Series-parallel battery equalization system based on multi-input single-output four-switch Buck-Boost converter and working method thereof

Abstract

The invention discloses a series-parallel battery equalization system based on a multi-input single-output four-switch Buck-Boost converter and a working method thereof, the system comprises the series-parallel battery equalization system based on the multi-input single-output four-switch Buck-Boost converter, the series-parallel battery equalization system based on the multi-input single-output four-switch Buck-Boost converter is characterized by comprising m battery subsystems Mi, Mi, Mi, Mi, Mi, Mi, Mi, Mi, the positive electrode of the battery subsystem Mi is connected with the positive electrode of the power supply / load through a bus, and the negative electrode of the battery subsystem Mi is connected with the negative electrode of the battery / load through a bus; the plurality of battery subsystems Mi are connected in parallel; the battery subsystem Mi comprises a battery pack Packi and a converter Fi; the battery pack Packi comprises a battery Bi1 to a battery Bin; the converter Fi comprises an MOS (Metal Oxide Semiconductor) tube Qij1, an MOS tube Qij2, an MOS tube Qi1, an MOS tube Qi2, an inductor Li and a capacitor Ci; according to the invention, the number of switches, inductors and capacitors is reduced, the system cost is reduced, the system has strong expansibility and fault tolerance, in addition, the system can realize the equalization between the battery packs and the equalization in the battery packs under the charging and discharging and static conditions, the consistency of the batteries is improved, and the service life of the system can be prolonged.

Description

Technical Field

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

[0002] In recent years, with the increasing energy crisis and environmental problems, the global power grid, manufacturing, transportation and other industries have gradually developed towards low energy consumption, low pollution and low carbon. The development and utilization of new energy is of great significance to the protection of ecology, but the new energy power generation based on natural resources such as wind energy and solar energy is random and intermittent, and its large-scale grid connection will have a significant impact on the stability and security of the power grid. At present, the use of energy storage technology can largely solve the problems caused by the grid connection of new energy power generation, improve the utilization rate of existing power grid equipment, the operating efficiency of the power grid, the quality of power and the efficiency of power consumption, and effectively deal with the occurrence of power grid failures.

[0003] Compared with other energy storage batteries, lithium-ion batteries have been widely used in electric vehicles, mobile communications, aerospace and other fields due to their many advantages such as high energy density, flexible grouping, long cycle life, no memory effect and environmental friendliness, and have become one of the focuses of large-scale energy storage technology research. In order to meet the voltage and capacity requirements of the energy storage system, it is usually necessary to combine multiple batteries in series or parallel to form a battery pack for use. However, due to the influence of 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 cells, which leads to inconsistency. As the number of battery cycles increases, the battery performance decays at different rates, further exacerbating the inconsistency of the battery pack, which will eventually 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 issues.

[0004] In order to solve or improve the problems caused by the inconsistency of battery packs, the industry has taken a series of measures, including optimizing the manufacturing process and strictly screening battery cells. However, these measures cannot completely eliminate the inconsistency between batteries. Therefore, the use of balancing technology has become another important solution. Balancing technology precisely controls the energy and charge state of the battery, redistributes the energy of the battery in the form of energy consumption or transfer, thereby narrowing the energy state difference between batteries. In addition, the current balancing method of large-scale battery energy storage systems still faces some challenges: the large number of devices and sensors required leads to increased system costs and volume; the circuit is complex and the control difficulty increases accordingly; the scalability and flexibility of non-modular balancing systems are poor, which increases the difficulty of later maintenance; some balancing circuits do not fully consider system failures, and the fault tolerance and reliability are insufficient. Summary of the invention

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

[0006] The present invention proposes a series-parallel battery balancing system based on a multi-input single-output four-switch Buck-Boost converter, which is characterized by comprising m battery subsystems Mi, wherein 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 a bus; a plurality of 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, Qij2, MOS transistors Qi1, Qi2, inductor Li and capacitor Ci, where 1≤i≤m, 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 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.

[0009] Preferably, 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 among battery modules, that is, residual energy state balance.

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

[0011] 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;

[0012] 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;

[0013] 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.

[0014] Preferably, 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.

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

[0016] 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;

[0017] 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.

