Battery equalization system based on series-parallel reconfigurable topology and control method

Abstract

The invention provides a series-parallel reconfigurable topology-based battery equalization system and a control method, the system comprises a flyback conversion unit and a working mode control unit, and the flyback conversion unit transmits energy from one side of a primary winding to one side of a secondary winding to complete battery equalization; the working mode control unit is used for controlling the working mode of the flyback conversion unit and comprises a charging control unit, a discharging control unit and a series-parallel connection switching unit, the charging control unit controls the single battery to be connected to one side of a secondary winding of the flyback conversion unit, and at the moment, the battery is in a charging state; the discharge control unit controls the single battery to be connected to one side of the primary winding of the flyback conversion unit, and the battery is in a discharge state at the moment; the switch of the series-parallel switching unit is switched off, the single batteries are respectively connected in parallel to two sides of the flyback conversion unit for battery equalization, after equalization is finished, the switch of the series-parallel switching unit is switched on, and the single batteries are sequentially connected in series to the battery pack to participate in discharging.

Description

Technical Field

[0001] The present invention relates to the technical field of battery management, and in particular to a battery balancing system and a control method based on a series-parallel reconfigurable topology. Background Art

[0002] As an energy storage device with high energy density, low self-discharge rate and low environmental pollution, lithium battery has been widely used in electric vehicles, consumer electronics, and aerospace fields. The voltage of a single lithium battery is not enough to meet engineering needs, so lithium battery cells are usually connected in series and parallel to form a battery pack. Due to the uneven battery manufacturing process, obvious differences in working environment, and different changes in internal resistance, even the cells of the same battery pack usually have inconsistencies that cannot be ignored. In order to reduce the harm of the "barrel effect" caused by the inconsistency of lithium batteries and extend the service life of the battery pack, it is necessary and effective to balance the battery pack.

[0003] Lithium battery balancing methods are divided into active balancing and passive balancing. Passive balancing dissipates the excess energy of lithium batteries in the form of heat by connecting energy-consuming elements such as resistors in parallel on both sides of the battery. Passive balancing is simple to control, low cost, and highly reliable, and is still the most widely used battery balancing method today. However, passive balancing also has problems such as low balancing efficiency, long balancing time, and energy waste. Active balancing technology can be divided into several types according to the energy transmission path: adjacent cell to cell, any cell to any cell, cell directly to cell, cell to battery pack, and battery pack to cell.

[0004] The current active balancing technology still faces technical problems such as low balancing speed and insufficient balancing efficiency. At the same time, when individual single-cell failures occur in the battery pack, the existing fixed topology balancing methods cannot effectively handle them because most of them rely on overall balancing and do not have individual processing capabilities. Therefore, a more targeted balancing solution that can identify and handle faulty single cells is needed. Reconfigurable battery topology provides a new method to solve the problem of inconsistent battery pack power balancing. It can bypass the faulty single cells by controlling the on-off of the switch on the basis of achieving battery balancing. Summary of the invention

[0005] According to the technical problems raised above, a battery balancing system and control method based on a series-parallel reconfigurable topology are provided. The present invention constructs a lithium battery balancing topology that controls the charging and discharging of lithium batteries by switches and transfers energy on demand through a flyback converter. By controlling the corresponding switch actions of the battery to change the series-parallel state between battery cells, battery balancing and elimination of abnormal battery cells are achieved, thereby ensuring the safety of the battery pack.

[0006] The technical means adopted by the present invention are as follows:

[0007] A battery balancing system based on a series-parallel reconfigurable topology connects battery cells and includes a flyback conversion unit and an operating mode control unit, wherein:

[0008] The flyback conversion unit is used to transfer energy from one side of the primary winding to one side of the secondary winding to complete battery balancing;

[0009] The working mode control unit is composed of a Schottky diode and an NMOS in parallel, which are respectively connected to the two sides of the flyback conversion unit to control the working mode of the flyback conversion unit; it includes a charging control unit, a discharging control unit and a series-parallel switching unit, wherein:

[0010] The charging control unit is used to control the battery cells whose SOC meets the control strategy requirements to be connected to one side of the secondary winding of the flyback conversion unit, and the battery is in a charging state at this time;

[0011] The discharge control unit is used to control the SOC to meet the control strategy requirements. The battery cell is connected to one side of the primary winding of the flyback conversion unit, and the battery is in a discharge state at this time;

[0012] The switch of the series-parallel switching unit is disconnected, and the battery cells are connected in parallel to the two sides of the flyback conversion unit for battery balancing. After the balancing is completed, the switch of the series-parallel switching unit is closed, and the battery cells are connected in series to the battery pack in turn to participate in discharge.

