Method for estimating SOH (state of health) of battery

Abstract

The invention provides a method for estimating the SOH of a battery, which can simply and accurately judge the SOH of the battery, and comprises the following steps of: 1, acquiring the rated charging current # imgabs0 # of a battery cell on a battery pack; 2, acquiring charging voltage curves of different SOHs under the same temperature condition and the same charging current; 3, acquiring voltage sets corresponding to different SOHs at a preset voltage interval # imgabs 1 #; 4, drawing a DCR-SOH scatter diagram, and observing whether the DCR in the scatter diagram meets a linear function # imgabs2 # along with the reduction of the SOH; 5, finding out that DCRs corresponding to at least five voltage values meet a linear function on all SOHs, and performing fitting calculation on values of # imgabs3 # and # imgabs4 #; 6, repeating the steps 1-5 to obtain a function relation between the DCR and the SOH under different temperature conditions and different charging currents; 7, amplifying all DCR and SOH function relations of all battery cells at different temperatures and different charging currents by # imgabs 5 # times, and inputting the amplified function relations to software of a BMS (battery management system); and 8, outputting an SOH value during charging.

Description

Technical Field

[0001] The present invention relates to the technical field of new energy battery calculation, and in particular to a method for estimating battery SOH. Background Art

[0002] SOH, or State of Health, refers to the health life state of the battery, that is, the ratio of the current available capacity of the battery to the rated capacity. Under different SOHs, the battery's charging and discharging power, heat generation, available power and other parameters are all different. For example, at low SOH, the battery's resistance is large and the heat generation is high. If the battery's charging and discharging power is not limited in time, it may overheat and cause thermal runaway. Accurately evaluating the battery's SOH can fully understand the battery's current state, make maintenance plans in advance, correct various parameter performance indicators, reduce or avoid the risk factor, or maintain and replace single cells whose performance does not meet the use requirements, thereby reducing use costs and safety risks.

[0003] At present, the conventional SOH calculation method is to obtain the capacity of a battery after full charge and discharge, and divide it by the initial (rated) capacity to obtain the current SOH of the battery. However, when the battery is in use, in many cases, the battery cannot be fully discharged. For example, if an electric car is parked on the road after it is fully discharged, it will not be fully charged when in use; and personal users of mobile phones generally do not shut down the phone to charge it, or the frequency of fully discharging is very low, and the time interval between two fully discharging is relatively long. Therefore, it is difficult to obtain a fully charged and discharged capacity, and even if it is obtained, it cannot reflect the current status of the battery at any time. Summary of the invention

[0004] The object of the present invention is to provide a method for estimating the SOH of a battery, so as to solve the problems existing in the prior art and to determine the SOH of the battery simply and accurately.

[0005] In order to achieve the above object, the solution of the present invention is: A method for estimating battery SOH, comprising: Step 1: Get the rated charging current of a cell in the battery pack ; Step 2: Use the rated charging current obtained in step 1 I The same type of battery cells are tested to obtain the charging voltage curve of the battery cell voltage changing with time under specific temperature conditions and different SOH: under the same temperature conditions, the charging voltage curve is drawn at each preset percentage of SOH interval, thereby obtaining the charging voltage curves of different SOH under the same temperature conditions and the same charging current; Step 3: According to the charging voltage curves of different SOH in step 2, the voltage corresponding to 100% SOH of the new battery cell Start from the full power voltage and go down to the voltage value. Take a voltage value once to get the voltage set corresponding to 100% SOH : , Indicates the serial number; The same is true for other SOHs, thus obtaining different SOHs at preset voltage intervals The corresponding voltage set below; Step 4: According to the calculation formula of charging DCR Different from step 3, SOH is at the preset voltage interval The corresponding voltage set is obtained to obtain the data corresponding to SOH and DCR and draw a DCR-SOH scatter plot, where Indicates voltage Corresponding , Indicates to be calculated The corresponding voltage, Indicates that voltage is detected The voltage after charging at rated current for 10 seconds. Indicates the rated charging current; observe whether DCR satisfies a linear function as SOH decreases in the scatter plot ,in is the value of DCR, The sequence number in step 3 The value of , ; Step 5: When the DCR corresponding to a certain voltage satisfies the above linear function on all SOHs, record the voltage value and find at least 5 voltage values ​​corresponding to the DCR that satisfy the linear function on all SOHs. If they cannot be satisfied, readjust the voltage interval. And calculate, increase the selected voltage value until at least 5 voltage values ​​that meet the conditions are obtained; calculate by fitting and The functional relationship between DCR and SOH is obtained by ; Step 6, repeat steps 1-5, and obtain the functional relationship between DCR and SOH under different temperature conditions and different charging currents by replacing the variable temperature condition and rated charging current; Step 7: When inputting the functional relationship between DCR and SOH into the BMS of the battery pack, assume that the total number of cells in the battery pack is , the functional relationship is , that is, to enlarge times; all the functional relationships between DCR and SOH of all cells at different temperatures and different charging currents are magnified After times, input into the BMS software; Step 8. Each time the battery pack is charged, if at least 3 charging voltages belonging to the voltage set are measured, the highest and lowest SOH values ​​corresponding to these charging voltages are removed, and the average of the remaining SOH values ​​is taken as the SOH value output by the current battery pack; if at least 3 charging voltages cannot be measured, the last SOH value is still output as the SOH value output by the battery pack.

