阅读说明：本技术 一种电池均衡方法 (Battery equalization method ) 是由 刘征宇 夏登威 尤勇 杨超 孟辉 于 2019-12-19 设计创作，主要内容包括：本发明属于电池技术领域,特别是涉及一种电池均衡方法。一种电池均衡方法,其包括：S1.获取多个电池中的每一电池的荷电状态,所述多个电池构成一电池组；S2.根据第一均衡条件,对所述荷电状态小于10％及所述荷电状态大于90％的每一所述电池判断是否进行快速充放电；S3.根据第二均衡条件,对所述荷电状态大于10％且所述荷电状态小于90％的每一所述电池判断是否进行修正充放电；S4.根据第三均衡条件,对所述电池组中每一所述电池判断是否进行充放电。本发明解决了传统电池均衡方法容易出现过充及过放的问题。(The invention belongs to the technical field of batteries, and particularly relates to a battery equalization method. A method of cell equalization, comprising: s1, acquiring the charge state of each battery in a plurality of batteries, wherein the plurality of batteries form a battery pack; s2, judging whether each battery with the charge state smaller than 10% and the charge state larger than 90% is rapidly charged and discharged according to a first balance condition; s3, judging whether each battery with the charge state larger than 10% and the charge state smaller than 90% is subjected to correction charging and discharging according to a second balance condition; and S4, judging whether each battery in the battery pack is charged or discharged according to a third balance condition. The invention solves the problem that the traditional battery equalization method is easy to cause overcharge and overdischarge.)

1. A method of balancing a battery, comprising:

s1, acquiring the charge state of each battery in a plurality of batteries, wherein the plurality of batteries form a battery pack;

s2, judging whether each battery with the charge state smaller than 10% and the charge state larger than 90% is rapidly charged and discharged according to a first balance condition;

s3, judging whether each battery with the charge state larger than 10% and the charge state smaller than 90% is subjected to correction charging and discharging according to a second balance condition; and

and S4, judging whether each battery in the battery pack is charged or discharged according to a third balance condition.

2. The battery equalization method according to claim 1, wherein the step S2 further comprises the steps of:

s21, setting a first threshold value;

s22, screening out the batteries with the state of charge smaller than 10% and the state of charge larger than 90%, otherwise, entering a step S3;

s23, after the batteries meeting the first equalization circuit condition are screened out, the batteries with the screened maximum voltage are quickly discharged, meanwhile, the batteries with the screened minimum voltage are quickly charged, and if not, the method goes to step S3.

3. A method for equalizing a battery according to claim 1, wherein the first equalization circuit condition is: and the difference between the screened maximum value of the battery voltage and the screened minimum value of the battery voltage is greater than or equal to the first threshold value.

4. The battery equalization method according to claim 1, wherein the step S3 further comprises the steps of:

s31, setting a second threshold value;

s32: screening out the batteries with the charge states of more than 10% and less than 90%;

s33, after the batteries meeting the second equalization circuit condition are screened out, the batteries with the screened-out voltage maximum value are quickly discharged, meanwhile, the batteries with the screened-out voltage minimum value are quickly charged, and if not, the method goes to step S4.

5. A method for equalizing a battery according to claim 1, wherein the second equalization circuit condition is: and the difference between the screened maximum value of the battery voltage and the screened minimum value of the battery voltage is greater than or equal to the second threshold value.

6. A method for equalizing a battery as in claim 1, wherein the first threshold is greater than the second threshold.

7. The battery equalization method according to claim 1, wherein the step S1 further comprises: calculating an average state of charge of the battery pack from the obtained state of charge of each of the plurality of cells.

8. The battery equalization method according to claim 1, wherein the step S4 further comprises the steps of:

s41: setting a third threshold value;

s42: obtaining the state of charge of each of the plurality of batteries;

s43: and discharging the batteries with the state of charge larger than the sum of the average state of charge and the third threshold value of the screened batteries after screening the batteries meeting the condition of a third equalizing circuit, and simultaneously charging the batteries with the state of charge smaller than the difference between the average state of charge and the third threshold value of the screened batteries, otherwise, stopping the operation of the battery equalizing method.

9. The battery equalization method according to claim 1, wherein the third equalization condition is: the state of charge of the battery is greater than the sum of the average state of charge and the third threshold or the state of charge of the battery is less than the difference between the average state of charge and the third threshold.

