Active balancing system and method for BMS

Abstract

The present invention provides an active balancing system and method for BMS, wherein the balancing system part includes a main control chip, a power module, a BUCK-BOOST circuit, a current detection circuit and a matrix switch; the BUCK-BOOST circuit is used to store and transfer energy, and transfer a part of the total energy of the battery pack to the single battery cell with the lowest energy; the current detection circuit is used to detect the circuit current during balancing, and adjust the duty cycle of PWM in real time according to the current size to realize the constant current function during the balancing process; the matrix switch is used to realize the opening and closing of the battery cell balancing; the main control chip is used to generate a PWM signal for controlling the BUCK-BOOST circuit and a control signal of the matrix switch, and receive a signal from the current detection circuit. At the same time, a corresponding active balancing method is provided, and the balancing strategy of the present invention combines multiple advantages such as high efficiency, low cost, and safety, and is an innovative technology with practical application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery balancing control in a battery management system, and in particular relates to an active balancing system and method for a BMS. Background Art

[0002] With the vigorous development of the new energy industry, especially the rapid rise of electric vehicles, energy storage and other fields, batteries, as key energy storage units, have attracted much attention for their performance, life and safety. However, during the use of multiple battery cells, it is inevitable that voltage imbalance will occur due to factors such as differences in chemical reactions and uneven temperatures, which leads to the problem of battery balancing. The key to solving this problem is to introduce balancing technology in the battery management system. Through an intelligent current control mechanism, balanced charging and discharging between battery cells can be achieved, the performance of the battery pack can be maximized, and its safe, stable and efficient operation can be ensured. Battery balancing technology has therefore become an indispensable key link in the new energy industry, providing a reliable energy storage solution for sustainable development. The current cell balancing strategies mainly include passive balancing and active balancing.

[0003] Passive balancing uses resistors to discharge high-voltage cells through energy consumption to maintain a consistent voltage difference between cells. This method relies on the electrochemical characteristics of the battery itself, and has a relatively slow response speed. It cannot quickly adapt to the energy differences between cells in the battery pack, and may affect the life of the battery to a certain extent. In particular, it may deeply discharge the battery during balancing, accelerating the aging process of the battery. Since passive balancing uses resistor discharge, the current is also limited to avoid system overheating. The balancing effect is not good for large-capacity cells, and a certain amount of electrical energy is wasted during balancing, reducing the energy utilization efficiency of the entire battery system.

[0004] Active balancing is through energy transfer. Currently, most commonly used active balancing methods use multiple capacitors to balance the cells separately. However, multi-capacitor balancing systems require the addition of controllable capacitors, electronic switches and other components, making the system design more complicated. The complexity of the system may increase the difficulty of maintenance and troubleshooting, and the introduction of controllable capacitors and related control circuits will increase the manufacturing cost of the system. In addition, there is an active balancing method based on multi-winding transformers, but the control algorithm and hardware technology of multi-winding transformers are more complex. Each winding requires an independent insulation and cooling system, which increases the cost of manufacturing and maintenance. In addition, the transformer itself has a certain amount of energy transmission loss, and the multi-winding structure may cause more energy loss, thus affecting the overall efficiency of the system. Summary of the invention

[0005] In order to solve the above-mentioned deficiencies in the prior art, an object of the present invention is to provide an active balancing system and method for BMS, so as to solve the problems of high cost, high system complexity, low energy efficiency and the like of the existing active balancing.

