WO2023077270A1

WO2023077270A1 - Battery cell capacity equalization method, battery management system and storage medium

Info

Publication number: WO2023077270A1
Application number: PCT/CN2021/128199
Authority: WO
Inventors: 彭雷; 周美娟; 徐广玉
Original assignee: 宁德时代新能源科技股份有限公司
Priority date: 2021-11-02
Filing date: 2021-11-02
Publication date: 2023-05-11
Also published as: CN116746021A

Abstract

Provided are a battery cell capacity equalization method, a battery management system (1), and a storage medium. The equalization method is applied to the battery management system (1), the battery management system (1) is electrically connected to a battery (2), and the battery (2) comprises N battery cells (21), N being an integer greater than 1. The method comprises: when a battery cell (21) is in a charging state, calculating the voltage change rate dV/dSOC of the battery cell (21), the voltage change rate being a value obtained by differentiating an output voltage V of the battery cell (21) from a current capacity SOC of the battery cell (21); recording the moment when the voltage change rate of the battery cell (21) meets a preset condition; and according to the moment when the voltage change rate of the battery cell (21) meets the preset condition and a function of the charging current changing with time for charging the battery cell (21), calculating an equalization capacity corresponding to the battery cell (21), and equalizing the battery cell (21) according to the equalization capacity. The capacity difference between the battery cells (21) is quantitatively calculated, and the battery cells (21) are directly subjected to one-time equalization according to the difference, thereby reducing the calculation amount and the time consumed during equalization.

Description

Cell capacity equalization method, battery management system and storage medium

technical field

The present application relates to the technical field of batteries, in particular to a battery cell capacity equalization method, a battery management system and a storage medium.

Background technique

The batteries used in new energy vehicles are usually composed of multiple cells connected in series and parallel. With the continuous use of the battery, there will often be differences between the state of charge (State of Charge, SOC) of each cell in the battery at the same time, and each cell in the battery is usually in a charging state or a discharging state at the same time , which will cause the cells with higher SOC to be overcharged during charging when the cells with lower SOC are not fully charged, or, during discharge, the cells with higher SOC When the battery is not fully discharged, the battery with a lower SOC has been over-discharged, which will cause greater damage to the battery.

At present, the method to balance the SOC difference between the cells is: first calculate the minimum value of the output voltage of each cell as the minimum cell voltage, when the difference between the output voltage of a certain cell and the minimum cell voltage exceeds the preset value, it is considered that the difference between the SOC of the cell and the cell with the minimum cell voltage is too large. At this time, the SOC of the cell will be used to subtract the preset capacity, for example, subtract 0.1% of the total capacity of the cell, as The updated SOC of the cell is to reduce the difference between the SOC of the cell and the cell with the minimum cell voltage output. If the difference between the output voltage of the cell and the minimum cell voltage after the update still exceeds the preset Set the value, then use the updated SOC of the cell to subtract the above preset capacity to further reduce the difference between the SOC until the difference between the voltage of all cells and the minimum cell voltage is less than or equal to the preset value .

Obviously, the above-mentioned method needs to judge and balance the SOC of the cell repeatedly, which requires a large amount of calculation, and the whole equalization process takes a long time.

Contents of the invention

The embodiment of the present application provides a cell capacity equalization method, a battery management system, and a storage medium, which can quantitatively calculate the capacity difference between the cells, and directly perform one-time equalization on the cells based on the difference, reducing the amount of calculation and the time taken for the equalization process.

In the first aspect, the embodiment of the present application provides a cell capacity equalization method, which is applied to a battery management system. The battery management system is electrically connected to the battery, and the battery includes N cells, where N is an integer greater than 1; the method Including: when the battery is in the charging state, calculate the voltage change rate dV/dSOC of the battery; where the voltage change rate is the value obtained by differentiating the output voltage V of the battery from the current capacity SOC of the battery; record the value of the battery The moment when the voltage change rate meets the preset condition; according to the moment when the voltage change rate of the battery cell meets the preset condition and the function of the charging current for charging the battery cell with time, the corresponding balanced capacity of the battery cell is calculated, and according to the balanced capacity Cells are balanced.

Compared with the related art, the technical solution of the embodiment of the present application can only judge and equalize multiple batteries until the difference between the batteries is reduced to the allowable range, while the embodiment of the present application can directly Calculate the difference between the SOC of each battery cell, and use this as the balance capacity to perform a balance on each battery cell, which reduces the amount of calculation required for multiple judgments and speeds up the process of battery SOC balance.