10. A battery equalization system, comprising:

at least one battery pack comprising a plurality of batteries;

a battery state of charge detection device for obtaining the state of charge of each of the plurality of batteries;

the charging and discharging module is used for charging and discharging the plurality of batteries;

when the state of charge is less than 10% and the state of charge is greater than 90%, the charge-discharge module judges whether each battery is charged and discharged quickly or not according to a first balance condition;

when the state of charge is more than 10% and less than 90%, the charge-discharge module judges whether each battery is charged and discharged quickly or not according to a second balance condition;

and the charge-discharge module judges whether each battery is charged and discharged quickly or not according to a third balance condition.

Technical Field

The invention belongs to the technical field of batteries, and particularly relates to a battery equalization method.

Background

The electric new energy electric automobile has the advantages of low noise and almost zero emission, and is an important way for solving the problems of energy shortage and environmental pollution. The power battery is an important component of the electric automobile, and determines the performance of the electric automobile to a great extent. The high power requirement of electric vehicles requires a large number of individual power cells to be connected in series to form a battery pack and to be charged as a whole. Due to the difference of the internal characteristics of the single batteries in the battery pack, the difference of the working environment and the use times of charging and discharging, the charging states of the single batteries are inconsistent in the charging and discharging process, so that the phenomenon of unbalance among the single batteries of the battery pack is caused, the service life of the battery pack is greatly shortened, and the performance of the automobile battery is seriously influenced. Therefore, the series battery pack needs to be subjected to balanced control to ensure that each single battery cannot be overcharged or overdischarged in advance in the charging and discharging process due to individual difference, so that the charging and discharging reliability of the battery pack is ensured.

However, the current equalization control method is easy to cause overcharge or overdischarge of the battery.

Disclosure of Invention

The invention aims to provide a battery equalization method, which has the advantage that the open-circuit voltage changes rapidly when the SOC is between two stages of 0-10% and 90% -100%. If the SOC is low, namely the voltage of the lithium battery is increased from a lower voltage limit value to a rated voltage section, the SOC is used as a unique balance variable, and under the condition of large-current discharging, the working voltage can be rapidly attenuated, so that the individual battery monomer is over-discharged. If the SOC is high, namely the voltage of the lithium battery is increased from the rated voltage to the upper voltage limit value, the SOC is used as the only balance variable, and the overcharge of the monomer with high electric quantity is easily caused. The SOC is between 10% and 90% in a voltage plateau period, the open-circuit voltage change is small, if the voltage is taken as the only balance variable, the voltage difference between the battery monomers is small, but the SOC difference is large, the balance speed is seriously reduced, and the error balance operation is easy to occur under the working condition that the current is changed sharply. The method adopts two variables of comprehensive voltage and SOC to evaluate whether each battery in the battery pack needs to be charged and discharged, and solves the problem that the traditional battery balancing method is easy to cause overcharge and overdischarge.

In order to solve the technical problems, the invention is realized by the following technical scheme:

the invention provides a battery equalization method, which comprises the following steps:

s1, acquiring the SOC of each battery in a plurality of batteries, wherein the plurality of batteries form a battery pack;

s2, judging whether each battery with the SOC smaller than 10% and the SOC larger than 90% is rapidly charged and discharged according to a first balance condition;

s3, judging whether to perform correction charging and discharging on each battery with the SOC greater than 10% and the SOC less than 90% according to a second balance condition; and

and S4, judging whether each battery in the battery pack is charged or discharged according to a third balance condition.

In one embodiment of the present invention, the plurality of cells are connected in series to form a battery pack.

In an embodiment of the present invention, the step S2 further includes the following steps:

s21, setting a first threshold value;

s22, screening out the batteries with the SOC less than 10% and the SOC greater than 90%, otherwise, entering the step S3;

s23, after the batteries meeting the first equalization circuit condition are screened out, the batteries with the screened maximum voltage are quickly discharged, meanwhile, the batteries with the screened minimum voltage are quickly charged, and if not, the method goes to step S3.

In one embodiment of the present invention, the first equalization circuit condition is:

and the difference between the screened maximum value of the battery voltage and the screened minimum value of the battery voltage is greater than or equal to the first threshold value. .

