Battery management method and system

Abstract

The invention relates to the technical field of battery management, and discloses a battery management method and system. A topological structure of a battery pack is reconstructed by introducing a first switch and a second switch, each battery pack is connected in parallel with a first equalization structure consisting of four third switches and an energy storage inductor, and the first switch, the second switch and the first equalization structure are controlled, so that electric quantity equalization between any two single batteries can be realized; a plurality of battery packs are connected in series, a bidirectional flyback converter is added, and the battery packs needing to be subjected to electric quantity equalization are used as input and output of the converter through the bidirectional flyback converter, so that energy is quickly transmitted between any battery packs, and direct equalization between any plurality of adjacent or non-adjacent battery packs is realized; meanwhile, equalization can be carried out when the battery pack does not work, the equalization efficiency of the battery pack is improved, and the problem of inconsistency of the battery pack is solved.

Description

Technical Field

[0001] The present application relates to the field of battery management technology, and in particular to a battery management method and system. Background Art

[0002] With the worsening of the global energy crisis and the improvement of human environmental awareness, lithium battery energy storage technology has been widely used in people's lives and has great development prospects. Since single lithium batteries often cannot meet the power requirements of energy storage systems, multiple single lithium batteries are usually connected in series or in parallel to form a battery pack to increase the output power of the energy storage system.

[0003] When multiple batteries work at the same time, the inconsistency problem of the battery pack will occur. This inconsistency problem originates from uncontrollable factors in the battery design, manufacturing, and storage links, which will lead to increased energy loss of the battery pack, increased heat generation, affecting the overall performance of the battery pack, and accelerating the aging of the battery. The existing approaches to solving the battery consistency problem mainly focus on passive balancing of battery packs, active balancing of battery packs, and reconfigurable balancing of battery packs. Among them, passive balancing mainly consumes the electric energy of some batteries with higher battery capacity on series resistors to achieve the same capacity of all batteries, but this method has the problems of slow balancing speed, low efficiency, and energy waste. Active balancing avoids the problem of energy waste by directly transferring electric energy between batteries to achieve the effect of the same capacity of each battery, but the existing active balancing circuit is affected by its topological structure and can only balance between adjacent batteries, resulting in longer balancing time and reduced balancing efficiency. The reconfigurable battery pack balancing circuit and balancing method bypasses some batteries through switches, thereby achieving the effect of giving priority to charging batteries with high capacity when the battery pack is charged, and giving priority to discharging batteries with low capacity when the battery pack is discharged, ultimately achieving overall capacity balancing of the battery pack. However, this balancing can only occur when the battery pack is charging and discharging, and the battery pack balancing effect cannot be achieved when the energy storage system is not working. Summary of the invention

[0004] To this end, the embodiments of the present application provide a battery management method and system, which can achieve balancing of non-adjacent batteries when they are not working, making the balancing more flexible and efficient.

[0005] In a first aspect, the present application provides a battery management method.

[0006] The present application is realized by the following technical solutions: a battery management method, applied to a battery management system, the battery management system comprising: a plurality of battery packs, a plurality of first balancing structures, a second balancing structure and a control module;

[0007] Each battery pack is composed of a plurality of single cells connected in series, a plurality of first switches and a plurality of second switches, each single cell is connected in series with a first switch, and each single cell is connected in series with a first switch and then connected in parallel with a second switch; a first balancing structure is connected in parallel at both ends of a battery pack, and the first balancing structure is composed of a storage inductor and four third switches; the second balancing structure includes a bidirectional flyback converter and a plurality of fourth switches, and the bidirectional flyback converter is connected to a plurality of battery packs through the fourth switches; a control module is connected to the battery pack, the first balancing structure and the second balancing structure;

[0008] The control module is used to perform the following steps:

[0009] Obtaining the SOC values ​​of all the single cells in each battery pack, determining a number of first single cells corresponding to the maximum SOC value and a number of second single cells corresponding to the minimum SOC value in the battery pack, and when a first difference between the maximum SOC value and the minimum SOC value is greater than a first balancing threshold, performing power balancing between the first single cells and the second single cells by regulating the first balancing structure, the first switch and the second switch until the SOC values ​​of the single cells in each battery pack are consistent;

[0010] The average SOC value of each battery group is obtained, and a number of first battery groups corresponding to the average SOC maximum value and a number of second battery groups corresponding to the average SOC minimum value are determined. When a second difference between the average SOC maximum value and the average SOC minimum value is greater than a second balancing threshold, the second balancing structure is adjusted to balance the power between the first battery group and the second battery group until the SOC average values ​​of all battery groups are consistent.

[0011] In a preferred example of the present application, it can be further configured that the first balancing structure, the first switch and the second switch are adjusted to balance the power between the first single cell and the second single cell, including:

[0012] By adjusting the conduction relationship between the first switch and the second switch, the first single cell and the second single cell are connected to the circuit, and the single cells other than the first single cell and the second single cell are bypassed;

[0013] By regulating the conduction relationship of the four third switches in the first balancing structure and controlling the closing of the energy storage inductor, a charge and discharge loop is formed between the first single cell and the second single cell, so that the first single cell and the second single cell are charged and balanced through the energy storage inductor.