In some embodiments, according to the time when the rate of change of the voltage of the battery cell satisfies the preset condition and the function of the charging current for charging the battery cell over time, the calculation of the corresponding balanced capacity of the battery cell includes: respectively obtaining the N battery cells The moment when the voltage change rate meets the preset conditions, and obtain the maximum value in the moment as the maximum moment value; calculate the definite integral of the time in the function of the charging current changing with time to charge the battery cell, and obtain the corresponding balanced capacity of the battery cell , where the lower limit of the definite integral is the moment when the voltage change rate of the cell meets the preset condition, and the upper limit of the definite integral is the maximum moment value.

In the foregoing embodiments, a specific implementation manner of calculating the balanced capacity is provided.

In some embodiments, before recording the moment when the voltage change rate of the battery cell satisfies the preset condition, the method further includes: acquiring the preset condition corresponding to the preset capacity range according to the preset capacity range in which the current capacity of the battery is located.

In the above embodiments, different preset capacity ranges where the current capacity of the battery is located correspond to preset conditions.

In some embodiments, when the preset capacity ranges from 0 to 50% of the total capacity of the battery, the corresponding preset condition is: the voltage change rate starts to be less than or equal to the first preset value.

In the above embodiment, a specific implementation manner of the preset condition corresponding to when the preset capacity ranges from 0 to 50% of the total capacity of the battery is provided.

In some embodiments, when the preset capacity range is 50% of the total capacity of the battery to 80% of the total capacity of the battery, the corresponding preset condition is: the voltage change rate is the maximum voltage change rate within a preset time period, Wherein, the preset time period includes the moment corresponding to the voltage change rate.

In the above embodiment, a specific implementation manner of the preset condition corresponding to when the preset capacity range is 50% of the total capacity of the battery to 80% of the total capacity of the battery is provided.

In some embodiments, when the preset capacity range is from 80% of the total capacity of the battery to the total capacity of the battery, the corresponding preset condition is: the voltage change rate starts to be greater than or equal to the second preset value.

In the above embodiment, a specific implementation manner of the preset condition corresponding to when the preset capacity ranges from 80% of the total capacity of the battery to the total capacity of the battery is provided.

In the second aspect, the embodiment of the present application provides a battery management system, the battery management system is electrically connected to the battery, and the battery includes N batteries, where N is an integer greater than 1; the system includes: a calculation module, a recording module and Balance module; the calculation module is used to calculate the voltage change rate dV/dSOC of the battery cell when the battery cell is in a charging state; where the voltage change rate is the value obtained by differentiating the output voltage V of the battery cell to the current capacity SOC of the battery cell The recording module is used to record the moment when the voltage change rate of the battery cell meets the preset condition; the equalization module is used to meet the time when the voltage change rate of the battery cell meets the preset condition and the function of the charging current for charging the battery cell over time, Calculate the balanced capacity corresponding to the battery cell, and balance the battery cell according to the balanced capacity.

In some embodiments, the equalization module is specifically used to obtain the time when the voltage change rates of the N batteries meet the preset conditions, and obtain the maximum value at the time as the maximum time value, and then adjust the charging current for charging the battery Calculate the definite integral of the time in the time-varying function to obtain the corresponding equilibrium capacity of the battery, wherein the lower limit of the definite integral is the moment when the voltage change rate of the battery meets the preset condition, and the upper limit of the definite integral is the maximum moment value.

In a third aspect, an embodiment of the present application provides a battery management system, including: at least one processor; and a memory communicatively connected to the at least one processor; wherein, the memory stores instructions executable by the at least one processor, The instructions are executed by at least one processor, so that the at least one processor can execute the above cell capacity balancing method.

In a fourth aspect, the embodiment of the present application provides a computer-readable storage medium, which stores a computer program, and implements the above cell capacity balancing method when the computer program is executed by a processor.

The above description is only an overview of the technical solution of the present application. In order to better understand the technical means of the present application, it can be implemented according to the contents of the description, and in order to make the above and other purposes, features and advantages of the present application more obvious and understandable , the following specifically cites the specific implementation manner of the present application.

Description of drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the accompanying drawings that need to be used in the embodiments of the present application. Obviously, the accompanying drawings described below are only some embodiments of the present application. Those of ordinary skill in the art can also obtain other drawings based on the accompanying drawings on the premise of not paying creative efforts.

Fig. 1 is a schematic structural view of a vehicle disclosed in an embodiment of the present application;

Fig. 2 is a schematic flow chart of a battery cell capacity equalization method disclosed in an embodiment of the present application;

Fig. 3 is a schematic flow diagram II of a cell capacity equalization method disclosed in an embodiment of the present application;

Fig. 4 is a schematic flow diagram III of a cell capacity equalization method disclosed in an embodiment of the present application;

Fig. 5 is a partial change curve 1 of the voltage change rate of the battery cell with the SOC in a cell capacity equalization method disclosed in an embodiment of the present application;

Fig. 6 is a partial change curve 2 of the voltage change rate of the battery cell with the SOC in a cell capacity equalization method disclosed in an embodiment of the present application;

Fig. 7 is a partial change curve 3 of the voltage change rate of the battery cell with the SOC in a cell capacity equalization method disclosed in an embodiment of the present application;

Fig. 8 is a schematic flow diagram 4 of a cell capacity equalization method disclosed in an embodiment of the present application;

Fig. 9 is a schematic block diagram of a battery management system disclosed in an embodiment of the present application;

In the drawings, the drawings are not drawn to scale.