In an embodiment of the present invention, the step S3 further includes the following steps:

s31, setting a second threshold value;

s32: screening out the batteries with the SOC greater than 10% and the SOC less than 90%;

s33, after the batteries meeting the second equalization circuit condition are screened out, the batteries with the screened-out voltage maximum value are quickly discharged, meanwhile, the batteries with the screened-out voltage minimum value are quickly charged, and if not, the method goes to step S4.

In one embodiment of the present invention, the second equalization circuit condition is: and the difference between the screened maximum value of the battery voltage and the screened minimum value of the battery voltage is greater than or equal to the second threshold value.

In one embodiment of the invention, the first threshold is greater than the second threshold.

In an embodiment of the present invention, the step S1 further includes: calculating an average SOC of the battery pack from the obtained SOC of each of the plurality of batteries.

In an embodiment of the present invention, the step S4 further includes:

s41: setting a third threshold value;

s42: obtaining the SOC of each of the plurality of batteries;

s43: and discharging the batteries with the SOC of the screened batteries larger than the sum of the average SOC and the third threshold value after screening the batteries meeting the condition of a third equalizing circuit, and simultaneously charging the batteries with the SOC of the screened batteries smaller than the difference between the average SOC and the third threshold value, otherwise, stopping the operation of the battery equalizing method.

The present invention also provides a battery equalization system, comprising:

at least one battery pack comprising a plurality of batteries;

a battery state of charge detection device for obtaining the state of charge of each of the plurality of batteries;

the charging and discharging module is used for charging and discharging the plurality of batteries;

when the state of charge is less than 10% and the state of charge is greater than 90%, the charge-discharge module judges whether each battery is charged and discharged quickly or not according to a first balance condition;

when the state of charge is more than 10% and less than 90%, the charge-discharge module judges whether each battery is charged and discharged quickly or not according to a second balance condition;

and the charge-discharge module judges whether each battery is charged and discharged quickly or not according to a third balance condition.

In one embodiment of the present invention, the third equalization condition is: the third equalization condition is: the SOC of the battery is greater than a sum of the average SOC and the third threshold and the SOC of the battery is less than a difference of the average SOC and the third threshold.

In one embodiment of the invention, the first threshold may be a range, for example, between 45mv and 55 mv.

In one embodiment of the invention, the second threshold may be a range, for example, between 5mv and 15 mv.

In one embodiment of the present invention, the third threshold may be a range, such as 1% to 10%.

In one embodiment of the present invention, in step S1, the method of acquiring the SOC of each of the plurality of batteries may be an open circuit voltage method.

In one embodiment of the present invention, the battery equalization method is applicable to various circuits such as an energy dissipation equalization circuit, an energy transfer equalization circuit, a shunt resistance dissipation type equalization circuit, a capacitance type equalization circuit, an inductance type equalization circuit, and a transformation type equalization circuit.

The invention provides a battery equalization method, which takes voltage and SOC as equalization variables at the same time to comprehensively formulate an equalization method, analyzes and judges the voltage and the SOC by stages, further performs charge-discharge equalization on single batteries, and finally realizes that the consistency of the voltage and the SOC of each single battery in a battery pack meets the expected requirement. The problem that overcharge and overdischarge are easy to occur in a traditional battery balancing method is solved.

The invention simultaneously takes the battery voltage and the SOC as balance variables, can fundamentally improve the consistency of each single battery in the battery pack, and realizes the balance of the voltage and the SOC among the single batteries of the battery pack through three times of balance on the premise of not increasing the program operation and the control complexity. The battery equalization method provided by the invention is simple and reliable, has small online operand, and can obviously improve the safety and reliability of the battery pack, improve the energy utilization rate of the battery pack and prolong the service life of the battery pack.

Of course, it is not necessary for any product in which the invention is practiced to achieve all of the above-described advantages at the same time.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.

FIG. 1 is a schematic flow chart of a battery equalization method according to the present invention;

FIG. 2 is a schematic flow chart of a battery equalization method according to the present invention;

fig. 3 is a system block diagram of a battery equalization method according to the present invention.

