DC bus voltage and battery cluster equalization control method of multi-level energy storage converter

Abstract

The invention discloses a DC bus voltage and battery cluster equalization control method for a multilevel energy storage converter, and the method comprises the steps: firstly, calculating the voltage offset of each DC bus, and inputting the voltage offset into a DC bus balance controller after the voltage offset is filtered; the DC bus balance controller outputs a total output current adjustment set value of all the DC / DC converters which are connected with the DC buses and are in the working state, so that the power of the DC buses is adjusted, the voltage of the DC buses is balanced, and the total output current adjustment set value is superposed on the total output current adjustment set value of all the DC / DC converters which are connected with the DC buses and are in the working state; according to the proportion of the chargeable or residual electric quantity of each battery cluster in the working state, the output current given value of the DC / DC converter connected with the battery cluster is distributed, and SOC balance between the battery clusters connected with the same direct current bus is achieved; and the DC / AC converter distributes the power of each DC bus to realize the SOC equalization of the battery clusters among the DC buses.

Description

Technical Field

[0001] This invention relates to the field of energy storage converters and power system technology, and in particular to a method for equalizing the DC bus voltage and battery clusters of a multi-level energy storage converter. Background Technology

[0002] Energy storage technology is a key support for addressing the volatility and intermittency of renewable energy sources such as wind and solar power, and ensuring the safe and stable operation of new power systems. The power conversion system (PCS), as the core interface connecting energy storage batteries and the power grid, plays a crucial role in bidirectional AC / DC power conversion and precise power control. Its performance directly affects the efficiency, reliability, and lifespan of the entire energy storage system.

[0003] To adapt to medium- and high-voltage, large-capacity applications and reduce switching losses and harmonic content, multi-level (e.g., modular multilevel, MMC) topologies for energy storage converters have become an important development direction. However, this topology includes multiple DC buses, each connected to an energy storage unit composed of multiple battery clusters. In actual operation, due to inconsistencies in initial capacity, internal resistance, and aging levels among the battery clusters, their State of Charge (SOC) will gradually differ, leading to a decrease in available system capacity, overcharging or over-discharging of some batteries, and accelerating overall degradation. Simultaneously, the SOC differences will be further reflected in the connected DC bus voltage. If left uncontrolled, this will result in DC bus voltage imbalance, jeopardizing the converter's safe and stable operation and even triggering protection shutdowns.

[0004] In existing technologies, DC bus voltage balance control and battery cluster SOC balance control are often treated as two relatively independent problems. The former focuses on maintaining the balance and stability of each DC bus voltage, while the latter is mostly adjusted at the battery management system (BMS) level or locally in the DC / DC converter. This decoupled control strategy makes it difficult to achieve global optimization at the system level, and suffers from problems such as control complexity, slow dynamic response, and low balancing efficiency. It fails to fundamentally coordinate the inherent contradiction between the voltage balance of each DC bus and the SOC balance of the battery cluster.

