Energy storage system and energy storage system control method

Abstract

The present application provides an energy storage system, comprising a plurality of battery clusters, power converters correspondingly connected to the battery clusters, and a main controller. The main controller is configured to, when the decrease of the load capacity of a power grid is greater than or equal to a first threshold or the increase of the load capacity of the power grid is greater than or equal to a second threshold, control j power converters among one or more power converters to stop power output, and control k power converters other than the j power converters to output reactive power, wherein the reactive power output by the k power converters is greater than or equal to reactive power absorbed by the j power converters from the power grid, so as to prevent the energy storage system from pulling down the voltage of the power grid in a standby state.

Description

An energy storage system and a control method for the energy storage system.

[0001] This application claims priority to Chinese Patent Application No. 202411021809.2, filed on July 27, 2024, entitled “An Energy Storage System and an Energy Storage System Control Method”, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of power electronics technology, and in particular to an energy storage system and an energy storage system control method. Background Technology

[0003] Energy storage systems can be applied to many fields such as large-scale photovoltaic power plants, industrial and commercial distributed power plants, residential photovoltaic power generation systems, and electric vehicles.

[0004] Energy storage systems can temporarily store electricity generated by a power generation system. When the power generation capacity decreases, the stored electricity is supplied to the load to ensure its power demand. This load can be the power grid. Energy storage systems can compensate for the instability of renewable energy generation systems and can be combined with them to form a unified power supply system. For example, a photovoltaic-energy storage system couples a photovoltaic power generation system with an energy storage system to jointly supply power to the load, ensuring stable power consumption. However, because the operating state of the energy storage system is affected by the power generation status of the renewable energy generation system, the energy storage system needs to maintain a standby state at all times. This results in power loss even when the energy storage system is not in operation, reducing its efficiency. Improving the efficiency of energy storage systems and reducing standby power consumption are important issues that need to be addressed. Summary of the Invention

[0005] This application provides an energy storage system and an energy storage system control method. Compared with traditional energy storage system designs, the design of this energy storage system or the energy storage system control method can reduce the standby loss of the energy storage system and increase the overall system efficiency.

[0006] In a first aspect, this application provides an energy storage system, including n battery clusters, n power converters corresponding to the n battery clusters, and a main controller. The DC terminals of the power converters are connected to the corresponding battery clusters, and the output terminals of the power converters are connected to the power grid. The main controller is configured to control one or more of the power converters to input electrical energy from the power grid to the corresponding battery clusters when the load capacity of the power grid is greater than the power demand of the load, or to control one or more of the power converters to output electrical energy from the corresponding battery clusters to the power grid when the load capacity of the power grid is less than the power demand of the load. The main controller is further configured to control the power converters to output electrical energy from the corresponding battery clusters to the power grid when the load capacity of the power grid decreases by more than or equal to the load demand of the load. When the load capacity increase of the power grid is greater than or equal to the first threshold, j power converters among the one or more power converters are controlled to stop power output, and k power converters other than the j power converters are controlled to output reactive power, and the reactive power output by the k power converters is greater than or equal to the reactive power absorbed by the j power converters from the power grid, where j+k≤n; wherein, the power converter includes a filter capacitor, which is used to filter out the ripple current in the AC output of the power converter; the magnitude of the reactive power absorbed by the j power converters from the power grid is positively correlated with the capacitance value of the filter capacitor in the j power converters.

[0007] In the aforementioned embodiments, the power converter in the energy storage system can adjust its operating status in a timely manner according to the grid demand. When the grid has a strong load capacity, the power converter stops working to reduce unnecessary power output. At this time, the power devices in the stopped power converter are blocked, do not perform switching actions, do not generate switching losses, and retain a reasonable number of power converters for reactive power output to ensure that the energy storage system provides stable reactive power support to the grid and maintains the stability of the grid voltage.

[0008] In one embodiment, the power converter includes a relay for controlling the connection or disconnection of the power converter from the power grid by turning it on or off; the main controller is further configured to control the relays in the j power converters and the k power converters to disconnect when the duration of the power output stoppage of the j power converters is greater than or equal to a time threshold.

