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

Abstract

A cell capacity equalization method, a battery management system (1), and a storage medium are provided. The equalization method is applied to the battery management system (1), which is electrically connected to a battery (2). The battery (2) includes N cells (21), where N is an integer greater than 1. The method includes: when the cell (21) is in a charging state, calculating the voltage change rate dV / dSOC of the cell (21); the voltage change rate is the value obtained by differentiating the output voltage V of the cell (21) with the current capacity SOC of the cell (21); recording the time when the voltage change rate of the cell (21) meets the preset condition; calculating the equalization capacity corresponding to the cell (21) based on the time when the voltage change rate of the cell (21) meets the preset condition and the function of the charging current of the cell (21) changing with time, and equalizing the cell (21) based on the equalization capacity. The capacity difference between the cells (21) is quantitatively calculated, and the cells (21) are directly equalized in one go based on the difference, reducing the amount of calculation and the time consumed in the equalization process.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a cell capacity equalization method, a battery management system, and a storage medium. Background Technology

[0002] The batteries used in new energy vehicles are typically composed of multiple cells connected in series and parallel. As the battery is used continuously, the state of charge (SOC) of each cell often differs at any given time. Since the cells are usually in a charging or discharging state simultaneously, this can lead to the following: during charging, the cell with the lower SOC may be overcharged before it is fully charged; conversely, during discharging, the cell with the higher SOC may be over-discharged before it is fully discharged. This can cause significant damage to the battery.

[0003] The current method for balancing the SOC differences among battery cells is as follows: First, the minimum output voltage of each cell is calculated as the minimum cell voltage. When the difference between the output voltage of a cell and the minimum cell voltage exceeds a preset value, it is considered that the difference in SOC between that cell and the cell with the minimum output cell voltage is too large. At this time, a preset capacity is subtracted from the SOC of that cell, for example, 0.1% of the total cell capacity is subtracted, to obtain the updated SOC of that cell, in order to reduce the difference in SOC between that cell and the cell with the minimum output cell voltage. If the difference between the output voltage of the updated cell and the minimum cell voltage still exceeds the preset value, the preset capacity is subtracted from the updated SOC of that cell again to further reduce the difference in SOC, until the difference between the voltage of all cells and the minimum cell voltage is less than or equal to the preset value.

[0004] Obviously, the above method requires repeated judgment and balancing of the cell's SOC, which involves a large amount of calculation and the entire balancing process is time-consuming. Summary of the Invention

[0005] This application provides a cell capacity equalization method, a battery management system, and a storage medium, which can quantitatively calculate the capacity difference between cells and directly equalize the cells in one go based on the difference, reducing the amount of calculation and the time consumed in the equalization process.

[0006] In a first aspect, embodiments of this application provide a cell capacity balancing method applied to a battery management system. The battery management system is electrically connected to a battery, which includes N cells, where N is an integer greater than 1. The method includes: calculating the cell's voltage change rate dV / dSOC when the cell is in a charging state; wherein the voltage change rate is the value obtained by differentiating the cell's output voltage V with respect to the cell's current capacity SOC; recording the moment when the cell's voltage change rate meets a preset condition; calculating the cell's corresponding balancing capacity based on the moment when the cell's voltage change rate meets the preset condition and the function of the charging current changing with time, and balancing the cells based on the balancing capacity.

[0007] Compared to related technologies, which can only perform multiple judgments and equalizations on multiple battery cells until the differences between the cells are reduced to an acceptable range, the technical solution of this application can directly calculate the difference in SOC between each battery cell and use this as the equalization capacity to equalize each battery cell once, reducing the amount of calculation required for multiple judgments and speeding up the process of battery cell SOC equalization.

[0008] In some embodiments, the equalization capacity of a battery cell is calculated based on the time when the voltage change rate of the battery cell meets a preset condition and the function of the charging current changing with time. This includes: obtaining the time when the voltage change rate of N battery cells meets the preset condition, and obtaining the maximum value among these times as the maximum time value; and taking a definite integral over time in the function of the charging current changing with time to obtain the equalization capacity of the battery cell, wherein the lower limit of the definite integral is the time when the voltage change rate of the battery cell meets the preset condition, and the upper limit of the definite integral is the maximum time value.