[0014] In a preferred example of the present application, it can be further configured that when the power balancing is performed between the first single battery and the second single battery, it includes:

[0015] The difference interval to which the first difference belongs is determined, and the magnitude of the balancing current is determined according to the difference interval.

[0016] In a preferred example of the present application, it can be further configured to include:

[0017] When the first difference belongs to the first difference interval (x 1 ,x 2 ], the first balancing current I 1 ;

[0018] When the first difference belongs to the second difference interval (x 2 ,x 3 ], the second balancing current I 2 ;

[0019] When the first difference belongs to the third difference interval (x 3 ,x 4 ], the third balancing current I 3 ;

[0020] where x 1 <x 2 <x 3 , I 1 <I 2 <I 3 , x 1 ,x 2 , x 3 ∈(0,1), I 1 , I 2 , I 3 ∈[0.3C, 2C], where C represents the current intensity when the battery is fully discharged in one hour.

[0021] In a preferred example of the present application, it can be further set as follows:

[0022] By regulating the second balancing structure, power balancing is performed between the first battery group and the second battery group, including:

[0023] The bidirectional flyback converter is connected to the positive terminals and negative terminals of the corresponding battery packs through the fourth switches;

[0024] The fourth switch is controlled to be turned on and off, and the first battery group and the second battery group are connected to the circuit, so that the first battery group and the second battery group are charged evenly through the bidirectional flyback converter.

[0025] In a preferred example of the present application, it can be further configured that when the power balancing is performed between the first battery group and the second battery group, the method includes:

[0026] Determine the difference interval to which the second difference belongs, and determine the magnitude of the balancing current according to the difference interval.

[0027] In a preferred example of the present application, it can be further configured to include:

[0028] When the second difference belongs to the first difference interval (x 1 ,x 2 ], the first balancing current I 1 ;

[0029] When the second difference belongs to the second difference interval (x 2 ,x 3 ], the second balancing current I 2 ;

[0030] When the second difference belongs to the third difference interval (x 3 ,x 4 ], the third balancing current I 3 ;

[0031] where x 1 <x 2 <x 3 , I 1 <I 2 <I 3 , x 1 ,x 2 , x 3 ∈(0,1),I 1 , I 2 , I 3 ∈[0.3C, 2C], where C represents the current intensity when the battery is fully discharged in one hour.

[0032] In a second aspect, the present application provides a battery management system based on double-layer balancing.

[0033] The present application is realized by the following technical solutions: a battery management system based on double-layer balancing, comprising a plurality of battery packs, a plurality of first balancing structures, a second balancing structure and a control module;

[0034] Each battery pack is composed of a plurality of single cells connected in series, a plurality of first switches and a plurality of second switches, wherein the positive electrode or the negative electrode of each single cell is connected in series with a first switch, and each single cell and a first switch are connected in parallel with a second switch, and the first switch and the second switch are in a complementary conduction relationship;

[0035] Each first balancing structure includes an energy storage inductor and four third switches, the energy storage inductor is connected to a battery pack through the four third switches, and the first balancing structure is used to balance the power between the single cells;

[0036] The second balancing structure includes a bidirectional flyback converter and a plurality of fourth switches, wherein the bidirectional flyback converter is connected to a positive terminal of a battery pack through a fourth switch and is connected to a negative terminal of a battery pack through a fourth switch; the second balancing structure is used to balance the power between the battery packs;

[0037] The control module is connected to the battery pack, the first balancing structure and the second balancing structure, and is used to obtain performance parameters of single cells, control structural changes of the battery pack, and control the first balancing structure and the second balancing structure.

[0038] In a preferred example of the present application, it can be further configured that the first switch is a conduction switch for connecting the corresponding single cells connected in series to the circuit; and the second switch is a bypass switch for disconnecting the corresponding single cells connected in parallel from the circuit.

[0039] In a preferred example of the present application, it can be further configured that the first switch, the second switch, the third switch and the fourth switch are all automatic control switches.

[0040] In summary, compared with the prior art, the technical solution provided in the embodiment of the present application has at least the following beneficial effects: by introducing the first switch and the second switch to reconstruct the topological structure of the battery pack, and connecting a first balancing structure consisting of four third switches and an energy storage inductor in parallel to each battery pack, and controlling the first switch, the second switch and the first balancing structure, it is possible to achieve power balancing between any two single cells; by connecting several battery packs in series and adding a bidirectional flyback converter, the battery pack that needs to be power balanced is used as the input and output of the converter through the bidirectional flyback converter, so that energy can be quickly transferred between any battery packs, and direct power balancing between any multiple adjacent or non-adjacent single cells and between battery packs is achieved. At the same time, power balancing can be performed when the battery is not working, which improves the balancing efficiency of the battery pack and solves the inconsistency problem of the battery pack, thereby improving the energy utilization efficiency of the battery pack, extending the life, and improving the safety performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 A schematic diagram of a conventional circuit for balancing adjacent single cells provided by an exemplary embodiment of the present application;

[0042] Figure 2 A schematic diagram of the structure of a battery management system provided by an exemplary embodiment of the present application;

[0043] Figure 3 A schematic structural diagram of a single cell and a first balancing structure provided by an exemplary embodiment of the present application;