[0009] In the aforementioned embodiments, when the power converter in the energy storage system does not supply power to the grid for a long period of time, it disconnects from the grid. The relay does not need to remain in the energized state. At this time, the relay coil does not consume power, thereby reducing the power loss of the power converter in the energy storage system due to maintaining the connection with the grid and reducing the operating energy consumption of the energy storage system.

[0010] In one embodiment, the power converter includes a relay for controlling the connection or disconnection of the power converter from the power grid by turning it on or off; the main controller is configured to control the relays in the j power converters and the k power converters to disconnect when the duration of the power output stoppage of the j power converters is greater than or equal to a time threshold and the power loss of the energy storage system is greater than or equal to a system loss threshold.

[0011] In the aforementioned embodiments, the power converter in the energy storage system disconnects from the grid when it does not supply power to the grid for a long period of time, and maintains the connection with the grid when it does not supply power to the grid for a short period of time. This reduces the power loss of the power converter in the energy storage system due to maintaining the connection with the grid, thereby reducing the operating energy consumption of the energy storage system, while maintaining the energy storage system's ability to respond to grid demands.

[0012] In one embodiment, the main controller is configured to, after disconnecting the relays in the j and k power converters, control the relays in one or more of the j and k power converters to turn on when the load capacity of the power grid increases by a factor greater than or equal to a third threshold, and control the one or more of the j and k power converters to input the power from the power grid to the corresponding battery cluster; or, the main controller is configured to, after disconnecting the relays in the j and k power converters, control the relays in one or more of the j and k power converters to turn on when the load capacity of the power grid decreases by a factor greater than or equal to a fourth threshold, and control the one or more of the j and k power converters to input the power from the corresponding battery cluster to the power grid.

[0013] In one embodiment, the demand response time of the power grid is greater than or equal to the demand response threshold; after the main controller controls the relays in the j power converters and k power converters to disconnect, the time required for the main controller to control the relays in one or more power converters to turn on and control the one or more power converters to start inputting electrical energy from the power grid to the battery cluster is less than or equal to the demand response threshold; or, after the main controller controls the relays in the j power converters and k power converters to disconnect, the time required for the main controller to control the relays in one or more power converters to turn on and control the one or more power converters to start outputting electrical energy from the battery cluster to the power grid is less than or equal to the demand response threshold.

[0014] In one embodiment, the power converter includes a slave controller and a power conversion circuit. The master controller is used to send control commands to the slave controller to enable the slave controller to control the power conversion circuit to work or stop working in order to achieve power output or stop power output of the power converter, and is also used to send control commands to the slave controller to enable the slave controller to control the relay to turn on or off.

[0015] In one embodiment, each of the power converters and its corresponding battery clusters are located inside the same energy storage container.

[0016] Secondly, this application provides a control method for an energy storage system, characterized in that, when the load capacity of the power grid is greater than the power demand of the load, one or more power converters are controlled to input the power energy of the power grid to the corresponding battery cluster, or when the load capacity of the power grid is less than the power demand of the load, one or more power converters are controlled to output the power energy of the corresponding battery cluster to the power grid; when the load capacity of the power grid decreases by a factor greater than or equal to a first threshold or the load capacity of the power grid increases by a factor greater than or equal to a second threshold, j of the power converters are controlled to stop. The system outputs power and controls k power converters other than the j power converters to output reactive power, wherein the reactive power output by the k power converters is greater than or equal to the reactive power absorbed by the j power converters from the power grid, j+k≤n, where n is the number of power converters in the energy storage system; wherein each power converter includes a filter capacitor, which is used to filter out the ripple current in the AC output of the power converter; the magnitude of the reactive power absorbed by the j power converters from the power grid is positively correlated with the capacitance value of the filter capacitor in the j power converters.

[0017] In one embodiment, when the duration for which the j power converters stop power output is greater than or equal to a time threshold, the relays in the j power converters and the k power converters are controlled to disconnect; wherein, the relays are used to control the connection or disconnection of the power converters with the power grid by turning them on or off.

