A Modular Active Equalization Method for Series Battery Packs Based on Inductive Energy Storage

Abstract

The present invention belongs to the technical field of battery energy storage system balancing, and discloses a modular active balancing method for a series battery pack based on inductive energy storage. The series battery pack includes 3n single cells, and every 3 single cells form 1 battery module; the balancing topology includes 6n + 2 MOS transistors, 2n - 2 diodes, and 2n + 1 inductors; the balancing process is divided into two cases: intra-module balancing and inter-module balancing; intra-module balancing can achieve charge and discharge balancing of any single cell, and inter-module balancing can achieve transfer of balancing energy between any modules; when the balancing energy transfers within a module, only one or two switching tubes need to be controlled, and the control is simple. When the balancing energy transfers between modules, only one inductor is required for the energy storage device, and the structure is simple. By modularly designing the battery pack, all modules can be balanced simultaneously, thereby improving the balancing speed.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery energy storage system balancing, and relates to a modular active balancing method for series-connected battery packs based on inductive energy storage, which is applicable to the energy balancing of battery energy storage systems. Background Art

[0002] Lithium batteries have been widely used in microgrid energy storage systems due to their advantages such as high energy density and low self-discharge rate. Since the capacity of a single battery cell (which can be simply referred to as a single cell) is limited and the voltage is low, multiple single cells are usually connected in series and parallel to form a battery pack to meet the application requirements. Due to the fact that the manufacturing process, materials, etc. cannot be completely consistent, there are slight differences in the capacity, impedance, etc. of single battery cells, and these differences will increase with the operation time of the battery pack, seriously affecting the overall performance and use safety of the battery pack. To improve the energy utilization rate of the battery pack and extend its cycle life, effective balancing must be introduced to reduce the inconsistency of the battery pack. The reliability of a series-connected battery pack is more easily affected by the inconsistency of single battery cells compared to a parallel-connected battery pack. The present invention focuses on the balancing of series-connected battery packs.

[0003] The research on balancing methods mainly focuses on the research of balancing topologies. According to the different ways of energy consumption during the balancing process, balancing topologies are mainly divided into passive balancing and active balancing. The typical topology of passive balancing is the resistor discharge type balancing topology. When a certain single battery cell has a high charge, the bypass resistor consumes the excess charge. The resistor discharge type balancing topology has a simple structure, small volume, and low cost, but the energy loss of the bypass resistor will greatly reduce the energy utilization rate of the battery pack, and the heat dissipation problem cannot be ignored. Moreover, this balancing topology cannot perform charging balancing on single battery cells with low capacity. In contrast, active balancing has the advantages of low energy loss and fast balancing speed, and is a research hotspot in balancing in recent years. Active balancing topologies generally transfer energy from high-charge single cells to low-charge single cells through energy storage devices such as capacitors, inductors, or transformers to achieve balancing. The balancing topology based on capacitive energy storage has the advantages of fast balancing speed and high balancing efficiency, but when the voltage of the capacitor is not much different from the balancing target voltage, the balancing speed drops significantly, resulting in the fact that capacitive balancing is not suitable for high-precision balancing. The balancing topology based on inductive energy storage has the characteristics of strong controllability of the balancing current and high balancing accuracy, but it often has a large number of switching tubes and a complex circuit structure. The balancing topology based on transformer energy storage has the advantages of high balancing efficiency and easy isolation, but the design of the winding transformer is relatively complex and there is a problem of magnetic saturation. The topology has a large volume, is not easy to be modularized, and has a high cost. Summary of the Invention

[0004] The object of the present invention is to overcome the disadvantages and deficiencies of the existing equalization methods. On the premise of improving the equalization function, combined with the characteristics of high equalization accuracy based on inductive energy storage, from the perspectives of simplifying the topological structure, simplifying the control process, and improving the equalization speed, a modular active equalization method for series battery packs based on inductive energy storage is proposed to improve the inconsistency problem of series battery packs and extend the cycle life of series battery packs.

[0005] The present invention adopts the following technical solutions:

[0006] A modular active equalization method for series battery packs based on inductive energy storage,

[0007] The series battery pack includes 3n single cells, and every 3 single cells form 1 battery module; the series battery pack is connected with an equalization topology;

[0008] The equalization topology includes 6n + 2 MOS transistors, 2n - 2 diodes, and 2n + 1 inductors;

[0009] The equalization method is as follows: the equalization process is divided into two cases: intra-module equalization and inter-module equalization, and the intra-module equalization has a higher priority;

[0010] The intra-module equalization can achieve charge and discharge equalization of any single cell, and the inter-module equalization can achieve the transfer of equalization energy between any modules;

[0011] When the equalization energy is transferred within a module, only one or two switching tubes need to be controlled, and the control is simple. When the equalization energy is transferred between modules, only one inductor is required for the energy storage device, and the structure is simple.

[0012] The 3n single cells in the series battery pack are divided into n battery modules, and the battery modules are sequentially labeled as B 1 , B 2 , …, B n , and the negative electrode of the battery module B 1 is connected to the positive electrode of the battery module B 2 , and so on, and the negative electrode of the battery module B n-1 is connected to the positive electrode of the battery module B n ; the single cells within the module are sequentially labeled as B 11 , B 12 , B 13 , …, B n1 , B n2 , B n3 , and the negative electrode of the single cell B 1 in the battery module B 11 is connected to the positive electrode of the single cell B 12 , and the negative electrode of the single cell B 12 is connected to the positive electrode of the single cell B 13 , and the rest of the modules are the same; the MOS transistors within the module are sequentially labeled as S11 , S 12 , S 13 , S 14 , …, S n1 , S n2 , S n3 , S n4 , the inductors within the module are sequentially labeled as L 1a , L 1b , …, L na , L nb , the left MOS transistors between the modules are sequentially labeled as S a , S 1a , …, S na , the right MOS transistors between the modules are sequentially labeled as S b , S 1b , …, S nb , the inductor between the modules is labeled as L;

