CN112104043A - Lithium battery equalization control circuit with charging and power supplementing functions and control method thereof - Google Patents

Abstract

The invention discloses a lithium battery balance control circuit with a charging and supplementary function and a control method thereof. The circuit comprises a MCU main control unit, a charging and discharging control unit, and a battery cell group formed by connecting a plurality of battery cells in series. The first end is electrically connected to each cell through a collection and equalization circuit unit, the charge and discharge control unit includes a MOS drive circuit, a charge MOS transistor Q _c and a discharge MOS transistor Q _d , and the second end of the MCU main control unit is connected to charge and discharge The input end of the control unit and the output end of the charge and discharge control unit are respectively connected to the gate of the charging MOS tube _Qc and the gate of the discharge MOS tube _Qd , and the two ends of the charging MOS tube _Qc are connected in parallel with a charging and power supply circuit; At the same time, a corresponding control method is disclosed. By adding a charging and power-supplying circuit, the invention greatly prolongs the on-time of passive equalization, significantly improves the equalization efficiency, reduces the probability of wrong equalization and wrong equalization of the lithium battery, and has high cost performance.

Description

Lithium battery equalization control circuit with charging and supplementing function and control method thereof

technical field

The invention relates to the technical field of batteries, in particular to a lithium battery balance control circuit with a charging and supplementing function and a control method thereof.

Background technique

With the continuous progress of society, lithium batteries have grown suddenly as a new energy source, and the application of lithium batteries has gradually become popular in various fields, especially in electric vehicles, such as electric cars, electric buses, electric vans, electric trucks, electric taxis Vehicles, etc., and have been gradually put into the market.

A lithium battery pack consists of N strings of cells. According to chemical characteristics, if the voltage of two strings of cells is too different, it will cause an imbalance of power. For example, the voltage of one string of cells is 3.6V, and the other string The voltage of the battery cell is 2.5V, and the difference is too large to easily cause the battery to be scrapped. If the difference between the maximum cell voltage and the minimum cell voltage reaches a certain limit, the probability of failure is extremely high, so neither discharge nor charge should continue. In order to avoid this situation as much as possible, the BMS battery management system equipped with lithium batteries will be designed with a voltage equalization function. BMS battery management system, the English full name is Battery Management System, that is, a module specially used for lithium battery operation management.

Voltage equalization is divided into two types: active and passive: passive equalization is to design hardware voltage, use voltage comparator, when the voltage of a string of batteries is too high compared to other battery voltages (for example, the difference reaches 50ms), or use other components to consume the power of the high-voltage battery, or to pour the power of the high-voltage battery into the low-voltage battery; the principle of active balancing is the same, but the program can control more details of the balancing, using serial-to-parallel The decoder is made into a switch circuit, the control system is only balanced during the charging process, and the balanced voltage threshold can be set more flexibly.

Lithium batteries have their special voltage plateau characteristics, especially lithium iron phosphate batteries. In the plateau stage, more than 85% of the capacity is accumulated in the voltage range of tens of millivolts, and the cell voltage-SOC correlation curve is very flat. At the end of charge and discharge, as the internal resistance of the cell increases, the cell voltage-SOC correlation curve becomes slightly steeper, but the capacity of the two stages of charge and discharge usually only accounts for about 10% of the total capacity.

Based on this feature of lithium batteries, the passive equalization function of the existing multi-series lithium battery BMS battery management system has the following limitations:

1. The equalization time is short. The turn-on time of passive equalization will be arranged at the charging end of the battery module, but the capacity of the charging end only occupies less than 5% of the capacity of the battery cell, so the passive equalization time can be turned on for a short time.

2. There are errors and errors. In order to prolong the equalization time, some BMSs lower the equalization turn-on voltage to the lithium battery voltage platform. However, due to the accuracy of the existing cell voltage acquisition circuit, there is a deviation in identifying the real cell voltage accuracy, resulting in the original SOC. The higher cells are not balanced, and the cells with lower SOC are turned on by mistake, resulting in further deterioration of the SOC non-uniformity of the module cells.

