Method for maintaining direct current balance of high-voltage cascade energy storage system by using grounding switch backflow

Abstract

The invention discloses a method for maintaining DC equalization of a high-voltage cascade energy storage system by using grounding switch backflow, and the method comprises the steps: collecting the data of a battery cell in a battery cluster in real time through a battery management system, carrying out the statistics of the voltage and current data of a battery cluster end, and uploading the data to a system main controller for calculation; the system main controller judges the state of each phase when the current is balanced according to the current battery data statistical state of each phase, and controls the on-off state of the MOSFET in each power module in the corresponding state; after the total charging or discharging current of each phase of battery cluster is determined, the cluster controller of each battery cluster controls the duty ratio of the MOSFET according to the current state of each battery PACK; and after the battery PACK receives the duty ratio parameter issued by the cluster controller, the output waveform of the MOSFET is modulated, and finally multi-level current equalization is realized. According to the invention, the duty ratio of the power module is controlled by applying a strategy, and the magnitude of equalization current between PACKs is controlled, so that multi-stage SOC equalization of the PACKs, clusters, bridge arms and phases is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of battery energy storage, and in particular to a method for maintaining DC balance of a high-voltage cascade energy storage system by utilizing backflow from a grounding switch. Background Art

[0002] Compared to multi-stage boosted parallel grid-connected energy storage systems, cascade battery energy storage systems use an H-bridge cascade topology to connect distributed energy storage packs in a cascaded manner. The module control board can achieve conversion between AC and DC. Therefore, the high-voltage cascade battery energy storage system can be directly connected to the 6-35kV grid without a transformer. It has significant advantages such as direct connection to the 6-35kV AC grid, no need for an AC transformer, independent control of battery clusters, high energy conversion efficiency, and excellent safety.

[0003] During grid-connected operation, the system forms a loop with the grid, so that the charge and discharge current of the PACK can be controlled by flexibly adjusting the duty cycle of the power switch of each power module in the power operation state. The battery balance between the PACKs is achieved through the current difference between different PACKs, and further current balance between battery clusters and phases is achieved. During maintenance, in order to achieve balance, a current loop needs to be built. The current loop is formed through the grid to perform current balancing. There is a coupling relationship between the transmission power and output voltage of each DC converter. It is necessary to take into account the independent power and voltage coordinated control of the battery modules and the system efficiency. There are requirements for the power input and the size of the balancing current of the system, which can easily cause fluctuations in the AC grid and pose certain risks to the system.

[0004] The reference paper "Cascaded Energy Storage Battery Pack Balancer and Its Self-Balancing Strategy" proposes a cascaded battery pack balancer. This balancer uses a simple balancing circuit module consisting of a switching tube and a balancing inductor, which can be connected to a common balancing capacitor to achieve seamless bidirectional energy flow. This technology is applied to balancing between battery cells, not a system-level balancing solution. Patent application number CN202311474645.4 describes a method for SOC balancing of MMC-type energy storage systems. This method calculates the SOC imbalance between phases, bridge arms, and submodules, and then calculates the duty cycle of the switching devices in the bidirectional DC / DC converter to achieve balancing.

[0005] The disadvantages of the prior art are as follows:

[0006] (1) Existing technologies all use SOC balancing methods during normal system operation, without considering whether the system is connected to the grid or supplies power to the load during maintenance. (2) When the conditions for grid connection are not met, the circuit topology cannot form a current loop and the relevant balancing strategy cannot be applied. (3) Whether the balancing strategy has an impact on the AC / DC power grid is not considered and corresponding preventive measures are not designed.

[0007] Therefore, it is an urgent problem for those skilled in the art to propose a method for maintaining DC balance of a high-voltage cascade energy storage system by utilizing the backflow of a grounding switch to solve the difficulties existing in the prior art. Summary of the Invention

[0008] The purpose of the present invention is to provide a method for maintaining DC balance in a high-voltage cascade energy storage system by utilizing grounding switch backflow. The method applies a strategy to control the duty cycle of the power module and the magnitude of the balancing current between the packs, thereby achieving multi-level SOC balance of the packs, clusters, bridge arms, and phases.