[0013] Battery module B 1 The left bridge arm of the positive electrode is connected to the MOS transistor S a , and the battery module B 1 The right bridge arm of the positive electrode is connected to the MOS transistor S b ; the battery module B 2 , B 3 , …, B n The left and right bridge arms of the positive electrode are connected to the series-connected MOS transistors and diodes; the battery module B n The left bridge arm of the negative electrode is connected to the MOS transistor S na , and the battery module B n The right bridge arm of the negative electrode is connected to the MOS transistor S nb ; the source of the MOS transistor S b is connected to the drain of other MOS transistors on the right side of the battery module, and the drain of the MOS transistor S na is connected to the source of other MOS transistors on the left side of the battery module; both ends of the balancing inductor L between the modules are respectively connected to the drains of the MOS transistor S na and the MOS transistor S nb ;

[0014] The internal connection method of the module takes the battery module B 1 in the series-connected battery pack as an example. The single cell B 11 is connected to the drains of the MOS transistors S 11 , S 13 , and the single cell B 13 is connected to the sources of the MOS transistors S 12 , S 14 ; the source of the MOS transistor S 11 is connected to the drain of the MOS transistor S 12 , and the source of the MOS transistor S 13 is connected to the MOS transistor S14 is connected to the drain; Inductor L 1a One end is connected to cell B 11 negative electrode, and one end is connected to the source of MOS transistor S 11 is connected to the source; Inductor L 1b One end is connected to cell B 12 negative electrode, and one end is connected to the source of MOS transistor S 13 is connected to the source;

[0015] And so on, cell B n1 is connected to the drains of MOS transistors S n1 , S n3 is connected to the sources of MOS transistors S n3 is connected to the sources of MOS transistors S n2 , S n4 is connected to the sources of MOS transistors S n1 The source of MOS transistor S is connected to the drain of MOS transistor S n2 The source of MOS transistor S is connected to the drain of MOS transistor S n3 The source of MOS transistor S is connected to the drain of MOS transistor S n4 is connected to the source; Inductor L na One end is connected to cell B n1 negative electrode, and one end is connected to the source of MOS transistor S n1 is connected to the source; Inductor L nb One end is connected to cell B n2 negative electrode, and one end is connected to the source of MOS transistor S n3 is connected to the source.

[0016] Preferably, the equalization method is as follows:

[0017] During the charge and discharge process of the series battery pack, the inter-module equalization uses the difference in the state of charge (SOC) between modules as the equalization judgment index. The SOC of the battery module is defined as the average value of the SOCs of the individual cells in the module. The intra-module equalization uses the difference between the SOC of each individual cell in the module and the average value of the SOCs of the individual cells in the module as the equalization judgment index; The series battery pack and the equalization topology are combined to form an equalization circuit;

[0018] Let the inter-module equalization threshold of the equalization circuit be The intra-module equalization threshold is

[0019] The highest charge of the battery module in the series battery pack is SOC max , and the lowest charge of the battery module is SOC min ; For the battery module with serial number n, the highest charge of the individual cells in the module is SOC maxn , and the lowest charge of the individual cells is SOC minn , and the average charge of the individual cells is SOC ave,n ;

[0020] If the SOC max，n , SOC ave，n , SOC min，n meet the in-module balancing start conditions, in-module balancing is performed, and there is imbalance between modules; if the SOC max，n , SOC ave，n , SOC min，n do not meet the in-module balancing start conditions, and the SOC max , SOC min meet the balancing start conditions, inter-module balancing is performed.

[0021] When performing in-module balancing:

[0022] If the difference between the SOC max，n and the SOC ave，n is greater than and the difference between the SOC ave，n and the SOC min，n is less than the balancing circuit performs high-power single-cell discharge balancing within the module;

[0023] If the difference between the SOC ave，n and the SOC min，n is greater than and the difference between the SOC max，n and the SOC ave，n is less than the balancing circuit performs low-power single-cell charging balancing within the module;

[0024] If the differences between the SOC max，n and the SOC ave，n , and between the SOC ave，n and the SOC min，n are both greater than , continue to compare the magnitudes of the two differences; if the difference between the SOC max，n and the SOC ave，n is greater than the difference between the SOC ave，n and the SOC min，n , the balancing circuit performs high-power single-cell discharge balancing within the module; if the difference between the SOC max，n and the SOC ave，n is less than the difference between the SOC ave，n and the SOC min，n , the balancing circuit performs low-power single-cell charging balancing within the module;

[0025] When performing inter-module balancing:

[0026] If the difference between the SOC max and the SOC min is greater than directly transfer the energy of the high-power battery module to the low-power battery module, otherwise there is imbalance between modules.

[0027] Repeat this process until reaching the SOC max，n and the SOC ave，n difference, the SOC ave，n and the SOC min，n differences are all less than and the SOC max and the SOC min difference is less than At this time, the balancing circuit stops working.

[0028] When the number of battery modules with the highest power or the number of battery modules with the lowest power is not 1, select the battery module with the highest power with the smallest serial number and the battery module with the lowest power with the largest serial number for balancing.

[0029] The balancing topology is connected with a control circuit. The frequency of the control signal of the control circuit should be determined according to the parameters of the balancing circuit, the switching loss of the MOS tube, the voltage of the series battery pack and the single cell, and the balancing current. The duty cycle of the driving signal output by the control circuit should reset the inductor current in each switching cycle, that is, the current passing through each inductor first rises from zero and finally drops to zero in each switching cycle.

[0030] Specifically, taking the in-module balancing of module B 1 as an example, the in-module balancing principle is explained.

[0031] If B 11 has the highest power, the balancing process of one switching cycle is divided into two stages.

[0032] The first stage is that B 11 transfers energy to inductor L 1a . At the initial moment, the current passing through inductor L 1a is zero. At this time, turn on MOS tube S 11 , and B 11 charges inductor L 1a . The current of inductor L 1a gradually increases. When the balancing current reaches the expected value, turn off MOS tube S 11 , and the first stage ends. In the second stage, no switch tube needs to be controlled. Inductor L 1a charges single cells B 12 and B 12 through the freewheeling diode of MOS tube S 13 , and the inductor current gradually drops to zero. So far, the energy transfer process of one switching cycle is completed.

[0033] If B 11 has the lowest power, the balancing process of one switching cycle is divided into two stages.

