BMS active equalization circuit and working method thereof

Abstract

The invention relates to the technical field of battery management, and discloses a BMS active equalization circuit and a working method thereof, in the circuit, each multi-winding transformer corresponds to two transformer selection switch groups which are respectively connected to two ends of a winding; each battery pack corresponds to two degree-of-freedom switch modules; in the battery pack, all the battery cell switch modules connected with the positive electrodes of the single battery cells are connected to one degree-of-freedom switch module, and all the battery cell switch modules connected with the negative electrodes of the single battery cells are connected to the other degree-of-freedom switch module; the two degree-of-freedom switch modules are respectively connected with the two transformer selection switch groups in a one-to-one correspondence manner; in the control module, an AFE chip collects a voltage signal of each single cell, and a main control chip controls on-off of each switch module. According to the invention, the cost and technical risk are reduced while functions are improved, random combination of adjacent battery cells can be realized, the charging and discharging balance freedom degree is increased, the number of transformers is reduced, and high cost performance is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of battery management, and in particular to a BMS active balancing circuit and a working method thereof. Background Art

[0002] The Battery Management System (BMS) is used to monitor the status of battery cells in real time, including parameters such as voltage, current, and temperature, and to prevent overcharging, over-discharging, and short circuits through set safety thresholds. Due to manufacturing differences or different working conditions, there may be capacity inconsistencies between individual battery cells. BMS uses active or passive balancing technology to adjust the status between each battery cell to maintain the consistency of overall performance. Among them, active balancing technology actively balances the individual capacity generated by the battery during use and the voltage difference generated by the self-discharge rate. Its main function is to actively balance the differences between battery cells during the charging, discharging, or placement of the battery pack, so as to eliminate various inconsistencies caused by the battery itself and during use after the battery is grouped.

[0003] At present, the BMS active balancing technology solution is not mature enough. For example, inductive active balancing is not easy to integrate in large quantities, and there are repeated battery charging and discharging. Capacitive active balancing cannot effectively control the balancing current, is not easy to control, and has high circuit risks. The existing active balancing circuit technology is not comprehensive enough. It only solves the problem of repeated battery charging and discharging, and only controls the balancing current; it lacks the ability to balance multiple cells in the same group at the same time, and has weak adaptability to working conditions; transformers are isolated between different groups, and adjacent cells cannot be bundled and balanced at the same time, and the balancing freedom is weak; the balancing ability is limited, and it is difficult to optimize the balancing current and speed under the current switching devices, the cost is high, and the cost performance is low; the isolation transformer is used multiple times, which further increases the cost and volume.

[0004] The current relatively reliable active balancing technology solution is to transfer the balancing energy to the bus or independent unit, which acts as an intermediate energy storage link for energy redistribution. However, this solution also has the following disadvantages: (1) The transformer and multi-way switch tube involved greatly increase the cost and volume of the balancing circuit, and a series of problems such as the freedom of balancing multiple cells at the same time cannot be taken into account, and its devices do not have cost advantages; (2) The smallest unit shares the transformer. If two of the smallest units (such as 4 groups of cells) need to be balanced at the same time, it cannot meet the requirements and can only be balanced step by step. The balancing rate is slow, and it cannot be taken into account when there are many abnormalities in the group, resulting in a large pressure on the balancing of a single branch, which poses a major challenge to the cost and structure. Therefore, how to provide a cost-effective active balancing circuit to address the problems of high cost, difficulty in improving power density, and low balancing efficiency encountered in the current BMS active balancing technology has become a technical problem that technicians in this field need to solve urgently. Summary of the invention

[0005] The purpose of the present invention is to provide a BMS active balancing circuit and a working method thereof, which can improve the function while reducing costs, technical risks and pressures by dividing the balancing circuit, and can realize any combination of adjacent battery cells, increase the freedom of charge and discharge balancing, reduce the number of transformers, improve utilization, and achieve high cost performance.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] A BMS active balancing circuit includes a plurality of cascaded battery packs, each of which includes N series-connected single cells, a control module, a cell switch module, a degree of freedom switch module, a transformer selection switch module, and a multi-winding transformer;

[0008] Each of the battery packs comprises N single cells connected in series, and is characterized in that it also comprises a control module, a cell switch module, a degree of freedom switch module, a transformer selection switch module and a multi-winding transformer;

[0009] Among them, at least two multi-winding transformers are provided, each multi-winding transformer corresponds to a transformer selection switch module, the transformer selection switch module includes a first transformer selection switch group and a second transformer selection switch group, the secondary side of the multi-winding transformer includes M windings, the first transformer selection switch group is respectively connected to one end of the M windings, and the second transformer selection switch group is respectively connected to the other end of the M windings; the first transformer selection switch group and the second transformer selection switch group respectively include M selection switch sub-modules connected in parallel;

[0010] Wherein, N and M are positive integers greater than 1;

[0011] Each battery pack corresponds to two degree-of-freedom switch modules. In the battery pack, the positive and negative electrodes of each single cell are connected to the cell switch modules respectively. All cell switch modules connected to the positive electrodes of the single cells are connected to one degree-of-freedom switch module, and all cell switch modules connected to the negative electrodes of the single cells are connected to the other degree-of-freedom switch module. Of the two degree-of-freedom switch modules, one is connected to the first transformer selection switch group, and the other is connected to the second transformer selection switch group.

[0012] The control module includes an AFE chip and a main control chip, wherein the AFE chip is respectively connected to each single cell to collect the voltage signal of each single cell, and the main control chip is respectively electrically connected to the AFE chip, the cell switch module, the degree of freedom switch module, the transformer selection switch module, and the multi-winding transformer;

[0013] The cell switch module is used to control the on / off of the charge / discharge circuit of each single cell and to form a new discharge combination; the freedom switch module is used to control the on / off of the charge / discharge circuit of each battery pack, divide the voltage stress caused by charging and discharging between different battery packs, and participate in the construction of different charge and discharge circuits; the transformer selection switch module is used to select different winding circuits connected to the multi-winding transformer, and cooperate with intermittent charging and discharging of the inner and outer rings to reduce the thermal stress of the device, etc., and can provide a variety of discharge combination circuits, making high cost performance possible.

[0014] Furthermore, the cell switch module is a MOS tube switch group, and the MOS tube switch group includes two MOS tubes connected in reverse series; the degree of freedom switch module is two MOS tubes connected in reverse series or one MOS tube.

[0015] Furthermore, the selection switch submodule in the first transformer selection switch group is a MOS tube switch group, and the first transformer selection switch group includes M parallel MOS tube switch groups, and each of the MOS tube switch groups includes two MOS tubes connected in reverse series;

[0016] The selection switch submodule in the second transformer selection switch group is a MOS tube, and the second transformer selection switch group includes M MOS tubes connected in parallel.