[0005] Therefore, in order to solve the problem that the DC bus voltage balance control and battery cluster SOC balance control are independent of each other in the existing technology and it is difficult to achieve the global optimization of the system, it is an urgent technical problem to be solved by those skilled in the art to provide a comprehensive control strategy that can unify and coordinate the DC bus voltage balance of multi-level energy storage converter and the SOC balance of battery cluster. Summary of the Invention In view of this, the present invention provides a method for equalizing the DC bus voltage and battery clusters of a multilevel energy storage converter.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A method for equalizing the DC bus voltage and battery cluster SOC of a multilevel energy storage converter includes the following steps: S1. Calculate the given value of the total output current of all DC / DC converters in operation within the multilevel energy storage converter. ; S2. Calculate the total output current setpoint of all DC / DC converters connected to each DC bus and in operation. ; S3. Obtain the real-time voltage of each DC bus of the multi-level energy storage converter. , , ..., , For multi-level energy storage converters K The real-time voltage of each DC bus, the total DC bus voltage is Calculate the average value of each DC bus voltage. ; Real-time voltage of each DC bus ( i =1, 2, ..., K Subtract the average value of each DC bus voltage. Obtain the offset of each DC bus voltage. ; S4. The voltage offset The input is fed into a filter to remove the main harmonic components, resulting in a filtered voltage offset signal. ; S5. The filtered voltage offset signal... The input is sent to the DC bus balancing controller, whose output is the setpoint for adjusting the total output current of all operating DC / DC converters connected to each DC bus. ( i =1, 2, ..., K (This is used to adjust the power of each DC bus and balance the voltage of each DC bus.) S6. Set the total output current of all operating DC / DC converters connected to the aforementioned DC buses. Adjusting the total output current setpoint of all operating DC / DC converters connected to each DC bus. By adding them together, we obtain the final total output current setpoint of all DC / DC converters in operation connected to each DC bus. ( i =1, 2, ..., K ); S7. Based on the charging and discharging operating status of the energy storage converter and the rechargeable or remaining charge of each battery cluster connected to each DC bus through the DC / DC converter, allocate the output current setpoint of each DC / DC converter connected to each DC bus. The S8 DC / AC converter dynamically allocates DC-side power based on the charging and discharging operating status of the energy storage converter and the ratio of the total rechargeable or remaining power of all battery clusters connected to each DC bus in operation, thereby achieving SOC balance among battery clusters on each DC bus. Preferably, in step S1, the specific method is as follows: when the total DC bus voltage is controlled by each connected DC / DC converter, such as... Figure 1 As shown, the given value of the total output current of all DC / DC converters. Generated by the total DC bus voltage controller, the setpoint value of the total DC bus voltage is... Subtract the actual value of the total DC bus voltage The total DC bus voltage deviation is obtained. The deviation amount The input is sent to the total DC bus voltage controller, which outputs the setpoint value of the total output current of all operating DC / DC converters within the multi-level energy storage converter. ; like Figure 3 As shown, when the total DC bus voltage is controlled by the connected DC / AC converter, the setpoint value of the active power output by the DC / AC converter is... Divide by the average voltage of all operating battery clusters The given value of the total output current of all DC / DC converters in operation within the multi-level energy storage converter is obtained. , ,in, The setpoint for the active power output of the DC / AC converter. This is the average voltage of all battery clusters in operation.

[0007] Preferably, in step S2, the specific method is as follows: The given value of the total output current of all DC / DC converters in operation within the multi-level energy storage converter is... Divide by the total number of DC buses K , K The given value is an integer greater than or equal to 2, which gives the total output current setpoint of all DC / DC converters in operation connected to each DC bus. ( i =1, 2, ..., K ), ; Alternatively, based on the charging and discharging state of the multi-level energy storage converter, and according to the proportion of the total rechargeable capacity or total remaining capacity of all operating battery clusters connected to each DC bus via the DC / DC converter, the total output current of all operating DC / DC converters connected to each DC bus can be given a setpoint. Distribute: When the energy storage converter is in the discharge state, the total output current setpoint of all DC / DC converters connected to each DC bus is distributed according to the proportion of the total remaining capacity of all battery clusters connected to each DC bus through the DC / DC converter. When the energy storage converter is in charging mode, the total output current setpoint of all operating DC / DC converters connected to each DC bus is distributed proportionally to the total rechargeable capacity of all operating battery clusters connected to each DC bus through the DC / DC converter.

[0008] Preferably, when the energy storage converter is operating in the discharge state, it is in conjunction with the first i The total output current setpoint of all operating DC / DC converters connected to the DC bus. for: ,in, In order to be with the first i The total state of charge of all battery clusters connected to the busbar that are in operation. In order to be with the first i The total capacity of all battery clusters in operation connected by the busbar. In order to be with the first i The total remaining charge of all battery clusters connected to the busbar that are in operation; When the energy storage converter is operating in the charging state, it is in relation to the first... i Total output current setpoint of all DC / DC converters connected to the DC bus for: ,in, In order to be with the first i The total rechargeable capacity of all battery clusters in operation connected to the busbar.

[0009] Preferably, in step S7, the specific method is as follows: when the energy storage converter is operating in the discharge state, the output current setpoint of each DC / DC converter connected to each DC bus in the operating state is allocated according to the proportion of the remaining power of the battery clusters connected to each DC / DC converter in the operating state; when the energy storage converter is operating in the charging state, the output current setpoint of each DC / DC converter connected to each DC bus in the operating state is allocated according to the proportion of the rechargeable amount of the battery clusters connected to each DC / DC converter in the operating state.