Marking instructions: 1—battery management system, 2—battery;

21—battery core;

501—calculation module, 502—recording module, 503—balance module.

Detailed ways

The implementation manner of the present application will be further described in detail below with reference to the drawings and embodiments. The detailed description and drawings of the following embodiments are used to illustrate the principles of the application, but not to limit the scope of the application, that is, the application is not limited to the described embodiments.

In the description of this application, it should be noted that, unless otherwise specified, the meaning of "plurality" is more than two; the terms "upper", "lower", "left", "right", "inner", " The orientation or positional relationship indicated by "outside" and so on are only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a reference to this application. Application Restrictions. In addition, the terms "first", "second", "third", etc. are used for descriptive purposes only and should not be construed as indicating or implying relative importance. "Vertical" is not strictly vertical, but within the allowable range of error. "Parallel" is not strictly parallel, but within the allowable range of error.

The orientation words appearing in the following description are the directions shown in the figure, and do not limit the specific structure of the application. In the description of this application, it should also be noted that, unless otherwise clearly specified and limited, the terms "installation", "connection", and "connection" should be interpreted in a broad sense, for example, it can be a fixed connection or a flexible connection. Disassembled connection, or integral connection; it can be directly connected or indirectly connected through an intermediary. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific situations.

Reference herein to an "embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the present application. The occurrences of this phrase in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. It is understood explicitly and implicitly by those skilled in the art that the embodiments described herein can be combined with other embodiments.

In the description of the embodiment of the present application, the term "and/or" is only a kind of association relationship describing associated objects, which means that there may be three kinds of relationships, such as A and/or B, which may mean: A exists alone, and A exists at the same time and B, there are three cases of B alone. In addition, the character "/" in this article generally indicates that the contextual objects are an "or" relationship.

The batteries used in new energy vehicles are usually composed of multiple cells connected in series and parallel. With the continuous use of the battery, there will often be differences between the state of charge (State of Charge, SOC) of each cell in the battery at the same time, for example, at the same time, the SOC of one cell is 30%, and the other cell The SOC of the cell is 40%, which will cause the cell with the higher SOC to be overcharged when the cell with the lower SOC is not fully charged during the charging process. For example, the battery with SOC=40% above will be fully charged before the battery with SOC=30%, if you want to fully charge the battery with SOC=30%, you must overcharge the battery with SOC=40%; or , during the discharge process, when the battery with a higher SOC has not been fully discharged, the battery with a lower SOC has been over-discharged. The cell is fully discharged first. If you want to fully discharge the cell with SOC=40%, you will definitely over-discharge the cell with SOC=30%, which will cause great damage to the battery.

At present, the method to balance the SOC difference between the cells is: first calculate the minimum value of the output voltage of each cell as the minimum cell voltage, when the difference between the output voltage of a certain cell and the minimum cell voltage exceeds the preset value, it is considered that the difference between the SOC of the cell and the cell with the minimum cell voltage is too large. At this time, the SOC of the cell will be used to subtract the preset capacity, for example, subtract 0.1% of the total capacity of the cell, as The updated SOC of the cell is to reduce the difference between the SOC of the cell and the cell with the minimum cell voltage output. If the difference between the output voltage of the cell and the minimum cell voltage after the update still exceeds the preset If the value is set, it is considered that the difference between the SOC of the cell and the cell with the minimum cell voltage is still too large, and then the updated SOC of the cell is subtracted from the above preset capacity to further reduce the difference between the SOC. until the difference between the voltages of all cells and the minimum cell voltage is less than or equal to the preset value.

Obviously, the above-mentioned method needs to judge and balance the SOC of the battery cells repeatedly, which requires a large amount of calculation, and the whole equalization process takes a long time.

Based on the above problems, the present application proposes the following technical idea: during the charging process of the battery cell with the platform area, calculate the voltage change rate dV/dSOC obtained by differentiating the output voltage V of the battery cell from the current capacity SOC of the battery cell, And according to the moment when the voltage change rate of the battery cell meets the preset condition and the charging current for charging the battery cell, calculate the corresponding equalization capacity of the battery cell, so as to directly balance the battery cell according to the calculated equalization capacity.