[0044] Figure 4A schematic structural diagram of a battery pack and a second balancing structure provided by an exemplary embodiment of the present application;

[0045] Figure 5 A flowchart of a battery management method provided by an exemplary embodiment of the present application;

[0046] Figure 6 A schematic diagram of the principle of balancing between single cells provided by an exemplary embodiment of the present application;

[0047] Figure 7 A schematic diagram of the principle of balancing between single cells provided by an exemplary embodiment of the present application;

[0048] Figure 8 A schematic diagram of the principle of a battery pack balancing process provided by an exemplary embodiment of the present application;

[0049] Fig. 9 A schematic diagram of simulation results of a simulation experiment provided for an exemplary embodiment of the present application;

[0050] Description of reference numerals:

[0051] Battery pack-10, first balancing structure-20, second balancing structure-30, control module-40, single battery-101, first switch-102, second switch-103, energy storage inductor-201, third switch-202, bidirectional flyback converter-301, fourth switch-302. DETAILED DESCRIPTION

[0052] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the present embodiment without any creative contribution as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

[0053] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0054] In addition, the term "and / or" in this application is only a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this application, unless otherwise specified, generally indicates that the associated objects before and after are in an "or" relationship.

[0055] In this application, the terms "first", "second", etc. are used to distinguish identical or similar items with basically the same effects and functions. It should be understood that there is no logical or temporal dependency between "first", "second", and "nth", nor is there any limitation on quantity and execution order.

[0056] In energy storage systems represented by lithium batteries, it is very important to ensure the consistency of batteries. If the performance of batteries is inconsistent, it may cause battery heating, reduced efficiency and even shortened life. At present, the main method to reduce battery inconsistency is to rely on battery balancing. Balancing control is to charge and discharge single cells so that each single cell in the battery pack reaches a consistent state of charge. Figure 1 As shown, it is a circuit schematic diagram of conventional balancing between adjacent single cells. If it is detected that the capacity of single cell B1 is higher than that of single cell B3, to achieve balancing between single cell B1 and single cell B3, single cell B1 must charge single cell B2 through inductor L1, and then single cell B2 must charge single cell B3 through inductor L2.

[0057] In order to realize that non-adjacent single cells can be directly balanced and to be able to balance when the battery is not in operation, that is, when the battery is not in a charging state or a non-discharging state, the present application designs a battery management system, such as Figure 2 As shown, the battery management system includes: a plurality of battery packs 10, a plurality of first balancing structures 20, a second balancing structure 30 and a control module 40;

[0058] Each battery pack 10 is composed of a plurality of single cells 101 connected in series, a plurality of first switches 102 and a plurality of second switches 103. The positive electrode or the negative electrode of each single cell 101 is connected in series with a first switch 102. Each single cell 101 and a first switch 102 are connected in parallel with a second switch 103. The first switch 102 and the second switch 103 are in a complementary conduction relationship.

[0059] Each first balancing structure 20 includes an energy storage inductor 201 and four third switches 202. The energy storage inductor 201 is connected to a battery pack 10 through the four third switches 202. The first balancing structure 20 is used to balance the power between the single cells 101.

[0060] The second balancing structure 30 includes a bidirectional flyback converter 301 and a plurality of fourth switches 302. The bidirectional flyback converter 301 is connected to the positive terminal of a battery pack 10 through a fourth switch 302, and is connected to the negative terminal of a battery pack 10 through a fourth switch 302. The second balancing structure 30 is used to balance the power between the battery packs 10.

[0061] The control module 40 is connected to the battery pack 10 , the first balancing structure 20 and the second balancing structure 30 , and is used to obtain performance parameters of the single battery 101 , control structural changes of the battery pack 10 , and control the first balancing structure 20 and the second balancing structure 30 .

[0062] like Figure 3 As shown, each battery pack is a reconfigurable battery pack, including a plurality of single cells B connected in series. 1 ~B n , a first switch Q connected in series with the positive or negative electrode of each single battery 1 ~Q n , a second switch Q connected in parallel with each single battery and the first switch 1s ~Q ns . Each single cell is connected in series with a first switch, and the connection mode can be set as: each first switch is connected to the positive electrode of the corresponding single cell, or each first switch is connected to the negative electrode of the corresponding single cell. The second switch is connected in parallel with the first switch and the corresponding single cell. The number of single cells contained in the reconfigurable battery pack is n, and n is a positive integer, which can be set according to actual needs. In this application, it can be 4 to 6. Among them, the opening relationship between the first switch and the second switch is complementary conduction. Specifically, the first switch is a conduction switch, and the second switch is a bypass switch; the function of the conduction switch is to connect the corresponding single cell in series to the circuit, and the function of the bypass switch is to bypass the corresponding single cell in parallel, that is, disconnect it from the circuit, while ensuring that the battery pack will not be broken. Complementary conduction means that when the first switch corresponding to a single cell is closed and turned on, the second switch corresponding to the single cell is disconnected; or when the first switch corresponding to the single cell is disconnected, the second switch corresponding to the single cell is closed and turned on. By controlling the conduction and closure of the first switch and the second switch, balancing can be achieved between any adjacent or non-adjacent single cells.

