Method for estimating SOH (state of health) of battery

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, taking at least one battery cell as a test battery cell, and carrying out charging test on each test battery cell for N times under different SOH values; s3, analyzing and judging the Vni and the corresponding tni under different SOH values obtained in the step S2, and judging whether a function relationship between the tni corresponding to at least five Vni and the SOH value fits one of the three functions or not; s4, repeating the step S2 to the step S3 to obtain a function relation between the tni and the SOH value under different temperature conditions and different charging currents, and inputting the function relation into a BMS (battery management system) of the battery; and S5, 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, at low SOH, 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 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 if the frequency of full discharge occurs very low (that is, the time interval between two full discharges is too long and has no calculation significance), so it is relatively difficult to obtain the capacity of a full charge and full discharge, and even if 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 N charging tests on each test battery cell at 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 during each charging test decreases 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 underI j Charge to obtain the charging curve of the voltage of the test battery cell varying with 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: Perform multiple quantitative charges on the test battery cell with the rated charging current used in step S21, and obtain the charging duration of the test battery cell for quantitative charging △t n_i ; Each quantitative charge causes the voltage of the test battery cell to increase by a preset charging voltage increment △V 0; The voltage of the test battery cell at the start of each quantitative 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 of each quantitative charge is V n_i , and the voltage of the test battery cell at the end of each quantitative charge is V n_i+ △V 0; Step S3: Analyze and judge the V n_i and the corresponding △t n_i obtained in step S2 at different SOH values to determine whether there are at least five V n_i corresponding △t n_i and 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 = d· x2 + e· x + f ; where y is the value of △ t n_i and x is the number corresponding to the SOH during each charge test of the test battery cell in step S2 (knowing the value of x can correspond to obtain the SOH value of the test battery cell). x takes values starting from zero, and k < 0, a > 0, b < 1, c > 0, d < 0, e > 0, f > 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 in step S2, so as to obtain the functional relationship between △t n_i and the SOH value under different temperature conditions and different charging currents and correspondingly input it into the BMS of the battery; Step S5: During each charge of the battery, if the BMS of the battery determines that there are more than three V n_i corresponding △t n_i meet the functional relationship between △t 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 △t n_i meet the functional relationship between △t n_i and the SOH value of the battery under different temperature conditions and different charging currents, then the BMS of the battery still outputs the previous SOH value.

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

[0007] In step S2, 0.5% SOH is used as the preset fixed percentage SOH interval △SOH; in step S5, 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 battery's BMS last time exceeds 0.5%, the battery's BMS still outputs the SOH value of the last time.

[0008] In step S5, when the battery's BMS determines that there are more than three V n_i corresponding △t n_i in line with the battery under different temperature conditions and different charging currents △t n_i Under the function relationship with SOH, if the deviation between the calculated SOH values exceeds 3%, the battery's BMS still outputs the SOH value of the last time.

[0009] After adopting the above scheme, the present invention obtains the charging duration required for the battery to increase the preset charging voltage increment △V 0 △t n_i The function relationship with the change of SOH value. Therefore, as long as the charging duration is obtained △t 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 △t n_i A comparison table with SOH.

[0012] Figure 3 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] As Figure 1 shown, 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 cell on the battery to obtain at least one rated charging current of the battery cell on the battery I j , jNumbers for different rated charging currents; Step S2: Select at least one battery cell as a test battery cell, and conduct charging tests on each test battery cell at N different SOH values; 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 preset test temperature T with a rated charging current obtained in step S1 I j to obtain a charging curve of the voltage of the test battery cell changing 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 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 quantitative chargings on the test battery cell with the rated charging current used in step S21, and obtain the charging duration of the test battery cell for quantitative charging △t n_i ; Each quantitative charging causes the voltage of the test battery cell to increase by a preset charging voltage increment △V 0; The voltages of the test battery cell at the start of each quantitative 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 of each quantitative charging is V n_i , while the voltage of the test battery cell at the end of each quantitative charging is V n_i+ △V 0; Step S3: For the V n_i obtained at different SOH values in step S2 and the corresponding △tn_i Perform an analysis and determination to determine whether there are at least five V n_i corresponding △t n_i Whether the functional relationship with the SOH value fits one of the following three functions; Function one is: y = k· x + a ; Function two is: y = b x + c ; Function three is: y = d· x 2 + e· x + f ; where y is the △ t 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, e > 0, f > 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 preset test temperature T and the rated charging current I j in step S2, so as to obtain the △t n_i functional relationship between the Step S5: During each charging of the battery, if the BMS of the battery determines that there are more than three V n_i corresponding △t n_i meet the functional relationship between the △t 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 among 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 △t n_iConsistent with the battery's △t n_i function relationship with the SOH value under different temperature conditions and different charging currents, the BMS of the battery still outputs the previous SOH value.

[0015] As can be seen from the above, the present invention obtains the charging duration required for the battery to rise to the preset charging voltage increment △V 0 △t n_i The function relationship that changes with the SOH value. Therefore, as long as the charging duration is obtained △t 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 value 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 S5, 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, thus avoiding errors.

