Series-Parallel Battery Equalization System Based on Multi-Input Single-Output Four-Switch Buck-Boost Converter and Its Working Method

Abstract

The present invention discloses a series-parallel battery equalization system based on a multi-input single-output four-switch Buck-Boost converter and its working method. The system includes: a series-parallel battery equalization system based on a multi-input single-output four-switch Buck-Boost converter, which is characterized by including m battery subsystems Mi. The positive pole of the battery subsystem Mi is connected to the positive pole of the power supply / load through a bus, and the negative pole of the battery subsystem Mi is connected to the negative pole of the battery / load through a bus; several battery subsystems Mi are connected in parallel; the battery subsystem Mi includes a battery pack Packi and a converter Fi; the battery pack Packi includes batteries Bi1 to Bin, and the converter Fi includes MOS transistors Qij1, MOS transistors Qij2, MOS transistors Qi1, MOS transistors Qi2, an inductor Li, and a capacitor Ci. The present invention reduces the number of switches, inductors, and capacitors, reduces the system cost, and has strong scalability and fault tolerance. In addition, the system can achieve equalization between battery packs and within battery packs under charging, discharging, and static conditions, improves the consistency of the batteries, and can extend the system life.

Description

Technical Field

[0001] The present invention relates to the field of automatic control, and particularly to a series-parallel battery equalization system based on a multi-input single-output four-switch Buck-Boost converter and its working method. Background Art

[0002] In recent years, with the increasing prominence of energy crises and environmental problems, industries such as the global power grid, manufacturing, and transportation have gradually developed towards low energy consumption, low pollution, and low carbonization. The development and utilization of new energy are of great significance for ecological protection. However, new energy generation mainly based on natural resources such as wind energy and solar energy is random and intermittent, and its large-scale grid connection operation will have a significant impact on the stability and security of the power grid. Currently, the use of energy storage technology can largely solve the problems brought about by the grid connection of new energy generation, improve the utilization rate of existing grid equipment, the operating efficiency of the power grid, as well as the power quality and power consumption efficiency, and can effectively respond to the occurrence of grid faults.

[0003] Compared with other energy storage batteries, lithium-ion batteries have been widely used in fields such as electric vehicles, mobile communications, and aerospace due to their many advantages such as high energy density, flexible battery-packing method, long cycle life, no memory effect, and environmental friendliness, and have become one of the key points in the research of large-scale energy storage technology. To meet the requirements of the energy storage system for voltage and capacity, multiple battery cells are usually combined into a battery pack in series or parallel. However, due to factors such as the manufacturing process and working conditions, there are differences in performance indicators such as capacity, voltage, internal resistance, and self-discharge rate among battery monomers, that is, inconsistency occurs. As the number of battery cycles increases, the battery performance declines at different rates, further exacerbating the inconsistency of the battery pack, which will ultimately have a negative impact on the performance of the battery energy storage system, shorten the service life of the battery pack, and may even cause safety problems.

[0004] To solve or improve the problems brought about by the inconsistency of the battery pack, the industry has taken a series of measures, including optimizing the manufacturing process and strictly screening battery monomers. However, these measures cannot completely eliminate the inconsistency between batteries. Therefore, the use of equalization technology has become another important solution. Equalization technology precisely controls the energy and state of charge of the battery, and redistributes the energy of the battery in the form of energy consumption or transfer, so as to narrow the difference in the energy state between batteries. And currently, the equalization methods for large-scale battery energy storage systems still face some challenges: the large number of required devices and sensors leads to an increase in system cost and volume; the circuit is complex, and the control difficulty increases accordingly; the scalability and flexibility of non-modular equalization systems are poor, increasing the difficulty of later maintenance; some equalization circuits do not fully consider system fault conditions, and the fault tolerance and reliability are insufficient. Summary of the Invention

[0005] The present invention aims to solve at least the technical problems existing in the prior art, and particularly innovatively proposes a series-parallel battery equalization system based on a multi-input single-output four-switch Buck-Boost converter and its working method.

[0006] The present invention provides a series-parallel battery equalization system based on a multi-input single-output four-switch Buck-Boost converter, which is characterized by including m battery subsystems Mi. The positive electrode of the battery subsystem Mi is connected to the positive electrode of the power supply / load through a bus, and the negative electrode of the battery subsystem Mi is connected to the negative electrode of the power supply / load through a bus; several battery subsystems Mi are connected in parallel.

