Energy storage system

Abstract

The invention discloses an energy storage system which comprises M battery pack strings and N energy storage converters, the first ends of the N energy storage converters are in coupling connection with at least one battery pack string in the M battery pack strings, and the second ends of the N energy storage converters are used for being connected with a power grid. The first end of the first energy storage converter is coupled with Q battery pack strings in the M battery pack strings, and the first energy storage converter comprises a DC / AC conversion unit and at least one DC / DC conversion unit. The first DC / DC conversion unit is in coupling connection with at least one battery pack string in the Q battery pack strings through the first end of the first energy storage converter, the first DC / DC conversion unit is in coupling connection with the DC / AC conversion unit, and the DC / AC conversion unit is coupled to a power grid through the second end of the first energy storage converter. And the first DC / DC conversion unit is used for adapting the voltage of the DC / AC conversion unit to the voltage of the battery pack string. Therefore, the battery capacity is fully utilized, and the waste of the battery capacity is reduced.

Description

[0001] This application is a divisional application. The application number of the original application is 202010076994.0, and the original application date is January 23, 2020. The entire content of the original application is incorporated into this application by reference. Technical Field

[0002] The present invention relates to the field of electricity, and in particular to an energy storage system and a photovoltaic energy storage system. Background Art

[0003] Photovoltaic power generation, as a clean, renewable energy source, is widely used, but its application also has drawbacks. Primarily, this is due to the unpredictability and volatility of output power. As photovoltaic power generation grows in the traditional power grid, its high penetration rate will significantly impact the grid, creating a series of issues with voltage stability, power quality, and operational control.

[0004] Currently, energy storage devices can be incorporated into photovoltaic power generation systems. Leveraging their charge and discharge characteristics, they can effectively address the unpredictability and volatility of output power in photovoltaic power plants caused by uneven sunlight. This can also reduce the phenomenon of abandoned photovoltaic power generation, promote large-scale photovoltaic power generation, and increase overall power generation returns.

[0005] Existing energy storage architectures include batteries, power conversion systems (PCSs), and transformers. The PCSs utilize a direct current / alternating current (DC / AC) power conversion topology. In this architecture, the PCSs typically have a narrow DC input voltage range, while the batteries operate over a wide voltage range. This results in inadequate battery capacity utilization and waste. Summary of the Invention

[0006] The present application provides an energy storage system and a photovoltaic energy storage system. In the energy storage system and the photovoltaic energy storage system, the DC / DC conversion topology can adapt the voltage of the battery string to the DC / AC conversion topology, so that the battery capacity can be fully utilized and the waste of battery capacity can be reduced.

[0007] In view of this, a first aspect of an embodiment of the present application provides an energy storage system, which includes M battery strings and N energy storage converters. The first end of any one of the N energy storage converters is coupled to at least one battery string in the M battery strings, and the second end of any one of the energy storage converters is used to connect to the power grid. M and N are integers greater than 0, and M ≥ N. The first end of the first energy storage converter is coupled to Q battery strings in the M battery strings. The first energy storage converter includes a DC / AC conversion unit and at least one DC / DC (direct current). A DC / DC (direct current, DC / DC) conversion unit, Q is an integer greater than 0, and Q≤M, the first energy storage converter is any one of the N energy storage converters; the first DC / DC conversion unit is coupled to at least one of the Q battery strings through the first end of the first energy storage converter, the first DC / DC conversion unit is coupled to the DC / AC conversion unit, the DC / AC conversion unit is coupled to the power grid through the second end of the first energy storage converter, and the first DC / DC conversion unit is any one of the at least one DC / DC conversion unit; the first DC / DC conversion unit is used to adapt the voltage of the DC / AC conversion unit to the voltage of at least one of the Q battery strings. The first DC / DC conversion unit can adapt the voltage of the DC / AC conversion unit to the voltage of at least one of the Q battery strings, thereby making full use of the battery capacity and reducing the waste of the battery capacity.

[0008] Optionally, in combination with the first aspect, in a first possible implementation of the first aspect, the energy storage system further includes a first transformer, through which the second end of any one of the N energy storage converters is coupled to the power grid. The first transformer can adapt the voltage of the energy storage converter to the power grid voltage, thereby enabling the energy storage system to transmit electrical energy to the power grid, or the energy storage system to store electrical energy from the power grid.

[0009] Optionally, in combination with the first aspect or the first possible implementation of the first aspect, in a second possible implementation of the first aspect, the energy storage system further includes X photovoltaic strings and Y photovoltaic inverters, the input end of any one of the Y photovoltaic inverters being coupled to the output end of at least one of the X photovoltaic strings, and the output ends of the Y photovoltaic inverters being coupled to the second ends of N energy storage converters, where X and Y are integers greater than 0. The energy storage system may include X photovoltaic strings and Y photovoltaic inverters, wherein the photovoltaic strings may convert light energy into direct current (DC) electricity, which is then converted into alternating current (AC) electricity via the photovoltaic inverters, thereby enabling the AC electricity to be transmitted to a power grid or the AC electricity to be converted into DC electricity via the energy storage converters for storage in battery strings. In this manner, the energy storage system may both transmit electrical energy to the power grid and store electrical energy in the battery strings.

[0010] Optionally, in combination with the second possible implementation of the first aspect, in a third possible implementation of the first aspect, the energy storage system further includes a second transformer, and the output end of any one of the Y photovoltaic inverters is coupled to the power grid via the second transformer. The second transformer can adapt the voltage at the output end of the photovoltaic inverter to the power grid voltage, thereby enabling the electrical energy generated by the photovoltaic string to be transmitted to the power grid.

[0011] Optionally, in combination with the first aspect, in a fourth possible implementation of the first aspect, switches are connected in parallel across any one of the at least one DC / DC conversion units. If the voltage of the battery string matches the voltage of the energy storage converter, the switches connected in parallel across the DC / DC conversion unit can be closed, thereby short-circuiting the DC / DC conversion unit, thereby reducing unnecessary energy consumption. If the voltage of the battery string does not match the voltage of the energy storage converter, the switches connected in parallel across the DC / DC conversion unit are disconnected, and the DC / DC conversion unit adapts the voltage of the battery string to the voltage of the energy storage converter.

[0012] Optionally, in combination with the fourth possible implementation of the first aspect, in the fifth possible implementation of the first aspect, the first energy storage converter is used to detect the voltage of Q battery strings. When the voltage of any one of the Q battery strings is greater than or equal to a first voltage threshold, the switch connected in parallel to the DC / DC conversion unit coupled to the battery string with a voltage greater than or equal to the first voltage threshold is closed; when the voltage of any one of the Q battery strings is less than or equal to a second voltage threshold, the switch connected in parallel to the DC / DC conversion unit connected to the battery string with a voltage less than or equal to the second voltage threshold is disconnected, and the first voltage threshold is greater than or equal to the second voltage threshold. The first voltage threshold and the second voltage threshold are related to the grid voltage and the output current.

[0013] Optionally, in combination with the second possible implementation of the first aspect, in a sixth possible implementation of the first aspect, the energy storage system further includes a controller, the controller being coupled and connected to each of the Y photovoltaic inverters, the controller being coupled and connected to each of the N energy storage converters, and the controller being configured to communicate with the Y photovoltaic inverters and the N energy storage converters. The controller can communicate with the Y photovoltaic inverters and the N energy storage converters, so that the controller can detect the power generation status of the X photovoltaic strings through the Y photovoltaic inverters and the power status of the M battery strings through the N energy storage converters.

[0014] Optionally, in combination with the sixth possible implementation of the first aspect, in the seventh possible implementation of the first aspect, the controller is further configured to obtain grid-connected power. When the controller detects that the total power of the Y photovoltaic inverters is greater than or equal to the grid-connected power, the controller controls the N energy storage converters to charge the M battery strings. When the controller detects that the total power of the Y photovoltaic inverters is less than the grid-connected power, the controller controls the M battery strings to discharge via the N energy storage converters. When the controller detects that the total power of the Y photovoltaic inverters is greater than or equal to the grid-connected power, it indicates that the total output power of the Y photovoltaic inverters is excessive, and the energy generated by the Y photovoltaic inverters can be stored. The controller can control the N energy storage converters to charge the M battery strings. When the controller detects that the total output power of the Y photovoltaic inverters is less than the grid-connected power, the controller can control the M battery strings to discharge via the N energy storage converters, thereby compensating for the insufficient output power of the photovoltaic inverter.

[0015] Optionally, in combination with the sixth possible implementation of the first aspect, in the eighth possible implementation of the first aspect, when the output voltage frequency of any one of the N energy storage converters or the Y photovoltaic inverters is higher than a first preset voltage-frequency threshold, each of the Y photovoltaic inverters reduces power output according to its own preset power curve, and the N energy storage converters charge the M battery strings; when the output terminal voltage frequency of any one of the N energy storage converters or the Y photovoltaic inverters is lower than a second preset voltage-frequency threshold, each of the Y photovoltaic inverters increases power output according to its own preset power curve, and the N energy storage converters control the discharge of the M battery strings, the first preset voltage-frequency threshold is greater than the preset normal frequency value of the grid voltage, and the second preset voltage-frequency threshold is less than the preset normal frequency value of the grid voltage. In this way, the power of the photovoltaic inverter can be kept within a normal range.

[0016] Optionally, in combination with the sixth to eighth possible implementations of the first aspect, in a ninth possible implementation of the first aspect, the controller is further configured to obtain the charge of each battery string in the M battery strings through N energy storage converters; when the N energy storage converters charge the M battery strings, the controller controls the N energy storage converters to preferentially charge the battery strings with lower charges in the M battery strings; and when the M battery strings discharge, the controller preferentially controls the discharge of the battery strings with higher charges in the M battery strings through the N energy storage converters. In this way, the battery strings with lower charges can be preferentially charged, and the battery strings with higher charges can be preferentially discharged, thereby maintaining the charge balance of each battery string in the battery string as much as possible.

[0017] Optionally, in combination with the first aspect, in a tenth possible implementation of the first aspect, the energy storage system further includes an electric meter, which is used to be connected to the second ends of the N energy storage converters, and the electric meter is used to measure the amount of electricity charged and discharged by the N energy storage converters.

[0018] Optionally, in combination with the first aspect, in an eleventh possible implementation of the first aspect, any one of the at least one DC / DC conversion unit is coupled to one of the Q battery strings. If the DC / DC conversion unit is connected to multiple parallel battery strings, higher requirements are placed on the consistency of the parallel battery strings. However, if the DC / DC conversion unit is connected to only one battery string, the consistency of the battery string is lower.

[0019] A second aspect of the present application provides an energy storage system, characterized in that the energy storage system includes M battery strings, N direct current / alternating current (DC / DC) power conversion devices and at least one DC / AC power conversion device, the first end of any one of the N DC / DC power conversion devices is coupled to at least one battery string in the M battery strings, the second end of any one of the DC / DC power conversion devices is coupled to the first end of one of the at least one DC / AC power conversion devices, the second end of the DC / AC power conversion device is used to connect to the power grid, M and N are integers greater than 0, and M≥N; the first end of the first DC / DC power conversion device is coupled to Q battery strings in the M battery strings, the first DC / DC power conversion device includes at least one DC / DC converter The first DC / DC power conversion device is any one of the N DC / DC power conversion devices, Q is an integer greater than 0, and Q≤M; the first DC / DC conversion unit is coupled to at least one of the Q battery strings via a first end of the first DC / DC power conversion device, the first DC / DC conversion unit is coupled to a first end of one of the at least one DC / AC power conversion devices via a second end of the first DC / DC power conversion device, and the first DC / DC conversion unit is any one of the at least one DC / DC conversion unit; the first DC / DC conversion unit is used to adapt the voltage of one of the at least one DC / AC power conversion devices to the voltage of at least one of the Q battery strings. The DC / DC conversion unit can adapt the voltage of the DC / AC power conversion device to the voltage of the battery string, thereby fully utilizing the battery capacity and reducing waste of battery capacity.

[0020] Optionally, in combination with the second aspect, in a first possible implementation of the second aspect, the energy storage system further includes a first transformer, and the second end of the at least one DC / AC power conversion device is coupled to the power grid via the first transformer. The first transformer can adapt the output voltage of the DC / AC power conversion device to the power grid voltage, thereby enabling the transmission of electrical energy from the photovoltaic energy storage system to the power grid, or the photovoltaic energy storage system can store electrical energy from the power grid.

[0021] Optionally, in combination with the second aspect or the first possible implementation of the second aspect, in a second possible implementation of the second aspect, the energy storage system further includes X photovoltaic strings and Y photovoltaic inverters, wherein the input end of any one of the Y photovoltaic inverters is coupled to the output end of at least one of the X photovoltaic strings, and the output ends of the Y photovoltaic inverters are coupled to the second end of at least one DC / AC power conversion device, where X and Y are integers greater than 0. The energy storage system may include X photovoltaic strings and Y photovoltaic inverters, wherein the photovoltaic strings can convert light energy into direct current (DC) power, which is then converted into alternating current (AC) power via the photovoltaic inverters, thereby transmitting the AC power to a power grid or converting the AC power into DC power via an energy storage converter for storage in battery strings. In this way, the energy storage system can both transmit electrical energy to the power grid and store electrical energy in the battery strings.

