Battery SOH estimation method

Abstract

The invention discloses a battery SOH (state of health) estimation method, which comprises the following steps of: S1, acquiring rated charging current Ij of a battery cell; s2, carrying out charging test on each test cell for N times under different SOH values; s3, analyzing and judging the Vni under different SOH values obtained in the step S2 and the corresponding Vni, and judging whether a function relationship between the Vni corresponding to at least five Vni and the SOH value fits one of three functions or not; s4, repeating the step S2 to the step S3 to obtain a function relation between the Vni and the SOH value under different temperature conditions and different charging currents; s5, amplifying the function relational expression of Vni and SOH obtained in the step S4 by m times, and inputting the amplified function relational expression into a BMS of the battery; and S6, calculating the SOH value when the battery is charged every time. According to the method, the SOH value can be quickly and accurately obtained.

Description

Technical Field

[0001] The present invention relates to the field of batteries, and particularly to a method for estimating the SOH of a battery. Background Art

[0002] SOH (State of Health) refers to the health life state of a battery, which is defined as the ratio of the actual available capacity of the current battery to the rated capacity of the battery. Under different SOHs, parameters such as the charge and discharge power, heat generation, and available power of the battery are different. For example, when the SOH is low, the resistance of the battery is large and the heat generation is high. If the charge and discharge power of the battery is not limited in time, it may overheat and cause thermal runaway. In addition, low SOH also affects the battery's endurance time and the user's judgment of the endurance time. Therefore, it is necessary to accurately evaluate the SOH of the necessary battery. Currently, the conventional method for estimating the SOH of a battery is to obtain the capacity of a full charge and full discharge of the battery at present and then divide it by the rated capacity (initial capacity) of the battery to obtain the current SOH of the battery. However, when the battery is in use, in many cases, the battery cannot be fully discharged, and even the frequency of full discharge is very low (that is, the time interval between two full discharges is too long and has no calculation significance). Therefore, it is difficult to obtain the capacity of a full charge and full discharge, and even if it is obtained, it may not be able to reflect the current state of the battery at any time.

[0003] In view of the existence of the above problems, it is necessary to study a method for estimating the SOH of a battery, which can simply and effectively estimate the SOH of the battery. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for estimating the SOH of a battery, which can simply and effectively estimate the SOH of the battery.

[0005] To achieve the above object, the solution of the present invention is: A method for estimating the SOH of a battery, which includes the following steps: Step S1: Obtain at least one rated charging current of the battery cell on the battery I j , j is the number for different rated charging currents; Step S2: Select at least one battery cell as a test battery cell, and perform charging tests on each test battery cell at N different SOH values; the SOH value of the test battery cell during the first charging test is 100% SOH, and the SOH values of the test battery cell during each charging test decrease sequentially at a preset fixed percentage SOH interval △SOH; N is a positive integer greater than 10; The charging test includes: Step S21: Charge the test battery cell at a rated charging current obtained in Step S1 at a preset test temperature T ​I j Charge it to obtain the charging curve of the voltage of the test battery cell varying with the current; Step S22: According to the charging curve of the test battery cell obtained in step S21, take voltage values downward from the full charge voltage of the test battery cell, and take a voltage value every preset voltage interval △v to obtain the voltage set corresponding to the test battery cell R i ; R i = V 0_i , _ V 1_i , V 2_i ...... V n_i , n where represents the serial number starting from zero, i and represents the SOH of the test battery cell during the current charging test; Step S23: Charge the test battery cell multiple times at a fixed time with the rated charging current used in step S21, and calculate the voltage change value of the test battery cell before and after the preset charging time △V n_i ; The time of each fixed-time charge is the preset charging time t ; The voltage of the test battery cell at the start moment of each fixed-time charge is taken from each value of the voltage set obtained in step S22 R i , that is, the voltage of the test battery cell at the start moment of each fixed-time charge is V n_i , while the voltage of the test battery cell at the final moment of each fixed-time charge is V f_n_i ; △V n_i = V f_n_i - V n_i ; Step S3: Analyze and judge for the obtained at different SOH values in step S2 V n_i and the corresponding △V n_i to determine whether there are at least five V n_i corresponding △V n_i whose functional relationship with the SOH value fits one of the following three functions; Function 1 is: y = k· x + a ; Function 2 is: y =b x + c ; Function three is: y = a· x 2 + c· x + d ; where y is the △ V n_i value, x is the number corresponding to the SOH during each charging test of the test battery cell in step S2 (knowing the x value can correspondingly obtain the SOH value of the test battery cell), x starts from zero, and k > 0, a > 0, b > 1, c > 0, d > 0; if it exists, go to step S4; if not, repeat step S2 and correspondingly reduce the preset voltage interval △v ; Step S4: Repeat steps S2 to S3, and replace the values of the preset test temperature T and the rated charging current I j to obtain the function relationship between △V n_i and the SOH value under different temperature conditions and different charging currents; Step S5: Multiply the function relationships between △V n_i and the SOH obtained in step S4 by m times under different temperature conditions and different charging currents to obtain the function relationships between m ·△V n_i and the SOH value of the battery under different temperature conditions and different charging currents, and correspondingly input them into the BMS of the battery, where m is the number of battery cells; Step S6: During each charging of the battery, if the BMS of the battery determines that there are more than three V n_i corresponding m ·△V n_i meet the function relationships between m ·△V n_i and the SOH value of the battery under different temperature conditions and different charging currents, then correspondingly calculate more than three SOH values, and after removing the maximum and minimum values of the calculated SOH values, take the average of the remaining SOH values as the SOH value output by the BMS; if the BMS of the battery determines that there are not more than three V n_i corresponding m ·△V n_i meet the function relationships between m ·△Vn_i For the functional relationship with the SOH value, the BMS of the battery still outputs the previous SOH value.

