CN112737015A

CN112737015A - Lithium battery equalization control system and control method based on SOC

Info

Publication number: CN112737015A
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: 2021-04-30
Anticipated expiration: 2040-12-22
Also published as: CN112737015B

Abstract

The invention provides a lithium battery equalization control system and method based on SOC (system on chip), which comprises an equalization topological structure circuit, a control unit and a signal acquisition module; the control unit comprises an SOC estimation unit, the signal acquisition module transmits current and voltage signals of the single batteries to the control unit, and the SOC estimation unit processes the received signals and converts the signals into SOC values of the single batteries; the control unit processes the SOC value and sends a control instruction to the balanced topology structure circuit to control the on-off of the corresponding power switch. In the charging and discharging processes, the relation between the SOC value of the battery and the threshold value is judged, the battery pack is controlled to alternately charge or discharge, and the charging and discharging balance 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. In addition, the invention adopts a modularized balanced topological structure circuit, has simple structure and is easy to expand.

Description

Lithium battery equalization control system and control method based on SOC

Technical Field

The invention relates to the technical field of Battery Management Systems (BMS), in particular to a SyStem and a method for controlling lithium Battery equalization based on SOC.

Background

Since the country and society continuously advocate environmental protection and oil resource saving, new energy vehicles have entered the era stage in recent years. 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. The balance in the battery management system is a control system which determines the reasonable charge and discharge of the battery and protects the battery, if the battery is not subjected to balance control, the wooden barrel effect can be easily generated, and the service life and the efficiency of the battery are reduced.

In order to solve the above problems, a battery pack balancing method has been studied. Currently, a common equalization control system utilizes a battery voltage signal to perform control through a control unit. As shown in fig. 1, in the case of the equalization control system having four unit batteries, such as B1-B4, fifteen power switches, such as S1-S15, are required to be connected in series or in parallel to each other to control charging of the battery pack. This system has the following disadvantages: (1) the balanced topological structure is complex, and the expansibility is limited; (2) the working voltage is used as a balance 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 conclusion, there is room for further improvement in the way of balancing the battery management system.

Disclosure of Invention

In order to overcome the defects of the above situations, prevent the overcharge and the overdischarge of the battery, avoid the wooden barrel effect, reduce the fault rate of the battery and improve the electricity utilization safety, the invention provides a lithium battery balance control system and a control method based on SOC. 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, and the SOC value of each single battery reaches the charging cut-off SOC threshold value. In the discharging process of the battery pack, the balancing battery replaces the single battery with the lowest SOC to form a new series battery pack for discharging, and the discharging balance of the single batteries is realized. The invention improves the defects of low balancing efficiency and high energy loss, improves the energy utilization rate of the single battery, realizes the charging and discharging balance of the battery pack, prevents the over-charging and over-discharging of the single battery, and prolongs the service life of the battery pack. In addition, the invention adopts a modularized balanced topological structure circuit, realizes quick conduction or short circuit of a certain single battery, and has simple structure and easy expansion.

In order to achieve the aim, 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 balancing topological structure circuit comprises 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 balancing topological circuit; 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 processed signals into an SOC value of the single battery; 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 a corresponding power switch.

Preferably, the balanced topology circuit is composed 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 balancing battery, wherein n is a positive integer and is greater than 1.

Preferably, the balanced topology structure circuit is modularized, each module is composed 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 connection switch respectively, and the on-off relationship of the short-circuit switch and the connection 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, controls the other n single batteries to be connected in series to form the battery pack to discharge; and when the SOC values of 2 single batteries in the whole battery pack are lower than a first threshold value, controlling the whole battery pack to stop discharging.

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

Preferably, in the charging process, the control unit controls the equalizing battery to replace the single battery with the highest SOC value among the n normally operating single batteries to form a new battery pack for charging, and the charging is stopped until the SOC value of more than 2 single batteries reaches a third threshold value.

Preferably, the first threshold is a cell discharge cut-off SOC value, preferably 10%; the third threshold is a discharge cut-off SOC value of the unit battery, and is preferably 100%.

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

in the charging process of the battery pack, when the difference value between the highest SOC value and the lowest SOC value of all the single batteries is detected to be larger than a third threshold value, the single battery with the highest SOC value in the n normally working single batteries is replaced by the equalizing battery to form a new battery pack for charging; when 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, the first n single batteries are connected in series to form a battery pack for charging; and in the charging process of all the batteries, when the SOC value of more than 2 single batteries reaches a third threshold value, stopping charging.

Wherein the first threshold is a discharge cut-off SOC, preferably 10%; the second threshold is an SOC difference threshold, preferably 2%; the third threshold value is a charge cut 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 value; and finally, the control unit sends a signal to the SOC balancing topological structure circuit to control the on-off of a switch in the balancing topological structure circuit, so that the balancing function of the control system is realized.