[0013] Furthermore, the flyback conversion unit includes a control unit, a protection unit and a conversion unit, wherein:

[0014] A control unit, comprising two N-channel metal oxide semiconductor field effect transistors M1 and M2;

[0015] The protection unit includes two Schottky diodes, each of which is connected in parallel with an NMOS, wherein the Schottky diode plays a role of freewheeling protection;

[0016] The conversion unit includes a flyback converter. After the conversion unit is connected to the battery cell, it transfers the excess energy of the high-power battery to the low-power battery to reduce the inconsistency of the batteries in the group.

[0017] Furthermore, in the working mode control unit:

[0018] The charging control unit includes n battery charging selection switches K n (n=1,2,3,…n), respectively connect the corresponding battery cells B n To the secondary winding side of the conversion unit;

[0019] The discharge control unit includes n battery discharge selection switches Q n(n=1,2,3…n), respectively connect the corresponding battery cells B n To the primary winding side of the conversion unit;

[0020] The series-parallel switching unit includes n-1 series-parallel switching switches S n-1 , located between n battery cells, and used to change the connection status of each battery cell in the group at different stages.

[0021] Furthermore, the n battery charging selection switches K in the charging control unit n (n=1,2,3,…n) is in the closed state, the battery cell B n Battery charging enable switch K n The secondary winding side connected to the conversion unit is in a charging state.

[0022] Furthermore, the n battery discharge gating switches Q in the discharge control unit n (n=1,2,3,…n) is in the closed state, the battery cell B n The battery discharge gate switch Q n The primary winding side connected to the conversion unit is in a discharge state.

[0023] Furthermore, the n battery charging selection switches K in the charging control unit n When (n=1,2,3,…n) is in the closed state, the n battery discharge gating switches Q in the corresponding discharge control unit n (n=1,2,3…n) is in the off state; the n battery discharge gating switches Q in the discharge control unit n When (n=1, 2, 3…n) is in the closed state, the corresponding n battery charging selection switches K in the charging control unit n (n=1,2,3,…n) is the off state; the n battery charging selection switches K in the charging control unit n (n=1, 2, 3, ... n) and n battery discharge gating switches Q in the discharge control unit n When (n=1, 2, 3...n) are in the off state at the same time, it indicates that the battery cells are in an unbalanced state.

[0024] Furthermore, the battery cell B n (n=1,2,3…n) When an abnormality occurs, the n-1 series-parallel switching switches S of the series-parallel switching unit n-1 (n=1,2,3…n) disconnect, battery discharge gate switch Q n or battery charging switch K n The positive switch of the battery is closed and the battery discharge gate switch Q n+1or battery charging switch K n+1 The positive switch is closed and the abnormal cell is removed from the battery pack.

[0025] The present invention also provides a battery stratified balancing control method implemented based on the battery balancing system based on the series-parallel reconfigurable topology, comprising:

[0026] S1. Determine the number of battery cells in each group; any number of battery cells can be grouped into one group, and multiple battery groups together constitute a battery pack for external discharge;

[0027] S2, collecting the voltage and current parameters of each battery cell, and estimating the SOC value of each battery cell;

[0028] S3, determine whether there is an abnormal battery cell, if so, remove the cell and then perform balancing;

[0029] S4, determining the intra-group and inter-group balance intervals, wherein the balance intervals include intra-group / inter-group balance start and end reference values ​​and intra-group / inter-group balance switching reference values;

[0030] S5. Determine the battery balancing state according to the SOC value of the battery cell and the intra-group / inter-group balancing interval. The balancing state includes discharge, charge, and imbalance.

[0031] S6. Carry out intra-group balance and inter-group balance in turn.

[0032] Further, step S6 specifically includes: adopting a battery stratified balancing control method to control the balancing within the battery pack in the order of first balancing within the group and then balancing between groups, wherein:

[0033] The internal balancing of the group includes: determining the SOC value of the lithium battery cells in the group, defining the average value of the SOC value of the lithium battery in the group as SOC averge ; Set the internal balancing start threshold STD and the balancing threshold δ; determine the charging and discharging of the battery cells according to the central threshold comparison method.

