A BMS active balancing circuit and its working method

Abstract

The present invention relates to the technical field of battery management, and discloses a BMS active balancing circuit and its working method. In this circuit, each multi-winding transformer corresponds to two transformer selection switch groups, which are respectively connected to both ends of the winding; each battery pack corresponds to two degree-of-freedom switch modules; in the battery pack, all cell switch modules connected to the positive electrode of the single cell are connected to one degree-of-freedom switch module, and all cell switch modules connected to the negative electrode of the single cell are connected to another degree-of-freedom switch module; the two degree-of-freedom switch modules are respectively connected to the two transformer selection switch groups in one-to-one correspondence; in the control module, the AFE chip collects the voltage signals of each single cell, and the main control chip controls the on / off of each switch module. The present invention improves functions while reducing costs and technical risks, can realize any combination of adjacent cells, increases the degree of freedom of charge and discharge balancing, reduces the number of transformers, and achieves high cost performance.

Description

Technical Field

[0001] The present invention relates to the technical field of battery management, and particularly to a BMS active equalization circuit and its working method. Background Art

[0002] A 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 prevent overcharging, over-discharging, short-circuiting, etc. through set safety thresholds. Due to manufacturing differences or different working conditions, there may be a problem of inconsistent capacity between individual battery cells. The BMS adjusts the status between battery cells through active or passive equalization techniques to maintain the consistency of overall performance. Among them, the active equalization technique actively equalizes the voltage differences caused by the individual capacity and self-discharge rate generated during the use of the battery. Its main function is to actively equalize the differences between battery monomers during the charging, discharging, or placement process of the battery pack, so as to eliminate various inconsistencies generated due to itself and during the use process after the battery is grouped.

[0003] Currently, the BMS active equalization technical solutions are not yet mature. For example, inductive active equalization is not easy to integrate in large quantities, and there is a situation of repeated charging and discharging of the battery. Capacitive active equalization cannot effectively control the equalization current, is not easy to control, and has a relatively high circuit risk. The existing active equalization circuit technology is not comprehensive enough. It only solves the problem of repeated charging and discharging of the battery and only controls the equalization current. It lacks the ability to equalize multiple battery cells in the same group simultaneously, and has weak working condition adaptability. There is transformer isolation between different groups, and it is impossible to bundle and equalize adjacent battery cells simultaneously, so the equalization freedom is weak. The equalization ability is limited, and it is difficult to greatly optimize the equalization current and speed under the current switching devices. The cost is relatively high and the cost performance is low. Repeated use of isolation transformers further increases the cost and volume.

[0004] Currently, the relatively reliable active equalization technical solution is to transfer the equalization energy to the bus or an independent unit, which serves as an intermediate energy storage link for energy redistribution. However, this solution also has the following disadvantages: (1) The transformers and multiple switching tubes involved increase the cost and volume of the equalization circuit significantly, and a series of problems such as the freedom of simultaneous equalization of multiple battery cells cannot be taken into account, and its components do not have a cost advantage either; (2) When sharing a transformer for the smallest unit, if two of the smallest units (such as 4 groups of battery cells) need to be equalized simultaneously, it cannot meet the requirements and can only be equalized step by step, with a slow equalization rate. When there are many abnormalities within the group, it cannot be taken into account, thus causing a relatively large equalization pressure on a single branch, posing a major challenge to cost and structure. Therefore, how to provide a high-cost-performance active equalization circuit for the problems of high cost, difficulty in improving power density, and low equalization efficiency encountered in the current BMS active equalization technology has become a technical problem that needs to be solved urgently by those skilled in the art. Summary of the Invention

[0005] The purpose of the present invention is to provide a BMS active equalization circuit and its working method. By dividing the equalization circuit, while improving the function, the cost, technical risks and pressure are reduced, and any combination between adjacent battery cells can be realized, increasing the freedom of charge and discharge equalization, reducing the number of transformers, improving the utilization rate, and achieving high cost performance.

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

[0007] A BMS active equalization circuit includes several cascaded battery packs. Each battery pack includes N series-connected single battery cells, and also includes a control module, a battery cell switch module, a freedom switch module, a transformer selection switch module, and a multi-winding transformer;

[0008] Each battery pack includes N series-connected single battery cells, characterized in that it also includes a control module, a battery cell switch module, a freedom switch module, a transformer selection switch module, and a multi-winding transformer;

[0009] Among them, at least 2 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 parallel selection switch sub-modules;

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

[0011] Each battery pack corresponds to two degrees of freedom switch modules. In the battery pack, the positive and negative electrodes of each single cell are respectively connected to the cell switch module. All the cell switch modules connected to the positive electrode of the single cell are connected to one degree of freedom switch module, and all the cell switch modules connected to the negative electrode of the single cell are connected to another degree of freedom switch module. Among the two degrees 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. The AFE chip is respectively connected to each single cell and is used to collect the voltage signal of each single cell. 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 form a new discharge combination, etc. The degree of 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 constructing different charge / discharge circuits, etc. The transformer selection switch module is used to select different winding circuits connected to the multi-winding transformer, and cooperate to perform intermittent charge / discharge such as inner and outer loops to reduce the thermal stress of devices, etc., and can provide multiple discharge combination circuits, making high cost performance possible.