[0007] The battery subsystem Mi includes a battery pack Packi and a converter Fi; the battery pack Packi includes batteries Bi1 to Bin, and the converter Fi includes MOS transistors Qij1, MOS transistors Qij2, MOS transistors Qi1, MOS transistors Qi2, an inductor Li, and a capacitor Ci, where 1 ≤ i ≤ m and 1 ≤ j ≤ n.

[0008] The connection relationship between the battery pack Packi and the converter Fi is as follows: the positive electrode of the battery Bi1 is connected to the drain of the MOS transistor Qi11, the negative electrode of the battery Bi1 is connected to the source of the MOS transistor Qi12, the positive electrode of the battery Bi2 is connected to the drain of the MOS transistor Qi21, the negative electrode of the battery Bi2 is connected to the source of the MOS transistor Qi22,..., the positive electrode of the battery Bin is connected to the drain of the MOS transistor Qin1, and the negative electrode of the battery Bin is connected to the source of the MOS transistor Qin2; the source of the MOS transistor Qi11 is connected to the drain of the MOS transistor Qi12, the source of the MOS transistor Qi21 is connected to the drain of the MOS transistor Qi22, the source of the MOS transistor Qin1 is connected to the drain of the MOS transistor Qin2; the source of the MOS transistor Qi11 and the drain of the MOS transistor Qi21 are connected to one end of the inductor Li, and the other end of the inductor Li is connected to the source of the MOS transistor Qi1 and the drain of the MOS transistor Qi2; the drain of the MOS transistor Qi1 is connected to one end of the capacitor Ci and the positive electrode of the bus, and the source of the MOS transistor Qi2 is connected to the other end of the capacitor Ci and the negative electrode of the bus; the negative electrode of the battery Bi1 and the source of the MOS transistor Qi12 are connected to the source of the MOS transistor Qi21 and the drain of the MOS transistor Qi22, the negative electrode of the battery Bi2 and the source of the MOS transistor Qi22 are connected to the source of the MOS transistor Qi31 and the drain of the MOS transistor Qi32,..., the negative electrode of the battery Bi(n - 1) and the source of the MOS transistor Qi(n - 1)2 are connected to the source of the MOS transistor Qin1 and the drain of the MOS transistor Qin2.

[0009] Preferably, the working timings of the MOS transistors Qi1 and Qi2 in the converter Fi are set, and the working mode is adjusted according to the current flow path and direction, so as to achieve the stability of the bus voltage and the SOC balance among the battery modules, that is, the balance of the remaining energy state.

[0010] Preferably, the adjustment of the working mode includes any one of the following adjustment methods:

[0011] Adjustment of working mode one: When the battery energy storage system supplies power to the load, that is, when the battery energy storage system discharges, according to the SOC states of the battery subsystems M1 to Mm, the duty cycles of the MOS transistors Q11 and Q12 to Qm1 and Qm2 in the converters F1 to Fm are set, so that the battery subsystems M1 to Mm discharge to the load through the bus with different powers, realizing the dynamic SOC balance among the battery subsystems M1 to Mm;

[0012] Adjustment of working mode two: When the power supply charges the battery energy storage system, according to the SOC states of the battery subsystems M1 to Mm, the duty cycles of the MOS transistors Q11 and Q12 to Qm1 and Qm2 in the converters F1 to Fm are set, and through the bus, the battery subsystems M1 to Mm are charged with different powers, realizing the dynamic SOC balance among the battery subsystems M1 to Mm;

[0013] Adjustment of working mode three: S3, when the bus is not connected to the load or the power supply, the duty cycles of the MOS transistors Q11 and Q12 to Qm1 and Qm2 in the converters F1 to Fm are set, and the battery subsystems M1 to Mm exchange energy through the bus, realizing the static SOC balance among the battery subsystems M1 to Mm.

[0014] Preferably, the working timings of the MOS transistors Qi11 and Qi12 to Qin1 and Qin2 in the converters F1 to Fm are set, and the working mode is adjusted according to the energy flow path and direction, so as to achieve the SOC balance of the batteries Bi1 to Bin within a single battery subsystem.