[0034] Furthermore, the battery stratified balancing control method is provided with an intra-group static balancing mode and an inter-group charge-discharge balancing mode, wherein:

[0035] In the static balance mode within the group, the start threshold STD is set to 0.1% and the balance threshold δ is 0.05%;

[0036] In the inter-group charge and discharge balance mode, the on threshold value STDM is set to 0.4% and the balance threshold value ε is set to 0.2%.

[0037] Compared with the prior art, the present invention has the following advantages:

[0038] 1. Aiming at the problems of battery pack inconsistency, short service life of lithium batteries, and easy failure of batteries, the present invention proposes a reconfigurable topology based on series-parallel connection. This structure can change the series-parallel connection state between battery cells by controlling the corresponding switch action of the battery, and is applicable to different levels within and between groups, and can achieve battery balancing and eliminate abnormal battery cells to ensure the safety of the battery pack.

[0039] 2. The present invention provides a battery balancing system based on a series-parallel reconfigurable topology, and its hierarchical balancing control strategy effectively reduces the balancing time of multiple lithium battery cells participating in balancing at the same time;

[0040] 3. The present invention provides a battery balancing system based on a series-parallel reconfigurable topology, which takes into account both safe operation and rapid balancing of batteries, and provides a certain basis and reference for future balancing designs.

[0041] Based on the above reasons, the present invention can be widely promoted in the fields of battery management and the like. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0043] Figure 1 The structure diagram of the battery balancing system based on the series-parallel reconfigurable topology of the present invention.

[0044] Figure 2 A diagram of the working principle of the balanced topology under a hypothetical situation provided by an embodiment of the present invention.

[0045] Figure 3 A bypass schematic diagram provided in an embodiment of the present invention assuming that the battery B2 fails.

[0046] Figure 4 A diagram of a balancing control strategy implemented by a reconfigurable balancing topology provided in an embodiment of the present invention.

[0047] Figure 5 A lithium balancing simulation model diagram of a series-parallel reconfigurable battery balancing topology structure provided in an embodiment of the present invention.

[0048] Figure 6 The static balance result within the group in Example 1 is obtained by relying on the simulation model provided in the embodiment of the present invention.

[0049] Figure 7The embodiment of the present invention provides an intra-group balancing result obtained by relying on a simulation model when the battery B2 in Embodiment 2 fails.

[0050] Figure 8 The inter-group discharge balancing result in Embodiment 2 obtained by relying on the simulation model provided in the embodiment of the present invention.

[0051] In the figure: 1. working mode control unit; 2. flyback conversion unit; 3. charging control unit; 4. discharging control unit; 5. series-parallel switching unit; 6. control unit; 7. protection unit; 8. conversion unit; 9. battery cell. DETAILED DESCRIPTION

[0052] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. 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 creative work should fall within the scope of protection of the present invention.

[0053] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0054] like Figure 1 As shown, the present invention provides a battery balancing system based on a series-parallel reconfigurable topology, connected to a battery cell 9, including: a flyback conversion unit 2 and an operating mode control unit 1, wherein:

[0055] The flyback conversion unit 2 is used to transfer energy from one side of the primary winding to one side of the secondary winding to complete battery balancing;

[0056] The working mode control unit 1 is composed of a Schottky diode and an NMOS in parallel, which are respectively connected to the two sides of the flyback conversion unit 2 to control the working mode of the flyback conversion unit 2; it includes a charging control unit 3, a discharging control unit 4 and a series-parallel switching unit 5, wherein:

[0057] The charging control unit 3 is used to control the battery cell 9 whose SOC meets the control strategy requirements to be connected to one side of the secondary winding of the flyback conversion unit 2, and the battery is in a charging state at this time;

[0058] The discharge control unit 4 is used to control the SOC to meet the control strategy requirements. The battery cell 9 is connected to one side of the primary winding of the flyback conversion unit 2. At this time, the battery is in a discharge state;

[0059] The switch of the series-parallel switching unit 5 is disconnected, and the battery cells 9 are connected in parallel to the two sides of the flyback conversion unit 2 for battery balancing. After the balancing is completed, the switch of the series-parallel switching unit 5 is closed, and each battery cell 9 is connected in series to the battery pack in turn to participate in discharge.