[0022] Optionally, in combination with the second possible implementation of the second aspect, in a third possible implementation of the second aspect, the energy storage system further includes a second transformer, and the output end of any one of the Y photovoltaic inverters is connected to the power grid via the second transformer. The second transformer can adapt the voltage at the output end of the photovoltaic inverter to the power grid voltage, thereby enabling the power generated by the photovoltaic string to be transmitted to the power grid.

[0023] Optionally, in combination with the second aspect, in a fourth possible implementation of the second aspect, switches are connected in parallel across any one of the at least one DC / DC conversion units. If the voltage of the battery string matches the voltage of the DC / AC power conversion device, the switches connected in parallel across the DC / DC conversion unit can be closed, thereby short-circuiting the DC / DC conversion unit, thereby reducing unnecessary energy consumption. If the voltage of the battery string does not match the voltage of the DC / AC power conversion device, the switches connected in parallel across the DC / DC conversion unit are disconnected, and the DC / DC conversion unit adapts the voltage of the battery string to the voltage of the energy storage converter.

[0024] Optionally, in combination with the fourth possible implementation of the second aspect, in the fifth possible implementation of the second aspect, the first DC / DC power conversion device is used to detect the voltage of Q battery strings. When the voltage of any one of the Q battery strings is greater than or equal to a first voltage threshold, the switch connected in parallel to the DC / DC conversion unit coupled to the battery string with a voltage greater than or equal to the first voltage threshold is closed; when the voltage of any one of the Q battery strings is less than or equal to a second voltage threshold, the switch connected in parallel to the DC / DC conversion unit connected to the battery string with a voltage less than or equal to the second voltage threshold is disconnected, and the first voltage threshold is greater than or equal to the second voltage threshold. The first voltage threshold and the second voltage threshold are related to the grid voltage and the output current.

[0025] Optionally, in combination with the second possible implementation of the second aspect, in a sixth possible implementation of the second aspect, the energy storage system further includes a controller, the controller being coupled and connected to each of the Y photovoltaic inverters, the controller being coupled and connected to each of the N DC / DC power conversion devices, and the controller being configured to communicate with the Y photovoltaic inverters and the N DC / DC power conversion devices. The controller can communicate with the Y photovoltaic inverters and the N DC / DC power conversion devices, so that the controller can detect the power generation status of the X photovoltaic strings through the Y photovoltaic inverters, and can detect the power status of the M battery strings through the N DC / DC power conversion devices.

[0026] Optionally, in combination with the sixth possible implementation of the second aspect, in the seventh possible implementation of the second aspect, the controller is further configured to obtain grid-connected power. When the controller detects that the total power of the Y photovoltaic inverters is greater than or equal to the grid-connected power, the controller controls the N DC / DC power conversion devices to charge the M battery strings. When the controller detects that the total power of the Y photovoltaic inverters is less than the grid-connected power, the controller controls the M battery strings to discharge via the N DC / DC power conversion devices. When the controller detects that the total power of the Y photovoltaic inverters is greater than or equal to the grid-connected power, it indicates that the total output power of the Y photovoltaic inverters is excessive, and the energy generated by the Y photovoltaic inverters can be stored. The controller can control the N energy storage converters to charge the M battery strings. When the controller detects that the total output power of the Y photovoltaic inverters is less than the grid-connected power, the controller can control the M battery strings to discharge via the N energy storage converters, thereby compensating for the insufficient output power of the photovoltaic inverter.

[0027] Optionally, in combination with the sixth possible implementation of the second aspect, in the eighth possible implementation of the second aspect, when the output voltage frequency of any one of the N DC / DC power conversion devices or the Y photovoltaic inverters is higher than a first preset voltage-frequency threshold, each of the Y photovoltaic inverters reduces power output according to its own preset power curve, and the N DC / DC power conversion devices charge the M battery strings; when the output terminal voltage frequency of any one of the N DC / DC power conversion devices or the Y photovoltaic inverters is lower than a second preset voltage-frequency threshold, each of the Y photovoltaic inverters increases power output according to its own preset power curve, and the N DC / DC power conversion devices control the discharge of the M battery strings, the first preset voltage-frequency threshold being greater than a preset normal grid voltage frequency value, and the second preset voltage-frequency threshold being less than the preset normal grid voltage frequency value. This ensures that the power of the photovoltaic inverter is within a normal range.

[0028] Optionally, in combination with any one of the sixth to eighth possible implementations of the second aspect, in the ninth possible implementation of the second aspect, the controller is further configured to obtain the power of each battery string in the M battery strings through N DC / DC power conversion devices; when the N DC / DC power conversion devices charge the M battery strings, the controller controls the N DC / DC power conversion devices to give priority to charging the battery strings with low power among the M battery strings; when the M battery strings discharge, the controller controls the N DC / DC power conversion devices to give priority to discharging the battery strings with high power among the M battery strings. In this way, the battery strings with low power can be charged first, and the battery strings with high power can be discharged first, so as to maintain the power balance of each battery string in the battery string as much as possible.

[0029] Optionally, in combination with the second aspect, in a tenth possible implementation of the second aspect, the energy storage system further includes an electric meter, which is used to be connected to the second end of the N DC / DC power conversion devices, and the electric meter is used to measure the amount of charge and discharge of the N DC / DC power conversion devices.

[0030] Optionally, in combination with the second aspect, in an eleventh possible implementation of the second aspect, any one of the at least one DC / DC conversion unit is coupled to one of the Q battery strings. If the DC / DC conversion unit is connected to multiple parallel battery strings and has a high requirement for consistency of the parallel battery strings, the DC / DC conversion unit is connected to only one battery string and has a low requirement for consistency of the battery string.

[0031] Optionally, in combination with the second aspect, in a twelfth possible implementation of the second aspect, the N DC / DC power conversion devices and the at least one DC / AC power conversion device are connected via a bus.

[0032] The third aspect of the present application provides a photovoltaic energy storage system, which includes M battery strings, N energy storage converters, X photovoltaic strings and Y photovoltaic inverters. The first end of any one of the N energy storage converters is coupled to at least one battery string in the M battery strings, and the second end of any one of the energy storage converters is used to connect to the power grid. The input end of any one of the Y photovoltaic inverters is coupled to the output end of at least one photovoltaic string in the X photovoltaic strings, and the output end of the Y photovoltaic inverters is coupled to the second end of the N energy storage converters, where M and N are integers greater than 0, and M≥N, and X and Y are integers greater than 0; the first end of the first energy storage converter is coupled to Q battery strings in the M battery strings, and the first storage The energy converter includes a DC / AC conversion unit and at least one DC / DC conversion unit, where Q is an integer greater than 0 and Q≤M. The first energy storage converter is any one of the N energy storage converters. The first DC / DC conversion unit is coupled to at least one of the Q battery strings via a first terminal of the first energy storage converter. The first DC / DC conversion unit is coupled to the DC / AC conversion unit. The DC / AC conversion unit is coupled to the power grid via a second terminal of the first energy storage converter. The first DC / DC conversion unit is any one of the at least one DC / DC conversion unit. The first DC / DC conversion unit is configured to adapt the voltage of the DC / AC conversion unit to the voltage of at least one of the Q battery strings. In this photovoltaic energy storage system, the first DC / DC conversion unit can adapt the voltage of the DC / AC conversion unit to the voltage of at least one of the Q battery strings, thereby fully utilizing the battery capacity and reducing battery capacity waste. Furthermore, in this photovoltaic energy storage system, the charge and discharge path does not include a transformer, which can shorten the charge and discharge path of the photovoltaic energy storage system, thereby improving the battery charge and discharge efficiency.

[0033] Optionally, in combination with the third aspect, in a first possible implementation of the third aspect, the photovoltaic energy storage system further includes a first transformer, and the second end of any one of the N energy storage converters is coupled to the grid via the first transformer. The first transformer can adapt the voltage of the energy storage converter to the grid voltage, thereby enabling the energy storage system to transmit electrical energy to the grid, or the energy storage system to store electrical energy from the grid.

[0034] Optionally, in combination with the third aspect, in a second possible implementation of the third aspect, switches are connected in parallel across any one of the at least one DC / DC conversion units. If the voltage of the battery string matches the voltage of the energy storage converter, the switches connected in parallel across the DC / DC conversion unit can be closed, thereby short-circuiting the DC / DC conversion unit, thereby reducing unnecessary energy consumption. If the voltage of the battery string does not match the voltage of the energy storage converter, the switches connected in parallel across the DC / DC conversion unit are disconnected, and the DC / DC conversion unit adapts the voltage of the battery string to the voltage of the energy storage converter.

[0035] Optionally, in combination with the second possible implementation of the third aspect, in the third possible implementation of the third aspect, the first energy storage converter is used to detect the voltage of Q battery strings. When the voltage of any one of the Q battery strings is greater than or equal to a first voltage threshold, the switch connected in parallel to the DC / DC conversion unit coupled to the battery string with a voltage greater than or equal to the first voltage threshold is closed; when the voltage of any one of the Q battery strings is less than or equal to a second voltage threshold, the switch connected in parallel to the DC / DC conversion unit connected to the battery string with a voltage less than or equal to the second voltage threshold is disconnected, and the first voltage threshold is greater than or equal to the second voltage threshold. The first voltage threshold and the second voltage threshold are related to the grid voltage and the output current.

[0036] Optionally, in combination with the third aspect, in a fourth possible implementation of the third aspect, the photovoltaic energy storage system further includes a controller, the controller being coupled to each of the Y photovoltaic inverters, the controller being coupled to each of the N energy storage converters, and the controller being configured to communicate with the Y photovoltaic inverters and the N energy storage converters. The controller can communicate with the Y photovoltaic inverters and the N energy storage converters, so that the controller can detect the power generation status of the X photovoltaic strings through the Y photovoltaic inverters and the power status of the M battery strings through the N energy storage converters.

[0037] Optionally, in combination with the fourth possible implementation of the third aspect, in a fifth possible implementation of the third aspect, the controller is further configured to obtain grid-connected power. When the controller detects that the total power of the Y photovoltaic inverters is greater than or equal to the grid-connected power, the controller controls the N energy storage converters to charge the M battery strings. When the controller detects that the total power of the Y photovoltaic inverters is less than the grid-connected power, the controller controls the M battery strings to discharge via the N energy storage converters. When the controller detects that the total power of the Y photovoltaic inverters is greater than or equal to the grid-connected power, it indicates that the total output power of the Y photovoltaic inverters is excessive, and the energy generated by the Y photovoltaic inverters can be stored. The controller can control the N energy storage converters to charge the M battery strings. When the controller detects that the total output power of the Y photovoltaic inverters is less than the grid-connected power, the controller can control the M battery strings to discharge via the N energy storage converters, thereby compensating for the insufficient output power of the photovoltaic inverter.

[0038] Optionally, in combination with the fourth possible implementation of the third aspect, in a sixth possible implementation of the third aspect, when the output voltage frequency of any one of the N energy storage converters or the Y photovoltaic inverters is higher than a first preset voltage-frequency threshold, each of the Y photovoltaic inverters reduces power output according to its own preset power curve, and the N energy storage converters charge the M battery strings; when the output terminal voltage frequency of any one of the N energy storage converters or the Y photovoltaic inverters is lower than a second preset voltage-frequency threshold, each of the Y photovoltaic inverters increases power output according to its own preset power curve, and the N energy storage converters control the discharge of the M battery strings, the first preset voltage-frequency threshold being greater than a preset normal grid voltage frequency value, and the second preset voltage-frequency threshold being less than the preset normal grid voltage frequency value. This ensures that the power of the photovoltaic inverter is within a normal range.

[0039] Optionally, in combination with any one of the fourth to sixth possible implementations of the third aspect, in the seventh possible implementation of the third aspect, the controller is further configured to obtain the power of each battery string in the M battery strings through N energy storage converters; when the N energy storage converters charge the M battery strings, the controller controls the N energy storage converters to preferentially charge the battery strings with low power among the M battery strings; when the M battery strings discharge, the controller preferentially controls the discharge of the battery strings with high power among the M battery strings through the N energy storage converters. In this way, the battery strings with low power can be charged preferentially, and the battery strings with high power can be discharged preferentially, thereby maintaining the power balance of each battery string in the battery string as much as possible.

[0040] Optionally, in combination with the third aspect, in an eighth possible implementation of the third aspect, the energy storage system further includes an electric meter, which is used to be connected to the second end of the N energy storage converters, and the electric meter is used to measure the amount of electricity charged and discharged by the N energy storage converters.