[0006] A first aspect of the present invention provides an active balancing system for a BMS, comprising a main control chip, a power module, a BUCK-BOOST circuit, a current detection circuit, and a matrix switch;

[0007] The first end of the BUCK-BOOST circuit is connected to the positive electrode of the battery pack, the second end of the BUCK-BOOST circuit is connected to the negative electrode of the battery pack, the third end of the BUCK-BOOST circuit is connected to the first end of the main control chip, the fourth end of the BUCK-BOOST circuit is connected to the third end of the matrix switch, and the fifth end of the BUCK-BOOST circuit is connected to the first end of the current detection circuit; the BUCK-BOOST circuit is used to store and transfer energy, and reduces the energy difference between cells by transferring part of the total energy of the battery pack to the single cell with the lowest energy;

[0008] The second end of the current detection circuit is connected to the second end of the main control chip, and the third end of the current detection circuit is connected to the fourth end of the matrix switch; the current detection circuit is used to detect the current of the circuit during balancing, and adjust the duty cycle of PWM in real time according to the size of the current to achieve a constant current function during the balancing process;

[0009] The first end of the matrix switch is connected to the fourth end of the main control chip, and the second end of the matrix switch is connected to the battery pack; the matrix switch is used to realize the opening and closing of the battery cell balance;

[0010] The power module is connected to the third terminal of the main control chip; the power module is used to provide low voltage power supply to the main control chip; the main control chip is used to generate a PWM signal for controlling the BUCK-BOOST circuit and a control signal for the matrix switch, and receive a signal from the current detection circuit.

[0011] Preferably, the BUCK-BOOST circuit includes a switch K, an inductor L, a capacitor C, a first diode D1, a second diode D2, a first fuse F1 and a second fuse F2; the first end of the second fuse F2 is connected to the positive electrode of the battery pack, and the second end of the second fuse F2 is connected to the first end of the switch K; the second end of the switch K is connected to the first end of the inductor L and short-circuited with the second end of the first diode D1, and the third end of the switch K is connected to the first end of the main control chip 11, and the MCU outputs a PWM signal to control the on-off frequency of the switch K; the second end of the inductor L is connected to the first end of the second diode D2 and short-circuited with the first end of the first fuse F1, the second end of the first fuse F1 is connected to the negative electrode of the battery pack, the second end of the second diode D2 is connected to the first end of the capacitor C and short-circuited with the first end of the current detection circuit, and the second end of the capacitor C is connected to the first end of the first diode D1 and short-circuited with the third end of the matrix switch.

[0012] Preferably, the current detection circuit includes a sampling resistor R and an ADC amplifier circuit, the first end of the sampling resistor R is connected to the first end of the ADC amplifier circuit and short-circuited with the first end of the capacitor C in the BUCK-BOOST circuit, the second end of the sampling resistor R is connected to the fourth end of the matrix switch and short-circuited with the second end of the ADC amplifier circuit, and the third end of the ADC amplifier circuit is connected to the second end of the main control chip.

[0013] Preferably, the matrix switch includes N positive switches K11~K1n, N diodes D11~D1n and N negative switches K21~K2n, the first end of the positive switch K11~K1n is connected to the fourth end of the main control chip, and the main control chip controls the on and off of the positive switches K11~K1n, the second end of the positive switch K11~K1n is connected to the first end of the diode D11~D1n, the third end of the positive switch K11~K1n is connected to the second end of the sampling resistor R in the current detection circuit, the second end of the diode D11~D1n is connected to the positive electrode of each battery cell, the first end of the negative switch K21~K2n is connected to the fourth end of the main control chip, and the main control chip controls the on and off of the negative switch K21~K2n, the second end of the negative switch K21~K2n is connected to the negative electrode of each battery cell, and the third end of the negative switch K21~K2n is connected to the second end of the capacitor C in the BUCK-BOOST circuit.

[0014] A second aspect of the present invention provides an active balancing method for a BMS, comprising the following process:

[0015] S1, connecting the active balancing system described in any one of claims 1 to 4 to a battery pack, and establishing communication with a battery management system BMS to facilitate data interaction;

[0016] S2, the active balancing system obtains the voltage, temperature and processed single cell charge state data collected by the battery management system through communication, including SOC;

[0017] S3, judging whether the single cell meets the conditions for balanced start-up, if the conditions are met, executing S4, if not, returning to S2;

[0018] S4, the main control chip in the active balancing system processes the obtained data and calculates the time required for balancing according to the information; the information includes SOC and capacity;

[0019] S5, start balancing in sequence, balancing only one cell at a time;