[0015] Preferably, the adjustment of the working mode includes any one of the following adjustment methods:

[0016] Working mode four adjustment: The conduction states of MOS transistor Qij1 and MOS transistor Qij2 determine the working state of battery Bij, where 1 ≤ j ≤ n. When MOS transistor Qij1 is conducting and MOS transistor Qij2 is off, battery Bij is connected in series to the battery pack. When MOS transistor Qij1 is off and MOS transistor Qij2 is conducting, battery Bij is bypassed. When the battery subsystem Mi discharges, according to the SOC states of batteries Bi1 to Bin, the duty cycles of MOS transistors Qi11 and Qi12 to MOS transistors Qin1 and Qin2 are set, so that batteries Bi1 to Bin discharge to the load through the converter Fi and the bus at different working times, realizing the SOC balance of batteries Bi1 to Bin.

[0017] Working mode five adjustment: When the battery subsystem Mi is charging, according to the SOC states of batteries Bi1 to Bin, the duty cycles of MOS transistors Qi11 and Qi12 to MOS transistors Qin1 and Qin2 are set, so that batteries Bi1 to Bin are charged by the power supply through the converter Fi and the bus at different working times, realizing the SOC balance of batteries Bi1 to Bin.

[0018] Preferably, it further includes judging whether the system meets the following conditions:

[0019] Condition 1, energy balance of the equalization circuit: The power of the battery subsystem Mi for energy exchange through the bus is P i , and the energy P load for energy exchange between the load / power supply and the bus should satisfy:

[0020] Condition 2, system-level energy equalization goal: Energy is transmitted between the battery pack, the load / power supply through the converters F1 to Fm and the bus. The equalization goal is to make the SOCs of the battery subsystems M1 to Mm consistent, achieving: SOC1 = SOC2 =... = SOC m ; The output terminals of each battery subsystem are connected in parallel to the DC bus. By controlling the input and output powers of the battery subsystems, the energy balance between the battery subsystems is realized.

[0021] Condition 3, module-level energy equalization goal: Set the duty cycles of MOS transistors Qi11 and Qi12 to MOS transistors Qin1 and Qin2, and adjust the working times of batteries Bi1 to Bin. The equalization goal is to make the SOCs of batteries Bi1 to Bin within a single battery subsystem consistent, achieving: SOC i1 = SOC i2 =... = SOC im .

[0022] For each cell in the same battery subsystem, the inductor current is the same. Therefore, controlling d ij adjusts the change rate of the SOC of each cell. When the battery pack discharges, the inductor current i Li > 0, then the larger d ij is, the more time the corresponding battery is bypassed, and the smaller the SOC drop. Therefore, for a battery with a smaller SOC, the actual working d ij should be larger, so as to realize the difference in the output energy of each cell; when the battery pack is charging, i Li < 0, then the larger d ij is, the smaller the SOC rise. Therefore, for a battery with a smaller SOC, the actual working d ij should be smaller.

[0023] In summary, due to the adoption of the above technical solution, the present invention is designed based on a multi-input single-output four-switch Buck-Boost converter. By adopting a structure in which the batteries within the subsystem are connected in series and the subsystems are connected in parallel, the number of batteries or battery packs can be flexibly increased or decreased according to application requirements, showing strong expandability. At the same time, this design also reduces the number of components such as switches, inductors, and capacitors, effectively reducing the system cost. The system can not only achieve the balance between battery packs and within the battery packs, but also has the ability of dynamic balance during charge and discharge states and static balance when there is no load or power connection, thus improving the consistency of the battery state under various working conditions and extending the service life of the system. In addition, the system also has the function of bypassing faulty batteries, so even if a battery fails, it will not affect the normal operation of the system, significantly improving the fault tolerance and safety of the system.

