A battery passive balancing control method

Abstract

The present invention relates to a battery passive balancing control method. Firstly, various information in the circuit, such as current, voltage, temperature and single cell voltage, is collected. Then, whether it is suitable to enter balancing is determined according to temperature and voltage conditions. Then, batteries that need to be balanced are selected and grouped. Adjacent battery cells with balancing are correspondingly dispersed so that adjacent single cells do not start balancing at the same time. This avoids mutual interference of balancing currents and excessive concentration of heat generated by discharge of the balancing circuit. The balancing method is simple and easy to implement. It also has the advantages of real-time balancing of charge and discharge, scientific screening of batteries that need to be balanced, low heat generation of the balancing circuit, low cost and high balancing efficiency.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery pack battery management, and more specifically relates to a battery passive balancing control method. Background Art

[0002] In a battery pack composed of lithium batteries connected in series, due to the individual differences of the cells, an imbalance will appear between the cells after several charge and discharge cycles, which manifests as a voltage difference between the cells. If this imbalance is not eliminated in time, the performance of the entire battery pack will be reduced, and even accidents such as leakage, combustion, and explosion will occur.

[0003] The existing balancing methods include active balancing and passive balancing:

[0004] 1) Active balancing is energy transfer balancing. The usual practice is to transfer the energy of a single cell with high energy to that of a single cell with low energy, or to use the energy of the entire battery pack to supplement the battery with the lowest energy. The control circuit is complex, the controller is large in size, the cost is high, and the control algorithm is complex. It is difficult to open multiple channels at the same time, resulting in low balancing efficiency. The technology is immature and generally difficult to popularize. It is currently only used in some projects that are not sensitive to cost and volume;

[0005] 2) Passive balancing is energy-consuming balancing with a simple control circuit. A resistor is connected in parallel to each single cell to shunt the current. When the battery consistency is poor, the balancing resistor can be controlled to consume the battery energy and align the high-voltage battery state to the low-voltage state. The essence of passive balancing is "peak shaving". In order to determine the single cell that needs to be balanced, most of them are determined based on the single cell voltage. In order to obtain the voltage value of the single cell, it can only be judged in the stage where the current is stable, such as the charging stage. Therefore, the disadvantage of most passive balancing methods now is that they can only do charging balancing, not real-time balancing. Since the battery charging time is relatively short every day, the balancing time becomes longer and the balancing efficiency is low. The existing passive balancing uses MOS tubes in series in the balancing circuit as control switches. After multiple channels are turned on, the heat generated by the MOS tubes and the balancing resistors will cause the temperature of the BMS circuit board to rise, affecting the normal operation of the BMS. Summary of the invention

[0006] The object of the present invention is to provide a battery passive balancing control method and device thereof.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is:

[0008] A battery passive balancing control method, comprising:

[0009] S1: BMS is turned on, enters normal working state, and collects current battery voltage and temperature;

[0010] S2: Collect battery data, detect the current current value I, and determine whether the current current value is greater than 0.05C. If I is greater than 0.05C, continue to wait. If I is not greater than 0.05C and lasts for 15 seconds, read t 1 Voltage value, t 1 It is the moment when the corresponding voltage is closest to 0.05C during 0 to 15 seconds;

[0011] S3: Measure t 1 The highest cell voltage in the battery at this moment V max , minimum single cell voltage V min , Single cell average voltage V avg The pressure difference between the cells V del =V max -V min ;

[0012] S4, judging whether to start balancing according to voltage conditions and temperature conditions, and proceeding to S5 when both voltage conditions and temperature conditions are met, otherwise proceeding to S7;

[0013] The voltage condition is as follows: when the V del >V x , V avg >V 0 , V min >V 1 , it means that the voltage condition is met, otherwise it does not meet the voltage condition, where V x = Cell voltage drop threshold, V 0 = Average cell voltage threshold, V 1 =Battery cell minimum voltage threshold;

[0014] The temperature condition is determined as follows: When T 0 <Current temperature T <T n , it means that the temperature condition is met, otherwise it does not meet the temperature condition, T 0 = The minimum temperature threshold for the cell to be balanced, T n =The maximum temperature threshold that allows the cell to be balanced;

[0015] S5: Screen the battery cells that need to be balanced and divide them into two groups, A and B. 1 The battery cells with voltage higher than the reference voltage at this moment are group A, and those with voltage lower than the reference voltage are group B. The reference voltage V ref =(V max *S 1 + V min *S 2 ), where S 1 Is the cell voltage at the average cell voltage V avg The proportion of the above number, S 2The voltage of the single cell is the average voltage of the single cell V avg The proportion of the number below

[0016] S6: Subdivide group A battery cells into A 1 and A 2 , the 1st, 3rd, 5th…n (odd numbers) are A 1 Group, 2nd, 4th, 6th…n+1th is A 2 Group A 1 Channel open t 2 Seconds at the same time A 2 The channel is closed, then A 2 Channel open t 2 Seconds at the same time A 1 The channel is closed at time t b Inner loop, t b It is the operating time of the battery within 24 hours;

[0017] S7: Close the cycle in S6 and turn off the BMS.