[0010] Preferably, when the energy storage converter is operating in the discharge state, it is in conjunction with the first i The first DC bus connected to j Output current setpoint of a DC / DC converter in operation for: ,in, In order to be with the first i The first DC bus connected to j The state of charge of a battery cluster in operation. In order to be with the first i The first DC bus connected to j The capacity of a battery cluster in operation. For connection with DC bus i The total number of all connected, active battery clusters. In order to be with the first i The first busbar connected j The remaining power of a battery cluster that is in operation; When the energy storage converter is operating in the charging state, it is in relation to the first... i The first DC bus connected to j Output current setpoint of each DC / DC converter for: ,in, In order to be with the first i The first busbar connected j The rechargeable capacity of a battery cluster in operation.

[0011] Preferably, in step S8, the specific method is as follows: controlling the power of each DC bus via a DC / AC converter, such as... Figure 7 As shown, when the energy storage converter is in the discharge operating state, the first... i The power setpoint of the DC bus is ,in, This is the power setpoint for the DC / AC converter; when the energy storage converter is in charging operation, the first... i The power setpoint of the DC bus is .

[0012] DC bus voltage of multi-level energy storage converter and SOC equalization control system of battery cluster, such as Figure 5As shown, the battery energy storage system consists of a DC / AC converter and multiple energy storage branches. The AC side of the DC / AC converter is connected to the power grid, and multiple energy storage branches are connected in parallel to the main DC bus of the DC / AC converter. Each energy storage branch consists of a filter inductor, an isolated DC / DC converter, and a battery pack. The filter inductor, the output terminal of the isolated DC / DC converter, and the battery pack are connected in series and then connected in parallel as a whole to the main DC bus of the DC / AC converter. The input terminal of each isolated DC / DC converter is connected in parallel to one of the multiple DC buses of the multi-level DC / AC converter. The input terminals of each isolated DC / DC converter are evenly connected in parallel to each DC bus to balance the input and output power of each DC bus.