SUMMARY OF THE INVENTION

The present invention provides a lithium battery balance control circuit with a charging and supplementary function and a control method thereof to solve the above technical problems.

In order to achieve the above object, the technical scheme adopted in the present invention is:

According to a first aspect of the embodiments of the present invention, a lithium battery balance control circuit is provided, including an MCU main control unit, a charge and discharge control unit, and a battery cell group formed by connecting a plurality of battery cells in series. One end is electrically connected to each cell through the acquisition and equalization circuit unit, the charge and discharge control unit includes a MOS drive circuit, a charge MOS tube Q _c and a discharge MOS tube Q _d , and the second end of the MCU main control unit is connected to the charge and discharge control unit The input terminal of the unit and the output terminal of the charge-discharge control unit are respectively connected to the gate of the charging MOS transistor _Qc and the gate of the discharging MOS transistor _Qd , and the drain of the charging MOS transistor _Qc is in phase with the drain of the discharging MOS transistor _Qd . The source of the discharge MOS transistor _Qd is connected to the negative pole of the cell group, and the two ends of the charging MOS transistor _Qc are connected in parallel with a charging and power supply circuit.

Preferably, the charging and compensating circuit includes a compensating MOS transistor Q _b and a compensating resistor R _p , the drain of the compensating MOS transistor Q _b is connected to the drain of the charging MOS transistor Q _c , and the compensating resistor R Both ends of _p are respectively connected to the source of the supplementary MOS transistor _Qb and the source of the charging MOS transistor _Qc .

Preferably, the acquisition and equalization circuit unit includes a sampling circuit and a plurality of cell equalization circuits connected in parallel to both ends of the cell, and the cell equalization circuit is electrically connected to the sampling circuit.

As a further preference, the cell balancing circuit includes a series-connected balancing resistor and a balancing MOS tube, the drain of the balancing MOS tube is connected to the positive electrode of the battery cell, and the two ends of the balancing resistor are respectively connected to the negative electrode of the battery cell and the balancing MOS tube. The source electrode and the gate electrode of the balanced MOS transistor are all electrically connected to the sampling circuit.

Preferably, if the voltage value of one of the cells is greater than the equalization turn-on voltage, and the difference between the voltage value of the cell and the lowest cell voltage value is greater than the first difference, the passive equalization of the cell is turned on; The voltage value after the passive equalization of the cell is turned on is less than the equalization open voltage, or the voltage value after the passive equalization of the cell is turned on is greater than the equalization open voltage and the difference between the cell voltage value and the lowest cell voltage value is smaller than the second difference value, then Turn off passive equalization for this cell.

As a further preference, the battery cell group is a lithium iron phosphate battery, the balanced turn-on voltage of each battery cell is 3.45V, the first difference is 50mV, and the second difference is 20mV.

Preferably, the cell group is a lithium iron phosphate battery. When the cell overvoltage protection is provided and the highest cell voltage value is less than 3.55V or the lowest cell voltage value is greater than the cell overvoltage protection recovery voltage value, the charging and power supply is turned on. Circuit; if the difference between the highest cell voltage value and the lowest cell voltage value is less than the second difference and the highest cell voltage value is greater than the equilibrium turn-on voltage, or the highest cell voltage value is greater than the cell overcharge protection voltage, turn off charging Supplementary circuit.

As a further preference, the balanced turn-on voltage of each cell is 3.45V, the cell overvoltage protection recovery voltage is 3.34V, the cell overcharge protection voltage is 3.65V, and the second difference is 20mV.