[0006] In step S1, the charging current of the adapted charger is used as the rated charging current.

[0007] In step S2, 0.5% SOH is used as the preset fixed percentage SOH interval △SOH; in step S6, after removing the maximum and minimum values from the calculated SOH values, if the deviation between the average value of the remaining SOH values and the SOH value output by the BMS of the battery last time exceeds 0.5%, the BMS of the battery still outputs the previous SOH value.

[0008] In step S6, when the BMS of the battery determines that there are more than three V n_i corresponding m ·△V n_i m that conforms to the battery under different temperature conditions and different charging currents ·△V n_i Under the functional relationship with SOH, if the deviation between the calculated SOH values exceeds 3%, the BMS of the battery still outputs the previous SOH value.

[0009] After adopting the above scheme, the present invention obtains the voltage change value m of the battery within the preset charging time ·△V n_i The functional relationship that increases with the attenuation of SOH. Therefore, as long as the obtained voltage change value m ·△V n_i The SOH value can be correspondingly obtained without considering whether the battery is fully discharged during use, and the SOH value of the battery can be obtained basically every time it is charged, and the SOH value of the battery can be updated more quickly and accurately. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a schematic flow chart of the steps of the present invention.

[0011] Figure 2 For the present invention △V n_i A comparison table with SOH.

[0012] Figure 3 For corresponding to Figure 2 Dot plot. DETAILED DESCRIPTION OF THE INVENTION

[0013] In order to further explain the technical solution of the present invention, the present invention will be elaborated in detail below through specific embodiments.

[0014] Such as Figure 1As shown in the figure, the present invention discloses a method for estimating the SOH of a battery, which includes the following steps: Step S1: Define various operating conditions of the battery cells on the battery to obtain at least one rated charging current of the battery cells on the battery I j , j is the number for different rated charging currents; Step S2: Select at least one battery cell as the test battery cell and conduct charging tests on each test battery cell at different SOH values for N times; among them, the SOH value of the test battery cell during the first charging test is 100% SOH, and the SOH values of the test battery cell during each charging test decrease successively at a preset fixed percentage SOH interval △SOH; N is a positive integer greater than 10; This charging test includes: Step S21: Charge the test battery cell at a rated charging current obtained in step S1 at a preset test temperature T to obtain a charging curve of the voltage of the test battery cell changing with the current; I j Step S22: According to the charging curve of the test battery cell obtained in step S21, take voltage values from the full charge voltage of the test battery cell downward, and take a voltage value every preset voltage interval △v to obtain a voltage set corresponding to the test battery cell R i ; R i = V 0_i , _ V 1_i , V 2_i …… V n_i , n represents the serial number starting from zero, i represents the SOH of the test battery cell during the current charging test; Step S23: Conduct multiple timed chargings on the test battery cell at the rated charging current used in step S21 and calculate the voltage change value of the test battery cell before and after the preset charging time △V n_i ; The time of each timed charging is the preset charging time t ; the voltages of the test battery cell at the start time of each timed charging are respectively taken from the values of the voltage set obtained in step S22 R i , that is, the voltage of the test battery cell at the start time of each timed charging is V n_i ​, while the voltage of the test battery cell at the end of each timed charge is V f_n_i ; △V n_i = V f_n_i - V n_i ; Step S3: Analyze and judge the V n_i obtained in different SOH values in step S2 and the corresponding △V n_i to determine whether there are at least five V n_i corresponding △V n_i and the function relationship with the SOH value fits one of the following three functions; Function 1 is: y = k· x + a ; Function 2 is: y = b x + c ; Function 3 is: y = a· x 2 + c· x + d ; where y is the value of △ V n_i , x is the number corresponding to the SOH during each charge test of the test battery cell in step S2 (knowing the x value can correspond to the SOH value of the test battery cell), x starts from zero, and k > 0, a > 0, b > 1, c > 0, d > 0; if there is, enter step S4; if not, repeat step S2 and correspondingly reduce the preset voltage interval △v ; Step S4: Repeat steps S2 to S3, and replace the preset test temperature T and the rated charging current I j in step S2, so as to obtain the function relationship between △V n_i and the SOH value under different temperature conditions and different charging currents; Step S5: Multiply the function relationships between △V n_i and the SOH obtained in step S4 by m times to obtain the m ·△V n_iThe functional relationship with the SOH value is correspondingly input into the BMS of the battery, where m is the number of battery cells; Step S6: During each charging of the battery, if the BMS of the battery determines that there are more than three V n_i corresponding m ·△V n_i m that conforms to the battery under different temperature conditions and different charging currents ·△V n_i with the functional relationship of the SOH value, then correspondingly calculate more than three SOH values, and after removing the maximum and minimum values among the calculated SOH values, take the average of the remaining SOH values as the SOH value output by the BMS to the outside; if the BMS of the battery determines that there are not more than three V n_i corresponding m ·△V n_i m that conforms to the battery under different temperature conditions and different charging currents ·△V n_i with the functional relationship of the SOH value, then the BMS of the battery still outputs the previous SOH value.