[0034] The first stage is that B 12 and B13 Transfer energy to the inductor L 1a At the initial moment, the current passing through the inductor L 1a is zero. At this time, turn on the MOS transistor S 12 , B 12 , B 13 charge the inductor L 1a . The current in the inductor L 1a gradually increases. When the balancing current reaches the expected value, turn off the MOS transistor S 12 , and the first stage ends. In the second stage, no switching transistors need to be controlled. The inductor L 1a charges the cell B 11 through the freewheeling diode of the MOS transistor S 11 . The inductor current gradually drops to zero. Thus, the energy transfer process of one switching cycle is completed.

[0035] If the charge of B 12 is the highest, divide the balancing process of one switching cycle into two stages.

[0036] In the first stage, at the initial moment, the current passing through the inductor L 1a , L 1b is zero. At this time, turn on the MOS transistors S 12 , S 13 , B 11 , B 12 charge the inductor L 1b . B 12 , B 13 charge the inductor L 1a . The current in the inductor L 1a , L 1b gradually increases. When the balancing current reaches the expected value, turn off the MOS transistors S 12 , S 13 , and the first stage ends. In the second stage, no switching transistors need to be controlled. The inductor L 1a charges the cell B 11 through the freewheeling diode of the MOS transistor S 11 . The inductor L 1b charges the cell B 14 through the freewheeling diode of the MOS transistor S 13 . The current in the inductor L 1a , L 1b gradually drops to zero. Thus, the energy transfer process of one switching cycle is completed.

[0037] If the charge of B 12 is the lowest, divide the balancing process of one switching cycle into two stages.

[0038] In the first stage, at the initial moment, the current passing through the inductor L 1a , L 1bThe current is zero, and at this time, MOS transistors S 11 and S 14 are turned on. B 11 charges the inductor L 1a . B 13 charges the inductor L 1b . The current in the inductor L 1a and L 1b gradually increases. When the balancing current reaches the expected value, the MOS transistors S 11 and S 14 are turned off, and the first stage ends. In the second stage, no switching transistors need to be controlled. The inductor L 1a charges the monomers B 12 and B 12 through the freewheeling diode of the MOS transistor S 13 . The inductor L 1b charges the monomers B 13 and B 11 through the freewheeling diode of the MOS transistor S 12 . The current in the inductor L 1a and L 1b gradually drops to zero. Thus, the energy transfer process of one switching cycle is completed.

[0039] The balancing principle of the monomer B 13 is the same as that of B 11 , and will not be elaborated here.

[0040] Specifically, the balancing principle between modules is as follows.

[0041] Suppose the battery module B 1 has the highest power, and B 2 has the lowest power. The balancing process of one switching cycle is divided into two stages.

[0042] In the first stage, the high-power battery module transfers energy to the inductor L. At the initial moment, the current through the inductor L is zero. At this time, the MOS transistors S a and S 1b are turned on. B 1 charges the inductor L, and the current in the inductor L gradually increases. When the balancing current reaches the expected value, the MOS transistors S a and S 1b are turned off, and the first stage ends. In the second stage, the inductor L charges the low-power battery module. While turning off the MOS transistors S a and S 1b , the MOS transistors S 1b and S 2a are turned on. The inductor L charges B 2 , and the current in the inductor L gradually drops to zero. Thus, the energy transfer process of one switching cycle is completed.

[0043] For the balanced topology to work smoothly, it is necessary to analyze and design the parameters of the core components of the circuit.

[0044] Taking the in-module balance of Module B 1 as an example, the switching loss of the MOS transistor and the cut-off loss of the diode are negligible compared to the on-state loss and can be ignored.

[0045] Assume that the voltage of the single cell B 11 in the module is the highest and is V 11 , and the voltages of the single cells B 12 , B 13 are V 12 , V 13 respectively, the forward voltage drop of the diode is V D , the control signal period of the MOS transistor is T, the frequency is f, and the duty cycles of the control signals corresponding to the inductor charging and discharging processes are D 1 and D 2 respectively.

[0046] In the first stage of balancing, when the MOS transistor S 11 conducts, the single cell B 11 discharges to charge the inductor L 1a . The current flowing through L 1a rises linearly, and L 1a stores energy. The inductor current i L1a is:

[0047]

[0048] The time for the inductor charging stage is D 1 T, then the maximum inductor current I L1a_max is:

[0049]

[0050] According to the maximum balancing current and the selected switching frequency, the inductor L 1a is:

[0051]

[0052] In the second stage of balancing, the inductor L 1a discharges to charge the single cells B 12 , B 13 . The expression of the inductor current is:

[0053]

[0054] To ensure that the inductor can be reset within one switching period, D 1 +D 2 < 1.

[0055] That is, it is necessary to satisfy:

[0056]

[0057] Further derivation shows that:

[0058]

[0059] Other cases of in-module balance (charging balance of single cell B 11 , charging and discharging balance of single cell B 12 , B 13 ) and the calculation process of inter-module balance parameters are similar to the above calculation process, only the number of single cells through which the current flows during the inductor charging and discharging process or the number of diodes passed through is different, so no re-derivation will be carried out here.

[0060] In the above calculation, first, the maximum balancing current needs to be set; second, on this basis, the inductor and switching frequency are set. If the switching frequency is too low, the balancing speed is fast, but the circuit loss is large. If it is too high, the switching loss is large; the inductor cannot be too large or too small either; if it is too large, the loss of the inductor increases, and if it is too small, it is easy to saturate.

[0061] Finally, the balancing efficiency is analyzed.

[0062] For the convenience of calculation, the balancing efficiency is studied according to the energy change during the inductor charging and discharging process.

[0063] Within one switching period, the energy W 11 released by the high-voltage single cell B 1 is the sum of the energy stored in the inductor and the energy consumed in the balancing path, which can be expressed as the following formula:

[0064]

[0065] Among them, R DS is the drain-source resistance of the MOS transistor. Combining the above formula with formula (1) gives:

[0066]

[0067] The energy W 12 absorbed by single cell B 13 and B 2 is the difference between the energy released by the inductor and the energy consumed in the balancing path, and the expression is as follows:

[0068]

[0069] Among them, V D is the forward voltage drop of the diode. Combining the above formula with formula (1) and formula (4) gives:

[0070]

[0071] According to the energy change before and after balancing within one cycle, the balancing efficiency η can be obtained as follows:

[0072]

[0073] As can be seen from Equation (11), the balancing efficiency is related not only to the magnitude of the inductor of the energy storage device, but also to parameters such as the voltage of the balancing object, the control signal frequency, and the control signal duty cycle.