[0006] In step 1, the charging current of the adapted charger is used as the rated charging current. .

[0007] After adopting the above technical solution, the present invention has the following technical effects: The present invention uses the functional relationship that the DCR of the battery increases as the SOH decays, and the corresponding SOH value can be obtained by obtaining the DCR value. There is no need to consider whether the battery is fully discharged during use. The SOH value can be obtained basically every time the battery is charged, and real-time updates are more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 It is a flowchart of a specific embodiment of the present invention; Figure 2 This is the scatter plot of DCR-SOH at 3.55V at 25°C. DETAILED DESCRIPTION

[0009] In order to further explain the technical solution of the present invention, the present invention is described in detail below through specific embodiments.

[0010] First, you need to understand a basic concept: charging DCR (DC Resistance during Charge) refers to the DC internal resistance of the battery during the charging process. This is a parameter that measures the internal impedance of the battery during charging, usually expressed in milliohms (mΩ). Charging DCR can provide important information about the efficiency of the chemical reactions inside the battery and the health of the battery. Measuring charging DCR usually needs to be done when the battery is in a charged state, by applying a known DC current for a certain period of time, and measuring the resulting voltage change, and then according to Ohm's law ( ) Calculate the internal resistance. Thus, taking the time interval of 10s of continuous current as an example, the charging DCR calculation formula used in the present invention is obtained as follows: ; in, Indicates voltage Corresponding , Indicates to be calculated The corresponding voltage, Indicates the voltage measured from The voltage after charging at rated current for 10 seconds. Indicates the rated charging current.

[0011] refer to Figure 1 As shown, the present invention discloses a method for estimating battery SOH, comprising: Step 1: Identify the various operating conditions of a certain cell in the battery pack and obtain the rated charging current of the cell in the battery pack ; Step 2: Use the rated charging current obtained in step 1 I The same type of battery cells are tested to obtain the charging voltage curve of the battery cell voltage changing with time under specific temperature conditions and different SOH: under the same temperature conditions, the charging voltage curve is drawn at each preset percentage of SOH (such as each interval of 0.5% SOH), thereby obtaining the charging voltage curves of different SOH under the same temperature conditions and the same charging current; Step 3: According to the charging voltage curves of different SOH in step 2, the voltage corresponding to 100% SOH of the new battery cell Start taking voltage values ​​from the full-charge voltage downwards (the reason for taking voltage values ​​from the full-charge voltage downwards is that the battery can be fully charged normally, and the higher the SOH, the easier it is to read during charging). (Unit: mv) Take a voltage value (e.g., take a voltage value every 50 mv) to get the voltage set corresponding to 100% SOH , Indicates the serial number; similarly, the voltage set corresponding to 99.5% SOH can be obtained , the same is true for other SOHs, thus obtaining different SOHs at preset voltage intervals The corresponding voltage set below; Step 4: According to the calculation formula of charging DCR Different from step 3, SOH is at the preset voltage interval The corresponding voltage set is obtained to obtain the data corresponding to SOH and DCR and draw a DCR-SOH scatter plot, where Indicates voltage Corresponding , Indicates to be calculated The corresponding voltage, Indicates that voltage is detected The voltage after charging at rated current for 10 seconds. Indicates the rated charging current; it is known that as the SOH decreases, the resistance of the battery cell increases, so observe whether the DCR satisfies the linear function as the SOH decreases in the scatter plot ,in is the value of DCR, The sequence number in step 3 The value of , ; Step 5: When the DCR corresponding to a certain voltage satisfies the above linear function on all SOHs, record the voltage value and find at least 5 voltage values ​​corresponding to the DCR that satisfy the linear function on all SOHs. If they cannot be satisfied, readjust the voltage interval. (Generally, to reduce the voltage interval) and calculate, increase the selected voltage value until at least 5 voltage values ​​that meet the conditions are obtained; calculate by fitting and The functional relationship between DCR and SOH is obtained by ; Step 6, repeat steps 1-5, and obtain the functional relationship between DCR and SOH under different temperature conditions and different charging currents by replacing the variable temperature condition and rated charging current; Step 7. When inputting the functional relationship between DCR and SOH into the BMS of the battery pack, in order to reduce the amount of calculation of the BMS software, only the DCR of the entire battery pack is calculated instead of the DCR of a single cell. Assume that the total number of cells in the battery pack is , then the DCR value is enlarged times, that is ; Amplify the functional relationship between all DCR and SOH of all cells at different temperatures and different charging currents and input them into the BMS software; Step 8. Each time the battery pack is charged, if at least 3 charging voltages belonging to the voltage set are measured, the highest and lowest SOH values ​​corresponding to these charging voltages are removed, and the average of the remaining SOH values ​​is taken as the SOH value output by the current battery pack; if at least 3 charging voltages cannot be measured, the last SOH value is still output as the SOH value output by the battery pack.