[0009] To achieve the above object, the present invention provides the following solutions:

[0010] A method for maintaining DC balancing of a high-voltage cascade energy storage system using grounding switch backflow. The high-voltage cascade energy storage system includes a three-phase AC power grid, a grounding switch, multiple energy units, and a battery management system. The energy units include power modules and battery packs. The multiple energy units are cascaded to form a battery cluster. Each phase of the three-phase AC power grid is connected to the battery cluster via the grounding switch. When not connected to the grid, the grounding switch is short-circuited on the AC side of the three-phase AC power grid to form an AC / DC circuit with the high-voltage cascade energy storage system, thereby achieving decoupling from the power grid. The DC balancing method includes:

[0011] S1. The battery management system collects data on the battery cells in the battery cluster in real time, collects data on the voltage and current of the battery cluster, and uploads the data to the cluster controller for aggregation, and then uploads it to the system main controller for calculation;

[0012] S2. The system main controller determines the current balancing state of each phase based on the current statistical status of each phase battery data, and controls the switching state of the MOSFET in each power module under the corresponding state;

[0013] S3. After determining the total charge or discharge current of each phase battery cluster, the cluster controller of each battery cluster controls the duty cycle of the MOSFET according to the current state of each battery pack;

[0014] S4. After receiving the duty cycle parameters sent by the cluster controller, the battery PACK modulates the output waveform of the MOSFET according to the duty cycle parameters, ultimately achieving multi-level power balancing.

[0015] Preferably, the cell data collected by the battery management system in S1 includes voltage, temperature, internal resistance, SOC, SOH, and equilibrium state.

[0016] Preferably, the DC balancing method specifically includes:

[0017] During operation, the AC voltage of each phase is v sa , vsb and v sc , the AC current of each phase i a 、i b 、i c The power flows through each power module respectively, and the MOSFET of the power module realizes rectification and charges the battery pack; the duty cycle of the MOSFET is controlled to control the current of the battery pack. When the SOC value of a battery pack is higher than the SOC value of other battery packs, the duty cycle of the MOSFET is reduced to reduce the current of the battery pack, making the battery pack charge slower than other battery packs; conversely, when discharging, the power module inverts the DC power of the battery pack into AC power and provides it to the grid. By controlling the duty cycle of the MOSFET, the discharge speed of the battery pack is adjusted, thereby forming a gap with the discharge speed of other battery packs.

[0018] Preferably, the system main controller in S2 determines the state of each phase during current balancing according to the current statistical state of each phase battery data, and controls the switching state of the MOSFET in each battery PACK power module under the corresponding state, specifically including:

[0019] The system main controller determines the state of each phase during current balancing based on the current SOC statistical status of each phase, including the charging state and the discharging state, and controls the switching state of the MOSFET in each power module under the corresponding state based on the conclusion.

[0020] Preferably, after determining the total charge or discharge current of each phase battery cluster in S3, the cluster controller of each battery cluster controls the duty cycle of the MOSFET according to the current state of each battery PACK, specifically including:

[0021] When the current phase battery cluster is in the charging state, the battery management system collects the total voltage of each power module and first sorts the SOC of each battery pack in the battery cluster. The balanced target SOC is calculated by combining the total voltage and the charging current configured for the battery cluster. The duty cycle coefficient is calculated according to the battery pack balancing order. The battery pack balancing order is that the battery pack farther away from the balanced target SOC value has a higher priority, while the battery pack closer to the balanced target SOC value has a lower priority. The MOSFET duty cycle corresponding to the high-priority battery pack is relatively higher, and the battery pack charges faster. Conversely, the duty cycle is lower, and the charging speed is slower. At the same time, the charging current of the battery cluster is adjusted in real time.

[0022] Preferably, the duty cycle coefficient is calculated according to the battery PACK balancing order. The battery PACK balancing order is that the battery PACK farther away from the balancing target SOC value has a higher priority, while the battery PACK closer to the balancing target SOC value has a lower priority. The specific calculation process is as follows:

[0023] First, calculate the SOC value of each battery PACK in the current cluster i , calculate the SOC regulation target SOC given by the battery cluster 额 The difference between the SOC of each battery pack and the maximum SOC of the difference is obtained diffmax , namely SOC diffmax =max(SOC 额 -SOC i ), where i is an integer from 1 to n; the calculation result is SOC diffmax The battery cluster is operated at full power, that is, the duty cycle is 100%, and the balancing time of the entire cluster is calculated, that is, T balance =SOC diffmax / I max , where I max It is the current when the battery cluster is running at full power; all battery packs in the current cluster are based on T balance The target time is used to obtain the charging power I of each PACK. i =SOC i / T balance ; You can get the duty cycle of each battery PACK DUTY i =I i / I max .