[0013] The present invention achieves the following technical effects compared to the prior art: This invention enables a unified and coordinated comprehensive control strategy for achieving DC bus voltage balance and battery cluster SOC equalization in multi-level energy storage converters. Attached Figure Description Figure 1 This is a block diagram of the charging and discharging control of the multi-level energy storage converter that controls the total DC bus voltage according to the present invention; Figure 2 This is a block diagram of the charging and discharging control of the three-level energy storage converter that controls the total DC bus voltage according to the present invention; Figure 3 This is a block diagram of the charging and discharging control of the multi-level energy storage converter that controls the total DC bus voltage according to the present invention; Figure 4 This is a block diagram of the charging and discharging control of the three-level energy storage converter that controls the total DC bus voltage according to the present invention; Figure 5 This is a schematic diagram of the charging and discharging states of the multi-level energy storage converter of the present invention; Figure 6 This is a schematic diagram of the charging and discharging states of the three-level energy storage converter of the present invention; Figure 7 This is a diagram showing the SOC equalization control of battery clusters between DC buses during the charging and discharging states of this invention. Detailed Implementation The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0014] Example 1: Three-level energy storage converter discharge state DC bus voltage balance and battery cluster SOC equalization control; this control strategy targets the battery energy storage system circuit topology such as Figure 6 As shown, the battery energy storage system consists of a DC / AC converter and multiple energy storage branches. The AC side of the DC / AC converter is connected to the power grid, and multiple energy storage branches are connected in parallel to the main DC bus of the DC / AC converter. Each energy storage branch consists of a filter inductor, an isolated DC / DC converter, and a battery pack. The filter inductor, the output terminal of the isolated DC / DC converter, and the battery pack are connected in series and then connected in parallel as a whole to the main DC bus of the DC / AC converter. The input terminal of each isolated DC / DC converter is connected in parallel to one of the two DC buses of the three-level DC / AC converter. The input terminals of each isolated DC / DC converter are evenly connected in parallel to each DC bus to balance the input and output power of each DC bus. The discharge control process of its DC / DC converter is as follows: 1. Calculate the setpoint value of the total output current of all DC / DC converters in operation within the three-level energy storage converter. The method is as follows: Figure 2 As shown, when the total DC bus voltage is controlled by each of the connected and operating DC / DC converters, the setpoint value of the total DC bus voltage is... Subtract the actual value of the total DC bus voltage The total DC bus voltage deviation is obtained. The deviation amount The input is sent to the total DC bus voltage controller, which outputs the setpoint value of the total output current of all operating DC / DC converters within the three-level energy storage converter. ;like Figure 4 As shown, when the total DC bus voltage is controlled by the connected DC / AC converter, the setpoint value of the active power output by the DC / AC converter is... Divide by the average voltage of all operating battery clusters The given value of the total output current of all DC / DC converters in operation within the three-level energy storage converter is obtained. , ,in, The setpoint for the active power output of the DC / AC converter. The average voltage of all operating battery clusters is calculated; then, the total output current setpoint of all operating DC / DC converters connected to each DC bus is calculated. The setpoint value of the total output current of all DC / DC converters in operation within the three-level energy storage converter. Divide by the total number of DC buses K=2, thus obtaining the total output current setpoint for all DC / DC converters in operation connected to each DC bus. ( i =1,2), Alternatively, the total output current of all operating DC / DC converters connected to each DC bus can be set according to the proportion of the total remaining charge of all battery clusters connected to each DC bus. The total output current setpoint of all operating DC / DC converters connected to each DC bus is allocated proportionally to the total remaining capacity of all operating battery clusters connected to each DC bus via the DC / DC converters. The total output current setpoint of all operating DC / DC converters connected to the first DC bus is... for: ,in, The total state of charge of all battery clusters connected to the first busbar that are in operation. This represents the total capacity of all battery clusters connected to the first busbar that are in operation. This represents the total remaining charge of all battery clusters connected to the first busbar that are in operation. The total state of charge of all battery clusters connected to the second busbar that are in operation. The total capacity of all battery clusters in operation connected to the second busbar. The total remaining charge of all battery clusters connected to the second bus and in operation; the total output current setpoint of all DC / DC converters connected to the second DC bus and in operation. for: Then, the real-time voltage of each DC bus is... ( i =1,2) minus the average value of each DC bus voltage Obtain the offset of each DC bus voltage. ; this voltage offset The input is fed to a notch filter whose center frequency is a third harmonic of the grid fundamental frequency. The main harmonic components contained in the filter are filtered out to obtain the filtered voltage offset signal. ; Filtered voltage offset signal The input is sent to the DC bus balancing controller, whose output is the setpoint for adjusting the total output current of all DC / DC converters connected to each DC bus. It is used to adjust the power of each DC bus and balance the voltage of each DC bus; and to set the total output current of all DC / DC converters connected to each DC bus in operation. Adjusting the total output current setpoint of all operating DC / DC converters connected to each DC bus. By adding them together, we obtain the final total output current setpoint of all DC / DC converters connected to each DC bus and in operation. ( i =1,2); 2. Based on the discharge operating state of the energy storage converter and the remaining charge of each battery cluster connected to each DC bus via the DC / DC converter, the output current setpoint of each operating DC / DC converter connected to each DC bus is allocated. The output current setpoint of each operating DC / DC converter connected to each DC bus is allocated according to the proportion of the remaining charge of each battery cluster connected to the first DC bus. j Output current setpoint of a DC / DC converter in operation for: ,in, For the first DC bus connected to the first j The state of charge of a battery cluster in operation. For the first DC bus connected to the first j The capacity of a battery cluster in operation. This represents the total number of all battery clusters in operation connected to DC bus 1. For the first busbar connected to the first busbar j The remaining charge of the battery cluster that is in operation; the battery cluster connected to the second DC bus. j Output current setpoint of a DC / DC converter in operation for: ,in, For the first DC bus connected to the second DC bus j The state of charge of a battery cluster in operation. For the first DC bus connected to the second DC bus j The capacity of a battery cluster in operation. This represents the total number of all battery clusters connected to DC bus 2 that are in operation. For the first bus connected to the second bus j The remaining power of each battery cluster in operation; the strategy achieves SOC balancing among all battery clusters connected to the same DC bus; Its DC / AC discharge power control method is as follows: based on the discharge operating state of the energy storage converter and the proportion of the total remaining capacity of all battery clusters connected to each DC bus through the DC / AC converter, the power of each DC bus is controlled through the DC / AC converter, such as... Figure 7 As shown, the discharge power setpoint for the first DC bus is... ,in, The discharge power setpoint for the DC / AC converter; the discharge power setpoint for the second DC bus is... The strategy described above achieves SOC balancing among battery clusters on each DC bus.

