Method for battery capacity estimation by optimized charge and discharge characteristics

Abstract

The invention relates to a method for optimizing the capacity estimation by creating a charge profile of a battery or creating a discharge profile of a battery, the method having the following steps: discharging the battery below an initial state of charge value according to i), charging the battery to the initial state of charge value with a first current in combination with a relaxation according to ii), and charging the battery to the initial state of charge value with a second current in combination with a relaxation according to iii), wherein the second current has an amplitude which is the same as the amplitude of the first current. Determining the capacity according to iv), wherein the discharge profile comprises at least the following steps: charging the battery above the initial state of charge value according to a), discharging the battery to the initial state of charge value with a third current in combination with a relaxation according to b), and discharging the battery to the initial state of charge value with a fourth current in combination with a relaxation according to c), wherein the fourth current has the same amplitude as the first current which is the same as the amplitude of the first current, and determining the capacity according to d).

Description

Technical Field

[0001] This invention relates to a method for optimizing capacity estimation based on the charging or discharging characteristics of batteries, particularly traction batteries in electrically driven vehicles. Furthermore, this invention relates to the application of said method to voltage-regulated systems. Background Technology

[0002] For lithium-ion batteries, accurately determining the state of charge (SOC) is crucial. SOC represents an input parameter for several important battery functions, such as state of health, single-cell balancing, and SOC-based current limiting. Currently, SOC is determined by measuring single-cell voltages using a set of open-circuit voltages. In the laboratory, the charging and discharging open-circuit voltages are determined separately, for example, by measuring during a 1 C discharge process. In the battery management system, the average open-circuit voltage is then stored and used for further calculations. The difference between the charging and discharging open-circuit voltages yields the health hysteresis, which is significantly influenced by the anode and cathode capacities. Crucially, the intensity of charging or discharging in terms of amplitude and charge level is critical.

[0003] BR 10 2020 0262 26 A2 relates to a method and a system for predicting the end of life of a secondary battery, applicable to any type of secondary battery. The method identifies end of life by monitoring voltage hysteresis cycles occurring between the charging and discharging phases of the battery. The method is non-invasive, low-cost, field-applicable, and requires no specialized equipment.

[0004] US 2011 / 0264381 A1 relates to a system comprising an electrochemical single cell, monitoring hardware, and a computer system. The power characteristics of the electrochemical single cell are detected by the monitoring hardware. The computer system derives information about the single cell from the power characteristics. This computer system further analyzes the single-cell data of the electrochemical single cell using a modified Butler-Volmer (BV) expression to determine the exchange current density of the electrochemical single cell, taking into account kinetic information about the single cell in terms of pulse time correlation, electrode area availability, or a combination of both. To determine the kinetic performance as a function of pulse time, a series of Sigmoid function-based expressions can be incorporated into the modified BV expression. The obtained exchange current density, using the modified BV with or without a Sigmoid function term, can be used to analyze other characteristics of the electrochemical single cell. Model parameters can be defined for single-cell aging. Thus, the overall kinetic model can predict the kinetic characteristics of the single cell over an aging period.

[0005] The capacity estimate is calculated using the following formula, following common methods: .

[0006] Two time points t start With t end The calculated charge integral is divided by the SOC offset. The SOC value (State of Charge) is obtained using the aging-related OCV curve (Open Circuit Voltage) and the measured OCV static voltage (U0). cell (t) start ) or U cell (t) start To calculate.

[0007] .

[0008] The calculated estimation error is used to evaluate the accuracy of capacity measurement. If the calculated accuracy is better than a threshold, the result is used; otherwise, it is discarded. Furthermore, the capacity estimation result is always partially incorporated into the existing capacity value. The higher the accuracy, the greater the impact of the newly calculated capacity value on the final result within the weighted framework.

[0009] According to the current processing method, due to the starting point of the measurement (ΔSC) start ) and endpoint (ΔSC) end The estimated SOC error caused by voltage error (voltage measurement error (sensor), incomplete relaxation) is used to estimate the error. Additionally, the integral error is also included in the result.