[0009] The above embodiments provide a specific implementation method for calculating the balanced capacity.

[0010] In some embodiments, before recording the moment when the voltage change rate of the battery cell meets a preset condition, the method further includes: obtaining a preset condition corresponding to the preset capacity range based on the current capacity range of the battery.

[0011] In the above embodiments, the different preset capacity ranges of the current capacity of the battery correspond to preset conditions.

[0012] In some embodiments, when the preset capacity range is 0 to 50% of the total battery capacity, the corresponding preset condition is: the voltage change rate begins to be less than or equal to a first preset value.

[0013] In the above embodiments, a specific implementation method is provided for the preset conditions corresponding to a preset capacity range of 0 to 50% of the total battery capacity.

[0014] In some embodiments, when the preset capacity range is 50% to 80% of the total battery capacity, 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.

[0015] In the above embodiments, a specific implementation method is provided for the preset conditions corresponding to a preset capacity range of 50% to 80% of the total battery capacity.

[0016] In some embodiments, when the preset capacity range is from 80% of the total battery capacity to the total battery capacity, the corresponding preset condition is: the voltage change rate begins to be greater than or equal to a second preset value.

[0017] In the above embodiments, a specific implementation method is provided for preset conditions corresponding to a preset capacity range of 80% of the total battery capacity to the total battery capacity.

[0018] Secondly, embodiments of this application provide a battery management system electrically connected to a battery, which includes N cells, where N is an integer greater than 1. The system includes a calculation module, a recording module, and an balancing module. The calculation module is used to calculate the voltage change rate dV / dSOC of a cell when the cell is in a charging state. The voltage change rate is the value obtained by differentiating the cell's output voltage V with respect to the cell's current capacity SOC. The recording module is used to record the moment when the cell's voltage change rate meets a preset condition. The balancing module is used to calculate the balancing capacity corresponding to the cell based on the moment when the cell's voltage change rate meets the preset condition and the function of the charging current changing with time, and to balance the cell based on the balancing capacity.

[0019] In some embodiments, the balancing module is specifically used to obtain the time when the voltage change rate of N cells meets the preset condition, and obtain the maximum value of the time as the maximum time value. Then, it calculates the definite integral of the time in the function of the charging current of the cell changing with time to obtain the balancing capacity corresponding to the cell. The lower limit of the definite integral is the time when the voltage change rate of the cell meets the preset condition, and the upper limit of the definite integral is the maximum time value.

[0020] Thirdly, embodiments of this application provide 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 being executed by the at least one processor to enable the at least one processor to perform the above-described cell capacity balancing method.

[0021] Fourthly, embodiments of this application provide a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the above-described cell capacity balancing method.

[0022] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of the structure of a vehicle disclosed in one embodiment of this application;

[0025] Figure 2 This is a flowchart illustrating a cell capacity balancing method disclosed in an embodiment of this application. Figure 1 ;

[0026] Figure 3 This is a flowchart illustrating a cell capacity balancing method disclosed in an embodiment of this application. Figure 2 ;

[0027] Figure 4 This is a flowchart illustrating a cell capacity balancing method disclosed in an embodiment of this application. Figure 3 ;

[0028] Figure 5 This is a partial curve showing the change rate of the cell voltage with SOC in a cell capacity equalization method disclosed in an embodiment of this application;

[0029] Figure 6 This is a partial curve showing the change rate of the cell voltage with SOC in a cell capacity equalization method disclosed in one embodiment of this application;

[0030] Figure 7 This is a partial curve showing the change rate of the cell voltage with SOC in a cell capacity equalization method disclosed in one embodiment of this application;

[0031] Figure 8 This is a flowchart illustrating a cell capacity balancing method disclosed in an embodiment of this application. Figure 4 ;

[0032] Figure 9This is a block diagram of a battery management system disclosed in an embodiment of this application;

[0033] The accompanying drawings are not drawn to scale.

