CN112737015B

CN112737015B - Lithium battery balance control system and control method based on SOC

Info

Publication number: CN112737015B
Application number: CN202011534134.3A
Authority: CN
Inventors: 张传伟; 黄静; 夏占; 李祎坤
Original assignee: Xian University of Science and Technology
Current assignee: Xian University of Science and Technology
Priority date: 2020-12-22
Filing date: 2020-12-22
Publication date: 2023-05-16
Anticipated expiration: 2040-12-22
Also published as: CN112737015A

Abstract

The invention provides a lithium battery equalization control system and method based on SOC, comprising an equalization topological structure circuit, a control unit and a signal acquisition module; the equalization topological structure circuit consists of a battery pack and a power switch connected with the battery pack, the control unit comprises an SOC estimation unit, the signal acquisition module transmits current and voltage signals of the single battery to the control unit, and the SOC estimation unit processes the received signals and converts the signals into SOC values of the single battery; the control unit processes the SOC value and sends a control instruction to the balanced topological structure circuit to control the on-off of the corresponding power switch. In the charging and discharging process, the relationship between the battery SOC value and the threshold value is judged, the battery pack is controlled to alternately charge or discharge, and the balance of the charge and discharge of the single battery is realized. The invention improves the energy utilization rate of the single battery and prolongs the service life of the battery pack. And the invention adopts modularized balanced topological structure circuit, has simple structure and is easy to expand.

Description

Lithium battery balance control system and control method based on SOC

Technical Field

The invention relates to the technical field of battery management systems (Battery Management SyStem, BMS), in particular to a lithium battery balance control SyStem and a lithium battery balance control method based on SOC.

Background

In recent years, new energy automobiles have been stepped into the stage of the era because countries and society are continually promoting environmental protection and saving petroleum resources. The lithium battery is the first choice of the power battery of the electric automobile because of the advantages of large specific energy, no memory effect, long cycle life and the like. Equalization in a battery management system is a control system for determining reasonable charge and discharge of a battery and protecting the battery, and if the battery is not subjected to equalization control, a wooden barrel effect can be easily generated, so that the service life and efficiency of the battery are reduced.

In order to solve the above problems, a battery pack equalization method has been an important point of research. Currently, a common equalization control system uses a battery voltage signal to control by a control unit. As shown in fig. 1, in the case where the equalization control system has four single batteries B1-B4, fifteen power switches S1-S15 are required to be connected in series or in parallel to each other, so as to control the charging of the battery pack. This system has the following disadvantages: the balanced topological structure is complex, and the expansibility is limited; (2) The working voltage is taken as an equalization control variable, and the energy of the battery cannot be fully utilized because the working voltage and the residual electric quantity are not directly related.

In summary, there is room for further improvement in the equalization of battery management systems.

Disclosure of Invention

In order to improve the defects of the conditions, prevent the battery from being overcharged and overdischarged, avoid generating a wooden barrel effect, reduce the failure rate of the battery and improve the electricity safety, the invention provides an equalization control system and a control method based on an SOC lithium battery. In the charging process, the battery pack is controlled to be alternately charged by judging the SOC difference value of the highest SOC single battery and the lowest SOC single battery, so that the SOC value of each single battery reaches the charge cut-off SOC threshold value. In the discharging process of the battery pack, the battery cells with the lowest SOC are replaced by the equalizing batteries to form a new series battery pack to discharge, so that the equalizing of the discharging of the battery cells is realized. The invention improves the defects of low equalization efficiency and high energy loss, improves the energy utilization rate of the single battery, realizes the equalization of the charge and discharge of the battery pack, prevents the overcharge and overdischarge of the single battery, and prolongs the service life of the battery pack. And the invention adopts modularized balanced topological structure circuit to realize the quick conduction or short circuit of a certain single battery, and has simple structure and easy expansion.

In order to achieve the above purpose, the invention provides a lithium battery equalization control system based on SOC, which comprises an equalization topological structure circuit, a control unit and a signal acquisition module; the equalization topological structure circuit consists of a battery pack and a power switch connected with the battery pack, the control unit comprises an SOC estimation unit, the signal acquisition module is connected with the battery pack and the control unit, and the control unit is connected with the signal acquisition module and the equalization topological structure circuit; the signal acquisition module transmits current and voltage signals of the single battery to the control unit, and the received signals are processed and converted into SOC values of the single battery by the SOC estimation unit; and the control unit processes the SOC value and sends a control instruction to the balanced topological structure circuit to control the on-off of the corresponding power switch.