[0020] S6, detecting the current in the balancing loop, and ensuring that the current is in a constant current state by adjusting the PWM duty cycle in real time;

[0021] S7, obtaining the cell information in the BMS through communication again, including voltage and temperature;

[0022] S8, determining whether the cell voltage and temperature obtained from the BMS are abnormal, if abnormal, executing S10, if not, executing S9;

[0023] S9, determining whether the single cell has reached the condition of balanced shutdown, if the condition is met, executing S11, otherwise executing S6;

[0024] S10, shut down the battery cell being balanced and stop the balancing process;

[0025] S11, the active balancing system transmits the balancing data to the BMS and updates the cell status to facilitate the BMS data processing and subsequent balancing work.

[0026] Preferably, active balancing can be performed during the entire charging and discharging process and in a stationary state; the conditions for starting balancing include that the voltage of the single cell is higher than the undervoltage protection threshold voltage and lower than the overvoltage protection threshold voltage, the temperature of the single cell is lower than the high temperature protection threshold temperature, and the SOC of the single cell differs from the highest SOC in the battery pack by more than the set balancing threshold.

[0027] Preferably, the time required for calculating the balance is:

[0028] Calculate the difference between the single cell SOC that meets the equilibrium condition and the highest SOC in the battery pack, SOC dif =SOC max -SOC cell , where SOC max The highest SOC in the battery pack, SOC cell The single-cell SOC that satisfies the equilibrium condition;

[0029] According to the obtained capacity data, calculate the capacity Q that needs to be balanced for the battery cells balance =SOC dif *Q, where Q is the capacity of the battery management system obtained by the active balancing system through communication;

[0030] Calculate the balancing time T based on the balancing capacity and the balancing current controlled by the active balancing system balance =Q balance / I balance , where I balance To set the required constant balancing current.

[0031] Preferably, the balancing is turned on in sequence, and the order of turning on active balancing is required to sort the SOCs of the battery cells that meet the balancing conditions from small to large, and first balance the battery cell with the smallest SOC. After the smallest SOC is balanced, balance the next smallest one, and so on, to ensure that only one battery cell is in a balanced state at the same time.

[0032] Preferably, the determination of whether the single cell voltage and temperature obtained from the BMS are abnormal, the abnormal state specifically being: the voltage of the single cell is lower than the undervoltage protection threshold voltage or higher than the overvoltage protection threshold voltage, and the temperature of the single cell is higher than the cell high temperature protection threshold temperature.

[0033] Preferably, the operation to be performed to turn on active balancing is to first close the positive switch and the negative switch in the matrix switch, and then control the switching frequency in the BUCK-BOOST circuit through PWM to realize the function of the capacitor of the BUCK-BOOST circuit charging the battery cell; the operation to be performed to turn off active balancing is to first control the BUCK-BOOST circuit to be disconnected, and then disconnect the positive switch and the negative switch in the matrix switch.

[0034] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0035] The active balancing method of the present invention is to transfer the energy of the total voltage of the series-connected battery cells to the single-cell voltage with relatively low energy, thereby improving the energy efficiency of the balancing process (>90% lossless energy transfer), which is not only applicable to the entire charging and discharging process, but also shows a good balancing effect when the battery pack is in a static state. The active balancing circuit of the present invention is simple in design and low in cost. It only needs to use a capacitor and an inductor to achieve energy storage, and the energy transfer is achieved through PWM control and a switch matrix. The balancing current can be flexibly adjusted by controlling PWM (recommended within 10A), which is applicable to battery cells of different capacities to achieve faster and more effective balancing. The balancing circuit of the present invention is equipped with anti-backflow devices and overcurrent protection strategies. By detecting the balancing current, the balancing process can be more accurately controlled, which helps to discover potential problems in advance and perform safety management and protection. Therefore, the balancing circuit combines multiple advantages such as high efficiency, low cost, and safety, and is an innovative technology with practical application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions of the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, what is described below is only one embodiment of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0037] Figure 1 A system architecture diagram of an active balancing system based on a BUCK-BOOST constant current circuit provided by the present invention.