[0060] In this embodiment, the battery cell 9 is a battery group composed of any number of battery cells. In this embodiment, each group contains n battery cells as an example;

[0061] In specific implementation, as a preferred embodiment of the present invention, the flyback conversion unit 2 includes a control unit 6, a protection unit 7 and a conversion unit 8, wherein:

[0062] A control unit 6, comprising two N-channel metal oxide semiconductor field effect transistors M1 and M2;

[0063] The protection unit 7 includes two Schottky diodes, each of which is connected in parallel with an NMOS, wherein the Schottky diode mainly plays a role of freewheeling protection;

[0064] The conversion unit 8 includes a flyback converter. After being connected to the battery cell 9, the conversion unit transfers the excess energy of the high-power battery to the low-power battery, so as to reduce the inconsistency of the batteries in the group.

[0065] In specific implementation, as a preferred embodiment of the present invention, in the working mode control unit:

[0066] The charging control unit 3 includes n battery charging selection switches K n (n=1,2,3,…n), respectively connect the corresponding battery cells B n To the secondary winding side of the transformation unit 8;

[0067] The discharge control unit 5 includes n battery discharge selection switches Q n (n=1,2,3…n), respectively connect the corresponding battery cells B n To the primary winding side of the transformation unit 8;

[0068] The series-parallel switching unit 6 includes n-1 series-parallel switching switches S n-1, located between n battery cells 9, and used to change the connection status of each battery cell 9 in the group at different stages.

[0069] In specific implementation, as a preferred embodiment of the present invention, the n battery charging selection switches K in the charging control unit 3 are n (n=1,2,3,…n) is in the closed state, the battery cell B n Battery charging enable switch K n The secondary winding side connected to the conversion unit 8 is in a charging state.

[0070] In specific implementation, as a preferred embodiment of the present invention, the n battery discharge gating switches Q in the discharge control unit 5 are n (n=1,2,3,…n) is in the closed state, the battery cell B n The battery discharge gate switch Q n The primary winding side connected to the conversion unit 8 is in a discharge state.

[0071] In specific implementation, as a preferred embodiment of the present invention, the n battery charging selection switches K in the charging control unit 3 are n When (n=1, 2, 3, ... n) is in a closed state, the n battery discharge gating switches Q in the corresponding discharge control unit (5) n (n=1, 2, 3…n) is in the off state; the n battery discharge gating switches Q in the discharge control unit 5 n When (n=1, 2, 3...n) is in the closed state, the corresponding n battery charging selection switches K in the charging control unit 3 n (n=1, 2, 3, ... n) is the off state; the n battery charging selection switches K in the charging control unit 3 n (n=1, 2, 3, ... n) and n battery discharge gating switches Q in the discharge control unit 5 n When (n=1, 2, 3 . . . n) are in the off state at the same time, it indicates that the battery cells 9 are in an unbalanced state.

[0072] In specific implementation, as a preferred embodiment of the present invention, the battery cell B n When an abnormality occurs (the SOC value is obviously unreasonable compared with other battery cells in the same group), the n-1 series-parallel switching switches S of the series-parallel switching unit 6 n-1 (n=1,2,3…n) disconnect, battery discharge gate switch Q n or battery charging switch K n The positive switch of the battery is closed and the battery discharge gate switch Q n+1 or battery charging switch Kn+1 The positive switch is closed and the abnormal cell is removed from the battery pack.

[0073] In specific implementation, as a preferred embodiment of the present invention, the n-1 series-parallel switching switches S of the series-parallel switching unit 6 n-1 (n=1,2,3…n) is disconnected, and the lithium battery cell is freely connected in parallel to one end of the flyback transformer; the n-1 series-parallel switching switches S of the series-parallel switching unit 6 n-1 (n=1,2,3…n)When closed, the lithium battery is connected in series to the battery pack for normal operation.

[0074] The present invention also provides a battery stratified balancing control method implemented based on the battery balancing system based on the series-parallel reconfigurable topology, comprising:

[0075] S1. Determine the number of battery cells 9 in each group; any number of battery cells 9 can be divided into one group, and multiple battery groups together constitute a battery pack to participate in external discharge; the balancing within and between groups is completed based on the balancing topology of the present invention, and the following description is based on 4 battery cells as one group;

[0076] S2, collecting the voltage and current parameters of each battery cell, and estimating the SOC value of each battery cell;

[0077] S3, determine whether there is an abnormal battery cell, if so, remove the cell and then perform balancing;

[0078] S4, determining the intra-group and inter-group balance intervals, wherein the balance intervals include intra-group / inter-group balance start and end reference values ​​and intra-group / inter-group balance switching reference values;

[0079] S5. Determine the battery balancing state according to the SOC value of the battery cell and the intra-group / inter-group balancing interval. The balancing state includes discharge, charge, and imbalance.