[0024] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0025] This invention proposes a solution for achieving balancing by using a short-circuited grounding switch to form a current loop. By designing circuits based on short-circuiting grounding switches for both a high-voltage cascade battery energy storage system and an MMC battery energy storage system, a potential difference can be formed between battery packs, between bridge arms, or between phases. This controls the opening and closing of power modules to form a current loop. By applying a strategy to control the duty cycle of the power modules and the magnitude of the balancing current between packs, this approach achieves multi-level SOC balancing across packs, clusters, bridge arms, and phases. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0027] Figure 1 This is a balancing circuit diagram of a high-voltage cascade energy storage system according to the present invention;

[0028] Figure 2This is a flow chart of the balanced control of the high-voltage cascade energy storage system of the present invention;

[0029] Figure 3 This is the balancing circuit diagram of the MMC type energy storage system of the present invention. DETAILED DESCRIPTION

[0030] 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 ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0031] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0032] The present invention provides a method for maintaining DC balance of a high-voltage cascade energy storage system by using a grounding switch backflow. The high-voltage cascade energy storage system includes a three-phase AC power grid, a grounding switch, several energy units, and a battery management system. Figure 1 As shown in Figure 1, the energy unit includes a power module and a battery PACK. Several energy units are cascaded to form a battery cluster. Each phase of the three-phase AC grid is connected to the battery cluster via a grounding switch. When not connected to the grid, the grounding switch is short-circuited on the AC side of the three-phase AC grid to form an AC / DC loop with the high-voltage cascade energy storage system to achieve decoupling from the grid. The DC balancing method is as follows: Figure 2 Shown include:

[0033] S1. The battery management system collects data on the battery cells in the battery cluster in real time, collects data on the voltage and current of the battery cluster, and uploads the data to the cluster controller for aggregation, and then uploads it to the system main controller for calculation;

[0034] S2. The system main controller determines the current balancing state of each phase based on the current statistical status of each phase battery data, and controls the switching state of the MOSFET in each power module under the corresponding state;

[0035] S3. After determining the total charge or discharge current of each phase battery cluster, the cluster controller of each battery cluster controls the duty cycle of the MOSFET according to the current state of each battery pack;

[0036] S4. After receiving the duty cycle parameters sent by the cluster controller, the battery PACK modulates the output waveform of the MOSFET according to the duty cycle parameters, ultimately achieving multi-level power balancing.

[0037] Specifically, the balancing circuit when the grounding switch of the high-voltage cascade energy storage system is short-circuited is as follows: Figure 1 As shown. S1-S4 are fully controlled components of the power module, typically MOSFETs. When the system is not connected to the grid, the SOC of the battery clusters in each phase varies. Assuming that the total voltage of phase B is higher than that of phases A and C, when the ground switch is shorted, a potential difference is generated from phase B to phases A and C. At this time, the MOSFETs of each pack power module are controlled to be on and off. For example, in phase C pack 1 in the figure, S1 and S4 are turned on, and S2 and S3 are turned off, forming a balancing current loop as indicated by the red arrow in the figure. In this balancing loop, the operating state of each battery pack is similar to that of the system when it is connected to the grid or when it is supplying power to the load.

[0038] When balancing the PACK, it is necessary to obey the commands of the controllers at various levels, such as the system, each phase, each submodule power module, etc. The BMS (Battery Management System) monitors the data of the single battery in each PACK in real time. The monitoring data mainly includes the calculation of the current temperature, voltage, current, internal resistance and other data, as well as the battery modeling and SOC estimation, which are used as the basis for regulation. The specific control flow chart is as follows Figure 2 shown.

[0039] Furthermore, the cell data collected by the battery management system in S1 includes voltage, temperature, internal resistance, SOC, SOH, and equilibrium status.