[0038] Figure 2 A circuit schematic diagram of an active balancing system based on a BUCK-BOOST constant current circuit provided by the present invention.

[0039] Figure 3 A control flow chart of an active balancing method based on a BUCK-BOOST constant current circuit provided by the present invention. DETAILED DESCRIPTION

[0040] 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 the present invention.

[0041] The technical problem to be solved by the present invention is to provide an active balancing system and method based on a BUCK-BOOST constant current circuit to solve the problems of high cost, high system complexity, low energy efficiency, etc. of the existing active balancing.

[0042] The present invention provides an active balancing system based on a BUCK-BOOST constant current circuit, specifically Figure 1 To realize the active balancing function, it is necessary to work in coordination with the battery management system BMS. The active balancing system includes: a main control chip 11, a power module 12, a BUCK-BOOST circuit 13, a current detection circuit 14 and a matrix switch 15.

[0043] A first end of the BUCK-BOOST circuit 13 is connected to the positive electrode of the battery pack, a second end of the BUCK-BOOST circuit 13 is connected to the negative electrode of the battery pack, a third end of the BUCK-BOOST circuit 13 is connected to the first end of the main control chip 11, a fourth end of the BUCK-BOOST circuit 13 is connected to the third end of the matrix switch 15, and a fifth end of the BUCK-BOOST circuit 13 is connected to the first end of the current detection circuit 14; a second end of the current detection circuit 14 is connected to the second end of the main control chip 11, and a third end of the current detection circuit 14 is connected to the fourth end of the matrix switch 15; the power module 12 is connected to the third end of the main control chip 11; a first end of the matrix switch 15 is connected to the fourth end of the main control chip 11, and a second end of the matrix switch 15 is connected to the battery pack.

[0044] In the embodiment of the present invention, the key function of the battery management system 21 (BMS) is to transmit the state of charge (SOC), cell voltage, and temperature information of each battery cell to the main control chip 11 in the active balancing system through communication to support the implementation of the balancing control algorithm.

[0045] The BUCK-BOOST circuit 13 of the present invention is used for energy storage and transfer in an active balancing system, and reduces the energy difference between cells by transferring part of the total energy of the battery pack to the single cell with the lowest energy, thereby achieving a balancing function.

[0046] One of the main functions of the main control chip 11 of the present invention is to generate PWM waves, and to control the energy in the BUCK-BOOST circuit by adjusting the duty cycle to achieve constant current active balancing; in addition, the main control chip 11 receives the current signal of the current detection circuit 14, and adjusts the PWM duty cycle in real time according to the current size to achieve the constant current function during the balancing process; at the same time, the main control chip 11 also controls the matrix switch 15 to achieve charging balancing control of monomers that meet the balancing conditions.

[0047] The power module 12 of the present invention supplies power to the main control chip 11 , thereby ensuring stable operation of the main control chip 11 .

[0048] The circuit schematic diagram of this embodiment is as follows Figure 2As shown. The BUCK-BOOST circuit 13 includes a switch K, an inductor L, a capacitor C, a first diode D1, a second diode D2, a first fuse F1 and a second fuse F2, wherein the first end of the second fuse F2 is connected to the positive electrode of the battery pack, the second end of the second fuse F2 is connected to the first end of the switch K, the second end of the switch K is connected to the first end of the inductor L and is short-circuited with the second end of the first diode D1, the third end of the switch K is connected to the first end of the main control chip 11, and the MCU outputs a PWM signal to control the on-off frequency of the switch K, the second end of the inductor L is connected to the first end of the second diode D2 and is short-circuited with the first end of the first fuse F1, the second end of the first fuse F1 is connected to the negative electrode of the battery pack, the second end of the second diode D2 is connected to the first end of the capacitor C and is short-circuited with the first end of the current detection circuit 14, and the second end of the capacitor C is connected to the first end of the first diode D1 and is short-circuited with the third end of the matrix switch 15.