[0010] Systems and methods for accurately determining the aging state of a corresponding module or single cell of a lithium-sulfur battery or for estimating the state of charge of the battery are known from US 2020 / 082631 A1 and CN 110286324 A, respectively. Summary of the Invention

[0011] According to the present invention, a method for optimizing capacity estimation by means of battery charging or discharging characteristics is proposed, wherein, regarding the creation of charging characteristics, the following method steps are traversed: i) Discharge the battery below its initial state of charge (SOC). ii) Charge the battery to its initial state of charge value with a first current, followed by relaxation. iii) Charging the battery to its initial state of charge value with a second current combined with relaxation, wherein the second current has the same magnitude as the first current, and iv) Determine the capacity, Furthermore, regarding the creation of discharge characteristics, the following method steps are traversed: a) Charge the battery to above its initial state of charge (SOC). b) Discharge the battery to its initial state of charge value using a third current, combined with relaxation. c) Discharging the battery to its initial state of charge value with a fourth current combined with relaxation, wherein the fourth current has the same amplitude as the first current, and d) Determine the capacity.

[0012] In an advantageous improvement to the method proposed according to the invention, the battery is discharged to 5% below its initial state of charge value, as implemented in step i).

[0013] Furthermore, in the method proposed according to the present invention, the battery is charged to 5% above the initial state of charge value in accordance with step a).

[0014] Furthermore, the method proposed according to the present invention is characterized in that the battery is charged with a first current according to method step ii), wherein the first current is in the range of 1 C to 10 C, preferably in the range of 1 C to 5 C, and particularly preferably 1 C.

[0015] Furthermore, in the method proposed according to the present invention, the battery is discharged with a first current according to method step b), wherein the first current is in the range of 1 C to 10 C, preferably in the range of 1 C to 5 C, and particularly preferably 1 C.

[0016] Furthermore, the method proposed according to the present invention is characterized by using a first formula to determine the capacity, which takes into account the initial state of charge value, the final state of charge value, and the change in charge.

[0017] Furthermore, it is advantageous to set the initial state of charge value in the range of 10% to 30%, preferably in the range of 15% to 25%, and particularly preferably 20%.

[0018] Furthermore, in the method proposed according to the present invention, the final state of charge value is set to be in the range of 45% to 60%, preferably in the range of 45% to 50%, and particularly preferably 50%.

[0019] Furthermore, in the method proposed according to the invention, it is advantageously configured to consider the charge change error during charge change.

[0020] Furthermore, in the method proposed according to the present invention, the hysteresis of the state of charge value is substantially eliminated when determining the capacity.

[0021] Furthermore, the present invention relates to the use of the method in voltage-regulated systems, particularly in the battery management system of the traction battery of an electric vehicle.

[0022] Advantages of the present invention.

[0023] The solution proposed according to the invention advantageously minimizes the SOC error for close SOC offsets and significantly improves the robustness of the method for estimating the remaining capacity of the battery. The accuracy of the capacity estimate can be further improved by avoiding SOC-OCV hysteresis using the method proposed according to the invention. The accuracy of determining the remaining battery capacity can be improved by generating the same or as similar as possible SOC-OCV hysteresis at the starting and ending measurement points using the method proposed according to the invention. SOC-OCV hysteresis is eliminated by forming a difference in SOC values ​​when determining the capacity.

[0024] The capacity is determined according to the following formula: .

[0025] In voltage-regulated systems, such as the on-board battery of an electric vehicle, the battery can be pre-set to a battery pack voltage and communicate this to a DC / DC converter. If the DC / DC converter sets a link voltage greater than or less than the battery pack's quiescent voltage, current flows into or out of the battery. This can be advantageously utilized when determining capacity by discharging the battery below its initial state of charge (SOC), for example, by reducing it by 5%, and then charging it with a defined current to the initial SOC plus relaxation. Subsequently, the battery is charged with a defined current to the final SOC plus relaxation, and finally, by means of the aforementioned parameters for Q... est,cell The formula is used to calculate the capacity.

[0026] An alternative feasible approach is to perform the measurement process in the reverse direction in an electric vehicle. For this, the battery is charged to a value higher than the initial SOC, for example, 5% higher, and then discharged at a limited current to the initial SOC plus relaxation. The battery is then discharged at a limited current to the final SOC plus relaxation, and finally, using the method described above for Q... est,cell The formula is used to calculate the capacity.