[0018] Preferably, the method further comprises determining whether the system satisfies the following conditions:

[0019] 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:

[0020] Condition 2: System-level energy balancing goal: Energy is transmitted between the battery pack and the load / power supply through the converter F1 to the converter Fm and the bus. The balancing goal is to achieve the same SOC of the battery subsystem M1 to the battery subsystem Mm, and achieve: SOC1 = SOC2 = ... = SOC m The output ends of each battery subsystem are connected in parallel to the DC bus, and energy balance between the battery subsystems is achieved by controlling the input and output power of the battery subsystem.

[0021] Condition 3: Module-level energy balancing goal: 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 goal is to achieve the same SOC of battery Bi1 to battery Bin in a single battery subsystem, and achieve: SOC i1 =SOC i2 =... =SOC im .

[0022] For each battery in the same battery subsystem, the inductor current is the same, so the control d ij Adjust the change rate of SOC of each battery cell. When the battery pack is discharged, the inductor current i Li >0, then d ij The larger the value, the more time the corresponding battery is bypassed and the smaller the SOC decreases. Therefore, the smaller the SOC of the battery, the smaller the actual working d ij should be larger, so as to achieve the difference in the output energy of each battery cell; when the battery pack is charged, i Li <0, then d ij The larger the value, the smaller the SOC rise. Therefore, the smaller the SOC of the battery, the smaller the actual working d ij It should be smaller.

[0023] In summary, due to the adoption of the above technical solution, the present invention is based on a multi-input single-output four-switch Buck-Boost converter design. By adopting a structure in which the batteries in 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 expansibility. At the same time, this design also reduces the number of components such as switches, inductors, capacitors, etc., effectively reducing the system cost. The system can not only achieve balance between battery packs and within the battery pack, but also has dynamic balance under charging and discharging conditions and static balance capabilities when there is no load and the power supply is connected, thereby 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. Even if the battery fails, it will not affect the normal operation of the system, which significantly improves 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 and in part will be obvious from the following description, or will be learned through 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 easily understood from the description of the embodiments in conjunction with the following drawings, in which:

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

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

[0028] Figure 3This is an equivalent diagram of the working mode 2 of the series-parallel battery balancing system based on the multi-input single-output four-switch Buck-Boost converter adopted by the present invention;

[0029] Figure 4 This is an equivalent diagram of the working mode 3 of the series-parallel battery balancing system based on the multi-input single-output four-switch Buck-Boost converter adopted in the present invention;

[0030] Figure 5 This is an equivalent diagram of the working mode 4 of the series-parallel battery balancing system based on the multi-input single-output four-switch Buck-Boost converter adopted in the present invention;

[0031] Figure 6 This is an equivalent diagram of the working mode 5 of the series-parallel battery balancing system based on the multi-input single-output four-switch Buck-Boost converter adopted in the present invention. DETAILED DESCRIPTION

[0032] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0033] In the description of the present invention, unless otherwise specified and limited, 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 internal connection between two components. It can be a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to the specific circumstances.

[0034] like Figure 1 As shown, the present invention provides a series-parallel battery balancing 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, wherein the positive electrode of the battery balancing system is connected to the positive electrode of the load / power supply through the energy bus, and the negative electrode of the battery balancing system is connected to the negative electrode 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, wherein each battery pack is connected in series. The battery subsystem Mi consists of a battery pack Packi and a multi-input single-output converter Fi, wherein 1≤i≤m; the battery pack Packi includes batteries Bi1 to Bin, and the multi-input single-output converter Fi includes MOS tube Qi1, MOS tube Qi2, inductor Li, capacitor Ci, and MOS tube Qi11 and MOS tube Qi12 to MOS tube Qin1 and MOS tube 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 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 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, ..., 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] At Figures 2 to 6 The working sequence, energy flow path and direction of the series-parallel battery balancing system circuit based on the multi-input single-output four-switch Buck-Boost converter are explained. For simplicity, if the components included in the circuit in the figure are ideal. In the circuit analysis, the working mode is described as follows:

[0038] When the battery energy storage system supplies power to the load, that is, when the battery energy storage system is discharging, the series-parallel battery balancing system based on the multi-input single-output four-switch Buck-Boost converter is as follows: Figure 2As shown. According to the SOC state of the battery subsystem M1 to the battery subsystem Mm, 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, so that the battery subsystem M1 to the battery subsystem Mm discharges to the load through the bus BUS at different powers, and the SOC dynamic balance between the battery subsystem M1 to the battery subsystem Mm is achieved.