[0017] Furthermore, each single cell corresponds to two cell switch modules, and each battery pack corresponds to 2N cell switch modules, wherein the N cell switch modules connected to the positive pole of the single cell are connected to one degree of freedom switch module, and the N cell switch modules connected to the negative pole of the single cell are connected to another degree of freedom switch module.

[0018] Furthermore, the number of the multi-winding transformers is less than the number of the battery packs; the multi-winding transformers are provided in plurality; each battery pack corresponds to two degree-of-freedom switch modules, one of which is connected to the first transformer selection switch group corresponding to the plurality of multi-winding transformers, and the other is connected to the second transformer selection switch group corresponding to the plurality of multi-winding transformers.

[0019] Furthermore, the multi-winding transformer is connected to an external power supply, and an NMOS tube is connected in series to the side connected to the external power supply, so that the transformer can be cut off and put into operation at any time according to needs.

[0020] Furthermore, the battery cell switch module and the transformer selection switch module can be selected according to the voltage level within the group, and a low-voltage MOS can be selected (if there are 4 battery cells in a group, the MOS has a withstand voltage of 20-30V. This type of selection has low cost, high efficiency, small size, and multiple specifications).

[0021] The present invention also provides a working method of a BMS active balancing circuit, which is applied to the above-mentioned BMS active balancing circuit and comprises the following steps:

[0022] The AFE chip collects the voltage signal of each single cell in real time to determine whether each single cell has overvoltage or undervoltage and whether it needs to be charged / discharged;

[0023] When a single cell needs to be charged / discharged, the main control chip controls the two cell switch modules connected to the positive and negative electrodes of the single cell to be turned on first, and then the two degree-of-freedom switch modules corresponding to the battery pack where the single cell is located are turned on; at the same time, a multi-winding transformer is selected, and the winding circuit of the multi-winding transformer to be connected is determined. Based on the winding circuit to be connected, the selection switch submodules to be turned on in the first transformer selection switch group and the second transformer selection switch group are determined, and the first charging / discharging circuit is formed with the winding circuit to be connected, and the single cell is charged / discharged using the first charging / discharging circuit;

[0024] When multiple adjacent single cells are over-voltage or under-voltage, they need to be charged / discharged, and multiple single cells are connected in series to form a charge / discharge unit. The main control chip controls the cell switch module connected to one end of the single cell at the head end of the charge / discharge unit and the other end of the single cell at the end of the charge / discharge unit to be turned on first, and then the corresponding degree of freedom switch module is turned on; at the same time, a multi-winding transformer is selected, and the winding circuit of the multi-winding transformer to be connected is determined. Based on the winding circuit to be connected, the selection switch submodules to be turned on in the first transformer selection switch group and the second transformer selection switch group are determined, and the second charge / discharge circuit is formed with the winding circuit to be connected, and the charge / discharge unit is charged / discharged by the second charge / discharge circuit; wherein, the first transformer selection switch group (TO1, TO2, TS1, TS2) corresponds to one end of the cell at the head end of the discharge unit, and the second transformer selection switch group (TO3, TS3) corresponds to the other end of the cell at the end of the discharge unit; similarly, if the second group of transformers is selected, they are also connected in this way.

[0025] Furthermore, the working method also includes a mode of balanced charging and discharging of inner and outer loops, and the balanced charging and discharging mode of inner and outer loops includes:

[0026] The first charge / discharge circuit is an inner ring charge / discharge circuit;

[0027] When a single cell needs to be charged / discharged, and the first charge / discharge circuit cannot meet the charge / discharge demand of the single cell, the single cell is connected in series with multiple single cells adjacent to its two ends to form a charge / discharge unit, which is used to construct an outer ring charge / discharge circuit. The main control chip controls the cell switch module and the degree of freedom switch module connected to the positive electrode of the single cell at the head end of the discharge unit and the negative electrode of the single cell at the end of the charge / discharge unit to be turned on in sequence; at the same time, a winding circuit of another transformer is selected, and based on the winding circuit, the selection switch submodule to be turned on in the corresponding transformer selection switch group is determined to form an outer ring charge / discharge circuit with the winding circuit; through the control of the main control chip, the inner ring charge / discharge circuit and the outer ring charge / discharge circuit are used to alternately charge / discharge the single cell, which can reduce the stress of the cell switch group and the transformer group, reduce the stress and heat loss of the single circuit device, etc. Under the same device specifications, the balancing current can be increased in this way, and the devices involved are almost the same as the traditional mode, but the balancing current is nearly doubled.

[0028] Further, the determining whether each single cell needs to be charged / discharged specifically includes:

[0029] When the voltage of a single cell is greater than a first set threshold value (for example, several times the average voltage value of all single cells, set according to the maximum overvoltage difference of the cell group actually acceptable to the designer), it is determined that the single cell needs to be discharged;

[0030] When the voltage of a single cell is less than a second set threshold (eg, several times the average voltage of all single cells, set according to the maximum undervoltage error of the cell group actually acceptable to the designer), it is determined that the single cell needs to be charged.

[0031] According to the specific embodiments provided by the present invention, the BMS active balancing circuit and the working method thereof provided by the present invention disclose the following technical effects:

[0032] The BMS active balancing circuit provided by the present invention includes a plurality of cascaded battery packs, each of which includes N single battery cells connected in series, and also includes a control module, a battery cell switch module, a degree of freedom switch module, a transformer selection switch module and a multi-winding transformer. The structure is simple and diversified control functions can be achieved through the cooperation of multiple switch modules.

[0033] The present invention eliminates some transformers on the basis of each battery group, adds a freedom switch module and a transformer (multi-winding transformer) selection switch, increases the balance freedom, balances the efficiency, reduces the number of components, saves costs, and reduces the structure. Different numbers of winding transformers can be selected according to needs for different numbers of battery groups, thereby improving the applicability and scalability of the circuit, and energy storage and redistribution can be completed on the primary side of the transformer (corresponding to the charge and discharge circuit).

[0034] The present invention adopts a multi-winding transformer, which can be selected to connect to different winding loops as needed to meet the balancing of different numbers of battery cells. In order to increase the degree of freedom and save costs, a degree of freedom switch module is added to the active balancing circuit while reducing the transformer. By increasing the withstand voltage of the degree of freedom switch module (the number of degree of freedom switches is small, and the selection of a higher withstand voltage is not very sensitive to cost, etc.), the voltage correlation of the entire balancing circuit is divided (decoupling), so that the withstand voltage of the battery cell balancing MOS switch is designed according to the intra-group balancing, further reducing the device voltage stress, facilitating selection, reducing losses and saving costs (because the withstand voltage of the MOS process is improved, the on-resistance will increase in a positive correlation).