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

(1) the SOC of the single battery is estimated through the control unit, the charge state of the single battery in the charging and discharging processes is judged, the balanced topological structure circuit is controlled, the overcharge and over-discharge of the single battery are avoided, the service life of the battery is prolonged, and the utilization rate of energy is improved;

(2) according to the invention, a single battery is added in the battery pack as the equalizing battery, so that other single batteries are alternately connected in series for discharging under the condition that the charge state of a certain single battery is lower, and the discharging stability of the battery pack is achieved; when charging, under the condition that the charge state of a certain single battery is high, other single batteries are alternately connected in series for charging, and the charge-discharge balance is realized.

(3) The balancing circuit in the invention is a modular balancing topological structure, each module consists of 1 single battery, a short-circuit switch and a connecting switch, and all the modules are connected in series.

Drawings

FIG. 1 is a circuit diagram of a conventional 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 according to an embodiment of the present invention;

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

fig. 5 is a graph showing the results of monitoring the change of the SOC of each unit cell with time by simulation using Simulink software in case one of the battery pack discharging process of the embodiment of fig. 2;

fig. 6 is a graph showing the results of monitoring the change of the SOC of each battery cell with time by simulation using Simulink software in case two of the battery pack discharging process of the embodiment of fig. 2;

fig. 7 is a graph showing the results of monitoring the change of the SOC of each unit cell with time by simulation using Simulink software in case three of the battery pack discharging process of the embodiment of fig. 2;

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

fig. 9 is a charge control flow diagram of a lithium battery equalization control system and control method according to an embodiment of the present 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 a balancing topology structure in a lithium battery balancing control system and a control method according to an embodiment of the present invention.

Detailed Description

As shown in fig. 2, an embodiment of the present invention provides an SOC-based lithium battery equalization control system, which includes an equalization topology circuit 103, a control Unit (MCU) 106, and a signal acquisition module 104. The balancing topological structure circuit 103 is composed of a battery pack 101 containing (n +1) single batteries and a power switch 102 connected with the battery pack, and the control unit 106 comprises 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 balanced 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 SOC estimation unit 105 processes the received signals and converts the processed signals into the SOC value of the single battery; the control unit 106 processes the SOC value and sends a control instruction to the balanced topology circuit 103 to control the on/off of the corresponding power switch, so as to realize the recombination charge and discharge of the battery pack and achieve the SOC balancing effect. 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 the n +1 single batteries are divided into n normal working batteries and 1 balancing battery. In the above equalization control system, the external power module is further included to charge the single battery in the equalization topology circuit structure.

In one embodiment, if n is 4, the battery pack includes a total of 5 single cells, including 1 balancing cell. As shown in fig. 2 and 3, in the system operation process, 4 single batteries in the battery pack 101 are charged or discharged, the signal acquisition module 104 acquires current and voltage signals and transmits 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 balancing topology circuit 103 to control the on/off of the power switch 102 in the balancing topology circuit 103, so as to control the alternation of the single batteries and the balancing batteries in the battery pack. The lithium battery balance control system realizes 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 balancing topology circuit 103 is modularized, each module is composed of 1 battery cell and 2 power switches, and the modules are connected in series, so that a user can easily expand the whole circuit according to an actual application scenario.

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

In one embodiment, 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 is connected in parallel with the single battery and the 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 short circuit of the battery caused by the fact that the battery forms a loop is avoided.

As shown in fig. 3, in the balancing topology circuit 103, the series battery pack realizes the alternate discharge function between the single batteries by switching on and off the power switch, wherein the circuit includes a connection switch and a short-circuit switch. In the example in fig. 3, the connection switches are: s1, S2, S3, S4 and S5, wherein the short-circuit switch is as follows: s6, S7, S8, S9 and 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 battery cell in the entire battery pack is lower than a first threshold, controls the other n battery cells to be connected in series to form the battery pack to discharge; and when the SOC values of 2 single batteries in the whole battery pack are lower than a first threshold value, controlling the whole battery pack to stop discharging.

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

In an embodiment, during the charging process, the control unit 106 controls the equalizing battery to replace the single battery with the highest SOC value among the n single batteries which normally work, so as to form a new battery pack for charging, and the charging is stopped until the SOC values of more than 2 single batteries reach the third threshold value.

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

The application principle of the lithium battery equalization control system provided by the invention is explained through a specific working process as follows: in the charging process of the battery pack:

1. and under the condition that all 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 operation.

When the SOC difference value is less 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 No. 5 battery is short-circuited. Namely, switches S1, S2, S3, S4, S10 and S11 are turned on, namely, a battery pack formed by connecting the single batteries B1, B2, B3 and B4 in series is charged.