[0019] Figure 2 Shows the comparison table with the SOH value under the condition of "taking 5 battery cells as test battery cells, preset test temperature T is 25°C, the preset fixed percentage SOH interval △SOH is 0.5% SOH, the charging rate is 0.5C, and the preset charging voltage increment △V 0 is 30 mV, V n_i is 3.65 V" △t n_i (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 are needed V n_iOnly then can it meet the requirements, but the amount of data is too large, so only one point is taken for illustration); in coordination with Figure 3 As shown, through the dot plot, y = - 0.101· x + 24.8 can be fitted, where y is the corresponding number for x (SOH decays at a rate of every 0.5% attenuation) corresponding to the SOH of the tested battery cell at a voltage of 3.65V △t n_i ; Similarly, the corresponding table of V n_i and SOH values under other △t n_i can be obtained. If there is an obvious functional relationship between △t n_i and the SOH value under this condition, then this V n_i is taken out; at least 5 corresponding △t n_i with an obvious functional relationship with the SOH value V n_i are taken out; in addition, similarly, the functional relationship between △t n_i and the SOH value when charging at other rates at 25°C can be tested; similarly, the relationship function between △t n_i and the SOH value under other temperature conditions can also be tested; finally, all △t n_i and the functional relationship formula of the SOH value of the battery cell under different temperature conditions and different charging currents are obtained.

[0020] Since the functional formulas of △t 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, △t n_i should be as small as possible. In addition, in step S5, when the BMS of the battery determines that there are more than three V n_i corresponding △ t n_i meets the functional relationship formula of △t 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.

[0021] 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 battery SOH, characterized in that: The steps include: Step S1: Obtain at least one rated charging current of the battery cell on the battery I j , j It is the number of different rated charging currents; Step S2: taking at least one battery cell as a test battery cell, and performing N charging tests at different SOH values ​​on each test battery cell; the SOH value of the test battery cell in the first charging test is 100% SOH, and the SOH value of the test battery cell in each charging test decreases in sequence according to a preset fixed percentage SOH interval △SOH; N is a positive integer greater than 10; The charging test includes: Step S21: Test the battery cell at a preset test temperature T Next, a rated charging current is obtained in step S1. I j Charging is performed to obtain a charging curve of the test cell's voltage versus current; Step S22: According to the charging curve of the test cell obtained in step S21, the test cell is charged from the full-charge voltage downward, and the voltage value is set at a preset voltage interval. △v Take a voltage value and get the voltage set corresponding to the test cell R i ; R i =[ V 0_i ,_ V 1_i , V 2_i … V n_i ], n Indicates a sequence number starting from zero. i Indicates the SOH of the test cell during the current charging test; Step S23: Perform multiple quantitative charging of the test cell with the rated charging current used in step S21, and obtain the charging time of the test cell for quantitative charging △t n_i Each quantitative charging causes the voltage of the test cell to increase by the preset charging voltage value. △V 0; The voltage of the test cell at the start of each quantitative charging is obtained from the voltage set obtained in step S22 R i The various values ​​of the test cell at the beginning of each quantitative charge are V n_i , and the voltage of the test cell at the end of each quantitative charge is V n_i+ △V 0; Step S3: The SOH values ​​obtained in step S2 are V n_i and the corresponding △t n_i Analyze and determine whether there are at least five V n_i Corresponding △t 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 three is: y= d· x 2 + e· x+ f ; where y is △t n_i , x is the number corresponding to the SOH of the test cell during each charging test in step S2 (the SOH value of the test cell can be obtained by knowing the x value), x starts from zero, and k <0, a >0, b <1, c >0, d <0, e >0, f >0; if it exists, go to step S4; if it does not exist, repeat step S2 and set the preset voltage interval accordingly. △v Turn down; Step S4: Repeat steps S2 to S3, and replace the preset test temperature T and rated charging current in step S2 I j The value of can be obtained under different temperature conditions and different charging currents. △t n_i The functional relationship with the SOH value is input into the battery's BMS accordingly; Step S5: Each time the battery is charged, if the battery's BMS determines that there are three or more V n_i Corresponding △t n_i Meet the battery under different temperature conditions and different charging currents △t 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 Corresponding △t n_i Meet the battery under different temperature conditions and different charging currents △t 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 method for estimating battery SOH according to claim 1, characterized in that: In step S1 , the charging current of the adapted charger is used as the rated charging current.

3. The method for estimating battery SOH according to claim 1, characterized in that: In step S2, 0.5% SOH is used as the preset fixed percentage SOH interval △SOH; in step S5, after removing the maximum and minimum values ​​of the calculated SOH values, if the average value of the remaining SOH values ​​deviates from the SOH value last output by the battery's BMS by more than 0.5%, the battery's BMS still outputs the last SOH value.

4. The method for estimating battery SOH according to claim 1, characterized in that: In step S5, the BMS of the battery determines that there are three or more V n_i Corresponding △t n_i Meet the battery under different temperature conditions and different charging currents △t n_i Under the functional relationship with SOH, if the deviation between the various SOH values ​​calculated accordingly exceeds 3%, the BMS of the battery will still output the previous SOH value.

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