The embodiment of the present application provides a cell capacity equalization method, which is applied to a battery management system (Battery Management System, BMS). Please refer to the schematic structural diagram of a vehicle in FIG. 1. The vehicle includes a battery management system 1 and a battery 2, and the battery The management system 1 is electrically connected to the battery 2, and the battery 2 includes N battery cells 21, where N is an integer greater than 1. Wherein the battery cell 21 can be a battery cell with a plateau area on the open circuit voltage curve, such as a lithium iron phosphate (molecular formula LiFePO ₄ , Lithium Iron Phosphate, LFP) battery cell, and the plateau area of the battery cell refers to the difference between the SOC and the battery cell. In the corresponding relationship between the output voltage V of the battery, there is an SOC interval in which the output voltage V of one or several sections of the battery cell remains basically unchanged. If the SOC of the battery cell is taken as the horizontal axis, the output voltage V of the battery cell is taken as the vertical axis , then in one or several intervals of the horizontal axis, the value of the vertical axis remains basically unchanged, forming a "platform area".

For cells with a platform area, the SOC of the cell is estimated only based on the output voltage V of the cell and the corresponding relationship between the SOC of the cell and the output voltage V of the cell. If the output voltage V of the cell corresponds to In the platform area of the battery cell, there may be situations where multiple SOCs have a corresponding relationship with the output voltage V, and it is difficult to accurately estimate the SOC of the battery cell.

In some embodiments, the battery management system 1 is electrically connected to the N cells 21 in the battery 2 (the connection structure is not shown in FIG. 1 ), so as to collect parameters such as temperature, voltage and current of each cell, and then observe The state of the battery cell, the battery management system 1 can also control each battery cell to be in a charging state or a discharging state.

According to some embodiments of the present application, the schematic flowchart of the cell capacity equalization method can refer to FIG. 2 , including:

Step 101, when the battery cell is in a charging state, calculate the voltage change rate dV/dSOC of the battery cell.

Step 102, recording the moment when the rate of change of the voltage of the cell satisfies a preset condition.

Step 103 , according to the time when the rate of change of the voltage of the battery cell satisfies the preset condition and the function of the charging current for charging the battery cell over time, calculate the corresponding equilibrium capacity of the battery cell.

Step 104, balancing the cells according to the balancing capacity.

The implementation details of the battery cell capacity equalization method in this embodiment will be described in detail below, and the following content is only implementation details provided for easy understanding, and is not necessary for implementing this solution.

Specifically, the voltage change rate dV/dSOC in step 101 is the value obtained by differentiating the output voltage V of the battery cell from the current capacity SOC of the battery cell. In some embodiments, the voltage change rate dV/dSOC can be approximately equal to ΔV /ΔSOC, where ΔSOC is the value obtained by integrating the current curve divided by the total capacity of the cell.

In step 103, the time-varying function of the charging current for charging the battery can be any function that conforms to the current for charging the battery. For example, it can be considered that the magnitude of the charging current for charging the battery is constant, that is The function is a constant function, or a sinusoidal function that changes sinusoidally, which is not limited here.

Compared with the related technology, which can only judge and equalize multiple batteries until the difference between the batteries is reduced to the allowable range, the embodiments of the present application can directly calculate the SOC of each battery. The amount of difference between them is used as the balance capacity to perform a balance on each battery cell, which reduces the amount of calculation required for multiple judgments and speeds up the process of battery SOC balance.

In some embodiments, a specific calculation formula for calculating the balanced capacity is provided. Please refer to FIG. 3 , step 201 , step 202 and step 205 are substantially the same as step 101 , step 102 and step 104 , and will not be repeated here.

In step 203 , respectively obtain the time when the voltage change rates of the N cells meet the preset condition, and obtain the maximum value among the time as the maximum time value.

Step 204, calculate the definite integral for the time in the function of the charging current changing with time for charging the battery cell, and obtain the corresponding equilibrium capacity of the battery cell, wherein the lower limit of the definite integral is the moment when the voltage change rate of the battery cell satisfies the preset condition , the upper limit of the definite integral is the maximum moment value.

When the voltage change rate of a battery cell meets the preset condition, the BMS will record this moment as the moment when the voltage change rate of the battery cell meets the preset condition. After the moment when the voltage change rate meets the preset conditions, the maximum value of these moments will be obtained as the maximum moment value, and then the definite integral will be calculated for the time in the function of the charging current changing with time to charge the battery cell, and the corresponding value of the battery cell will be obtained. Among them, the lower limit of the definite integral is the moment when the voltage change rate of the cell meets the preset condition, and the upper limit of the definite integral is the maximum moment value, that is, the balance capacity corresponding to the cell is calculated using the ampere-hour integral method.

