virtual synchronous control on the droop active power of the PCS and the active power of the PCS to obtain the seventh parameter of the PCS; further, the PCS controller obtains the frequency reference amount based on the sum of the seventh parameter and the second standard frequency.

[0056] Therefore, the PCS controller can generate a pulse width modulation signal according to the internal potential reference amount and the frequency reference amount to adjust the output voltage of the power conversion circuit, thereby making the PCC voltage return to the preset voltage range. Description of the Drawings

[0057] Figure 1 It is a schematic structural diagram of a photovoltaic energy storage system provided by an embodiment of the present application;

[0058] Figure 2a It is a schematic architecture diagram of a reactive power coordination control provided by an embodiment of the present application;

[0059] Figure 2b It is another schematic architecture diagram of a reactive power coordination control provided by an embodiment of the present application;

[0060] Figure 3a It is a schematic diagram of a photovoltaic energy storage collaborative reactive power control loop provided by an embodiment of the present application;

[0061] Figure 3b It is another schematic architecture diagram of a photovoltaic energy storage collaborative reactive power control loop provided by an embodiment of the present application;

[0062] Figure 3c It is another schematic architecture diagram of a photovoltaic energy storage collaborative reactive power control loop provided by an embodiment of the present application;

[0063] Figure 4a It is another schematic architecture diagram of a photovoltaic energy storage collaborative reactive power control loop provided by an embodiment of the present application;

[0064] Figure 4b Another schematic diagram of the architecture of the photovoltaic-storage collaborative reactive power control loop provided by the embodiment of the present application;

[0065] Figure 4c Another schematic diagram of the architecture of the photovoltaic-storage collaborative reactive power control loop provided by the embodiment of the present application;

[0066] Figure 5 A schematic diagram of the architecture of a secondary voltage regulation loop provided by the embodiment of the present application;

[0067] Figure 6a Another schematic diagram of the architecture of a secondary voltage regulation loop provided by the embodiment of the present application;

[0068] Figure 6b Another schematic diagram of the architecture of a secondary voltage regulation loop provided by the embodiment of the present application;

[0069] Figure 7 A schematic diagram of the process of a reactive power coordination control method provided by the embodiment of the present application;

[0070] Figure 8 Another schematic diagram of the process of a reactive power coordination control method provided by the embodiment of the present application;

[0071] Figure 9 Another schematic diagram of the process of a reactive power coordination control method provided by the embodiment of the present application;

[0072] Figure 10 Another schematic diagram of the process of a reactive power coordination control method provided by the embodiment of the present application;

[0073] Figure 11 Another schematic diagram of the process of a reactive power coordination control method provided by the embodiment of the present application;

[0074] Figure 12a A schematic diagram of the simulation comparison of a reactive power coordination control method provided by the embodiment of the present application;

[0075] Figure 12b Another schematic diagram of the simulation comparison of a reactive power coordination control method provided by the embodiment of the present application;

[0076] Figure 12c Another schematic diagram of the simulation comparison of a reactive power coordination control method provided by the embodiment of the present application;

[0077] Figure 12d Another schematic diagram of the simulation comparison of a reactive power coordination control method provided by the embodiment of the present application. Detailed implementation manners

[0078] For the convenience of description and understanding, first, technical terms in this field applied in this application are introduced as follows:

[0079] I. Microgrid

[0080] A microgrid refers to a small power network composed of distributed generation equipment, electrical loads, monitoring / protection, and automation devices, etc., which is used to achieve a basic balance of internal power and electricity. It can either operate in parallel with the external power grid or operate independently off-grid to form a "power island".

[0081] II. PCS

[0082] PCS refers to a converter in an electrochemical energy storage system that is connected between the battery system and the power grid (and / or load) to achieve bidirectional power conversion of electric energy.

[0083] III. Photovoltaic Inverter

[0084] A photovoltaic inverter refers to an electrical device used to convert the direct current generated by solar cells into alternating current and then feed it into the power grid.

[0085] To make the objectives, technical solutions, and advantages of this application clearer, the scenarios in which the technical solutions in the embodiments of this application are applied and the technical problems to be solved are clearly and completely described below:

[0086] In an islanded microgrid, the PCS is mainly used to build the grid voltage and provide the reactive power required for transient voltage support and secondary voltage regulation under load disturbances. However, the output capacity of the PCS reactive power is greatly restricted by the battery charge and discharge state. For example, when the energy storage battery has a low power level and has a fast charging demand, or when the PCS is performing microgrid frequency support and active power regulation, the demand for the PCS active power output is very large, resulting in less PCS output reactive power.

[0087] In addition, restricted by the lighting conditions and energy storage capacity, the active power of the photovoltaic inverter in the islanded microgrid is lower than its rated capacity for a long time every day. Therefore, the photovoltaic inverter has the potential to undertake the system reactive power. For example, in the case of poor lighting conditions, the active power output capacity of the photovoltaic inverter is weak, while the reactive power output capacity is enhanced, and it can undertake the system reactive power.

[0088] However, there are the following technical challenges in using photovoltaics to undertake the reactive power of the microgrid load:

[0089] Firstly, it is difficult to accurately obtain the specific reactive power demand of local loads in the microgrid. Especially when there are multiple loads in the system, the cost of the load reactive power measurement scheme is high and the accuracy is poor;

[0090] In a second aspect, affected by the impedance of the tie line, there is a voltage difference between the PCS port and the PCC voltage. It is difficult for the PCS implementing the VSG control algorithm to ensure that its reactive power is reduced to the target reactive power. For example, when the target reactive power of the PCS is zero, due to the built-in droop control of the VSG control algorithm, when it detects that the PCC voltage deviates from the rated voltage, the PCS will output reactive power to support the PCC voltage, resulting in the inability of the PCS reactive power to be stably zero. If the PCS reactive power is forced to be reduced to zero, a large static error is likely to occur in the PCC voltage, exceeding the voltage safety operating boundary, thus affecting the stable operation of the system.

[0091] Therefore, how to control the inverter to bear the reactive power demand of the system and reduce the reactive power output by the PCS is a technical problem that needs to be solved urgently at present.

[0092] Based on the above problems, the embodiments of the present application provide a photovoltaic energy storage system and a reactive power coordinated control method to solve the problems of limited reactive power output capacity of the PCS and the difficulty for the inverter to accurately provide reactive power.

[0093] The following introduces the photovoltaic energy storage system provided by the embodiments of the present application. It should be understood that the scenarios to which the technical solutions in the embodiments of the present application are applied are not limited to the microgrid in the island state, and can also be scenarios where the grid-connected microgrid or the photovoltaic energy storage power station participates in grid voltage regulation or auxiliary services. The present application makes no limitation in this regard.

[0094] As Figure 1 shown, the photovoltaic energy storage system in the embodiments of the present application includes a grid controller 101, at least one energy storage converter PCS (shown as PCS1 - PCSj in the drawings of the present application), and at least one inverter (shown as inverter 1 - inverter i in the drawings of the present application);

[0095] The DC side of each inverter is connected to the corresponding photovoltaic module (shown as PV1 - PVn in the drawings of the present application), the DC side of each PCS is connected to the corresponding energy storage component (shown as BAT1 - BATn in the drawings of the present application), and the AC side of each PCS, the AC side of each inverter, and at least one load (shown as load 1 - load n in the drawings of the present application) are electrically connected at the common connection point PCC;

[0096] The grid controller 101 is configured to reduce the reactive power output amount of each PCS to the PCC and increase the reactive power output amount of each inverter based on the active power and apparent power of each inverter and the PCS status information.