[0015] Example 2: Three-level energy storage converter DC bus voltage balance and battery cluster SOC equalization control during charging; this control strategy targets the battery energy storage system circuit topology such as... Figure 6 As shown, the battery energy storage system consists of a DC / AC converter and multiple energy storage branches. The AC side of the DC / AC converter is connected to the power grid, and multiple energy storage branches are connected in parallel to the main DC bus of the DC / AC converter. Each energy storage branch consists of a filter inductor, an isolated DC / DC converter, and a battery pack. The filter inductor, the output terminal of the isolated DC / DC converter, and the battery pack are connected in series and then connected in parallel as a whole to the main DC bus of the DC / AC converter. The input terminal of each isolated DC / DC converter is connected in parallel to one of the two DC buses of the three-level DC / AC converter. The input terminals of each isolated DC / DC converter are evenly connected in parallel to each DC bus to balance the input and output power of each DC bus. The charging control process of its DC / DC converter is as follows: 1. Calculate the setpoint value of the total output current of all DC / DC converters in the three-level energy storage converter. The method is as follows: Figure 2 As shown, when the total DC bus voltage is controlled by each of the connected and operating DC / DC converters, the setpoint value of the total DC bus voltage is... Subtract the actual value of the total DC bus voltage The total DC bus voltage deviation is obtained. The deviation amount The input is sent to the total DC bus voltage controller, which outputs the setpoint value of the total output current of all operating DC / DC converters within the three-level energy storage converter. ;like Figure 4 As shown, when the total DC bus voltage is controlled by the connected DC / AC converter, the setpoint value of the active power output by the DC / AC converter is... Divide by the average voltage of all operating battery clusters The given value of the total output current of all DC / DC converters in operation within the three-level energy storage converter is obtained. , ,in The setpoint for the active power output of the DC / AC converter. The average voltage of all operating battery clusters is calculated; then, the total output current setpoint of all operating DC / DC converters connected to each DC bus is calculated. The setpoint value of the total output current of all DC / DC converters in operation within the three-level energy storage converter. Divide by the total number of DC buses K =2, thus obtaining the total output current setpoint for all DC / DC converters in operation connected to each DC bus. ( i =1,2), Alternatively, the total output current of all operating DC / DC converters connected to each DC bus can be set according to the proportion of the total rechargeable capacity of all battery clusters connected to each DC bus. The total output current setpoint of all DC / DC converters connected to each DC bus and in operation is allocated proportionally to the total rechargeable capacity of all battery clusters connected to each DC bus via the DC / DC converters. The total output current setpoint of all DC / DC converters connected to the first DC bus is... for: ,in, The total state of charge of all battery clusters connected to the first busbar that are in operation. The total capacity of all battery clusters connected to the first busbar. The total rechargeable capacity of all battery clusters connected to the first busbar. The total state of charge of all battery clusters connected to the second busbar. The total capacity of all battery clusters in operation connected to the second busbar. The total rechargeable capacity of all battery clusters in operation connected to the second bus; the total output current setpoint of all DC / DC converters connected to the second DC bus. for: Then, the real-time voltage of each DC bus is... ( i =1,2) minus the average value of each DC bus voltage Obtain the offset of each DC bus voltage. ; this voltage offset The input is fed to a notch filter whose center frequency is a third harmonic of the grid fundamental frequency. The main harmonic components contained in the filter are filtered out to obtain the filtered voltage offset signal. ; Filtered voltage offset signal The input is sent to the DC bus balancing controller, whose output is the setpoint for adjusting the total output current of all operating DC / DC converters connected to each DC bus. It is used to adjust the power of each DC bus and balance the voltage of each DC bus; and to set the total output current of all DC / DC converters connected to each DC bus in operation. Adjusting the total output current setpoint of all operating DC / DC converters connected to each DC bus. By adding them together, we obtain the final total output current setpoint of all DC / DC converters connected to each DC bus and in operation. ( i =1,2); 2. Based on the charging operation status of the energy storage converter and the rechargeable capacity of each battery cluster connected to each DC bus via the DC / DC converter, the output current setpoint of each DC / DC converter connected to each DC bus is allocated. The output current setpoint of each DC / DC converter connected to each DC bus is allocated proportionally to the rechargeable capacity of each battery cluster connected to each DC / DC converter. j Output current setpoint of a DC / DC converter in operation for: ,in, For the first DC bus connected to the first j The state of charge of a battery cluster in operation. For the first DC bus connected to the first j The capacity of a battery cluster in operation. This represents the total number of all battery clusters in operation connected to DC bus 1. For the first busbar connected to the first busbar j The rechargeable capacity of the battery cluster in operation; the first one connected to the second DC bus. j Output current setpoint of a DC / DC converter in operation for: ,in, For the first DC bus connected to the second DC bus j The state of charge of a battery cluster in operation. For the first DC bus connected to the second DC bus j The capacity of a battery cluster in operation. This represents the total number of all battery clusters connected to DC bus 2 that are in operation. For the first bus connected to the second busj The rechargeable capacity of a battery cluster in operation; the strategy achieves SOC balancing among all battery clusters connected to the same DC bus. Its DC / AC charging power control method is as follows: based on the charging operating state of the energy storage converter and the proportion of the total rechargeable capacity of all battery clusters in operation connected to each DC bus through the DC / AC converter, the power of each DC bus is controlled through the DC / AC converter, such as... Figure 7 As shown, the charging power setpoint for the first DC bus is... ,in, The charging power setpoint for the DC / AC converter; the charging power setpoint for the second DC bus is... The strategy described above achieves SOC balancing among battery clusters on each DC bus.