[0074] Preferably, a control circuit is connected to the series battery pack balancing topology; the frequency of the control signal of the control circuit should be determined according to the parameters of the balancing circuit, the switching loss of the MOS transistor, the voltage of the series battery pack and the single cell, and the balancing current; the duty cycle of the drive signal output by the control circuit should reset the inductor current within each switching cycle, that is, the current passing through each inductor within each switching cycle first rises from zero and finally drops back to zero.

[0075] The present invention achieves the following beneficial effects:

[0076] Compared with the prior art, the present invention establishes a modular active balancing method for series battery packs based on inductor energy storage. Compared with the current mainstream balancing methods, the features are as follows:

[0077] 1) By modularizing the battery pack design, all modules can be balanced simultaneously, thereby improving the balancing speed;

[0078] 2) It alleviates the problem that when the number of single cells is large, the number of single cells with the highest or lowest battery power is not 1, resulting in the inability to accurately identify the balancing object.

[0079] 3) During intra-module balancing, only one switch needs to be controlled for the charge and discharge balancing of the single cells at both ends, and only two switches need to be controlled for the charge and discharge balancing of the single cells in the middle, and the control method is simple; during inter-module balancing, only one inductor is required for the energy storage device, and the structure is simple. Description of the Drawings

[0080] To more clearly illustrate the principle of the present invention and the technical solutions in the implementation, the technical solutions related to the present invention will be further introduced below using the drawings. The following drawings are only partial embodiments of the present invention. For those skilled in the art, other technical solutions can be obtained based on the following drawings without creative efforts.

[0081] Figure 1 It is the structural diagram of the balancing circuit of Embodiment 1 of the present invention;

[0082] Figure 2 It is the control strategy flowchart of the active balancing method of Embodiment 1 of the present invention;

[0083] Figure 3It is the structural diagram of the balancing circuit in Embodiment 2 of the present invention;

[0084] Figure 4 It is the monomer B in Embodiment 2 of the present invention 11 Discharge balancing working principle diagram;

[0085] Figure 5 It is the monomer B in Embodiment 2 of the present invention 11 Inductor L during the discharge balancing process of the monomer B 1a Schematic diagram of current change;

[0086] Figure 6 It is the monomer B in Embodiment 2 of the present invention 11 Charge balancing working principle diagram;

[0087] Figure 7 It is the monomer B in Embodiment 2 of the present invention 11 Inductor L during the charge balancing process of the monomer B 1a Schematic diagram of current change;

[0088] Figure 8 It is the monomer B in Embodiment 2 of the present invention 12 Discharge balancing working principle diagram;

[0089] Figure 9 It is the monomer B in Embodiment 2 of the present invention 12 Inductor L during the discharge balancing process of the monomer B 1a 、L 1b Schematic diagram of current change;

[0090] Figure 10 It is the monomer B in Embodiment 2 of the present invention 12 Charge balancing working principle diagram;

[0091] Figure 11 It is the monomer B in Embodiment 2 of the present invention 12 Inductor L during the charge balancing process of the monomer B 1a 、L 1b Schematic diagram of current change;

[0092] Figure 12 It is the inter-module balancing working principle diagram in Embodiment 2 of the present invention;

[0093] Figure 13 It is the schematic diagram of the current change of inductor L during the inter-module balancing process in Embodiment 2 of the present invention;

[0094] Figure 14 It is the SOC balancing simulation result of the series battery pack in Embodiment 2 of the present invention;

[0095] Figure 15 It is the SOC balancing simulation result of the monomers within each module in Embodiment 2 of the present invention;

[0096] Figure 16is the SOC extreme difference variation curve of each module in Example 2 of the present invention;

[0097] Figure 17 This is the simulation result of SOC balancing between modules in Example 2 of the present invention;

[0098] Figure 18 This is the SOC extreme difference variation curve between modules in Example 2 of the present invention. DETAILED DESCRIPTION

[0099] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. The illustrative embodiments of the present invention are used to explain the present invention, but are not intended to limit the present invention.

[0100] Example 1

[0101] like Figure 1 FIG. 1 is a structural diagram of an equalizing circuit according to Embodiment 1 of the present invention.

[0102] The series-connected battery pack contains 3n cells, where every 3 cells form a battery module;

[0103] The balancing topology includes 6n+2 MOS tubes, 2n-2 diodes, and 2n+1 inductors; the series battery pack and the balancing topology are combined to form a balancing circuit;

[0104] The balancing process is divided into two cases: intra-module balancing and inter-module balancing, where intra-module balancing has a higher priority;

[0105] The balance within the module can realize the charge and discharge balance of any single cell, and the balance between modules can realize the transfer of balanced energy between any modules;

[0106] When the balanced energy is transferred within the module, only one or two switching tubes need to be controlled, and the control is simple. When the balanced energy is transferred between modules, the energy storage device only needs one inductor, and the structure is simple.

[0107] The 3n cells in the series battery pack are divided into n battery modules, and the battery modules are marked as B 1 , B 2 , …, B n , battery module B 1 The negative pole of module B 2 The positive electrode of battery module B is connected to the positive electrode of battery module B. n-1 The negative pole of module B n The positive electrode of the module is connected; the monomers in the module are marked as B 11 , B 12 , B 13 , …, B n1 , B n2 , B n3 , battery module B 1 Medium monomer B11 The negative electrode of 12 is connected to the positive electrode of B 12 The negative electrode of 13 is connected to the positive electrode of B 11 , and the MOS transistors in the module are sequentially labeled as S 12 , S 13 , S 14 , …, S n1 , S n2 , S n3 , S n4 , and the inductors in the module are sequentially labeled as L 1a , L 1b , …, L na , L nb , and the left-side MOS transistors between the modules are sequentially labeled as S a , S 1a , …, S na , and the right-side MOS transistors between the modules are sequentially labeled as S b , S 1b , …, S nb , and the inductor between the modules is labeled as L;