According to the second aspect of the embodiment of the present invention, a lithium battery balance control method is provided, which is applied to the lithium battery balance control circuit as described above. The cell group includes n cells CELL _i , and i and n are positive integers. And 1≤i≤n, the battery cell group is a lithium iron phosphate battery, including the following steps:

Step 101, the MCU main control unit charges the battery cell group through the charging MOS transistor _Qc , and collects the voltage value of each battery cell through the acquisition and equalization circuit unit;

Step 102, when the voltage value U _CELLi of the i-th cell is higher than the equalization turn-on voltage, if the difference between the voltage value of the i-th cell and the lowest cell voltage value is greater than the first difference, turn on the cell _CELLi The equalization switch Q _i , turns on the passive equalization of the cell CELL _i ;

Step 103, continue to charge the cell group through the charging MOS transistor Q _c , until the highest cell voltage value U _CELLmax is greater than 3.65V to trigger the overcharge protection, and turn off the charging MOS transistor Q _c ;

Step 104, during the charging process, when the highest cell voltage value U _CELLmax < 3.55V and the lowest cell voltage value U _{CELLmin is} higher than the cell overvoltage protection recovery voltage value, turn on the supplementary power MOS transistor _Qb to continuously supplement the power supply through the supplementary power circuit. When the highest cell voltage value U _{CELLmax is} higher than the cell overcharge protection voltage, turn off the supplementary MOS transistor Q _b ;

Step 105, during the subsequent fall of the highest cell voltage value U _CELLmax , when the highest cell voltage value U _CELLmax <3.55V and the lowest cell voltage value U _{CELLmin is} higher than the cell overvoltage protection recovery voltage value, restart the power supply MOS transistor Q _b , repeat step 104, so that the voltage of each cell whose balance has been started is always kept above the balance turn-on voltage;

Step 106, when the difference between the voltage value U _CELLi of the cell CELL _i that has been equalized and the lowest cell voltage value U _CELLmin is less than the second difference, and the voltage value U _CELLi of the cell CELL _i is greater than the equalization turn-on voltage, or When the voltage value U _CELLi of the _{cell CELLi} is lower than the equalization turn-on voltage, the equalization switch _CELLi of the cell _CELLi is turned off, and the passive equalization of the cell _CELLi is turned off;

Step 107, when the difference between the highest cell voltage value and the lowest cell voltage value U _CELLmax - U _CELLmin is smaller than the second difference and the highest cell voltage value U _CELLmax is greater than the equalization turn-on voltage, turn off the power-supplying MOS transistor Q _b , Disable all passive balancing cells that have passive balancing turned on.

Preferably, the balanced turn-on voltage of each cell is 3.45V, the cell overvoltage protection recovery voltage is 3.34V, the cell overcharge protection voltage is 3.65V, the first difference is 50mV, and the second difference is 50mV. 20mV.

Compared with the prior art, the present invention adds a charging and power supply circuit in the charging control loop of the BMS battery management system, which greatly prolongs the on-time of passive equalization, significantly improves the equalization efficiency, and reduces lithium battery equalization errors and errors. The probability of uniformity is high, and the cost performance is high; through the charging and power supply circuit, the voltage of all series cells can be controlled within a small range (such as 20mV) under certain conditions, and the single-cell charging protection will not be triggered, reducing single-cell charging protection. During body overcharge protection, the risk of voltage breakdown when the charging switch cuts off a large current increases the reliability of the BMS operation.

Description of drawings

FIG. 1 is a circuit diagram of a lithium battery balance control circuit with a charging and supplementing function of the present invention.

In the figure, 1-MCU main control unit, 2-charging and discharging control unit, 3-collecting and equalizing circuit unit, 4-charging and power supply circuit, 5-MOS driving circuit, 6-sampling circuit.

Detailed ways

The present invention will be described in detail below with reference to the specific embodiments shown in the accompanying drawings. However, these embodiments do not limit the present invention, and structural, method, or functional changes made by those skilled in the art according to these embodiments are all included in the protection scope of the present invention.