[0016] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the technical scope of the present invention. Therefore, any minor modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A method for equalizing the DC bus voltage and battery clusters of a multi-level energy storage converter, characterized in that, Includes the following steps: S1. Calculate the given value of the total output current of all DC / DC converters in operation within the multilevel energy storage converter. ; S2. Calculate the total output current setpoint of all DC / DC converters connected to each DC bus and in operation. ; S3. Obtain the real-time voltage of each DC bus of the multi-level energy storage converter. , , ..., , For multi-level energy storage converters K The real-time voltage of each DC bus, the total DC bus voltage is Calculate the average value of each DC bus voltage. ; Real-time voltage of each DC bus ( i =1, 2, ..., K Subtract the average value of each DC bus voltage. Obtain the offset of each DC bus voltage. ; S4. The voltage offset The input is fed into a filter to remove the main harmonic components, resulting in a filtered voltage offset signal. ; S5. The filtered voltage offset signal... The input is sent to the DC bus balancing controller, whose output is the setpoint for adjusting the total output current of all operating DC / DC converters connected to each DC bus. ( i =1, 2, ..., K (This is used to adjust the power of each DC bus and balance the voltage of each DC bus.) S6. Set the total output current of all operating DC / DC converters connected to the aforementioned DC buses. Adjusting the total output current setpoint of all operating DC / DC converters connected to each DC bus. By adding them together, we obtain the final total output current setpoint of all DC / DC converters in operation connected to each DC bus. ( i =1, 2, ..., K ); S7. Based on the charging and discharging operating status of the energy storage converter and the proportion of the rechargeable or remaining charge of each battery cluster connected to each DC bus through the DC / DC converter, the output current setpoint of each DC / DC converter connected to each DC bus is allocated. S8. The DC / AC converter dynamically allocates power to each DC bus based on the charging and discharging status of the energy storage converter and the proportion of the total rechargeable or remaining power of all battery clusters connected to each DC bus through the DC / AC converter, thereby achieving SOC balance among battery clusters on each DC bus.

2. The DC bus voltage and battery cluster balancing control method for a multi-level energy storage converter according to claim 1, characterized in that, In step S1, the specific method is as follows: when the total DC bus voltage is controlled by each DC / DC converter connected to it, the given value of the total output current of all DC / DC converters is... Generated by the total DC bus voltage controller, the setpoint value of the total DC bus voltage is... Subtract the actual value of the total DC bus voltage The total DC bus voltage deviation is obtained. The deviation amount The input is sent to the total DC bus voltage controller, which outputs the setpoint value of the total output current of all operating DC / DC converters within the multi-level energy storage converter. ; When the total DC bus voltage is controlled by the connected DC / AC converter, the setpoint value of the active power output of the DC / AC converter is given. Divide by the average voltage of all operating battery clusters The given value of the total output current of all DC / DC converters in operation within the multi-level energy storage converter is obtained. , ,in, The setpoint for the active power output of the DC / AC converter. This is the average voltage of all battery clusters in operation.