[0041] Optionally, in combination with the third aspect, in a ninth possible implementation of the third aspect, any one of the at least one DC / DC conversion units is coupled to one of the Q battery strings. If the DC / DC conversion unit is connected to multiple parallel battery strings and has a high requirement for consistency of the parallel battery strings, the DC / DC conversion unit is only connected to one battery string, and the consistency of the battery string is low.

[0042] A fourth aspect of the present application provides a photovoltaic energy storage system, characterized in that the photovoltaic energy storage system includes M battery strings, N DC / AC power conversion devices, at least one DC / AC power conversion device, X photovoltaic strings and Y photovoltaic inverters, the first end of any one of the N DC / DC power conversion devices is coupled to at least one battery string in the M battery strings, the second end of any one of the DC / DC power conversion devices is coupled to the first end of one of the at least one DC / AC power conversion devices, the second end of the DC / AC power conversion device is used to connect to the power grid, the input end of any one of the Y photovoltaic inverters is coupled to the output end of at least one photovoltaic string in the X photovoltaic strings, the output end of the Y photovoltaic inverters is coupled to the second end of the at least one DC / AC power conversion device, X and Y are integers greater than 0, M and N are integers greater than 0, and M≥N; the first DC The first end of a DC / DC power conversion device is coupled to Q battery strings among the M battery strings. The first DC / DC power conversion device includes at least one DC / DC conversion unit. The first DC / DC power conversion device is any one of the N DC / DC power conversion devices, where Q is an integer greater than 0 and Q≤M. The first DC / DC conversion unit is coupled to at least one battery string among the Q battery strings via the first end of the first DC / DC power conversion device. The first DC / DC conversion unit is coupled to the first end of one DC / AC power conversion device among the at least one DC / AC power conversion device via the second end of the first DC / DC power conversion device. The first DC / DC conversion unit is any one of the at least one DC / DC conversion unit. The first DC / DC conversion unit is configured to adapt the voltage of the one DC / AC power conversion device among the at least one DC / AC power conversion device to the voltage of at least one battery string among the Q battery strings. The DC / DC conversion unit can adapt the voltage of the DC / AC power conversion device to the voltage of the battery string, thereby fully utilizing the battery capacity and reducing battery capacity waste. Secondly, in the photovoltaic energy storage system, the charging and discharging path does not include a transformer, which can shorten the charging and discharging path of the photovoltaic energy storage system, thereby improving the charging and discharging efficiency of the battery.

[0043] Optionally, in combination with the fourth aspect, in a first possible implementation of the fourth aspect, the photovoltaic energy storage system further includes a first transformer, and the second end of the at least one DC / AC power conversion device is coupled to the power grid via the first transformer. The first transformer can adapt the output voltage of the DC / AC power conversion device to the power grid voltage, thereby enabling the photovoltaic energy storage system to transmit power to the power grid, or the photovoltaic energy storage system to store power from the power grid.

[0044] Optionally, in combination with the fourth aspect, in a second possible implementation of the fourth aspect, switches are connected in parallel at both ends of any one of the at least one DC / DC conversion units. If the voltage of the battery string and the voltage of the DC / AC power conversion device are compatible, the switches connected in parallel at both ends of the DC / DC conversion unit can be closed, thereby short-circuiting the DC / DC conversion unit, thereby reducing unnecessary energy consumption; if the voltage of the battery string and the voltage of the DC / AC power conversion device are not compatible, the switches connected in parallel at both ends of the DC / DC conversion unit are disconnected, and the DC / DC conversion unit adapts the voltage of the battery string to the voltage of the energy storage converter.

[0045] Optionally, in combination with the second possible implementation of the fourth aspect, in the third possible implementation of the second aspect, the first DC / DC power conversion device is used to detect the voltage of Q battery strings. When the voltage of any one of the Q battery strings is greater than or equal to a first voltage threshold, the switch connected in parallel to the DC / DC conversion unit coupled to the battery string with a voltage greater than or equal to the first voltage threshold is closed; when the voltage of any one of the Q battery strings is less than or equal to a second voltage threshold, the switch connected in parallel to the DC / DC conversion unit connected to the battery string with a voltage less than or equal to the second voltage threshold is disconnected, and the first voltage threshold is greater than or equal to the second voltage threshold. The first voltage threshold and the second voltage threshold are related to the grid voltage and the output current.

[0046] Optionally, in combination with the fourth aspect, in a fourth possible implementation of the fourth aspect, the energy storage system further includes a controller, the controller being coupled and connected to each of the Y photovoltaic inverters, the controller being coupled and connected to each of the N DC / DC power conversion devices, and the controller being configured to communicate with the Y photovoltaic inverters and the N DC / DC power conversion devices. The controller can communicate with the Y photovoltaic inverters and the N DC / DC power conversion devices, so that the controller can detect the power generation status of the X photovoltaic strings through the Y photovoltaic inverters, and can detect the power status of the M battery strings through the N DC / DC power conversion devices.

[0047] Optionally, in combination with the fourth possible implementation of the fourth aspect, in a fifth possible implementation of the fourth aspect, the controller is further used to obtain grid-connected power. When the controller detects that the total power of Y photovoltaic inverters is greater than or equal to the grid-connected power, the controller controls N DC / DC power conversion devices to charge M battery strings. When the controller detects that the total power of Y photovoltaic inverters is less than the grid-connected power, the controller controls the M battery strings to discharge through the N DC / DC power conversion devices. When the controller detects that the total output power of the Y photovoltaic inverters is less than the grid-connected power, the controller can control the M battery strings to discharge through the N DC / DC power conversion devices, thereby compensating for the insufficient output power of the photovoltaic inverter.

[0048] Optionally, in combination with the fourth possible implementation of the fourth aspect, in a sixth possible implementation of the fourth aspect, when the output voltage frequency of any one of the N DC / DC power conversion devices or the Y photovoltaic inverters is higher than a first preset voltage-frequency threshold, each of the Y photovoltaic inverters reduces power output according to its own preset power curve, and the N DC / DC power conversion devices charge the M battery strings; when the output terminal voltage frequency of any one of the N DC / DC power conversion devices or the Y photovoltaic inverters is lower than a second preset voltage-frequency threshold, each of the Y photovoltaic inverters increases power output according to its own preset power curve, and the N DC / DC power conversion devices control the discharge of the M battery strings, the first preset voltage-frequency threshold being greater than a preset normal grid voltage frequency value, and the second preset voltage-frequency threshold being less than the preset normal grid voltage frequency value. This ensures that the power of the photovoltaic inverter is within a normal range.

[0049] Optionally, in combination with any one of the fourth to sixth possible implementations of the fourth aspect, in the seventh possible implementation of the fourth aspect, the controller is further used to obtain the power of each battery string in the M battery strings through N DC / DC power conversion devices; when the N DC / DC power conversion devices charge the M battery strings, the controller controls the N DC / DC power conversion devices to give priority to charging the battery strings with low power in the M battery strings; when the M battery strings discharge, the controller controls the N DC / DC power conversion devices to give priority to discharging the battery strings with high power in the M battery strings. In this way, the battery strings with low power can be charged first, and the battery strings with high power can be discharged first, so as to maintain the power balance of each battery string in the battery string as much as possible.

[0050] Optionally, in combination with the fourth aspect, in an eighth possible implementation of the fourth aspect, the energy storage system further includes an electric meter, which is used to be connected to the second end of the N DC / DC power conversion devices, and the electric meter is used to measure the amount of charge and discharge of the N DC / DC power conversion devices.

[0051] Optionally, in combination with the fourth aspect, in a ninth possible implementation of the fourth aspect, any one of the at least one DC / DC conversion units is coupled to one of the Q battery strings. If the DC / DC conversion unit is connected to multiple parallel battery strings and has a high requirement for consistency of the parallel battery strings, the DC / DC conversion unit is only connected to one battery string, and the consistency of the battery string is low.

[0052] Optionally, in combination with the fourth aspect, in a tenth possible implementation of the fourth aspect, the N DC / DC power conversion devices and at least one DC / AC power conversion device are connected through a bus.

[0053] An embodiment of the present application provides an energy storage system, which includes M battery strings and N energy storage converters. The first end of any one of the N energy storage converters is coupled to at least one battery string in the M battery strings, and the second end of any one of the energy storage converters is used to connect to the power grid. M and N are integers greater than 0, and M ≥ N. The first end of the first energy storage converter is coupled to Q battery strings in the M battery strings. The first energy storage converter includes a DC / AC conversion unit and at least one direct current / direct current converter. A DC / DC (current, DC / DC) conversion unit, Q is an integer greater than 0, and Q≤M, the first energy storage converter is any one of the N energy storage converters; the first DC / DC conversion unit is coupled to at least one of the Q battery strings through the first end of the first energy storage converter, the first DC / DC conversion unit is coupled to the DC / AC conversion unit, the DC / AC conversion unit is coupled to the power grid through the second end of the first energy storage converter, and the first DC / DC conversion unit is any one of the at least one DC / DC conversion unit; the first DC / DC conversion unit is used to adapt the voltage of the DC / AC conversion unit to the voltage of at least one of the Q battery strings. The first DC / DC conversion unit can adapt the voltage of the DC / AC conversion unit to the voltage of at least one of the Q battery strings, thereby making full use of the battery capacity and reducing the waste of the battery capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 A schematic diagram of an embodiment of an energy storage system in the prior art provided in this application;

[0055] Figure 2 This is a schematic diagram of an embodiment of a battery string connected in parallel in the prior art provided by the present application;

[0056] Figure 3A schematic diagram of an embodiment of an energy storage system provided in this application;

[0057] Figure 4 A schematic diagram of an embodiment of an energy storage system provided in this application;

[0058] Figure 5 A schematic diagram of an embodiment of an energy storage system provided in this application;

[0059] Figure 6 A schematic diagram of an embodiment of an energy storage system provided in this application;

[0060] Figure 7 A schematic diagram of an embodiment of an energy storage system provided in this application;

[0061] Figure 8 A schematic diagram of an embodiment of a photovoltaic energy storage system provided in this application;

[0062] Figure 9 A schematic diagram of an embodiment of a photovoltaic energy storage system provided in this application;

[0063] Figure 10 A schematic diagram of an embodiment of a photovoltaic energy storage system provided in this application. DETAILED DESCRIPTION

[0064] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making any creative efforts shall fall within the scope of protection of the present invention.

[0065] The terms "first," "second," and the like in the specification and claims of this application and in the accompanying drawings are used to distinguish similar objects and are not necessarily used to describe a particular order or precedence. It should be understood that the terms used in this manner are interchangeable where appropriate so that the embodiments described herein can be implemented in an order other than that illustrated or described herein. In addition, the terms "including" and "having," as well as any variations thereof, are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or apparatus comprising a series of steps or modules is not necessarily limited to those steps or modules explicitly listed, but may include other steps or modules that are not explicitly listed or that are inherent to these processes, methods, products, or apparatus.

[0066] Photovoltaic power generation, as a clean, renewable energy source, is widely used, but its application also has drawbacks. Primarily, it suffers from unpredictable and volatile output power. As photovoltaic power generation grows in proportion to traditional power grids, its high penetration will significantly impact the grid, creating a series of challenges with voltage stability, power quality, and operational control. Energy storage devices can be incorporated into photovoltaic power generation systems. Leveraging their charge and discharge characteristics, these devices can effectively address the unpredictable and volatile output power of photovoltaic power stations caused by uneven sunlight. This can also reduce the phenomenon of curtailed photovoltaic power generation, promote large-scale photovoltaic power generation, and increase overall power generation returns.

[0067] See Figure 1 The present application provides an energy storage system in the prior art, which includes a photovoltaic string, a string inverter, a first transformer, a second transformer, an energy storage converter, and a battery string. The string inverter can convert the direct current (DC) generated by the photovoltaic string into alternating current (AC). This AC power can be boosted by the first transformer and then fed into the grid. Alternatively, it can be passed through the first and second transformers and then through the energy storage converter to the battery string, where the energy is stored.

[0068] And in Figure 1 In the energy storage system shown, the energy storage converter adopts a DC / AC topology, and its DC input voltage range is narrow, while the operating voltage range of the battery string is wide, resulting in insufficient utilization of the battery capacity and waste of battery capacity.

[0069] Secondly, in the existing technology, a DC / AC topology is used to connect multiple battery strings in one energy storage converter. Figure 2 , Figure 2 A schematic diagram of a conventional parallel battery string is provided. Inconsistent battery types and internal resistance within the battery string can lead to uneven current distribution. For example, if one battery in battery string 2 (the rightmost one) degrades, increasing its internal resistance, the internal resistance of battery string 2 will be greater than that of battery string 1. This can cause the battery string with the lower internal resistance to discharge with excessively high current, exceeding the battery's application specifications.