[0049] The current detection circuit 14 includes a sampling resistor R and an ADC amplifier circuit. The first end of the sampling resistor R is connected to the first end of the ADC amplifier circuit and is short-circuited with the first end of the capacitor C in the BUCK-BOOST circuit. The second end of the sampling resistor R is connected to the fourth end of the matrix switch 15 and is short-circuited with the second end of the ADC amplifier circuit. The third end of the ADC amplifier circuit is connected to the second end of the main control chip 11.

[0050] The matrix switch 15 includes N positive switches K11~K1n, N diodes D11~D1n and N negative switches K21~K2n. The first end of the positive switches K11~K1n is connected to the fourth end of the main control chip 11, and the on and off of the positive switches K11~K1n are controlled by the MCU. The second end of the positive switches K11~K1n is connected to the first end of the diodes D11~D1n, the third end of the positive switches K11~K1n is connected to the second end of the sampling resistor R in the current detection circuit 14, the second end of the diodes D11~D1n is connected to the positive electrode of each battery cell, the first end of the negative switches K21~K2n is connected to the fourth end of the main control chip 11, and the on and off of the negative switches K21~K2n are controlled by the main control chip 11, the second end of the negative switches K21~K2n is connected to the negative electrode of each battery cell, and the third end of the negative switches K21~K2n is connected to the second end of the capacitor C in the BUCK-BOOST circuit 13.

[0051] Optionally, in some embodiments, the switch K of the BUCK-BOOST circuit 13, the positive switches K11-K1n and the negative switches K21-K2n of the switch matrix 15 include but are not limited to switching devices such as MOS tubes, triodes, relays, and optocoupler switches;

[0052] Optionally, in some embodiments, the main control chip 11 includes but is not limited to a single chip microcomputer, an embedded chip, etc. In this embodiment, the main control chip 11 adopts an MCU.

[0053] In this example, 24 strings of 105Ah lithium iron phosphate battery packs are used, the operating voltage range of each battery cell is 2.5V~3.65V, the inductor L is 33uH, the capacitor C is 220uF, the frequency of the switch K in the BUCK-BOOST circuit 13 is set to f=50KHz, T=20us, and the fuse F in the current detection circuit 14 is a 20A fuse.

[0054] The maximum total voltage of the battery pack is U = 24 * 3.65V = 87.6V

[0055] Due to the characteristic that the inductor current cannot change suddenly, when balancing is turned on, according to the total voltage U of the battery pack and the parameters of the inductor, the current rise rate can be obtained as Δi=U / L=87.6V / 33uH=2.65A / us, the sampling resistor R=5mΩ, and the active balancing current is set to 5A. If the feedback voltage exceeds 25mV, the PWM duty cycle will be automatically adjusted to maintain the active balancing current of 5A.

[0056] In this example, if the mth battery cell (m<24) meets the conditions for balanced opening, the MCU first controls the positive switch K1m and the negative switch K2m in the closed matrix switch 15, and then the MCU controls the switching frequency of the switch K in the BUCK-BOOST circuit 13 through PWM to realize the constant current charging of the capacitor C in the BUCK-BOOST circuit 13 to the mth battery cell.

[0057] In this example, if the mth battery cell (m<24) meets the conditions for balancing on or an abnormality occurs and the balancing control needs to be turned off, the MCU first controls the switch K in the BUCK-BOOST circuit 13 to be disconnected, and then the MCU controls the positive switch K1m and the negative switch K2m in the matrix switch 15 to be disconnected.

[0058] In this example, in order to prevent reverse current from being generated during the balancing process, a diode is added to each positive switch, and two diodes are also added to the BUCK-BOOST circuit 13.

[0059] In order to prevent accidental short circuit between the positive and negative electrodes of the battery and the battery being balanced and enhance the safety of the system, a fuse F is added to the current detection circuit 14 in this embodiment. When the current in the loop exceeds 20A during balancing, the fuse is disconnected.