[0040] Furthermore, the DC balancing method specifically includes:

[0041] During operation, the AC voltage of each phase is v sa , v sb and v sc , the AC current of each phase i a 、i b 、i c The power flows through each power module respectively, and the MOSFET of the power module realizes rectification and charges the battery pack; the duty cycle of the MOSFET is controlled to control the current of the battery pack. When the SOC value of a battery pack is higher than the SOC value of other battery packs, the duty cycle of the MOSFET is reduced to reduce the current of the battery pack, so that the battery pack charges slower than other battery packs, thereby achieving balance between different battery packs; conversely, when discharging, the power module inverts the DC power of the battery pack into AC power and provides it to the grid. By controlling the duty cycle of the MOSFET, the discharge speed of the battery pack is adjusted, thereby forming a gap with the discharge speed of other battery packs and achieving balance between the battery packs.

[0042] Furthermore, the system main controller in S2 determines the current balancing state of each phase based on the current statistical state of each phase battery data, and controls the switching state of the MOSFET in each battery pack power module under the corresponding state. Specifically, the following steps are performed:

[0043] The system main controller determines the state of each phase during current balancing based on the current SOC statistical status of each phase, including the charging state and the discharging state, and controls the switching state of the MOSFET in each power module under the corresponding state based on the conclusion.

[0044] Specifically, Figure 1 For example, if the total voltage of phase B is higher than that of phase A and phase A is higher than that of phase C, then phase B needs to be discharged as a whole and phases A and C need to be charged. The specific balancing current size, i.e., the charge and discharge power, is achieved by modulating the control waveform of the power module controller of each phase and controlling the duty cycle of the switch tube. Figure 1 In this example, each cluster in each phase needs to send a calculated charge and discharge current configuration instruction, which is further converted by each cluster into a duty cycle control signal and sent to each battery pack controller. Assuming that the duty cycle of phase B is 100%, that is, fully engaged, and phases A and C are in the charging state, then the duty cycle of phase A will be smaller than that of phase C, that is, the charging power of phase A is smaller than that of phase C. In this way, the charging speed of phase C can be faster than that of phase A, and the discharge speed of phase B is higher than that of phases A and C, thereby achieving rapid balancing of the three phases. In addition, the duty cycle is not a constant value. During the balancing process, the BMS continues to collect various data from all single cells, and the stack controller continuously performs corresponding PI adjustments to the charge and discharge currents of each phase and cluster.

[0045] Furthermore, after determining the total charge or discharge current of each phase battery cluster in S3, the cluster controller of each battery cluster controls the duty cycle of the MOSFET according to the current state of each battery pack, specifically including:

[0046] When the current phase battery cluster is in the charging state, the battery management system collects the total voltage of each power module and first sorts the SOC of each battery pack in the battery cluster. The balanced target SOC is calculated by combining the total voltage and the charging current configured for the battery cluster. The duty cycle coefficient is calculated according to the battery pack balancing order. The battery pack balancing order is that the battery pack farther away from the balanced target SOC value has a higher priority, while the battery pack closer to the balanced target SOC value has a lower priority. The MOSFET duty cycle corresponding to the high-priority battery pack is relatively higher, and the battery pack charges faster. Conversely, the duty cycle is lower, and the charging speed is slower. At the same time, the charging current of the battery cluster is adjusted in real time.

[0047] The duty cycle coefficient is calculated according to the battery pack balancing order. The battery packs farther away from the balancing target SOC value have higher priority, while those closer to the balancing target SOC value have lower priority. The specific calculation process is as follows:

[0048] First, calculate the SOC value of each battery PACK in the current cluster i , calculate the SOC regulation target SOC given by the battery cluster 额 The difference between the SOC of each battery pack and the maximum SOC of the difference is obtained diffmax , namely SOC diffmax =max(SOC 额 -SOC i ), where i is an integer from 1 to n; the calculation result is SOC diffmax The battery cluster is operated at full power, that is, the duty cycle is 100%, and the balancing time of the entire cluster is calculated, that is, T balance =SOC diffmax / I max , where the current value when the battery cluster is running at full power is I max Depends on the electrical design, no additional discussion; all battery packs in the current cluster are based on T balance The target time is used to obtain the charging power I of each PACK. i =SOC i / T balance ; You can get the duty cycle of each battery PACK DUTY i =I i / I max .