[0018] In one embodiment, when the duration for which the j power converters stop power output is greater than or equal to a time threshold and the power loss of the energy storage system is greater than or equal to a system loss threshold, the relays in the j power converters and the k power converters are controlled to disconnect; wherein, the relays are used to control the connection or disconnection of the power converters with the power grid by turning them on or off.

[0019] It should be understood that the implementations and beneficial effects of the above-mentioned aspects of this application can be referenced from each other. Attached Figure Description

[0020] Figure 1 is a schematic diagram of an energy storage system architecture provided in this application;

[0021] Figure 2 is a schematic diagram of the internal structure of a power converter provided in this application;

[0022] Figure 3 is a schematic diagram of the internal structure of another power converter provided in this application;

[0023] Figure 4 is a schematic diagram of the internal structure of another power converter provided in this application;

[0024] Figure 5 is a schematic diagram of a power converter control flow provided in this application. Detailed Implementation

[0025] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0026] The term "an embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of this application. The phrase "in one embodiment" appearing in different places throughout this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that excludes other embodiments. Unless otherwise specified, the terms "connected," "linked," and "connected" used herein to indicate electrical connection mean direct or indirect electrical connection.

[0027] In the following description, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0028] The technical solutions provided in this application can be applied to different application scenarios, such as large-scale photovoltaic power plants, industrial and commercial distributed power plants, and residential photovoltaic power generation systems.

[0029] To facilitate understanding of the technical solutions provided in the embodiments of this application, the following section selects one scenario to illustrate the specific application of the technical solutions provided in the embodiments of this application.

[0030] Referring to Figure 1, a schematic diagram of an energy storage system provided in an embodiment of the application is shown. As shown in Figure 1, the energy storage system 100 includes a controller 110, multiple battery clusters 120, and n power converters 130, wherein the power converters 130 are also referred to as PCS (Power Conversion System). The multiple battery clusters 120 are correspondingly connected to the n power converters 130. It should be understood that the corresponding connection relationship between the battery clusters 120 and the power converters 130 can be one-to-one, many-to-one, one-to-many, etc. In one possible embodiment, the battery clusters 120 and the power converters 130 are placed in the same energy storage container; in another possible embodiment, the battery clusters 120 and the power converters 130 are placed in different locations. The DC terminal of the power converter 130 is connected to the corresponding battery cluster 120, and the AC terminal of the power converter 130 is used to connect to the power grid. The controller 110 can be used to control one or more power converters 130 to input the power from the grid to the battery cluster 120 when the grid's load capacity is greater than the load's power demand, that is, when the grid has redundant power. Alternatively, when the grid's load capacity is less than the load's power demand, for example, when the load connected to the grid has a large power demand and the current grid does not have enough capacity to provide stable power to the load, the energy storage system 100 needs to supply power to the grid to improve the grid's load capacity. In this case, the controller 110 can control one or more power converters 130 to output the power from their corresponding battery clusters 120 to the grid to ensure that the grid can provide sufficient power to the load.

[0031] It should be noted that as the electricity demand of the loads connected to the grid fluctuates, the operating status of the energy storage system needs to be adjusted in a timely manner to improve the operating efficiency of the energy storage system and the stability of the power supply from the grid.

[0032] In one embodiment provided in this application, the power converter 130 used in the energy storage system 100 is a bidirectional power converter. When charging through the power grid, the power output of the power converter 130 is received by the battery cluster 110, and the power supply for the power output of the power converter 130 comes from the power grid, thereby storing excess power in the battery cluster 110 when the power grid has redundant power supply capacity. When the power grid has insufficient load capacity, the power output of the power converter 130 is received by the power grid, and the power supply for the power output of the power converter 130 comes from the battery cluster 110, thereby realizing the output of the power stored in the battery cluster 110 to the power grid.