[0035] The present invention provides a plurality of multi-winding transformers, for example, two multi-winding transformers, which can perform energy conversion in the form of staggered parallel connection. Regardless of whether a single battery cell or multiple battery packs are balanced, energy can be transferred alternately between the two multi-winding transformers in the form of staggered parallel connection to reduce the thermal stress of the transformer and the line, improve the balancing efficiency of the whole machine, and reduce losses.

[0036] The present invention improves functions while reducing costs and technical risks. Under certain device specification parameters, any combination of adjacent battery cells can be achieved through internal and external ring discharge and degree of freedom combination, thereby increasing the degree of freedom of charge and discharge balance, reducing heat loss, increasing efficiency, improving power density, and achieving high cost performance.

[0037] In summary, the present invention provides a cost-effective BMS active balancing circuit, which can provide more functions by dividing the balancing circuit, while further reducing costs, technical risks and pressures. At the same time, it can also allow adjacent cells of each battery pack to be combined and stacked at will, thereby increasing the freedom of charge and discharge balancing. It can also reduce the number of transformers, maximize the use of transformers by switching between battery packs, reduce costs and volume, and improve cost-effectiveness. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0039] FIG1 is a hardware topology diagram of a BMS active balancing circuit according to an embodiment of the present invention, wherein (a) is a schematic diagram of the overall circuit, (b) is a schematic diagram of the connection structure of a battery pack, a cell switch module, and a degree of freedom switch module; (c) is a schematic diagram of the connection structure of a transformer selection switch module and a multi-winding transformer;

[0040] Figure 2 It is an interactive diagram of the BMS active balancing circuit of the present invention, the AFE voltage sampling, and the auxiliary power supply outside the main control chip;

[0041] Figure 3 This is a schematic diagram of a working mode 1 of a BMS active balancing circuit according to an embodiment of the present invention;

[0042] Figure 4 This is a schematic diagram of the second working mode of the BMS active balancing circuit according to an embodiment of the present invention;

[0043] Figure 5 Schematic diagram of the third working mode of the BMS active balancing circuit according to an embodiment of the present invention;

[0044] Figure 6 FIG. 4 is a schematic diagram of a fourth working mode of a BMS active balancing circuit according to an embodiment of the present invention. DETAILED DESCRIPTION

[0045] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0046] The purpose of the present invention is to provide a BMS active balancing circuit and a working method thereof, so as to solve the problems existing in the current BMS active balancing circuit, such as low balancing freedom, slow balancing speed, low efficiency, contradiction between capacity expansion and cost due to device specifications, large number of transformers, high cost and large volume, etc., and to improve a cost-effective active balancing circuit.

[0047] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0048] As shown in Figure 1- Figure 2 As shown, the BMS active balancing circuit provided by the present invention includes: a plurality of cascaded battery packs, each of which includes N series-connected single cells, a control module, a cell switch module, a degree of freedom switch module, a transformer selection switch module, and a multi-winding transformer;

[0049] Each of the battery packs comprises N single cells connected in series, and is characterized in that it also comprises a control module, a cell switch module, a degree of freedom switch module, a transformer selection switch module and a multi-winding transformer;

[0050] Among them, at least two multi-winding transformers are provided, each multi-winding transformer corresponds to a transformer selection switch module, the transformer selection switch module includes a first transformer selection switch group and a second transformer selection switch group, the secondary side of the multi-winding transformer includes M windings, the first transformer selection switch group is respectively connected to one end of the M windings, and the second transformer selection switch group is respectively connected to the other end of the M windings; the first transformer selection switch group and the second transformer selection switch group respectively include M selection switch sub-modules connected in parallel;

[0051] Wherein, N and M are positive integers greater than 1;

[0052] Each battery pack corresponds to two degree-of-freedom switch modules. In the battery pack, the positive and negative electrodes of each single cell are connected to the cell switch modules respectively. All cell switch modules connected to the positive electrodes of the single cells are connected to one degree-of-freedom switch module, and all cell switch modules connected to the negative electrodes of the single cells are connected to the other degree-of-freedom switch module. Of the two degree-of-freedom switch modules, one is connected to the first transformer selection switch group, and the other is connected to the second transformer selection switch group.

[0053] The control module includes an AFE chip and a main control chip, wherein the AFE chip is respectively connected to each single cell to collect the voltage signal of each single cell, and the main control chip is respectively electrically connected to the AFE chip, the cell switch module, the degree of freedom switch module, the transformer selection switch module, and the multi-winding transformer;

[0054] The cell switch module is used to control the on / off of the charge / discharge circuit of each single cell and to form a new discharge combination; the freedom switch module is used to control the on / off of the charge / discharge circuit of each battery pack, divide the voltage stress caused by charging and discharging between different battery packs, and participate in the construction of different charge and discharge circuits; the transformer selection switch module is used to select different winding circuits connected to the multi-winding transformer, and cooperate with intermittent charging and discharging of the inner and outer rings to reduce the thermal stress of the device, etc., and can provide a variety of discharge combination circuits, making high cost performance possible.

[0055] Specifically, the cell switch module is a MOS tube switch group, and the MOS tube switch group includes two MOS tubes connected in reverse series; the degree of freedom switch module includes two MOS tubes connected in reverse series.

[0056] The selection switch submodule in the first transformer selection switch group is a MOS tube switch group, and the first transformer selection switch group includes M parallel MOS tube switch groups, that is, the number of MOS tube switch groups is determined according to the number of transformer windings, and each of the MOS tube switch groups includes two MOS tubes connected in reverse series;

[0057] The selection switch submodule in the second transformer selection switch group is a MOS tube, and the second transformer selection switch group includes M parallel-connected MOS tubes, that is, the number of MOS tubes is determined according to the number of transformer windings.

[0058] The multi-winding transformer can select windings according to the actual sampling voltage; the multi-winding transformer is provided with a plurality of them; each battery pack corresponds to two degree-of-freedom switch modules, one of which is connected to the first transformer selection switch group corresponding to the plurality of multi-winding transformers, and the other is connected to the second transformer selection switch group corresponding to the plurality of multi-winding transformers. Take battery pack 1 as an example: the degree-of-freedom switch module Z1 is connected to the first transformer selection switch group (TO1, TO2, TS1, TS2) and (T2O1, T2O2, T2S1, T2S2) corresponding to the multi-winding transformer; the degree-of-freedom switch module Z2 is connected to the other end of the second transformer selection switch group corresponding to all multi-winding transformers (TO3, TS3, T2O3, T2S3); and so on, the degree-of-freedom switch modules corresponding to battery packs 2 and 3 also maintain the same connection method.