[0108] Battery module B 1 The left bridge arm of the positive electrode is connected to the MOS transistor S a , and the right bridge arm of the positive electrode of battery module B 1 is connected to the MOS transistor S b ; The left and right bridge arms of the positive electrode of battery module B 2 , B 3 , …, B n are connected to the series-connected MOS transistors and diodes; The left bridge arm of the negative electrode of battery module B n is connected to the MOS transistor S na , and the right bridge arm of the negative electrode of battery module B n is connected to the MOS transistor S nb ; The source electrode of the MOS transistor S b is connected to the drain electrodes of other MOS transistors on the right side of the battery module, and the drain electrode of the MOS transistor S na is connected to the source electrodes of other MOS transistors on the left side of the battery module; The two ends of the balancing inductor L between the modules are respectively connected to the drain electrodes of the MOS transistors S na and S nb ;

[0109] Taking the battery module B 1 in the series-connected battery pack as an example, the single cell B 11 is connected to the drain electrodes of the MOS transistors S 11 , S 13 , and the single cell B 13 is connected to the MOS transistors S 12 , S14 is connected to the source electrode of; MOS transistor S 11 The source electrode of is connected to the MOS transistor S 12 is connected to the drain electrode of, MOS transistor S 13 The source electrode of is connected to the MOS transistor S 14 is connected to the drain electrode of; Inductor L 1a One end is connected to the negative electrode of monomer B 11 and one end is connected to the source electrode of the MOS transistor S 11 is connected to the source electrode of, Inductor L 1b One end is connected to the negative electrode of monomer B 12 and one end is connected to the source electrode of the MOS transistor S 13 is connected to the source electrode of;

[0110] The equalization idea is as follows: the inductor within the module is used to achieve charge and discharge equalization of the monomers within the module, and the inductor between the modules is used to achieve charge and discharge equalization between the modules.

[0111] Such as Figure 2 shown, it is the control strategy flow chart of the active equalization method in Embodiment 1 of the present invention.

[0112] During the charge and discharge process of the series battery pack, the equalization between the modules uses the SOC difference between the modules as the equalization judgment index, where the SOC of the battery module is defined as the average value of the SOCs of the monomers in the module, and the equalization within the module uses the difference between the SOC of each monomer in the module and the average value of the SOCs of the monomers in the module as the equalization judgment index;

[0113] Let the equalization threshold between the modules of the equalization circuit be and the equalization threshold within the module be

[0114] The highest battery level of the battery module in the series battery pack is SOC max , and the lowest battery level of the battery module is SOC min ; For the battery module with the serial number n, the highest battery level of the monomers within the module is SOC max,n , and the lowest battery level of the monomers is SOC min,n , and the average battery level of the monomers is SOC ave,n ;

[0115] If SOC max，n , SOC ave，n , SOC min，n meet the in-module equalization start condition, then in-module equalization is performed and there is no inter-module imbalance; if SOC max，n , SOC ave，n , SOC min，n do not meet the in-module equalization start condition, and SOC max , SOC min meet the equalization start condition, then inter-module equalization is performed.

[0116] When performing in-module balancing:

[0117] If the SOC max，n and the SOC ave，n difference is greater than and the SOC ave，n and the SOC min，n difference is less than the balancing circuit performs high-power single-cell discharging balancing within the module;

[0118] If the SOC ave，n and the SOC min，n difference is greater than and the SOC max，n and the SOC ave，n difference is less than the balancing circuit performs low-power single-cell charging balancing within the module;

[0119] If the difference between the SOC max，n and the SOC ave，n , and the difference between the SOC ave，n and the SOC min，n are both greater than continue to compare the magnitudes of the two differences; if the difference between the SOC max，n and the SOC ave，n is greater than the difference between the SOC ave，n and the SOC min，n the balancing circuit performs high-power single-cell discharging balancing within the module; if the difference between the SOC max，n and the SOC ave，n is less than the difference between the SOC ave，n and the SOC min，n the balancing circuit performs low-power single-cell charging balancing within the module;

[0120] When performing inter-module balancing:

[0121] If the difference between the SOC max and the SOC min is greater than directly transfer the energy of the high-power battery module to the low-power battery module, otherwise there is inter-module imbalance.

[0122] Repeat this process until the difference between the SOC max，n and the SOC ave，n , and the difference between the SOC ave，n and the SOC min，n are both less than and the difference between the SOC max and the SOC min is less than the balancing circuit stops working.

[0123] It should be noted that as the number of single cells in the series-connected battery pack increases, the number of battery modules increases synchronously. At the same time, the probability that the number of battery modules with the highest power and the number of battery modules with the lowest power are greater than 1 gradually increases. How to effectively select the balancing object has become the core issue of balancing control. When the number of battery modules corresponding to the maximum power or the minimum power is not 1, by formulating corresponding selection rules, all battery modules can be sequentially selected at different balancing stages. The rule formulated by the present invention is: when the number of battery modules with the highest power or the lowest power is not 1, select the battery module with the highest power and the smallest serial number or the battery module with the lowest power and the largest serial number for balancing.

[0124] Embodiment 2

[0125] As Figure 3 shown, it is the structural diagram of the balancing circuit according to Embodiment 2 of the present invention.

[0126] The series-connected battery pack includes 9 single cells, and every 3 single cells form 1 battery module;

[0127] The balancing topology includes 20 MOS transistors, 4 diodes, and 7 inductors; the series-connected battery pack and the balancing topology are combined to form a balancing circuit;

[0128] The balancing process is divided into two cases: intra-module balancing and inter-module balancing, and the intra-module balancing has a higher priority;

[0129] Intra-module balancing can achieve charge and discharge balancing of any single cell, and inter-module balancing can achieve transfer of balancing energy between any modules;

[0130] When the balancing energy is transferred within a module, only one or two switching tubes need to be controlled, and the control is simple. When the balancing energy is transferred between modules, only one inductor is required for the energy storage device, and the structure is simple.