Preferably, the equalization topological structure circuit consists of n+1 single batteries and 2 (n+1) power switches; the n+1 single batteries are divided into n normal working batteries and 1 equalizing battery, wherein n is a positive integer, and n is more than 1.

Preferably, the equalization topological structure circuit is modularized, each module consists of 1 single battery and 2 power switches, and the modules are connected in series.

Preferably, the 2 power switches are a short-circuit switch and a connecting switch respectively, and the on-off relationship of the short-circuit switch and the connecting switch is mutual exclusion.

Preferably, the single battery in each module is connected in series with the connection switch to control the on-off of the single battery, and the connection switch and the single battery are connected in parallel with the short-circuit switch to control the short-circuit of the single battery.

Preferably, in the discharging process, the control unit further performs fault detection, and when the control unit detects that the SOC value of 1 single battery in the whole battery pack is lower than a first threshold value, the control unit controls other n single batteries to be connected in series to form the battery pack for discharging; and when the SOC value of 2 single batteries in the whole battery pack is lower than the first threshold value, controlling the whole battery pack to stop discharging.

Preferably, in the discharging process, when the control unit detects that all the single battery SOC values are higher than a first threshold value, controlling all the single batteries to perform alternate recombination discharging; and the alternate recombination discharge is to replace the single battery with the lowest SOC value in n normal working batteries by the equalizing battery to form a new battery pack for discharging until the SOC value of more than two single batteries is lower than a first threshold value.

Preferably, in the charging process, the control unit controls the equalizing battery to replace a battery cell with the highest SOC value in n battery cells in normal operation, so as to form a new battery pack for charging, and when the SOC value of more than 2 battery cells reaches a third threshold value, the charging is stopped.

Preferably, the first threshold is a single battery discharge cutoff SOC value, preferably 10%; the third threshold is a battery cell discharge cutoff SOC value, preferably 100%.

In addition, the invention also provides a method based on the lithium battery balance control system, which comprises the steps of performing fault detection in the discharging process of the battery pack, and stopping discharging the whole battery pack when more than 2 single battery SOC values are detected to be lower than a first threshold value; when detecting that the SOC value of 1 single battery is lower than a first threshold value, the rest n single batteries are serially discharged until the SOC value of more than 2 single batteries is lower than the first threshold value, stopping discharging; when all the single battery SOC values are detected to be higher than a first threshold value, the whole battery pack is subjected to alternate battery pack recombination discharge; when detecting that the difference value between the highest SOC value and the lowest SOC value of all the single batteries is larger than a second threshold value, replacing the lowest single battery with the SOC value by an equalization control battery to form a new battery pack for discharging; when detecting that the difference value between the highest SOC value and the lowest SOC value of all the single batteries is smaller than a second threshold value, discharging a battery pack consisting of the first n single batteries;

in the charging process of the battery pack, when detecting that the difference value between the highest SOC value and the lowest SOC value of all the single batteries is larger than a third threshold value, replacing the single battery with the highest SOC value in n single batteries which normally work by an equalizing battery to form a new battery pack for charging; when detecting that the difference value between the highest SOC value and the lowest SOC value of all the single batteries is smaller than a third threshold value, connecting the first n single batteries in series to form a battery pack for charging; and in the charging process of all the batteries, stopping charging when the SOC values of more than 2 single batteries reach a third threshold value.

Wherein the first threshold is a discharge cutoff SOC, preferably 10%; the second threshold is an SOC difference threshold, preferably 2%; the third threshold is the charge cutoff SOC, preferably 100%.

The signal acquisition module acquires current and voltage signals of the battery pack and the single battery in real time and transmits the current and voltage signals to the control unit; then, the control unit processes the received current and voltage signals to estimate an SOC value and compares the SOC value with a trigger SOC threshold; and finally, the control unit sends a signal to the SOC balance topological structure circuit to control the on-off of a switch in the balance topological structure circuit, so as to realize the balance function of the control system.