[0059] The multi-winding transformer is connected to an external power supply, and an NMOS tube is connected in series on the side connected to the external power supply. Figure 2 As shown, the external power supply is responsible for the energy transfer of charging and discharging of the single battery cells.

[0060] The main control chip conditions and calculates the voltage signal sampled by the AFE chip according to the circuit topology and operation mode, confirms the overcharged and overdischarged cells, and determines the discharge mode to be adopted; sends corresponding drive signals to switch on and off the cell switch module, degree of freedom switch module, transformer selection switch group, etc. for charging and discharging; and other auxiliary circuits are built accordingly. The AFE chip performs single cell voltage detection to detect the voltage of each single cell.

[0061] The cell switch module and the transformer selection switch module can both use low-voltage MOS that meets the voltage level within the group. This type of MOS has the advantages of low cost, low conduction loss and high efficiency.

[0062] The withstand voltage parameters of the battery cell switch module and the transformer selection switch module are basically the same, and the type can be selected according to the voltage level in the battery cell group (if there are 4 batteries in a group, the type selected at 20-30V basically meets the requirements).

[0063] Embodiment 1:

[0064] As shown in Figure 1- Figure 6 As shown, the present invention provides an embodiment of three battery packs and two multi-winding transformers, each battery pack includes 4 single cells connected in series, that is, in this embodiment, there are a total of 12 single cells, namely bat1-bat12; the two degree of freedom switch modules corresponding to the first battery pack are Z1 and Z2, respectively, the two degree of freedom switch modules corresponding to the second battery pack are Z3 and Z4, respectively, and the two degree of freedom switch modules corresponding to the third battery pack are Z5 and Z6. In this embodiment, Z1-Z5 use two reverse series MOS tubes, and Z6 uses a single MOS tube. Since the battery group corresponding to Z6 is the group with the lowest voltage level in the series battery group, the potential of the circuit where Z6 is located is the lowest, so the single MOS tube here can also complete the voltage stress division and degree of freedom adjustment functions. In actual design, it can be selected according to its own needs, or two reverse series MOS tubes can be used.

[0065] This embodiment uses two identical multi-winding transformers T1 and T2, and the secondary side of each multi-winding transformer includes two windings. The first transformer selection switch group is connected to one end of the two windings, and the second transformer selection switch group is connected to the other end of the two windings; the first transformer selection switch group includes two parallel MOS transistor switch groups, each of which includes two reverse-series MOS transistors, and the second transformer selection switch group includes two parallel MOS transistors; in the multi-winding transformer T1, the first transformer selection switch groups are TO1 and TO2, TS1 and TS2, and the second transformer selection switch group includes two parallel MOS transistors, TO3 and TS3; in the multi-winding transformer T2, the first transformer selection switch groups are T2O1 and T2O2, T2S1 and T2S2, and the second transformer selection switch group includes two parallel MOS transistors, T2O3 and T2S3.

[0066] The primary side of the multi-winding transformer T1 is connected in series with a MOS tube MOS121, and the primary side of the multi-winding transformer T2 is connected in series with a MOS tube MOS122. The MOS tubes described in the embodiment of the present invention are all NMOS tubes.

[0067] The embodiment of the present invention increases the degree of freedom of balance, balance efficiency, reduces the number of components, saves costs, and reduces the structure by removing some transformers on the basis of each group of battery cells, adding freedom switch modules (Z1, Z2, Z3, Z4, Z5, Z6) and transformer (multi-winding transformer) selection switches (TO1-TO3, TS1-TS3). This embodiment only embodies three groups of cascades, but according to this topology scheme, it is only necessary to add switches on the positive and negative ends of the multi-winding transformer isolation circuit and then connect them to the multi-winding transformer. The number of groups is continuously increased according to design requirements, not limited to 3 levels or more. The energy storage and redistribution is completed on the primary side of the multi-winding transformer (corresponding to the charge and discharge circuit). The actual circuit can be superimposed with the number of cascade levels according to requirements.

[0068] As shown in Figure 1- Figure 2As shown, the design of this embodiment also incorporates a multi-winding transformer. Considering that if one or several single cells have a very large imbalance, in order not to affect the overall efficiency of the system, it is necessary to speed up the charging and discharging speed. Under a 50% duty cycle, the single cell can be continuously transferred with two winding transformers at the same time (the switches of the T1 and T2 transformers are switched on alternately to accelerate the balance). This method further improves the effective value of the balancing current on the existing basis and accelerates the balance. However, the transformer parameters are designed according to the small current, which can save space and cost, and the balancing current can be doubled under the same device specifications. It can also be compared with the outer loop and inner loop in the control loop. If the current device specifications are limited and the MOS tube itself has limited loss and heat generation, it is impossible to continuously balance the single cell under large current, T1 can be used to directly balance the maximum current alone, and T2 can be used to select a continuous cell group composed of adjacent cells for small current outer loop balance, so that the balancing effect is better, with the ability of fast balancing, and can reduce the pressure of power device selection, reduce cost and structural layout.

[0069] A brief example: if the voltage of bat4 cell is very different from that of other cells, the current required for balancing is large, and the balancing rate needs to be accelerated, then on the one hand, it can continuously switch the windings of T1 and T2 transformers to alternately conduct for charging and discharging at a 50% duty cycle, and adopt the method of balancing within the whole cycle to achieve the purpose of rapid balancing. At this time, for a single transformer, its energy loss is only half of the effective value of the total balancing current. Regardless of whether T1 or T2 is designed, it can be designed according to the smaller current requirements, and the heat loss is small, and the cost and volume can be optimized. However, at this time, the current value of the switch tube and wiring directly connected to the bat4 cell is twice the normal value. If there is a risk of thermal stress on the device and line, the internal and external loop balancing method can be used: such as placing bat4 in the combined circuit of bat5-bat3 (you can also choose the remaining circuits including bat4, according to the design requirements of multi-winding transformers), and adopting the principle of derating charging and discharging for this circuit (to avoid too much impact on the other normal cells). At this time, the charging and discharging circuit is borne by the remaining switch tubes, which can reduce the thermal stress of the device. Under the same device, the balancing effect is improved, the balancing is accelerated, and the balancing can be further accelerated for extreme working conditions.

[0070] Reasons for using a multi-winding transformer: The present invention takes into account the balance between single cells and adjacent battery cells (as well as the balance between internal and external loops). The isolation transformer uses a flyback topology and uses a continuous mode or a discontinuous mode. If the turns ratio is fixed, it can only meet a certain mode and cannot meet the balance of different numbers of battery cells. Therefore, a multi-winding transformer is incorporated and a transformer selection switch module is used. According to the voltage sampling information, the serial number of the overcharged or over-discharged single cell is confirmed after processing, and the corresponding switch is turned on for balancing to achieve the optimal balancing goal.