If the function of the charging current changing with time for charging the battery cell is a constant function, that is, during the charging process of the battery cell, the magnitude of the charging current of the battery cell is constant, so the battery cell corresponding to the maximum moment value is actually For the cell with the lowest SOC, the BMS will use the cell with the lowest SOC as the benchmark to measure the difference between the SOC of the remaining cells and the cell with the lowest SOC. Specifically, the BMS will first subtract the moment when the voltage change rate of each battery cell meets the preset condition from the maximum time value, and obtain the difference corresponding to each battery cell as the equalization time, and then multiply the equalization time by the constant charging current , as the equilibrium capacity corresponding to each cell.

For example, the battery includes 3 cells, and when the 3 cells are in the charging state, the BMS sequentially acquires time t ₁ , t ₂ and t ₃ when the voltage change rates of the 3 cells meet the preset conditions. Among them, t ₃ is the maximum time value. For the first cell, the equalization time is equal to t ₃ -t ₁ , and the equalization capacity is (t ₃ -t ₁ )*I, where I is the charging time for each cell Charging current, for the second cell, the equalization time is equal to t ₂ -t ₁ , the equalization capacity is (t ₂ -t ₁ )*I, for the third cell, the equalization time is equal to t ₃ -t ₃ =0, the balance capacity is also 0.

In some embodiments, when the voltage change rate of some cells does not meet the preset condition, each cell will stop being charged. In this case, the BMS will not obtain the voltage change of all cells. The moment when the rate of change meets the preset condition, the BMS can record the moment when each cell stops being charged, as the moment corresponding to the cell whose voltage change rate does not meet the preset condition.

For example, the battery includes 3 cells. When the 3 cells are in the charging state, the BMS sequentially obtains the time t ₁ and t ₂ when the voltage change rate of the 2 cells meets the preset conditions, and the remaining When the voltage change rate of one battery cell does not meet the preset condition, each battery cell stops being charged. At this time, the BMS will record the time t ₀ when the battery cell stops being charged, as the voltage change rate that does not meet the preset condition. The moment corresponding to one cell, obviously, t ₀ is greater than t ₁ and t ₂ , so t ₀ is taken as the maximum moment value. At this time, for the first cell, the equalization time is equal to t ₀ -t ₁ , and the equalization capacity is (t ₀ -t ₁ )*I, for the second cell, the equalization time is equal to t ₀ -t ₁ , and the equalization capacity is (t ₀ -t ₁ )*I, for the third cell , the equalization time is equal to t ₀ −t ₀ =0, and the equalization capacity is also 0.

In some embodiments, please refer to FIG. 4 , step 301 , step 303 , step 304 and step 305 are substantially the same as step 101 , step 102 , step 103 and step 104 , and will not be repeated here.

Step 302, according to the preset capacity range where the current capacity of the battery is located, the preset condition corresponding to the preset capacity range is acquired.

There is a corresponding relationship between the preset capacity range where the current capacity of the battery is located and the preset condition.

For cells with a platform area, taking a battery containing LFP cells as an example, when the current capacity of the battery is within 0 to 35% of the total capacity of the battery, it can be considered that each cell is at the low end of the charge of the cell. When the current capacity of the battery is within 35% of the total capacity of the battery to 80% of the total capacity of the battery, it can be considered that each battery cell is in the charging platform area of the battery cell; when the current capacity of the battery is greater than 80% of the total capacity of the battery , it can be considered that each battery cell is at the charging end of the battery cell.

Please refer to the part of the change curve of the voltage change rate of the battery cell with the SOC in Figure 5. The charging rate of the battery cell corresponding to the different curves is different. The curve corresponding to the charging rate of the battery cell, it can be seen from the figure that when the battery cell is charged from the low charging end to the platform area, the voltage change rate of the battery cell will gradually approach 0, and it can be charged to this area by different batteries to identify the size of the SOC of different batteries. In Figure 5, the value of the ordinate corresponding to the differential point 1 is equal to the first preset value as an example, and the voltage change rate of each battery is recorded in turn to be less than or equal to the first preset value. From the time t _1n of a preset value until the time t _1max of the last battery cell is recorded, (t _1max -t _1n )*I is used as the equalization capacity corresponding to each battery cell for equalization. Specifically, the equalization capacity (t _1max -t _1n )*I can be divided by the equalization current for the battery cell to obtain the specific time for the battery cell to be balanced, and the battery cell is balanced according to the specific time, specifically The timer can be used to balance the battery cells, and the balance will stop after the timer expires.

Among them, the setting of the first preset value is usually obtained by technicians through a large number of experimental tests before leaving the factory, specifically by testing the charging curves of different charging ratios, different charging temperatures and different aging degrees of the battery cells. The SOC value corresponding to differential point 1 is obtained.