Compared with the prior art, the invention has the following advantages:

(1) The invention estimates the SOC of the single battery through the control unit, judges the charge state of the single battery in the charging and discharging processes, controls the balanced topological structure circuit, avoids the overcharge and overdischarge of the single battery, and improves the service life of the battery and the energy utilization rate;

(2) According to the invention, one single battery is added into the battery pack to serve as an equalizing battery, so that the battery pack is alternately connected with other single batteries in series for discharging under the condition that the charge state of one single battery is low, and the discharging stability of the battery pack is achieved; when in charging, other single batteries are alternately connected in series to charge under the condition that the charge state of one single battery is higher, so that the charge and discharge balance is realized.

(3) The equalization circuit is in a modularized equalization topological structure, each module consists of 1 single battery, a short-circuit switch and a connecting switch, the modules are connected in series, the circuit structure is simple, the cost is low, the expansion is easy, and the application range is wide.

Drawings

FIG. 1 is a circuit diagram of a prior art lithium battery equalization control system;

FIG. 2 is a schematic diagram of a lithium battery equalization control system according to an embodiment of the present invention;

fig. 3 is an exemplary circuit diagram of a lithium battery equalization control system in an embodiment of the present invention;

FIG. 4 is a graph of results of simulation monitoring of the SOC of each battery cell over time using Simulink software during the battery pack charging process of the embodiment of FIG. 2;

FIG. 5 is a graph of the results of simulation monitoring of the SOC of each cell over time using the Simulink software in the first instance of the battery pack discharging process of the embodiment of FIG. 2;

FIG. 6 is a graph of the results of simulation monitoring of the SOC of each cell over time using the Simulink software in case two of the discharging process of the battery pack of the embodiment of FIG. 2;

FIG. 7 is a graph of the results of simulation monitoring of the SOC of each cell over time using the Simulink software in case three of the battery pack discharging process of the embodiment of FIG. 2;

FIG. 8 is a graph of results of simulation monitoring of the SOC of each unit cell over time using the Simulink software in case four of the battery pack discharging process of the embodiment of FIG. 2;

fig. 9 is a charge control flow chart of a lithium battery equalization control system and control method according to an embodiment of the invention;

fig. 10 is a discharge control flow chart of a lithium battery equalization control system and control method according to an embodiment of the present invention;

fig. 11 is a schematic circuit diagram of an equalization topology structure in a lithium battery equalization control system and a control method according to an embodiment of the invention.

Detailed Description

As shown in fig. 2, an embodiment of the present invention provides a lithium battery equalization control system based on SOC, which includes an equalization topology circuit 103, a control unit (micro control unit Microcontroller Unit; MCU) 106, and a signal acquisition module 104. Wherein the equalization topology circuit 103 is composed of a battery pack 101 containing (n+1) unit cells and a power switch 102 connected thereto, and the control unit 106 includes an SOC estimation unit 105; the signal acquisition module 104 is connected with the battery pack 101 and the control unit 106, and the control unit 106 is connected with the signal acquisition module 104 and the equalization topology circuit 103; the signal acquisition module 104 transmits the current and voltage signals of the single battery to the control unit 106, and the received signals are processed and converted into the SOC value of the single battery by the SOC estimation unit 105; the control unit 106 processes the SOC value and sends a control instruction to the equalization topological structure circuit 103 to control the on-off of the corresponding power switch, so that the recombination charge and discharge of the battery pack are realized, and the equalization effect of the SOC is achieved. Wherein n is a positive integer and n >1.

In one embodiment, as shown in fig. 3, the equalization topology circuit 103 is composed of n+1 single cells and 2 (n+1) power switches; wherein n+1 single batteries are divided into n normal working batteries and 1 equalizing battery. The equalization control system further comprises an external power supply module for charging the single batteries in the equalization topological circuit structure.

In one embodiment, taking n=4, the battery pack contains 5 single cells in total, which contains 1 balanced cell. As shown in fig. 2 and 3, during the operation of the system, 4 single cells in the battery pack 101 are charged or discharged, the signal acquisition module 104 acquires current and voltage signals and sends the current and voltage signals to the micro control unit 106, and the micro control unit 106 estimates and processes the transmitted current and voltage signals into SOC signals through the SOC estimation unit 105 and performs a series of control operations. Next, the micro control unit 106 sends a signal to the equalization topology circuit 103, and controls the power switch 102 in the equalization topology circuit 103 to be turned on or off, so as to control the alternation of the unit cells and the equalization cells in the battery pack. The lithium battery balance control system realizes the real-time monitoring of the battery, forms a negative feedback loop, ensures the balance of the battery and prevents overcharge and overdischarge.