[0063] The first balancing structure is a structure for balancing the internal charge of the battery pack, such as Figure 3As shown, it includes an energy storage inductor L and four third switches S1 to S4, and the third switch is a loop selection switch. The energy storage inductor is connected to a battery pack through the conduction and closure of the four loop selection switches. An energy storage inductor and four loop selection switches are added on the basis of the battery pack, wherein the energy storage inductor is connected to the positive end of the battery pack through two loop selection switches and to the negative end of the battery pack through two loop selection switches, for example, the energy storage inductor is connected to the positive end of the battery pack through the first loop selection switch and the third loop selection switch, and is connected to the negative end of the battery pack through the second loop selection switch and the fourth loop selection switch. The energy storage inductor can be connected to the battery pack to form a charging circuit or a discharging circuit by the conduction and closure of the four loop selection switches, so as to realize the charging and discharging between any single cells in the reconfigurable battery pack.

[0064] The second balancing structure is a structure for balancing the power between different battery groups, such as Figure 4 As shown, it includes a bidirectional flyback converter and a plurality of fourth switches K 1 ~K 2n The fourth switch can be called a module selection switch. The bidirectional flyback converter is connected to the corresponding battery packs M through a plurality of module selection switches. 1 ~M n The positive and negative ends of the battery pack are connected. The number of module selection switches is twice the number of battery packs, and the bidirectional flyback converter and each battery pack are connected through two module selection switches. By turning the module selection switch on and off, the bidirectional flyback converter realizes the storage and transmission of energy between battery packs. It should also be noted that the bidirectional flyback converter has a high energy conversion efficiency and can reduce energy loss. Secondly, the bidirectional flyback converter has the characteristics of fast response speed, which can speed up the energy transfer between battery packs. In addition, because the bidirectional flyback converter has the function of electrical isolation, when balancing between different battery packs, the output can be kept stable.

[0065] The control module is connected to several battery packs, several first balancing structures and second balancing structures, and is used to obtain the performance parameters of the single battery, control the structural change of the battery pack, and control the first balancing structure and the second balancing structure. The control module can be a microcontroller, a digital signal processor, and for example, a BMS management system can be used.

[0066] The control module obtains the SOC value (state of charge value) of each single cell in the reconfigurable battery pack, determines the first difference between the maximum state of charge and the minimum state of charge, and determines whether the first difference is greater than the preset first balancing threshold value. If so, the first balancing structure is controlled to balance the first single cells corresponding to the maximum state of charge and the second single cells corresponding to the minimum state of charge until all single cells in the reconfigurable battery pack are balanced to the same state of charge value. After the control module determines the first single cell and the second single cell that need to be balanced in the reconfigurable battery pack, the control module adjusts the conduction and disconnection of the first switch and the second switch corresponding to the single cell so that the single cell that needs to be balanced is connected to the balancing circuit, and the remaining single cells are bypassed; and by controlling the conduction and disconnection of the circuit selection switch of the energy storage inductor, the single cell with a high state of charge value is charged to the energy storage inductor, and the energy storage inductor is discharged to the single cell with a low state of charge value, so that the state of charge value of the single cell with a high state of charge value and the single cell with a low state of charge value are consistent. After all the single cells are balanced, all switches are turned off to end the power balance between the single cells in the battery pack.

[0067] The control module further determines the first battery group and the second battery group that need to be balanced, closes the module selection switch between the first battery group and the second battery group and the bidirectional flyback converter, and realizes the transmission of electric energy between the battery groups by controlling the bidirectional flyback converter until the two battery groups are balanced, disconnects the module selection switch between the two battery groups and the bidirectional flyback converter, and balances the remaining battery groups. The switches in this application are all automatically controlled switches, that is, the first switch, the second switch, the third switch, and the fourth switch are all automatically controlled switches.

[0068] The battery management system can directly balance non-adjacent single cells, avoiding energy transfer loss in the middle single cells and improving the equalization efficiency of the battery pack; at the same time, it can balance the single cells when they are not working, avoiding interference and influence on the battery caused by equalization during the battery charging or discharging process; it helps to improve the overall performance of the battery pack.

[0069] In some preferred embodiments, the control module includes a balancing current determination unit.

[0070] In some preferred embodiments, the balancing current determining unit is used to determine the difference interval to which the first difference belongs according to the first difference in the state of charge values ​​of the first single cell and the second single cell to be balanced, and determine the magnitude of the balancing current according to the difference interval.

[0071] In some preferred embodiments, the balancing current determination unit is used to determine a difference interval to which the second difference belongs according to the second difference in the state of charge values ​​of the first battery group and the second battery group to be balanced, and determine the magnitude of the balancing current according to the difference interval.

[0072] Specifically, the balancing current determination unit stores a plurality of preset difference intervals, each difference interval corresponding to a balancing current of different magnitudes. The balancing current determination unit compares the first difference with the difference interval in the balancing current determination unit, and determines the magnitude of the balancing current according to the difference interval to which the first difference belongs; and compares the second difference with the difference interval in the balancing current determination unit, and determines the difference interval to which the second difference belongs, and thus determines the magnitude of the balancing current.