[0080] S6. Carry out intra-group balance and inter-group balance in turn.

[0081] In specific implementation, as a preferred embodiment of the present invention, step S6 specifically includes: adopting a battery stratified balancing control method to control the balancing within the battery pack in the order of first balancing within the group and then balancing between groups, wherein:

[0082] The internal balancing of the group includes: determining the SOC value of the lithium battery cells in the group, defining the average value of the SOC value of the lithium battery in the group as SOC averge ; Set the internal balancing start threshold STD and the balancing threshold δ; determine the charging and discharging of the battery cells according to the central threshold comparison method.

[0083] In specific implementation, as a preferred embodiment of the present invention, the battery stratified balancing control method is provided with an intra-group static balancing mode and an inter-group charge and discharge balancing mode, wherein:

[0084] In the static balance mode within the group, the start threshold STD is set to 0.1% and the balance threshold δ is 0.05%;

[0085] In the inter-group charge and discharge balance mode, the on threshold value STDM is set to 0.4% and the balance threshold value ε is set to 0.2%.

[0086] Example 1

[0087] Set the initial SOC values ​​of the 4 battery cells in the group according to the following table, such as Figure 2 As shown, it is a schematic diagram of the intra-group balancing principle of the series-parallel reconfigurable battery balancing topology provided by the present invention under hypothetical conditions.

[0088]

[0089] During the intra-group balancing process, the balancing process includes the following steps:

[0090] Step 1: Calculate the average SOC value of the batteries in the group averge and standard deviation STD;

[0091] Step 2: Set the threshold for in-group balancing to 0.1%, that is, when the standard deviation STD is greater than 0.1%, in-group balancing is enabled, otherwise in-group balancing is not performed, and the balancing threshold δ is set to 0.05%;

[0092] Step 3: Control the SOC value to be greater than SOC averge +δ battery discharge, control SOC value less than SOC averge -δ batteries are charged, and the other batteries do not participate in balancing;

[0093] Step 4: Repeat the above steps until STD is less than 0.1% and the intra-group equilibrium is completed.

[0094] According to the above balancing steps, batteries B1 and B3 are discharged, and batteries B2 and B4 are charged, wherein the discharge control switches Q1 and Q3 are closed, the charge control switches K2 and K4 are closed, and the other switches are in the off state. During the balancing process, when M1 is turned on and M2 is turned off, batteries B1 and B3 release electrical energy, I p The current I sThe slope on the primary side is reduced, thereby transferring energy to the secondary winding of the transformer, further charging the battery cells connected to the secondary winding of the transformer. The balancing current in the balancing process can be changed by changing the duty cycle of the PWM signal that controls the operation of M1 and M2.

[0095] Example 2

[0096] The initial SOC value of battery B2 is set to 10%, and the other batteries are set as in Example 1, such as Figure 3 As shown, it is a bypass schematic diagram of battery B2 failure in the series-parallel reconfigurable battery balancing topology of the present invention. Both paths shown can eliminate B2 to ensure the normal operation of the remaining batteries in the group. It should be noted that the voltage fluctuation caused by battery failure can be eliminated by the internal stability control of the DC-DC converter connected thereto.

[0097] Example 3

[0098] like Figure 4 As shown, it is a diagram of the balancing control strategy of the series-parallel reconfigurable battery balancing topology structure of the present invention. The hierarchical control is divided into intra-group balancing and inter-group balancing. Taking into account the characteristics of the balancing topology reconstruction proposed in the present invention, the hierarchical balancing strategy is set to perform intra-group balancing first, and then perform inter-group balancing after the intra-group balancing is completed and the battery cells are connected in series into groups.