[0024] Additional aspects and advantages of the present invention will be given in part in the following description, become apparent in part from the following description, or be learned through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The above and / or additional aspects and advantages of the present invention will become apparent and be readily understood from the description of the embodiments in conjunction with the following drawings, wherein:

[0026] Figure 1 is the topological structure diagram of the series-parallel battery equalization system of the present invention based on a multi-input single-output four-switch Buck-Boost converter;

[0027] Figure 2 is the equivalent diagram of working mode 1 of the series-parallel battery equalization system of the present invention based on a multi-input single-output four-switch Buck-Boost converter;

[0028] Figure 3It is the equivalent diagram of operating mode 2 of the series-parallel battery equalization system adopting a multi-input single-output four-switch Buck-Boost converter according to the present invention;

[0029] Figure 4 It is the equivalent diagram of operating mode 3 of the series-parallel battery equalization system adopting a multi-input single-output four-switch Buck-Boost converter according to the present invention;

[0030] Figure 5 It is the equivalent diagram of operating mode 4 of the series-parallel battery equalization system adopting a multi-input single-output four-switch Buck-Boost converter according to the present invention;

[0031] Figure 6 It is the equivalent diagram of operating mode 5 of the series-parallel battery equalization system adopting a multi-input single-output four-switch Buck-Boost converter according to the present invention. Specific embodiments

[0032] The embodiments of the present invention will be described in detail below. Examples of the embodiments are shown in the drawings, where the same or similar reference numerals indicate the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the drawings are exemplary and are only used to explain the present invention and should not be construed as a limitation of the present invention.

[0033] In the description of the present invention, unless otherwise specified and defined, it should be noted that the terms "installed", "connected", and "connected" should be understood in a broad sense. For example, it can be a mechanical connection or an electrical connection, or it can be the communication inside two elements. It can be directly connected or indirectly connected through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to specific situations.

[0034] As Figure 1 shown, the present invention provides a series-parallel battery equalization system based on a multi-input single-output four-switch Buck-Boost converter, including m battery subsystems (battery subsystem M1 to battery subsystem Mm) and an energy bus BUS. The positive pole of the battery equalization system is connected to the positive pole of the load / power supply through the energy bus, and the negative pole of the battery equalization system is connected to the negative pole of the load / power supply through the energy bus; the m battery subsystems are connected in parallel through the energy bus.

[0035] Each battery subsystem consists of a battery pack and a multi-input single-output converter. Among them, the battery packs are connected in series. The battery subsystem Mi consists of the battery pack Packi and the multi-input single-output converter Fi, where 1 ≤ i ≤ m; the battery pack Packi includes batteries Bi1 to Bin, and the multi-input single-output converter Fi includes MOS transistors Qi1, MOS transistors Qi2, inductor Li, capacitor Ci, and MOS transistors Qi11 and MOS transistors Qi12 to MOS transistors Qin1 and MOS transistors Qin2;

[0036] The connection relationship between the battery pack Packi and the multi-input single-output converter Fi is as follows: the positive electrode of battery Bi1 is connected to the drain of MOS transistor Qi11, the negative electrode of battery Bi1 is connected to the source of MOS transistor Qi12, the positive electrode of battery Bi2 is connected to the drain of MOS transistor Qi21, the negative electrode of battery Bi2 is connected to the source of MOS transistor Qi22,..., the positive electrode of battery Bin is connected to the drain of MOS transistor Qin1, and the negative electrode of battery Bin is connected to the source of MOS transistor Qin2; the source of MOS transistor Qi11 is connected to the drain of MOS transistor Qi12, the source of MOS transistor Qi21 is connected to the drain of MOS transistor Qi22, and the source of MOS transistor Qin1 is connected to the drain of MOS transistor Qin2; the source of MOS transistor Qi11 and the drain of MOS transistor Qi21 are connected to one end of inductor Li, and the other end of inductor Li is connected to the source of MOS transistor Qi1 and the drain of MOS transistor Qi2; the drain of MOS transistor Qi1 is connected to one end of capacitor Ci and the positive electrode of bus BUS, and the source of MOS transistor Qi2 is connected to the other end of capacitor Ci and the negative electrode of bus BUS; the negative electrode of battery Bi1 and the source of MOS transistor Qi12 are connected to the source of MOS transistor Qi21 and the drain of MOS transistor Qi22, the negative electrode of battery Bi2 and the source of MOS transistor Qi22 are connected to the source of MOS transistor Qi31 and the drain of MOS transistor Qi32,..., and the negative electrode of battery Bi(n - 1) and the source of MOS transistor Qi(n - 1)2 are connected to the source of MOS transistor Qin1 and the drain of MOS transistor Qin2.