[0033] The controller 110 is also used to perform wave blocking control on one or more power converters 130 when the load capacity of the power grid decreases by a certain amount, such as when the load capacity decreases by a first threshold. Specifically, this means controlling the switching transistors in one or more power converters 130 to stop switching, and the power converters 130 will stop power output. For instance, assuming the first threshold is set to 200kW, and the maximum operating power of a power converter 130 is 200kW, it means that when the load capacity of the power grid decreases by 200kW or more, at least one power converter 130 will stop power output. If the load capacity of the power grid decreases by 600kW, then three power converters 130 need to be controlled to stop power output.

[0034] Similarly, controller 110 is also used to perform wave blocking control on one or more power converters 130 when the increase in the load capacity of the power grid is greater than or equal to a certain amount, such as when the increase in the load capacity of the power grid is greater than or equal to a second threshold. That is, it controls one or more power converters 130 to stop power output. Specifically, assuming the second threshold is also set to 200 kW, and the maximum operating power of a power converter 130 is 200 kW, it means that when the increase in the load capacity of the power grid is greater than or equal to 200 kW, at least one power converter 130 is controlled to stop power output. If the increase in the load capacity of the power grid is 600 kW, then three power converters 130 need to be controlled to stop power output.

[0035] Referring again to Figure 2, the power conversion of the power converter 130 is achieved by the switching action of the switching transistors in the power conversion circuit 131. The switching transistors 1311, 1312, 1313, and 1314 shown in Figure 2 represent a common connection and combination method for switching transistors in an inverter bridge arm. In one embodiment provided in this application, the power conversion circuit 131 typically consists of three similar inverter bridge arms. The switching action of the transistors on these inverter bridge arms converts the AC power from the grid into DC power for output to the battery cluster 120, or converts the DC power output from the battery cluster 120 into AC power for output to the grid. The power converter 130 also includes a filter capacitor C, which, together with the filter inductor L, forms an LC filter circuit connected between the AC output terminal of the power conversion circuit 131 and the grid. This filter capacitor C can filter out the ripple current output by the power conversion circuit 131, thereby making the AC power output from the power converter 130 to the grid smoother.

[0036] It should be noted that when the power converter 130 stops outputting power, that is, when the switching transistor in the power conversion circuit 131 stops switching, the energy exchange between the battery cluster 120 and the power grid will cease. However, due to the presence of the filter capacitor C, the reactive power in the power grid will be absorbed by the power converter 130, and the amount of reactive power absorbed by the power converter 130 is positively correlated with the capacitance value of the filter capacitor C. At this time, the reactive power support in the power grid will decrease, causing the grid voltage to drop and resulting in grid voltage fluctuations. To avoid this adverse effect, the other power converters 130 in the energy storage system 100, except for the power converter 130 that has stopped outputting power, can output reactive power to compensate for the reactive power absorbed by the power converter 130 that has stopped outputting power, thereby stabilizing the reactive power support of the power grid and maintaining the stability of the grid voltage.

[0037] In one embodiment provided in this application, the controller 110 is also used to control j power converters 130 among one or more power converters 130 to stop power output, and to control k power converters 130 other than j power converters 130 to output reactive power, and the reactive power output by the k power converters 130 is greater than or equal to the reactive power absorbed by the j power converters 130 from the power grid. It can be understood that when there are n power converters 130 in the energy storage system 100, j+k≤n.

[0038] For example, to meet the grid's discharge demand, assume the energy storage system 100 has eight power converters 130, each corresponding to a battery cluster 120. Each power converter 130 has a maximum power output of 200 kW. When the grid's load capacity decreases, at least one power converter 130 must output power to transfer the released energy from the grid to the battery cluster 120. If the grid's initial redundant load capacity is 1600 kW, all eight power converters 130 will operate at full power. When the grid's load capacity drops to 600 kW, the controller 110 will control five of the power converters 130 to stop outputting power. At this time, five power converters 130 will absorb reactive power from the grid, causing a power outage. In this situation, one, two, or three of these five power converters 130 can be selected to output reactive power to compensate for the reactive power absorbed by the remaining four, three, or two power converters 130. The specific number of power converters 130 required to output reactive power can be determined based on the amount of reactive power absorbed by each power converter 130 and the reactive power output capacity of each power converter 130. As long as the total reactive power output of the energy storage system 100 to the grid is greater than or equal to the reactive power absorbed from the grid, it is sufficient.