[0097] It should be noted that the sum of the output amounts of the reactive power reduction of each PCS is equal to the sum of the output amounts of the reactive power increase of each inverter; the PCS status information includes the reactive power of each PCS, or, the PCS status information includes the reactive power of any one PCS and the total number of PCSs.

[0098] In addition, the grid controller in the embodiments of the present application can be configured according to the type of the photovoltaic energy storage system. Taking the photovoltaic energy storage system as a microgrid system as an example, the grid controller 101 in the embodiments of the present application can be a microgrid central controller (MGCC).

[0099] Based on the technical solution in this embodiment, the grid controller 101 can obtain the ability of each inverter to bear reactive power according to the active power and apparent power of each inverter. The grid controller 101 can obtain the total reactive power output of the PCSs in the photovoltaic energy storage system according to the PCS status information and use this as the reactive power demand of the load;

[0100] Furthermore, the grid controller 101 can allocate the reactive power demand of the load based on the ability of each inverter to bear reactive power, so as to increase the reactive power output of the inverter and reduce the reactive power output of the PCS, thereby solving the problems of limited reactive power output capacity of the PCS and wasted reactive power output capacity of the inverter;

[0101] Even when the impedance of the connection line between the power generation side and the grid is different and unknown, this solution can also reduce the reactive power output of the PCS. When the photovoltaic capacity is sufficient, if the inverters in the system can bear all the reactive power demands, the grid controller 101 can adjust the reactive power output of the PCS to zero, so that the PCS can provide more energy storage power support and maintain the frequency modulation ability of the PCS; and because the PCS is no longer limited by the output reactive power, therefore, on the premise of ensuring power supply reliability and microgrid stability, the photovoltaic energy storage system can reduce the energy storage installation quantity and save the construction cost of a type of photovoltaic energy storage system such as a microgrid system.

[0102] In a possible embodiment, the grid controller 101 is used for:

[0103] Based on the product of the power generation weight coefficient and the reactive power reference quantity of each inverter, respectively control each inverter to output reactive power;

[0104] It should be noted that the power generation weight coefficients of each inverter are the ratios of the reactive power margins of each inverter to the total reactive power margin. The reactive power margins of each inverter are obtained based on the active power and apparent power of each inverter, and the total reactive power margin is the sum of the reactive power margins of each inverter; the reactive power reference quantity is obtained based on the PCS status information.

[0105] It can be understood that, as Figure 1 shown, the inverter includes an inverter controller (shown as inverter 1 controller - inverter i controller in the attached drawings of this application) and an inverter circuit (shown as inverter circuit 1 - inverter circuit i in the attached drawings of this application). The DC side of the inverter circuit is connected to the photovoltaic module, and the AC side of the inverter circuit is connected to the PCC. The power generation weight coefficient of the inverter is determined by the ratio of the real-time reactive power margin of the inverter circuit to the total reactive power margin of the photovoltaic inverters in the photovoltaic energy storage system. The power generation weight coefficient is used to determine the proportion it shares in the total photovoltaic reactive power reference value. Further, based on the product of the power generation weight coefficient of each inverter and the reactive power reference quantity, the grid controller can calculate the reference value of the reactive power that each inverter needs to bear, and the inverter controller controls each inverter circuit to output reactive power based on the reference value of the reactive power calculated by the grid controller.

[0106] In a possible implementation manner, as Figure 2a shown, inverter i sends its apparent power S PV,i and active power P PV,i to the power generation weight coefficient calculation module 201 in the grid controller 101, and the power generation weight coefficient calculation module 201 outputs the power generation weight coefficient k PV，i . The function inside the power generation weight coefficient calculation module 201 can be seen in Formula 1:

[0107]

[0108] where k PV，i is the power generation weight coefficient of the i-th inverter, S PV,i is the apparent power of the i-th inverter, P PV,i is the active power of the i-th inverter, Q PV,i is the reactive power margin of the i-th inverter, is the total reactive power margin of each inverter, N PV is the number of inverters participating in reactive power coordination in the photovoltaic energy storage system.

[0109] Those skilled in the art should know that each inverter controller can calculate the corresponding real-time power generation coefficient based on the apparent power and the output active power of the inverter, and the inverter sends the real-time power generation coefficient to the grid controller 101. Therefore, the grid controller 101 can also calculate the power generation weight coefficient based on the real-time power generation coefficient;

[0110] Exemplarily, as Figure 2b shown, inverter i sends its apparent power S PV,i and real-time power generation coefficient ε PV,i to the power generation weight coefficient calculation module 201 in the grid controller, and the power generation weight coefficient calculation module 201 outputs the power generation weight coefficient kPV，i , the function inside the power generation weight coefficient calculation module 201 can be seen in Formula 2:

[0111]

[0112] Where, k PV，i is the power generation weight coefficient of the i-th inverter, S PV,i is the apparent power of the i-th inverter, P PV,i is the active power of the i-th inverter, Q PV,i is the reactive power margin of the i-th inverter, is the total reactive margin of each inverter, N PV is the number of inverters participating in reactive power coordination in the photovoltaic energy storage system, ε PV,i is the real-time power generation coefficient of the i-th inverter.

[0113] In a possible implementation manner, the calculation method of the reference value of the reactive power output by each inverter in this embodiment can be seen in Formula 3:

[0114] Q PV，ref,i = k PV，i ·Q sum , (i = 1, 2,..., N PV ) Formula 3

[0115] Where, k PV，i is the power generation weight coefficient of the i-th inverter, Q PV，ref,i is the reference value of the reactive power output by the i-th inverter, Q sum is the reactive power reference quantity.

[0116] Based on the technical solution in this embodiment, the grid controller calculates the reactive power reference quantity required by the load according to the status information of the PCS, and sends a control instruction containing the reactive power reference value to each inverter according to the reactive power reference quantity and the reactive power output capacity of the photovoltaic inverter. The controller of each photovoltaic inverter executes the power closed-loop control algorithm to track the input reactive power reference value without error, so as to undertake the reactive power demand of the load under the steady state of the photovoltaic energy storage system.

[0117] In a possible embodiment, the reactive power reference quantity can be obtained by any of the following methods:

[0118] Embodiment 1: The reactive power reference quantity is the sum of the deviation powers of each PCS;

[0119] It should be noted that the deviation power is the difference between the preset target reactive power and the reactive power of the PCS;

[0120] It can be understood that if faster operation speed and simplified algorithm architecture are considered, the reactive power reference can be directly calculated based on the sum of the deviation powers of each PCS.

[0121] Exemplarily, in combination with Figure 3a , the calculation method of the reactive power reference is shown in Formula 4:

[0122]

[0123] where N PCS is the number of PCSs participating in reactive power coordination in the photovoltaic energy storage system, Q PCS,tar,j is the preset target reactive power of the jth PCS, and Q PCS,j is the reactive power output by the jth PCS.

[0124] Embodiment 2: The reactive power reference is the sum of the deviation powers obtained after proportional-integral operation of each PCS.

[0125] It should be noted that the deviation power is the difference between the preset target reactive power and the reactive power of the PCS.

[0126] It can be understood that if faster operation speed and higher calculation accuracy are considered, the reactive power reference can be calculated based on the sum of the deviation powers after proportional-integral of each PCS;

[0127] Exemplarily, in combination with Figure 3b , the calculation method of the reactive power reference is shown in Formula 5:

[0128]

[0129] where N PCS is the number of PCSs participating in reactive power coordination in the photovoltaic energy storage system, Q PCS,tar,j is the preset target reactive power of the jth PCS, Q PCS，j is the reactive power output by the jth PCS, G PIq (s) is the proportional-integral control (PI) transfer function; G PI,q (s) can be where k p,q is the proportionality coefficient, and k i,q is the integral coefficient.