In an embodiment, as shown in fig. 3, the balanced topology circuit 103 is modularized, each module is composed of 1 single battery and 2 power switches, and the modules are connected in series, so that the effect of expanding the whole circuit by a user according to an actual application scene is easy.

In an embodiment, the 2 power switches are a short-circuit switch and a connection switch, respectively, where the on-off relationship of the short-circuit switch and the connection switch is mutually exclusive.

In an embodiment, the single battery in each module is connected in series with a connection switch to control the on-off of the single battery, and the connection switch and the single battery are connected in parallel with a short-circuit switch to control the short-circuit of the single battery. Through the circuit connection mode, any single battery in the battery pack can be short-circuited, and the battery pack can be disconnected, so that the danger of battery short circuit caused by the formation of a loop of the battery is avoided.

As shown in fig. 3, in the balanced topology circuit 103, the series battery pack realizes an alternate discharging function between the unit cells by switching on and off of the power switch, wherein the circuit includes a connection switch and a short-circuit switch. In the example in fig. 3, the connection switch is: s1, S2, S3, S4 and S5, and the short-circuit switch is as follows: s6, S7, S8, S9, S10.

In an embodiment, during the discharging process, the control unit 106 further performs fault detection, and when the control unit 106 detects that the SOC value of 1 single battery in the whole battery pack is lower than the first threshold value, the control unit controls the other n single batteries to be connected in series to form the battery pack for discharging; and when the SOC value of 2 single batteries in the whole battery pack is lower than the first threshold value, controlling the whole battery pack to stop discharging.

In an embodiment, during the discharging process, when the control unit 106 detects that the SOC values of all the battery cells are higher than the first threshold value, the control unit controls all the battery cells to perform the alternate recombination discharging; the alternate recombination discharge is to replace the single battery with the lowest SOC value in n normal working batteries by the equalizing battery to form a new battery pack to discharge until more than two single batteries have the SOC value lower than a first threshold value.

In an embodiment, during the charging process, the control unit 106 controls the equalizing battery to replace the cell with the highest SOC value of the n cells that normally operate, so as to form a new battery pack for charging, until the SOC value of more than 2 cells reaches the third threshold value, and the charging is stopped.

In the above process, the MCU compares the estimated SOC value with a threshold value. The first threshold P1 is a single battery discharge cutoff SOC value, and the value thereof is preferably 10%; the second threshold P2 is an SOC difference threshold, preferably 2%; the third threshold value P3 is the charge cutoff SOC, and its value is preferably 100%. In other embodiments, the three thresholds may be adjusted by a manager according to the actual application scenario.

The application principle of the lithium battery balance control system provided by the invention is explained by a specific working process: during the charging process of the battery pack:

1. under the condition that all the five single batteries are smaller than the third threshold value P3, the control unit judges the lowest SOC and the highest SOC and performs difference value operation.

And when the SOC difference value is smaller than or equal to a second threshold value P2, the single batteries No. 1, no. 2, no. 3 and No. 4 are charged in series, and the battery No. 5 is short-circuited. That is, the switches S1, S2, S3, S4, S10, S11 are turned on, that is, the battery pack formed by connecting the unit batteries B1, B2, B3, B4 in series is charged.

When the SOC difference value is equal to or greater than the second threshold value P2:

(1) When the SOC of the battery cell B1 is highest, the switches S6, S2, S3, S4, S5, S11 are turned on, that is, the battery pack formed by connecting the battery cells B2, B3, B4, B5 in series is charged.

(2) When the SOC of the battery cell B2 is highest, the switches S1, S7, S3, S4, S5, S11 are turned on, that is, the battery pack formed by connecting the batteries B1, B3, B4, and B5 in series is charged.

(3) When the SOC of the battery cell B3 is highest, the switches S1, S2, S8, S4, S5, S11 are turned on, that is, the battery pack formed by connecting the batteries B1, B2, B4, and B5 in series is charged.