[0034] Labeling explanation: 1—Battery Management System, 2—Battery;

[0035] 21—Battery cell;

[0036] 501—Calculation module, 502—Recording module, 503—Balancing module. Detailed Implementation

[0037] The embodiments of this application will be described in further detail below with reference to the accompanying drawings and examples. The detailed description of the following embodiments and the accompanying drawings are used to illustrate the principles of this application by way of example, but should not be used to limit the scope of this application, that is, this application is not limited to the described embodiments.

[0038] In the description of this application, it should be noted that, unless otherwise stated, "a plurality of" means two or more; the terms "upper," "lower," "left," "right," "inner," and "outer," etc., indicating orientation or positional relationships, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this application. Furthermore, the terms "first," "second," and "third," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance. "Vertical" is not vertical in the strict sense, but within the allowable tolerance range. "Parallel" is not parallel in the strict sense, but within the allowable tolerance range.

[0039] The directional terms used in the following description refer to the directions shown in the figures and are not intended to limit the specific structure of this application. It should also be noted in the description of this application that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0040] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0041] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0042] The batteries used in new energy vehicles are typically composed of multiple cells connected in series and parallel. As the battery is used continuously, the state of charge (SOC) of each cell in the battery often differs at the same time. For example, at the same time, one cell may have an SOC of 30% and another cell may have an SOC of 40%. This can lead to the situation where, during the charging process, the cell with the lower SOC is not fully charged while the cell with the higher SOC is usually overcharged. For example, a cell with a SOC of 40% will be fully charged before a cell with a SOC of 30%. If you want to fully charge the cell with a SOC of 30%, you will inevitably overcharge the cell with a SOC of 40%. Or, during the discharge process, the cell with a lower SOC will be over-discharged before the cell with a higher SOC is fully discharged. For example, a cell with a SOC of 30% will be fully discharged before a cell with a SOC of 40%. If you want to fully discharge the cell with a SOC of 40%, you will inevitably over-discharge the cell with a SOC of 30%. This will cause significant damage to the battery.

[0043] The current method for balancing the SOC differences among battery cells is as follows: First, the minimum output voltage of each cell is calculated as the minimum cell voltage. When the difference between the output voltage of a cell and the minimum cell voltage exceeds a preset value, it is considered that the difference in SOC between that cell and the cell with the minimum output cell voltage is too large. At this time, a preset capacity is subtracted from the SOC of that cell, for example, 0.1% of the total cell capacity is subtracted, to obtain the updated SOC of that cell, in order to reduce the difference in SOC between that cell and the cell with the minimum output cell voltage. If the difference between the output voltage of that cell and the minimum cell voltage still exceeds the preset value after the update, it is considered that the difference in SOC between that cell and the cell with the minimum output cell voltage is still too large. The updated SOC of that cell is then subtracted from the aforementioned preset capacity to further reduce the difference in SOC, until the difference between the voltage of all cells and the minimum cell voltage is less than or equal to the preset value.

[0044] Obviously, the above method requires repeated judgment and balancing of the cell's SOC, which involves a large amount of calculation and the entire balancing process is time-consuming.

[0045] Based on the above problems, this application proposes the following technical concept: During the charging process of a battery cell with a plateau region, the voltage change rate dV / dSOC is obtained by differentiating the output voltage V of the battery cell with respect to the current capacity SOC of the battery cell. Based on the time when the voltage change rate of the battery cell meets the preset conditions and the charging current for charging the battery cell, the equalization capacity corresponding to the battery cell is calculated, so as to directly equalize the battery cell based on the calculated equalization capacity.

[0046] This application provides a cell capacity balancing method applied to a battery management system (BMS). Please refer to [link / reference]. Figure 1 This is a schematic diagram of a vehicle structure. The vehicle includes a battery management system 1 and a battery 2. The battery management system 1 is electrically connected to the battery 2. The battery 2 includes N cells 21, where N is an integer greater than 1. The cells 21 can be cells with a plateau region in their open-circuit voltage curve, such as lithium iron phosphate (LiFePO4, Lithium Iron Phosphate, LFP) cells. The plateau region of a cell refers to one or more segments in the relationship between the cell's State of Charge (SOC) and its output voltage V, where the output voltage V remains essentially constant. If the cell's SOC is taken as the horizontal axis and the cell's output voltage V as the vertical axis, then within one or more segments of the horizontal axis range, the value of the vertical axis remains essentially constant, forming a "plateau region."