The terminology used in the present invention is for the purpose of describing particular embodiments only and is not intended to limit the present invention. As used in this specification and the appended claims, the singular forms "a," "the," and "the" are intended to include the plural forms as well, unless the context clearly dictates otherwise. It will also be understood that the term "and/or" as used herein refers to and includes any and all possible combinations of one or more of the associated listed items.

As shown in Figure 1, a lithium battery balance control circuit with charging and power supply function includes a MCU main control unit 1, a charging and discharging control unit 2, and a battery cell group formed by a number of battery cells in series. The MCU main control unit The first end of 1 is electrically connected to each cell through the acquisition and equalization circuit unit 3. The charge and discharge control unit 1 includes a MOS drive circuit 5, a charge MOS transistor Q _c and a discharge MOS transistor Q _d , and the MCU main control unit 1 has a The second terminal is connected to the input terminal of the charging and discharging control unit 2, and the output terminal of the charging and discharging control unit 2 is respectively connected to the gate of the charging MOS transistor _Qc , the gate of the discharging MOS transistor _Qd , the drain of the charging MOS transistor _Qc and the The drain of the discharge MOS transistor _Qd is connected, the source of the discharge MOS transistor _Qd is connected to the negative electrode of the cell group, and the two ends of the charging MOS transistor _Qc are connected in parallel with a charging and power supply circuit 4.

The cell group used in the present invention is generally formed by connecting n cells CELL _i in series, wherein i and n are positive integers and 1≤i≤n. The MCU main control unit 1 is the main control chip and peripheral circuit of the BMS battery management system, which is used for the collection of battery cell data and the drive of the charge and discharge control unit 2 to realize the balance control of the lithium battery.

In an embodiment of the present invention, the charging and supplementing circuit 4 may include _a charging MOS transistor _Qb and a charging resistor _Rp , wherein the drain of the charging MOS transistor Qb is connected to the drain of the charging MOS transistor _Qc , Two ends of the supplementary resistor _Rp are respectively connected to the source of the supplementary MOS transistor _Qb and the source of the charging MOS transistor _Qc .

The acquisition and equalization circuit unit 3 includes a sampling circuit 6 for acquiring the voltage value of each cell and several cell equalization circuits connected in parallel at both ends of the cell for equalizing the voltage of the cell. The cell equalization circuit is electrically connected to the sampling circuit 6 . connect.

Specifically, each cell balancing circuit includes a series-connected balancing resistor and a balancing MOS tube. The drain of the balancing MOS tube is connected to the positive electrode of the battery cell, and the two ends of the balancing resistor are respectively connected to the negative electrode of the battery cell and the balance MOS tube. The source, as shown in FIG. 1 , is connected in parallel with the equalizing resistor R _n and the equalizing MOS transistor Q _n at both ends of the cell CELL _n , and the gate of each equalizing MOS transistor is connected to the sampling circuit 6 . The structure of the sampling circuit 6 and the connection between the gate of the equalizing MOS transistor and the sampling circuit 6 are all conventional circuits, which will not be repeated here.

Here, the passive equalization logic of each cell is as follows: if the voltage value of one of the cells is greater than the equalization turn-on voltage, and the difference between the voltage value of the cell and the voltage value of the lowest cell is greater than the first difference, the cell is turned on If the voltage value of one of the cells after passive balancing is turned on is less than the balanced turn-on voltage, or the voltage value of the cell after passive balancing is turned on is greater than the balanced turn-on voltage and the difference between the voltage value of the cell and the lowest cell voltage value If the value is less than the second difference, the passive equalization of the cell is turned off.

Here, the battery pack generally uses lithium iron phosphate batteries, which are generally equipped with overvoltage protection. The opening and closing conditions of the charging and power supply circuit 4 are as follows: when the cell overvoltage protection is in progress, and the highest cell voltage value is less than 3.55V or the minimum cell voltage value is greater than the cell overvoltage protection recovery voltage value, the charging power supply is turned on. The circuit is to turn on the supplementary MOS transistor _Qb ; if the difference between the highest cell voltage value and the lowest cell voltage value is less than the second difference and the highest cell voltage value is greater than the equilibrium turn-on voltage, or the highest cell voltage value is greater than the power If the core overcharge protection voltage is exceeded, the charging and supplementary circuit is turned off, that is, the supplementary power MOS transistor Q _b is turned off.