[0130] Embodiment 3: The reactive power reference is the sum of the reactive powers after low-pass filtering of each PCS and the deviation powers obtained after proportional-integral operation of each PCS.

[0131] It should be noted that the deviation power is the difference between the preset target reactive power and the reactive power of the PCS.

[0132] It is understandable that if we consider calculating as precisely as possible, the high-frequency noise in the reactive power output by the PCS can be filtered out through the low-pass filter control loop, avoiding large jumps in the reactive power reference value output by the grid controller 101 to the inverter. Additionally, in this solution, the deviation power is adjusted through the proportional-integral control loop. Further, the reactive power reference quantity can be calculated based on the sum of the reactive power after low-pass filtering for each PCS and the deviation power after proportional-integral processing for each PCS.

[0133] It is worth mentioning that the low-pass filter control loop, as the feed-forward loop in the photovoltaic-storage collaborative reactive power control loop, operates faster than the proportional-integral control loop. Therefore, the low-pass filter control loop can achieve the effect of open-loop predictive control, while the proportional-integral control loop can provide high-precision closed-loop control. Thus, this embodiment can balance the rapidity and non-difference of reactive power coordinated control.

[0134] Exemplarily, in combination with Figure 3c , the calculation method of the reactive power reference quantity can be seen in Formula 6:

[0135]

[0136] where N PCS is the number of PCSs participating in reactive power coordination in the photovoltaic-storage system, Q PCS,tar,j is the preset target reactive power of the jth PCS, Q PCS，j is the reactive power output by the jth PCS, G LPF，q (s) is the transfer function of the low-pass filter (LPF), G PI，q (s) is the PI transfer function; G PI,q (s) can be where k p,q is the proportional coefficient, and k i,q is the integral coefficient.

[0137] In a possible embodiment, the reactive power reference quantity can be obtained through any of the following methods:

[0138] Embodiment 1: The reactive power reference quantity is the product of the deviation power of any PCS and the total number of PCSs.

[0139] It should be noted that the deviation power is the difference between the preset target reactive power and the reactive power of the PCS.

[0140] It can be understood that in the actual application scenario, it is costly to obtain the reactive power of each PCS, and the calculation time is long, which affects the control effect. Therefore, considering that the PCS specifications in the photovoltaic energy storage system are basically the same, and the difference in the actual reactive power output of different PCSs is not large, the reactive power reference can be directly estimated by the product of the deviation power of any one PCS and the total number of PCSs, so as to obtain a faster operation speed and simplify the algorithm architecture.

[0141] Exemplarily, combined with Figure 4a , the calculation method of the reactive power reference is shown in Formula 7:

[0142] Q sum =(Q PCS,tar,j -Q PCS,j )·N PCS , (j = 1, 2,..., N PCS ) Formula 7

[0143] where N PCS is the number of PCSs participating in reactive power coordination in the photovoltaic energy storage system, Q PCS,tar,j is the preset target reactive power of the jth PCS, and Q PCS,j is the reactive power output by the jth PCS.

[0144] Embodiment 2: The reactive power reference is the product of the deviation power obtained by the proportional-integral operation of any one PCS and the total number of PCSs.

[0145] It should be noted that the deviation power is the difference between the preset target reactive power and the reactive power of the PCS.

[0146] It can be understood that if a faster operation speed and higher calculation accuracy are considered, the reactive power reference can be estimated by the product of the deviation power after the proportional-integral operation of any one PCS and the total number of PCSs.

[0147] Exemplarily, combined with Figure 4b , the calculation method of the reactive power reference is shown in Formula 8:

[0148] Q sum =G PI,q (s)·(Q PCS,tar,j -Q PCS,j )·N PCS , (j = 1, 2,..., N PCS ) Formula 8

[0149] where N PCS is the number of PCSs participating in reactive power coordination in the photovoltaic energy storage system, Q PCS，tar，j is the preset target reactive power of the jth PCS, Q PCS,j is the reactive power output by the jth PCS, GPI,q (s) is a PI transfer function, for example, it can be where k p,q is the proportionality coefficient, and k i,q is the integral coefficient.

[0150] Embodiment 3: The reactive power reference quantity is the product of the first parameter and the total number of PCSs.

[0151] It should be noted that the deviation power is the difference between the preset target reactive power and the reactive power of the PCS, and the first parameter is the sum of the reactive power after low-pass filtering of any one PCS and the deviation power obtained after its proportional-integral operation.

[0152] It can be understood that if high-precision calculation is considered, the high-frequency noise in the reactive power output by any one PCS can be filtered out through the low-pass filter control loop to avoid large jumps in the reactive power reference value output by the grid controller 101 to the inverter. Additionally, the deviation power is adjusted through the proportional-integral control loop. Further, based on the reactive power after low-pass filtering of any one PCS and its proportional-integrated deviation power, the reactive power reference quantity is estimated by multiplying by the total number of PCSs;

[0153] It is worth mentioning that the low-pass filter control loop, as the feedforward loop in the photovoltaic-storage collaborative reactive power control loop, operates faster than the proportional-integral control loop. Therefore, the low-pass filter control loop can achieve the effect of open-loop predictive control, while the proportional-integral control loop can provide high-precision closed-loop control. Thus, this embodiment can balance the rapidity and non-difference of reactive power coordinated control.

[0154] Exemplarily, in combination with Figure 4c , the calculation method of the reactive power reference quantity is shown in Equation 9:

[0155] Q sum =[G PI,q (s)·(Q PCS,tar,j -Q PCS,j )+G LPF,q (s)·Q PCS,j ·N PCS , (j = 1, 2,..., N PCS ) Equation 9

[0156] where N PCS is the number of PCSs participating in reactive power coordination in the photovoltaic-storage system, Q PCS,tar,j is the preset target reactive power of the jth PCS, Q PCS,j is the reactive power output by the jth PCS, G LPF,q (s) is the LPF transfer function, and G PI,q (s) is a PI transfer function, for example, it can be Among them, k p,q is a proportionality coefficient, and k i,q is an integral coefficient.

[0157] In a possible embodiment, the grid controller 101 is further configured to:

[0158] In response to the PCC voltage not being within the preset voltage range, based on the PCC voltage and the preset common reference voltage, respectively output an internal potential reference adjustment amount to each PCS controller.

[0159] It should be noted that the preset voltage range is obtained based on the common reference voltage, and the common reference voltage may be the PCC rated voltage.

[0160] Each PCS includes a PCS controller (shown as PCS1 controller - PCSj controller in the drawings of this application) and a power conversion circuit (shown as power conversion circuit 1 - power conversion circuit j in the drawings of this application). Each PCS controller is configured to:

[0161] Based on the internal potential reference quantity and the frequency reference quantity, adjust the output voltage of the power conversion circuit to adjust the PCC voltage to within the preset voltage range.

[0162] It should be noted that the internal potential reference quantity is obtained based on the reactive power of the PCS and the internal potential reference adjustment amount, and the frequency reference quantity is obtained based on the active power of the PCS.

[0163] It can be understood that since the PCC voltage may change after adjusting the reactive power output of the inverter and the PCS, the controller provided with the virtual synchronous control module will automatically output reactive power to support the PCC voltage to recover to within the preset voltage range. For example, after adjusting the reactive power output of the PCS to zero, the PCC voltage drops, resulting in a rapid increase in the reactive power output by the PCS. Therefore, the ideal adjustment result is that after the inverter undertakes part or all of the reactive power, the voltage of the PCC can quickly recover to the preset common reference voltage to avoid changes in the reactive power output by the PCS.