[0049] The balancing circuit of the MMC energy storage system is as follows: Figure 3 As shown, unlike the high-voltage cascade system, the MMC system's short-circuiting grounding switch method requires short-circuiting the upper and lower bridge arms of the three phases separately. This is to avoid the difficulty of forming an effective balancing circuit when the voltage difference between the battery clusters of the upper and lower bridge arms is in opposite directions. For example, when the voltage of the upper bridge arm of phase B is higher than that of the upper bridge arm of phase A, and the voltage of the lower bridge arm of phase B is lower than that of the lower bridge arm of phase A, short-circuiting on only one common DC bus makes it difficult to form a high voltage due to the opposite directions of the voltage on the common DC bus, and it is impossible to form a high balancing current, which is not conducive to balancing maintenance. In addition, the upper and lower bridge arms of the equipment themselves are located in different containers, so short-circuiting the grounding switches separately has the advantages of simple maintenance and high safety factor.

[0050] Its specific balancing principle is similar to that of the high-voltage cascade type, such as Figure 3As shown, assuming that the voltage of phase B is higher than that of phase A and phase C, the self-balancing of the three-phase upper bridge arm PACK can be achieved by controlling the duty cycle of the control module control board, and its current is shown by the red arrow; the balancing principle of the lower bridge arm is similar to that of the upper bridge arm. Assuming that the voltage of phase B is higher than that of phase A and phase C, the self-balancing of the three-phase lower bridge arm PACK can be achieved by controlling the duty cycle of the control module control board, and its current is shown by the corresponding red arrow.

[0051] The present invention is based on the basic circuit topology of a high-voltage cascade battery energy storage system and an MMC-type battery energy storage system, and analyzes its implementation method during balancing. It is found that the two systems can form a current loop through the grid or load when in grid-connected or off-grid operation, and achieve balancing of all levels of the system during dynamic operation. However, if balancing is performed in grid connection during system maintenance, it is easy to cause disturbances in the AC and DC grids, which poses certain operational risks to the grid and the system; and when the system is off-grid and in a no-load state, and maintenance is required to achieve balancing, it is impossible to form a balancing loop, resulting in balancing. The only way to achieve balancing between PACKs and between phases is to add an additional active balancing circuit. Therefore, in response to such problems, the present invention proposes to form a balancing current loop based on the short-circuiting of the grounding switch.

[0052] The present invention is a method for achieving DC balancing during maintenance in a high-voltage cascade energy storage system. This method is applicable to high-voltage cascade battery energy storage systems or MMC-based cascade battery energy storage systems. These two systems share many similarities in circuit topology and control strategies. Specifically, each phase of a three-phase AC power grid is connected to one or more battery clusters cascaded by PACKs and their control modules. By controlling the charge and discharge power at the PACK level, flexible control of the output voltage and current of each phase of the system is achieved. This method achieves decoupling from the grid by short-circuiting the AC-side grounding switch when not connected to the grid, forming an AC / DC loop with the system. The control strategy employed achieves battery balancing between PACKs, between clusters, and between phases, resulting in high application value and innovation.

[0053] Through the description of the above embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus a necessary general hardware platform, or of course, by hardware. Based on this understanding, the essence of the above technical solution or the part that contributes to the existing technology can be embodied in the form of a software product. The computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, a magnetic disk, an optical disk, etc., and includes a number of instructions for enabling a computer device (which can be a personal computer, a server, or a network device, etc.) to execute the methods described in each embodiment or certain parts of the embodiments.

[0054] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only intended to help understand the method and core concept of the present invention. At the same time, those skilled in the art will find that the specific implementation methods and application scopes may vary based on the concept of the present invention. In summary, the contents of this specification should not be construed as limiting the present invention.

Claims

1. A method for maintaining DC balance of a high-voltage cascade energy storage system by using a grounding switch backflow, wherein the high-voltage cascade energy storage system comprises a three-phase AC power grid, a plurality of energy units and a battery management system, wherein the energy unit comprises a power module and a battery PACK, wherein a plurality of energy units are cascaded to form a battery cluster, and each phase of the three-phase AC power grid is respectively connected to the battery cluster via a grounding switch; when not connected to the grid, the AC side of the three-phase AC power grid is short-circuited with the grounding switch to form an AC / DC loop with the high-voltage cascade energy storage system to achieve decoupling from the power grid, wherein the method comprises: The DC balancing method includes: S1. The battery management system collects the data of the battery cells in the battery cluster in real time, and counts the voltage and current data of the battery cluster end, and uploads the data of the battery cells, voltage and current to the cluster controller for aggregation, and then uploads it to the system main controller for calculation; S2, the system main controller determines the state of each phase when the current is balanced according to the current statistical state of each phase battery data, and controls the switching state of the MOSFET in each power module under the corresponding state; S3, after determining the total charging or discharging current of each phase battery cluster, the cluster controller of each battery cluster controls the duty cycle of the MOSFET according to the current state of each battery PACK; S4. After receiving the duty cycle parameter sent by the cluster controller, the battery PACK modulates the output waveform of the MOSFET according to the duty cycle parameter, and finally realizes multi-level power balancing.