[0060] The present invention provides an active balancing method based on a BUCK-BOOST constant current circuit, which not only includes a control algorithm for constant current balancing, but also has a protection function for cell balancing. The specific control flow chart is as follows: Figure 3 shown.

[0061] S1, connect the active balancing system to the battery pack and establish communication with the battery management system (BMS) to facilitate data exchange;

[0062] S2, the active balancing system obtains data such as voltage, temperature and single cell state of charge (SOC) after data processing collected by the battery management system through communication;

[0063] S3, judging whether the single cell meets the conditions for balanced start-up, if the conditions are met, executing S4, if not, returning to S2;

[0064] S4, the main control chip in the active balancing system processes the obtained data and calculates the time required for balancing based on information such as SOC and capacity;

[0065] S5, start balancing in sequence, balancing only one cell at a time;

[0066] S6, detecting the current in the balancing loop, and ensuring that the current is in a constant current state by adjusting the PWM duty cycle in real time;

[0067] S7, obtaining the cell voltage, temperature and other information in the BMS through communication again;

[0068] S8, determining whether the cell voltage and temperature obtained from the BMS are abnormal, if abnormal, executing S10, if not, executing S9;

[0069] S9, determining whether the single cell has reached the condition of balanced shutdown, if the condition is met, executing S11, otherwise executing S6;

[0070] S10, shut down the battery cell being balanced and stop the balancing process;

[0071] S11, the active balancing system transmits the balancing data to the BMS and updates the battery cell SOC and other statuses to facilitate the BMS data processing and subsequent balancing work.

[0072] Specifically, active balancing can only be enabled if all of the following conditions are met:

[0073] The voltage of the single cell is higher than the undervoltage protection threshold voltage and lower than the overvoltage protection threshold voltage;

[0074] The temperature of the single cell is lower than the cell high temperature protection threshold temperature;

[0075] The difference between the SOC of a single cell and the highest SOC in the battery pack exceeds the set balancing threshold.

[0076] Specifically, the specific process of calculating the time required for equilibrium is as follows:

[0077] Calculate the difference between the single cell SOC that meets the equilibrium condition and the highest SOC in the battery pack, SOC dif =SOC max -SOC cell , where SOC max The highest SOC in the battery pack, SOC cell The single-cell SOC that satisfies the equilibrium condition;

[0078] According to the obtained capacity data, calculate the capacity Q that needs to be balanced for the battery cells balance =SOC dif *Q, where Q is the capacity of the battery management system obtained by the active balancing system through communication;

[0079] Calculate the balancing time T based on the balancing capacity and the balancing current controlled by the active balancing system balance =Q balance / I balance , where I balance To set the required constant balancing current.

[0080] Specifically, the order of arrangement for turning on active balancing is to sort the SOCs of the cells that meet the balancing conditions from small to large, and balance the cell with the smallest SOC first. After the smallest SOC is balanced, balance the next smallest one, and so on, to ensure that only one cell is in a balanced state at the same time.

[0081] Specifically, if one of the following conditions occurs, the active balancing process needs to be terminated and the active balancing needs to be turned off:

[0082] The voltage of the single cell is lower than the undervoltage protection threshold voltage or higher than the overvoltage protection threshold voltage;

[0083] The temperature of the single battery cell is higher than the battery cell high temperature protection threshold temperature.

[0084] Specifically, if no abnormal situation occurs, the condition for the active balancing to end closing is that the above-mentioned balancing time is reached.

[0085] The above description is combined with the accompanying drawings to fully illustrate the specific embodiments of this article so that those skilled in the art can practice them. Parts and features of some embodiments may be included in or replace parts and features of other embodiments. The scope of the embodiments of the present invention includes the entire scope of the claims, and all available equivalents of the claims. In the present invention, the terms "first", "second", etc. are only used to distinguish one element from another, without requiring or implying any actual relationship or order between these elements. In fact, the first element can also be called the second element, and vice versa. Moreover, the terms "include", "include" or any other variant thereof are intended to cover non-exclusive inclusion, so that the structure, device or equipment including a series of elements includes not only those elements, but also other elements that are not explicitly listed, or also include elements inherent to such structure, device or equipment. In the absence of more restrictions, the elements defined by the sentence "include one..." do not exclude the existence of other identical elements in the structure, device or equipment including the elements. Each embodiment is described in a progressive manner herein, and each embodiment focuses on the differences from other embodiments, and the same and similar parts between the embodiments can be referred to each other.