[0037] In Figures 2 to 6 the working timing, energy flow path and direction of the series-parallel battery equalization system circuit based on the multi-input single-output four-switch Buck-Boost converter are described. For simplicity, it is assumed that all the devices included in the circuit in the figure are ideal. In the circuit analysis, the working modes are described as follows:

[0038] When the battery energy storage system supplies power to the load, that is, when the battery energy storage system discharges, the series-parallel battery equalization system based on the multi-input single-output four-switch Buck-Boost converter is as Figure 2As shown in the figure. According to the SOC states of battery subsystems M1 to Mm, the duty cycles of MOS transistors Q11 and Q12 to Qm1 and Qm2 in converters F1 to Fm are set, so that battery subsystems M1 to Mm discharge to the load through bus BUS at different powers, realizing the dynamic SOC balance among battery subsystems M1 to Mm.

[0039] When the power supply charges the battery energy storage system, the series-parallel battery equalization system based on the multi-input single-output four-switch Buck-Boost converter is as Figure 3 shown in the figure. According to the SOC states of battery subsystems M1 to Mm, the duty cycles of MOS transistors Q11 and Q12 to Qm1 and Qm2 in converters F1 to Fm are set, and through bus BUS, battery subsystems M1 to Mm are charged at different powers, realizing the dynamic SOC balance among battery subsystems M1 to Mm.

[0040] When the bus is not connected to the load or the power supply, the series-parallel battery equalization system based on the multi-input single-output four-switch Buck-Boost converter is as Figure 4 shown in the figure. The duty cycles of MOS transistors Q11 and Q12 to Qm1 and Qm2 in converters F1 to Fm are set, and battery subsystems M1 to Mm exchange energy through bus BUS, realizing the static SOC balance among battery subsystems M1 to Mm.

[0041] When the battery energy storage system supplies power to the load, the working states (working time sequences) of the MOS transistors in battery subsystem Mi are as Figure 5 shown in the figure: The conduction states of MOS transistors Qij1 and Qij2 determine the working state of battery Bij, where 1 ≤ j ≤ n, i represents the i-th converter, and j represents the j-th MOS transistor; when MOS transistor Qij1 is conducting and MOS transistor Qij2 is off, battery Bij is connected in series to the battery pack, and when MOS transistor Qij1 is off and MOS transistor Qij2 is conducting, battery Bij is bypassed; when battery subsystem Mi discharges, according to the SOC states of batteries Bi1 to Bin, the duty cycles of the connected MOS transistors Qi11 and Qi12 to Qin1 and Qin2 are set, so that batteries Bi1 to Bin discharge to the load through converter Fi and bus BUS at different working times, realizing the SOC balance of batteries Bi1 to Bin.

[0042] When the power supply charges the battery energy storage system, the working states of the MOS transistors in battery subsystem Mi are as Figure 6As shown: The conduction states of MOS transistors Qij1 and Qij2 determine the operating state of battery Bij, where 1 ≤ j ≤ n, i represents the i-th converter, and j represents the j-th MOS transistor; when MOS transistor Qij1 is conducting and MOS transistor Qij2 is off, battery Bij is connected in series to the battery pack, and when MOS transistor Qij1 is off and MOS transistor Qij2 is conducting, battery Bij is bypassed; when the battery subsystem Mi is charging, according to the SOC states of batteries Bi1 to Bin, the duty cycles of the MOS transistors Qi11 and Qi12 to Qin1 and Qin2 connected thereto are set, so that batteries Bi1 to Bin are charged by the power supply through converter Fi and bus BUS for different working times, achieving the SOC balance of batteries Bi1 to Bin.

[0043] To achieve energy balance in the series-parallel battery equalization system based on a multi-input single-output four-switch Buck-Boost converter, it is necessary to meet the energy balance of the equalization circuit, the system-level energy balance target, and the module-level energy balance target.

[0044] (1) Energy balance of the equalization circuit

[0045] According to the law of conservation of energy, the powers P1 to P of the energy (electrical energy) exchange between battery subsystems M1 to Mm through bus BUS m and the energy P of the energy exchange between the load / power supply and the bus BUS load should satisfy:

[0046] Among them, P i > 0 indicates that energy flows from the battery pack side to the bus side, P i < 0 indicates that energy flows from the bus side to the battery pack side, P load > 0 indicates that energy flows from the bus side to the load / power supply side, P load < 0 indicates that energy flows from the load / power supply side to the bus side.