[0015] As can be seen from the above, the present invention obtains the voltage change value m of the battery within the preset charging time ·△V n_i varying with the SOH value. Therefore, as long as the voltage change value m is obtained ·△V n_i the SOH value can be correspondingly obtained without considering whether the battery is fully discharged during use, and the SOH value can be obtained basically every time it is charged, and the SOH value of the battery can be updated more quickly and accurately.

[0016] To facilitate the understanding of the present invention, the following specifically introduces each step of the present invention.

[0017] Regarding step S1, since the discharge current of the battery cell cannot be controlled and the discharge current fluctuates continuously, while the charging current can obtain a definite current magnitude according to the adapted charger, and the current during the charging of the battery cell is relatively stable and has relatively small fluctuations; therefore, the present invention can use the charging current of the adapted charger as the rated charging current I j .

[0018] Regarding step S2, 0.5% SOH can be used as the preset fixed percentage SOH interval △SOH; correspondingly, in step S6, after removing the maximum and minimum values among the calculated SOH values, if the deviation between the average value taken from the remaining SOH values and the SOH value output by the BMS of the battery last time exceeds 0.5%, then the BMS of the battery still outputs the previous SOH value, thus avoiding errors.

[0019] Figure 2 shows the comparison table of SOH values under the condition of "taking 5 battery cells as test battery cells, with the preset test temperature T being 25 °C, the preset fixed percentage SOH interval △SOH being 0.5% SOH, the charging rate being 0.5C, and the preset charging time t being 60 s, V n_i being 3.65 V"; (It should be noted that taking 5 battery cells as test battery cells can reduce errors, and the number of battery cells can be more; and 3.65 V is just one of them △V n_i , at least 4 more V n_i are required to meet the requirements, but the amount of data is too large, and only one point is taken for illustration); As shown in V n_i , through the dot plot, y = Figure 3 can be fitted, where y is the corresponding number x (SOH decays at a decay number of every 0.5%) of the SOH of the test battery cell at 3.65 V voltage 0.288· x + 23.1 ; Similarly, the corresponding table of △V n_i and SOH values under other V n_i can be obtained. If there is an obvious functional relationship between △V n_i and the SOH value under this △V n_i , then take out this V n_i ; At least take out 5 corresponding △V n_i with an obvious functional relationship between V n_i and the SOH value; In addition, similarly, the functional relationship between △V n_i and the SOH value when charging at other rates at 25 °C can be tested; Similarly, the functional relationship between △V n_i and the SOH value under other temperature conditions can also be tested; Finally, all △V n_i functional relationships between

[0020] Regarding step S5, in order to reduce the calculation amount of the BMS of the battery, only calculate the voltage change value of the entire battery pack, and do not calculate the voltage change value of a single battery cell △V n_i ; Therefore, when the number of battery cells in the battery is m, then △V n_iMagnify by m times. For example, for the △V n_i The functional relationship with the SOH value is y = 0.288· x + 23.1 ; then for the battery pack's m ·△V n_i The functional relationship with the SOH value is y / m = 0.288· x + 23.1 .

[0021] Since the functional relationships between △V n_i and the SOH value at different temperatures are different, and the temperature of the battery changes during charging. Therefore, the temperature corresponding to the voltage point V n_i is the average temperature during the voltage change process; in order to improve the accuracy of the SOH value, then △V n_i should be as small as possible. In addition, in step S6, when the BMS of the battery determines that there are more than three V n_i corresponding m · △V n_i meets the functional relationship between m ·△V n_i and SOH of the battery under different temperature conditions and different charging currents. If the deviation between the calculated SOH values exceeds 3%, then the BMS of the battery still outputs the previous SOH value.