[0073] In some embodiments, the balanced current determination unit stores three preset different difference intervals. The first difference interval (x 1 ,x 2 ] corresponds to the first balancing current I 1 ; The second difference interval (x 2 ,x 3 ], corresponding to the second balancing current I 2 ; The third difference interval (x 3 ,x 4 ], corresponding to the third balancing current I 3 , where x 1 <x 2 <x 3 , and are all values ​​greater than 0 and less than 1. The relationship between the balancing currents is I 1 <I 2 <I 3 , x 1 ,x 2 , x 3 ∈(0,1), I 1 , I 2 , I 3 ∈[0.3C, 2C]. For example, when the difference interval is in the first difference interval (0.1, 0.2], the first balancing current 0.3C is used; when the difference interval is in the second difference interval (0.2, 0.4], the second balancing current 1.0C is used; when the difference interval is in the third difference interval (0.4, 1.0], the third balancing current 2.0C is used, and 1.0C represents the current intensity when the battery is fully discharged in one hour. In the bottom balancing and top balancing processes, different balancing currents are set according to the state of charge difference of the object to be balanced. When the state of charge difference is large, a larger balancing current is used to improve the balancing efficiency. When the state of charge difference is small, a smaller balancing current is used to ensure the balancing accuracy.

[0074] like Figure 5 As shown, the present application also provides a battery management method, which is based on the above-mentioned battery management system, and the control module performs the following steps:

[0075] S10: Obtain the SOC values ​​of all single cells in each battery pack, determine a number of first single cells corresponding to the maximum SOC value and a number of second single cells corresponding to the minimum SOC value in the battery pack, and when a first difference between the maximum SOC value and the minimum SOC value is greater than a first balancing threshold, perform power balancing between the first single cells and the second single cells by regulating the first balancing structure, the first switch and the second switch until the SOC values ​​of the single cells in each battery pack are consistent.

[0076] In the actual implementation process, the specific steps are as follows: the control module obtains the state of charge value of each single cell in the battery pack, that is, the SOC value. Determine the single cell corresponding to the maximum SOC value, which can correspond to one or more single cells; determine the single cell corresponding to the minimum SOC value, which can be one or more single cells. Determine the first difference between the maximum SOC value and the minimum SOC value, and judge whether the first difference is greater than the preset first balancing threshold. If the first difference is greater than the first balancing threshold, balance the first single cell corresponding to the maximum SOC value and the second single cell corresponding to the minimum SOC value until the SOC values ​​of all single cells in the battery pack are consistent, and all battery packs are balanced. For example, the battery management system contains n battery packs M 1 ~M n After this step of balancing, the battery pack M 1 The SOC values ​​of all the cells inside are consistent, and the battery pack M 2 The SOC values ​​of all the cells inside are consistent, and the battery pack M n-1 The SOC values ​​of all the cells inside are consistent, and the battery pack M n The SOC values ​​of all internal single batteries are consistent.

[0077] For example, get the battery pack M 1 All single cells in B 1 ~B n State of charge value SOC 1 ~SOC n , sort the state of charge values ​​from large to small, and determine the maximum state of charge SOC max and the minimum state of charge SOC min The first difference ΔSOC between 1 , determine the first difference ΔSOC 1 Is it greater than the preset first equilibrium threshold σ 1 , when ΔSOC 1>σ 1 When the maximum state of charge SOC max The corresponding single battery and the minimum state of charge SOC min The corresponding single cells are balanced until the state of charge values ​​of the single cells being balanced are the same. The above-mentioned balanced single cells are regarded as a balanced state of charge value SOC′, and are sorted with the state of charge values ​​of the remaining single cells to determine the single cells that need to be balanced. The above process is iterated until all single cells are balanced. The first balancing threshold σ 1 It can be set according to actual needs. In this application, the first balance threshold σ 1 Set to 0.1.

[0078] S20: Obtain the average SOC value of each battery group, determine a number of first battery groups corresponding to the average SOC maximum value and a number of second battery groups corresponding to the average SOC minimum value, and when the second difference between the average SOC maximum value and the average SOC minimum value is greater than a second balancing threshold, perform power balancing between the first battery group and the second battery group by adjusting the second balancing structure until the SOC averages of all battery groups are consistent.

[0079] In the actual implementation process, the specific steps are as follows: the control module obtains the average state of charge values ​​of all single cells of each battery group as the state of charge value of the battery group. Determine that the average SOC maximum value corresponds to the first battery group, which may correspond to one battery group or multiple battery groups; determine that the average SOC minimum value corresponds to the second battery group, which may correspond to one battery group or multiple battery groups. Calculate the second difference between the average SOC maximum value and the average SOC minimum value, and determine whether the second difference is greater than the preset second balancing threshold. If the second difference is greater than the preset second balancing threshold, the first battery group corresponding to the average SOC maximum value and the second battery group corresponding to the average SOC minimum value are balanced, and the balancing is terminated when the state of charge values ​​of all battery groups are consistent.

[0080] For example, the control module obtains all battery packs M 1 ~M n The average state of charge SOC 1 ′~SOC n ′, determine the maximum state of charge average SOC′ max and the minimum state of charge average SOC′ min and a second difference ΔSOC′ between the two, and determining whether the second difference ΔSOC′ is greater than a preset second balancing threshold σ 2 , that is, ΔSOC′>σ 2 If so, set SOC′ max The corresponding first battery pack and SOC′ minThe corresponding battery groups are balanced until all battery groups M 1 ~M n If the state of charge of the two devices is consistent, the balancing ends. The second balancing threshold σ 2 It can be set according to actual needs and is set to 0.1 in this application.