[0047] For a battery cell with a plateau region, the SOC of the battery cell can only be estimated based on the output voltage V of the battery cell and the correspondence between the SOC of the battery cell and the output voltage V. If the output voltage V of the battery cell corresponds to the plateau region of the battery cell, there may be multiple SOCs that correspond to the output voltage V, making it difficult to accurately estimate the SOC of the battery cell.

[0048] In some embodiments, the battery management system 1 is electrically connected to N cells 21 in the battery 2. Figure 1 (The connection structure is not shown in the figure) to collect parameters such as temperature, voltage and current of each cell, and then observe the cell status. The battery management system 1 can also control each cell to be in a charging state or a discharging state.

[0049] According to some embodiments of this application, a flowchart of the cell capacity equalization method can be referred to. Figure 2 ,include:

[0050] Step 101: When the battery cell is in the charging state, calculate the voltage change rate dV / dSOC of the battery cell.

[0051] Step 102: Record the moment when the voltage change rate of the battery cell meets the preset condition.

[0052] Step 103: Calculate the equalization capacity of the battery cell based on the time when the voltage change rate of the battery cell meets the preset conditions and the function of the charging current changing with time.

[0053] Step 104: Equalize the cells according to the equalization capacity.

[0054] The following is a detailed description of the implementation details of the cell capacity balancing method in this embodiment. The following content is only for the convenience of understanding and is not necessary for implementing this solution.

[0055] Specifically, the voltage change rate dV / dSOC in step 101 is the value obtained by differentiating the output voltage V of the battery cell with 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 and dividing it by the total capacity of the battery cell.

[0056] In step 103, the function of the charging current for charging the battery cell as a function of time can be any function that conforms to the charging current for charging the battery cell. For example, the magnitude of the charging current for charging the battery cell can be considered to be constant, that is, the function is a constant function, or it can be a sinusoidal function that changes in a sinusoidal manner. There are no restrictions here.

[0057] Compared to related technologies that can only perform multiple judgments and equalizations on multiple cells until the differences between cells are reduced to an acceptable range, the embodiments of this application can directly calculate the difference in SOC between each cell and use this as the equalization capacity to equalize each cell once, reducing the amount of calculation required for multiple judgments and speeding up the process of cell SOC equalization.

[0058] In some embodiments, a specific formula for calculating the balanced capacity is provided. Please refer to... Figure 3 Steps 201, 202, and 205 are largely the same as steps 101, 102, and 104, and will not be repeated here.

[0059] Step 203: Obtain the time when the voltage change rate of each of the N cells meets the preset condition, and obtain the maximum value of the time as the maximum time value.

[0060] Step 204: Calculate the definite integral of time in the function of the charging current changing with time to obtain the equalization capacity of the battery cell. The lower limit of the definite integral is the moment when the voltage change rate of the battery cell meets the preset condition, and the upper limit of the definite integral is the maximum moment value.

[0061] When the voltage change rate of a cell meets a preset condition, the BMS records this moment as the moment when the voltage change rate of that cell meets the preset condition. In some embodiments, after recording the moments when the voltage change rate of all cells meets the preset condition, the BMS obtains the maximum value among these moments as the maximum moment value. Then, it calculates the definite integral of the time in the function of the charging current changing with time to obtain the equalization capacity corresponding to the cell. 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 equalization capacity corresponding to the cell is calculated using the ampere-hour integration method.

[0062] If the charging current of a battery cell changes as a constant over time, meaning the magnitude of the charging current remains constant during charging, then the cell corresponding to the maximum time value is actually the cell with the lowest State of Charge (SOC). The Battery Management System (BMS) uses the cell with the lowest SOC as a benchmark to measure the difference between the SOC of the other cells and that of the cell with the lowest SOC. Specifically, the BMS first subtracts the time when the voltage change rate of each cell meets a preset condition from the maximum time value to obtain the difference for each cell as the equalization time. Then, it multiplies the equalization time by the constant charging current to obtain the equalization capacity for each cell.