2. A method for maintaining DC balance of a high-voltage cascade energy storage system using grounding switch backflow according to claim 1, characterized in that: The cell data collected by the battery management system in S1 includes voltage, temperature, internal resistance, SOC, SOH, and equilibrium state.

3. The method for maintaining DC balance of a high-voltage cascade energy storage system by using a grounding switch backflow according to claim 1, characterized in that: The DC balancing method specifically includes: During operation, the AC voltage of each phase is v sa , v sb and v sc , the AC current i of each phase a 、i b 、i c The power flows through each power module respectively, and the MOSFET of the power module realizes rectification and charges the battery PACK; the duty cycle of the MOSFET is controlled to control the current of the battery PACK. When the SOC value of a battery PACK is higher than the SOC value of other battery PACKs, the duty cycle of the MOSFET is reduced to reduce the current of the battery PACK, so that the charging of the battery PACK is slower than that of other battery PACKs; conversely, when discharging, the power module inverts the DC power of the battery PACK into AC power and provides it to the power grid. The discharge speed of the battery PACK is adjusted by controlling the duty cycle of the MOSFET, thereby forming a gap with the discharge speed of other battery PACKs.

4. The method for maintaining DC balance of a high-voltage cascade energy storage system by using a grounding switch backflow according to claim 1, characterized in that: The system main controller in S2 determines the state of each phase when the current is balanced according to the current statistical state of each phase battery data, and controls the switching state of the MOSFET in each battery PACK power module under the corresponding state, specifically including: The system main controller determines the state of each phase during current balancing according to the current SOC statistical state of each phase, which includes the charging state and the discharging state, and controls the switching state of the MOSFET in each power module under the corresponding state according to the conclusion.

5. The method for maintaining DC balance of a high-voltage cascade energy storage system by using grounding switch backflow according to claim 1, characterized in that: After the total charging or discharging current of each phase battery cluster is determined in S3, the cluster controller of each battery cluster controls the duty cycle of the MOSFET according to the current state of each battery PACK, specifically including: When the current phase battery cluster is in charging state, the battery management system collects the total voltage of each power module, and first sorts the SOC of each battery PACK of the battery cluster, calculates the balanced target SOC by combining the total voltage and the charging current configured for the battery cluster, and calculates the duty cycle coefficient according to the battery PACK balancing order. The battery PACK balancing order is that the battery PACK far away from the balanced target SOC value has a higher priority, and the battery PACK close to the balanced target SOC value has a lower priority; the MOSFET duty cycle corresponding to the high-priority battery PACK is relatively higher, and the battery PACK charges faster, and vice versa, it is lower and the charging speed is slower; at the same time, the charging current of the battery cluster is adjusted in real time.

6. A method for maintaining DC balance of a high-voltage cascade energy storage system using grounding switch backflow according to claim 5, characterized in that: The duty cycle coefficient is calculated according to the battery PACK balancing order. The battery PACK balancing order is that the battery PACK far away from the balanced target SOC value has a higher priority, and the battery PACK close to the balanced target SOC value has a lower priority. The specific calculation process is as follows: First, count the SOC value of each battery PACK in the current cluster SOC i , calculate the SOC regulation target SOC given by the battery cluster 额 The difference between the SOC of each battery PACK and the maximum SOC of the difference is obtained diffmax , i.e. SOC diffmax =max(SOC 额 -SOC i ), where i is an integer from 1 to n; the calculation result is SOC diffmax The battery cluster is operated at full power, i.e., the duty cycle is 100%, and the balancing time of the entire cluster is calculated, i.e., T balance =SOC diffmax / I max , where I max It is the current when the battery cluster is running at full power; all battery PACKs in the current cluster are at T balance The target time is obtained, so as to obtain the charging power I of each PACK i =SOC i / T balance ; You can get the duty cycle of each battery PACK DUTY i =I i / I max .

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