[0081] Considering that when the power difference of single cells is large, balancing between battery groups at the beginning will further increase the inconsistency between single cells. Therefore, this application adopts the method of first balancing within the battery group, and then further balancing between battery groups after the power of single cells reaches a high consistency, which can make the battery consistency higher after balancing, and at the same time improve the balancing efficiency and shorten the balancing time.

[0082] It should be noted that in this application, the single cells and / or battery packs are balanced based on the state of charge value (SOC value), and the battery management method can be configured to balance the battery pack based on other performance parameters. Other performance parameters may be voltage value, current value, resistance value, rated capacity value, remaining capacity value, etc.

[0083] In step S10, by adjusting the conduction relationship between the first switch and the second switch, the first single cell and the second single cell are connected to the circuit, and the single cells other than the first single cell and the second single cell are bypassed; by adjusting the conduction relationship between the four third switches in the first balancing structure and controlling the closing of the energy storage inductor, a charge and discharge loop is formed between the first single cell and the second single cell, so that the first single cell and the second single cell are charged and balanced through the energy storage inductor.

[0084] In the actual implementation process, first control the single battery corresponding to the maximum value of the state of charge The first switch closure and single cell The second switch of the battery is turned off, the first switch of the remaining single battery is turned off and the second switch is turned on, the first circuit selection switch and the second circuit selection switch of the energy storage inductor are closed to connect to the charging circuit, the third circuit selection switch and the fourth circuit selection switch are turned off, and the single battery Charge the energy storage inductor; control the minimum state of charge corresponding to the single battery The first switch closure and single cell The corresponding second switch is turned off, the first switch of the remaining single battery is turned on and the second switch is turned off, the third circuit selection switch and the fourth circuit selection switch of the energy storage inductor are closed to connect to the discharge circuit, the first circuit selection switch and the second circuit selection switch are turned off, and the energy storage inductor is discharged to the single battery. Discharge.

[0085] In some embodiments, when performing power balancing on single cells, it is necessary to determine the difference interval to which the first difference belongs, and determine the magnitude of the balancing current to be used according to the difference interval. 1 ,x 2 ], the first balancing current I 1 ; If the first difference belongs to the second difference interval (x 2 ,x 3 ], the second balancing current I 2 ; If the first difference belongs to the third difference interval (x 3 ,x 4 ], the third balancing current I 3 ; where x 1 <x 2 <x 3 , I 1 <I 2 <I 3 , x 1 ,x 2 , x 3 ∈(0,1),I 1 , I 2 , I 3 ∈[0.3C, 2C].

[0086] In step S20, the bidirectional flyback converter is connected to the positive and negative ends of the corresponding battery groups through the fourth switches; the fourth switches are controlled to be turned on and off, and the first battery group and the second battery group are connected to the circuit, so that the first battery group and the second battery group are charged and balanced through the bidirectional flyback converter.

[0087] In the actual implementation process, first determine the battery pack corresponding to the maximum state of charge average value and the minimum state of charge average battery pack Place the battery pack The module selection switch between the positive and negative terminals of the battery pack and the input terminal of the bidirectional flyback converter is closed, The module selection switch between the output terminal of the bidirectional flyback converter is closed, and the battery pack The energy is delivered to the battery pack via a bidirectional flyback converter. transmission.

[0088] In some embodiments, when balancing the battery pack, it is necessary to determine the difference interval to which the second difference belongs, and determine the corresponding balancing current according to the difference interval. 1 ,x 2 ], the first balancing current I 1 ; If the second difference belongs to the second difference interval (x 2 ,x3 ], the second balancing current I 2 ; If the second difference belongs to the third difference interval (x 3 ,x 4 ], the third balancing current I 3 ; where x 1 <x 2 <x 3 , I 1 <I 2 <I 3 , x 1 ,x 2 , x 3 ∈(0,1),

[0089] I 1 , I 2 , I 3 ∈[0.3C, 2C].

[0090] The following is an example of a reconfigurable battery pack including four single cells, a battery management system with a first balancing structure and a second balancing structure. 1 ,B 2 ,B 3 ,B 4 State of charge value SOC 1 ,SOC 2 ,SOC 3 ,SOC 4 , after sorting, determine the single battery B 1 and B 3 The state of charge value is the largest and the same, recorded as SOC max , single cell B 2 and B 4 The state of charge value is the smallest and the same, recorded as SOC min , and ΔSOC 1 Greater than the first equilibrium threshold σ 1 , and ΔSOC 1 ∈(x 2 ,x 3 ], set the balancing current to I 2 Specific examples include Figure 6 As shown, control single battery B 1 and B 3 The corresponding conduction switches Q1 and Q3 are closed, controlling the single battery B 1 and B 3 The corresponding bypass switches Q1s and Q3s are disconnected, controlling the single battery B. 2 and B 4The conduction switches Q2 and Q4 are opened to prevent access to the charging circuit, and the bypass switches Q2s and Q4s are closed to enable the charging circuit. The first circuit selection switch S1 and the second circuit selection switch S2 are controlled to be closed to connect the energy storage inductor to the charging circuit, so that the single battery B 1 and B 3 The process of charging the energy storage inductor.