[0063] For example, a battery consists of three cells. When these three cells are charging, the BMS sequentially acquires the times t1, t2, and t3 when the voltage change rate of these three cells meets a preset condition. Here, t3 is the maximum value. For the first cell, the balancing time is equal to t3-t1, and the balancing capacity is (t3-t1)*I, where I is the charging current for each cell. For the second cell, the balancing time is equal to t2-t1, and the balancing capacity is (t2-t1)*I. For the third cell, the balancing time is equal to t3-t3=0, and the balancing capacity is also 0.

[0064] In some embodiments, there may be a situation where the voltage change rate of some cells has not yet met the preset condition, and the cells stop being charged. In this case, the BMS will not obtain the time when the voltage change rate of all cells meets the preset condition. The BMS can record the time when each cell stops being charged as the time corresponding to the cell whose voltage change rate has not yet met the preset condition.

[0065] For example, a battery consists of three cells. When these three cells are charging, the BMS sequentially obtains the times t1 and t2 when the voltage change rate of two cells meets the preset condition. When the voltage change rate of the remaining cell does not meet the preset condition, all cells stop being charged. At this time, the BMS records the time t0 when the cell stops being charged, which is the time corresponding to the cell whose voltage change rate does not meet the preset condition. Obviously, t0 is greater than t1 and t2, so t0 is taken as the maximum time value. At this time, for the first cell, the balancing time is equal to t0-t1, and the balancing capacity is (t0-t1)*I. For the second cell, the balancing time is equal to t0-t1, and the balancing capacity is (t0-t1)*I. For the third cell, the balancing time is equal to t0-t0=0, and the balancing capacity is also 0.

[0066] In some embodiments, please refer to Figure 4 Steps 301, 303, 304 and 305 are largely the same as steps 101, 102, 103 and 104, and will not be repeated here.

[0067] Step 302: Based on the preset capacity range in which the current capacity of the battery is located, obtain the preset conditions corresponding to the preset capacity range.

[0068] There is a corresponding relationship between the current capacity of the battery and the preset capacity range and the preset conditions.

[0069] In some embodiments, when the preset capacity range is 0 to 50% of the total battery capacity, the corresponding preset condition is: the voltage change rate begins to be less than or equal to a first preset value.

[0070] For cells with a charging plateau, taking a battery containing LFP cells as an example, when the current capacity of the battery is between 0 and 35% of the total capacity, each cell can be considered to be at the low end of the charging process. When the current capacity of the battery is between 35% and 80% of the total capacity, each cell can be considered to be in the charging plateau region. When the current capacity of the battery is greater than 80% of the total capacity, each cell can be considered to be at the end of the charging process.

[0071] Please refer to Figure 5 The graph shows partial curves of the voltage change rate of a battery cell as a function of its State of Charge (SOC). Different curves correspond to different charging rates for the cells. The graph illustrates the curves for charging rates of 01C, 015C, 02C, 025C, and 033C cells. As can be seen, the voltage change rate of a battery cell gradually approaches zero as it charges from the low end to the plateau region. The order in which different cells reach this plateau region can be used to identify the SOC of different cells. Figure 5Taking the value of the ordinate corresponding to the differential point 1 being equal to the first preset value as an example, the time t when the voltage change rate of each cell begins to be less than or equal to the first preset value is recorded sequentially. 1n Until the moment t of the last battery cell was recorded. 1max , using (t 1max -t 1n *I is used as the equalization capacity for each cell to achieve equalization. Specifically, the equalization capacity (t) can be used. 1max -t 1n Divide I by the equalization current used to equalize the battery cell to obtain the specific time required to equalize the battery cell, and then equalize the battery cell according to the specific time. Specifically, a timer can be used to equalize the battery cell until the timer ends and the equalization stops.

[0072] The setting of the first preset value is usually obtained by technicians through a large number of pre-shipment experiments. Specifically, it is obtained by testing the SOC value corresponding to the differential point 1 under different charging rates, different charging temperatures and different aging degrees of the battery cells.

[0073] In some embodiments, when the preset capacity range is 50% to 80% of the total battery capacity, 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 preset time period is typically set by technicians through extensive pre-shipment testing.