[0047] (2) System-level energy balance target

[0048] Energy is transferred between the battery pack and the load / power supply through converters F1 to Fm and bus BUS. The equalization target is to achieve the same SOC for battery subsystems M1 to Mm, that is, to achieve: SOC1 = SOC2 =... = SOC m .

[0049] Among them, SOC i represents the state of charge of the corresponding i-th battery pack.

[0050] (3) Module-level energy balance target

[0051] By setting the duty cycles of MOS transistors Qi11 and Qi12 to MOS transistors Qin1 and Qin2, the working time of batteries Bi1 to Bin is adjusted. The goal of balancing is to make the SOCs of batteries Bi1 to Bin in a single battery subsystem consistent, that is, to achieve: SOC i1 = SOC i2 =... = SOC im .

[0052] Among them, SOC ij represents the state of charge of the j-th battery in the i-th battery pack.

[0053] Although the embodiments of the present invention have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the claims and their equivalents.

Claims

1. A series-parallel battery balancing system based on a multi-input single-output four-switch Buck-Boost converter, characterized in that: It includes m battery subsystems Mi, the positive electrode of the battery subsystem Mi is connected to the positive electrode of the power source / load through a bus, and the negative electrode of the battery subsystem Mi is connected to the negative electrode of the power source / load through the bus; a plurality of battery subsystems Mi are connected in parallel; The battery subsystem Mi includes a battery pack Packi and a converter Fi; the battery pack Packi includes batteries Bi1 to Bin, and the converter Fi includes MOS transistors Qij1, Qij2, MOS transistors Qi1, Qi2, inductor Li and capacitor Ci, where 1≤i≤m, 1≤j≤n; The connection relationship between the battery pack Packi and the converter Fi is as follows: the positive electrode of the battery Bi1 is connected to the drain of the MOS tube Qi11, the negative electrode of the battery Bi1 is connected to the source of the MOS tube Qi12, the positive electrode of the battery Bi2 is connected to the drain of the MOS tube Qi21, the negative electrode of the battery Bi2 is connected to the source of the MOS tube Qi22, ..., the positive electrode of the battery Bin is connected to the drain of the MOS tube Qin1, the negative electrode of the battery Bin is connected to the source of the MOS tube Qin2; the source of the MOS tube Qi11 is connected to the drain of the MOS tube Qi12, the source of the MOS tube Qi21 is connected to the drain of the MOS tube Qi22, the source of the MOS tube Qin1 is connected to the drain of the MOS tube Qin2; the source of the MOS tube Qi11 and the MOS tube Qi The drain of MOS transistor Qi21 is connected to one end of inductor Li, and the other end of inductor Li is connected to the source of MOS transistor Qi1 and the drain of MOS transistor Qi2; the drain of MOS transistor Qi1 is connected to one end of capacitor Ci and the positive electrode of the bus, and the source of MOS transistor Qi2 is connected to the other end of capacitor Ci and the negative electrode of the bus; the negative electrode of battery Bi1 and the source of MOS transistor Qi12 are connected to the source of MOS transistor Qi21 and the drain of MOS transistor Qi22, the negative electrode of battery Bi2 and the source of MOS transistor Qi22 are connected to the source of MOS transistor Qi31 and the drain of MOS transistor Qi32, ..., the negative electrode of battery Bi(n-1) and the source of MOS transistor Qi(n-1)2 are connected to the source of MOS transistor Qin1 and the drain of MOS transistor Qin2.

2. The working method of the series-parallel battery balancing system based on the multi-input single-output four-switch Buck-Boost converter according to claim 1, characterized in that: The working timing of MOS tube Qi1 and MOS tube Qi2 in converter Fi is set, and the working mode is adjusted according to the current flow path and flow direction, so as to achieve bus voltage stability and SOC balance between battery modules, that is, residual energy state balance.