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

[0015] Further, the selection switch sub-module in the first transformer selection switch group is a MOS transistor switch group. The first transformer selection switch group includes M parallel MOS transistor switch groups, and each MOS transistor switch group includes two MOS transistors connected in reverse series;

[0016] The selection switch sub-module in the second transformer selection switch group is a MOS transistor, and the second transformer selection switch group includes M parallel MOS transistors.

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

[0018] Further, the number of the multi-winding transformers is less than that of the battery packs; there are multiple multi-winding transformers; for each battery pack, two degrees-of-freedom switch modules, one of which is connected to the first transformer selection switch group corresponding to the multiple multi-winding transformers, and the other is connected to the second transformer selection switch group corresponding to the multiple multi-winding transformers.

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

[0020] Further, both the cell switch module and the transformer selection switch module can be selected according to the voltage level within the group, and low-voltage MOS is selected (for example, if four cells are in a group, the MOS withstand voltage is 20-30V. This type of selection has low cost, high efficiency, small size, and many specifications, etc.).

[0021] The present invention also provides a working method for the BMS active equalization circuit, which is applied to the above BMS active equalization circuit, and includes the following steps:

[0022] The voltage signals of each single cell are collected in real time through the AFE chip to judge whether there is over-voltage or under-voltage in each single cell and whether charging / discharging is required.

[0023] When a certain 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 conduct first, and then the two degrees-of-freedom switch modules corresponding to the battery pack where the single cell is located conduct; at the same time, a multi-winding transformer is selected, the winding circuit of the multi-winding transformer to be connected is determined, and based on the winding circuit to be connected, the selection switch sub-modules to be conducted in the first transformer selection switch group and the second transformer selection switch group are determined, and a first charging / discharging circuit is formed with the winding circuit to be connected, and the single cell is charged / discharged by using the first charging / discharging circuit.

[0024] When multiple adjacent single cells are over-voltage or under-voltage, they need to be charged / discharged. 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 modules 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 sub-modules to be turned on in the first transformer selection switch group and the second transformer selection switch group are determined to form a second charge / discharge circuit 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 (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 the inner and outer rings, and the balanced charging and discharging mode of the inner and outer rings 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 requirements 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. The charge / discharge unit is used to construct an outer-loop 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, the winding circuit of another transformer is selected. 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-loop charge / discharge circuit with the winding circuit. Under the control of the main control chip, the single cell is alternately charged / discharged using the inner-loop charge / discharge circuit and the outer-loop charge / discharge circuit. This can reduce the stress of the cell switch group and the transformer group, and reduce the stress and heat loss of single-loop components. Under the same device specifications, this method can increase the balancing current. The devices involved are almost the same as the traditional mode, but the balancing current is nearly doubled.

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

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

[0030] When the voltage of a single battery cell is less than the second set threshold (for example, several times the average voltage of all single battery cells, set according to the maximum allowable under-voltage error of the battery pack that the designer can actually accept), it is determined that the single battery cell needs to be charged.

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

[0032] The BMS active balancing circuit provided by the present invention includes several cascaded battery packs, each of the battery packs includes N serially connected single battery cells, and further 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 through the cooperation of multiple switch modules, diversified control functions are realized.

[0033] Based on each battery pack, the present invention removes some transformers, adds a degree-of-freedom switch module and a transformer (multi-winding transformer) selection switch, increases the degree of freedom of balancing, the balancing efficiency, reduces the number of devices, saves costs, and reduces the structure. For different numbers of battery packs, different numbers of winding transformers can be selected according to requirements, improving the applicability and expandability of the circuit. Energy storage and redistribution can be completed at the primary side of the transformer (corresponding to the charge and discharge circuit).

[0034] The present invention adopts a multi-winding transformer, which can select different winding circuits according to needs to meet the balancing of different numbers of single battery cells. To increase the degree of freedom and save costs, while reducing the transformer, a degree-of-freedom switch module is added to the active balancing circuit. 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 has little sensitivity to costs, etc.), the voltage correlation (decoupling) of the entire balancing circuit is segmented, so that the withstand voltage of the battery cell balancing MOS switch is designed according to the in-group balancing, further reducing the voltage stress of the device, facilitating component selection, reducing losses, and saving costs (because as the MOS process withstand voltage increases, the on-resistance will increase in positive correlation).

[0035] The present invention sets multiple multi-winding transformers, for example, two multi-winding transformers, which can perform energy conversion in a staggered parallel form. Whether it is for a single battery cell or multiple battery packs for balancing, the staggered parallel form can be adopted to alternately transfer energy between the two multi-winding transformers, reducing the thermal stress of the transformer and the circuit, improving the overall balancing efficiency of the machine, and reducing losses.

[0036] While improving the functions, the present invention reduces costs and technical risks. Under the condition that the device specification parameters are certain, through internal and external loop discharges, degree-of-freedom combinations, etc., any combination of adjacent battery cells can be realized, increasing the degree of freedom of charge and discharge balancing, reducing heat loss, increasing efficiency, improving power density, and achieving high cost performance.