[0074] Please refer to Figure 6 The graph shows partial curves of voltage change rate as a function of State of Charge (SOC) for each battery cell. Different curves correspond to different charging rates for the cells. The graph lists the curves corresponding to the charging rates of 01C, 015C, 02C, 025C, and 033C cells. As can be seen from the graph, after a cell reaches a charging plateau, the voltage change rate of the cell will have a peak between two small plateaus. The order in which different cells reach this peak can be used to identify the SOC of different cells. Figure 6 Taking the value of the ordinate corresponding to the differential point 2 as equal to the peak value as an example, the time t when the voltage change rate of each cell reaches the maximum voltage change rate within the preset time period is recorded sequentially. 2n Until the moment t of the last battery cell was recorded. 2max , using (t 2max -t 2n *I is used as the equalization capacity for each cell to achieve equalization. Specifically, the equalization capacity (t) can be used. 2max -t 2nDivide I by the equalization current used to equalize the battery cell to obtain the specific time required to equalize the battery cell, and then equalize the battery cell according to the specific time. Specifically, a timer can be used to equalize the battery cell until the timer ends and the equalization stops.

[0075] In some embodiments, when the preset capacity range is from 80% of the total battery capacity to the total battery capacity, the corresponding preset condition is: the voltage change rate begins to be greater than or equal to a second preset value.

[0076] Please refer to Figure 7 The graph shows partial curves of voltage change rate as a function of State of Charge (SOC) for each battery cell. Different curves correspond to different charging rates for the cells. The graph illustrates the curves for charging rates of 01C, 015C, 02C, 025C, and 033C cells. As can be seen, the voltage change rate of a cell increases sharply after it reaches the end of the charging process. The order in which different cells are charged to this region can be used to identify the SOC of different cells. Figure 7 Taking the value of the ordinate corresponding to the differential point 3 being equal to the second preset value as an example, the time t when the voltage change rate of each cell begins to be greater than or equal to the second preset value is recorded sequentially. 3n Until the moment t of the last battery cell was recorded. 3max , using (t 3max -t 3n *I is used as the equalization capacity for each cell to achieve equalization. Specifically, the equalization capacity (t) can be used. 3max -t 3n Divide I by the equalization current used to equalize the battery cell to obtain the specific time required to equalize the battery cell, and then equalize the battery cell according to the specific time. Specifically, a timer can be used to equalize the battery cell until the timer ends and the equalization stops.

[0077] The setting of the second preset value is usually obtained by technicians through a large number of pre-shipment experiments. Specifically, it is obtained by testing the SOC value corresponding to the differential point 3 under different charging rates, different charging temperatures and different aging degrees of the battery cells.

[0078] It should be noted that the order of steps 301 and 302 is not limited in the embodiments of this application. That is, the preset conditions corresponding to the preset capacity range can be obtained first, or the voltage change rate dV / dSOC of the battery cell can be obtained first.

[0079] Furthermore, the above only illustrates three specific preset capacity ranges and their corresponding preset conditions. It does not limit the preset capacity range of the battery cell to only the above three specific preset capacity ranges, nor does it limit the number of preset capacity ranges to three, nor does it limit the preset conditions corresponding to each preset capacity range to the above three preset conditions. Any technical solution that meets the charging characteristics of a battery cell with a plateau region is within the protection scope of this application.

[0080] In some embodiments, please refer to Figure 8 A flowchart.

[0081] Step 401: Determine whether the battery cell is in a charging state. If yes, proceed to step 402; otherwise, repeat step 401.

[0082] Step 402: When the current capacity of the battery is within the preset capacity range, read the voltage and temperature parameters of the battery cell.

[0083] Step 403: Calculate the voltage change rate of the battery cell based on parameters such as voltage and temperature.

[0084] Step 404: Determine whether the voltage change rate of the battery cell meets the preset conditions. If yes, proceed to step 405; otherwise, return to step 403.

[0085] Step 405: Record the moment when the voltage change rate of the battery cell meets the preset condition.

[0086] Step 406: After recording the times 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 Among them, t max For the maximum current value, t n I represents the moment when the voltage change rate of each cell meets a preset condition, and I represents the charging current for charging the cell. bal This is to provide the balancing current required for cell balancing.

[0087] Step 407, according to the balancing current I required for balancing. bal The time required for cell balancing is used to balance the cells until the time required for balancing all cells is 0.