[0071] As shown in Figure 1: In order to increase the degree of freedom and save costs, the present invention reduces the transformer and also adds a degree of freedom switch module in the active balancing circuit. The advantages of the degree of freedom switch module are analyzed as follows: As shown in Figure 1, there are three different specifications of switches in this topology. The withstand voltage and other parameters of the transformer selection switch module are basically consistent with the battery switch module. The selection can be made according to the voltage in the battery group. (If a group of 4 batteries is used, and the maximum voltage of a single battery cell is 3.6V, then the selection according to about 20-30V basically meets the requirements. The most severe working condition is: bat4 is charged and discharged, and there are three batteries between bat1 The switch tube must meet the voltage resistance (the switching spikes will also be superimposed, leaving a margin). If there is no free switch, after cascading 3 groups, the potential difference between the BAT12 battery cell and the battery cell 1 in the third group will be particularly large, 3-4 times that of the group, making it difficult to select the switch, and putting great pressure on the cost and structure. In addition, as the MOS voltage resistance increases, its on-resistance will also increase rapidly, and the resulting loss and heat dissipation will also become a key issue, posing a greater challenge to the design of BMS active balancing products. Therefore, the free switch is introduced here, which not only allows for free adjustment, but also serves the effect of separating the pressure of devices between groups, such as Figure 3 As shown: Due to the existence of the freedom switch modules Z1-Z6, as the cascade increases, the voltage resistance of the freedom switch can be increased (the number of freedom switch modules is small, and the selection of a higher voltage resistance is not very sensitive to cost, etc.), and the voltage correlation of the entire balancing circuit can be divided (decoupling). This makes the voltage resistance of the MOS tube switches that balance the cell monomers to be designed according to the balance within the group, further reducing the device voltage stress, facilitating selection, reducing losses and saving costs.

[0072] Embodiment 2:

[0073] Here we only make a simple comparison of power devices to illustrate the advantages of the invention: if we take 4 groups of battery packs as an example and evaluate them as a BMS unit, the current traditional array switch type BMS active balancing circuit has the same number of cell switch modules as the current invention; the freedom switch added in this invention is a redundant device, and its relationship with the cell group is 2 times; the number of transformers: the number of transformers in the present invention is temporarily evaluated in the same way as the traditional number. Overall, the cost only increases the freedom switch and the transformer multi-way selection switch.

[0074] According to the overall evaluation, the number is far less than 2 times of the traditional devices. If evaluated according to the current topology of 3 groups of battery cells, the number of added freedom switches and selection switches is about 20 (6 groups of freedom 2*12, two groups of transformer selection switches 3*2*2, but the traditional transformer also has a selection switch, the difference is about 20 power tubes), but the power tubes of the entire traditional loop are 4*4*3 (array switch) + 4 (transformer switch) = 48+4 = 52. In short, the number of power tubes increases by less than 0.4 times. In addition, if the number of battery cell groups cascaded according to the present invention is greater, the proportion of added devices will be further reduced.

[0075] The control loop is not mentioned here, but the AFE and main control mentioned above are basically included, and no additional devices are required. The cost will not be much different, but the staggered discharge, inner and outer ring discharge, and device stress division included in the present invention are convenient for structure and layout during circuit design. At the same time, with the same device specifications, the present invention can almost double the balancing current, and the cells can be freely combined and discharged at the same time, etc., further improving the power density. Its overall cost performance is much higher than that of traditional methods.

[0076] Therefore, in summary, this invention not only solves the current problems of low cell balancing efficiency, large size, high cost, slow balancing rate, etc., but also effectively controls the cost, which has great advantages in practicality.

[0077] Function comparison compared with traditional equalizer:

[0078] The present invention can achieve continuous and simultaneous balancing of adjacent battery cells between groups, increase balancing efficiency, and improve the degree of freedom, and has been demonstrated.

[0079] The transformer winding is optional, making it possible to balance multiple cells synchronously. It only requires processing the sampled voltage signal in the software and switching the corresponding switch. With little increase in hardware cost, the balancing current can be doubled, the balancing efficiency can be increased, and the balancing effect can be achieved quickly.

[0080] The device stress can be reduced. The current energy storage BMS active balancing technology has gradually increased from 2-3A to 5A, and 10A is under development, etc. However, the composition of a product involves all aspects. The increase in power and current levels will inevitably cause a series of problems such as device volume and flow, resulting in rapid cost growth and volume growth. However, this problem can be effectively avoided in the present invention. For example, a 2-3A power tube is used for module balancing. If there are adjacent or one or more cells with particularly large differences and need to be quickly balanced, a continuous balancing method can be used to balance multiple cells at the same time or use the inner ring to balance the maximum current separately. According to the surrounding sampling results, the abnormal cell is placed in a group composed of continuous cells in an outer ring, and then the group is balanced in the outer ring (the balancing current can be appropriately reduced by 1-2A at this time). At this time, the current no longer flows through the original path, but is balanced in the new loop. In this way, the 4-5A balancing capacity can also be met, but the power device continues to be selected as 2-3A, so that the contradiction between performance and cost is suppressed.

[0081] It can be cascaded continuously without increasing the withstand voltage of the entire battery cell string switch (the increase in the withstand voltage of the device will increase the cost and volume, and reduce efficiency). It is convenient for multi-cascading and integrated design, so that the MOS withstand voltage selection is no longer a key bottleneck, providing a technical direction for active balancing of multi-cell balancing.

[0082] To sum up the above analysis, the technical effects of the present invention have been verified through practice. The present invention can solve the contradiction between cost, structure and balancing efficiency encountered by traditional BMS active balancing solutions, so that the balancing capability is increased on the basis of the original cost device structure. It can be used as a cost-effective BMS active balancing solution to achieve cell balancing.

[0083] On the other hand, the present invention further provides a working method of a BMS active balancing circuit, which is applied to the above-mentioned BMS active balancing circuit and comprises the following steps:

[0084] The voltage signal of each single cell is collected in real time through the AFE chip to determine whether each single cell needs to be charged / discharged; the embodiment of the present invention takes the normal working voltage of 2.8V-3.6V of the lithium iron phosphate cell as an example, and samples the voltage of the series-connected cell through the AFE chip and the main control chip. This embodiment is for the case of 3 battery packs and 12 single cells.

[0085] Working mode 1:

[0086] When a single cell needs to be charged / discharged, the main control chip controls the two cell switch modules connected to the positive and negative poles of the single cell to be turned on first, and then the two degree of freedom switch modules corresponding to the battery pack where the single cell is located are turned on; at the same time, a multi-winding transformer is selected, and the winding circuit of the multi-winding transformer to be connected is determined (the upper winding in the transformer topology diagram currently corresponds to a single single cell, and the lower winding corresponds to the charging and discharging of the cell group). Based on the winding circuit to be connected, the switch sub-modules to be turned on in the first transformer selection switch group and the second transformer selection switch group are determined, and the first charging / discharging circuit is formed with the winding circuit to be connected, and the single cell is charged / discharged using the first charging / discharging circuit.