[0037] In summary, the present invention provides a BMS active equalization circuit with high cost performance. By dividing the equalization circuit, it has more functions while further reducing costs, technical risks and pressures. At the same time, it also allows the adjacent battery cells of each battery pack to be combined and stacked arbitrarily, increasing the freedom of charge and discharge equalization. It can also reduce the number of transformers. By switching between battery packs, the transformers are utilized to the maximum extent, reducing costs and volume and improving cost performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0039] FIG. 1 is a hardware topology diagram of the BMS active equalization circuit according to an embodiment of the present invention. Among them, (a) is a schematic diagram of the overall circuit, (b) is a connection structure diagram of the battery pack, the battery cell switch module, and the freedom switch module; (c) is a connection structure diagram of the transformer selection switch module and the multi-winding transformer;

[0040] Figure 2 is an interaction diagram of the BMS active equalization circuit of the present invention with the AFE voltage sampling and the auxiliary power supply externally supplied by the main control chip;

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

[0042] Figure 4 is a schematic diagram of working mode 2 of the BMS active equalization circuit according to an embodiment of the present invention;

[0043] Figure 5 is a schematic diagram of working mode 3 of the BMS active equalization circuit according to an embodiment of the present invention;

[0044] Figure 6 is a schematic diagram of working mode 4 of the BMS active equalization circuit according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0045] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0046] The object of the present invention is to provide a BMS active equalization circuit and its working method, which solve the problems existing in the current BMS active equalization circuit, such as low equalization freedom, slow equalization speed, low efficiency, the contradiction between capacity expansion and cost restricted by device specifications, a large number of transformers, high cost and large volume, aiming to improve an active equalization circuit with high cost performance.

[0047] In order to make the above objects, features and advantages of the present invention more obvious and understandable, the present invention will be 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 equalization circuit provided by the present invention includes: a number of cascaded battery packs, each battery pack includes N series-connected single cells, and further includes a control module, a cell switch module, a freedom switch module, a transformer selection switch module and a multi-winding transformer;

[0049] Each battery pack includes N series-connected single cells, characterized in that it further includes a control module, a cell switch module, a 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 parallel selection switch sub-modules;

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

[0052] Each battery pack corresponds to two freedom switch modules. In the battery pack, the positive and negative electrodes of each single cell are respectively connected to the cell switch module. All the cell switch modules connected to the positive electrode of the single cell are connected to one freedom switch module, and all the cell switch modules connected to the negative electrode of the single cell are connected to another freedom switch module; among the two 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. The AFE chip is respectively connected to each single cell for collecting the voltage signal of each single cell. The main control chip is respectively electrically connected to the AFE chip, the cell switch module, the 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 charging / discharging circuit of each single cell and form new discharge combinations, etc.; the degree-of-freedom switch module is used to control the on / off of the charging / discharging circuit of each battery pack, divide the voltage stress caused by charging and discharging between different battery packs, and participate in constructing different charging and discharging circuits, etc.; the transformer selection switch module is used to select different winding circuits of the multi-winding transformer, and cooperate to perform intermittent charging and discharging such as inner and outer loops to reduce the thermal stress of devices, etc., and can provide multiple discharge combination circuits, making high cost performance possible.

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

[0056] In the first transformer selection switch group, the selection switch sub-module is a MOS transistor switch group, and the first transformer selection switch group includes M parallel MOS transistor switch groups, that is, the number of MOS transistor switch groups is determined according to the number of transformer windings, and each MOS transistor switch group includes two MOS transistors connected in reverse series;

[0057] In the second transformer selection switch group, the selection switch sub-module is a MOS transistor, and the second transformer selection switch group includes M parallel MOS transistors, that is, the number of MOS transistors is determined according to the number of transformer windings.

[0058] For the multi-winding transformer, its winding can be selected according to the actual sampled voltage; there are multiple multi-winding transformers; for the two degree-of-freedom switch modules corresponding to each battery pack, one 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. Taking battery pack 1 as an example: the degree-of-freedom switch module Z1 is connected to the first transformer selection switch groups (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 ends of the selection switch groups of the second transformers 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 transistor is connected in series on the side connected to the external power supply. As Figure 2 shown, the external power supply is responsible for the energy transfer for charging and discharging the single cells.

[0060] The master control chip adjusts and calculates the voltage signals sampled by the AFE chip according to the circuit topology and operating mode, identifies overcharged and discharged battery cells, and determines the discharge mode to be adopted; it issues corresponding drive signals to turn on and off the battery cell switch module, degree of freedom switch module, transformer selection switch group, etc. for charging and discharging; the remaining auxiliary circuits, etc. are used to build the corresponding circuits. The AFE chip detects the voltage of each individual battery cell to detect the voltage of each individual battery cell.

[0061] For both the battery cell switch module and the transformer selection switch module, low-voltage MOSs that meet the voltage level within the group can be selected. Such MOSs have advantages such as low cost, low conduction loss, and high efficiency.

[0062] The voltage withstand parameters of the battery cell switch module and the transformer selection switch module are basically the same, and they can be selected according to the voltage level within the battery cell group (for example, if there are 4 battery cells in a group, the selection within 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 with three battery packs and two multi-winding transformers. Each battery pack includes 4 series-connected individual battery cells, that is, a total of 12 individual battery cells are included in this embodiment, 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 respectively. In this embodiment, Z1 - Z5 use two reversely connected series MOS tubes, and Z6 uses a single MOS tube. Since the battery pack corresponding to Z6 is the one with the lowest voltage level in the series battery packs, the potential of the loop where Z6 is located is the lowest. Therefore, a single MOS tube can also complete the functions of voltage stress division and degree of freedom adjustment here. In actual design, it can be selected according to its own needs, or two reversely connected series MOS tubes can also be used.