[0039] Through the above control methods, the energy storage system 100 can ensure that it can provide power to the grid at any time, and can also maintain the stability of the grid voltage when power output stops.

[0040] Referring again to Figure 3, the power converter 130 also includes a grid-connected switch S1, which is connected between the LC filter circuit and the AC output terminal of the power converter 130. The grid-connected switch S1 controls the connection or disconnection of the power converter 130 from the power grid by turning it on or off.

[0041] In one embodiment provided in this application, the grid-connected switch S1 is a relay. When the duration for which j power converters 130 stop power output is greater than or equal to a time threshold, the controller 110 controls the relays in the j power converters 130 and the k power converters 130 to open. Specifically, when the power converters 130 stop power output, keeping the relays closed allows the power converters 130 to output power at any time when the grid's discharge demand or power demand recovers, ensuring the responsiveness of the power converters 130. However, keeping the relays closed for a long time, with the relay coils continuously energized, consumes a certain amount of energy. If the grid's load capacity remains at a low redundancy or low deficit for a long time, causing multiple power converters 130 to remain connected to the grid, the system power consumption of the energy storage system 100 will increase, resulting in unnecessary energy consumption. Therefore, when the duration for which one or more power converters 130 stop power output is greater than or equal to a time threshold, the controller 110 controls the relays in these power converters 130 to open. In the aforementioned embodiment, when some power converters 130 stop outputting power, another part of the power converters 130 provides reactive power output. When the power converters 130 that have stopped outputting power disconnect from the power grid, these power converters 130 no longer absorb reactive power from the power grid, and therefore no longer need other power converters 130 to provide reactive power compensation. Therefore, the controller 110 will also control the relays in the power converters 130 that provide reactive power compensation to disconnect.

[0042] In another embodiment provided in this application, when the duration for which j power converters stop power output is greater than or equal to a time threshold and the power loss of the energy storage system 100 exceeds a system loss threshold, the controller 110 controls the relays in the j power converters 130 and the k power converters 130 to disconnect. In this embodiment, the design of the energy storage system 100 not only considers the time of the power converters 130, but also sets a certain threshold for the system's power loss to avoid disconnecting the power converters 130 from the grid under low-loss conditions, sacrificing some of the speed at which the power converters 130 respond to grid demands. When the duration for which one or more power converters 130 stop power output is greater than or equal to the time threshold and the power loss of the energy storage system 100 is greater than or equal to the system loss threshold, the controller 110 controls the relays in these power converters 130 to disconnect, and simultaneously controls the relays in other power converters 130 that provide reactive power compensation to disconnect.

[0043] It should be noted that regardless of whether the power converter 130 disconnects from the grid due to an increase or decrease in the grid's load capacity, or whether the energy storage system 100 has not yet started supplying power to the grid or receiving redundant power from the grid, when the grid's load capacity is less than the load's power demand or greater than the load's power demand, the relays in one or more power converters 130 must first be turned on, and then these power converters 130 must be controlled to output the power from the battery cluster 120 to the grid or to output the power from the grid to the battery cluster 120.