Component number:

the system comprises a charger 1, a battery pack 2, a battery 201, a battery 3, a battery charge state detection device, an equalization circuit module 4 and an equalization control module 5.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The invention simultaneously takes the battery voltage and the SOC as balance variables, can fundamentally improve the consistency of each single battery 201 in the battery pack 2, and simultaneously realizes the balance of the voltage and the SOC among the single batteries 201 of the battery pack 2 through multiple times of balance on the premise of not increasing the complexity of program operation and control. The battery equalization method provided by the invention is simple and reliable, has small online operand, can obviously improve the safety and reliability of the battery pack 2, improves the energy utilization rate of the battery pack 2 and prolongs the service life of the battery pack 2.

Referring to fig. 1-2, in the present embodiment, the battery equalization method at least includes the following steps: acquiring the SOC of each battery 201 in a plurality of batteries 201, wherein the batteries 201 form a battery pack 2; (step S1); judging whether to perform rapid charge and discharge on each of the batteries 201 with the SOC less than 10% and the SOC greater than 90% according to a first equalization condition (step S2); judging whether to perform correction charge and discharge on each battery with the SOC greater than 10% and the SOC less than 90% according to a second balance condition (step S3); it is determined whether or not each of the cells 201 in the battery pack 2 is charged and discharged based on a third equalization condition (step S4).

Referring to fig. 1-3, in the present embodiment, the SOC of each battery 201 of the plurality of batteries 201 is first obtained, the plurality of batteries 201 form a battery pack 2, and then the batteries 201 with the SOC less than 10% and the SOC greater than 90% are screened out, and the process proceeds to step S2, where the step S2 includes: s21, setting a first threshold value; s22, screening out the batteries 201 with the SOC less than 10% and the SOC greater than 90%, otherwise, entering the step S3; s23, after the batteries 201 meeting the first equalization circuit condition are screened out, the batteries 201 with the screened-out maximum voltage are quickly discharged, meanwhile, the batteries 201 with the screened-out minimum voltage are quickly charged, otherwise, the method goes to the step S3, and the first equalization condition comprises the following steps: the difference between the screened maximum voltage value of the battery 201 and the screened minimum voltage value of the battery 201 is greater than or equal to the first threshold value. In step 2, the voltage is used as the amount for determining whether the single battery 201 needs to be equalized, because when the battery SOC is less than 10%, that is, when the battery SOC is low, the terminal voltage of the battery 201 rises from the lower voltage limit to the rated voltage end, and if the battery SOC is used as the only equalization variable, the working operating voltage will be rapidly attenuated under the condition of large-current discharge, so that some single batteries 201 may have over-discharge; when the battery SOC is greater than 90%, that is, when the battery SOC is high, the terminal voltage of the battery 201 rises from the rated voltage to the upper voltage limit, and if the SOC is used as the only equalization variable, overcharging of the high-capacity unit battery 201 is likely to occur. The remaining SOC is greater than 10% and less than 90% of the battery 201, and the step S3 is executed, where the step S3 at least includes: 31: setting a second threshold value; s32: screening out the battery 201 with the SOC greater than 10% and the SOC less than 90%; s33: after the batteries 201 meeting the second equalization circuit condition are screened out, the batteries 201 with the screened-out maximum voltage value are quickly discharged, meanwhile, the batteries 201 with the screened-out minimum voltage value are quickly charged, otherwise, the method goes to step S4, and the second equalization condition is as follows: the difference between the screened maximum value of the cell voltage and the screened minimum value of the cell 201 voltage is equal to or greater than the second threshold value. In step S3, the voltage is still used as the amount for determining whether the cell 201 needs to be equalized, so as to further reduce the power difference between the cells 201 in the battery pack 2. Step S4 is to perform balance screening of all the batteries 201, and step S4 includes: s41: setting a third threshold value; s42: acquiring the SOC of each of the plurality of batteries 201; s43: after the batteries 201 meeting a third equalization circuit condition are screened out, discharging the batteries 201 with the SOC of the screened batteries 201 larger than the sum of the average SOC and the third threshold value, and simultaneously charging the batteries with the SOC of the screened batteries 201 smaller than the difference between the average SOC and the third threshold value, otherwise, stopping the battery equalization method, wherein the third equalization condition is as follows: the SOC of the battery 201 is greater than the sum of the average SOC and the third threshold value or the SOC of the battery 201 is less than the difference between the average SOC and the third threshold value. In step S4, the SOC is used as the amount for determining whether the cell 201 needs to be equalized, because the open-circuit voltage changes little when the SOC of the battery is 10% to 90%, that is, during the voltage plateau, and if the voltage is used as the only equalization variable, the difference between the cells 201 is small, but the SOC difference between the cells 201 is large, which will seriously reduce the overall equalization speed, and the erroneous equalization operation is likely to occur under the condition of a sudden change in current.