[0131] The 9 single cells in the series-connected battery pack are divided into 3 battery modules, and the battery modules are sequentially marked as B 1 , B 2 , B 3 . The negative electrode of battery module B 1 is connected to the positive electrode of module B 2 . The negative electrode of battery module B 2 is connected to the positive electrode of module B 3 . The single cells within the module are sequentially marked as B 11 , B 12 , B 13 , B 21 , B 22 , B 23 , B 31 , B 32 , B 33, battery module B 1 monomer B in it 11 The negative electrode of is connected to B 12 The positive electrode of monomer B 12 The negative electrode of is connected to B 13 The positive electrode of, and so on for the rest of the modules; the MOS transistors in the module are sequentially marked as S 11 , S 12 , S 13 , S 14 , S 21 , S 22 , S 23 , S 24 , S 31 , S 32 , S 33 , S 34 , the inductors in the module are sequentially marked as L 1a , L 1b , L 2a , L 2b , L 3a , L 3b , the left MOS transistors between the modules are sequentially marked as S a , S 1a , S 2a , S 3a , the right MOS transistors between the modules are sequentially marked as S b , S 1b , S 2b , S 3b , the inductor between the modules is marked as L;

[0132] Battery module B 1 The left bridge arm of the positive electrode is connected to the MOS transistor S a , battery module B 1 The right bridge arm of the positive electrode is connected to the MOS transistor S b ; battery module B 2 , B 3 The left and right bridge arms of the positive electrode are connected to the series-connected MOS transistors and diodes; battery module B 3 The left bridge arm of the negative electrode is connected to the MOS transistor S 3a , battery module B 3 The right bridge arm of the negative electrode is connected to the MOS transistor S 3b ; the source electrode of the MOS transistor S b is connected to the drain electrodes of the other MOS transistors on the right side of the battery module, and the drain electrode of the MOS transistor S 3a is connected to the source electrodes of the other MOS transistors on the left side of the battery module; both ends of the balancing inductor L between the modules are respectively connected to the drain electrodes of the MOS transistors S 3a and S 3b ;

[0133] The internal connection method within the module takes battery module B 1 as an example. Monomer B 11 is connected to the drains of MOS transistors S 11 and S 13 . Monomer B 13 is connected to the sources of MOS transistors S 12 and S 14 . The source of MOS transistor S 11 is connected to the drain of MOS transistor S 12 . The source of MOS transistor S 13 is connected to the drain of MOS transistor S 14 . One end of inductor L 1a is connected to the negative electrode of monomer B 11 , and one end is connected to the source of MOS transistor S 11 . One end of inductor L 1b is connected to the negative electrode of monomer B 12 , and one end is connected to the source of MOS transistor S 13 .

[0134] The equalization idea is as follows: Use the inductor within the module to achieve charge and discharge equalization of the monomers within the module, and use the inductor between modules to achieve charge and discharge equalization between modules.

[0135] The specific equalization principle is described as follows:

[0136] The in-module equalization is described taking module B 1 as an example. The working principle of in-module equalization is as follows:

[0137] In the in-module equalization, the equalization principle of monomer B 11 and monomer B 13 is the same. Here, monomer B 11 is taken as an example for description. Assume that B 11 has the highest charge. The equalization process in one switching cycle is divided into two stages.

[0138] The first stage is that B 11 transfers energy to inductor L 1a . At the initial moment, the current passing through inductor L 1a is zero. At this time, MOS transistor S 11 is turned on, and B 11 charges inductor L 1a . The current of inductor L 1a gradually increases. When the equalization current reaches the expected value, MOS transistor S 11 is turned off, and the first stage ends. In the second stage, no switching transistor needs to be controlled. Inductor L 1a discharges through the freewheeling diode of MOS transistor S 12 to monomers B 12 and B 13During charging, the inductor current gradually decreases to zero. Thus, the energy transfer process of one switching cycle is completed. As Figure 4 shown, it is the working schematic diagram of the discharging equalization of monomer B in Embodiment 2 of the present invention 11 ; the equalization current paths in the two stages of the discharging equalization of monomer B are respectively as 11 shown by loop i and loop ii in Figure 4 .

[0139] As Figure 5 shown, it is the working schematic diagram of the charging equalization of monomer B in Embodiment 2 of the present invention 11 ; the inductor L 1a current variation diagram during the charging equalization process of monomer B.

[0140] Assume that the charge of B 11 is the lowest, and the equalization process of one switching cycle is divided into two stages.

[0141] In the first stage, B 12 , B 13 transfer energy to the inductor L 1a . At the initial moment, the current passing through the inductor L 1a is zero. At this time, turn on the MOS transistor S 12 , and B 12 , B 13 charge the inductor L 1a . The current of the inductor L 1a gradually increases. When the equalization current reaches the expected value, turn off the MOS transistor S 12 , and the first stage ends. In the second stage, no switch tube needs to be controlled. The inductor L 1a charges the monomer B 11 through the freewheeling diode of the MOS transistor S 11 . The inductor current gradually decreases to zero. Thus, the energy transfer process of one switching cycle is completed. As Figure 6 shown, it is the working schematic diagram of the charging equalization of monomer B in Embodiment 2 of the present invention 11 ; the equalization current paths in the two stages of the charging equalization of monomer B are respectively as 11 shown by loop i and loop ii in Figure 6 .

[0142] As Figure 7 shown, it is the inductor L 11 current variation diagram during the charging equalization process of monomer B in Embodiment 2 of the present invention 1a .

[0143] Assume that the charge of B 12 is the highest, and the equalization process of one switching cycle is divided into two stages.

[0144] In the first stage, at the initial moment, through the inductor L 1a , L 1bThe current is zero, and at this time, MOS transistors S 12 and S 13 are turned on. B 11 and B 12 charge the inductor L 1b . B 12 and B 13 charge the inductor L 1a . The current of the inductor L 1a and L 1b gradually increases. When the balancing current reaches the set value, the MOS transistors S 12 and S 13 are turned off, and the first stage ends. In the second stage, no switching transistors need to be controlled. The inductor L 1a charges the single cell B 11 through the freewheeling diode of the MOS transistor S 11 . The inductor L 1b charges the single cell B 14 through the freewheeling diode of the MOS transistor S 13 . The current of the inductor L 1a and L 1b gradually decreases to zero. Thus, the energy transfer process of one switching cycle is completed. As Figure 8 shown, it is the working principle diagram of the discharge balancing of the single cell B 12 in Embodiment 2 of the present invention; the balancing current path in the first stage of the discharge balancing of the single cell B 12 is as shown by the loops i and ii in Figure 8 , and the balancing current path in the second stage is as shown by the loops iii and iv in Figure 8 .