[0065] In this embodiment, two identical multi-winding transformers T1 and T2 are adopted. 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, and each MOS transistor switch group includes two MOS transistors connected in reverse series. The second transformer selection switch group includes two parallel MOS transistors; in multi-winding transformer T1, the first transformer selection switch group is TO1 and TO2, TS1 and TS2 respectively, and the second transformer selection switch group includes two parallel MOS transistors, namely TO3 and TS3; in multi-winding transformer T2, the first transformer selection switch group is T2O1 and T2O2, T2S1 and T2S2 respectively, and the second transformer selection switch group includes two parallel MOS transistors, namely T2O3 and T2S3.

[0066] A MOS transistor MOS121 is connected in series to the primary side of multi-winding transformer T1, and a MOS transistor MOS122 is connected in series to the primary side of multi-winding transformer T2. All the MOS transistors in the embodiments of the present invention adopt NMOS transistors.

[0067] In the embodiments of the present invention, by removing some transformers on the basis of each group of battery cells, adding freedom switches (Z1, Z2, Z3, Z4, Z5, Z6) and transformer (multi-winding transformer) selection switches (TO1 - TO3, TS1 - TS3), the equalization freedom and efficiency are increased, the number of devices is reduced, the cost is saved, and the structure is reduced. Only three groups of cascades are shown in this embodiment. However, according to this topology scheme, only switches need to be added to the positive and negative ends of the multi-winding transformer isolation circuit and then connected to the multi-winding transformer. The number of groups can be continuously increased according to design requirements, not limited to three levels or more. An energy storage unit is used to complete the storage and redistribution of energy on the primary side (corresponding to the charge and discharge circuit) of the multi-winding transformer. The actual circuit can perform the superposition of the cascade levels according to requirements.

[0068] As shown in Figure 1 - Figure 2As shown, this embodiment also incorporates a multi-winding transformer. Considering that if one or more individual cells experience significant imbalance, their charge and discharge rates need to be accelerated to avoid compromising overall system efficiency, two winding transformers can be used to simultaneously transfer energy to these individual cells at a 50% duty cycle (by staggering the conduction of transformers T1 and T2 to accelerate balancing). This method further improves the effective value of the balancing current and accelerates balancing, while transformer parameters are designed for low currents. This saves space and cost, and can double the balancing current for equivalent device specifications. This can also be compared to the outer and inner loops in a control loop. If, due to current device specifications, the MOS tube's inherent heat dissipation is limited, making continuous balancing of a single cell at high current impossible, T1 can be used to directly balance the maximum current, while T2 selects a continuous cell group consisting of adjacent cells for low-current outer-loop balancing. This results in better balancing, faster balancing, and reduced power device selection pressure, cost, and structural layout.

[0069] For example, if the voltage of bat4 cell differs significantly from that of the other cells, the balancing current required is high, and the balancing rate needs to be accelerated, then on the one hand, it can continuously switch the windings of the T1 and T2 transformers at a 50% duty cycle to alternately conduct charge and discharge, and adopt a full-cycle balancing method 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. Both T1 and T2 can be designed according to the smaller current requirement, 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 circuit, the inner and outer loop balancing method can be used: for example, bat4 can be placed in the combined circuit of bat5-bat3 (or the remaining circuit including bat4 can be selected according to the design requirements of the multi-winding transformer), and the charging and discharging principle of this circuit can be reduced (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 under extreme working conditions.

[0070] The reason 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 of internal and external rings). 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 and 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: To increase degrees of freedom and save costs, while reducing the transformer, a degrees-of-freedom switch module is added to the active equalization circuit. The advantages of the degrees-of-freedom switch module are analyzed as follows: As shown in Figure 1, there are three different specifications of switches in this topology. The voltage withstand and other parameters of the transformer selection switch module are basically the same as those of the cell switch module, and they can be selected according to the voltage within the cell group. (If 4 cells are used in a group and the maximum voltage of a single cell is 3.6V, selecting around 20 - 30V basically meets the requirements. The most severe working condition is that bat4 is charged and discharged, and there is a voltage difference of three cells between it and bat1. The switching tube must meet this voltage withstand (switching spikes will also be superimposed, with a margin). Without the degrees-of-freedom switch, after cascading 3 groups, the potential difference between the BAT12 cell and cell 1 in the third group will be extremely large, 3 - 4 times that within the group, causing difficulties in switch selection and imposing great pressure on costs and structure. Additionally, as the MOS voltage withstand increases, its on-resistance will also increase rapidly, resulting in key issues such as increased loss and heat dissipation, posing an even greater challenge to the design of BMS active equalization products. Therefore, the degrees-of-freedom switch is introduced here, which can not only adjust the degrees of freedom but also serve as the effect of separating the device pressure between groups. For example Figure 3 As shown: Due to the existence of the degrees-of-freedom switch modules Z1 - Z6, with the increase in cascading, by increasing the voltage withstand of the degrees-of-freedom switches (the number of degrees-of-freedom switch modules is small, and the sensitivity to cost and other factors is not significant when selecting a higher voltage withstand), the voltage correlation of the entire equalization circuit can be segmented (decoupled), enabling the MOS tube switches for cell-to-cell equalization to be designed according to the within-group equalization, further reducing the device voltage stress, facilitating selection, reducing losses, and saving costs.