[0164] Based on the technical solution in this embodiment, when the PCC voltage deviates from the preset voltage range, the grid controller 101 adjusts the internal potential of the PCS to adjust its own port voltage; since the PCS port voltage is the difference between the PCS internal potential and the voltage drop on the virtual impedance, and the PCC voltage is the sum of the differences between the port voltages of each PCS and the voltage drops on the line impedance from the PCS to the PCC, therefore, the grid controller 101 can quickly restore the PCC voltage to within the preset voltage range by adjusting the PCS internal potential, thereby avoiding changes in the reactive power output by the PCS.

[0165] In a possible embodiment, the internal potential reference adjustment amount is obtained by proportional-integral operation on the common voltage deviation value.

[0166] It should be noted that the common voltage deviation value is the difference between the common reference voltage and the PCC voltage.

[0167] Exemplarily, the calculation method of the internal potential reference adjustment amount is shown in Formula Ten:

[0168] ΔE = G PI,v (s)·(V PCC,norm - V PCC ) Formula Ten

[0169] Where, ΔE is the internal potential reference adjustment amount, V PCCnorm is the common reference voltage, V PCC is the PCC voltage, G PIv (s) is the PI transfer function, for example, it can be Where, k p,v is the proportionality coefficient, k i,v is the integral coefficient.

[0170] Based on the technical solution of this embodiment, by the internal potential reference adjustment amount obtained by proportional-integral output of the common voltage deviation value, precise control of the PCC voltage can be achieved.

[0171] In a possible embodiment, if the PCC voltage is greater than or equal to the maximum value of the preset voltage range, the internal potential reference adjustment amount is obtained by proportional-integral operation on the second parameter.

[0172] It should be noted that the maximum value of the preset voltage range is the sum of the common reference voltage and the first threshold, and the second parameter is the difference between the maximum value of the preset voltage range and the PCC voltage;

[0173] If the PCC voltage is less than or equal to the minimum value of the preset voltage range, the internal potential reference adjustment amount is obtained by proportional-integral operation on the third parameter.

[0174] It should be noted that the minimum value of the preset voltage range is the difference between the common reference voltage and the second threshold, and the third parameter is the difference between the minimum value of the preset voltage range and the PCC voltage.

[0175] Exemplarily, combined with Figure 5 , the calculation method of the internal potential reference adjustment amount is shown in Formula Eleven:

[0176]

[0177] Where, ΔE is the internal potential reference adjustment amount, V PCC,norm is the common reference voltage, V PCC is the PCC voltage, V PCC,max is the maximum value of the preset voltage range, V PCC,min is the minimum value of the preset voltage range, GPI,v (s) is a PI transfer function, for example, it can be where k p,v is the proportionality coefficient, and k i,v is the integral coefficient.

[0178] It should be noted that, as Figure 5 shown, V in Formula Eleven PCC,max and V PCC,min can be the secondary regulation dead zone based on the PCC voltage [+V th , -V th .

[0179] Based on the technical solution in this embodiment, if the PCC voltage is too large, then the difference between the maximum value of the preset voltage range and the PCC voltage is proportionally integrated to obtain the internal potential reference regulation amount; if the PCC voltage is moderate and within the preset voltage range, then there is no need to adjust the PCC voltage, and the internal potential reference regulation amount is zero; if the PCC voltage is small, then the difference between the minimum value of the preset voltage range and the PCC voltage is proportionally integrated to obtain the internal potential reference regulation amount.

[0180] In a possible embodiment, the internal potential reference quantity is the sum of the fourth parameter of the PCS, the internal potential reference regulation amount, and the preset first standard internal potential. The fourth parameter of the PCS is obtained by the PCS controller performing virtual synchronous control on the reactive power of the PCS and the preset reactive power reference.

[0181] In addition, the frequency reference quantity is the sum of the fifth parameter of the PCS and the preset first standard frequency. The fifth parameter is obtained by the PCS controller performing virtual synchronous control on the active power of the PCS and the preset active power reference.

[0182] It should be noted that the first standard internal potential can be the rated internal potential of the PCS, and the first standard frequency can be the rated frequency of the PCS.

[0183] Exemplarily, in combination with Figure 6a , the calculation method of the internal potential reference quantity is shown in Formula Twelve:

[0184] E ref,j = E VSG,j + E norm,j + ΔE, (j = 1, 2,..., N PCS ) Formula Twelve

[0185] where ΔE is the internal potential reference regulation amount, E VSG,j is the fourth parameter of the jth PCS, E norm,j is the first standard internal potential of the jth PCS, E ref,j is the internal potential reference quantity of the jth PCS, and N PCSIt is the total number of PCSs.

[0186] Taking PCSj as an example, the following illustrates how to adjust the output voltage of the power conversion circuit:

[0187] As Figure 6a shown, the VSG control module 601 in the PCSj controller performs virtual synchronous control on the reactive power Q output by the PCS PCS,j and the preset reactive power reference quantity Q PCS,ref,j to output the fourth parameter E of the PCS VSG,j . The PCSj controller sums the fourth parameter E of the PCS VSG,j , the internal potential reference adjustment quantity ΔE, and the first standard internal potential E norm and outputs the internal potential reference quantity E ref,j to the voltage loop control module 602;

[0188] On the other hand, the VSG control module 601 performs virtual synchronous control on the active power P output by the PCS PCS,j and the preset active reference power P PCS,ref,j to output the frequency parameter ω of the PCS VSG,j . Further, the PCSj controller sums the fifth parameter ω of the PCS VSG,j and the first standard frequency ω norm and outputs the frequency reference quantity ω ref,j to the voltage loop control module 602;

[0189] The voltage loop control module 602 in the PCSj controller generates a pulse width modulation wave V ref,j based on the internal potential reference quantity E ref,j and the frequency reference quantity ω pwm,j and outputs it to the power conversion circuit j to adjust the port voltage of the PCSj. Similarly, the power conversion circuits of other PCSs in the photovoltaic energy storage system adjust the output voltage of the ports accordingly, thereby restoring the PCC voltage to the preset voltage range.

[0190] Based on the technical solution in this embodiment, when the voltage of the PCC deviates from the preset voltage range, the local controller of the energy storage PCS adopts a grid-forming control strategy based on VSG, simulates the operating characteristics of a traditional synchronous generator, adjusts the internal potential of the PCS, and thus adjusts the port voltage of the PCS, enabling the voltage of the PCC to be restored to the preset voltage range, ensuring the load power supply quality and the stability of the photovoltaic energy storage system.

[0191] In a possible embodiment, the internal potential reference quantity is the sum of the sixth parameter of the PCS and the preset second standard internal potential. The sixth parameter is obtained by the PCS controller performing virtual synchronous control on the droop reactive power of the PCS and the reactive power output by the PCS. The droop reactive power of the PCS is obtained by the PCS controller performing droop control on the difference between the target output voltage and the output voltage of the PCS based on the preset reactive-voltage droop coefficient. The target output voltage is the sum of the standard output voltage of the PCS and the internal potential reference adjustment quantity;

[0192] The frequency reference quantity is the sum of the seventh parameter of the PCS and the preset second standard frequency. The seventh parameter is obtained by the PCS controller performing virtual synchronous control on the droop active power of the PCS and the active power of the PCS. The droop active power of the PCS is obtained by the PCS controller performing droop control on the difference between the second standard frequency and the output frequency of the PCS based on the preset active-frequency droop coefficient.