[0099] Example 4

[0100] like Figure 5 As shown in the figure, it is a lithium balancing simulation model diagram of the series-parallel reconfigurable battery balancing topology structure of the present invention. The series-parallel reconfigurable battery balancing topology structure of the present invention couples four Battery models to form a battery pack model. The parameters of each component in the simulation model include: Battery model type selects lithium battery, rated voltage 3.7V, rated capacity 3.5AH, and the excitation inductance L of the flyback converter p Set to 0.001H, primary-secondary transformation ratio set to 1:1, primary-secondary internal resistance and leakage inductance are both set to 0, primary-secondary N-channel Mos field effect transistor resistance set to 0.1hms, internal diode inductance 0H, internal diode resistance 0.01hms, internal diode forward voltage 0V, buffer resistance 105hms, buffer capacitance set to inf, switching frequency 10KHZ, and the rest remain default.

[0101] Example 5

[0102] like Figure 6As shown, the static balancing result of the group in Example 1 obtained by the present invention based on the simulation model, the controlled current source input is set to 0, that is, the battery is in a static state, the group balancing start threshold δ is set to 0.1%, and the balancing threshold θ is set to 0.05%. The simulation model is run to obtain the SOC change of the battery cells in the group under the control of the balancing method proposed in the present invention;

[0103] Example 6

[0104] like Figure 7 As shown in the figure, the group balancing result when battery B2 fails in Example 2 obtained by the present invention based on the simulation model. Since battery failure mainly occurs during the discharge process, the simulation experiment will also simulate the topological reconstruction of the faulty battery cells in the group during discharge. The initial SOC value of battery B2 in the group is set to 10%, and the initial SOC values ​​of other battery cells in the group remain unchanged. At the beginning of balancing, it is considered that battery B2 fails. Figure 7 The middle path bypasses it out of the battery pack, and the remaining batteries participate in balancing normally.

[0105] Example 8

[0106] like Figure 8 As shown, the inter-group discharge balancing result in Example 2 obtained by the present invention based on the simulation model is shown. After the intra-group balancing of three battery groups is completed, the inter-group balancing is started. After the balancing is completed at 455.9s and the monomers are connected in series, they continue to release energy to the outside.

[0107] In summary, according to the above technical solution, the removal of abnormal battery cells and the energy balance of other battery cells can be achieved by reasonably controlling the corresponding switches of each battery, that is, the inconsistency in the battery pack is effectively reduced and the safe operation of the battery pack is ensured.

[0108] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A battery balancing system based on a series-parallel reconfigurable topology, characterized in that: A battery cell (9) is connected, comprising: a flyback conversion unit (2) and an operating mode control unit (1), wherein: The flyback conversion unit (2) is used to transfer energy from one side of the primary winding to one side of the secondary winding to achieve battery balancing; The working mode control unit (1) is composed of a Schottky diode and an NMOS connected in parallel, respectively connected to two sides of the flyback conversion unit (2), and is used to control the working mode of the flyback conversion unit (2); it includes a charging control unit (3), a discharging control unit (4) and a series-parallel switching unit (5), wherein: The charging control unit (3) is used to control the battery cells (9) whose SOC meets the requirements of the control strategy to be connected to one side of the secondary winding of the flyback conversion unit (2), and the battery is in a charging state at this time; The discharge control unit (4) is used to control the SOC to meet the control strategy requirements. The battery cell (9) is connected to one side of the primary winding of the flyback conversion unit (2), and the battery is in a discharge state at this time; The switch of the series-parallel switching unit (5) is disconnected, and the battery cells (9) are respectively connected in parallel to the two sides of the flyback conversion unit (2) for battery balancing. After the balancing is completed, the switch of the series-parallel switching unit (5) is closed, and each battery cell (9) is connected in series to the battery pack in sequence to participate in discharge.

2. A battery balancing system based on a series-parallel reconfigurable topology according to claim 1, characterized in that: The flyback conversion unit (2) comprises a control unit (6), a protection unit (7) and a conversion unit (8), wherein: A control unit (6), comprising two N-channel metal oxide semiconductor field effect transistors M1 and M2; A protection unit (7), comprising two Schottky diodes, each Schottky diode being connected in parallel with an NMOS, wherein the Schottky diode plays a role of freewheeling protection; The conversion unit (8) includes a flyback converter. After the conversion unit is connected to the battery cell (9), the excess energy of the high-power battery is transferred to the low-power battery, so as to reduce the inconsistency of the batteries in the group.