In some embodiments, when the preset capacity range is 50% of the total capacity of the battery to 80% of the total capacity of the battery, the corresponding preset condition is: the voltage change rate is the maximum voltage change rate within a preset time period, Wherein, the preset time period includes the moment corresponding to the voltage change rate. The setting of the preset time period is usually obtained by technicians through a large number of experimental tests before leaving the factory.

Please refer to the partial change curve of the voltage change rate of each battery cell with the SOC in Figure 6, where the charging rate of the battery cells corresponding to different curves is different, and the figure lists 01C, 015C, 02C, 025C and 033C The curves corresponding to the charge rate of different batteries can be seen from the figure. After the battery is charged to the platform area, the voltage change rate of the battery will have a peak value between the two small platforms, which can be charged to the platform area by different batteries. The order of the peak values is used to identify the SOC of different cells. In Figure 6, the value of the ordinate corresponding to the differential point 2 is equal to the peak value as an example, and the voltage change rate of each cell is recorded sequentially to become within the preset time period. From the time t _2n of the maximum voltage change rate until the time t _2max of the last battery cell is recorded, (t _2max -t _2n )*I is used as the equalization capacity corresponding to each battery cell for equalization. Specifically, the equalization capacity (t _2max -t _2n )*I can be divided by the equalization current for the battery cell to obtain the specific time for the battery cell to be balanced, and the battery cell is balanced according to the specific time, specifically The timer can be used to balance the battery cells, and the balance will stop after the timer expires.

Please refer to the partial change curve of the voltage change rate of each battery cell with the SOC in Figure 7, where the charging rate of the battery cell corresponding to different curves is different, and the figure lists 01C, 015C, 02C, 025C and 033C. The curve corresponding to the charging rate of different batteries can be seen from the figure. After the battery is charged to the charging end, the voltage change rate of the battery will increase dramatically. It can be identified by the order in which different batteries are charged to this area. For the size of the SOC of different batteries, in Figure 7, take the value of the ordinate corresponding to the differential point 3 equal to the second preset value as an example, and sequentially record the moment when the voltage change rate of each battery cell starts to be greater than or equal to the second preset value t _3n , until the time t _3max of the last cell is recorded, use (t _3max -t _3n )*I as the equalization capacity corresponding to each cell for equalization. Specifically, the equalization capacity (t _3max -t _3n )*I can be divided by the equalization current for the battery cell to obtain the specific time for the battery cell to be balanced, and the battery cell is balanced according to the specific time, specifically The timer can be used to balance the battery cells, and the balance will stop after the timer expires.

Among them, the setting of the second preset value is usually obtained by technicians through a large number of experimental tests before leaving the factory, specifically by testing the charging curves of different charging ratios, different charging temperatures and different aging degrees of the battery cells. The SOC value corresponding to the differential point 3 is obtained.

It should be noted that the embodiment of the present application does not limit the sequence of

steps

301 and 302, that is, the preset conditions corresponding to the preset capacity range can be obtained first, and the voltage change rate dV/dSOC of the battery cell can also be obtained first.

In addition, the above only exemplifies three specific preset capacity ranges and their corresponding preset conditions, and does not limit the preset capacity range of the battery cell to the above three specific preset capacity ranges, nor does it limit the preset The number of capacity ranges is not necessarily three, and there is no limit to the preset conditions corresponding to each preset capacity range is the above three preset conditions, as long as any technical solution that meets the charging characteristics of the battery in the platform area is in within the protection scope of this application.

In some embodiments, please refer to the schematic flowchart of FIG. 8 .

In step 401, it is determined whether the battery cell is in a charging state, if yes, enter step 402; if not, repeat step 401.

Step 402, when the current capacity of the battery is within the preset capacity range, read parameters such as the voltage and temperature of the battery cell.

Step 403, calculate the voltage change rate of the battery cell according to the parameters such as the voltage and temperature of the battery cell.

Step 404 , judging whether the voltage change rate of the cell meets the preset condition, if yes, proceed to step 405 ; if not, return to step 403 .

Step 405, recording the moment when the rate of change of the voltage of the cell meets the preset condition.

Step 406 , after recording the moment when the voltage change rates of all cells meet the preset condition, calculate the time required for each cell to be balanced: (t _max -t _n )*I/I _bal . Among them, t _max is the maximum current value, t _n is the moment when the voltage change rate of each cell meets the preset condition, I is the charging current for charging the cell, and I _bal is the balancing current required for balancing the cell.

Step 407 , balancing the cells according to the balancing current I _bal required for balancing and the balancing time of the cells until the balancing time of all cells is 0.