(4) When the SOC of the battery cell B4 is highest, the switches S1, S2, S3, S9, S5, S11 are turned on, that is, the battery pack formed by connecting the battery cells B1, B2, B3, B5 in series is charged.

(5) When the SOC of the battery cell B5 is highest, the switches S1, S2, S3, S4, S10, S11 are turned on, that is, the battery pack formed by connecting the batteries B1, B2, B3, and B4 in series is charged.

And according to the equalization control scheme, stopping charging until the SOC value of two or more single batteries in the battery pack reaches a third threshold value. In this example, simulation was performed in Simulink software, and the change of the SOC of each unit cell with time under this condition was monitored, and as shown in fig. 4, the initial SOCs of the No. 1, 2, 3, 4, and 5 cells were 5%, 10%, 8%, 12%, and 15%, respectively.

As can be seen from fig. 4, the SOC difference of the battery pack is reduced from 10% to 2%, and finally, the SOC difference of the battery pack is kept within 2% by alternating recharging, thereby achieving the effect of equalization control.

During the discharging process of the battery pack:

1. when the SOC value of any one of the battery cells B1, B2, B3, B4, B5 is smaller than the first threshold value P1, this is the case of the failure detection condition:

(1) When the single battery B1 is smaller than the threshold value P1, the switches S6, S2, S3, S4, S5 and S11 are turned on, and the batteries B2, B3, B4 and B5 are connected in series to form a battery pack to supply power to the load.

(2) When the single battery B2 is smaller than the threshold value P1, the switches S1, S7, S3, S4, S5, S11 are turned on, and the batteries B1, B3, B4, B5 are connected in series to form a battery pack to supply power to the load.

(3) When the single battery B3 is smaller than the threshold value P1, the switches S1, S2, S8, S4, S5 and S11 are turned on, and the batteries B1, B2, B4 and B5 are connected in series to form a battery pack to supply power to the load.

(4) When the single battery B4 is smaller than the threshold value P1, the switches S1, S2, S3, S9, S5, S11 are turned on, and the batteries B1, B2, B3, B5 are connected in series to form a battery pack to supply power to the load.

(5) When the single battery B5 is smaller than the threshold value P1, the switches S1, S2, S3, S4, S10, S11 are turned on, and the batteries B1, B2, B3, B4 are connected in series to form a battery pack to supply power to the load.

In this example, simulation was performed in Simulink software, and the change of the SOC of each unit cell with time under this condition was monitored, and as shown in fig. 5, initial SOCs of No. 1, 2, 3, 4, and 5 were 95%, 90%, 85%, 80%, and 5%, respectively.

At this time, only the SOC of the No. 5 single battery is less than 10% of the first threshold, and the No. 1, 2, 3, and 4 batteries in the battery pack can still be discharged in series. After 2500 seconds of discharge, when the SOC of the No. 4 cell is less than 10%, the entire battery pack is discharged, and the SOC of each cell remains unchanged.

2. When the SOC value of two or more of the unit batteries B1, B2, B3, B4, B5 is smaller than the first threshold value P1, all the connection switches and the short-circuit switches are turned off, and the battery pack stops discharging. This case is the case two of the fault detection condition:

in this example, simulation was performed in the Simulink software, and the change of the SOC of each unit cell with time under this condition was monitored, and as shown in fig. 6, the initial SOCs of the No. 1, 2, 3, 4, and 5 cells were 95%, 90%, 85%, 8%, and 5%, respectively.

At this time, the SOC of the number 4 and the number 5 single batteries in the battery pack is lower than the first threshold by 10%, and the control unit controls the equalizing circuit to turn off all the switches and not supply power to the load.

3. When the SOC values of the battery cells B1, B2, B3, B4, B5 are all greater than or equal to the first threshold value P1, the control unit determines the lowest SOC and the highest SOC, and performs a difference operation.

And when the SOC difference value is smaller than or equal to a second threshold value P2, the single batteries No. 1, no. 2, no. 3 and No. 4 are charged in series, and the battery No. 5 is short-circuited. That is, the switches S1, S2, S3, S4, S10, S11 are turned on, that is, the battery pack formed by connecting the unit batteries B1, B2, B3, B4 in series is discharged.