3. The working method of the series-parallel battery balancing system based on the multi-input single-output four-switch Buck-Boost converter according to claim 2 is characterized in that: The working mode adjustment includes any of the following adjustment methods: Adjustment of working mode 1: When the battery energy storage system supplies power to the load, that is, when the battery energy storage system discharges, the duty ratio of the MOS tubes Q11 and Q12 to the MOS tubes Qm1 and Qm2 in the converter F1 to the converter Fm is set according to the SOC state of the battery subsystems M1 to Mm, so that the battery subsystems M1 to Mm discharge to the load through the bus at different powers, thereby realizing dynamic balance of the SOC between the battery subsystems M1 to Mm; Adjustment of the second working mode: when the power supply charges the battery energy storage system, according to the SOC state of the battery subsystem M1 to the battery subsystem Mm, the duty cycle of the MOS tube Q11 and MOS tube Q12 to the MOS tube Qm1 and MOS tube Qm2 in the converter F1 to the converter Fm is set, and the battery subsystem M1 to the battery subsystem Mm are charged at different powers through the bus, so as to realize the dynamic balance of the SOC between the battery subsystem M1 to the battery subsystem Mm; Working mode three adjustment: S3, when the bus is not connected to the load or power supply, the duty cycle of MOS tubes Q11 and MOS tubes Q12 to MOS tubes Qm1 and MOS tubes Qm2 in converter F1 to converter Fm is set, and battery subsystem M1 to battery subsystem Mm exchange energy through the bus to achieve SOC static balance between battery subsystem M1 to battery subsystem Mm.

4. The working method of the series-parallel battery balancing system based on the multi-input single-output four-switch Buck-Boost converter according to claim 1, characterized in that: The working sequence of MOS tube Qi11 and MOS tube Qi12 to MOS tube Qin1 and MOS tube Qin2 in converter F1 to converter Fm is set, and the working mode is adjusted according to the energy flow path and flow direction, so as to achieve SOC balance of battery Bi1 to battery Bin inside a single battery subsystem.

5. The working method of the series-parallel battery balancing system based on the multi-input single-output four-switch Buck-Boost converter according to claim 4, characterized in that: The working mode adjustment includes any of the following adjustment methods: Adjustment of the fourth working mode: The conduction state of MOS tube Qij1 and MOS tube Qij2 determines the working state of battery Bij, wherein 1≤j≤n, when MOS tube Qij1 is turned on and MOS tube Qij2 is turned off, battery Bij is connected in series to the battery pack, and when MOS tube Qij1 is turned off and MOS tube Qij2 is turned on, battery Bij is bypassed; when the battery subsystem Mi is discharged, the duty cycle of MOS tube Qi11 and MOS tube Qi12 to MOS tube Qin1 and MOS tube Qin2 is set according to the SOC state of battery Bi1 to battery Bin, so that battery Bi1 to battery Bin discharges to the load through converter Fi and bus at different working times, so as to achieve SOC balance of battery Bi1 to battery Bin; Adjustment of working mode five: When the battery subsystem Mi is charging, the duty cycle of MOS tube Qi11 and MOS tube Qi12 to MOS tube Qin1 and MOS tube Qin2 is set according to the SOC status of battery Bi1 to battery Bin, so that battery Bi1 to battery Bin are charged by the power supply through converter Fi and the bus at different working times, thereby achieving SOC balance of battery Bi1 to battery Bin.

6. The working method of the series-parallel battery balancing system based on a multi-input single-output four-switch Buck-Boost converter according to any one of claims 2 to 5, characterized in that: It also includes determining whether the system meets the following conditions: Condition 1: Balanced circuit energy balance: The power of the battery subsystem Mi for energy exchange through the bus is P i , the energy P of the load / power supply through the bus load The following should be satisfied: ; Condition 2: System-level energy balancing goal: Energy is transmitted between the battery pack and the load / power supply through converter F1 to converter Fm and the bus. The balancing goal is to achieve consistent SOC from battery subsystem M1 to battery subsystem Mm, achieving: ; Condition three, module-level energy balancing target: set the duty cycle of MOS tube Qi11 and MOS tube Qi12 to MOS tube Qin1 and MOS tube Qin2, adjust the working time of battery Bi1 to battery Bin, and the balancing target is to achieve the same SOC of battery Bi1 to battery Bin in a single battery subsystem, and achieve: .

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