[0086] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

[0087] Although the above describes the specific implementation methods of the present invention, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solution of the present invention without creative work are still within the scope of protection of the present invention.

Claims

1. An active balancing system for BMS, characterized by: Including main control chip, power module, BUCK-BOOST circuit, current detection circuit and matrix switch; The first end of the BUCK-BOOST circuit is connected to the positive electrode of the battery pack, the second end of the BUCK-BOOST circuit is connected to the negative electrode of the battery pack, the third end of the BUCK-BOOST circuit is connected to the first end of the main control chip, the fourth end of the BUCK-BOOST circuit is connected to the third end of the matrix switch, and the fifth end of the BUCK-BOOST circuit is connected to the first end of the current detection circuit; the BUCK-BOOST circuit is used to store and transfer energy, and reduces the energy difference between cells by transferring part of the total energy of the battery pack to the single cell with the lowest energy; The second end of the current detection circuit is connected to the second end of the main control chip, and the third end of the current detection circuit is connected to the fourth end of the matrix switch; The current detection circuit is used to detect the current of the circuit during balancing, and adjust the duty cycle of PWM in real time according to the current size to achieve a constant current function during the balancing process; The first end of the matrix switch is connected to the fourth end of the main control chip, and the second end of the matrix switch is connected to the battery pack; the matrix switch is used to realize the opening and closing of the battery cell balance; The power module is connected to the third terminal of the main control chip; the power module is used to provide low voltage power to the main control chip; the main control chip is used to generate a PWM signal for controlling the BUCK-BOOST circuit and a control signal for the matrix switch, and receive a signal from the current detection circuit; The BUCK-BOOST circuit includes a switch K, an inductor L, a capacitor C, a first diode D1, a second diode D2, a first fuse F1 and a second fuse F2; the first end of the second fuse F2 is connected to the positive electrode of the battery pack, and the second end of the second fuse F2 is connected to the first end of the switch K; the second end of the switch K is connected to the first end of the inductor L and short-circuited with the second end of the first diode D1, the third end of the switch K is connected to the first end of the main control chip 11, and the MCU outputs a PWM signal to control the on-off frequency of the switch K; the second end of the inductor L is connected to the first end of the second diode D2 and short-circuited with the first end of the first fuse F1, the second end of the first fuse F1 is connected to the negative electrode of the battery pack, the second end of the second diode D2 is connected to the first end of the capacitor C and short-circuited with the first end of the current detection circuit, and the second end of the capacitor C is connected to the first end of the first diode D1 and short-circuited with the third end of the matrix switch.

2. The active balancing system for BMS according to claim 1, characterized in that: The current detection circuit includes a sampling resistor R and an ADC amplifier circuit. The first end of the sampling resistor R is connected to the first end of the ADC amplifier circuit and is short-circuited with the first end of the capacitor C in the BUCK-BOOST circuit. The second end of the sampling resistor R is connected to the fourth end of the matrix switch and is short-circuited with the second end of the ADC amplifier circuit. The third end of the ADC amplifier circuit is connected to the second end of the main control chip.

3. An active balancing system for BMS as claimed in claim 2, characterized in that: The matrix switch includes N positive switches K11~K1n, N diodes D11~D1n and N negative switches K21~K2n. The first end of the positive switch K11~K1n is connected to the fourth end of the main control chip, and the main control chip controls the on and off of the positive switch K11~K1n. The second end of the positive switch K11~K1n is connected to the first end of the diode D11~D1n. The third end of the positive switch K11~K1n is connected to the second end of the sampling resistor R in the current detection circuit. The second end of the diode D11~D1n is connected to the positive electrode of each battery cell. The first end of the negative switch K21~K2n is connected to the fourth end of the main control chip, and the main control chip controls the on and off of the negative switch K21~K2n. The second end of the negative switch K21~K2n is connected to the negative electrode of each battery cell. The third end of the negative switch K21~K2n is connected to the second end of the capacitor C in the BUCK-BOOST circuit.