Referring to fig. 3, in the present embodiment, specifically, in the present embodiment, a plurality of batteries 201 are connected in series to form a battery pack 2.

Referring to fig. 3, in the present embodiment, specifically, in the present embodiment, the battery 201 may be an aluminate battery or a lithium battery.

Referring to fig. 1-2, in the present embodiment, specifically, the step S2 further includes the following steps:

s21, setting a first threshold, which may be determined according to actual situations, where the first threshold may be in a range, for example, 45mv to 55mv, and the first threshold is set to be larger because the voltage difference between the terminals of the single cells 201 participating in the equalization is larger, and if the voltage threshold is set to be too small, the equalization circuit may be activated frequently, resulting in larger energy consumption.

S22, screening out the batteries with the SOC less than 10% and the SOC greater than 90%, otherwise, entering the step S3;

s23, after the batteries 201 meeting the first equalizing circuit condition are selected, the batteries 201 with the selected maximum voltage are quickly discharged, and the batteries 201 with the selected minimum voltage are quickly charged, where the first equalizing circuit condition is: if the difference between the maximum value of the voltage of the screened battery 201 and the minimum value of the voltage of the screened battery 201 is equal to or greater than the first threshold value, the process proceeds to step S3.

Referring to fig. 1-3, in the present embodiment, the step S3 further includes the following steps:

s31: setting a second threshold, which may be determined according to actual conditions, and the second threshold may be a range, for example, between 5mv and 15mv, and the second threshold may be set to be smaller because the difference between the terminal voltages of the single cells 201 after the equalization in step S2 is smaller, and if the second threshold is set to be too large, the equalization circuit may be activated less, and the equalization effect may be less obvious, and the predetermined requirement may not be met.

S32: screening out the battery 201 with the SOC greater than 10% and the SOC less than 90%;

s33: after the batteries 201 meeting the second equalization circuit condition are screened out, the batteries 201 with the screened maximum voltage values are quickly discharged, meanwhile, the batteries 201 with the screened minimum voltage values are quickly charged, and the second equalization condition is as follows: the difference between the maximum value of the voltage of the screened battery 201 and the minimum value of the voltage of the screened battery 201 is equal to or greater than the second threshold value, otherwise, the process proceeds to step S4.

Referring to fig. 1-3, in the present embodiment, the first threshold is greater than the second threshold, and the first threshold is set to be greater than the second threshold because the equalizing body is the battery 201 with the SOC less than 10% and the SOC greater than 90% in step S2, and the voltage difference is also greater in the range of the SOC less than 10% and the SOC greater than 90%, and if the first threshold is set to be greater, the equalizing circuit is frequently started, resulting in greater energy loss. The reason why the second threshold is smaller than the first threshold is that in step S3, the equalization subject is the battery 201 having an SOC greater than 10% and an SOC less than 90%, and the difference between the terminal voltages of the battery cells participating in the equalization within this range is small, and if the second threshold is set too large, the equalization circuit is rarely started, and the equalization effect is not significant enough and does not meet the predetermined requirement.

Referring to fig. 1-2, in the present embodiment, step S1 further includes: the average SOC of the battery pack 2 is calculated from the acquired SOC of each of the plurality of cells 201.

Referring to fig. 1-2, in the present embodiment, the step S4 further includes:

s41: the third threshold value is set, and the third threshold value can be determined according to actual conditions, and can be a range, such as 1% -10%, a smaller settable value with high requirement on voltage equalization, such as 1%, and a larger settable value with lower requirement on voltage equalization, such as 10%.