[0087] For example, Figure 3 As shown, for example, bat1 has the highest voltage among the series-connected cells (greater than the first set threshold value), so it needs to be charged and discharged: first, turn on the cell switch module connected to bat1, and then turn on the degree of freedom switches Z1 and Z2 corresponding to the battery pack where the single cell is located, and then select T1 or T2, turn on the corresponding transformer winding selection switch submodule in the switch group, and select the upper winding here (the upper winding has been defined to correspond to the charging and discharging of a single cell). If it is assumed that the T1 transformer is selected, that is, turn on TO1 and TO2, and TO3 enters the PWM mode for balancing. The circuit is as follows Figure 3 The black dotted line circuit is shown, and the shutdown sequence will be closed in the reverse order of the opening switch sequence. Figure 3 As shown: If bat1 is being charged and discharged, bat6, bat7, and bat8 also have charging and discharging requirements, then Figure 3 The blue dotted circuit in the middle is charged and discharged, and the two charging and discharging circuits are opened in an intermittent manner (after the bat1 discharge circuit is opened for a period of time, the bat6, bat7, and bat8 battery cell groups are stopped from discharging). It can be found that if the blue dotted circuit is opened and running, the terminal voltage of bat6 will raise the right side potential of the freedom switch Z1 to a potential equal to the bat6 terminal voltage. At this time, there is a division of the freedom switch module Z1, and the pressure difference between the two can be blocked by the freedom switch module. If there is no freedom switch module, the potential difference is greater than the maximum potential difference in the battery pack (if there are more cascades and the potential difference is greater, it will inevitably cause an increase in structure and cost, and bring pressure to product design). Therefore, the idea of ​​dividing the device stress and gradually discharging alternately can be adopted.

[0088] Working mode 2:

[0089] When multiple adjacent single cells need to be charged / discharged (if there are single cells that do not need to be charged / discharged among the multiple single cells), the multiple single cells can be connected in series to form a charge / discharge unit, and the main control chip controls the cell switch module and the freedom switch module connected to one end (positive pole) of the single cell at the head end of the discharge unit and the other end (negative pole) of the single cell at the end of the charge / discharge unit to be turned on; at the same time, a multi-winding transformer is selected, and the winding circuit of the multi-winding transformer to be connected is determined. Based on the winding circuit to be connected, the switches to be turned on in the first transformer selection switch group and the second transformer selection switch group are determined, and a second charge / discharge circuit is formed with the winding circuit to be connected, and the charge / discharge unit is charged / discharged using the second charge / discharge circuit; wherein the first transformer selection switch group corresponds to one end of the freedom switch at the head end of the discharge unit, and the second transformer selection switch group corresponds to one end of the freedom switch of the single cell at the end of the discharge unit.

[0090] For example, continue with Figure 4 Take bat4, bat5, bat6 and bat7 as an example. If the voltage of bat6 is normal and does not need to be balanced, and the voltages of the other three are obviously overcharged or over-discharged and need to be balanced, then continue to follow Figure 4 As shown (blue dotted line), balanced charging and discharging are performed, and the switch opening and method are the same as those of a normal multi-cell group. As the single cell is charged and discharged for a long time, when the voltages of bat4, bat5, and bat7 are gradually balanced, the voltage of bat6 will inevitably become abnormal. In this case, it is considered to prioritize balancing the abnormal cell group, and at the same time, alternately add the inner loop to adjust the voltage of bat6 during balancing. According to this process current loop (black dotted line), it can balance quickly and is shorter and more efficient than a single balancing loop. On the contrary, if bat4, bat5, and bat7 are balanced separately, it will inevitably result in a long balancing time and an increased loop, and the efficiency and rate will deteriorate. Similarly, if Figure 4 There are other situations as shown: for example, when the AFE chip samples the voltage of the series cells and is processed by the main control chip, bat4, bat5, bat6, and bat7 appear, and the voltage is too high (voltage> the first set threshold). If the cells are discharged individually at this time, it is easy to cause the cells to be discharged untimely and the single cells to be overvoltage, and the charging is stopped. When the screening finds that the voltages of adjacent cells are all high, the main control chip first controls the discharge unit (because there are continuous uneven voltage cells, they are combined into a balanced cell group), opens the cell switch modules at the head and end of the cell group, calculates the total voltage of the discharge unit, and then opens the freedom switch module; judges the voltage and continues to select the winding circuit of the multi-winding transformer (this time Figure 3The example uses transformer T1, if T2 is used, the method is the same). The main control chip can drive TS1, TS2, and TS3 of the multi-winding transformer to perform PWM ripple generation, control its discharge, and continue to sample and monitor its voltage (the sampling time can be set by yourself) until the voltage balance requirement is met (in this process, if bat4 is balanced and restored to normal voltage first, the switches from the transformer side are gradually closed to the battery side, and then other voltages are detected to re-plan the real-time detection of the balancing group, which can be cross-developed with the first case), enriching the charging and discharging conditions, increasing the charging and discharging combinations, and being able to adapt to more conditions.

[0091] Working mode three:

[0092] The working method also includes a mode of balanced charging and discharging of inner and outer rings, and the balanced charging and discharging mode of inner and outer rings includes:

[0093] The first charge / discharge circuit is an inner ring charge / discharge circuit;

[0094] When a single cell needs to be charged / discharged, and the first charge / discharge circuit cannot meet the charge / discharge demand of the single cell, the single cell is connected in series with multiple single cells adjacent to its two ends to form a charge / discharge unit, which is used to construct an outer ring charge / discharge circuit. The main control chip controls the cell switch module and the degree of freedom switch module connected to the positive electrode of the single cell at the head end of the discharge unit and the negative electrode of the single cell at the end of the charge / discharge unit to be turned on in sequence; at the same time, a winding circuit of another transformer is selected, and based on the winding circuit, the switch submodule to be turned on in the corresponding transformer selection switch group is determined to form an outer ring charge / discharge circuit with the winding circuit; through the control of the main control chip, the inner ring charge / discharge circuit and the outer ring charge / discharge circuit are used to alternately charge / discharge the single cell, which can reduce the stress of the cell switch group and the transformer group, reduce the stress and heat loss of the single circuit device, etc. Under the same device specifications, the balancing current can be increased in this way, and the devices involved are almost the same as the traditional mode, but the balancing current is nearly doubled.