[0091] Figure 7 The energy storage inductor is supplied to the single battery B 2 and B 4 Schematic diagram of discharge. Since it is in the discharge state at this time, and based on the principle that the current of the energy storage inductor does not change suddenly, the third circuit selection switch S3 and the fourth circuit selection switch S4 are closed to connect the energy storage inductor to the discharge circuit, and the single battery B 2 and B 4 The conduction switches Q2 and Q4 are closed, the bypass switches Q6 and Q8 are disconnected, and the single battery B 1 and B 3 The conduction switches Q1 and Q3 are disconnected to prevent access to the charging circuit, and the bypass switches Q5 and Q7 are closed to enable the discharge circuit. 2 and B 4 During the entire bottom-level charge balancing process, all switches are turned on and off in a complementary manner until the SOC of each single cell is the same, then all switches are turned off and the bottom-level balancing is completed. The charge balancing process of the single cells between the remaining battery packs will not be described in detail.

[0092] like Figure 8 As shown, after the power balancing between the single cells at the bottom layer is completed, the power balancing between the battery groups at the top layer is performed. The SOC' value of each battery group (the average value of the SOC values ​​of all the single cells in the battery group) is obtained and calculated, and then the maximum state of charge SOC' is found respectively. max Corresponding battery pack M i and the minimum state of charge SOC′ min Corresponding battery pack M j , and ΔSOC 2 Greater than the second equilibrium threshold σ 2 , and ΔSOC 2 ∈(x 1 ,x 2 ], set the balancing current to I 1 By closing and conducting the module selection switch, one end of the bidirectional flyback converter is connected to the battery pack M i The output ends of the bidirectional flyback converter are connected to the battery pack M j Through the control of the bidirectional flyback converter, the battery pack M iTo the battery pack M j The power is delivered until the state of charge (SOC) of the two battery packs is equal. i and battery pack M j Considered as an identical battery pack, it is balanced with the other battery packs through the module selection switch until all battery packs are balanced, the top-level balancing is completed, and the balancing of the entire battery management system when not working is completed.

[0093] In order to verify the effectiveness of the proposed battery management system and method based on double-layer balancing, a battery management system based on double-layer balancing was built on the MATLAB Simulink simulation platform and simulated according to the battery management method. This simulation took 4 single cells as a reconfigurable battery pack, a total of 8 single cells, or two battery packs, as an example. The simulation results are as follows Fig. 9 shown.

[0094] In this simulation result, the battery pack M1 contains four cells, which are denoted as B1, B2, B3 and B4, and their initial SOC values ​​are 47%, 50%, 38% and 40% respectively. Another battery pack M2 contains four cells, which are denoted as B5, B6, B7 and B8, and their initial SOC values ​​are 58%, 60%, 45% and 40% respectively. At t = 0 seconds, the two battery packs start bottom balancing. When t=5.54 seconds, the state of charge values ​​of the two single cells B5 and B6 with higher SOC in the battery pack M2 first reach the same state, and at this time, single cells B5 and B6 jointly charge single cell B8. It can be seen from the simulation result diagram that the SOC growth rate of single cell B8 is accelerated at this moment; similarly, at t=9.58 seconds, the state of charge values ​​of the two single cells B1 and B2 with higher SOC in the battery pack M1 first reach the same state, and at this time, these two single cells jointly charge single cell B3, and the charging rate of single cell B3 is also accelerated to a certain extent. When t=12.6 seconds, the state of charge values ​​of the two single cells B3 and B4 with lower SOC in the battery pack M1 also reach the same state, and at this time, single cells B1 and B2 jointly charge single cells B3 and B4. When t=24.1 seconds, the battery pack M2 also reaches the same state of two batteries charging two batteries as the battery pack M1. When t=36 seconds, battery pack M1 completed balancing; when t=56 seconds, battery pack M2 completed balancing, and the bottom-level balancing ended. The system starts top-level balancing, and electric energy is transmitted through a bidirectional flyback converter. When t=86.5 seconds, the SOC values ​​of the two battery packs reach the same state, and the SOC values ​​of all single cells reach the same state. The double-layer active balancing is completed, and the energy storage system reaches a balanced state. The battery management system and method proposed in this application can effectively deal with the inconsistency problem of battery packs, solve the problem that traditional battery packs cannot be balanced during non-working hours, and solve the problem that traditional active balancing topologies cannot achieve power transfer between non-adjacent batteries. It greatly improves the balancing time and balancing efficiency of the battery pack while ensuring circuit flexibility.

[0095] Those skilled in the art can clearly understand that for the convenience and simplicity of description, only the above-mentioned functional modules and module divisions are used as examples. In actual applications, the above-mentioned functions can be distributed and completed by different functional modules and modules as needed, that is, the internal structure of the system described in the present application is divided into different functional modules or modules to complete all or part of the functions described above.