In some embodiments, there is a corresponding relationship between the preset capacity range and the preset condition. Specifically, when the preset capacity range is 0 to 50% of the total capacity of the battery, the corresponding preset conditions are: the voltage change rate starts to be less than or equal to the first preset value; 50% to 80% of the total capacity of the battery, the corresponding preset condition is: the voltage change rate is the maximum voltage change rate within a preset time period, wherein the preset time period includes the moment corresponding to the voltage change rate; When the preset capacity range is from 80% of the total capacity of the battery to the total capacity of the battery, the corresponding preset condition is: the voltage change rate starts to be greater than or equal to the second preset value.

For example, the BMS first needs to obtain the current capacity of the battery. For example, if the current capacity of the battery is 30% of the total battery capacity, it can be judged that the current capacity of the battery is between 0 and 50% of the total capacity of the battery. It is set within the capacity range, so the preset condition at this time is: the voltage change rate starts to be less than or equal to the first preset value, that is, the BMS needs to obtain the moment when each battery cell is charged to the differential point 1 in Figure 5; for example, the battery If the current capacity of the battery is 65% of the total capacity of the battery, it can be judged that the current capacity of the battery is within the preset capacity range of 50% of the total capacity of the battery to 80% of the total capacity of the battery, so the preset conditions at this time are: The voltage change rate is the maximum voltage change rate within the preset time period, wherein the preset time period includes the moment corresponding to the voltage change rate, at this time, the BMS needs to obtain the moment when each cell is charged to the differential point 2 in Figure 6; For example, if the current capacity of the battery is obtained as 85% of the total battery capacity, it can be judged that the current capacity of the battery is within the preset capacity range from 80% of the total capacity of the battery to the total capacity of the battery, so the preset condition at this time is : The voltage change rate starts to be greater than or equal to the second preset value, that is, the BMS needs to obtain the moment when each battery cell is charged to the differential point 3 in FIG. 7 .

After recording the moment when the voltage change rate of all cells meets the preset conditions, calculate the time required for each cell to be balanced: (t _max -t _n )*I/I _bal , and then calculate the balance current I _bal required for the balance Equalize the cells according to the time needed to balance the cells, until the time required to equalize all the cells is 0, the process of equalizing the cells can be completed.

An embodiment of the present application provides a battery management system, the battery management system is electrically connected to a battery, and the battery includes N cells, where N is an integer greater than 1. Wherein, the battery cell may be a battery cell with a plateau area in the open circuit voltage curve.

Please refer to FIG. 9 , the battery management system includes: a calculation module 501 , a recording module 502 and an equalization module 503 , the calculation module 501 is connected to the recording module 502 , and the recording module 502 is connected to the equalization module 503 .

The calculation module 501 will calculate the voltage change rate dV/dSOC of the battery cell when the battery cell is in the charging state, wherein the voltage change rate is the value obtained by differentiating the output voltage V of the battery cell from the current capacity SOC of the battery cell, and then by The recording module 502 records the moment when the voltage change rate of the battery cell meets the preset condition, and finally the balance module 503 calculates according to the time when the voltage change rate of the battery cell meets the preset condition and the function of the charging current for charging the battery cell over time. The corresponding balance capacity of the battery cell, and balance the battery cell according to the balance capacity.

It is not difficult to find that this embodiment is a system embodiment corresponding to the embodiment corresponding to FIG. 2 , and this embodiment can be implemented in cooperation with the embodiment corresponding to FIG. 2 . The relevant technical details mentioned in the embodiment corresponding to FIG. 2 are still valid in this embodiment, and are not repeated here to reduce repetition. Correspondingly, the relevant technical details mentioned in this embodiment may also be applied in the embodiment corresponding to FIG. 2 .

In some embodiments, the equalization module 503 will respectively obtain the time when the voltage change rates of the N batteries meet the preset conditions, and obtain the maximum value in the time as the maximum time value, and then adjust the charging current for charging the battery cells with Calculate the definite integral of the time in the function of time change to obtain the corresponding equilibrium capacity of the battery, wherein the lower limit of the definite integral is the moment when the voltage change rate of the battery meets the preset condition, and the upper limit of the definite integral is the maximum moment value.

It is not difficult to find that this embodiment is a system embodiment corresponding to the embodiment corresponding to FIG. 3 , and this embodiment can be implemented in cooperation with the embodiment corresponding to FIG. 3 . The relevant technical details mentioned in the embodiment corresponding to Fig. 3 are still valid in this embodiment, and will not be repeated here in order to reduce repetition. Correspondingly, the relevant technical details mentioned in this embodiment may also be applied in the embodiment corresponding to FIG. 3 .

An embodiment of the present application provides a computer-readable storage medium, which stores a computer program, and implements the above cell capacity balancing method when the computer program is executed by a processor.