[0193] Exemplarily, in combination with Figure 6b , for the output voltage adjustment method of the power conversion circuit, refer to Equation XIII:

[0194]

[0195] where Q PCS,ref,j is the droop reactive power of the j-th PCS, D q is the preset reactive-voltage droop coefficient, V PCS,norm,j is the standard output voltage of the j-th PCS, ΔE is the internal potential reference adjustment quantity, V PCS,j is the output voltage of the j-th PCS, E VSG,j is the sixth parameter of the j-th PCS, E norm,j is the second standard internal potential of the j-th PCS, N PCS is the total number of PCSs.

[0196] The following takes PCSj as an example to illustrate how to adjust the output voltage of the power conversion circuit:

[0197] As Figure 6b shown, the PCSj controller calculates the target output voltage based on the sum of the standard output voltage V PCS,norm,j of the PCS and the internal potential reference adjustment quantity ΔE. The primary frequency modulation / voltage regulation loop 603 in the PCSj controller performs droop control on the difference between the target output voltage and the output voltage V q of the PCS based on the preset reactive-voltage droop coefficient D PCS,j , and outputs the droop reactive power Q PCS,ref,j of the PCS; the VSG control module 601 performs processing on the reactive power Q PCS,j output by the PCS and the droop reactive power Q PCS,ref,jPerform virtual synchronous control and output the sixth parameter E of the PCS VSG,j Further, for the sixth parameter E of the PCS VSG,j and the second standard internal potential E of the PCS norm,j Sum them up and output the internal potential reference quantity E to the voltage loop control module 602 ref,j ;

[0198] On the other hand, the primary frequency regulation / voltage regulation loop 603 in the PCSj controller is based on a preset active - frequency droop coefficient D p Perform droop control on the sum of the rated frequency ω norm,j and the output frequency ω of the PCS PCS,j and output the active reference power P of the PCS PCS,ref,j ; The VSG control module 601 performs virtual synchronous control on the active power P output by the PCS PCS,j and a preset active reference power P PCS,ref,j and output the seventh parameter ω of the PCS VSG,j For the seventh parameter ω of the PCS VSG,j and the second standard frequency ω norm,j Sum them up and output the frequency reference quantity ω to the voltage loop control module 602 ref,j ;

[0199] The voltage loop control module 602 generates a pulse - width modulation wave V ref,j based on the internal potential reference quantity E ref,j and the frequency reference quantity ω pwm,j and outputs it to the power conversion circuit j to adjust the port voltage of the PCSj. Similarly, the power conversion circuits of other PCSs in the energy storage and photovoltaic system adjust the output voltage of the ports, so as to restore the PCC voltage to the preset voltage range.

[0200] Based on the technical solution in this embodiment, if the local controller of the energy storage PCS is configured with a primary frequency regulation / voltage regulation loop 603, droop control can be performed on the received parameters through the primary frequency regulation / voltage regulation loop 603, and then the frequency reference quantity and the internal potential reference quantity are output through the virtual synchronous control of the VSG, so as to adjust the port voltage of the PCS, making the voltage of the PCC restored to the preset voltage range, ensuring the load power supply quality and the stability of the energy storage and photovoltaic system.

[0201] Based on the same technical concept, the embodiment of the present application also provides a reactive power coordination control method, which is applied to Figure 1 the energy storage and photovoltaic system shown, and the implementation of this method can refer to the implementation of the above - mentioned energy storage and photovoltaic system, and the repeated parts will not be described again.

[0202] As Figure 7 shown, the reactive power coordination control method provided by the present application includes:

[0203] Step 701: Obtain the active power, apparent power, and PCS status information of each inverter.

[0204] It should be noted that the PCS status information includes the reactive power of each PCS, or the PCS status information includes the reactive power of any one PCS and the total number of PCSs.

[0205] Step 702: Based on the active power, apparent power, and PCS status information of each inverter, reduce the reactive power output of each PCS to the PCC and increase the reactive power output of each inverter.

[0206] It should be noted that the sum of the reduced output amounts of the reactive power of each PCS is equal to the sum of the increased output amounts of the reactive power of each inverter.

[0207] Based on the technical solution in this embodiment, the grid controller can obtain the reactive power handling capacity of each inverter according to the active power and apparent power of each inverter, and the grid controller can obtain the total reactive power output of the PCSs in the photovoltaic and energy storage system according to the PCS status information and use this as the reactive power demand of the grid; further, the grid controller can increase the reactive power output of the inverter and reduce the reactive power output of the PCS based on the reactive power handling capacity of each inverter and the reactive power demand of the load, thereby solving the problems of limited reactive power output capacity of the PCS and wasted reactive power output capacity of the inverter.

[0208] In a possible embodiment, as Figure 8 shown, the method includes:

[0209] Step 801: Obtain the active power, apparent power, and PCS status information of each inverter.

[0210] Step 802: Based on the product of the power generation weight coefficient and the reactive power reference value of each inverter, control the reactive power output of each inverter respectively.

[0211] It should be noted that the power generation weight coefficients of each inverter are the ratios of the reactive power margins of each inverter to the total reactive power margin. The reactive power margins of each inverter are obtained based on the active power and apparent power of each inverter, and the total reactive power margin is the sum of the reactive power margins of each inverter; the reactive power reference value is obtained based on the PCS status information.

[0212] Step 803: Based on the preset target reactive power of each PCS, reduce the reactive power output of each PCS respectively.

[0213] Based on the technical solution in this embodiment, the grid controller can increase the reactive power output of the inverter and reduce the reactive power output of the PCS based on the reactive power capacity of each inverter and the reactive power demand of the load, thereby solving the problems of limited reactive power output capacity of the PCS and waste of the reactive power output capacity of the inverter caused by the difficulty in accurately obtaining the reactive power demand.

[0214] In a possible embodiment, the reactive power reference quantity is the sum of the deviation powers of each PCS; or the reactive power reference quantity is the sum of the deviation powers obtained by proportional-integral operation of each PCS; or the reactive power reference quantity is the sum of the reactive power after low-pass filtering of each PCS and the deviation powers obtained by proportional-integral operation of each PCS.

[0215] It should be noted that the deviation power is the difference between the preset target reactive power and the reactive power of the PCS.

[0216] In a possible embodiment, the reactive power reference quantity is the product of the deviation power of any one PCS and the total number of PCSs; or the reactive power reference quantity is the product of the deviation power obtained by proportional-integral operation of any one PCS and the total number of PCSs; or the reactive power reference quantity is the product of the first parameter and the total number of PCSs.

[0217] It should be noted that the deviation power is the difference between the preset target reactive power and the reactive power of the PCS; the first parameter is the sum of the reactive power after low-pass filtering of any one PCS and the deviation power obtained by its proportional-integral operation.

[0218] In a possible embodiment, as Figure 9 shown, the method includes:

[0219] Step 901, obtain the active power, apparent power of each inverter, and PCS status information.

[0220] Step 902, based on the active power, apparent power of each inverter, and PCS status information, reduce the reactive power output of each PCS to the PCC and increase the reactive power output of each inverter.

[0221] Step 903, in response to the PCC voltage not being within the preset voltage range, based on the PCC voltage and the preset common reference voltage, output the internal potential reference adjustment quantity to each PCS controller respectively.

[0222] It should be noted that the preset voltage range is obtained based on the common reference voltage.

[0223] Step 904, adjust the output voltage of the power conversion circuit based on the internal potential reference quantity and the frequency reference quantity to adjust the PCC voltage within the preset voltage range.