3. The battery balancing system based on a series-parallel reconfigurable topology according to claim 1, characterized in that: In the working mode control unit: The charging control unit (3) comprises n battery charging selection switches K n (n=1,2,3,…n), respectively connected to the corresponding battery cells (9) B n To the secondary winding side of the conversion unit (8); The discharge control unit (5) comprises n battery discharge selection switches Q n (n=1,2,3…n), respectively connected to the corresponding battery cells (9) B n To the primary winding side of the conversion unit (8); The series-parallel switching unit (6) comprises n-1 series-parallel switching switches S n-1 , located between n battery cells (9), and used to change the connection state of each battery cell (9) in the group at different stages.

4. The battery balancing system based on a series-parallel reconfigurable topology according to claim 1, characterized in that: The n battery charging selection switches K in the charging control unit (3) n (n=1, 2, 3, ... n) is in a closed state, the battery cell (9) B n Battery charging enable switch K n The secondary winding side connected to the conversion unit (8) is in a charging state.

5. The battery balancing system based on a series-parallel reconfigurable topology according to claim 1, characterized in that: The n battery discharge selection switches Q in the discharge control unit (5) n (n=1, 2, 3, ... n) is in a closed state, the battery cell (9) B n The battery discharge gate switch Q n The primary winding side connected to the conversion unit (8) is in a discharge state.

6. The battery balancing system based on a series-parallel reconfigurable topology according to claim 1, characterized in that: The n battery charging selection switches K in the charging control unit (3) n When (n=1, 2, 3, ... n) is in a closed state, the n battery discharge gating switches Q in the corresponding discharge control unit (5) n (n=1, 2, 3...n) is in the off state; the n battery discharge gating switches Q in the discharge control unit (5) n (n=1, 2, 3...n) is in a closed state, the corresponding n battery charging selection switches K in the charging control unit (3) n (n=1, 2, 3, ... n) is in the off state; the n battery charging selection switches K in the charging control unit (3) n (n=1, 2, 3, ... n) and n battery discharge gating switches Q in the discharge control unit (5) n When (n=1, 2, 3...n) are in the off state at the same time, it indicates that the battery cells (9) are in an unbalanced state.

7. The battery balancing system based on a series-parallel reconfigurable topology according to claim 1, characterized in that: The battery cell B n (n=1, 2, 3...n) When an abnormality occurs, the n-1 series-parallel switching switches S of the series-parallel switching unit (6) n-1 (n=1,2,3…n) disconnect, battery discharge gate switch Q n or battery charging switch K n The positive switch of the battery is closed and the battery discharge gate switch Q n+1 or battery charging switch K n+1 The positive switch of the battery is closed and the abnormal single cell is removed from the battery pack.

8. A battery stratified balancing control method implemented by the battery balancing system based on the series-parallel reconfigurable topology according to any one of claims 1 to 7, characterized in that: include: S1. Determine the number of battery cells (9) in each group; any number of battery cells (9) can be grouped into one group, and multiple groups of battery cells together constitute a battery pack for external discharge; S2, collecting the voltage and current parameters of each battery cell, and estimating the SOC value of each battery cell; S3, determine whether there is an abnormal battery cell, if so, remove the cell and then perform balancing; S4, determining the intra-group and inter-group balance intervals, wherein the balance intervals include intra-group / inter-group balance start and end reference values ​​and intra-group / inter-group balance switching reference values; S5. Determine the battery balancing state according to the SOC value of the battery cell and the intra-group / inter-group balancing interval. The balancing state includes discharge, charge, and imbalance. S6. Carry out intra-group balance and inter-group balance in turn.

9. The battery stratification balancing control method according to claim 8, characterized in that: Step S6 specifically includes: adopting a battery stratified balancing control method to control the balancing within the battery pack in the order of first balancing within the group and then balancing between groups, wherein: The internal balancing of the group includes: determining the SOC value of the lithium battery cells in the group, defining the average value of the SOC value of the lithium battery in the group as SOC averge ; Set the internal balancing start threshold STD and the balancing threshold δ; determine the charging and discharging of the battery cells according to the central threshold comparison method.

10. The battery stratification balancing control method according to claim 9, characterized in that: The battery stratified balancing control method is provided with an intra-group static balancing mode and an inter-group charge and discharge balancing mode, wherein: In the static balance mode within the group, the start threshold STD is set to 0.1% and the balance threshold δ is 0.05%; In the inter-group charge and discharge balance mode, the on threshold value STDM is set to 0.4% and the balance threshold value ε is set to 0.2%.

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