4. An active balancing method for BMS, characterized in that: The process includes: S1, connecting the active balancing system described in any one of claims 1 to 3 to a battery pack, and establishing communication with a battery management system BMS to facilitate data interaction; S2, the active balancing system obtains the voltage, temperature and processed single cell charge state data collected by the battery management system through communication, including SOC; S3, judging whether the single cell meets the conditions for balanced start-up, if the conditions are met, executing S4, if not, returning to S2; S4, the main control chip in the active balancing system processes the obtained data and calculates the time required for balancing according to the information; the information includes SOC and capacity; S5, start balancing in sequence, balancing only one cell at a time; S6, detecting the current in the balancing loop, and ensuring that the current is in a constant current state by adjusting the PWM duty cycle in real time; S7, obtaining the cell information in the BMS through communication again, including voltage and temperature; S8, determining whether the cell voltage and temperature obtained from the BMS are abnormal, if abnormal, executing S10, if not, executing S9; S9, determining whether the single cell has reached the condition of balanced shutdown, if the condition is met, executing S11, otherwise executing S6; S10, shut down the battery cell being balanced and stop the balancing process; S11, the active balancing system transmits the balancing data to the BMS and updates the cell status to facilitate the BMS data processing and subsequent balancing work.

5. An active balancing method for BMS as claimed in claim 4, characterized in that: Active balancing can be performed during the entire charging and discharging process and when stationary; the conditions for starting balancing include that the voltage of the single cell is higher than the undervoltage protection threshold voltage and lower than the overvoltage protection threshold voltage, the temperature of the single cell is lower than the high temperature protection threshold temperature, and the SOC of the single cell differs from the highest SOC in the battery pack by more than the set balancing threshold.

6. The active balancing method for BMS according to claim 4, characterized in that: The time required for calculating equilibrium is: Calculate the difference between the single cell SOC that meets the equilibrium condition and the highest SOC in the battery pack, SOC dif = SOC max -SOC cell , where SOC max The highest SOC in the battery pack, SOC cell The single-cell SOC that satisfies the equilibrium condition; According to the obtained capacity data, calculate the capacity Q that needs to be balanced for the battery cells balance =SOC dif *Q, where Q is the capacity of the battery management system obtained by the active balancing system through communication; Calculate the balancing time T based on the balancing capacity and the balancing current controlled by the active balancing system balance = Q balance / I balance , where I balance To set the required constant balancing current.

7. The active balancing method for BMS according to claim 4, characterized in that: The balancing is turned on in sequence, and the order of turning on active balancing is required to sort the SOCs of the cells that meet the balancing conditions from small to large, and first balance the cell with the smallest SOC. After the smallest SOC is balanced, balance the next smallest one, and so on, to ensure that only one cell is in a balanced state at the same time.

8. The active balancing method for BMS according to claim 4, characterized in that: The determination of whether the single cell voltage and temperature obtained from the BMS are abnormal, the abnormal state specifically being: the voltage of the single cell is lower than the undervoltage protection threshold voltage or higher than the overvoltage protection threshold voltage, and the temperature of the single cell is higher than the cell high temperature protection threshold temperature.

9. The active balancing method for BMS according to claim 4, characterized in that: The operations required to turn on active balancing are: first close the positive switch and the negative switch in the matrix switch, and then control the switching frequency in the BUCK-BOOST circuit through PWM to realize the function of the capacitor of the BUCK-BOOST circuit charging the battery cell; the operations required to turn off active balancing are: first control the BUCK-BOOST circuit to disconnect, and then disconnect the positive switch and the negative switch in the matrix switch.

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