[0022] The above embodiments and diagrams do not limit the product form and style of the present invention. Any appropriate changes or modifications made by those of ordinary skill in the art shall be regarded as not departing from the patent scope of the present invention.

Claims

1. A method for estimating the state of health (SOH) of a battery, characterized in that: Including the following steps: Step S1: Obtain at least one rated charging current of the battery cell on the battery I j , j which is the number for different rated charging currents Step S2: Take at least one battery cell as a test battery cell, and conduct charging tests on each test battery cell at N different SOH values; the SOH value of the test battery cell during the first charging test is 100% SOH, and the SOH value of the test battery cell in each charging test decreases sequentially at a preset fixed percentage SOH interval △SOH; N is a positive integer greater than 10; This charging test includes: Step S21: At a preset test temperature for the test battery cell T charge the test battery cell with a rated charging current obtained in step S1 I j to obtain a charging curve showing the variation of the voltage of the test battery cell with the current; Step S22: According to the charging curve of the test battery cell obtained in Step S21, take voltage values from the full charge voltage downwards for the test battery cell, and take a voltage value every preset voltage interval △v to obtain a voltage set corresponding to the test battery cell R i ; R i = V 0_i ,_ V 1_i , V 2_i …… V n_i , n represents the serial number starting from zero, i and represents the SOH of the test battery cell during the current charging test; Step S23: Charge the test battery cell multiple times at a constant charging current used in Step S21 for a preset charging time, and calculate the voltage change value of the test battery cell before and after the preset charging time △V n_i ; The time of each timed charge is the preset charging time t ; The voltage of the test battery cell at the start time of each timed charge is taken from each value in the voltage set obtained in Step S22 R i , that is, the voltage of the test battery cell at the start time of each timed charge is V n_i , and the voltage of the test battery cell at the final time of each timed charge is V f_n_i ; △V n_i = V f_n_i - V n_i ; Step S3: For those obtained in Step S2 under different SOH values V n_i and the corresponding △V n_i perform an analysis and determination to judge whether there are at least five V n_i corresponding △V n_i Whether the functional relationship with the SOH value fits one of the following three functions; Function 1 is: y = k· x + a ; Function 2 is: y = b x + c ; Function 3 is: y = a· x 2 + c· x + d ; where y is the value of △V n_i , x is the number corresponding to the SOH of the test battery cell during each charge test in step S2 (knowing the value of x can correspondingly obtain the SOH value of the test battery cell), x starts from zero, and k > 0, a > 0, b > 1, c > 0, d > 0; If it exists, go to step S4; if not, repeat step S2 and correspondingly reduce the preset voltage interval △v . Step S4: Repeat Step S2 to Step S3, and replace the values of the preset test temperature T and the rated charging current in Step S2, so as to obtain the functional relationship between △V and the SOH value under different temperature conditions and different charging currents; I j so as to obtain the △V n_i functional relationship between and the SOH value; Step S5: For the △V n_i function relations between and SOH obtained in Step S4 under different temperature conditions and different charging currents, magnify them by m times to obtain the function relations between m ·△V n_i and the SOH values of the battery under different temperature conditions and different charging currents, and input them into the BMS of the battery accordingly, where m is the number of battery cells; Step S6: When the battery is charged each time, if the battery BMS determines that there are three or more V n_i The corresponding m ·△V n_i Meet the battery m under different temperature conditions and different charging currents ·△V n_i If the function relationship between the battery and the SOH value is calculated, more than three SOH values are obtained, and after removing the maximum and minimum values of the calculated SOH values, the average value of the remaining SOH values is taken as the SOH value output by the BMS. If the BMS of the battery determines that there are no more than three V n_i The corresponding m · △V n_i Meet the battery m under different temperature conditions and different charging currents ·△V n_i The functional relationship between the battery and the SOH value is as follows: the BMS of the battery still outputs the last SOH value.

2. The battery SOH estimation method according to claim 1, characterized in that: In step S1, use the charging current of the adapted charger as the rated charging current.

3. The battery SOH estimation method according to claim 1, characterized in that: In step S2, use 0.5% SOH as the preset fixed percentage SOH interval △SOH; in step S6, after removing the maximum and minimum values of the calculated SOH values, if the deviation between the average value of the remaining SOH values and the SOH value output by the battery's BMS last time exceeds 0.5%, the battery's BMS still outputs the SOH value last time.

4. The battery SOH estimation method according to claim 1, wherein: In step S6, when the BMS of the battery determines that there are more than three V n_i corresponding m ·△V n_i which conforms to the function relationship between m and SOH of the battery under different temperature conditions and different charging currents, if the deviation between the calculated SOH values exceeds 3%, the BMS of the battery still outputs the previous SOH value. ·△ V n_i ​

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