[0018] Preferably, in S2, t 1 is 12 seconds.

[0019] Preferably, in S6, t b The range is 8 to 12 hours.

[0020] Preferably, in S6, t 2 is 1 second.

[0021] Preferably, in S6, once the equilibrium condition is met, the equilibrium is started in real time until the time reaches t b or after the BMS is shut down.

[0022] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0023] The present invention provides a battery passive balancing control method, which can perform balancing in real time when the battery is in any state, and does not need to wait until the end of charging or when it is stationary to perform balancing. The balancing efficiency is higher than before. Whether balancing is required is determined according to voltage conditions, and whether balancing can be started is determined according to temperature conditions. Otherwise, the temperature is too high, which affects the health of the battery. After the batteries that need to be balanced are selected, they are grouped, and the adjacent battery cells with balancing are dispersed accordingly so that the adjacent single cells are not started to balance at the same time, which avoids mutual interference of balancing currents and avoids excessive concentration of heat generated by the discharge of the balancing circuit. The balancing method is simple, easy to implement, low cost, and easy to promote. It also has the advantages of real-time balancing of charge and discharge, scientific screening of batteries that need to be balanced, low heat generation of the balancing circuit, low cost, high balancing efficiency, and the like. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Hereinafter, some specific embodiments of the present invention will be described in detail in an exemplary and non-limiting manner with reference to the accompanying drawings. The same reference numerals in the accompanying drawings indicate the same or similar components or parts. It should be understood by those skilled in the art that these drawings are not necessarily drawn to scale. In the accompanying drawings:

[0025] Figure 1 It is a schematic diagram of a flow chart of determining a power battery working mode according to a preferred embodiment of the present invention;

[0026] Figure 2 This is the battery voltage data graph before equalization;

[0027] Figure 3 This is the battery voltage data graph after equalization. DETAILED DESCRIPTION

[0028] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] In the description of the present invention, it should be noted that the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside", etc. indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, they should not be understood as limitations on the present invention.

[0030] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0031] A battery passive balancing control method, the control method comprises the following steps, referring to Figure 1 :

[0032] S1: BMS is turned on, enters normal working state, and collects current battery voltage and temperature;

[0033] S2: Collect battery data, detect the current value I, and determine whether the absolute value of the current value I is greater than 0.05C. If the absolute value of I is greater than 0.05C, continue to wait until it is no greater than 0.05C. If the absolute value of I is no greater than 0.05C and lasts for 15 seconds, read t 1 The overall battery voltage at time t 1It is the moment when the corresponding voltage is closest to 0.05C in 0~15 seconds. Normally, the data at the 12th second is selected because the data at 12 seconds reaches a peak, which is not only closest to 0.05C but also relatively stable without too much fluctuation.

[0034] S3: Measure t 1 The highest cell voltage in the battery at this moment V max , minimum single cell voltage V min , Single cell average voltage V avg The pressure difference between the cells V del =V max -V min ;

[0035] S4, judging whether to start balancing according to voltage conditions and temperature conditions, and proceeding to S5 when both voltage conditions and temperature conditions are met, otherwise proceeding to S7;

[0036] The temperature condition is used to determine whether the current battery is suitable for equalization. It cannot be too high or too low. The voltage condition is used to determine whether the battery needs to be equalized. When the voltage difference, average value and minimum value between the cells are higher than the various pressure difference thresholds of the cells, it means that the voltage difference between the cells is too large and needs to be equalized.

[0037] The voltage condition is as follows: when the V del >V x , V avg >V 0 , V min >V 1 , it means that the voltage condition is met, otherwise it does not meet the voltage condition, where V x = Cell voltage drop threshold, V 0 = Average cell voltage threshold, V 1 =Minimum voltage threshold of the battery cell; the voltage threshold is the open circuit voltage value corresponding to the lower limit of the remaining power (such as 20% of SOC) that the battery or battery cell allows to work normally;

[0038] The temperature condition is determined as follows: When T 0 <Current temperature T <T n , it means that the temperature condition is met, otherwise it does not meet the temperature condition, T 0 = The minimum temperature threshold for the cell to be balanced, T n =The maximum temperature threshold that allows the cell to be balanced; T 0 and T n It is the temperature range within which the battery is allowed to charge, and serves as the upper and lower temperature limits for equalization.