[0072] Embodiment 2:

[0073] Here, only a simple comparison of power devices is made to illustrate the advantages of this invention: Taking 4 battery groups as an example and evaluating it as a BMS unit, the number of cell switch modules used in the current traditional array switch-type BMS active equalization circuit is the same as that of the current invention; the degrees-of-freedom switches added in this invention are redundant devices, and their relationship with the cell group is a 2-fold relationship; Number of transformers: The number of transformers in this invention is temporarily evaluated in the same way as the traditional number. Generally speaking, the cost only increases by the degrees-of-freedom switches and the transformer multiplexer switch.

[0074] The overall evaluation shows that the quantity during this period is far less than twice that of traditional devices in terms of quantity. If evaluated according to the topology of the current 3 groups of battery cells, a total of about 20 additional degree-of-freedom switches and selection switches are added (12 for 6 groups of degrees of freedom, 12 for two groups of transformer selection switches, but traditional transformers also have selection switches, and the approximate difference is about 20 power tubes). However, the total number of power tubes in the entire traditional circuit is 4×4×3 (array switches) + 4 (transformer switches) = 48 + 4 = 52. All in all, the number of power tubes increases by less than 0.4 times that of the previous ones. Additionally, if the cascaded number of battery cell groups in the present invention is larger, the proportion of increased devices will be further reduced.

[0075] The control loop is not mentioned here, but the basic components such as AFE and main control mentioned before are all included. There is no significant increase in devices, so the cost will not vary much. However, during circuit design, the interleaved discharge, inner and outer loop discharge, and device stress segmentation included in the present invention are all convenient for structure and layout. At the same time, with the same device specifications, the present invention can almost double the equalization current, and the battery cells can be freely combined for simultaneous discharge, etc., further improving the power density. Its overall cost performance is much higher than the traditional method.

[0076] Therefore, in summary, while solving the problems of low equalization efficiency, large volume, high cost, slow equalization rate, etc. of current battery cells, the present invention effectively controls the cost and has great advantages in terms of practicality.

[0077] Function comparison with traditional equalization:

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

[0079] The transformer winding is optional, making synchronous equalization of multiple battery cells possible. Only by processing the sampled voltage signal inside the software and switching the corresponding switches, the equalization current can be doubled with very little increase in hardware cost, increasing the equalization efficiency and achieving a fast equalization effect.

[0080] The device stress can be reduced. The current active equalization technology of energy storage BMS has gradually increased from 2 - 3A to 5A, and 10A, etc. are under research. However, the composition of a product involves various aspects. The increase in the power current level will inevitably cause a series of problems such as the increase in the volume of devices and current-carrying capacity, resulting in a rapid increase in cost and volume. But in the present invention, this problem can be effectively avoided. For example, a power transistor of 2 - 3A is used for module equalization. When there are particularly large differences among adjacent or one or more battery cells that need to be equalized quickly, a continuous equalization method can be adopted to equalize multiple battery cells simultaneously, or the maximum current can be used for individual equalization in the inner loop. According to the surrounding sampling results, the abnormal battery cell is placed in a group composed of continuous battery cells in a certain outer loop, and then outer loop equalization is performed on this group (at this time, the equalization current can be appropriately reduced by 1 - 2A). At this time, the current no longer flows through the original path and is equalized in the new loop. Through this method, an equalization ability of 4 - 5A can also be satisfied, but the power device continues to be selected as 2 - 3A, suppressing the contradiction between performance and cost.

[0081] It can be cascaded continuously without increasing the voltage withstand of the battery cell array switch (the increase in the voltage withstand of this device causes an increase in cost, volume, and low efficiency), which is convenient for multi-stage cascading and integrated design, making the MOS voltage withstand selection no longer a key bottleneck, providing a technical direction for active equalization of multiple battery cells.

[0082] Based on the above analysis, the technical effects described in the present invention have all been demonstrated through practice. The present invention can solve the contradiction among cost, structure, and equalization efficiency encountered in the traditional BMS active equalization scheme, increasing the equalization ability on the basis of the original cost device structure, and can be used as a high-cost-performance BMS active equalization scheme to achieve battery cell equalization.

[0083] On the other hand, the present invention also provides a working method for a BMS active equalization circuit, which is applied to the above-mentioned BMS active equalization circuit and includes the following steps:

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

[0085] Working mode 1:

[0086] When a certain single-cell battery 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 battery to conduct first, and then the two-degree-of-freedom switch modules corresponding to the battery pack where the single-cell battery is located conduct; at the same time, a multi-winding transformer is selected, and the winding circuit of the multi-winding transformer to be connected is determined (currently it is tentatively assumed that the upper winding in the transformer topology diagram corresponds to a single single-cell battery, and the lower winding corresponds to the charge and discharge of the cell group). Based on the winding circuit to be connected, the switch sub-modules to be conducted in the first transformer selection switch group and the second transformer selection switch group are determined, and a first charge / discharge circuit is formed with the winding circuit to be connected, and the single-cell battery is charged / discharged using the first charge / discharge circuit.