[0070] For example, if there are only battery string 1 and battery string 2 in the parallel battery string. When battery string 1 and battery string 2 are normal, the voltage of each battery group is 1000 volts, the internal resistance is 0.01 ohms, and the battery current specification is 100 amperes. The energy storage converter outputs 200 kilowatts. At this time, the internal resistance of battery string 1 and battery string 2 are equal, and each battery string outputs 100 amperes. If one of the batteries in battery string 2 degrades, causing the internal resistance of the entire battery string 2 to increase to 0.02 ohms, the energy storage converter outputs 200 kilowatts. At this time, the internal resistance of battery string 1 and battery string 2 are not equal, the output current of battery string 2 is 66.7 amperes, and the output current of battery string 1 is 133.3 amperes, which exceeds the battery specifications and is not allowed for application.

[0071] If the battery types used in the battery strings are inconsistent, the operating range of the battery strings will be inconsistent, resulting in low battery capacity utilization. For example, if there are only battery strings 1 and 3 in the parallel battery strings, battery string 1 uses 48 volt batteries, a total of 20 ( Figure 2 Only 3 are shown for reference only); Battery string 3 uses 50V batteries, a total of 20 ( Figure 2 Only three are shown for reference. The charge cutoff voltage for battery string 1 is 960 volts, while the charge cutoff voltage for battery string 3 is 1000 volts. Because battery strings 1 and 3 are connected in parallel, the charge cutoff voltage is 960 volts. This will prevent battery string 3 from being fully charged, resulting in wasted battery capacity. Therefore, this solution does not support the mixing of multiple battery types.

[0072] In view of the above problems, the present application provides an energy storage system. Figure 3 The energy storage system includes: M battery strings and N energy storage converters. A first end of any one of the N energy storage converters is coupled to at least one battery string in the M battery strings, and a second end is used to connect to the power grid. M and N are integers greater than 0, and M ≥ N. Figure 3 Only two energy storage converters (the first energy storage converter and the Nth energy storage converter) are shown in the figure, but this is not a limitation. The first energy storage converter is any one of the N energy storage converters.

[0073] The first end of the first energy storage converter is connected to Q battery strings in the M battery strings, and the first energy storage converter includes a DC / AC conversion unit and at least one DC / DC conversion unit. Figure 3 In the example, the first energy storage converter includes two DC / DC conversion units, a first DC / DC conversion unit and a Wth DC / DC conversion unit, but is not limited thereto. ) Q is an integer greater than 0, and Q≤M.

[0074] Any one DC / DC conversion unit in the first energy storage converter is coupled to at least one battery string in the Q battery strings via the first end of the first energy storage converter. Figure 3 In the example, the first DC / DC conversion unit is connected to the first battery string through the first end of the first energy storage converter, and the Wth DC / DC conversion unit is connected to the Qth battery string through the first end of the first energy storage converter, but the present invention is not limited thereto. Any one of the DC / DC conversion units in the first energy storage converter is coupled to the DC / AC conversion unit. Figure 3 In the example, the first DC / DC conversion unit and the Wth DC / DC conversion unit are coupled to the DC / AC conversion unit, but the present invention is not limited thereto.) The DC / AC conversion unit is coupled to the power grid via the second end of the first energy storage converter.

[0075] The DC / DC conversion unit in the energy storage system is used to adapt the voltage of the DC / AC conversion unit to the voltage of the battery string. Figure 3 In the energy storage system, the first DC / DC conversion unit is used to adapt the voltage of the DC / AC conversion unit to the voltage of the first battery string, and the Wth DC / DC conversion unit is used to adapt the voltage of the DC / AC conversion unit to the voltage of the Qth battery string. This can fully utilize the battery capacity and reduce battery capacity waste.

[0076] It should be noted that in the energy storage system, the positive port of each DC / DC conversion unit is coupled to the positive port of the battery string, and the negative port of each DC / DC conversion unit is connected to the negative port of the battery string.

[0077] The energy storage system may further include a first transformer, and the second ends of the N energy storage converters included in the energy storage system may be coupled to the power grid through the first transformer. Figure 3 The example in which the second end of the first energy storage converter is connected to the grid via the first transformer is taken as an example, but the present invention is not limited thereto. The first transformer can adapt the voltage of the energy storage converter to the grid voltage, thereby enabling the electric energy of the energy storage system to be transmitted to the grid, or the energy storage system can store electric energy from the grid.

[0078] It should be noted that the first end of the energy storage converter in this energy storage system is used to connect to the battery string, and the second end is used to connect to the power grid. These first and second ends can function as input or output ends in different situations. Specifically, during charging, the first end of the energy storage converter serves as the output end, and the second end as the input end; during discharging, the first end of the energy storage converter serves as the input end, and the second end as the output end. The second end can also be connected to any electrical appliance, allowing the energy storage system to serve as a power source for the appliance.

[0079] It is understandable that in Figure 3 The energy storage system shown in the figure can also include photovoltaic strings and photovoltaic inverters, so that the energy storage system can be used as a photovoltaic energy storage system. Figure 4 , Figure 4 by Figure 3 Based on Figure 3 On the basis of, the energy storage system may further include X photovoltaic strings and Y photovoltaic inverters, the input end of any one of the Y photovoltaic inverters is coupled to the output end of at least one photovoltaic string of the X photovoltaic strings, the output ends of the Y photovoltaic inverters are coupled to the second ends of the N energy storage converters, X and Y are integers greater than 0. ( Figure 4 Taking a photovoltaic string connected to a photovoltaic inverter as an example, but not limited to this example, the photovoltaic string can convert solar energy into direct current (DC), which is then converted to alternating current (AC) by the photovoltaic inverter. This AC can then be transmitted to the grid, or the AC can be converted back to DC by an energy storage converter and stored in the battery string. In this way, the energy storage system can both transmit power to the grid and store it in the battery string.

[0080] Please refer to Figure 4 The energy storage system may further include a second transformer, through which the output end of any one of the Y photovoltaic inverters is coupled to the grid. The second transformer may adapt the voltage at the output end of the photovoltaic inverter to the grid voltage, thereby transmitting the electric energy generated by the photovoltaic string to the grid.

[0081] The two ends of the DC / DC conversion unit in any one of the energy storage converters in the energy storage system are connected in parallel with switches. (Exemplary, Figure 3 and Figure 4 A switch is connected in parallel at both ends of the first and second DC / DC converter units. If the voltage of the battery string matches the voltage of the energy storage converter, the switches connected in parallel at both ends of the DC / DC converter units can be closed, thereby short-circuiting the DC / DC converter units and reducing unnecessary energy consumption. If the voltage of the battery string does not match the voltage of the energy storage converter, the switches connected in parallel at both ends of the DC / DC converter units are opened, and the DC / DC converter units adapt the voltage of the battery string to the voltage of the energy storage converter.

[0082] It should be noted that in the energy storage system, the energy storage converter and the photovoltaic inverter may be provided with a control module ( Figure 3 and Figure 4(not shown), the control module in the energy storage converter can monitor the voltage of the battery string connected to the energy storage converter, and the control module in the photovoltaic string can monitor the power generation of the photovoltaic string. Figure 3 and Figure 4 In the embodiment, the first energy storage converter can detect the voltage of the Q battery strings connected to the first energy storage converter through the control module. When the voltage of any one of the Q battery strings is greater than or equal to the first voltage threshold, the switch connected in parallel to the DC / DC conversion unit coupled to the battery string with a voltage greater than or equal to the first voltage threshold is closed; when the voltage of any one of the Q battery strings is less than or equal to the second voltage threshold, the switch connected in parallel to the DC / DC conversion unit connected to the battery string with a voltage less than or equal to the second voltage threshold is disconnected, and the first voltage threshold is greater than or equal to the second voltage threshold. The first voltage threshold and the second voltage threshold are related to the grid voltage and the output current. The first photovoltaic inverter can also monitor the power generation of the first photovoltaic string through the control module.

[0083] The energy storage system may further include a controller coupled to each of the Y photovoltaic inverters, coupled to each of the N energy storage converters, and configured to communicate with the Y photovoltaic inverters and the N energy storage converters. Figure 4 In the example, the controller is connected to the first photovoltaic inverter, the Yth photovoltaic inverter, and the first energy storage converter, but the present invention is not limited thereto. Specifically, the controller can communicate with the control modules in the Y photovoltaic inverters and the control modules in the N energy storage converters. The controller can communicate with the Y photovoltaic inverters and the N energy storage converters, so that the controller can detect the power generation status of the X photovoltaic strings through the Y photovoltaic inverters and the power status of the M battery strings through the N energy storage converters.

[0084] The controller receives real-time grid-connected power from the power grid company or solar-storage power station via cables or wirelessly, and then detects the total power of Y photovoltaic inverters. When the controller detects that the total power of the Y photovoltaic inverters is greater than or equal to the grid-connected power, it controls N energy storage converters to charge M battery strings. When the controller detects that the total power of the Y photovoltaic inverters is less than the grid-connected power, it controls the M battery strings to discharge via the N energy storage converters. When the controller detects that the total power of the Y photovoltaic inverters is greater than or equal to the grid-connected power, it indicates that the total output power of the Y photovoltaic inverters is excessive, and the energy generated by the Y photovoltaic inverters can be stored. The controller can then control the N energy storage converters to charge the M battery strings. When the controller detects that the total output power of the Y photovoltaic inverters is less than the grid-connected power, it controls the M battery strings to discharge via the N energy storage converters, thereby compensating for the insufficient output power of the photovoltaic inverters.

[0085] When the output voltage frequency of any one of the N energy storage converters or the Y photovoltaic inverters is higher than a first preset voltage-frequency threshold, each of the Y photovoltaic inverters reduces power output according to its own preset power curve, and the N energy storage converters charge the M battery strings. When the output voltage frequency of any one of the N energy storage converters or the Y photovoltaic inverters is lower than a second preset voltage-frequency threshold, each of the Y photovoltaic inverters increases power output according to its own preset power curve, and the N energy storage converters control the discharge of the M battery strings. The first preset voltage-frequency threshold is greater than the preset normal grid voltage frequency value, and the second preset voltage-frequency threshold is less than the preset normal grid voltage frequency value. This ensures that the power of the photovoltaic inverter is within the normal range.

[0086] The controller is also used to obtain the power of each battery string in the M battery strings through N energy storage converters. When the N energy storage converters are charging the M battery strings, the controller controls the N energy storage converters to prioritize charging the battery strings with lower power among the M battery strings. When the M battery strings are discharging, the controller controls the N energy storage converters to prioritize discharging the battery strings with higher power among the M battery strings. This allows the battery strings with lower power to be charged first and the battery strings with higher power to be discharged first, thus maintaining the power balance among the battery strings as much as possible.

[0087] The energy storage system may further include an electric meter, which may be connected to the second end of the N energy storage converters and is used to measure the amount of electricity charged and discharged by the N energy storage converters. Figure 4The output end of the first photovoltaic inverter is connected to an electric meter A, which can measure the power generation of the photovoltaic string corresponding to the first photovoltaic inverter. The output end of the Y-th photovoltaic inverter is connected to an electric meter B, which can measure the power generation of the photovoltaic string corresponding to the Y-th photovoltaic inverter. The first energy storage converter can be connected to an electric meter C, which can measure the charge and discharge amount of the first energy storage converter. The N-th energy storage converter can be connected to an electric meter D, which can measure the charge and discharge amount of the N-th energy storage converter. In this energy storage system, the location of the electric meter is not limited. An electric meter can be connected to the second end of each energy storage converter to measure the charge and discharge amount of the energy storage converter, or only one electric meter can be set to measure the charge and discharge amount of all energy storage converters. All electric meters in this energy storage system can communicate with the controller.

[0088] See also Figure 3 as well as Figure 4 In this energy storage system, a DC / DC converter unit can be connected to only one or more battery strings. Optimally, in this energy storage system, one DC / DC converter unit is connected to one battery string. If a DC / DC converter unit is connected to multiple parallel battery strings, the consistency requirements for these parallel battery strings will be higher. If a DC / DC converter unit is connected to only one battery string, the consistency requirements for this battery string will be lower.

[0089] The second end of the energy storage converter in the energy storage system can be coupled to the power grid through a transformer. The low-voltage winding of the transformer is connected to the photovoltaic inverter and the energy storage converter, and the high-voltage winding is connected to the power grid. The grid voltage can be 10 kV, 35 kV, or 110 kV three-phase AC power, and the low-voltage winding output end voltage can be 0.4 kV, 0.48 kV, 0.6 kV, or 0.8 kV phase AC voltage.

[0090] Optionally, in the energy storage system, in the energy storage converter, the DC / DC conversion unit can also be connected to a switch in series, and connected to the battery string through the first end of the energy storage converter; the DC / AC conversion unit can also be connected to a switch in series, and can be connected to the low-voltage winding through the DC / AC power conversion device and the first transformer.

[0091] The energy storage converter described in the first embodiment may be: a string DC energy storage converter, a string AC energy storage converter, a double-stage string energy storage converter, a string PCS, a double-stage PCS, or a DC / AC PCS.