[0224] It should be noted that the internal potential reference quantity is obtained based on the reactive power of the PCS and the internal potential reference adjustment quantity, and the frequency reference quantity is obtained based on the active power of the PCS.

[0225] Based on the technical solution of this embodiment, after the photovoltaic inverter undertakes the reactive power demand, if the PCC voltage exceeds the limit, the grid controller quickly restores the PCC voltage to the normal range by adjusting the output voltage of the PCS, avoiding the change of the reactive power output of the PCS caused by the fluctuation and over-limit of the PCC voltage.

[0226] In a possible embodiment, the internal potential reference adjustment quantity is obtained by proportional-integral operation on the common voltage deviation value.

[0227] It should be noted that the common voltage deviation value is the difference between the common reference voltage and the PCC voltage.

[0228] In a possible embodiment, if the PCC voltage is greater than or equal to the maximum value of the preset voltage range, the internal potential reference adjustment quantity is obtained by proportional-integral operation on the second parameter; wherein, the maximum value of the preset voltage range is the sum of the common reference voltage and the first threshold, and the second parameter is the difference between the maximum value of the preset voltage range and the PCC voltage;

[0229] If the PCC voltage is less than or equal to the minimum value of the preset voltage range, the internal potential reference adjustment quantity is obtained by proportional-integral operation on the third parameter; wherein, the minimum value of the preset voltage range is the difference between the common reference voltage and the second threshold, and the third parameter is the difference between the minimum value of the preset voltage range and the PCC voltage.

[0230] Based on the technical solution in this embodiment, if the PCC voltage is too large, proportional-integral operation is performed on the difference between the maximum value of the preset voltage range and the PCC voltage to obtain the internal potential reference adjustment quantity; if the PCC voltage is moderate and within the preset voltage range, there is no need to adjust the PCC voltage; if the PCC voltage is small, proportional-integral operation is performed on the difference between the minimum value of the preset voltage range and the PCC voltage to obtain the internal potential reference adjustment quantity.

[0231] In a possible embodiment, as Figure 10 shown, the method further includes:

[0232] Step 1001, obtaining the active power, apparent power and PCS status information of each inverter.

[0233] Step 1002, based on the active power, apparent power and PCS status information of each inverter, reducing the reactive power output quantity of each PCS to the PCC and increasing the reactive power output quantity of each inverter.

[0234] Step 1003: Perform virtual synchronous control on the reactive power of the PCS and the preset reactive reference power to obtain the fourth parameter of the PCS. Based on the sum of the fourth parameter of the PCS, the internal potential reference adjustment amount, and the preset first standard internal potential, obtain the internal potential reference quantity.

[0235] Step 1004: Perform virtual synchronous control on the active power of the PCS and the preset active reference power to obtain the fifth parameter of the PCS. Based on the sum of the fifth parameter of the PCS and the preset first standard frequency, obtain the frequency reference quantity.

[0236] Step 1005: Adjust the output voltage of the power conversion circuit based on the internal potential reference quantity and the frequency reference quantity to adjust the PCC voltage within the preset voltage range.

[0237] Based on the technical solution in this embodiment, the local controller of the energy storage PCS adopts a grid-forming control strategy based on VSG, simulates the operating characteristics of a traditional synchronous generator, adjusts the internal potential of the PCS, and thus adjusts the port voltage of the PCS; this solution enables the voltage of the PCC to be restored within the preset voltage range, ensuring the quality of load power supply and the stability of the photovoltaic energy storage system.

[0238] In a possible embodiment, as Figure 11 shown, the method further includes:

[0239] Step 1101: Obtain the active power, apparent power, and PCS status information of each inverter.

[0240] Step 1102: Based on the active power, apparent power, and PCS status information of each inverter, reduce the reactive power output of each PCS to the PCC and increase the reactive power output of each inverter.

[0241] Step 1103: Based on the sum of the standard output voltage of the PCS and the internal potential reference adjustment amount, obtain the target output voltage; perform droop control on the difference between the target output voltage and the output voltage of the PCS based on the preset reactive-voltage droop coefficient to obtain the droop reactive power of the PCS; perform virtual synchronous control on the droop reactive power of the PCS and the reactive power output by the PCS to obtain the sixth parameter of the PCS; based on the sum of the sixth parameter and the preset second standard internal potential, obtain the internal potential reference quantity.

[0242] Step 1104: Perform droop control on the difference between the preset second standard frequency and the output frequency of the PCS based on the preset active-frequency droop coefficient to obtain the droop active power of the PCS; perform virtual synchronous control on the droop active power of the PCS and the active power of the PCS to obtain the seventh parameter of the PCS; based on the sum of the seventh parameter and the second standard frequency, obtain the frequency reference quantity.

[0243] Step 1105: Adjust the output voltage of the power conversion circuit based on the internal potential reference quantity and the frequency reference quantity to adjust the PCC voltage to within a preset voltage range.

[0244] Based on the technical solution in this embodiment, if the controller of the energy storage PCS locally is configured with a primary frequency modulation / voltage regulation loop, the parameters received can be droop-controlled through the primary frequency modulation / voltage regulation loop, and then the internal potential of the PCS can be adjusted through the virtual synchronous control of the VSG, thereby adjusting the port voltage of the PCS; this solution enables the voltage of the PCC to be restored to within the preset voltage range, ensuring the quality of the load power supply and the stability of the photovoltaic energy storage system.

[0245] The following further describes the photovoltaic energy storage system and the reactive power coordination control method in the above embodiment with reference to the simulation comparison diagrams:

[0246] The photovoltaic energy storage system includes a grid controller, PCS1, PCS2, inverter 1, and inverter 2. The photovoltaic energy storage system operates in an island mode. The grid controller exchanges information with the controllers of each PCS and inverter in the system and obtains the real-time sampling information of the PCC voltage.

[0247] The total reactive power demand of the load connected to the photovoltaic energy storage system is 10 MVar. As Figure 12a - 12d shown, the reactive power output by PCS1 and PCS2 at the initial state (at 0 s) is 5 MVar, and the reactive power output by inverter 1 and inverter 2 at the initial state (at 0 s) is 0 MVar. The reactive power output targets of PCS1 and PCS2 are reduced to 0 MVar, and all the reactive power required by the load is borne by inverter 1 and inverter 2.

[0248] At 0.5 s, the power of the PCS and the inverter in the photovoltaic energy storage system is controlled respectively based on the traditional reactive power coordination control method and the reactive power coordination control method of this application. As Figure 12a and Figure 12b shown, under the control of the traditional reactive power coordination control method, inverter 1 undertakes 2 MVar of the reactive power demand, and inverter 2 undertakes 4 MVar of the reactive power demand. Obviously, the expected goal that all the reactive power required by the load is borne by inverter 1 and inverter 2 is not achieved; also refer to Figure 12a and Figure 12b , under the control of the reactive power coordination control method of this application, inverter 1 undertakes 4 MVar of the reactive power demand, and inverter 2 undertakes 6 MVar of the reactive power demand, achieving the expected goal that all the reactive power required by the load is borne by inverter 1 and inverter 2.

[0249] On the other hand, as Figure 12c and Figure 12dAs shown, under the control of the traditional reactive power coordination control method, the reactive power output by PCS1 and PCS2 drops to 1 MVar, but cannot drop to 0 MVar. This is because the PCC voltage is too low, and PCS1 and PCS2 automatically increase the reactive power output to support the PCC voltage to recover to the preset range. Therefore, the goal of reducing the reactive power output of PCS1 and PCS2 to 0 MVar cannot be achieved; also see Figure 12c and Figure 12d , under the control of the reactive power coordination control method of this application, the reactive power output by PCS1 and PCS2 both drops to 0 MVar and quickly reaches a stable state.