[0088] In some embodiments, there is a correspondence between preset capacity ranges and preset conditions. Specifically, when the preset capacity range is from 0 to 50% of the total battery capacity, the corresponding preset condition is: the voltage change rate begins to be less than or equal to a first preset value; when the preset capacity range is from 50% to 80% of the total battery capacity, 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% to the total battery capacity, the corresponding preset condition is: the voltage change rate begins to be greater than or equal to a second preset value.

[0089] For example, the BMS first needs to obtain the current capacity of the battery. If the current capacity is 30% of the total battery capacity, it can be determined that the current capacity is within a preset range of 0 to 50% of the total battery capacity. Therefore, the preset condition is: the voltage change rate begins to be less than or equal to a first preset value. That is, the BMS needs to obtain the charging status of each cell. Figure 5 The time of differential point 1 in the equation; for example, if the current capacity of the battery is 65% of the total battery capacity, it can be determined that the current capacity of the battery is within the preset capacity range of 50% to 80% of the total battery capacity. Therefore, the preset condition at this time is: the voltage change rate is the maximum voltage change rate within a preset time period, where the preset time period includes the time corresponding to the voltage change rate. At this time, the BMS needs to obtain the charging time of each cell. Figure 6 At the moment of differential point 2; for example, if the current capacity of the battery is 85% of the total battery capacity, it can be determined that the current capacity of the battery is within the preset capacity range of 80% to 10% of the total battery capacity. Therefore, the preset condition at this time is: the voltage change rate begins to be greater than or equal to the second preset value, that is, the BMS needs to obtain the charging status of each cell to the specified value. Figure 7 The moment of differential point 3 in the equation.

[0090] After recording the times when the voltage change rate of all cells meets the preset conditions, calculate the time required for each cell to achieve equalization: (t max -t n )*I / I bal Then, according to the balancing current I required for balancing... bal The balancing process involves balancing the cells until the balancing time for all cells is zero, at which point the balancing process is complete.

[0091] One embodiment of this application provides a battery management system electrically connected to a battery, which includes N cells, where N is an integer greater than 1. The cells can be cells whose open-circuit voltage curves have a plateau region.

[0092] Please refer to Figure 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.

[0093] The calculation module 501 calculates the voltage change rate dV / dSOC of the battery cell when the cell is in the charging state. The voltage change rate is the value obtained by differentiating the output voltage V of the battery cell with the current capacity SOC of the battery cell. The recording module 502 records the moment when the voltage change rate of the battery cell meets the preset condition. Finally, the balancing module 503 calculates the balancing capacity of the battery cell based on the moment when the voltage change rate of the battery cell meets the preset condition and the function of the charging current changing with time, and balances the battery cell according to the balancing capacity.

[0094] It is not difficult to see that this embodiment is related to Figure 2 The corresponding system implementation embodiment, this embodiment can be compared with Figure 2 The corresponding implementation examples are carried out in conjunction with each other. Figure 2 The relevant technical details mentioned in the corresponding embodiments remain valid in this embodiment, and will not be repeated here to avoid repetition. Correspondingly, the relevant technical details mentioned in this embodiment can also be applied to... Figure 2 In the corresponding embodiment.

[0095] In some embodiments, the balancing module 503 will obtain the time when the voltage change rate of N cells meets the preset condition, and obtain the maximum value of the time as the maximum time value. Then, it will calculate the definite integral of the time in the function of the charging current of the cell changing with time to obtain the balancing capacity corresponding to the cell. The lower limit of the definite integral is the time when the voltage change rate of the cell meets the preset condition, and the upper limit of the definite integral is the maximum time value.

[0096] It is not difficult to see that this embodiment is related to Figure 3 The corresponding system implementation embodiment, this embodiment can be compared with Figure 3 The corresponding implementation examples are carried out in conjunction with each other. Figure 3 The relevant technical details mentioned in the corresponding embodiments remain valid in this embodiment, and will not be repeated here to avoid repetition. Correspondingly, the relevant technical details mentioned in this embodiment can also be applied to... Figure 3 In the corresponding embodiment.

[0097] One embodiment of this application provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the above-described cell capacity balancing method.