[0092] Embodiment 1 provides an energy storage system, which includes M battery strings and N energy storage converters. The first end of any one of the N energy storage converters is coupled to at least one battery string in the M battery strings, and the second end of any one of the energy storage converters is used to connect to the power grid. M and N are integers greater than 0, and M ≥ N. The first end of the first energy storage converter is coupled to Q battery strings in the M battery strings. The first energy storage converter includes a DC / AC conversion unit and at least one DC / DC conversion unit. Q is an integer greater than 0, and Q ≤ M. The first The energy storage converter is any one of N energy storage converters; the first DC / DC conversion unit is coupled to at least one of the Q battery strings via the first end of the first energy storage converter; the first DC / DC conversion unit is coupled to the DC / AC conversion unit; the DC / AC conversion unit is coupled to the power grid via the second end of the first energy storage converter; the first DC / DC conversion unit is any one of the at least one DC / DC conversion units; the first DC / DC conversion unit is used to adapt the voltage of the DC / AC conversion unit to the voltage of at least one of the Q battery strings. In this energy storage system, the DC / DC conversion unit can adapt the voltage of the DC / AC conversion unit to the voltage of the battery string, thereby fully utilizing the battery capacity and reducing battery capacity waste.

[0093] In the above embodiment 1, the energy storage converter in the energy storage system can be split into an independent DC / DC power conversion device and an independent DC / AC power conversion device. Figure 5 .

[0094] Embodiment 2 provides another energy storage system, comprising: M battery strings, N direct current (DC) / alternating current (AC) / DC power conversion devices, and at least one DC / AC power conversion device. A first end of any one of the N DC / DC power conversion devices is coupled to at least one of the M battery strings, a second end of any one of the DC / DC power conversion devices is coupled to a first end of one of the at least one DC / AC power conversion devices, and a second end of the DC / AC power conversion device is configured to be connected to a power grid. M and N are integers greater than 0, and M ≥ N.

[0095] like Figure 5, including first to Nth DC / DC power conversion devices, N DC / DC power conversion devices. Also including at least one DC / AC power conversion device. The first DC / DC power conversion device is any one of the N DC / DC power conversion devices, and the first DC / AC power conversion device is one of the at least one DC / AC power conversion device.

[0096] A first end of the first DC / DC power conversion device is coupled to Q battery strings among the M battery strings, and the first DC / DC power conversion device includes at least one DC / DC conversion unit. Figure 5 In the example, the first DC / DC power conversion device includes two DC / DC conversion units, a first DC / DC conversion unit and a second DC / DC power conversion unit, but is not limited thereto. ) Q is an integer greater than 0, and Q≤M.

[0097] Any one DC / DC conversion unit in the first DC / DC power conversion device is coupled to at least one battery string in the Q battery strings via the first end of the first DC / DC power conversion device. Figure 5 In the example, the first DC / DC conversion unit is coupled to the first battery string via the first end of the first DC / DC power conversion device, and the Wth DC / DC conversion unit is coupled to the Qth battery string via the first end of the first energy storage converter, but the present invention is not limited thereto.

[0098] Any one DC / DC conversion unit in the first DC / DC power conversion device is coupled to the first end of one of the at least one DC / AC power conversion devices via the second end of the first DC / DC power conversion device. Figure 5 In the example, the first DC / DC conversion unit and the second DC / DC conversion unit are both connected to the first end of the first DC / AC power conversion device through the second end of the first DC / DC power conversion device, but the present invention is not limited thereto.

[0099] The DC / DC conversion unit in the energy storage system is used to adapt the voltage of the DC / AC conversion unit to the voltage of the battery string. Figure 5 In the energy storage system, the first DC / DC conversion unit is used to adapt the voltage of the DC / AC conversion unit to the voltage of the first battery string, and the Wth DC / DC conversion unit is used to adapt the voltage of the DC / AC conversion unit to the voltage of the Qth battery string. This can fully utilize the battery capacity and reduce battery capacity waste.

[0100] It should be noted that in the energy storage system, the positive port of each DC / DC conversion unit is coupled to the positive port of the battery string, and the negative port of each DC / DC conversion unit is connected to the negative port of the battery string.

[0101] The energy storage system further includes a first transformer, and the second end of at least one DC / AC power conversion device included in the energy storage system is coupled to the power grid through the first transformer. Figure 5 (The example in which the second end of the first DC / AC power conversion device is connected to the grid via the first transformer is used.) The first transformer can adapt the output voltage of the DC / AC power conversion device to the grid voltage, thereby enabling the photovoltaic energy storage system to transmit power to the grid, or the photovoltaic energy storage system to store power from the grid.

[0102] In one embodiment, the N DC / DC power conversion devices and at least one DC / AC power conversion device in the energy storage system can be connected via a bus. Each of the N DC / DC power conversion devices and at least one DC / AC power conversion device can be connected to the bus via a switch. For details, please refer to Figure 6 Please understand and I will not elaborate on it here.

[0103] It is understandable that in Figure 5 The energy storage system shown in the figure can also include photovoltaic strings and photovoltaic inverters, so that the energy storage system can be used as a photovoltaic energy storage system. Figure 7 , Figure 7 by Figure 5 Based on. Figure 5 On the basis of, the energy storage system may further include X photovoltaic strings and Y photovoltaic inverters, the input end of any one of the Y photovoltaic inverters is coupled to the output end of at least one photovoltaic string in the X photovoltaic strings, the output end of the Y photovoltaic inverters is coupled to the second end of at least one DC / AC power conversion device, X and Y are integers greater than 0. ( Figure 7 Taking a photovoltaic string connected to a photovoltaic inverter as an example, but not limited to this example, the photovoltaic string can convert light energy into direct current (DC), which is then converted into alternating current (AC) by the photovoltaic inverter. This AC can then be transmitted to the grid, or the AC can be converted to DC by an energy storage converter and stored in a battery string. In this way, the energy storage system can both transmit electrical energy to the grid and store it in the battery string.

[0104] See Figure 7The energy storage system may further include a second transformer, through which the output of any one of the Y photovoltaic inverters is connected to the grid. The second transformer can adapt the voltage at the output of the photovoltaic inverter to the grid voltage, thereby transmitting the electrical energy generated by the photovoltaic string to the grid.

[0105] In this energy storage system, switches can be connected in parallel at both ends of any DC / DC conversion unit. Figure 5 and Figure 7 A switch is connected in parallel at both ends of the first and second DC / DC conversion units. If the voltage of the battery string matches the voltage of the DC / AC power conversion device, the switches connected in parallel at both ends of the DC / DC conversion unit can be closed, thereby short-circuiting the DC / DC conversion unit and reducing unnecessary energy consumption. If the voltage of the battery string does not match the voltage of the DC / AC power conversion device, the switches connected in parallel at both ends of the DC / DC conversion unit are opened, and the DC / DC conversion unit adapts the voltage of the battery string to the voltage of the DC / AC power conversion device.

[0106] It should be noted that in the energy storage system, a control module may be provided in the DC / DC power conversion device, and the control module may monitor the voltage of the battery string connected to the DC / DC power conversion device. The DC / DC power conversion device is used to detect the voltage of the battery string connected to the DC / DC power conversion device. For example, in Figure 5 and Figure 7 In the embodiment of the present invention, the first DC / DC power conversion device can detect the voltage of Q battery strings connected to the first DC / DC power conversion device. When the voltage of any one of the Q battery strings is greater than or equal to a first voltage threshold, the switch connected in parallel to the DC / DC conversion unit coupled to the battery string with a voltage greater than or equal to the first voltage threshold is closed; when the voltage of any one of the Q battery strings is less than or equal to a second voltage threshold, the switch connected in parallel to the DC / DC conversion unit connected to the battery string with a voltage less than or equal to the second voltage threshold is opened, and the first voltage threshold is greater than or equal to the second voltage threshold. The first voltage threshold and the second voltage threshold are related to the grid voltage and the output current.

[0107] The energy storage system may further include a controller, the controller being coupled to each of the Y photovoltaic inverters, the controller being coupled to each of the N DC / DC power conversion devices, and the controller being configured to communicate with the Y photovoltaic inverters and the N DC / DC power conversion devices. Figure 7(In the example, the controller is connected to a first photovoltaic inverter and a first DC / DC power conversion device, but is not limited thereto.) The controller can communicate with Y photovoltaic inverters and N DC / DC power conversion devices, so that the controller can detect the power generation status of X photovoltaic strings through the Y photovoltaic inverters and the power status of M battery strings through the N DC / DC power conversion devices. Specifically, the controller can communicate with the control modules in the Y photovoltaic inverters and the control modules in the N DC / DC power conversion devices.

[0108] The controller receives real-time grid-connected power from the power grid company or solar-storage power station via cables or wirelessly, and then detects the total power of Y photovoltaic inverters. When the controller detects that the total power of the Y photovoltaic inverters is greater than or equal to the grid-connected power, it controls N DC / DC power conversion devices to charge M battery strings. When the controller detects that the total power of the Y photovoltaic inverters is less than the grid-connected power, it controls the M battery strings to discharge via the N DC / DC power conversion devices. When the controller detects that the total power of the Y photovoltaic inverters is greater than or equal to the grid-connected power, it indicates that the total output power of the Y photovoltaic inverters is excessive, and the energy generated by the Y photovoltaic inverters can be stored. The controller can then control N energy storage converters to charge the M battery strings. When the controller detects that the total output power of the Y photovoltaic inverters is less than the grid-connected power, it controls the M battery strings to discharge via the N energy storage converters, thereby compensating for the insufficient output power of the photovoltaic inverters.

[0109] When the output voltage frequency of any one of the N DC / DC power conversion devices or the Y photovoltaic inverters is higher than a first preset voltage-frequency threshold, each of the Y photovoltaic inverters reduces power output according to its own preset power curve, and the N DC / DC power conversion devices charge the M battery strings. When the output voltage frequency of any one of the N DC / DC power conversion devices or the Y photovoltaic inverters is lower than a second preset voltage-frequency threshold, each of the Y photovoltaic inverters increases power output according to its own preset power curve, and the N DC / DC power conversion devices control the discharge of the M battery strings. The first preset voltage-frequency threshold is greater than the preset normal grid voltage frequency value, and the second preset voltage-frequency threshold is less than the preset normal grid voltage frequency value. This ensures that the power of the photovoltaic inverter is within the normal range.

[0110] The controller is also used to obtain the power of each battery string in the M battery strings through N DC / DC power conversion devices. When the N DC / DC power conversion devices are charging the M battery strings, the controller controls the N DC / DC power conversion devices to prioritize charging the battery strings with lower power among the M battery strings. When the M battery strings are discharging, the controller controls the N DC / DC power conversion devices to prioritize discharging the battery strings with higher power among the M battery strings. This allows the battery strings with lower power to be charged first and the battery strings with higher power to be discharged first, thus maintaining the power balance among the battery strings as much as possible.

[0111] The energy storage system further includes an electric meter, which is used to be connected to the second end of the N DC / DC power conversion devices and is used to measure the amount of electricity charged and discharged by the N DC / DC power conversion devices. Figure 7 In the example, the electric meter C is connected to the second end of the first DC / AC power converter and can measure the charge and discharge amounts of the Q battery strings connected to the first DC / DC power converter. It should be noted that the electric meter can also be directly installed at the second end of the DC / DC power converter. The output end of the first photovoltaic inverter is connected to the electric meter A, which can measure the power generation of the photovoltaic string connected to the first photovoltaic inverter. The output end of the Yth photovoltaic inverter can be connected to the electric meter B, which can measure the power generation of the photovoltaic string corresponding to the Yth photovoltaic inverter. In this energy storage system, the location of the electric meter is not limited. An electric meter can be connected to the second end of each energy storage converter to measure the charge and discharge amount of the energy storage converter, or only one electric meter can be installed to measure the charge and discharge amount of all energy storage converters. All electric meters in this energy storage system can communicate with the controller.

[0112] See also Figure 5 、 Figure 6 as well as Figure 7 In this energy storage system, a DC / DC converter unit can be connected to one or more battery strings. Optimally, the unit can be connected to only one battery string. If a DC / DC converter unit is connected to multiple parallel battery strings, the consistency requirements for the parallel battery strings are high. If the DC / DC converter unit is connected to only one battery string, the consistency requirements for the battery string are low.

[0113] The second end of the DC / AC power conversion device in the energy storage system can be coupled to the power grid through a transformer. The low-voltage winding of the transformer is connected to the photovoltaic inverter and the energy storage converter, and the high-voltage winding is connected to the power grid. The grid voltage can be 10 kV, 35 kV, or 110 kV three-phase AC power, and the low-voltage winding output end voltage can be 0.4 kV, 0.48 kV, 0.6 kV, or 0.8 kV phase AC voltage.

[0114] Optionally, in the energy storage system, the DC / DC conversion unit can also be connected to a switch in series, and connected to the battery string through the first end of the DC / DC power conversion device; the DC / AC conversion unit can also be connected to a switch in series, and can be connected to the low-voltage winding through the DC / AC power conversion device and the first transformer.