[0250] Furthermore, at 1 s, the reactive power demand of the load is suddenly increased to 15 MVar, and the changes in the reactive power output by the inverter and PCS under the influence of the load step are observed. As Figure 12a and Figure 12b shown, under the control of the traditional reactive power coordination control method, Inverter 1 undertakes a reactive power demand of 4.5 MVar, and Inverter 2 undertakes a reactive power demand of 6.5 MVar. Obviously, the expected goal that all the reactive power required by the load is borne by Inverter 1 and Inverter 2 is not achieved; also see Figure 12a and Figure 12b , under the control of the reactive power coordination control method of this application, Inverter 1 undertakes a reactive power demand of 6 MVar, and Inverter 2 undertakes a reactive power demand of 9 MVar, achieving the expected goal that all the reactive power required by the load is borne by Inverter 1 and Inverter 2.

[0251] On the other hand, as Figure 12c and Figure 12d shown, under the control of the traditional reactive power coordination control method, the reactive power output by PCS1 and PCS2 both rises to 2 MVar. Obviously, the goal of reducing the reactive power output of PCS1 and PCS2 to 0 MVar is not achieved; also see Figure 12c and Figure 12d , under the control of the reactive power coordination control method of this application, the reactive power output by PCS1 and PCS2 both remains at 0 MVar, achieving a stable and efficient control effect.

[0252] In summary, the present application provides a photovoltaic energy storage system and a reactive power coordination control method. By using the active and apparent power of the inverter, the reactive power output capacity of each inverter is calculated. The grid controller distributes the reactive power according to the reactive power output capacity of each photovoltaic inverter and the reactive power demand in the system, and transfers the reactive power output of the PCS to the photovoltaic inverter by using a closed-loop control method, releasing more energy storage power support and frequency modulation capabilities, reducing the energy storage installation under the premise of ensuring power supply reliability and microgrid stability, and saving the construction cost of the microgrid system;

[0253] The reactive power demand is calculated by the grid controller according to the reactive power output by the PCS in real time and the preset target reactive power, which can solve the problems that it is difficult to accurately obtain the specific reactive power demand of local loads in the microgrid and the cost of using the load reactive power measurement scheme is relatively high when there are multiple loads in the system;

[0254] In addition, the grid controller in the present application adjusts the internal potential of the PCS to adjust the port voltage of the PCS, and further realizes the secondary regulation of the PCC voltage to ensure the load power supply quality and system stability.

[0255] Those skilled in the art should understand that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present application can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0256] The present application is described with reference to the flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to the present application. It should be understood that each process and / or block in the flowchart and / or block diagram, and the combination of processes and / or blocks in the flowchart and / or block diagram, can be realized by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing devices generate a device for realizing the functions specified in Figure 1 one process or multiple processes and / or blocks Figure 1 one block or multiple blocks.

[0257] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer-readable memory generate a manufactured article including an instruction device, and the instruction device realizes the functions in the process Figure 1One or more processes and / or blocks Figure 1 The functions specified in one or more blocks.

[0258] These computer program instructions can also be loaded onto a computer or other programmable data processing device, so that a series of operation steps are executed on the computer or other programmable device to generate a computer-implemented process. Thus, the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in one Figure 1 One or more processes and / or blocks Figure 1 The steps of the functions specified in one or more blocks.

[0259] Obviously, those skilled in the art can make various changes and modifications to this application without departing from the scope of this application. Thus, if these modifications and variations of this application fall within the scope of the claims of this application and their equivalent technologies, this application is also intended to include these changes and modifications.

Claims

1. A photovoltaic energy storage system, characterized in that, The described photovoltaic and energy storage system includes a grid controller, at least one energy storage converter PCS, and at least one inverter; The DC side of each inverter is connected to the corresponding photovoltaic module, the DC side of each PCS is connected to the corresponding energy storage module, and the AC side of each PCS, the AC side of each inverter, and at least one load are electrically connected at the point of common coupling PCC; The grid controller is configured to reduce the reactive power output of each PCS to the PCC and increase the reactive power output of each inverter based on the active power and apparent power of each inverter and the PCS status information; wherein, the sum of the reduced reactive power output of each PCS is equal to the sum of the increased reactive power output of each inverter; The PCS status information includes the reactive power of each PCS, or, the PCS status information includes the reactive power of any one PCS and the total number of PCSs.

2. The optical storage system according to claim 1, characterized in that, The grid controller is used for: Controlling the reactive power output of each inverter respectively based on the product of the power generation weight coefficient and the reactive power reference value of each inverter; Wherein, the power generation weight coefficient of each inverter is the ratio of the reactive power margin of each inverter to the total reactive power margin, the reactive power margin of each inverter is obtained based on the active power and apparent power of each inverter, and the total reactive power margin is the sum of the reactive power margins of each inverter; the reactive power reference value is obtained based on the PCS status information.

3. The optical storage system according to claim 1 or 2, characterized in that, The reactive power reference value is the sum of the deviation powers of each PCS; wherein, the deviation power is the difference between the preset target reactive power and the reactive power of the PCS; Or The reactive power reference value is the sum of the deviation powers obtained by proportional-integral operation of each PCS; Or The reactive power reference value is the sum of the reactive power of each PCS after low-pass filtering and the deviation power obtained by proportional-integral operation of each PCS.

4. The optical storage system according to claim 1 or 2, characterized in that, The reactive power reference value is the product of the deviation power of any one PCS and the total number of PCSs; wherein, the deviation power is the difference between the preset target reactive power and the reactive power of the PCS; Or The reactive power reference value is the product of the deviation power obtained by proportional-integral operation of any one PCS and the total number of PCSs; Or The reactive power reference value is the product of the first parameter and the total number of PCSs; wherein, the first parameter is the sum of the reactive power of any one PCS after low-pass filtering and the deviation power obtained by proportional-integral operation of it.

5. The optical storage system according to any one of claims 1-4, characterized in that, The grid controller is further used for: In response to the PCC voltage not being within the preset voltage range, based on the PCC voltage and the preset common reference voltage, respectively outputting the internal potential reference adjustment amount to each PCS controller; wherein, the preset voltage range is obtained based on the common reference voltage; Each PCS includes a PCS controller and a power conversion circuit, and each PCS controller is used for: Adjust the output voltage of the power conversion circuit based on the internal potential reference quantity and the frequency reference quantity to adjust the PCC voltage within the preset voltage range; wherein, the internal potential reference quantity is obtained based on the reactive power of the PCS and the internal potential reference adjustment quantity, and the frequency reference quantity is obtained based on the active power of the PCS.

6. The optical storage system according to claim 5, characterized in that The internal potential reference adjustment quantity is obtained by proportional-integral operation on the common voltage deviation value; wherein, the common voltage deviation value is the difference between the common reference voltage and the PCC voltage.

7. The optical storage system according to claim 5, characterized in that, If the PCC voltage is greater than or equal to the maximum value of the preset voltage range, the internal potential reference adjustment quantity is obtained by proportional-integral operation on the second parameter; wherein, the maximum value of the preset voltage range is the sum of the common reference voltage and the first threshold, and the second parameter is the difference between the maximum value of the preset voltage range and the PCC voltage; If the PCC voltage is less than or equal to the minimum value of the preset voltage range, the internal potential reference adjustment quantity is obtained by proportional-integral operation on the third parameter; wherein, the minimum value of the preset voltage range is the difference between the common reference voltage and the second threshold, and the third parameter is the difference between the minimum value of the preset voltage range and the PCC voltage.