[0044] In one embodiment provided in this application, after the controller 110 controls the relays in the j power converters 130 and the k power converters 130 to disconnect, when the load-carrying capacity of the power grid increases to a value greater than or equal to a third threshold, the controller 110 controls the relays in one or more of the j power converters 130 and the k power converters 130 to turn on, and controls one or more of the j power converters 130 and the k power converters 130 to input the electrical energy from the power grid to the corresponding power source. Battery cluster 120; or, after the controller 110 controls the relays in the j power converters 130 and the k power converters 130 to disconnect, when the load capacity of the power grid decreases to a value greater than or equal to a fourth threshold, the controller 110 controls the relays in one or more of the j power converters 130 and the k power converters 130 to conduct, and controls one or more of the j power converters 130 and the k power converters 130 to input the electrical energy of the corresponding battery cluster 120 into the power grid. For example, for simplicity, the third threshold and the fourth threshold are also taken as 200kW. In practical applications, the values ​​of the first threshold, the second threshold, the third threshold, and the fourth threshold can all be different. When the load capacity of the power grid redundancy is increased from 600kW to 1000kW, the maximum power output of each power converter 130 is 200kW. Therefore, it is necessary to select three power converters 130 that have stopped outputting power to output power. After the power converters 130 that have stopped outputting power resume outputting power, they will stop absorbing reactive power from the power grid, and the number of power converters 130 that need to output reactive power will also decrease. The controller 110 will continue to use the aforementioned control logic to retain a certain number of power converters 130 for reactive power output compensation, as long as the total reactive power output of this part of the power converters 130 is greater than or equal to the total reactive power absorbed by the other power converters 130 that have stopped outputting power.

[0045] In another embodiment provided in this application, in addition to the aforementioned power converter 130 that stops power output, there are other power converters 130 in the energy storage system 100. The controller 110 will control any one or more of the power converter 130 that stops power output and the other power converters 130 to output power to meet the load requirements of the power grid.

[0046] It should be understood that after the controller 110 receives a demand from the power grid, the process of controlling the relay in the power converter 130 to turn on and then controlling the power converter 130 to output power requires a certain amount of time. The power grid typically has certain requirements regarding the response time to these demands. For example, in energy storage frequency regulation scenarios, the power grid has higher requirements for the response time of the energy storage system 100, meaning it requires the energy storage system 100 to respond faster. In peak shaving scenarios, the power grid has lower requirements for the response time of the energy storage system 100, meaning it requires a slower response speed. Therefore, in different application scenarios, the time required for the controller 110 to turn on the relay in the power converter 130 and start controlling the power converter 130 to input power from the power grid to the battery cluster 120, or the time required for the controller 110 to turn on the relay in the power converter 130 and start controlling the power converter 130 to input power from the battery cluster 120 to the power grid, must be less than or equal to the power grid's demand response threshold.

[0047] Referring again to Figure 4, in one embodiment provided in this application, the power converter 130 also includes a controller 132. The controller 110 is the main controller, also known as a data acquisition unit, which can collect information such as grid load demand and grid voltage, and can also send operating commands to the controller 132. The controller 132, as a slave controller, is responsible for receiving commands from the controller 110, controlling the power conversion circuit 131 in the power converter 130, and controlling the on / off state of relays. By differentiating the functions of the main and slave controllers and rationally configuring the controller's computing power, the energy storage system 100 can achieve higher response efficiency.

[0048] In one embodiment provided in this application, the power converter 130 and its corresponding battery cluster 120 are placed in the same battery cabinet to form an energy storage unit, and the energy storage units are combined to form an energy storage system 100. In this way, each energy storage unit in the energy storage system 100 is an independent working unit, and each power converter 130 and its corresponding battery cluster 120 cooperate with each other to independently control the power output of the energy storage unit.

[0049] Referring again to Figure 5, a control flow of a power converter 130 provided in an embodiment of this application is shown.

[0050] When the energy storage system 100 is connected to the power grid, if the power grid has insufficient load capacity or redundant load capacity, step S101 is executed.

[0051] S101: Control one or more power converters 130 to output / input electrical energy. That is, when the power grid generates electricity demand, control one or more power converters 130 to output electrical energy from the battery cluster 120 to the power grid, and when the power grid generates discharge demand, control one or more power converters 130 to output electrical energy from the power grid to the battery cluster 120.

[0052] If the load capacity of the power grid decreases by more than or equal to the first threshold / the load capacity of the power grid increases by more than or equal to the second threshold, proceed to step S102; otherwise, continue to proceed to step S101.