3. The DC bus voltage and battery cluster balancing control method for the multi-level energy storage converter according to claim 1, characterized in that, In step S2, the specific method is as follows: The given value of the total output current of all DC / DC converters in operation within the multi-level energy storage converter is... Divide by the total number of DC buses K , K The given value is an integer greater than or equal to 2, which gives the total output current setpoint of all DC / DC converters in operation connected to each DC bus. ( i =1, 2, ..., K), ; Alternatively, based on the charging and discharging state of the multi-level energy storage converter, and according to the proportion of the total rechargeable capacity or total remaining capacity of all operating battery clusters connected to each DC bus via the DC / DC converter, the total output current of all operating DC / DC converters connected to each DC bus can be given a setpoint. Distribute: When the energy storage converter is in the discharge state, the total output current setpoint of all DC / DC converters connected to each DC bus is distributed according to the proportion of the total remaining capacity of all battery clusters connected to each DC bus through the DC / DC converter. When the energy storage converter is in charging mode, the total output current setpoint of all operating DC / DC converters connected to each DC bus is distributed proportionally to the total rechargeable capacity of all operating battery clusters connected to each DC bus through the DC / DC converter.

4. The DC bus voltage and battery cluster balancing control method for a multi-level energy storage converter according to claim 2, characterized in that, When the energy storage converter is operating in the discharge state, it is in relation to the first i The total output current setpoint of all operating DC / DC converters connected to the DC bus. for: ,in, In order to be with the first i The total state of charge of all battery clusters connected to the busbar that are in operation. In order to be with the first i The total capacity of all battery clusters in operation connected by the busbar. In order to be with the first i The total remaining charge of all battery clusters connected to the busbar that are in operation; When the energy storage converter is operating in the charging state, it is in relation to the first... i Total output current setpoint of all DC / DC converters connected to the DC bus for: ,in, In order to be with the first i The total rechargeable capacity of all battery clusters in operation connected to the busbar.

5. The DC bus voltage and battery cluster balancing control method for a multi-level energy storage converter according to claim 1, characterized in that, In step S7, the specific method is as follows: when the energy storage converter is operating in the discharge state, the output current setpoint of each DC / DC converter connected to each DC bus in the operating state is allocated according to the proportion of the remaining power of the battery clusters connected to each DC / DC converter in the operating state; when the energy storage converter is operating in the charging state, the output current setpoint of each DC / DC converter connected to each DC bus in the operating state is allocated according to the proportion of the rechargeable amount of the battery clusters connected to each DC / DC converter in the operating state.

6. The DC bus voltage and battery cluster balancing control method for a multi-level energy storage converter according to claim 5, characterized in that, When the energy storage converter is in the discharge operating state, it is in relation to the first i The first DC bus connected to j Output current setpoint of a DC / DC converter in operation for: ,in, In order to be with the first i The first DC bus connected to j The state of charge of a battery cluster in operation. In order to be with the first i The first DC bus connected to j The capacity of a battery cluster in operation. For connection with DC bus i The total number of all connected, active battery clusters. In order to be with the first i The first busbar connected j The remaining power of a battery cluster that is in operation; When the energy storage converter is in charging operation, it is in conjunction with the first i The first DC bus connected to j Output current setpoint of each DC / DC converter for: ,in, In order to be with the first i The first busbar connected j The rechargeable capacity of a battery cluster in operation.

7. The DC bus voltage and battery cluster balancing control method for a multi-level energy storage converter according to claim 1, characterized in that, In step S8, the specific method is as follows: The power of each DC bus is controlled by the DC / AC converter. When the energy storage converter is in the discharge operating state, the first... i The power setpoint of the DC bus is ,in, This is the power setpoint for the DC / AC converter; when the energy storage converter is in charging operation, the first... i The power setpoint of the DC bus is .

8. A DC bus voltage and battery cluster balancing control system for a multi-level energy storage converter, characterized in that, The battery energy storage system consists of a DC / AC converter and multiple energy storage branches. The AC side of the DC / AC converter is connected to the power grid, and multiple energy storage branches are connected in parallel to the main DC bus of the DC / AC converter. Each energy storage branch consists of a filter inductor, an isolated DC / DC converter, and a battery pack. The filter inductor, the output terminal of the isolated DC / DC converter, and the battery pack are connected in series and then connected in parallel as a whole to the main DC bus of the DC / AC converter. The input terminal of each isolated DC / DC converter is connected in parallel to one of the multiple DC buses of the multi-level DC / AC converter. The input terminals of each isolated DC / DC converter are evenly connected in parallel to each DC bus to balance the input and output power of each DC bus.

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