8. The optical storage system according to any one of claims 5-7, characterized in that The internal potential reference quantity is the sum of the fourth parameter of the PCS, the internal potential reference adjustment quantity, and the preset first standard internal potential. The fourth parameter of the PCS is obtained by the PCS controller performing virtual synchronous control on the reactive power of the PCS and the preset reactive power reference; The frequency reference quantity is the sum of the fifth parameter of the PCS and the preset first standard frequency. The fifth parameter of the PCS is obtained by the PCS controller performing virtual synchronous control on the active power of the PCS and the preset active power reference.

9. The optical storage system according to any one of claims 5-7, characterized in that, The internal potential reference quantity is the sum of the sixth parameter of the PCS and the preset second standard internal potential. The sixth parameter of the PCS is obtained by the PCS controller performing virtual synchronous control on the droop reactive power of the PCS and the reactive power output by the PCS. The droop reactive power of the PCS is obtained by the PCS controller performing droop control on the difference between the target output voltage and the output voltage of the PCS based on the preset reactive-voltage droop coefficient. The target output voltage is the sum of the standard output voltage of the PCS and the internal potential reference adjustment quantity; The frequency reference quantity is the sum of the seventh parameter of the PCS and the preset second standard frequency. The seventh parameter of the PCS is obtained by the PCS controller performing virtual synchronous control on the droop active power of the PCS and the active power of the PCS. The droop active power of the PCS is obtained by the PCS controller performing droop control on the difference between the second standard frequency and the output frequency of the PCS based on the preset active-frequency droop coefficient.

10. A reactive power coordinated control method, characterized in that, Applied to a photovoltaic energy storage system, the photovoltaic energy storage system includes at least one PCS and at least one inverter; The DC side of each inverter is connected to the corresponding photovoltaic module, the DC side of each PCS is connected to the corresponding energy storage module, and the AC side of each PCS, the AC side of each inverter, and at least one load are electrically connected at the PCC; The reactive power coordinated control method includes: Based on the active power and apparent power of each inverter and the PCS status information, reducing the reactive power output of each PCS to the PCC and increasing the reactive power output of each inverter; wherein, the sum of the reduced reactive power output of each PCS is equal to the sum of the increased reactive power output of each inverter; The PCS status information includes the reactive power of each PCS, or the PCS status information includes the reactive power of any one of the PCSs and the total number of the PCSs.

11. The reactive power coordinated control method according to claim 10, wherein The reducing the reactive power output of each PCS to the PCC and increasing the reactive power output of each inverter based on the active power and apparent power of each inverter and the PCS status information includes: Controlling each inverter to output reactive power respectively based on the product of the power generation weight coefficient and the reactive power reference value of each inverter; Wherein, the power generation weight coefficients of each inverter are the ratios of the reactive power margins of each inverter to the total reactive power margin, the reactive power margins of each inverter are obtained based on the active power and apparent power of each inverter, and the total reactive power margin is the sum of the reactive power margins of each inverter; the reactive power reference value is obtained based on the PCS status information.

12. The reactive power coordinated control method according to claim 10 or 11, wherein, The reactive power reference value is the sum of the deviation powers of each PCS; wherein, the deviation power is the difference between the preset target reactive power and the reactive power of the PCS; or The reactive power reference value is the sum of the deviation powers obtained by proportional-integral operation of each PCS; or The reactive power reference value is the sum of the reactive power of each PCS after low-pass filtering and the deviation power obtained by proportional-integral operation of each PCS.

13. The reactive power coordinated control method according to claim 10 or 11, wherein, The reactive power reference value is the product of the deviation power of any one of the PCSs and the total number of the PCSs; wherein, the deviation power is the difference between the preset target reactive power and the reactive power of the PCS; or The reactive power reference value is the product of the deviation power obtained by proportional-integral operation of any one of the PCSs and the total number of the PCSs; or The reactive power reference value is the product of the first parameter and the total number of the PCSs; wherein, the first parameter is the sum of the reactive power of any one of the PCSs after low-pass filtering and the deviation power obtained by proportional-integral operation of it.

14. The reactive power coordinated control method according to any one of claims 10-13, characterized in that The reactive power coordinated control method further includes: In response to the PCC voltage not being within the preset voltage range, based on the PCC voltage and a preset common reference voltage, respectively output an internal potential reference adjustment amount to each of the PCS controllers; wherein, the preset voltage range is obtained based on the common reference voltage. Adjust the output voltage of the power conversion circuit based on the internal potential reference amount and the frequency reference amount to adjust the PCC voltage to within the preset voltage range; wherein, the internal potential reference amount is obtained based on the reactive power of the PCS and the internal potential reference adjustment amount, and the frequency reference amount is obtained based on the active power of the PCS.

15. The reactive power coordinated control method according to claim 14, wherein The internal potential reference adjustment amount is obtained by proportional-integral operation on the common voltage deviation value; wherein, the common voltage deviation value is the difference between the common reference voltage and the PCC voltage.

16. The reactive power coordinated control method according to claim 14, wherein If the PCC voltage is greater than or equal to the maximum value of the preset voltage range, the internal potential reference adjustment amount is obtained by proportional-integral operation on a second parameter; wherein, the maximum value of the preset voltage range is the sum of the common reference voltage and a first threshold, and the second parameter is the difference between the maximum value of the preset voltage range and the PCC voltage. If the PCC voltage is less than or equal to the minimum value of the preset voltage range, the internal potential reference adjustment amount is obtained by proportional-integral operation on a third parameter; wherein, the minimum value of the preset voltage range is the difference between the common reference voltage and a second threshold, and the third parameter is the difference between the minimum value of the preset voltage range and the PCC voltage.

17. The reactive power coordinated control method according to any one of claims 14-16, characterized in that, The internal potential reference amount is obtained based on the reactive power of the PCS and the internal potential reference adjustment amount, including: Perform virtual synchronous control on the reactive power of the PCS and a preset reactive reference power to obtain a fourth parameter of the PCS; Based on the sum of the fourth parameter of the PCS, the internal potential reference adjustment amount, and a preset first standard internal potential, obtain the internal potential reference amount; The frequency reference amount is obtained based on the active power of the PCS, including: Perform virtual synchronous control on the active power of the PCS and a preset active reference power to obtain a fifth parameter of the PCS; Based on the sum of the fifth parameter of the PCS and a preset first standard frequency, obtain the frequency reference amount.

18. The reactive power coordinated control method according to any one of claims 14-16, characterized in that, The internal potential reference amount is obtained based on the reactive power of the PCS and the internal potential reference adjustment amount, including: Based on the sum of the standard output voltage of the PCS and the internal potential reference adjustment amount, obtain the target output voltage; Perform droop control on the difference between the target output voltage and the output voltage of the PCS based on a preset reactive-voltage droop coefficient to obtain the droop reactive power of the PCS; Perform virtual synchronous control on the droop reactive power of the PCS and the reactive power output by the PCS to obtain a sixth parameter of the PCS; Based on the sum of the sixth parameter and a preset second standard internal potential, obtain the internal potential reference amount; The frequency reference amount is obtained based on the active power of the PCS, including: Perform droop control on the difference between the preset second standard frequency and the output frequency of the PCS based on the preset active-frequency droop coefficient to obtain the droop active power of the PCS; Perform virtual synchronous control on the droop active power of the PCS and the active power of the PCS to obtain the seventh parameter of the PCS; Obtain the frequency reference quantity based on the sum of the seventh parameter and the second standard frequency.

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