Wherein, the balanced turn-on voltage of each cell is 3.45V, the overvoltage protection recovery voltage of the cell is 3.34V, the overcharge protection voltage of the cell is 3.65V, and the second difference is 20mV. The selection of these values is based on many experiments and experience.

In the present invention, a charging and power supply circuit 4 composed of an electronic switch and a power resistor connected in series is connected in parallel with the lithium battery BMS charging circuit control switch to construct a new BMS battery management system connected with the battery cell group. After the lithium battery is fully charged and meets a certain voltage condition, by turning on the charging and power supply circuit 4, the battery can be charged with a small current, the equalization time can be prolonged, and the risk of equalization mis-leveling and mis-leveling can be reduced. Under the condition of high current, control the voltage of all series-connected cells in the module within a small range (such as 20mV) to avoid triggering the single-cell charging protection, reduce the probability of turning off the charging protection switch under high current conditions, and increase the reliability of the system.

Based on the above-mentioned lithium battery balance control circuit, the present invention provides a lithium battery balance control method, which includes the following steps:

Step 101, the MCU main control unit charges the battery cell group through the charging MOS transistor _Qc , and collects the voltage value of each battery cell through the acquisition and equalization circuit unit;

Step 102, when the voltage value U _CELLi of the i-th cell is higher than the equalization turn-on voltage, if the difference between the voltage value of the i-th cell and the lowest cell voltage value is greater than the first difference, turn on the cell _CELLi The equalization switch Q _i , turns on the passive equalization of the cell CELL _i ;

Step 103, continue to charge the cell group through the charging MOS transistor Q _c , until the highest cell voltage value U _CELLmax is greater than 3.65V to trigger the overcharge protection, and turn off the charging MOS transistor Q _c ;

Step 104, during the charging process, when the highest cell voltage value U _CELLmax < 3.55V and the lowest cell voltage value U _{CELLmin is} higher than the cell overvoltage protection recovery voltage value, turn on the supplementary power MOS transistor _Qb to continuously supplement the power supply through the supplementary power circuit. When the highest cell voltage value U _{CELLmax is} higher than the cell overcharge protection voltage, the supplementary MOS transistor Q _b is turned off. At this time, the battery is in the charging terminal stage, the cell voltage-SOC curve is steep, and a relatively small supplementary current can maintain the cell voltage above the equilibrium turn-on voltage, and the passive equalization of CELL _n can continue;

Step 105, during the subsequent fall of the highest cell voltage value U _CELLmax , when the highest cell voltage value U _CELLmax <3.55V and the lowest cell voltage value U _{CELLmin is} higher than the cell overvoltage protection recovery voltage value, restart the power supply MOS transistor Q _b , repeat step 104, so that the voltage of each cell whose balance has been started is always kept above the balance turn-on voltage;

Step 106, when the difference between the voltage value U _CELLi of the cell CELL _i that has been equalized and the lowest cell voltage value U _CELLmin is less than the second difference, and the voltage value U _CELLi of the cell CELL _i is greater than the equalization turn-on voltage, or When the voltage value U _CELLi of the _{cell CELLi} is lower than the equalization turn-on voltage, the equalization switch _CELLi of the cell _CELLi is turned off, and the passive equalization of the cell _CELLi is turned off;

Step 107, when the difference between the highest cell voltage value and the lowest cell voltage value U _CELLmax - U _CELLmin is smaller than the second difference and the highest cell voltage value U _CELLmax is greater than the equalization turn-on voltage, turn off the power-supplying MOS transistor Q _b , Disable all passive balancing cells that have passive balancing turned on.