When the SOC difference value is equal to or greater than the second threshold value P2 (case three),

(1) When the SOC of the single battery B1 is lowest, the switches S6, S2, S3, S4, S5, S11 are turned on, and the batteries B2, B3, B4, B5 are connected in series to form a battery pack to supply power to the load.

(2) When the SOC of the battery cell B2 is lowest, the switches S1, S7, S3, S4, S5, S11 are turned on, and the batteries B1, B3, B4, B5 are connected in series to form a battery pack to supply power to the load.

(3) When the SOC of the battery cell B3 is lowest, the switches S1, S2, S8, S4, S5, S11 are turned on, and the batteries B1, B2, B4, B5 are connected in series to form a battery pack to supply power to the load.

(4) When the SOC of the battery cell B4 is lowest, the switches S1, S2, S3, S9, S5, S11 are turned on, and the batteries B1, B2, B3, B5 are connected in series to form a battery pack to supply power to the load.

(5) When the SOC of the battery cell B5 is lowest, the switches S1, S2, S3, S4, S10, S11 are turned on, and the batteries B1, B2, B3, B4 are connected in series to form a battery pack to supply power to the load.

In this example, simulation was performed in Simulink software, and the change of the SOC of each unit cell with time under this condition was monitored, and as shown in fig. 7, initial SOCs of No. 1, 2, 3, 4, and 5 were 95%, 90%, 85%, 80%, and 75%, respectively.

When the discharge is started, the SOC of each single battery is larger than the first threshold value by 10%, and the initial SOC difference value is 20%. With the implementation of the alternate recombination discharge scheme, the SOC difference of the battery pack is gradually reduced to 2% at about 2500S. And in the subsequent discharging process, the SOC difference value is kept within 2% until the discharging is finished, so that the effect of discharging balance control is achieved.

4. The equalization control principle is the same as the third case, but the SOC values of 5 single batteries are 100% (the fourth case), and the simulation result in Simulink is shown in fig. 8.

As shown in fig. 8, 5 single cells are alternately recombined and discharged, so that the SOC difference of the battery pack is always controlled within 2%. And the discharge time reaches 4080S, exceeds the theoretical discharge time 3600S of 4 single batteries in series connection, and the scheme not only achieves the effect of balance control, but also increases the working time of the battery pack.

In addition, in an embodiment, the invention further provides a control method based on the lithium battery balance topological structure control system, which comprises the following steps:

in the discharging process of the battery pack, fault detection is carried out, and when more than 2 single batteries are detected to be lower than a first threshold value in SOC value, the whole battery pack stops discharging; when detecting that the SOC value of 1 single battery is lower than a first threshold value, the rest n single batteries are serially discharged until the SOC value of more than 2 single batteries is lower than the first threshold value, stopping discharging; when all the single battery SOC values are detected to be higher than a first threshold value, the whole battery pack is subjected to alternate battery pack recombination discharge; when detecting that the difference value between the highest SOC value and the lowest SOC value of all the single batteries is larger than a second threshold value, replacing the lowest single battery with the SOC value by an equalization control battery to form a new battery pack for discharging; when detecting that the difference value between the highest SOC value and the lowest SOC value of all the single batteries is smaller than a second threshold value, discharging a battery pack consisting of the first n single batteries;

Wherein the first threshold is a single battery discharge cut-off SOC value, preferably 10%; the second threshold is an SOC difference threshold, preferably 2%; the third threshold value is a charge cutoff SOC value, preferably 100%.

As shown in fig. 9, in a charge control flow implemented by the lithium battery equalization control system and the control method of the present invention, firstly, a battery pack with 4 serial single batteries is charged, a signal acquisition module 104 sends acquired current and voltage signals to a control unit 106, an SOC estimation unit 105 in the control unit 106 processes the signals and obtains SOC values of each single battery, and performs difference value operation on the highest and lowest SOC values to determine whether the difference value exceeds a second threshold value P2, if yes, a control equalization circuit 103 temporarily stops charging the single battery with the lowest SOC value, and uses 1 equalization battery to be charged in series with other 3 single batteries to implement an alternate charging function; if the SOC of the battery cell reaches the third threshold P3, the equalization circuit 103 is controlled to charge the battery cell reaching the third threshold if the SOC of the battery cell reaches the third threshold P3, and the battery cell reaches the third threshold P2. Until two or more single-body powers satisfy the threshold value P3, all the power switches 102 of the equalizing circuit 103 are controlled to be turned off, and charging is ended.