[0012] Through the above scheme, the present invention uses the functional relationship that the DCR of the battery increases as the SOH decays, and the DCR value can be obtained to obtain the corresponding SOH value. There is no need to consider whether the battery is fully discharged during use. The SOH value can be obtained basically every time the battery is charged, and real-time updates are more accurate.

[0013] Specific embodiments of the present invention are shown below.

[0014] Regarding step 1, since the discharge current cannot be controlled and the current fluctuates all the time, the charging current obtained from the test may be multiple. The charging current can be fixed according to the adapted charger, and the current is relatively stable and the fluctuation is relatively small during charging. Therefore, the charging current of the adapted charger can be used as the rated charging current. .

[0015] Regarding step 2, taking the temperature condition of 25℃ as an example, from 100%SOH to 70%SOH, the charging voltage curve is tested once every 0.5%SOH, and the charging voltage curve of this battery cell at different SOH at 25℃ can be obtained. The same can be done for other temperatures.

[0016] See the table below and Figure 2 , is a table showing the SOH and DCR of 5 samples of a battery cell at 25°C and 0.5C rate at 3.55V (the number of samples is 5 to reduce the error, the number can be more, 3.55V is one of the charging voltages, at least 4 charging voltages are required to meet the requirements, but the amount of data is too large, so only one point is taken for illustration). The dot graph can be fitted ,in At 3.55V, the serial number is (SOH attenuation number of every 0.5%) corresponding to the DCR, similarly, the corresponding table of DCR and SOH under other charging voltages can be obtained. If SOH and DCR under this voltage have an obvious functional relationship, then take out the voltage value, and take out at least 5 voltage values ​​with obvious functional relationship between DCR and SOH; similarly, the functional relationship between DCR and SOH charged at other rates at 25°C can be tested; similarly, the relationship function of DCR and SOH under other temperature conditions and the relationship function of DCR and SOH under different charging currents can also be tested, and finally the functional relationship between all DCR and SOH of the battery cell under different temperature conditions and different charging currents is obtained.

[0017]

[0018] The above embodiments and drawings do not limit the product form and style of the present invention. Any appropriate changes or modifications made by ordinary technicians in the relevant technical field should be deemed to be within the patent scope of the present invention.

Claims

1. A method for estimating battery SOH, characterized in that include: Step 1: Get the rated charging current of a cell in the battery pack ; Step 2: Use the rated charging current obtained in step 1 I The same type of battery cells are tested to obtain the charging voltage curve of the battery cell voltage changing with time under specific temperature conditions and different SOH: under the same temperature conditions, the charging voltage curve is drawn at each preset percentage of SOH interval, thereby obtaining the charging voltage curves of different SOH under the same temperature conditions and the same charging current; Step 3: According to the charging voltage curves of different SOH in step 2, the voltage corresponding to 100% SOH of the new battery cell Start from the full power voltage and take the voltage value downwards, each voltage interval Take a voltage value once to get the voltage set corresponding to 100% SOH : , Indicates the serial number; The same is true for other SOHs, thus obtaining different SOHs at preset voltage intervals The corresponding voltage set below; Step 4: According to the calculation formula of charging DCR Different from step 3, SOH is at the preset voltage interval The corresponding voltage set is obtained to obtain the data corresponding to SOH and DCR and draw a DCR-SOH scatter plot, where Indicates voltage Corresponding , Indicates to be calculated The corresponding voltage, Indicates that voltage is detected The voltage after charging at rated charging current for 10 seconds is: Indicates the rated charging current; observe whether DCR satisfies a linear function as SOH decreases in the scatter plot ,in is the value of DCR, The sequence number in step 3 The value of , ; Step 5: When the DCR corresponding to a certain voltage satisfies the above linear function on all SOHs, record the voltage value and find at least 5 voltage values ​​corresponding to the DCR that satisfy the linear function on all SOHs. If they cannot be satisfied, readjust the voltage interval. And calculate, increase the selected voltage value until at least 5 voltage values ​​that meet the conditions are obtained; calculate by fitting and The functional relationship between DCR and SOH is obtained by ; Step 6, repeat steps 1-5, and obtain the functional relationship between DCR and SOH under different temperature conditions and different charging currents by replacing the variable temperature condition and rated charging current; Step 7: When inputting the functional relationship between DCR and SOH into the BMS of the battery pack, assume that the total number of cells in the battery pack is , the functional relationship is , that is, to enlarge times; all the functional relationships between DCR and SOH of all cells at different temperatures and different charging currents are magnified After times, input into the BMS software; Step 8: Each time the battery pack is charged, if at least three charging voltages belonging to the voltage set are measured, the highest and lowest SOH values ​​corresponding to these charging voltages are removed, and the average of the remaining SOH values ​​is taken as the SOH value output by the current battery pack; If at least three charging voltages cannot be measured, the last SOH value will still be output as the SOH value output by the battery pack.

2. The method for estimating battery SOH according to claim 1, characterized in that: In step 1, the charging current of the adapted charger is used as the rated charging current. .

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