[0087] Exemplarily, as Figure 3 shown, for example, if the voltage of bat1 is the highest among the series-connected cells at this time (greater than the first set threshold), then it needs to be charged and discharged: First, open the cell switch module connected to bat1. Secondly, open the degree-of-freedom switches Z1 and Z2 corresponding to the battery pack where the single-cell battery is located. Then, select T1 or T2 and open the switch sub-modules in the corresponding transformer winding selection switch group. Here, the upper winding is selected (it has been defined that the upper winding corresponds to the charge and discharge operation of a single single-cell battery). If it is assumed that the selected transformer is T1, that is, open TO1 and TO2, and TO3 enters the PWM mode for balancing. Its circuit is as Figure 3 shown by the black dotted line circuit, and the turn-off order will be the reverse order of the turn-on switch order. At the same time, as Figure 3 shown: If bat6, bat7, and bat8 also have charging and discharging requirements when charging and discharging the single cell of bat1, then the charging and discharging will be carried out according to the Figure 3 blue dotted line circuit in. The two charging and discharging circuits are combined intermittently in an interleaved turn-on manner (after the bat1 discharge circuit is turned on for a period of time, stop discharging the cell groups of bat6, bat7, and bat8). It can be found that when the blue dotted line circuit is turned on and running, the terminal voltage of bat6 will raise the potential on the right side of the degree-of-freedom switch Z1 to the same potential as the terminal voltage of bat6. At this time, with the division of the degree-of-freedom switch module Z1, the potential difference between the two can be blocked by the degree-of-freedom switch module. Without the degree-of-freedom switch module, its potential difference is already greater than the maximum potential difference in the battery pack (if more are cascaded, the potential difference is even greater, which will inevitably cause an increase in structure and cost and bring pressure to product design). Therefore, the idea of dividing the device stress and discharging alternately step by step can be adopted.

[0088] Operating mode two:

[0089] When multiple adjacent single cells all need to be charged / discharged (if there are single cells that do not need to be charged or discharged among multiple single cells), multiple single cells can be connected in series to form a charge / discharge unit. The main control chip controls the cell switch module and the degree-of-freedom switch module connected to one end (positive electrode) of the single cell at the head end of the discharge unit and the other end (negative electrode) of the single cell at the end of the charge / discharge unit to conduct; at the same time, select a multi-winding transformer, determine the winding circuit of the multi-winding transformer to be connected, and based on the winding circuit to be connected, determine the switches to be conducted in the first transformer selection switch group and the second transformer selection switch group, and form a second charge / discharge circuit with the winding circuit to be connected, and use the second charge / discharge circuit to charge / discharge the charge / discharge unit; wherein, the first transformer selection switch group corresponds to one end of the degree-of-freedom switch at the head end of the discharge unit, and the second transformer selection switch group corresponds to one end of the degree-of-freedom switch of the single cell at the end of the discharge unit.

[0090] Exemplarily, continue to take Figure 4 as an example for further illustration. If among bat4, bat5, bat6, and bat7, the voltage of bat6 is normal and does not require balancing, while the voltages of the other 3 are significantly overcharged or over-discharged and require balancing, then continue to perform balanced charge and discharge first according to Figure 4 shown (blue dotted line). The switch opening and method are the same as those of a normal multi-cell group. As the single cells are charged and discharged for a long time, when the voltages of bat4, bat5, and bat7 are gradually balanced, the voltage of bat6 will surely become abnormal. Then consider preferentially balancing the abnormal cell group, and at the same time, alternately add the inner loop to adjust the voltage of bat6 during balancing and perform according to this current loop (black dotted line). This can achieve fast balancing and has a shorter and more efficient single balancing loop compared to it. On the contrary, if bat4, bat5, and bat7 are balanced separately, it will surely result in a long balancing time, an increased loop, and a worse efficiency and rate. Similarly, if there are other situations as Figure 4 shown: such as when the AFE chip samples the voltages of the series-connected cells and after being processed by the main control chip, the voltages of bat4, bat5, bat6, and bat7 are all too high (voltage > the first set threshold). If a single discharge is performed at this time, it is very easy to cause the cells to discharge untimely and the single cells to be overvoltage, and stop charging. When it is found through screening that the voltages of adjacent cells are all high, the main control chip first controls the discharge unit (because there are continuously uneven voltage cells, and they are formed 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 degree-of-freedom switch module; determines the voltage and continues to select the winding circuit of the multi-winding transformer (this time Figure 3The selected example is transformer T1. If T2 is selected, the method is the same. The TS1, TS2, and TS3 of the multi-winding transformer can be driven by the main control chip to generate PWM waves, control the discharge, and continue to sample and monitor its voltage (the sampling duration can be set by oneself) until the voltage balance requirement is met. (During this process, if bat4 is the first to balance and return to the normal voltage, the switches on the transformer side are gradually turned off to the cell side, and then the voltages of others are detected to re-plan the balance group for real-time detection, which can be carried out crosswise with the first case), enriching the charging and discharging conditions, increasing the charging and discharging combinations, and adapting to more working conditions.