That is, those skilled in the art can understand that all or part of the steps in the method of the above-mentioned embodiments can be completed by instructing related hardware through a program, the program is stored in a storage medium, and includes several instructions to make a device ( It may be a single-chip microcomputer, a chip, etc.) or a processor (processor) to execute all or part of the steps of the methods described in the various embodiments of the present application. The aforementioned storage media include: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), magnetic disk or optical disc, etc., which can store program codes. .

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit it; although the application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: It is still possible to modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the technical solutions of the various embodiments of the present application. All of them should be covered by the scope of the claims and description of the present application. In particular, as long as there is no structural conflict, the technical features mentioned in the various embodiments can be combined in any manner. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

A cell capacity equalization method applied to a battery management system, the battery management system is electrically connected to a battery, and the battery includes N cells, where N is an integer greater than 1;

The methods include:

When the battery cell is in a charging state, calculate the voltage change rate dV/dSOC of the battery cell;

Wherein, the voltage change rate is a value obtained by differentiating the output voltage V of the battery cell from the current capacity SOC of the battery cell;

Recording the moment when the voltage change rate of the cell satisfies a preset condition;

According to the time when the voltage change rate of the battery cell meets the preset condition and the function of the charging current for charging the battery cell over time, calculate the corresponding balanced capacity of the battery cell, and calculate the corresponding balance capacity of the battery cell according to the balanced capacity. The cells are balanced.
The cell capacity balancing method according to claim 1, wherein the function according to the time when the voltage change rate of the cell satisfies the preset condition and the charging current for charging the cell varies with time, Calculate the balanced capacity corresponding to the cell, including:

Obtaining the times at which the voltage change rates of the N cells meet the preset conditions respectively, and obtaining the maximum value among the times as the maximum time value;

Calculate the definite integral of the time in the function of the charging current changing with time for charging the battery to obtain the equilibrium capacity corresponding to the battery, wherein the lower limit of the definite integral is that the rate of change of the voltage of the battery satisfies At the moment of the preset condition, the upper limit of the definite integral is the maximum moment value.
The cell capacity equalization method according to claim 1 or 2, wherein, before recording the moment when the voltage change rate of the cell satisfies a preset condition, further comprising:

The preset condition corresponding to the preset capacity range is acquired according to the preset capacity range in which the current capacity of the battery is located.
The battery capacity balancing method according to claim 3, wherein when the preset capacity range is 0 to 50% of the total capacity of the battery, the corresponding preset condition is: the voltage change rate starts less than or equal to the first preset value.
The cell capacity balancing method according to claim 3 or 4, wherein when the preset capacity range is 50% to 80% of the total capacity of the battery, the corresponding preset The assumption is that the voltage change rate is the largest voltage change rate within a preset time period, wherein the preset time period includes the moment corresponding to the voltage change rate.
The cell capacity equalization method according to any one of claims 3 to 5, wherein when the preset capacity range is from 80% of the total capacity of the battery to the total capacity of the battery, the corresponding preset The assumption condition is: the voltage change rate is initially greater than or equal to a second preset value.
A battery management system, the battery management system is electrically connected to a battery, and the battery includes N cells, where N is an integer greater than 1;

The system includes: a calculation module, a recording module and an equalization module;

The calculation module is used to calculate the voltage change rate dV/dSOC of the battery when the battery is in a charging state;

Wherein, the voltage change rate is a value obtained by differentiating the output voltage V of the battery cell from the current capacity SOC of the battery cell;

The recording module is used to record the moment when the voltage change rate of the battery meets a preset condition;

The equalization module is used to calculate the equalization capacity corresponding to the battery cell according to the time when the voltage change rate of the battery cell meets the preset condition and the function of the charging current for charging the battery cell over time, and The battery cells are balanced according to the balanced capacity.
The battery management system according to claim 7, wherein,

The equalization module is specifically used to respectively obtain the time when the voltage change rates of the N batteries meet the preset conditions, and obtain the maximum value in the time as the maximum time value, and then give the battery cell Calculate the time definite integral of the function of the charging current changing with time to obtain the equilibrium capacity corresponding to the battery cell, wherein the lower limit of the definite integral is the voltage change rate of the battery cell that satisfies the preset condition time, the upper limit of the definite integral is the maximum time value.
A battery management system comprising:

at least one processor; and,

a memory communicatively coupled to the at least one processor; wherein,

The memory is stored with instructions executable by the at least one processor, the instructions are executed by the at least one processor, so that the at least one processor can perform any one of claims 1 to 6 cell capacity balancing method.
A computer-readable storage medium storing a computer program, the computer program implementing the cell capacity balancing method according to any one of claims 1 to 6 when the computer program is executed by a processor.