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

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

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

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

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

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

And according to the balance control scheme, stopping charging until the SOC values of two or more single batteries in the battery pack reach a third threshold value. In this example, the simulation was performed in Simulink software, and the SOC of each cell was monitored over time under the conditions, as shown in fig. 4, and the initial SOC of batteries No. 1, 2, 3, 4, and 5 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 within 2%, and finally the SOC difference of the battery pack is maintained within 2% by the alternate recombination charging, thereby achieving the effect of the equalization control.

In the discharging process of the battery pack:

1. when the SOC value of any one of the unit batteries B1, B2, B3, B4, and B5 is smaller than the first threshold P1, this is the case one of the fault detection conditions:

(1) when the single battery B1 is smaller than the threshold 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 a load.

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

(3) When the single battery B3 is smaller than the threshold 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 a load.

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

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

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

At the moment, the SOC of the No. 5 single battery is less than the first threshold value of 10%, and the No. 1, 2, 3 and 4 batteries in the battery pack can still be discharged in series. After 2500s of discharge, when the SOC of the No. 4 single battery is less than 10%, the whole battery pack finishes discharging, and the SOC of each single battery is kept unchanged.

2. When the SOC values of two or more of the unit batteries B1, B2, B3, B4, and B5 are smaller than the first threshold 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, the simulation was performed in Simulink software in which the SOC of each cell was monitored over time, and as shown in fig. 6, the initial SOC of batteries nos. 1, 2, 3, 4, and 5 were 95%, 90%, 85%, 8%, and 5%, respectively.

At the moment, the SOC of the No. 4 and No. 5 single batteries in the battery pack is lower than the first threshold value by 10%, and the control unit controls the balancing circuit to disconnect all the switches and does not supply power to the load.

3. When the SOC values of the single batteries B1, B2, B3, B4 and B5 are all larger than or equal to a first threshold value P1, the control unit judges the lowest SOC and the highest SOC and carries out difference operation.

When the SOC difference value is less 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 No. 5 battery is short-circuited. Namely, switches S1, S2, S3, S4, S10 and S11 are turned on, namely, the battery pack formed by the unit batteries B1, B2, B3 and 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 the lowest, 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 a load.

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

(3) When the SOC of the single battery B3 is the lowest, 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 a load.

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

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

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

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

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

As shown in fig. 8, 5 single batteries are alternately discharged in a recombination manner, so that the SOC difference of the battery pack is always controlled within 2%. And the discharge time reaches 4080S, which exceeds the theoretical discharge time 3600S of the series connection of 4 single batteries, 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 present invention further provides a control method based on a lithium battery balancing topology control system, including:

during the discharging process of the battery pack, fault detection is carried out, and when more than 2 single batteries with SOC values lower than a first threshold value are detected, the whole battery pack stops discharging; when detecting that the SOC value of 1 single battery is lower than a first threshold value, discharging the rest n single batteries in series until the SOC value of more than 2 single batteries is lower than the first threshold value; when detecting that the SOC values of all the single batteries are higher than a first threshold value, the whole battery pack carries out alternate battery pack recombination discharge; when the difference value between the highest SOC value and the lowest SOC value of all the single batteries is detected to be larger than a second threshold value, the balance control battery replaces the single battery with the lowest SOC value to form a new battery pack to discharge; when 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, the battery pack consisting of the first n single batteries discharges;

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

As shown in fig. 9, in the charging 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 is charged, the signal acquisition module 104 sends the acquired current and voltage signals to the control unit 106, the SOC estimation unit 105 in the control unit 106 processes the signals and obtains the SOC value of each cell, and performs a difference operation on the highest and lowest SOC values to determine whether the difference exceeds the second threshold P2, if so, the equalization circuit 103 is controlled to temporarily stop charging the cell with the lowest SOC value, and 1 equalization battery is connected in series with other 3 cells to implement an alternate charging function; if the SOC of the single battery is lower than the second threshold P2, it is determined whether the SOC of the single battery reaches a charge cut-off threshold P3, that is, a third threshold P3, and if only one single battery reaches, the equalizing circuit 103 is controlled to end the charging of the single battery reaching the third threshold, and continue to charge other single batteries. And controlling all the power switches 102 of the equalizing circuit 103 to be switched off until two or more single batteries meet the threshold value P3, and finishing charging.

As shown in fig. 10, in a discharging control flow implemented by the lithium battery balancing control system and the control method of the present invention, firstly, a battery pack with 4 cells connected in series is discharged to 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 an SOC value of each cell, if the SOC of a cell is lower than a first threshold P1, the number of cells lower than the first threshold P1 is determined, if the SOC of only one cell is lower than a first threshold P1, a balancing circuit 103 is controlled to stop discharging of the cell, and the balancing cell is connected in series with other 3 cells to continue supplying power to the load; if the number of the single batteries lower than the first threshold P1 is greater than 1, the balancing circuit 103 is controlled to open all the switches, and the power supply to the load is ended.