[0053] S102: Control j power converters 130 to block the waveform, and control k power converters 130 to output reactive power. It should be understood that controlling j power converters 130 to block the waveform means controlling one or more of the power converters 130 in step S101 to stop power output, and controlling k power converters 130 to output reactive power means controlling the remaining k power converters 130 to output reactive power. In other words, when the load capacity of the power grid decreases to a level greater than or equal to the first threshold, one or more of the power converters 130 that output power from the power grid to the corresponding battery cluster 120 are selected to stop outputting power from the power grid to the corresponding battery cluster 120. In addition to the power converters 130 that have stopped outputting power, one or more power converters 130 are selected to output reactive power to provide reactive power compensation to the power grid. When the load capacity of the power grid increases to a level greater than or equal to the second threshold, one or more of the power converters 130 that output power from the battery cluster 120 to the power grid are selected to stop outputting power from the battery cluster 120 to the power grid. In addition to the power converters 130 that have stopped outputting power, one or more power converters 130 are selected to output reactive power to provide reactive power compensation to the power grid, thereby ensuring the stability of the power grid voltage.

[0054] When the sealing time of j power converters 130 is greater than or equal to the time threshold, execute S103.

[0055] S103: Disconnect the relays of j+k power converters 130. That is, when the time during which the power converter 130 that stopped power output in step S102 stops operating is greater than or equal to a time threshold, the relays in j and k of these power converters 130 are disconnected. In other words, when the time during which the power converter 130 that stopped power output in step S102 stops operating is greater than or equal to a time threshold, the relays in both the power converter 130 that stopped power output and the power converter 130 that provides reactive power compensation are disconnected to reduce system power loss.

[0056] In another embodiment provided in this application, the triggering condition for executing S103 is relaxed, taking into account not only time but also the current system loss. That is, when the duration for which the j power converters 130 stop power output is greater than or equal to the time threshold and the power loss of the energy storage system 100 exceeds the system loss threshold, step S103 is executed to balance the power loss of the energy storage system 100 and the response requirements of the energy storage system 100 to the grid.

[0057] Furthermore, in one embodiment provided in this application, when some power converters 130 stop outputting power due to changes in the grid's load capacity, and the grid's load capacity changes again, the aforementioned power converters 130 that stopped outputting power will be controlled to resume power output. In another embodiment provided in this application, in addition to the aforementioned power converters 130 that stopped outputting power, the energy storage system 100 also has other power converters 130. The controller 110 will control any one or more of the power converters 130 that stopped outputting power and the other power converters 130 to output power to meet the grid's load requirements.

[0058] The preferred embodiments disclosed above are merely illustrative of this application. These preferred embodiments do not exhaustively describe all details, nor do they limit the application to the specific implementations described. Clearly, many modifications and variations can be made based on the embodiments of this application. These embodiments are selected and specifically described in this application to better explain the principles and practical applications of this application, thereby enabling those skilled in the art to better understand and utilize this application. This application is limited only by the claims and their full scope and equivalents.

Claims

1. An energy storage system, characterized in that, It includes multiple battery clusters, n power converters and a main controller connected to the multiple battery clusters respectively, wherein the DC terminal of the power converter is connected to the corresponding battery cluster, and the AC terminal of the power converter is used to connect to the power grid; The main controller is used to control one or more of the power converters to input the power energy of the power grid to the corresponding battery cluster when the load capacity of the power grid is greater than the power demand of the load, or to control one or more of the power converters to output the power energy of the corresponding battery cluster to the power grid when the load capacity of the power grid is less than the power demand of the load. The main controller is further configured to, when the load capacity reduction of the power grid is greater than or equal to a first threshold or the load capacity increase of the power grid is greater than or equal to a second threshold, control j of the power converters to stop power output and control k power converters other than the j power converters to output reactive power, and the reactive power output by the k power converters is greater than or equal to the reactive power absorbed by the j power converters from the power grid, where j+k≤n; The power converter includes a filter capacitor, which is used to filter out the ripple current in the AC output of the power converter; the amount of reactive power absorbed by the j power converters from the power grid is positively correlated with the capacitance value of the filter capacitor in the j power converters.