[0095] For example, when a single cell has a high voltage, such as during the bat6 voltage charging process, according to the current active balancing selection device 5A, overvoltage discharge cannot meet the requirements, and it continues to be greater than the first set threshold or even greater. At this time, the entire power circuit cannot perform a larger current balance, and the inner and outer loop balanced charging and discharging mode can be adopted:

[0096] AFE sampling and main control chip calculation get bat6 overvoltage, priority in order to gradually open the cell switch module, degree of freedom switch module, transformer selection switch, etc., the temperature sampling signal feedback main control chip discharge circuit overtemperature and the core can not further increase the discharge current (power device parameters, etc. are limited), but the cell balance abnormality is not resolved, then the inner and outer loop balance charge and discharge mode, alternating discharge mode, such as Figure 5 As shown, the black dotted line circuit can be fully loaded and discharged for a period of time. When the detected temperature is close to the protection level, the switches are disconnected in sequence (gradually shut down from the transformer selection switch module to the degree of freedom switch module and then to the cell switch module); then the cell group discharge mode is adopted (the switch conduction sequence is basically the same as the discharge of a single cell), and the circuit is Figure 5 As shown in the blue dotted circuit, (it can be found that except for part of the transformer circuit, the two key charging and discharging circuit components are basically not reused and overlapped, and the risk of thermal runaway will inevitably be reduced. This allows the risk of overcharging and over-discharging to be determined through control and sampling (AFE and main control chip, etc.) calculation and processing under the same package and specifications, and the transformer winding switching and degree of freedom switch conduction to be controlled, so that the device packaging specifications (device packaging specifications, etc. determine the product volume and cost) remain unchanged, and the discharge circuit is more fully utilized, so that the entire battery group is quickly balanced, and the balanced current and power density are improved. In addition, if the transformer circuit before and after discharge still has the thermal risk caused by long-term charging and discharging, the function of alternating charging and discharging of multiple multi-winding transformers can be used, and the black solid line path in the figure is used for charging and discharging, which can also reduce the pressure of transformer selection and save costs.

[0097] Working mode 4:

[0098] Based on the above working mode three and working mode two, if the voltage difference between multiple adjacent battery cells is too large and cannot be further balanced due to the thermal risk of the power device, two groups of multi-winding transformers can be used to use different winding circuits with high voltages, and alternate conduction can be adopted at the same time to quickly discharge multiple groups of battery cells. Under the condition of certain device parameters, the device parameters can be used to the maximum extent to improve the balancing effect and power density.

[0099] Working mode description: Figure 5 As shown: if multiple single cells need to be balanced at the same time (cell group composed of bat4, bat5, bat6, and bat7), the main control chip will control the upper cell switch module of bat4 and the lower cell switch module of bat7 according to the sampling results, and then open the freedom switch modules Z1 and Z4 according to the loop selection; since the cell group is balanced this time (the upper winding of the transformer in the figure is a single cell balancing winding, and the lower winding is a cell group balancing winding), the selection switches TS1 and TS2 of the multi-winding transformer T1 are controlled to open, and then the flyback energy transfer is performed - this process is a normal balancing process, as shown Figure 5The black dashed line in the figure represents the energy flow (the flow direction arrow is not marked because the loop is consistent. If the battery cell is discharged, the current flows from the battery cell to the transformer, and if it is charged, it is vice versa). In actual operation, if the battery cell is overcharged or over-discharged, the power transformer and its power tube specifications require that the current cannot meet the current demand, and it is necessary to continue to increase the balancing current to accelerate the balancing; then consider the staggered method; in certain cycles (the time can be adjusted by yourself), turn on the switch in turn according to the black dashed charge and discharge path in the figure for balancing, and then turn it off, and use the blue dashed line loop for balancing. If it is performed alternately, the thermal stress of the entire loop will be evenly distributed by the two transformer components, and smaller package or cost devices can also be used in the design, so that a larger balancing current can be achieved in this way.

[0100] The above working modes are only analyses of some charging and discharging circuits of the present invention. The modes and their mutual combinations are not limited to four modes. New combinations of the modes can be further performed according to the discharge requirements, and no further examples will be given here.

[0101] In summary, under the current energy storage BMS active balancing strategy, the present invention can maximize the degree of freedom of balancing, improve the rate, and reduce the loss under the current architecture, and can further reduce the cost, the number of transformers and the MOS withstand voltage when cascading. The technical advantages of the present invention are as follows:

[0102] 1) Adding a degree of freedom switch module and a multi-winding transformer can adapt to more balancing conditions, overcoming the problem that only a single cell can be balanced at a time and the stress of the switch device is large in the traditional active balancing solution; the setting of the degree of freedom switch in the present invention can combine the cells, and the combination of the multi-winding transformer selection switch can charge and discharge the cell group (a combination of multiple cells to be balanced) at the same time, increasing the degree of freedom of choice, and the actual balancing effect will be better than that of a single cell. There will be more balancing time during charging and discharging, and there is no need to balance a cell before balancing the next one. This innovation has a great effect on the improvement of cost, structural power density and balancing.

[0103] 2) Overcome the problem that the transformer volume is large, the power MOS loss is large and the power density cannot be improved in the traditional solution; the present invention adopts two transformers for staggered parallel balancing during the balancing process, which can reduce the stress and loss of a single transformer and its switch tube. At the same time, the above-mentioned inner and outer ring balancing solution can solve the current stress of the battery cell switch module, and adopt the wheel-cut inner and outer ring charging and discharging method to improve the balancing current under the same device parameters, increase the power density and reduce the loss. The above transformer selection switch module and degree of freedom selection switch module can help a certain single battery cell or multiple continuous single battery cells to further improve the balancing current under the same power devices and lines (the balancing current can almost double), but the cost and the like remain almost unchanged (almost no redundant power devices are added, and the device specifications and parameters remain unchanged). The circuit structure and balancing method of inner and outer loops and full-cycle accelerated balancing are also the protection points of the present invention.

[0104] 3) The stress splitting effect of the inter-group devices of the freedom switch module. The current cost, volume, and heat dissipation loss involved in active balancing have become bottlenecks in the development of this technology. Here, the stress splitting concept is proposed. When selecting devices, you can first select them according to the group. At present, the withstand voltage of the entire battery pack reaches about 400V or even higher. If you use this to select devices (the cost, power consumption, and volume are all unacceptable), through the device stress splitting of the freedom switch, you only need to select the freedom switch with a high withstand voltage, and the remaining devices are selected according to the highest voltage in their group. This invention point (making the active balancing board design of the entire battery pack possible) solves the bottleneck that the number of series cells could not be increased due to high-voltage MOS (cost, volume, power consumption, heat dissipation, etc.). It can further reduce the device voltage, reduce the package, and reduce the loss and cost. This design method and idea are also the protection points of the present invention.