In this way, the balance of the lithium battery module is completed, and the voltage difference of all the series-connected cells is controlled to be less than the second difference.

Wherein, the balanced turn-on voltage of each cell is 3.45V, the overvoltage protection recovery voltage of the cell is 3.34V, the overcharge protection voltage of the cell is 3.65V, the first difference is 50mV, and the second difference is 20mV .

Other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or conventional techniques in the art not disclosed by the invention . The specification and examples are to be regarded as exemplary only, with the true scope and spirit of the invention being indicated by the claims of this application.

It should be understood that the present invention is not limited to the precise structures described above and illustrated in the accompanying drawings, and that various modifications and changes may be made without departing from its scope. The scope of the present invention is limited only by the appended claims.

Claims (10)

1. The utility model provides a lithium cell equalization control circuit of function of replenishing electricity charges in area, a serial electric core group of forming is established ties including MCU main control unit, charge-discharge control unit and a plurality of electricity core, the first end of MCU main control unit is connected with each electricity core electricity through gathering and equalizer circuit unit, charge-discharge control unit includes MOS drive circuit, the MOS pipe Q that charges_cAnd discharge MOS tube Q_dThe second end of the MCU main control unit is connected with the input end of the charge and discharge control unit, and the output end of the charge and discharge control unit is respectively connected with the charging MOS tube Q_cGrid and discharge MOS tube Q_dGrid of (1), charging MOS tube Q_cDrain electrode of and discharge MOS tube Q_dIs connected with the drain electrode of the discharge MOS tube Q_dThe source electrode of the charging MOS tube Q is connected with the negative electrode of the electric core group_cThe two ends of the charging circuit are connected in parallel with a charging compensation circuit.

2. The lithium battery equalization control circuit with charging and power-supplementing functions as claimed in claim 1, wherein the charging and power-supplementing circuit comprises a power-supplementing MOS (metal oxide semiconductor) tube Q_bAnd a compensation resistor R_pThe power supply MOS tube Q_bDrain electrode of and charging MOS tube Q_cIs connected with the drain electrode of the resistor R_pAre respectively connected with a power-compensating MOS tube Q_bSource electrode, charging MOS tube Q_cOf the substrate.

3. The lithium battery equalization control circuit with the charging and power supplementing function according to claim 2, wherein the acquisition and equalization circuit unit comprises a sampling circuit and a plurality of cell equalization circuits connected in parallel to two ends of the cell, and the cell equalization circuits are electrically connected with the sampling circuit.

4. The lithium battery equalization control circuit with the charging and power supplementing function according to claim 3, wherein the cell equalization circuit comprises an equalization resistor and an equalization MOS (metal oxide semiconductor) tube which are connected in series, a drain electrode of the equalization MOS tube is connected with an anode of the cell, two ends of the equalization resistor are respectively connected with a cathode of the cell and a source electrode of the equalization MOS tube, and a grid electrode of the equalization MOS tube is electrically connected with the sampling circuit.

5. The lithium battery equalization control circuit with the charging and power-supplementing function according to claim 4, wherein if the voltage value of one of the battery cells is greater than the equalization start voltage, and the difference between the battery cell voltage value and the lowest battery cell voltage value is greater than a first difference, the passive equalization of the battery cell is started; and if the voltage value of one of the battery cells after the passive equalization is started is smaller than the equalization starting voltage, or the voltage value of the battery cell after the passive equalization is started is larger than the equalization starting voltage and the difference value between the battery cell voltage value and the lowest battery cell voltage value is smaller than a second difference value, the passive equalization of the battery cell is closed.

6. The lithium battery equalization control circuit with the charging and power-supplementing function according to claim 5, wherein the battery core group is a lithium iron phosphate battery, the equalization starting voltage of each battery core is 3.45V, the first difference is 50mV, and the second difference is 20 mV.