[0145] As Figure 9 shown, it is the schematic diagram of the current change of the inductors L 12 and L 1a and L 1b during the discharge balancing process of the single cell B

[0146] Assume that the charge of B 12 is the lowest, and the balancing process of one switching cycle is divided into two stages.

[0147] In the first stage, at the initial moment, the current passing through the inductors L 1a and L 1b is zero. At this time, the MOS transistors S 11 and S 14 are turned on. B 11 charges the inductor L 1a . B 13 charges the inductor L 1b . The current of the inductor L 1a and L 1b gradually increases. When the balancing current reaches the expected value, the MOS transistor S 11, S 14 , the first stage ends. In the second stage, no switching tube needs to be controlled, and the inductor L 1a charges the single cell B through the freewheeling diode of the MOS tube S 12 , and the single cell B 12 , B 13 is charged. The current of the inductor L 1b charges the single cell B through the freewheeling diode of the MOS tube S 13 , and the single cell B 11 , B 12 is charged. The current of the inductor L 1a , L 1b gradually drops to zero. So far, the energy transfer process of a switching cycle is completed. As Figure 10 shown, it is the working principle diagram of the charging equalization of the single cell B in Embodiment 2 of the present invention; the equalization current path in the first stage of the charging equalization of the single cell B is as shown by the loops i and ii in 12 ; the equalization current path in the second stage is as shown by the loops iii and iv in 12 . Figure 10 Figure 10 .

[0148] As Figure 11 shown, it is the schematic diagram of the current change of the inductors L 12 and L 1a during the charging equalization process of the single cell B in Embodiment 2 of the present invention. 1b

[0149] Working principle of inter-module equalization:

[0150] Suppose the battery module B 1 has the highest power, and B 2 has the lowest power. The equalization process of a switching cycle is divided into two stages.

[0151] In the first stage, the high-power battery module transfers energy to the inductor L. At the initial moment, the current passing through the inductor L is zero. At this time, turn on the MOS tubes S a , S 1b , and B 1 charges the inductor L. The current of the inductor L gradually increases. When the equalization current reaches the expected value, turn off the MOS tubes S a , S 1b , and the first stage ends. The second stage is the process of the inductor L charging the low-power battery module. While turning off the MOS tubes S a , S 1b , turn on the MOS tubes S 1b , S 2a . The inductor L charges B 2 . The current of the inductor L gradually drops to zero. So far, the energy transfer process of a switching cycle is completed. As Figure 12 ​​As shown, it is the schematic diagram of the balanced operation principle between modules in Embodiment 2 of the present invention; the balanced current paths in the two stages of balancing between modules are respectively as shown in Figure 12 the middle loops i and ii.

[0152] As Figure 13 shown, it is the schematic diagram of the current change of inductor L during the balancing process between modules in Embodiment 2 of the present invention.

[0153] In the above situation, during the entire switching cycle of the balancing process, the inductor must operate in the discontinuous current mode to avoid the occurrence of inductor hysteresis saturation. To ensure the reliability of the balancing control, within one switching cycle, after the balancing is completed, a dead time needs to be left before starting the balancing of the next cycle.

[0154] To verify the actual balancing effect of the topology in the present invention, a balancing simulation model of Embodiment 2 of the present invention was built in MATLAB / Simulink. Taking the balancing of the battery pack in the idle state as an example, the rated capacity of the selected single lithium-ion battery is 2.6 Ah, and the rated voltage is 3.7 V. The specific parameter settings of the simulation model are shown in Table 1.

[0155] Table 1 Simulation parameters of the balancing circuit

[0156]

[0157] Figure 14 is the simulation result of the SOC balancing of the series battery pack in Embodiment 2 of the present invention. As Figure 14 can be seen, during the balancing process, the difference in SOC of each single cell in the series battery pack gradually decreases. Figure 15 is the simulation result of the SOC balancing of each single cell within each module in Embodiment 2 of the present invention. Figure 16 is the curve of the change in the maximum difference in SOC of each single cell within each module in Embodiment 2 of the present invention. At the beginning moment, the difference in SOC of each single cell meets the working conditions for the in-module balancing of the balancing circuit, and the balancing circuit starts to perform in-module balancing. As the working time of the balancing circuit continues, the difference in SOC of each single cell gradually decreases. Finally, the three modules complete the balancing at 41.4 s, 28.9 s, and 30.7 s respectively, and the maximum difference in SOC of each single cell within each module is less than or equal to 2%, meeting the requirements for stopping the balancing. After that, the maximum difference in SOC within each module remains unchanged. Figure 17 is the simulation result of the SOC balancing between modules in Embodiment 2 of the present invention. Figure 18It is the curve of the change in the SOC difference between modules in Embodiment 2 of the present invention. During a period of time after the start of balancing, the difference between modules does not significantly decrease. This is because the balancing circuit is performing intra-module balancing at this time. After all intra-module balancing is completed, the balancing circuit starts inter-module balancing. After starting inter-module SOC balancing, the SOC difference between modules starts to rapidly decrease and finally decreases to less than 1% at 76.5 s, meeting the balancing threshold requirement, and the balancing circuit stops working. After that, the SOC difference between modules remains unchanged. Finally, the SOC of each module and the SOC of each single cell within the module meet the balancing stop condition, and the balancing ends.

[0158] The technical solution of the present invention is not limited to the limitations of the above specific embodiments. Any technical deformation made according to the technical solution of the present invention falls within the protection scope of the present invention.