S42: acquiring the SOC of each of the plurality of batteries 201;

s43: the battery 201 having the SOC of the battery 201 greater than the sum of the average SOC and the third threshold is discharged while the battery 201 having the SOC of the battery 201 less than the difference between the average SOC and the third threshold is charged, if a third equalization circuit condition is satisfied: the SOC of the battery 201 is greater than the sum of the average SOC and the third threshold value and the SOC of the battery 201 is less than the difference between the average SOC and the third threshold value, otherwise, the equalizing circuit stops operating.

Referring to fig. 3, in the present embodiment, the present invention further provides a battery equalization system, which includes:

at least one battery pack 2 comprising a plurality of cells 201, wherein the cells 201 can be aluminum acid cells or lithium cells

The battery state-of-charge detection device 3 is used for acquiring the state of charge of each battery 201 in the plurality of batteries 201, the battery state-of-charge detection device 3 is connected with the battery pack 2, and the battery state-of-charge detection device 3 is composed of a voltage sensor, a current sensor, a communication chip and a storage chip and is used for acquiring the terminal voltage and the working current of each single battery 201 and transmitting the acquired data to the balance control module 5.

The charging and discharging module is used for charging and discharging a plurality of batteries 201, is connected with the battery pack 2 and the battery charge state detection device 3, and comprises a charger 1, an equalization circuit module 4 and an equalization control module 5. The equalization control module 5 receives the data signal transmitted by the battery state of charge monitoring device, and selects different equalization control methods according to different stages of the battery pack 2. The equalizing circuit module 4 may be an equalizing circuit based on a flyback dc converter, and includes at least one isolated multi-winding transformer, a plurality of switching tubes, a plurality of rectifier diodes and a plurality of filter capacitors, for equalizing the electric quantity of each battery cell 201.

When the state of charge is less than 10% and the state of charge is greater than 90%, the charge-discharge module judges whether each battery 201 is charged and discharged quickly or not according to a first balance condition;

when the state of charge is greater than 10% and less than 90%, the charge-discharge module judges whether each battery 201 is charged and discharged quickly according to a second balance condition;

the charging and discharging module determines whether to perform fast charging and discharging on each battery 201 according to a third equalization condition.

Referring to fig. 1-3, in the present embodiment, a battery equalization method is applied to various circuits, such as an energy dissipation equalization circuit, an energy transfer equalization circuit, a shunt resistance dissipation equalization circuit, a capacitance equalization circuit, an inductance equalization circuit, and a transformer equalization circuit.

Specifically, in one embodiment, there is a battery pack 2 formed by connecting 5 lithium iron phosphate batteries in series, and the open-circuit voltage method is used to estimate the SOC of the battery 201, and the screened SOC is less than 10%

And the battery 201 with the SOC greater than 90% enters step 2, in this embodiment, for example, two batteries 201, one of which has an SOC of 95% and the other of which has an SOC of 5%, the SOC of the battery 201 becomes 45% by performing the discharging process on the battery 201 with an SOC of 95%, the SOC of the battery 201 becomes 35% by performing the charging process on the battery 201 with an SOC of 5%, so that the two batteries 201 satisfy the first equalization condition, and the two batteries 201 enter step S3, and in step S3, it is determined whether or not any battery 201 satisfies the condition based on the second equalization condition, and if so, the battery 201 satisfying the maximum value of the condition voltage is discharged. Meanwhile, the battery 201 with the minimum voltage is charged, and the determination of whether the second equalization condition is satisfied is repeated until 5 batteries 201 that are determined not to satisfy the second equalization condition jump to step S4. In step S4, battery 201 having the SOC of battery 201 greater than the sum of the average SOC and the third threshold is discharged while battery 201 having the SOC of battery 201 less than the difference between the average SOC and the third threshold is charged, if the third equalization circuit condition is satisfied: the SOC of the battery 201 is greater than the sum of the average SOC and the third threshold and the SOC of the battery 201 is less than the difference between the average SOC and the third threshold until 5 batteries 201 meet the condition that the SOC is less than the sum of the average SOC and the third threshold and the SOC of 5 batteries 201 is greater than the difference between the average SOC and the third threshold, otherwise, the third equalization circuit stops working.

The preferred embodiments of the invention disclosed above are intended to be illustrative only. The preferred embodiments are not intended to be exhaustive or to limit the invention to the precise embodiments disclosed. Obviously, many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, to thereby enable others skilled in the art to best utilize the invention. The invention is limited only by the claims and their full scope and equivalents.