7. The lithium battery equalization control circuit with the charging and power-supplementing function according to claim 5, wherein the battery core group is a lithium iron phosphate battery, and when the cell overvoltage protection is performed and the highest cell voltage value is less than 3.55V or the lowest cell voltage value is greater than the cell overvoltage protection recovery voltage value, the charging and power-supplementing circuit is started; and if the difference value between the highest cell voltage value and the lowest cell voltage value is smaller than the second difference value and the highest cell voltage value is larger than the equalizing starting voltage or the highest cell voltage value is larger than the cell over-charging protection voltage, closing the charging and electricity supplementing circuit.

8. The lithium battery equalization control circuit with the charging and power-supplementing function according to claim 7, wherein the equalization start voltage of each battery cell is 3.45V, the battery cell overvoltage protection recovery voltage value is 3.34V, the battery cell overcharge protection voltage value is 3.65V, and the second difference value is 20 mV.

9. A lithium battery equalization control method is applied to the lithium battery equalization control circuit of any one of claims 3 to 8, and the battery core group comprises n battery CELLs CELL_iI and n are positive integers, i is more than or equal to 1 and less than or equal to n, and the electric core group is a lithium iron phosphate battery, and is characterized by comprising the following steps:

101, the MCU main control unit charges the MOS tube Q_cCharging the cell group and acquiring the voltage value of each cell through the acquisition and equalization circuit unit;

step 102, when the voltage value U of the ith battery cell _CELLiAfter the voltage is higher than the equilibrium starting voltage, if the difference value between the ith CELL voltage value and the lowest CELL voltage value is larger than the first difference value, the CELL CELL is opened_iIs balanced to the switch Q_iCELL CELL of open CELL_iPassive equalization of (2);

step 103, charging the MOS transistor Q_cContinuously charging the cell group until the highest cell voltage value U_CELLmaxOver-charge protection is triggered to turn off the charging MOS tube Q by more than 3.65V_c；

104, in the charging process, when the highest cell voltage value U is obtained_CELLmax<3.55V and lowest cell voltage value U_CELLminThe voltage value is higher than the overvoltage protection recovery voltage value of the battery cell, and the power-supplementing MOS tube Q is opened_bContinuously supplementing electricity through an electricity supplementing circuit when the highest cell voltage value U is reached_CELLmaxWhen the voltage is higher than the overcharge protection voltage of the battery cell, the power-supplementing MOS tube Q is closed_b；

Step 105, the highest cell voltage value U thereafter_CELLmaxIn the falling process, when the highest cell voltage value U is obtained_CELLmax<3.55V and lowest cell voltage value U_CELLminHigher than the over-voltage protection recovery voltage value of the battery coreRe-starting the power-compensating MOS transistor Q_bStep 104 is repeatedly executed, so that the voltage of each cell which starts the balancing is always kept above the balancing starting voltage;

step 106, when the CELL CELL of the balance is started_iVoltage value U of _CELLi With the lowest cell voltage value U_CELLminIs less than the second difference, and the CELL CELL_iVoltage value U of _CELLi Greater than the equilibrium turn-on voltage or CELL CELL_iVoltage value U of _CELLi CELL CELL is closed when the voltage is lower than the balanced starting voltage_iIs balanced to the switch Q_iCELL CELL is closed_iPassive equalization of (2);

step 107, when the difference value U between the highest cell voltage value and the lowest cell voltage value_CELLmax-U_CELLminLess than the second difference and the highest cell voltage value U_CELLmaxWhen the voltage is larger than the balanced opening voltage, the power-supplementing MOS tube Q is closed_bAnd closing all the passive equalization of the started passive equalization cells.

10. The lithium battery equalization control method of claim 9, wherein the equalization start voltage of each cell is 3.45V, the cell overvoltage protection recovery voltage value is 3.34V, the cell overcharge protection voltage value is 3.65V, the first difference is 50mV, and the second difference is 20 mV.

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