Claims

1. A modular active equalization method for a series battery pack based on inductive energy storage, characterized in that: The series battery pack includes 3n single cells, and every 3 single cells form 1 battery module; The series battery pack is connected with an equalization topology; The equalization topology includes 6n + 2 MOS transistors, 2n - 2 diodes, and 2n + 1 inductors; The equalization method is: The equalization process is divided into intra-module equalization and inter-module equalization, and intra-module equalization has a higher priority; Intra-module equalization can achieve charge and discharge equalization of any single cell, and inter-module equalization can achieve transfer of equalization energy between any modules; In the series battery pack, 3n single cells are divided into n battery modules, which are sequentially labeled as B 1 , B 2 , …, B n . The negative electrode of battery module B 1 is connected to the positive electrode of battery module B 2 , and so on. The negative electrode of battery module B n-1 is connected to the positive electrode of battery module B n ; The single cells within the module are sequentially labeled as B 11 , B 12 , B 13 , …, B n1 , B n2 , B n3 . The negative electrode of single cell B 1 in battery module B 11 is connected to the positive electrode of single cell B 12 , and the negative electrode of single cell B 12 is connected to the positive electrode of single cell B 13 , and the rest of the modules are the same; The MOS transistors within the module are sequentially labeled as S 11 , S 12 , S 13 , S 14 , …, S n1 , S n2 , S n3 , S n4 . The inductors within the module are sequentially labeled as L 1a , L 1b , …, L na , L nb . The left MOS transistors between the modules are sequentially labeled as S a , S 1a , …, S na . The right MOS transistors between the modules are sequentially labeled as S b , S 1b , …, S nb . The inductor between the modules is labeled as L; Battery module B 1 The left bridge arm of the positive electrode is connected to MOS transistor S a ; Battery module B 1 The right bridge arm of the positive electrode is connected to MOS transistor S b ; Battery module B 2 , B 3 , …, B n The left and right bridge arms of the positive electrode are connected to the series-connected MOS transistors and diodes; Battery module B n The left bridge arm of the negative electrode is connected to MOS transistor S na ; Battery module B n The right bridge arm of the negative electrode is connected to MOS transistor S nb ; The source electrode of MOS transistor S b is connected to the drain electrodes of other MOS transistors on the right side of the battery module, and the drain electrode of MOS transistor S na is connected to the source electrodes of other MOS transistors on the left side of the battery module; The two ends of the inter-module balancing inductor L are respectively connected to the drain electrodes of MOS transistor S na and MOS transistor S nb ; The internal connection method within the module is as follows: monomer B 11 is connected to the drain electrodes of MOS transistors S 11 and S 13 . Monomer B 13 is connected to the source electrodes of MOS transistors S 12 and S 14 . The source electrode of MOS transistor S 11 is connected to the drain electrode of MOS transistor S 12 . The source electrode of MOS transistor S 13 is connected to the drain electrode of MOS transistor S 14 . One end of inductor L 1a is connected to the negative electrode of monomer B 11 and one end is connected to the source electrode of MOS transistor S 11 . One end of inductor L 1b is connected to the negative electrode of monomer B 12 and one end is connected to the source electrode of MOS transistor S 13 . And so on, monomer B n1 is connected to the drain of MOS transistor S n1 and S n3 ; monomer B n3 is connected to the source of MOS transistor S n2 and S n4 ; the source of MOS transistor S n1 is connected to the drain of MOS transistor S n2 ; the source of MOS transistor S n3 is connected to the drain of MOS transistor S n4 ; one end of inductor L na is connected to the negative electrode of monomer B n1 and one end is connected to the source of MOS transistor S n1 ; one end of inductor L nb is connected to the negative electrode of monomer B n2 and one end is connected to the source of MOS transistor S n3 .

2. A modular active equalization method for a series battery pack based on inductive energy storage according to claim 1, characterized in that: During the charge and discharge process of the series battery pack, the inter-module equalization uses the SOC difference between modules as the equalization discrimination index, where the SOC of a battery module is defined as the average value of the SOCs of the single cells in the module, and the intra-module equalization uses the difference between the SOC of each single cell in the module and the average value of the SOCs of the single cells in the module as the equalization discrimination index.

3. A modular active equalization method for a series battery pack based on inductive energy storage according to any one of claims 1-2, characterized in that: The series battery pack and the equalization topology are combined to form an equalization circuit; Set the equalization threshold between equalization circuit modules as The equalization threshold within the module is The maximum power of the battery module in the series battery pack is SOC max , and the minimum power of the battery module in the series battery pack is SOC min ; for the battery module numbered n, the maximum power of the single cell in the module is SOC max,n , and the minimum power of the single cell is SOC min,n , and the average power of the single cell is SOC ave,n ; If the SOC max,n , SOC ave,n , SOC min,n meets the in-module balancing start condition, in-module balancing is performed, and there is imbalance between modules; if the SOC max,n , SOC ave,n , SOC min,n does not meet the in-module balancing start condition, and the SOC max , SOC min meets the balancing start condition, inter-module balancing is performed; When performing intra-module equalization: If the SOC max,n and the SOC ave,n difference is greater than and the SOC ave,n and the SOC min,n difference is less than the equalization circuit performs high-power single-cell discharge equalization within the module; If the SOC ave,n and the SOC min,n the difference is greater than and the SOC max,n and the SOC ave,n the difference is less than the equalization circuit performs low-battery single-cell charging equalization within the module; If the SOC max,n and the SOC ave,n difference, the SOC ave,n and the SOC min,n differences are both greater than Continue to compare the magnitudes of the two differences; if the SOC max,n and the SOC ave,n difference is greater than the SOC ave,n and the SOC min,n difference, the balancing circuit performs high - power cell discharging balancing within the module; if the SOC max,n and the SOC ave,n difference is less than the SOC ave,n and the SOC min,n difference, the balancing circuit performs low - power cell charging balancing within the module; When performing inter-module equalization: If the SOC max and the SOC min have a difference greater than directly transfer the energy of the high - power battery module to the low - power battery module, otherwise there will be imbalance between modules; Repeat this process until SOC max,n and SOC ave,n The difference, SOC ave,n and SOC min,n The differences are all less than or equal to and SOC max and SOC min The difference is less than or equal to When this happens, the balancing circuit stops working.

4. A modular active equalization method for a series battery pack based on inductive energy storage according to claim 3, characterized in that: When the number of battery modules with the highest charge or the number of battery modules with the lowest charge is not 1, select the highest-charge battery module with the smallest serial number and the lowest-charge battery module with the largest serial number for equalization.

5. A modular active equalization method for a series battery pack based on inductive energy storage according to claim 1, characterized in that: The equalization topology is connected with a control circuit, and the frequency of the control signal of the control circuit should be determined according to the parameters of the equalization circuit, the switching loss of the MOS transistor, the voltage of the series battery pack and the single cells, and the equalization current; The duty cycle of the driving signal output by the control circuit should reset the inductor current in each switching cycle, that is, the current passing through each inductor rises from zero first and then drops to zero in each switching cycle.

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