As shown in fig. 10, in a discharging control flow implemented by the lithium battery equalization control system and the control method of the present invention, firstly, a battery pack with 4 cells connected in series discharges a load, a signal acquisition module 104 sends acquired current and voltage signals to a control unit 106, an SOC estimation unit 105 in the control unit 106 processes the signals and obtains SOC values of each cell, if the SOC of the cell is lower than a first threshold P1, the number of cells lower than the first threshold P1 is determined, and if the SOC of only one cell is lower than the first threshold P1, the equalization circuit 103 is controlled to stop discharging the cell, and the other 3 cells connected in series by the equalization cell continue to supply power to the load; if the number of the single batteries below the first threshold P1 is greater than 1, the equalizing circuit 103 is controlled to turn off all the switches, ending the power supply to the load.

If the SOC of the single battery is higher than the first threshold value P1, the control unit 106 determines whether the SOC difference value is greater than or equal to the second threshold value P2, and if the SOC difference value is greater than or equal to the second threshold value P2, the control equalization circuit 103 pauses the discharging of the single battery with the lowest SOC value, and the equalization battery is connected with the other 3 single batteries in series to continue to supply power to the load; if the SOC difference is smaller than the second threshold P2, the power switch 102 in the equalization topology circuit 103 is controlled to be turned on or off, so that the series discharge of the first 4 single batteries is realized.

Fig. 11 shows an equalization topology circuit 103 used in a lithium battery equalization control system and a control method according to the present invention. Wherein there are (n+1) single cells, wherein the switch S ₁ To S _n+1 For connecting the switch, a serial circuit corresponding to the single battery is realized; switch S _n+2 To S _2n+2 The short-circuit switch can be used for short-circuiting any single battery in the battery pack, and also can be used for disconnecting the single battery in the battery pack, so that the battery is prevented from forming a loop, and the danger of short-circuiting the battery is avoided. It can be seen that the balanced topology circuit 103 is modularized, and is formed by modules connected in series, each module is formed by mutually exclusive switches and battery cells, so that the connection or short circuit of the single battery is realized, the structure is simple, and the expansion is easy. The single battery in each module is connected in series with a connecting switch to control the on-off of the single battery, and the connecting switch and the single battery are connected in parallel with a short-circuit switch which is mutually exclusive to the short-circuit switch so as to control the short-circuit of the single battery. The circuit diagram shows that the lithium battery equalization topological structure circuit is extensible and can be applied to series battery packs with different numbers. The circuit has simple structure, easy expansion and high battery energy utilization rate.

In summary, the SOC of a single battery is estimated in the control unit, the state of charge of the single battery in the charging and discharging processes is judged, the control unit is utilized to control the equalizing circuit, and the equalizing single battery is added in the battery pack, so that the battery pack is alternately connected with other single batteries in series for discharging under the condition that the state of charge of one single battery is lower, and the discharging stability of the battery pack is achieved; when in charging, other single batteries are alternately connected in series to charge under the condition that the charge state of one single battery is higher, so that the overcharge phenomenon is prevented, and the charge and discharge balance is realized. Meanwhile, the equalization circuit is of an equalization topological structure, is simple in structure, low in cost, easy to expand and wide in application range, avoids overcharge and overdischarge of the single battery, and prolongs the service life of the battery and improves the energy utilization rate of the battery.

The present invention has been described in detail with reference to the drawings and embodiments, and various modifications of the invention can be made by those skilled in the art based on the above description. Accordingly, the invention is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims.