[0115] Embodiment 2 provides an energy storage system, which includes M battery strings, N direct current (DC) / alternating current (DC) / alternating current (AC) power conversion devices, and at least one DC / AC power conversion device. A first end of any one of the N DC / DC power conversion devices is coupled to at least one of the M battery strings, a second end of any one of the DC / DC power conversion devices is coupled to a first end of one of the at least one DC / AC power conversion devices, and a second end of the DC / AC power conversion device is used to connect to a power grid. M and N are integers greater than 0, and M ≥ N. A first end of the first DC / DC power conversion device is coupled to Q battery strings of the M battery strings, and the first DC / DC power conversion device includes at least one DC / DC conversion unit. The first DC / DC power conversion device is any one of the N DC / DC power conversion devices, where Q is an integer greater than 0 and Q ≤ M. The first DC / DC conversion unit is coupled to at least one of the Q battery strings via a first end of the first DC / DC power conversion device, and the first DC / DC conversion unit is coupled to a first end of a DC / AC power conversion device in at least one DC / AC power conversion device via a second end of the first DC / DC power conversion device. The first DC / DC conversion unit is any one of the at least one DC / DC conversion unit. The first DC / DC conversion unit is configured to adapt the voltage of the DC / AC power conversion device in the at least one DC / AC power conversion device to the voltage of at least one of the Q battery strings. In this energy storage system, the DC / DC power conversion device can adapt the voltage of the DC / AC power conversion device to the voltage of the battery string, thereby fully utilizing the battery capacity and reducing waste of battery capacity.

[0116] Example 3 provides a photovoltaic energy storage system, see Figure 8 The photovoltaic energy storage system includes: M battery strings, N energy storage converters, X photovoltaic strings and Y photovoltaic inverters. The first end of any one of the N energy storage converters is coupled to at least one battery string in the M battery strings, and the second end of any one of the energy storage converters is used to connect to the power grid. Figure 8The first energy storage converter is any one of the N energy storage converters. The input end of any one of the Y photovoltaic inverters is coupled to the output end of at least one photovoltaic string among the X photovoltaic strings. The output ends of the Y photovoltaic inverters are coupled to the second ends of the N energy storage converters. M and N are integers greater than 0, and M≥N. X and Y are integers greater than 0. Figure 8 Take a battery string connected to a photovoltaic inverter as an example (the first photovoltaic string is connected to the first photovoltaic inverter, and the Xth photovoltaic string is connected to the Yth photovoltaic inverter). However, this is not limited thereto.

[0117] The first end of the first energy storage converter is coupled to Q battery strings among the M battery strings. The first energy storage converter includes a DC / AC conversion unit and at least one DC / DC conversion unit. ( Figure 8 In the example, the first energy storage converter includes two DC / DC conversion units, a first DC / DC conversion unit and a Wth DC / DC conversion unit, but is not limited thereto). Q is an integer greater than 0, and Q≤M.

[0118] Any one DC / DC conversion unit in the first energy storage converter is coupled to at least one battery string in the Q battery strings via the first end of the first energy storage converter, ( Figure 8 In the example, the first DC / DC conversion unit is connected to the first battery string through the first end of the first energy storage converter, and the Wth DC / DC conversion unit is connected to the Qth battery string through the first end of the first energy storage converter, but the present invention is not limited thereto. Any one of the DC / DC conversion units in the first energy storage converter is coupled to the DC / AC conversion unit, ( Figure 8 In the example, the first DC / DC conversion unit and the Wth DC / DC conversion unit are coupled to the DC / AC conversion unit, but the present invention is not limited thereto.) The DC / AC conversion unit is coupled to the power grid via the second end of the first energy storage converter.

[0119] The DC / DC conversion unit in the photovoltaic energy storage system is used to adapt the voltage of the DC / AC conversion unit to the voltage of the battery string. Figure 8 In the photovoltaic energy storage system, the first DC / DC conversion unit is used to adapt the voltage of the DC / AC conversion unit to the voltage of the first battery string, and the Wth DC / DC conversion unit is used to adapt the voltage of the DC / AC conversion unit to the voltage of the Qth battery string. This can fully utilize the battery capacity and reduce battery capacity waste.

[0120] Secondly, in this PV energy storage system, the charging path includes: PV strings, PV inverters, energy storage converters, and battery strings. The discharging path includes: battery strings and energy storage converters. Neither the charging nor the discharging path includes a transformer, which shortens the charging and discharging paths of the PV energy storage system, thereby improving the battery charging and discharging efficiency.

[0121] It should be noted that in the energy storage system, the positive port of each DC / DC conversion unit is coupled to the positive port of the battery string, and the negative port of each DC / DC conversion unit is connected to the negative port of the battery string.

[0122] The photovoltaic energy storage system may further include a first transformer, and the second ends of the N energy storage converters included in the photovoltaic energy storage system may be coupled to the power grid through the first transformer. Figure 8 The example in which the second end of the first energy storage converter is connected to the grid via the first transformer is taken as an example, but the present invention is not limited thereto. The first transformer can adapt the voltage of the energy storage converter to the grid voltage, thereby enabling the electric energy of the energy storage system to be transmitted to the grid, or the energy storage system can store electric energy from the grid.

[0123] It should be noted that the first end of the energy storage converter in this photovoltaic energy storage system is used to connect to the battery string, and the second end is used to connect to the power grid. These first and second ends can serve as input or output ends in different situations. Specifically, during charging, the first end of the energy storage converter serves as the output end, and the second end serves as the input end. During discharge, the first end of the energy storage converter serves as the input end, and the second end serves as the output end. The second end can also be connected to any electrical appliance, allowing the photovoltaic energy storage system to serve as a power source for the appliance.

[0124] A switch is connected in parallel at both ends of the DC / DC conversion unit in any energy storage converter in the photovoltaic energy storage system. Figure 8 A switch is connected in parallel at both ends of the first and second DC / DC converter units. If the voltage of the battery string matches the voltage of the energy storage converter, the switches connected in parallel at both ends of the DC / DC converter units can be closed, thereby short-circuiting the DC / DC converter units and reducing unnecessary energy consumption. If the voltage of the battery string does not match the voltage of the energy storage converter, the switches connected in parallel at both ends of the DC / DC converter units are opened, and the DC / DC converter units adapt the voltage of the battery string to the voltage of the energy storage converter.

[0125] It should be noted that in the photovoltaic energy storage system, the energy storage converter and the photovoltaic inverter may be provided with a control module. The control module in the energy storage converter can monitor the voltage of the battery string connected to the energy storage converter, and the control module in the photovoltaic string can monitor the power generation of the photovoltaic string. The energy storage converter is used to detect the voltage of the battery string connected to the energy storage converter. For example, Figure 8 In the embodiment, the first energy storage converter can detect the voltages of the Q battery strings connected to the first energy storage converter. When the voltage of any one of the Q battery strings is greater than or equal to a first voltage threshold, the switch connected in parallel to the DC / DC conversion unit coupled to the battery string with a voltage greater than or equal to the first voltage threshold is closed; when the voltage of any one of the Q battery strings is less than or equal to a second voltage threshold, the switch connected in parallel to the DC / DC conversion unit connected to the battery string with a voltage less than or equal to the second voltage threshold is disconnected, and the first voltage threshold is greater than or equal to the second voltage threshold. The first voltage threshold and the second voltage threshold are related to the grid voltage and the output current. The first photovoltaic inverter can detect the power generation status of the first photovoltaic string.

[0126] The photovoltaic energy storage system may further include a controller, the controller being coupled to each of the Y photovoltaic inverters, the controller being coupled to each of the N energy storage converters, and the controller being configured to communicate with the Y photovoltaic inverters and the N energy storage converters. Figure 8 In the example, the controller is connected to the first photovoltaic inverter, the Yth photovoltaic inverter, and the first energy storage converter, but is not limited thereto. The controller can communicate with Y photovoltaic inverters and N energy storage converters, so that the controller can detect the power generation status of X photovoltaic strings through the Y photovoltaic inverters and the power status of M battery strings through the N energy storage converters. Specifically, the controller can communicate with the control modules in the Y photovoltaic inverters and the control modules in the N energy storage converters.

[0127] The controller receives real-time grid-connected power from the power grid company or solar-storage power station via cables or wirelessly, and then detects the total power of Y photovoltaic inverters. When the controller detects that the total power of the Y photovoltaic inverters is greater than or equal to the grid-connected power, it controls N energy storage converters to charge M battery strings. When the controller detects that the total power of the Y photovoltaic inverters is less than the grid-connected power, it controls the M battery strings to discharge via the N energy storage converters. When the controller detects that the total power of the Y photovoltaic inverters is greater than or equal to the grid-connected power, it indicates that the total output power of the Y photovoltaic inverters is excessive, and the energy generated by the Y photovoltaic inverters can be stored. The controller can then control the N energy storage converters to charge the M battery strings. When the controller detects that the total output power of the Y photovoltaic inverters is less than the grid-connected power, it controls the M battery strings to discharge via the N energy storage converters, thereby compensating for the insufficient output power of the photovoltaic inverters.

[0128] When the output voltage frequency of any one of the N energy storage converters or the Y photovoltaic inverters is higher than a first preset voltage-frequency threshold, each of the Y photovoltaic inverters reduces power output according to its own preset power curve, and the N energy storage converters charge the M battery strings. When the output voltage frequency of any one of the N energy storage converters or the Y photovoltaic inverters is lower than a second preset voltage-frequency threshold, each of the Y photovoltaic inverters increases power output according to its own preset power curve, and the N energy storage converters control the discharge of the M battery strings. The first preset voltage-frequency threshold is greater than the preset normal grid voltage frequency value, and the second preset voltage-frequency threshold is less than the preset normal grid voltage frequency value. This ensures that the power of the photovoltaic inverter is within the normal range.

[0129] The controller is also used to obtain the power of each battery string in the M battery strings through N energy storage converters. When the N energy storage converters are charging the M battery strings, the controller controls the N energy storage converters to prioritize charging the battery strings with lower power among the M battery strings. When the M battery strings are discharging, the controller controls the N energy storage converters to prioritize discharging the battery strings with higher power among the M battery strings. This allows the battery strings with lower power to be charged first and the battery strings with higher power to be discharged first, thus maintaining the power balance among the battery strings as much as possible.

[0130] The second end of the energy storage converter in the photovoltaic energy storage system can be coupled to the power grid through a transformer. The low-voltage winding of the transformer is connected to the photovoltaic inverter and the energy storage converter, and the high-voltage winding is connected to the power grid. The grid voltage can be 10 kV, 35 kV, or 110 kV three-phase AC power, and the voltage at the output end of the low-voltage winding can be 0.4 kV, 0.48 kV, 0.6 kV, or 0.8 kV phase AC voltage.

[0131] The photovoltaic energy storage system may also include an electric meter, which may be connected to the second end of the N energy storage converters and is used to measure the amount of electricity charged and discharged by the N energy storage converters. Figure 8 The output end of the first photovoltaic inverter is connected to an electric meter A, which can measure the power generation of the photovoltaic string corresponding to the first photovoltaic inverter. The output end of the Yth photovoltaic inverter is connected to an electric meter B, which can measure the power generation of the photovoltaic string corresponding to the Yth photovoltaic inverter. The first energy storage converter can be connected to an electric meter C, which can measure the charge and discharge amount of the first energy storage converter. The output end of the first transformer is connected to an electric meter D, which can measure the power generated by the photovoltaic energy storage system. The output end of the Nth photovoltaic energy storage system is connected to an electric meter E, which can measure the charge and discharge amount of the Nth energy storage converter. In this energy storage system, the location of the electric meter is not limited. An electric meter can be connected to the second end of each energy storage converter to measure the charge and discharge amount of the energy storage converter, or only one electric meter can be set to measure the charge and discharge amount of all energy storage converters. All electric meters in the photovoltaic energy storage system can communicate with the controller.

[0132] See also Figure 8 In this photovoltaic energy storage system, a DC / DC converter unit can be connected to only one or more battery strings. Optimally, in this photovoltaic energy storage system, one DC / DC converter unit is connected to one battery string. If a DC / DC converter unit is connected to multiple parallel battery strings, the consistency requirements for these parallel battery strings will be higher. If a DC / DC converter unit is connected to only one battery string, the consistency requirements for this battery string will be lower.

[0133] The second end of the energy storage converter in the photovoltaic energy storage system can be coupled to the power grid through a transformer. The low-voltage winding of the transformer is connected to the photovoltaic inverter and the energy storage converter, and the high-voltage winding is connected to the power grid. The grid voltage can be 10 kV, 35 kV, or 110 kV three-phase AC power, and the voltage at the output end of the low-voltage winding can be 0.4 kV, 0.48 kV, 0.6 kV, or 0.8 kV phase AC voltage.

[0134] Optionally, in the energy storage converter of the photovoltaic energy storage system, the DC / DC conversion unit can also be connected to a switch in series, and connected to the battery string through the first end of the energy storage converter; the DC / AC conversion unit can also be connected to a switch in series, and can be connected to the low-voltage winding through a DC / AC power conversion device and a first transformer.