If the SOC of the single battery is higher than the first threshold P1, the control unit 106 determines whether the SOC difference is greater than or equal to a second threshold P2, and if the SOC difference is greater than or equal to the second threshold P2, the balancing circuit 103 is controlled to suspend the discharging of the single battery with the lowest SOC value, and the balancing battery is connected in series with the other 3 single batteries to continue to supply power to the load; and if the SOC difference value is smaller than a second threshold value P2, controlling the on-off of a power switch 102 in the balanced topology structure circuit 103 to realize the series discharge of the first 4 single batteries.

Fig. 11 shows an equalization topology circuit 103 used in the lithium battery equalization control system and control method according to the present invention. Wherein there are (n +1) single cells, wherein switch S₁To S_n+1The series circuit of the corresponding single batteries is realized for connecting the switch; switch S_n+2To S_2n+2The short-circuit switch can short-circuit any single battery in the battery pack and can also disconnect the single battery in the battery pack, so that the battery is prevented from forming a loop, and the danger of short circuit of the battery is avoided. It can be seen that the balanced topology circuit 103 is modularized, and is composed of modules connected in series, each module is composed of mutually exclusive switches and a single battery, so as to implement conduction or short circuit of the single battery, and the balanced topology circuit is simple in structure and easy to expand. The single battery in each module is connected with the connecting switch in series to control the on-off of the single battery, and the connecting switch is connected with the mutually exclusive short-circuit switch of the single battery and the relative short-circuit switch in parallel to controlAnd making the single battery short-circuited. The circuit diagram shows that the lithium battery balancing topological structure circuit can be expanded and can be applied to series battery packs with different numbers. The circuit structure is simple, the expansion is easy, and the utilization rate of the battery energy is high.

In summary, the SOC of the 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 used for controlling 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 a certain single battery is lower, and the discharging stability of the battery pack is achieved; when charging, under the condition that the charge state of a certain single battery is higher, the single batteries are alternately connected in series to charge, so that the overcharge phenomenon is prevented, and the charge-discharge balance is realized. Meanwhile, the equalizing circuit in the invention is an equalizing topological structure, has simple circuit structure, low cost, easy expansion and wide application range, avoids overcharge and overdischarge of the single battery, and improves the service life of the battery and the utilization rate of energy.

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

Claims

1. A lithium battery equalization control system based on SOC is characterized by comprising: the device comprises a balanced topological structure circuit, a control unit and a signal acquisition module; the balancing topological structure circuit comprises 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 balancing topological circuit; and

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 processed signals into an SOC value of the single battery; 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 a corresponding power switch.

2. The lithium battery equalization control system according to claim 1, wherein the equalization topology circuit is composed 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 balancing battery, wherein n is a positive integer and is greater than 1.

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

4. The lithium battery equalization control system of claim 3, wherein the 2 power switches are a short-circuit switch and a connection switch, and the on-off relationship between the short-circuit switch and the connection switch is mutually exclusive.

5. The lithium battery equalization control system as claimed in claim 4, wherein 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.

6. The lithium battery equalization control system according to claim 1, wherein during 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 entire battery pack is lower than a first threshold value, controls the other n single batteries to be connected in series to form the battery pack for discharging; and when the SOC values of 2 single batteries in the whole battery pack are lower than a first threshold value, controlling the whole battery pack to stop discharging.

7. The lithium battery equalization control system according to claim 6, wherein in the discharging process, when the control unit detects that the SOC values of all the single batteries are higher than the first threshold value, all the single batteries are controlled to perform alternate recombination discharging; and the alternate recombination discharge is realized by replacing the single battery with the lowest SOC value in the n normal working batteries with the balance battery to form a new battery pack for discharge, and the discharge is stopped until the SOC values of more than two single batteries are lower than a first threshold value.

8. The lithium battery equalization control system of claim 1, wherein in the charging process, the control unit controls the equalization battery to replace the single battery with the highest SOC value in the n normally operating single batteries to form a new battery pack for charging, and the charging is stopped until the SOC values of more than 2 single batteries reach a third threshold value.

9. The lithium battery equalization control system according to claim 6 or 8, characterized in that the first threshold value is a cell discharge cut-off SOC value, preferably 10%; the third threshold is a discharge cut-off SOC value of the unit battery, and is preferably 100%.

10. A control method for a lithium battery equalization control system according to any one of claims 1 to 9, characterized in that:

in the charging process of the battery pack, when the difference value between the highest SOC value and the lowest SOC value of all the single batteries is detected to be larger than a third threshold value, the single battery with the highest SOC value in the n normally working single batteries is replaced by the equalizing battery to form a new battery pack for charging; when 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, the first n single batteries are connected in series to form a battery pack for charging; in the charging process of all the batteries, when the SOC values of more than 2 single batteries reach a third threshold value, stopping charging;