[0091] Working mode three:

[0092] The working method further includes an internal and external loop balance charging and discharging mode, and the internal and external loop balance charging and discharging mode includes:

[0093] The first charging / discharging loop is the internal loop charging / discharging loop;

[0094] When a certain single cell needs to be charged / discharged and the first charging / discharging loop cannot meet the charging / discharging requirements of this single cell, this single cell is connected in series with multiple adjacent single cells at its two ends to form a charging / discharging unit, and this charging / discharging unit is used to construct the external loop charging / discharging loop. 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 charging / discharging unit to conduct successively; at the same time, select the winding loop of another transformer, and based on this winding loop, determine the switch sub-module to be conducted in the corresponding transformer selection switch group, and form the external loop charging / discharging loop with this winding loop; through the control of the main control chip, the single cell is alternately charged and discharged by using the internal loop charging / discharging loop and the external loop charging / discharging loop, which can reduce the stress of the cell switch group and the transformer group, reduce the stress and heat loss of the devices in a single loop, etc. Under the same device specifications, the balance current can be increased in this way, and the involved devices are almost the same as those in the traditional mode, but the balance current is nearly doubled.

[0095] Exemplarily, when the current single cell has a high voltage, for example, during the charging of the voltage of bat6, according to the current active balance selection device of 5A, overvoltage discharge cannot meet the requirements, and it continues to be greater than the first set threshold or even larger. At this time, the entire power loop cannot perform a larger current balance, and the internal and external loop balance charging and discharging mode can be adopted:

[0096] AFE sampling and the main control chip calculate that bat6 is overvoltage. First, wave is sent in sequence to gradually turn on the cell switch module, degree-of-freedom switch module, transformer selection switch, etc. The temperature sampling signal feeds back to the main control chip that the discharge circuit is overheated and the core cannot further increase the discharge current (limited by power device parameters, etc.). However, if the cell balance abnormality is not resolved, the internal and external loop balance charge and discharge mode and the alternating discharge mode are adopted. For example, 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 protection, the switches are turned off in sequence (gradually turned off 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 that of a single cell discharge). The circuit is Figure 5 the blue dotted line circuit shown. (It can be found that except for some circuits of the transformer, the two key charge and discharge circuit devices of the two charge and discharge key circuits are basically not reused and overlapped, and the risk of its thermal runaway will inevitably be reduced. This can, under the same package and specification, judge the risk of overcharge and over-discharge through control and sampling (AFE and main control chip, etc.) calculation and processing, control the transformer winding switching and the conduction of the degree-of-freedom switch, etc., so that under the condition that the device package specification (the device package specification, etc. determines the product volume and cost) remains unchanged, the discharge circuit can be utilized more fully, so that the entire cell group is quickly balanced, and the balance current and power density are improved. In addition, if there is still a long-term charge and discharge thermal risk in the transformer circuit before and after discharge, the function of alternating charge and discharge of multiple multi-winding transformers can be adopted, and the black solid line path in the figure is used for charge and discharge, which can also reduce the transformer selection pressure and save costs.)

[0097] Working mode four:

[0098] Combining the above working mode three and working mode two, if the voltage difference between multiple adjacent cells is too large and it is restricted by the thermal risk of power devices and cannot be further balanced, two sets of different winding circuits of the high voltage of the multi-winding transformer can be used to simultaneously adopt the alternating conduction method to quickly discharge multiple groups of cells. Under the condition of certain device parameters, the device parameters can be utilized to the maximum extent to improve the balance effect and power density, etc.

[0099] Working mode description: As Figure 5 shown: If multiple single cells need to be balanced simultaneously (the cell group composed of bat4, bat5, bat6, and bat7), at this time, according to the sampling result and the control of the main control chip, first open the upper cell switch module of bat4 and the lower cell switch module of bat7, and then open the degree-of-freedom switch modules Z1 and Z4 according to the circuit selection; since this is the balance of the cell group (the upper winding of the transformer in the figure is the balance winding of a single cell, and the lower winding is the balance winding of the cell group), the selection switches TS1 and TS2 of the multi-winding transformer T1 are controlled to be opened, and then the flyback energy transfer is carried out - this process is the normal balance process, as Figure 5The energy flow represented by the black dashed line in (the flow direction arrows are not marked because the circuit is consistent. If the battery cell discharges, the current flows from the battery cell to the transformer, and vice versa for charging). In the actual working process, if the overcharging and over-discharging conditions of the battery cell are severe and the current requirements of the power transformer and its power transistor specifications cannot meet the current demand, it is necessary to continue to increase the balancing current to accelerate the balancing; then consider using the interleaved method at this time; in a certain number of cycles (the time can be adjusted by oneself), the switches are sequentially turned on for balancing according to the charging and discharging paths of the black dashed line in the figure, and then turned off, and the balancing is carried out using the blue dashed line circuit. By alternating in this way, the thermal stress of the entire circuit will be evenly shared by the two transformer components, and devices with smaller packages or costs can also be used in the design. In this way, a larger balancing current can be achieved.

[0100] The above working modes are only the analysis of some charging and discharging circuits of the present invention. The combinations between and among the modes are not limited to 4 modes, and new combinations between the modes can be further carried out according to the discharge requirements. No further examples will be given here.

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

[0102] 1) By adding a freedom switch module and a multi-winding transformer, it can adapt to more balancing working conditions and overcome the problems in traditional active balancing schemes that only one battery cell can be balanced at a time and the stress on the switching devices is large; in the present invention, the setting of the freedom switch can combine the battery cells, and the selection switch combined with the multi-winding transformer can combine the battery cell groups (combinations of multiple battery cells to be balanced) to charge and discharge simultaneously, increasing the selection freedom. Compared with the charging and discharging of a single battery cell, the actual balancing effect will be better, and there will be more balancing time during charging and discharging, and it is not necessary to wait for a certain battery cell to complete the balancing before balancing the next one. This innovation point has a great effect on the improvement of cost, structural power density and balancing.