[0039] When the power source charges the battery energy storage system, the series-parallel battery balancing system based on the multi-input single-output four-switch Buck-Boost converter is as follows Figure 3 As shown. According to the SOC state of the battery subsystem M1 to the battery subsystem Mm, 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, and the battery subsystem M1 to the battery subsystem Mm are charged with different powers through the bus BUS, so as to realize the dynamic balance of the SOC between the battery subsystem M1 to the battery subsystem Mm.

[0040] When the bus is not connected to a load or power source, a series-parallel battery balancing system based on a multi-input single-output four-switch Buck-Boost converter is shown in Figure 2. Figure 4 The duty ratios of MOS tubes Q11 and Q12 to MOS tubes Qm1 and Qm2 in converters F1 to Fm are set, and the battery subsystem M1 to the battery subsystem Mm exchange energy through the bus BUS to achieve static SOC balance between the battery subsystem M1 to the battery subsystem Mm.

[0041] When the battery energy storage system supplies power to the load, the working state (working sequence) of the MOS tube in the battery subsystem Mi is as follows: Figure 5 As shown in the figure: the conduction state of MOS transistor Qij1 and MOS transistor Qij2 determines the working state of battery Bij, wherein 1≤j≤n, i represents the i-th converter, and j represents the j-th MOS transistor; when MOS transistor Qij1 is turned on and MOS transistor Qij2 is turned off, battery Bij is connected in series to the battery pack, and when MOS transistor Qij1 is turned off and MOS transistor Qij2 is turned on, battery Bij is bypassed; when the battery subsystem Mi is discharged, the duty cycle of MOS transistor Qi11 and MOS transistor Qi12 connected thereto to MOS transistor Qin1 and MOS transistor Qin2 is set according to the SOC state of battery Bi1 to battery Bin, so that battery Bi1 to battery Bin discharge to the load through converter Fi and bus BUS at different working times, so as to achieve SOC balance of battery Bi1 to battery Bin.

[0042] When the power supply charges the battery energy storage system, the working state of the MOS tube in the battery subsystem Mi is as follows: Figure 6As shown in the figure: the conduction state of MOS transistor Qij1 and MOS transistor Qij2 determines the working state of battery Bij, wherein 1≤j≤n, i represents the i-th converter, and j represents the j-th MOS transistor; when MOS transistor Qij1 is turned on and MOS transistor Qij2 is turned off, battery Bij is connected in series to the battery pack, and when MOS transistor Qij1 is turned off and MOS transistor Qij2 is turned on, battery Bij is bypassed; when the battery subsystem Mi is charged, the duty cycle of MOS transistor Qi11 and MOS transistor Qi12 connected thereto to MOS transistor Qin1 and MOS transistor Qin2 is set according to the SOC state of battery Bi1 to battery Bin, so that battery Bi1 to battery Bin are charged by the power supply through converter Fi and bus BUS at different working times, so as to achieve SOC balance of battery Bi1 to battery Bin.

[0043] The series-parallel battery balancing system based on a multi-input single-output four-switch Buck-Boost converter achieves energy balancing, which needs to meet the energy balance of the balancing circuit, the system-level energy balancing target, and the module-level energy balancing target.

[0044] (1) Balanced circuit energy balance

[0045] According to the law of conservation of energy, the power P1 to P2 of energy (electric energy) exchanged from the battery subsystem M1 to the battery subsystem Mm through the bus BUS m , the energy P of the load / power supply through the bus BUS load The following should be satisfied:

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

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

[0048] Energy is transmitted between the battery pack and the load / power supply through the converter F1 to the converter Fm and the bus BUS. The balancing goal is to achieve the same SOC from the battery subsystem M1 to the battery subsystem Mm, that is, to achieve: SOC1 = SOC2 = ... = SOC m .

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

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

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

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

[0053] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that 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. A working method of a series-parallel battery balancing system based on a multi-input single-output four-switch Buck-Boost converter, 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. A working method of a series-parallel battery balancing system based on a multi-input single-output four-switch Buck-Boost converter, 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 the converter F1 to the converter Fm and the bus. The balancing goal is to achieve the same SOC of the battery subsystem M1 to the battery subsystem Mm, and achieve: SOC1 = SOC2 = ... = SOC m ; Condition 3: Module-level energy balancing goal: 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 goal is to achieve the same SOC of battery Bi1 to battery Bin in a single battery subsystem, and achieve: SOC i1 =SOC i2 =... =SOC im .

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