Claims

1. An SOC-based lithium battery equalization control system, comprising: the system comprises an equalization topological structure circuit, a control unit and a signal acquisition module; the equalization topological structure circuit consists of a battery pack and a power switch connected with the battery pack, the control unit comprises an SOC estimation unit, the signal acquisition module is connected with the battery pack and the control unit, and the control unit is connected with the signal acquisition module and the equalization topological structure circuit; the signal acquisition module transmits current and voltage signals of the single battery to the control unit, and the received signals are processed and converted into SOC values of the single battery by the SOC estimation unit; the control unit processes the SOC value and sends a control instruction to the equalization topological structure circuit to control the on-off of the corresponding power switch so as to control the alternation of the single batteries and the equalization batteries in the battery pack;

the equalization topological structure circuit consists of n+1 single batteries and 2 (n+1) power switches; the n+1 single batteries are divided into n normal working batteries and 1 equalizing battery, wherein n is a positive integer, and n is more than 1;

in the charging process, the control unit controls the balanced battery to replace a single battery with the highest SOC value in n single batteries which normally work to form a new battery pack for charging; when detecting that the difference value between the highest SOC value and the lowest SOC value of all the single batteries is smaller than a third threshold value, connecting the first n single batteries in series to form a battery pack for charging; stopping charging until the SOC value of more than 2 single batteries reaches a third threshold value;

in the discharging process, the control unit also performs fault detection, and when the control unit detects that the SOC value of 1 single battery in the whole battery pack is lower than a first threshold value, the control unit controls other n single batteries to be connected in series to form the battery pack for discharging; when the SOC value of 2 single batteries in the whole battery pack is lower than a first threshold value, controlling the whole battery pack to stop discharging;

in the discharging process, when the control unit detects that the SOC values of all the single batteries are higher than a first threshold value, controlling all the single batteries to carry out alternate recombination discharging; and the alternate recombination discharge is to replace the single battery with the lowest SOC value in n normal working batteries by the equalizing battery to form a new battery pack for discharging until the SOC value of more than two single batteries is lower than a first threshold value.

2. The lithium battery equalization control system of claim 1, wherein the equalization topology circuit is modular, each module is composed of 1 single battery and 2 power switches, and the modules are connected in series.

3. The lithium battery equalization control system according to claim 2, wherein the 2 power switches are a short-circuit switch and a connection switch, and the connection and disconnection relationship of the short-circuit switch and the connection switch are mutually exclusive.

4. The lithium battery equalization control system of claim 3, wherein the cells in each module are connected in series with the connection switch to control the on-off of the cells, and the connection switch and the cells are connected in parallel with a short circuit switch to control the shorting of the cells.

5. The lithium battery equalization control system of claim 1, wherein the first threshold is a battery cell discharge cutoff SOC value of 10%; the third threshold is a single battery discharge cut-off SOC value of 100%.

6. A control method based on the lithium battery balance control system according to any one of claims 1 to 5, characterized in that:

in the discharging process of the battery pack, fault detection is carried out, and when more than 2 single batteries are detected to be lower than a first threshold value in SOC value, the whole battery pack stops discharging; when detecting that the SOC value of 1 single battery is lower than a first threshold value, the rest n single batteries are serially discharged until the SOC value of more than 2 single batteries is lower than the first threshold value, stopping discharging; when all the single battery SOC values are detected to be higher than a first threshold value, the whole battery pack is subjected to alternate battery pack recombination discharge; the alternate recombination discharge is to replace the single battery with the lowest SOC value in n normal working batteries by the equalizing battery to form a new battery pack to discharge until more than two single batteries have the SOC value lower than a first threshold value; when detecting that the difference value between the highest SOC value and the lowest SOC value of all the single batteries is larger than a second threshold value, replacing the lowest single battery with the SOC value by an equalization control battery to form a new battery pack for discharging; when detecting that the difference value between the highest SOC value and the lowest SOC value of all the single batteries is smaller than a second threshold value, discharging a battery pack consisting of the first n single batteries;

in the charging process of the battery pack, when detecting that the difference value between the highest SOC value and the lowest SOC value of all the single batteries is larger than a third threshold value, replacing the single battery with the highest SOC value in n single batteries which normally work by an equalizing battery to form a new battery pack for charging; when detecting that the difference value between the highest SOC value and the lowest SOC value of all the single batteries is smaller than a third threshold value, connecting the first n single batteries in series to form a battery pack for charging; in the charging process of all the batteries, stopping charging when the SOC values of more than 2 single batteries reach a third threshold value;

wherein the first threshold is a discharge cutoff SOC of 10%; the second threshold is an SOC difference threshold of 2%; the third threshold is the charge cutoff SOC, which is 100%.