Claims

1. A battery management method, characterized in that: Applied to a battery management system, the battery management system comprises: a plurality of battery packs, a plurality of first balancing structures, a second balancing structure and a control module; Each battery pack is composed of a plurality of single cells connected in series, a plurality of first switches and a plurality of second switches, each single cell is connected in series with a first switch, and each single cell is connected in series with a first switch and then connected in parallel with a second switch; a first balancing structure is connected in parallel at both ends of a battery pack, and the first balancing structure is composed of a storage inductor and four third switches; the second balancing structure includes a bidirectional flyback converter and a plurality of fourth switches, and the bidirectional flyback converter is connected to a plurality of battery packs through the fourth switches; a control module is connected to the battery pack, the first balancing structure and the second balancing structure; The control module is used to perform the following steps: Obtaining the SOC values ​​of all the single cells in each battery pack, determining a number of first single cells corresponding to the maximum SOC value and a number of second single cells corresponding to the minimum SOC value in the battery pack, and when a first difference between the maximum SOC value and the minimum SOC value is greater than a first balancing threshold, performing power balancing between the first single cells and the second single cells by regulating the first balancing structure, the first switch and the second switch until the SOC values ​​of the single cells in each battery pack are consistent; The average SOC value of each battery group is obtained, and a number of first battery groups corresponding to the average SOC maximum value and a number of second battery groups corresponding to the average SOC minimum value are determined. When a second difference between the average SOC maximum value and the average SOC minimum value is greater than a second balancing threshold, the second balancing structure is adjusted to balance the power between the first battery group and the second battery group until the SOC average values ​​of all battery groups are consistent.

2. The method according to claim 1, characterized in that By regulating the first balancing structure, the first switch and the second switch, power balancing is performed between the first single cell and the second single cell, including: By adjusting the conduction relationship between the first switch and the second switch, the first single cell and the second single cell are connected to the circuit, and the single cells other than the first single cell and the second single cell are bypassed; By regulating the conduction relationship of the four third switches in the first balancing structure and controlling the closing of the energy storage inductor, a charge and discharge loop is formed between the first single cell and the second single cell, so that the first single cell and the second single cell are charged and balanced through the energy storage inductor.

3. The method according to claim 2, characterized in that When the power balancing is performed between the first single battery and the second single battery, it includes: The difference interval to which the first difference belongs is determined, and the magnitude of the balancing current is determined according to the difference interval.

4. The method according to claim 3, characterized in that Also includes: When the first difference belongs to the first difference interval (x1, x2], the first balancing current I1 is used; When the first difference belongs to the second difference interval (x2, x3], the second balancing current I2 is used; When the first difference belongs to the third difference interval (x3, x4], the third balancing current I3 is used; Where x1<x2<x3, I1<I2<I3, x1,x2,x3∈(0,1), I1,I2,I3∈[0.3C,2C], C represents the current intensity when the battery is fully discharged in one hour.

5. The method according to claim 1, characterized in that By regulating the second balancing structure, power balancing is performed between the first battery group and the second battery group, including: The bidirectional flyback converter is connected to the positive terminals and negative terminals of the corresponding battery packs through the fourth switches; The fourth switch is controlled to be turned on and off, and the first battery group and the second battery group are connected to the circuit, so that the first battery group and the second battery group are charged evenly through the bidirectional flyback converter.

6. The method according to claim 5, characterized in that When performing power balancing between the first battery group and the second battery group, it includes: The difference interval to which the second difference belongs is determined, and the magnitude of the balancing current is determined according to the difference interval.

7. The method according to claim 6, characterized in that Also includes: When the second difference belongs to the first difference interval (x1, x2], the first balancing current I1 is used; When the second difference belongs to the second difference interval (x2, x3], the second balancing current I2 is adopted; When the second difference belongs to the third difference interval (x3, x4], the third balancing current I3 is adopted; Where x1<x2<x3, I1<I2<I3, x1,x2,x3∈(0,1), I1,I2,I3∈[0.3C,2C], C represents the current intensity when the battery is fully discharged in one hour.

8. A battery management system, characterized in that: include: A plurality of battery packs, a plurality of first balancing structures, a second balancing structure and a control module; Each battery pack is composed of a plurality of single cells connected in series, a plurality of first switches and a plurality of second switches, wherein the positive electrode or the negative electrode of each single cell is connected in series with a first switch, and each single cell and a first switch are connected in parallel with a second switch, and the first switch and the second switch are in a complementary conduction relationship; Each first balancing structure includes an energy storage inductor and four third switches, the energy storage inductor is connected to a battery pack through the four third switches, and the first balancing structure is used to balance the power between the single cells; The second balancing structure includes a bidirectional flyback converter and a plurality of fourth switches, wherein the bidirectional flyback converter is connected to a positive terminal of a battery pack through a fourth switch and is connected to a negative terminal of a battery pack through a fourth switch; the second balancing structure is used to balance the power between the battery packs; The control module is connected to the battery pack, the first balancing structure and the second balancing structure, and is used to obtain performance parameters of single cells, control structural changes of the battery pack, and control the first balancing structure and the second balancing structure.

9. The system according to claim 8, characterized in that The first switch is a conduction switch, which is used to connect the corresponding single battery connected in series to the circuit; the second switch is a bypass switch, which is used to disconnect the corresponding single battery connected in parallel from the circuit.

10. The system according to claim 8, characterized in that The first switch, the second switch, the third switch and the fourth switch are all automatically controlled switches.

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