[0105] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A BMS active balancing circuit, comprising a plurality of cascaded battery packs, each of which comprises N series-connected single cells, characterized in that: It also includes a control module, a cell switch module, a degree of freedom switch module, a transformer selection switch module, and a multi-winding transformer; Among them, at least two multi-winding transformers are provided, each multi-winding transformer corresponds to a transformer selection switch module, the transformer selection switch module includes a first transformer selection switch group and a second transformer selection switch group, the secondary side of the multi-winding transformer includes M windings, the first transformer selection switch group is respectively connected to one end of the M windings, and the second transformer selection switch group is respectively connected to the other end of the M windings; the first transformer selection switch group and the second transformer selection switch group respectively include M selection switch sub-modules connected in parallel; Wherein, N and M are positive integers greater than 1; Each battery pack corresponds to two degree-of-freedom switch modules. In the battery pack, the positive and negative electrodes of each single cell are connected to the cell switch modules respectively. All cell switch modules connected to the positive electrodes of the single cells are connected to one degree-of-freedom switch module, and all cell switch modules connected to the negative electrodes of the single cells are connected to the other degree-of-freedom switch module. Of the two degree-of-freedom switch modules, one is connected to the first transformer selection switch group, and the other is connected to the second transformer selection switch group. The control module includes an AFE chip and a main control chip, wherein the AFE chip is respectively connected to each single cell to collect the voltage signal of each single cell, and the main control chip is respectively electrically connected to the AFE chip, the cell switch module, the degree of freedom switch module, the transformer selection switch module, and the multi-winding transformer; The cell switch module is used to control the on / off of the charge / discharge circuit of each single cell, the freedom switch module is used to control the on / off of the charge / discharge circuit of each battery pack and to divide the voltage stress caused by charging and discharging between different battery packs, and the transformer selection switch module is used to select different winding circuits connected to the multi-winding transformer, and cooperate with the battery pack to perform intermittent charging and discharging of the inner and outer rings, etc., to construct a variety of charging and discharging combination circuits.

2. The BMS active balancing circuit according to claim 1, characterized in that: The cell switch module is a MOS tube switch group, and the MOS tube switch group includes two MOS tubes connected in reverse series; the degree of freedom switch module is two MOS tubes connected in reverse series or one MOS tube.

3. The BMS active balancing circuit according to claim 1, characterized in that: The selection switch submodule in the first transformer selection switch group is a MOS tube switch group, the first transformer selection switch group includes M parallel MOS tube switch groups, and each of the MOS tube switch groups includes two MOS tubes connected in reverse series; The selection switch submodule in the second transformer selection switch group is a MOS tube, and the second transformer selection switch group includes M MOS tubes connected in parallel.

4. The BMS active balancing circuit according to claim 1, characterized in that: Each single cell corresponds to two cell switch modules, and each battery pack corresponds to 2N cell switch modules, wherein the N cell switch modules connected to the positive pole of the single cell are connected to one degree of freedom switch module, and the N cell switch modules connected to the negative pole of the single cell are connected to another degree of freedom switch module.

5. The BMS active balancing circuit according to claim 1, characterized in that: The multi-winding transformer is provided with multiple; each battery group corresponds to two degree-of-freedom switch modules, one of which is connected to the first transformer selection switch group corresponding to multiple multi-winding transformers, and the other is connected to the second transformer selection switch group corresponding to multiple multi-winding transformers.

6. The BMS active balancing circuit according to claim 1, characterized in that: The multi-winding transformer is connected to an external power supply, and an NMOS tube is connected in series on the side connected to the external power supply.

7. A working method of a BMS active balancing circuit, applied to the BMS active balancing circuit according to any one of claims 1 to 6, comprising the following steps: The AFE chip collects the voltage signal of each single cell in real time to determine whether each single cell has overvoltage or undervoltage and whether it needs to be charged / discharged; When a single cell needs to be charged / discharged, the main control chip controls the two cell switch modules connected to the positive and negative electrodes of the single cell to be turned on first, and then the two degree-of-freedom switch modules corresponding to the battery pack where the single cell is located are turned on; at the same time, a multi-winding transformer is selected, and the winding circuit of the multi-winding transformer to be connected is determined. Based on the winding circuit to be connected, the selection switch submodules to be turned on in the first transformer selection switch group and the second transformer selection switch group are determined, and the first charging / discharging circuit is formed with the winding circuit to be connected, and the single cell is charged / discharged using the first charging / discharging circuit; When multiple adjacent single cells are over-voltage or under-voltage, they need to be charged / discharged, and the multiple single cells are connected in series to form a charge / discharge unit. The main control chip controls the cell switch modules connected to one end of the single cell at the head end of the charge / discharge unit and the other end of the single cell at the end of the charge / discharge unit to be turned on first, and then the corresponding degree of freedom switch module is turned on; at the same time, a multi-winding transformer is selected, and the winding circuit of the multi-winding transformer to be connected is determined. Based on the winding circuit to be connected, the selection switch sub-module to be turned on in the first transformer selection switch group and the second transformer selection switch group is determined, and a second charge / discharge circuit is formed with the winding circuit to be connected, and the charge / discharge unit is charged / discharged using the second charge / discharge circuit.

8. The working method of the BMS active balancing circuit according to claim 7, characterized in that: The working method also includes a mode of balanced charging and discharging of inner and outer rings, and the balanced charging and discharging mode of inner and outer rings includes: The first charge / discharge circuit is an inner ring charge / discharge circuit; When a single cell needs to be charged / discharged, and the first charge / discharge circuit cannot meet the charge / discharge demand of the single cell, the single cell is connected in series with multiple adjacent single cells at both ends to form a charge / discharge unit, and the charge / discharge unit is used to construct an outer ring charge / discharge circuit. The main control chip controls the cell switch module and the degree of freedom switch module connected to the positive electrode of the single cell at the head end of the discharge unit and the negative electrode of the single cell at the end of the charge / discharge unit to be turned on in sequence; at the same time, a winding circuit of another transformer is selected, and based on the winding circuit, the selection switch sub-module to be turned on in the corresponding transformer selection switch group is determined to form an outer ring charge / discharge circuit with the winding circuit; through the control of the main control chip, the inner ring charge / discharge circuit and the outer ring charge / discharge circuit are used to alternately charge / discharge the single cell.

9. The working method of the BMS active balancing circuit according to claim 7, characterized in that: The step of judging whether each single cell needs to be charged / discharged specifically includes: When the voltage of a single cell is greater than a first set threshold, it is determined that the single cell needs to be discharged; When the voltage of a single battery cell is less than a second set threshold, it is determined that the single battery cell needs to be charged.

Images