[0098] That is, those skilled in the art will understand that all or part of the steps in the methods of the above embodiments can be implemented by a program instructing related hardware. This program is stored in a storage medium and includes several instructions to cause a device (which may be a microcontroller, chip, etc.) or processor to execute all or part of the steps of the methods described in the various embodiments of this application. The aforementioned storage medium includes various media capable of storing program code, such as a USB flash drive, a portable hard drive, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk.

[0099] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A cell capacity balancing method, applied to a battery management system, wherein the battery management system is electrically connected to a battery, and the battery includes N cells, wherein... N is an integer greater than 1; The method includes: When the battery cell is in a charging state, calculate the voltage change rate dV / dSOC of the battery cell; The voltage change rate is the value obtained by differentiating the output voltage V of the battery cell with respect to the current capacity SOC of the battery cell. Record the moment when the voltage change rate of the battery cell meets the preset condition; Based on the moment when the voltage change rate of the battery cell meets the preset condition and the function of the charging current changing with time, the equalization capacity of the battery cell is calculated, and the battery cell is equalized according to the equalization capacity. The step of calculating the equalization capacity of the battery cell based on the time when the voltage change rate of the battery cell meets the preset condition and the function of the charging current changing with time, includes: Obtain the times when the voltage change rate of N cells satisfies the preset condition, and obtain the maximum value among the times as the maximum time value; The equalization capacity of the battery cell is obtained by taking the definite integral of the time in the function of the charging current changing with time. The lower limit of the definite integral is the moment when the voltage change rate of the battery cell meets the preset condition, and the upper limit of the definite integral is the maximum moment value. The preset conditions include: the voltage change rate is within a preset value range.

2. The cell capacity equalization method according to claim 1, wherein, Before the time when the voltage change rate of the battery cell meets the preset condition, the method further includes: Based on the preset capacity range in which the current capacity of the battery falls, obtain the preset conditions corresponding to the preset capacity range.

3. The cell capacity equalization method according to claim 2, wherein, When the preset capacity range is from 0 to 50% of the total capacity of the battery, the corresponding preset condition is: the voltage change rate begins to be less than or equal to the first preset value.

4. The cell capacity equalization method according to claim 2 or 3, wherein, When the preset capacity range is 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.

5. The cell capacity equalization method according to any one of claims 2 to 3, 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 condition is: the voltage change rate begins to be greater than or equal to the second preset value.

6. A battery management system, wherein the battery management system is electrically connected to a battery, the battery comprising N cells, wherein, 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 cell when the battery cell is in a charging state. The voltage change rate is the value obtained by differentiating the output voltage V of the battery cell with respect 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 a preset condition; The equalization module is used to calculate the equalization capacity of the battery cell based on the time when the voltage change rate of the battery cell meets the preset condition and the function of the charging current of the battery cell changing with time, and to equalize the battery cell based on the equalization capacity. The equalization module is further used for: Obtain the times when the voltage change rate of N cells satisfies the preset condition, and obtain the maximum value among the times as the maximum time value; The equalization capacity of the battery cell is obtained by taking the definite integral of the time in the function of the charging current changing with time. The lower limit of the definite integral is the moment when the voltage change rate of the battery cell meets the preset condition, and the upper limit of the definite integral is the maximum moment value. The preset conditions include: the voltage change rate is within a preset value range.

7. The battery management system according to claim 6, wherein, The equalization module is specifically used to obtain the times when the voltage change rate of N cells meets the preset condition, and obtain the maximum value among the times as the maximum time value. Then, it calculates the definite integral of the time in the function of the charging current changing with time to obtain the equalization capacity corresponding to the cell. The lower limit of the definite integral is the time when the voltage change rate of the cell meets the preset condition, and the upper limit of the definite integral is the maximum time value.

8. A battery management system, comprising: At least one processor; as well as, A memory communicatively connected to the at least one processor; wherein, The memory stores instructions that can be executed by the at least one processor to enable the at least one processor to perform the cell capacity balancing method as described in any one of claims 1 to 5.

9. A computer-readable storage medium storing a computer program that, when executed by a processor, implements the cell capacity balancing method according to any one of claims 1 to 5.

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