[0039] S5: Screen the battery cells that need to be balanced and divide them into two groups, A and B. 1The battery cells with voltage higher than the reference voltage at this moment are group A, and the battery cells with voltage lower than the reference voltage are group B. The reference voltage V ref =(V max *S 1 + V min *S 2 ), where S 1 Is the cell voltage at the average cell voltage V avg The proportion of the above number, S 2 The voltage of the single cell is the average voltage of the single cell V avg The proportion of the number below

[0040] S6: Subdivide group A battery cells into A 1 and A 2 , the 1st, 3rd, 5th…n (odd numbers) are A 1 Group, 2nd, 4th, 6th…n+1th is A 2 Group A 1 Channel open t 2 Seconds at the same time A 2 The channel is closed, then A 2 Channel open t 2 Seconds at the same time A 1 The channel is closed at time t b Inner loop, t b It is the battery operation time within 24 hours; the battery operation time within a day is 8 to 12 hours;

[0041] In S6, once the balancing conditions are met, balancing starts in real time. No need to wait for charging or static state. 2 1 second, 1 second is not too long to cause a sudden change in battery voltage. Turning on in turn can prevent the temperature of the balanced MOS from rising too high and prevent adjacent cells from interfering with each other.

[0042] S7: until the time reaches T b The cycle stops after the BMS is turned off.

[0043] During specific use, there is no need to wait, and real-time balancing can be performed when not charging or in silence. The BMS system collects the battery current, voltage, temperature, voltage of the single battery and the difference between the single batteries, etc., selects the appropriate time to take the value, and calculates the value. The balancing control can only be entered when the value meets the voltage and temperature conditions. Then the battery cells that need to be balanced are divided into two groups, and the adjacent cells that need to be balanced are divided into two groups to avoid heating at the same time. Then the two groups take turns to balance, and one group is closed when the other group is balanced. This cycle is repeated until the battery working time ends when the balancing conditions are met.

[0044] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with this technology to understand the contents of the present invention and implement them accordingly. They cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A battery passive balancing control method, It is characterized in that The following steps are included S1: BMS is turned on, enters normal working state, and collects current battery voltage and temperature; S2: Collect battery data, detect the current current value I, and determine whether the current current value is greater than 0.05C. If I is greater than 0.05C, continue to wait. If I is not greater than 0.05C and lasts for 15 seconds, read t 1 Voltage value, t 1 It is the moment when the corresponding voltage is closest to 0.05C during 0 to 15 seconds; S3: Measure t 1 The highest cell voltage in the battery at this moment V max , minimum single cell voltage V min , Single cell average voltage V avg The pressure difference between the cells V del =V max -V min ; S4, judging whether to start balancing according to voltage conditions and temperature conditions, and proceeding to S5 when both voltage conditions and temperature conditions are met, otherwise proceeding to S7; The voltage condition is as follows: when the V del >V x , V avg >V 0 , V min >V 1 , it means that the voltage condition is met, otherwise it does not meet the voltage condition, where Vx = battery cell voltage difference threshold, V0 = battery cell average voltage threshold, V1 = battery cell minimum voltage threshold; The temperature condition is judged as follows: When T 0 <Current temperature T <T n , it means that the temperature condition is met, otherwise it does not meet the temperature condition, T 0 = The minimum temperature threshold for the cell to be balanced, T n =The maximum temperature threshold that allows the battery cell to be balanced; S5: Screen the battery cells that need to be balanced and divide them into two groups, A and B. 1 The battery cells with voltage higher than the reference voltage at this moment are group A, and those with voltage lower than the reference voltage are group B. The reference voltage V ref =(V max *S 1 + V min *S 2 ), where S 1 Is the cell voltage at the average cell voltage V avg The proportion of the above number, S 2 The voltage of the single cell is the average voltage of the single cell V avg The proportion of the number below S6: Subdivide group A battery cells into A 1 and A 2 , the 1st, 3rd, 5th…n (odd numbers) are A 1 Group, 2nd, 4th, 6th…n+1th is A 2 Group A 1 Channel open t 2 Seconds at the same time A 2 The channel is closed, then A 2 Channel open t 2 Seconds at the same time A 1 The channel is closed at time t b Inner loop, t b The operating time period of the battery within 24 hours; S7: Close the cycle in S6 and turn off the BMS.

2. A battery passive balancing control method according to claim 1, Features: In S2, t 1 is 12 seconds.

3. A battery passive balancing control method according to claim 1, Features: In S6, t b The range is 8 to 12 hours.

4. A battery passive balancing control method according to claim 1, It is characterized in that In S6, t 2 is 1 second.

5. A battery passive balancing control method according to claim 4, It is characterized in that In S6, once the equilibrium condition is met, the equilibrium is started in real time until the time reaches t b or after the BMS is shut down.

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