[0135] Embodiment 3 provides a photovoltaic energy storage system, which includes M battery strings, N energy storage converters, X photovoltaic strings and Y photovoltaic inverters, wherein the first end of any one of the N energy storage converters is coupled to at least one battery string in the M battery strings, the second end of any one of the energy storage converters is used to connect to the power grid, the input end of any one of the Y photovoltaic inverters is coupled to the output end of at least one photovoltaic string in the X photovoltaic strings, the output end of the Y photovoltaic inverters is coupled to the second end of the N energy storage converters, M and N are integers greater than 0, and M≥N, X and Y are integers greater than 0; the first end of the first energy storage converter is coupled to Q battery strings in the M battery strings, the first energy storage converter is coupled to Q battery strings in the M battery strings, and the second end of the first energy storage converter is coupled to Q battery strings in the M battery strings. The converter includes a DC / AC conversion unit and at least one DC / DC conversion unit, Q is an integer greater than 0, and Q≤M, the first energy storage converter is any one of the N energy storage converters; the first DC / DC conversion unit is coupled to at least one battery string among the Q battery strings through the first end of the first energy storage converter, the first DC / DC conversion unit is coupled to the DC / AC conversion unit, the DC / AC conversion unit is coupled to the power grid through the second end of the first energy storage converter, and the first DC / DC conversion unit is any one of the at least one DC / DC conversion unit; the first DC / DC conversion unit is used to adapt the voltage of the DC / AC conversion unit to the voltage of at least one battery string among the Q battery strings.

[0136] In this photovoltaic energy storage system, the DC / DC conversion unit can adapt the voltage of the DC / AC conversion unit to the voltage of the battery string, thereby fully utilizing the battery capacity and reducing battery capacity waste. Secondly, in this photovoltaic energy storage system, neither the charging path nor the discharging path includes a transformer, which can shorten the charging and discharging paths of the photovoltaic energy storage system and thus improve the charging and discharging efficiency of the battery.

[0137] In the photovoltaic energy storage system provided in the third embodiment above, the energy storage converter can be split into an independent DC / DC power conversion device and an independent DC / AC power conversion device. Figure 9 .

[0138] Embodiment 4 provides another photovoltaic energy storage system, which includes M battery strings, N direct current / alternating current (DC / DC) power conversion devices, at least one DC / AC power conversion device, X photovoltaic strings, and Y photovoltaic inverters. The first end of any one of the N DC / DC power conversion devices is coupled to at least one battery string in the M battery strings, the second end of any one of the DC / DC power conversion devices is coupled to the first end of one of the at least one DC / AC power conversion devices, the second end of the DC / AC power conversion device is used to connect to the power grid, the input end of any one of the Y photovoltaic inverters is coupled to the output end of at least one photovoltaic string in the X photovoltaic strings, the output ends of the Y photovoltaic inverters are coupled to the second end of the at least one DC / AC power conversion device, X and Y are integers greater than 0, M and N are integers greater than 0, and M ≥ N.

[0139] Figure 9 The N power conversion devices are comprised of a first DC / DC power conversion device to an Nth DC / DC power conversion device. At least one DC / AC power conversion device is provided. The first DC / DC power conversion device is any one of the N DC / DC power conversion devices, and the first DC / AC power conversion device is one of the at least one DC / AC power conversion device.

[0140] A first end of the first DC / DC power conversion device is coupled to Q battery strings among the M battery strings, and the first DC / DC power conversion device includes at least one DC / DC conversion unit. Figure 9 In the example, the first DC / DC power conversion device includes two DC / DC conversion units, a first DC / DC conversion unit and a second DC / DC power conversion unit, but is not limited thereto. ) Q is an integer greater than 0, and Q≤M.

[0141] Any one DC / DC conversion unit in the first DC / DC power conversion device is coupled to at least one battery string in the Q battery strings via the first end of the first DC / DC power conversion device. Figure 9 In the example, the first DC / DC conversion unit is coupled to the first battery string through the first end of the first DC / DC power conversion device, and the Wth DC / DC conversion unit is connected to the Qth battery string through the first end of the first energy storage converter.

[0142] Any one DC / DC conversion unit in the first DC / DC power conversion device is coupled to the first end of one of the at least one DC / AC power conversion devices via the second end of the first DC / DC power conversion device. Figure 9 In the example, the first DC / DC conversion unit and the second DC / DC conversion unit are both connected to the first end of the first DC / AC power conversion device through the second end of the first DC / DC power conversion device.

[0143] The DC / DC conversion unit in the photovoltaic energy storage system is used to adapt the voltage of the DC / AC conversion unit to the voltage of the battery string. Figure 9 In the photovoltaic energy storage system, the first DC / DC conversion unit is used to adapt the voltage of the DC / AC conversion unit to the voltage of the first battery string, and the Wth DC / DC conversion unit is used to adapt the voltage of the DC / AC conversion unit to the voltage of the Qth battery string. This can fully utilize the battery capacity and reduce battery capacity waste.

[0144] Secondly, in the photovoltaic energy storage system, the charging and discharging path does not include a transformer, which can shorten the charging and discharging path of the photovoltaic energy storage system, thereby improving the charging and discharging efficiency of the battery.

[0145] It should be noted that in the photovoltaic energy storage system, the positive port of each DC / DC conversion unit is coupled to the positive port of the battery string, and the negative port of each DC / DC conversion unit is connected to the negative port of the battery string.

[0146] The photovoltaic energy storage system further includes a first transformer, and the second end of at least one DC / AC power conversion device included in the photovoltaic energy storage system is coupled to the power grid through the first transformer. Figure 9 (The example in which the second end of the first DC / AC power conversion device is connected to the grid via the first transformer is used.) The first transformer can adapt the output voltage of the DC / AC power conversion device to the grid voltage, thereby enabling the photovoltaic energy storage system to transmit power to the grid, or the photovoltaic energy storage system to store power from the grid.

[0147] In this photovoltaic energy storage system, switches can be connected in parallel at both ends of any DC / DC conversion unit. Figure 9A switch is connected in parallel at both ends of the first and second DC / DC conversion units. If the voltage of the battery string matches the voltage of the DC / AC power conversion device, the switches connected in parallel at both ends of the DC / DC conversion unit can be closed, thereby short-circuiting the DC / DC conversion unit and reducing unnecessary energy consumption. If the voltage of the battery string does not match the voltage of the DC / AC power conversion device, the switches connected in parallel at both ends of the DC / DC conversion unit are opened, and the DC / DC conversion unit adapts the voltage of the battery string to the voltage of the DC / AC power conversion device.

[0148] It should be noted that in the energy storage system, a control module may be provided in the DC / DC power conversion device, and the control module may monitor the voltage of the battery string connected to the DC / DC power conversion device. The DC / DC power conversion device is used to detect the voltage of the battery string connected to the DC / DC power conversion device. For example, in Figure 9 In the embodiment of the present invention, the first DC / DC power conversion device can detect the voltage of Q battery strings connected to the first DC / DC power conversion device. When the voltage of any one of the Q battery strings is greater than or equal to a first voltage threshold, the switch connected in parallel to the DC / DC conversion unit coupled to the battery string with a voltage greater than or equal to the first voltage threshold is closed; when the voltage of any one of the Q battery strings is less than or equal to a second voltage threshold, the switch connected in parallel to the DC / DC conversion unit connected to the battery string with a voltage less than or equal to the second voltage threshold is opened, and the first voltage threshold is greater than or equal to the second voltage threshold. The first voltage threshold and the second voltage threshold are related to the grid voltage and the output current.

[0149] The energy storage system may further include a controller, the controller being coupled to each of the Y photovoltaic inverters, the controller being coupled to each of the N DC / DC power conversion devices, and the controller being configured to communicate with the Y photovoltaic inverters and the N DC / DC power conversion devices. Figure 9 In the example, the controller is connected to a first photovoltaic inverter and a first DC / DC power conversion device. The controller can communicate with Y photovoltaic inverters and N DC / DC power conversion devices, thereby detecting the power generation status of X photovoltaic strings through the Y photovoltaic inverters and the power status of M battery strings through the N DC / DC power conversion devices. Specifically, the controller can communicate with the control modules in the Y photovoltaic inverters and the control modules in the N DC / DC power conversion devices.

[0150] The controller receives real-time grid-connected power from the power grid company or solar-storage power station via cables or wirelessly, and then detects the total power of Y photovoltaic inverters. When the controller detects that the total power of the Y photovoltaic inverters is greater than or equal to the grid-connected power, it controls N DC / DC power conversion devices to charge M battery strings. When the controller detects that the total power of the Y photovoltaic inverters is less than the grid-connected power, it controls the M battery strings to discharge via the N DC / DC power conversion devices. When the controller detects that the total power of the Y photovoltaic inverters is greater than or equal to the grid-connected power, it indicates that the total output power of the Y photovoltaic inverters is excessive, and the energy generated by the Y photovoltaic inverters can be stored. The controller can then control N energy storage converters to charge the M battery strings. When the controller detects that the total output power of the Y photovoltaic inverters is less than the grid-connected power, it controls the M battery strings to discharge via the N energy storage converters, thereby compensating for the insufficient output power of the photovoltaic inverters.

[0151] When the output voltage frequency of any one of the N DC / DC power conversion devices or the Y photovoltaic inverters is higher than a first preset voltage-frequency threshold, each of the Y photovoltaic inverters reduces power output according to its own preset power curve, and the N DC / DC power conversion devices charge the M battery strings. When the output voltage frequency of any one of the N DC / DC power conversion devices or the Y photovoltaic inverters is lower than a second preset voltage-frequency threshold, each of the Y photovoltaic inverters increases power output according to its own preset power curve, and the N DC / DC power conversion devices control the discharge of the M battery strings. The first preset voltage-frequency threshold is greater than the preset normal grid voltage frequency value, and the second preset voltage-frequency threshold is less than the preset normal grid voltage frequency value. This ensures that the power of the photovoltaic inverter is within the normal range.

[0152] The controller is also used to obtain the power of each battery string in the M battery strings through N DC / DC power conversion devices. When the N DC / DC power conversion devices are charging the M battery strings, the controller controls the N DC / DC power conversion devices to prioritize charging the battery strings with lower power among the M battery strings. When the M battery strings are discharging, the controller controls the N DC / DC power conversion devices to prioritize discharging the battery strings with higher power among the M battery strings. This allows the battery strings with lower power to be charged first and the battery strings with higher power to be discharged first, thus maintaining the power balance among the battery strings as much as possible.

[0153] The energy storage system further includes an electric meter, which is used to be connected to the second end of the N DC / DC power conversion devices and is used to measure the amount of electricity charged and discharged by the N DC / DC power conversion devices. Figure 9In the example, the electric meter C is connected to the second end of the first DC / AC power conversion device and can measure the charge and discharge amounts of the Q battery strings connected to the first DC / DC power conversion device. It should be noted that the electric meter can also be directly set at the second end of the DC / DC power conversion device. The output end of the first photovoltaic inverter is connected to the electric meter A, which can measure the power generation of the photovoltaic string connected to the first photovoltaic inverter. The output end of the Yth photovoltaic inverter can be connected to the electric meter B, which can measure the power generation of the photovoltaic string corresponding to the Yth photovoltaic inverter. In this energy storage system, the location of the electric meter is not limited. An electric meter can be connected to the second end of each energy storage converter to measure the charge and discharge amount of the energy storage converter, or only one electric meter can be set to measure the charge and discharge amount of all energy storage converters.

[0154] See also Figure 9 In this photovoltaic energy storage system, a DC / DC converter unit can be connected to one or more battery strings. Optimally, the unit can be connected to only one battery string. If a DC / DC converter unit is connected to multiple parallel battery strings, the consistency requirements for the parallel battery strings are high. If the DC / DC converter unit is connected to only one battery string, the consistency requirements for the battery string are low.

[0155] The second end of the DC / AC power conversion device in the photovoltaic energy storage system can be coupled to the power grid through a transformer. The low-voltage winding of the transformer is connected to the photovoltaic inverter and the energy storage converter, and the high-voltage winding is connected to the power grid. The grid voltage can be 10 kV, 35 kV, or 110 kV three-phase AC power, and the low-voltage winding output end voltage can be 0.4 kV, 0.48 kV, 0.6 kV, or 0.8 kV phase AC voltage.

[0156] Optionally, in the photovoltaic energy storage system, in the energy storage converter, the DC / DC conversion unit can also be connected to a switch in series, and connected to the battery string through the first end of the DC / DC power conversion device; the DC / AC conversion unit can also be connected to a switch in series, and can be connected to the low-voltage winding through the DC / AC power conversion device and the first transformer.

[0157] In one embodiment, the N DC / DC power conversion devices and at least one DC / AC power conversion device in the photovoltaic energy storage system can be connected via a bus. Each of the N DC / DC power conversion devices and at least one DC / AC power conversion device can be connected to the bus via a switch. Figure 10 Please understand and I will not elaborate on it here.