2. The energy storage system according to claim 1, characterized in that, The power converter includes a relay, which is used to control the connection or disconnection of the power converter from the power grid by turning it on or off. The main controller is also configured to control the relays in the j power converters and the k power converters to disconnect when the duration of the power output stoppage of the j power converters is greater than or equal to a time threshold.

3. The energy storage system according to claim 1, characterized in that, The power converter includes a relay, which is used to control the connection or disconnection of the power converter from the power grid by turning it on or off. The main controller is used to control the relays in the j power converters and the k power converters to disconnect when the duration of the power output stop of the j power converters is greater than or equal to a time threshold and the power loss of the energy storage system is greater than or equal to a system loss threshold.

4. The energy storage system according to claim 2 or 3, characterized in that, The main controller is used to, after disconnecting the relays in the j and k power converters, and when the increase in the load capacity of the power grid is greater than or equal to a third threshold, control the relays in one or more of the j and k power converters to turn on, and control the one or more of the j and k power converters to input the power from the power grid to the corresponding battery cluster; or The main controller is used to control the relays in one or more of the j power converters and k power converters to turn on when the load capacity of the power grid decreases by a factor greater than or equal to a fourth threshold after the relays in the j power converters and k power converters are disconnected, and to control one or more of the j power converters and k power converters to input the electrical energy of the corresponding battery cluster into the power grid.

5. The energy storage system according to claim 4, characterized in that, The demand response time of the power grid is greater than or equal to the demand response threshold. After the main controller disconnects the relays in the j power converters and the k power converters, it controls the relays in one or more power converters to turn on and controls the one or more power converters to start inputting electrical energy from the grid to the battery cluster. The time required for this is less than or equal to the demand response threshold. or After the main controller disconnects the relays in the j power converters and the k power converters, it controls the relays in one or more power converters to turn on and controls the one or more power converters to start outputting electrical energy from the battery cluster to the power grid. The time required for this is less than or equal to the demand response threshold.

6. The energy storage system according to any one of claims 1-3 or 5, characterized in that, The power converter includes a slave controller and a power conversion circuit. The master controller is used to send control commands to the slave controller so that the slave controller controls the power conversion circuit to work or stop working in order to realize the power output of the power converter or stop the power output. The master controller is also used to send control commands to the slave controller so that the slave controller controls the relay to turn on or off.

7. The energy storage system according to claim 6, characterized in that, Each of the power converters and its corresponding battery clusters are located inside the same energy storage container.

8. A control method for an energy storage system, characterized in that, When the load capacity of the power grid is greater than the power demand of the load, control one or more power converters to input the power energy of the power grid to the corresponding battery cluster; or when the load capacity of the power grid is less than the power demand of the load, control one or more power converters to output the power energy of the corresponding battery cluster to the power grid. When the load capacity of the power grid decreases by a factor greater than or equal to a first threshold or the load capacity of the power grid increases by a factor greater than or equal to a second threshold, j of the power converters among the one or more power converters are controlled to stop power output, and k power converters other than the j power converters are controlled to output reactive power, and the reactive power output by the k power converters is greater than or equal to the reactive power absorbed by the j power converters from the power grid, j+k≤n, where n is the number of power converters in the energy storage system; The power converter includes a filter capacitor, which is used to filter out the ripple current in the AC output of the power converter; the amount of reactive power absorbed by the j power converters from the power grid is positively correlated with the capacitance value of the filter capacitor in the j power converters.

9. The energy storage system control method according to claim 8, characterized in that, When the duration of the power output stoppage of the j power converters is greater than or equal to a time threshold, the relays in the j power converters and the k power converters are controlled to disconnect. The relay is used to control the connection or disconnection of the power converter from the power grid by turning it on or off.

10. The energy storage system control method according to claim 8, characterized in that, When the duration of the power output stoppage of the j power converters is greater than or equal to a time threshold and the power loss of the energy storage system is greater than or equal to a system loss threshold, the relays in the j power converters and the k power converters are controlled to disconnect. The relay is used to control the connection or disconnection of the power converter from the power grid by turning it on or off.

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