[0103] 2) Overcome the problems in the traditional solution, such as large transformer volume, high power MOS loss, and inability to improve power density. In the balancing process of the present invention, two transformers are used for interleaved parallel balancing, which can reduce the stress and loss of a single transformer and its switching tubes. At the same time, the above-mentioned inner and outer ring balancing solutions can solve the current stress of the cell switching module. By adopting the way of alternately switching the inner and outer rings for charging and discharging under the same device parameters, the balancing current can be increased, the power density can be increased, and the loss can be reduced. The above transformer selection switching module and the degree-of-freedom selection switching module can help a single cell or multiple consecutive cells to further increase the balancing current (the balancing current can almost be doubled) under the same power devices and circuits, but the cost etc. remains almost unchanged (almost no additional power devices are added and the device specification parameters remain unchanged). The circuit structure and balancing method adopting the inner and outer rings and full-cycle accelerated balancing are also the protection points of the present invention.

[0104] 3) The role of stress segmentation of devices between groups in the degree-of-freedom switching module. Currently, the cost, volume, heat dissipation loss, etc. involved in active balancing have become bottlenecks in the development of this technology. Here, the concept of stress segmentation is proposed. When selecting devices, they can be selected according to the group first. Currently, the withstand voltage of the entire battery pack reaches about 400V or even higher. If device selection is carried out based on this (its cost, power consumption, and volume are unacceptable), through the stress segmentation of devices of the degree-of-freedom switch, only the degree-of-freedom switch needs to be selected with high withstand voltage, and the remaining devices are selected according to the highest voltage within their respective groups. This invention point (making it possible to design the active balancing board of the entire battery pack) solves the bottleneck that the number of series-connected cells could not be increased due to high-voltage MOS (cost, volume, power consumption, heat dissipation, etc.) before. 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] In this article, specific examples are used to elaborate on the principle and implementation mode of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention. At the same time, for those of ordinary skill in the art, based on the idea of the present invention, there will be changes in the specific implementation mode and application scope. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. A working method of a BMS active equalization circuit, the BMS active equalization circuit comprising a plurality of cascaded battery packs, each of the battery packs comprising N series-connected single cells, characterized in that, The BMS active equalization circuit further 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, and 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 parallel selection switch sub-modules; Among them, 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 respectively connected to the cell switch module. All the cell switch modules connected to the positive electrode of the single cell are connected to one degree-of-freedom switch module, and all the cell switch modules connected to the negative electrode of the single cell are connected to another degree-of-freedom switch module; among 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. The AFE chip is respectively connected to each single cell for collecting the voltage signal of each single cell. 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 degree-of-freedom switch module is used to control the on / off of the charge / discharge circuit of each battery pack and divide the voltage stress caused by charging and discharging between different battery packs. 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 charge and discharge in the inner and outer loops to construct various charge / discharge combination circuits; The working method of the BMS active equalization circuit includes the following steps: The voltage signals of each single cell are collected in real time through the AFE chip to judge whether each single cell has over-voltage or under-voltage and whether it needs to be charged / discharged; When a certain 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 conduct first, and then the two degree-of-freedom switch modules corresponding to the battery pack where the single cell is located conduct; 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-modules to be conducted in the first transformer selection switch group and the second transformer selection switch group are determined, and a first charge / discharge circuit is formed with the winding circuit to be connected, and the single cell is charged / discharged by using the first charge / discharge circuit; When multiple adjacent single-cell batteries are over-voltage or under-voltage, they need to be charged / discharged. The multiple single-cell batteries 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 battery at the head end of the charge / discharge unit and the other end of the single-cell battery at the end of the charge / discharge unit to be turned on first, and then the corresponding degree of freedom switch modules 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 sub-modules 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.

2. The working method of 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 working method of 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 transistor switch group, and the first transformer selection switch group includes M parallel MOS transistor switch groups, and each MOS transistor switch group includes two MOS transistors connected in reverse series; The selection switch submodule in the second transformer selection switch group is a MOS transistor, and the second transformer selection switch group includes M MOS transistors connected in parallel.

4. The working method of the BMS active equalization 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, among which 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 working method of the BMS active balancing circuit according to claim 1, characterized in that, The multi-winding transformer is provided with multiple; 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 multiple multi-winding transformers, and the other is connected to the second transformer selection switch group corresponding to multiple multi-winding transformers.

6. The working method of 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 transistor is connected in series on the side connected to the external power supply.

7. The working method of the BMS active balancing circuit according to claim 1, characterized in that The working method also includes a mode of balanced charging and discharging of the inner and outer rings, and the balanced charging and discharging mode of the 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 requirements 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. 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 charge / 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, the 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.

8. The working method of the BMS active balancing circuit according to claim 1, characterized in that, The judgment on whether each single cell needs to be charged / discharged specifically includes: When the voltage of a certain single cell is greater than the first set threshold, it is determined that the single cell needs to be discharged; When the voltage of a certain single cell is less than the second set threshold, it is determined that the single cell needs to be charged.

Images