[0158] The energy storage converter described in the fourth embodiment may be: a string DC energy storage converter, a string AC energy storage converter, a double-stage string energy storage converter, a string PCS, a double-stage PCS, or a DC / AC PCS.

[0159] Embodiment 4 provides a photovoltaic energy storage system, which includes M battery strings, N direct current / alternating current (DC / DC) power conversion devices, at least one DC / AC power conversion device, X photovoltaic strings, and Y photovoltaic inverters. The first end of any one of the N DC / DC power conversion devices is coupled to at least one battery string in the M battery strings, the second end of any one of the DC / DC power conversion devices is coupled to the first end of one of the at least one DC / AC power conversion devices, the second end of the DC / AC power conversion device is used to connect to the power grid, the input end of any one of the Y photovoltaic inverters is coupled to the output end of at least one photovoltaic string in the X photovoltaic strings, the output end of the Y photovoltaic inverters is coupled to the second end of the at least one DC / AC power conversion device, X and Y are integers greater than 0, M and N are integers greater than 0, and M ≥ N; the first DC / DC power The first end of the power conversion device is coupled to Q battery strings among the M battery strings, the first DC / DC power conversion device includes at least one DC / DC conversion unit, the first DC / DC power conversion device is any one DC / DC power conversion device among the N DC / DC power conversion devices, Q is an integer greater than 0, and Q≤M; the first DC / DC conversion unit is coupled to at least one battery string among the Q battery strings through the first end of the first DC / DC power conversion device, the first DC / DC conversion unit is coupled to the first end of one DC / AC power conversion device in at least one DC / AC power conversion device through the second end of the first DC / DC power conversion device, the first DC / DC conversion unit is any one of the at least one DC / DC conversion unit; the first DC / DC conversion unit is used to adapt the voltage of one DC / AC power conversion device in the at least one DC / AC power conversion device to the voltage of at least one battery string among the Q battery strings.

[0160] In this photovoltaic energy storage system, the DC / DC conversion unit can adapt the voltage of the DC / AC conversion unit to the voltage of the battery string, thereby fully utilizing the battery capacity and reducing battery capacity waste. Secondly, in this photovoltaic energy storage system, neither the charging path nor the discharging path includes a transformer, which can shorten the charging and discharging paths of the photovoltaic energy storage system and thus improve the charging and discharging efficiency of the battery.

[0161] It should be noted that the energy storage converters mentioned in the above embodiments may include: a string DC energy storage converter, a string AC energy storage converter, a two-stage string energy storage converter, a string PCS, a two-stage PCS, or a DC / AC PCS. The energy storage converter may be a standalone device as described in Examples 1 and 3, or may be composed of an independent DC / DC power conversion device coupled with an independent DC / AC power conversion device as described in Examples 2 and 4, without limitation herein.

[0162] The above is a detailed introduction to an energy storage system and a photovoltaic energy storage system provided by the embodiments of the present invention. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scopes. In summary, the content of this specification should not be understood as limiting the present invention. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. An energy storage system, characterized in that: The energy storage system includes Q battery strings and a first energy storage converter, wherein a first end of the first energy storage converter is coupled to the Q battery strings, and a second end of the first energy storage converter is used to be connected to a power grid; The first energy storage converter includes a DC / AC conversion unit and at least two DC / DC conversion units, Q is an integer greater than 1, and Q≤M; A first DC / DC conversion unit among the at least two DC / DC conversion units is coupled to a first battery string among the Q battery strings via a first end of the first energy storage converter, a Wth DC / DC conversion unit among the at least two DC / DC conversion units is coupled to a Qth battery string among the Q battery strings via a first end of the first energy storage converter, the first DC / DC conversion unit and the Wth DC / DC conversion unit are both coupled to the DC / AC conversion unit, and the DC / AC conversion unit is coupled to a power grid via a second end of the first energy storage converter; The first DC / DC conversion unit is used to adapt the voltage of the DC / AC conversion unit to the voltage of the first battery string; the Wth DC / DC conversion unit is used to adapt the voltage of the DC / AC conversion unit to the voltage of the Qth battery string; Switches are connected in parallel at both ends of the first DC / DC conversion unit and the Wth DC / DC conversion unit; The first energy storage converter is used to detect the voltages of the Q battery strings, and when the voltage of any one of the Q battery strings is greater than or equal to a first voltage threshold, the switch connected in parallel to the DC / DC conversion unit coupled to the battery string having a voltage greater than or equal to the first voltage threshold is closed; When the voltage of any one of the Q battery strings is less than or equal to a second voltage threshold, the switch connected in parallel with the DC / DC conversion unit connected to the battery string whose voltage is less than or equal to the second voltage threshold is disconnected, and the first voltage threshold is greater than or equal to the second voltage threshold.

2. The energy storage system according to claim 1, characterized in that The energy storage system further includes a first transformer, and the second end of the first energy storage converter is coupled to the power grid through the first transformer.

3. The energy storage system according to claim 1 or 2, characterized in that: The energy storage system further includes X photovoltaic strings and Y photovoltaic inverters, wherein an input end of any one of the Y photovoltaic inverters is coupled to an output end of at least one of the X photovoltaic strings, and an output end of the Y photovoltaic inverters is coupled to a second end of the first energy storage converter, where X and Y are integers greater than 0.

4. The energy storage system according to claim 3, characterized in that The energy storage system further includes a second transformer, and the output end of any one of the Y photovoltaic inverters is coupled to the power grid via the second transformer.

5. The energy storage system according to claim 1, characterized in that: The first energy storage converter is used to detect the voltages of the Q battery strings, and when the voltage of any one of the Q battery strings is greater than or equal to a first voltage threshold, the switch connected in parallel to the DC / DC conversion unit coupled to the battery string having a voltage greater than or equal to the first voltage threshold is closed; When the voltage of any one of the Q battery strings is less than or equal to a second voltage threshold, the switch connected in parallel with the DC / DC conversion unit connected to the battery string whose voltage is less than or equal to the second voltage threshold is disconnected, and the first voltage threshold is greater than or equal to the second voltage threshold.

6. The energy storage system according to claim 3, characterized in that: The energy storage system also includes a controller, which is coupled to each of the Y photovoltaic inverters and coupled to the first energy storage converter. The controller is used to communicate with the Y photovoltaic inverters and the first energy storage converter.

7. The energy storage system according to claim 6, characterized in that: The controller is further configured to obtain grid-connected power, and when the controller detects that the total power of the Y photovoltaic inverters is greater than or equal to the grid-connected power, the controller controls the first energy storage converter to charge the Q battery strings; When the controller detects that the total power of the Y photovoltaic inverters is less than the grid-connected power, the controller controls the Q battery strings to discharge through the first energy storage converter.

8. The energy storage system according to claim 6, characterized in that: When the output voltage frequency of the first energy storage converter or any one of the Y photovoltaic inverters is higher than a first preset voltage-frequency threshold, each of the Y photovoltaic inverters reduces power output according to its own preset power curve, and the first energy storage converter charges the Q battery strings; When the output terminal voltage frequency of the first energy storage converter or any one of the Y photovoltaic inverters is lower than a second preset voltage-frequency threshold, each of the Y photovoltaic inverters increases power output according to its own preset power curve, and the first energy storage converter controls the discharge of the M battery strings. The first preset voltage-frequency threshold is greater than a preset normal frequency value of the grid voltage, and the second preset voltage-frequency threshold is less than the preset normal frequency value of the grid voltage.

9. The energy storage system according to any one of claims 6 to 8, characterized in that: The controller is further configured to obtain the power of each battery string in the Q battery strings through the first energy storage converter; When the first energy storage converter charges the Q battery strings, the controller controls the first energy storage converter to preferentially charge the battery string with low power among the Q battery strings; When the Q battery strings are discharging, the controller preferentially controls the battery string with the highest charge among the Q battery strings to discharge through the first energy storage converter.

10. The energy storage system according to claim 1, characterized in that: The energy storage system further includes an electric meter, which is used to be connected to the second end of the first energy storage converter and is used to measure the amount of electricity charged and discharged by the first energy storage converter.

11. An energy storage system, characterized in that: The energy storage system includes Q battery strings, a first direct current (DC) / alternating current (DC) / DC power conversion device, and a first DC / AC power conversion device, wherein a first end of the first DC / DC power conversion device is coupled to the Q battery strings, a second end of the first DC / DC power conversion device is coupled to the first end of the first DC / AC power conversion device, and the second end of the first DC / AC power conversion device is used to connect to a power grid; the first DC / DC power conversion device includes at least two DC / DC conversion units, and Q is an integer greater than 2; The first DC / DC conversion unit in the first DC / AC power conversion device is coupled to the first battery string in the Q battery strings via the first end of the first DC / DC power conversion device; The Wth DC / DC conversion unit in the first DC / AC power conversion device is coupled to the Qth battery string among the Q battery strings via the first terminal of the first DC / DC power conversion device; the first DC / DC conversion unit and the Wth DC / DC conversion unit are both coupled to the first terminal of the first DC / AC power conversion device via the second terminal of the first DC / DC power conversion device; The first DC / DC conversion unit is used to adapt the voltage of the first DC / AC power conversion device to the voltage of the first battery string among the Q battery strings; the Wth DC / DC conversion unit is used to adapt the voltage of the first DC / AC power conversion device to the voltage of the Qth battery string; Switches are connected in parallel at both ends of the first DC / DC conversion unit and the Wth DC / DC conversion unit; The first DC / DC power conversion device is used to detect the voltages of the Q battery strings, and when the voltage of any one of the Q battery strings is greater than or equal to a first voltage threshold, a switch connected in parallel to a DC / DC conversion unit coupled to the battery string having a voltage greater than or equal to the first voltage threshold is closed; When the voltage of any one of the Q battery strings is less than or equal to a second voltage threshold, the switch connected in parallel with the DC / DC conversion unit connected to the battery string whose voltage is less than or equal to the second voltage threshold is disconnected, and the first voltage threshold is greater than or equal to the second voltage threshold.

12. The energy storage system according to claim 11, characterized in that: The energy storage system further includes a first transformer, and the second end of the first DC / AC power conversion device is coupled to the power grid through the first transformer.

13. The energy storage system according to claim 11 or 12, characterized in that: The energy storage system further includes X photovoltaic strings and Y photovoltaic inverters, wherein an input end of any one of the Y photovoltaic inverters is coupled to an output end of at least one of the X photovoltaic strings, and an output end of the Y photovoltaic inverters is coupled to a second end of the first DC / AC power conversion device, where X and Y are integers greater than 0.

14. The energy storage system according to claim 13, characterized in that: The energy storage system further includes a second transformer, and the output end of any one of the Y photovoltaic inverters is connected to the power grid via the second transformer.

15. The energy storage system according to claim 13, characterized in that: The energy storage system also includes a controller, which is coupled to each of the Y photovoltaic inverters, and is coupled to the first DC / DC power conversion device. The controller is used to communicate with the Y photovoltaic inverters and the first DC / DC power conversion device.

16. The energy storage system according to claim 15, characterized in that: The controller is further configured to obtain grid-connected power, and when the controller detects that the total power of the Y photovoltaic inverters is greater than or equal to the grid-connected power, the controller controls the first DC / DC power conversion device to charge the Q battery strings; When the controller detects that the total power of the Y photovoltaic inverters is less than the grid-connected power, the controller controls the Q battery strings to discharge through the N DC / DC power conversion devices.

17. The energy storage system according to claim 15, characterized in that: When the output voltage frequency of the first DC / DC power conversion device or any one of the Y photovoltaic inverters is higher than a first preset voltage-frequency threshold, each of the Y photovoltaic inverters reduces power output according to its own preset power curve, and the first DC / DC power conversion device charges the Q battery strings; When the output terminal voltage frequency of the first DC / DC power conversion device or any one of the Y photovoltaic inverters is lower than a second preset voltage-frequency threshold, each of the Y photovoltaic inverters increases power output according to its own preset power curve, and the first DC / DC power conversion device controls the Q battery strings to discharge, the first preset voltage-frequency threshold is greater than the preset normal frequency value of the grid voltage, and the second preset voltage-frequency threshold is less than the preset normal frequency value of the grid voltage.

18. The energy storage system according to any one of claims 15 to 17, characterized in that: The controller is further configured to obtain the power of each battery string in the Q battery strings through the first DC / DC power conversion device; When the first DC / DC power conversion device charges the Q battery strings, the controller controls the first DC / DC power conversion device to preferentially charge a battery string with low power among the Q battery strings; When the Q battery strings are discharging, the controller preferentially controls the battery string with the highest charge among the Q battery strings to discharge through the first DC / DC power conversion device.

19. The energy storage system according to claim 11, characterized in that: The energy storage system further includes an electric meter, which is used to be connected to the second end of the first DC / DC power conversion device and is used to measure the amount of electricity charged and discharged by the first DC / DC power conversion device.

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