[0027] The method described above can minimize or completely eliminate the SOC-OCV hysteresis error in an advantageous manner because the initial SOC value and the final SOC value are always applied on the same charge or discharge open-circuit voltage curve when measuring capacity. Attached Figure Description

[0028] Embodiments of the present invention will be explained in detail with reference to the accompanying drawings and the following description. Wherein: Figure 1 The open-circuit voltage curves of aged batteries, with capacity estimates, determined in the laboratory, are shown. Figure 2 The hysteresis process is shown for batteries in different aging states. Figure 3.1 A comparison of the charging no-load voltage curve and the discharging no-load voltage curve is shown. Figure 3.2 The deviation of the no-load voltage curve plotted with respect to the state of charge is shown. Figure 4.1 The optimized charging characteristics with open-circuit voltage plotted with respect to the time axis are shown, and Figure 4.2 It shows the result of Figure 4.1 The deviation of the no-load voltage curve plotted with respect to the state of charge was obtained. Detailed Implementation

[0029] In the following description of embodiments of the invention, the same or similar elements are designated by the same reference numerals, wherein repeated descriptions of these elements are omitted in certain cases. The accompanying drawings are merely schematic illustrations of the subject matter of the invention.

[0030] By following Figure 1 The diagram shows the aging and open-circuit voltage (Figure 100). The curve showing the change in open-circuit voltage (Figure 104) is plotted with respect to the state of charge (SOC). Following... Figure 1 In the aging and open circuit voltage diagram 100, a set of aging open circuit voltage curves 106 (open circuit voltage = OCV) are plotted. These aging open circuit voltage curves 106 are plotted for a certain number of different aged batteries. The aforementioned aging open circuit voltage curves 106 are created in a laboratory measurement series for various battery types and, for example, stored in a battery management system.

[0031] By following Figure 1 The diagram is obtained. Figure 1 Different aging no-load voltage curves 106, plotted as group 106, are shown for different capacities, such as 71%, 80%, 73%, 90%, and 100%. Particular deviations are observed between the initial state of charge value 112 (30% state of charge 102) and, for example, the final state of charge value 114 corresponding to 85% state of charge 102.

[0032] By following Figure 1The diagram further shows that for the initial state of charge value 112, there is a first maximum single-cell voltage error 108 and a second maximum single-cell voltage error 110 below it. For the final state of charge value 114, after experiencing the change in charge 116, that is, the change in state of charge 102, there is a third first maximum single-cell voltage error 118 and a fourth first maximum single-cell voltage error 119.

[0033] In accordance with Figure 1 In the diagram, the limit of the state of charge error is indicated by reference numeral 122 for the final state of charge value 114.

[0034] Depend on Figure 2 The diagram shows a number of state-of-charge (SOHC) hysteresis curves in plot 200, representing the battery's different states of charge (Ladezustand) 206, different states of discharge 208, and different states of health listed in Table 210. Plot 210 shows that the different curves represent different SOHC levels / values ​​for either state of charge 206 or state of discharge 208, where "Chrg SOHC" indicates a charged state of health and "Dcha SOHC" indicates a discharged state of health. The X-axis shows the SOHC values ​​202 from 0% to 100%, while the Y-axis reflects the SOHC change ΔSOC 204 from -4% to +4%.

[0035] The state-of-charge (POC) hysteresis plot 200 shows the POC variability curves for a number of batteries with different states of charge (206) and discharge (208). Furthermore, the corresponding POC variability curves illustrate the POC variability (Verlauf) 202 at different states of charge and discharge (206, 208) and its impact on the health state 210 according to the tabular values.

[0036] As the state of charge (SOC) 202 increases, the corresponding state curve initially rises sharply, while a gradual decline is observed as SOC 202 decreases. Furthermore, the state curves show that the SOC response differs depending on the corresponding battery health state 210. Newer batteries exhibit faster SOC changes, while older batteries tend to react more slowly, attributed to delays in the electrochemical processes occurring within the battery. Hysteresis can be determined, for example, by analyzing the difference between the SOC value during charging state 206 and discharging state 208. In the SOC hysteresis plot 200, these differences are shown as curves, which correspondingly represent the changes in SOC 202 during charging and discharging periods 206 and 208.

[0037] exist Figure 3.1In the figure, the no-load voltage OCV 104 is plotted with respect to the state of charge 102 (SOC) expressed as a percentage. This is based on... Figure 3.1 The diagram shows that there is a hysteresis in the initial state of charge value 112 on the discharge curve 304 compared with the final state of charge value 114 on the charging curve 302.

[0038] Figure 3.2 The variation 204 of the state of charge (SOC) value is also shown, plotted as a percentage of the SOC 102. Therefore, a larger deviation occurs at the initial SOC 112 compared to the deviation that occurs when the final SOC 114 is reached (see the spacing of the measurement points). The deviation at the final SOC 114 is smaller compared to the deviation present at the initial SOC 112.

[0039] Depend on Figure 4.1 and Figure 4.2 It can be seen that: regarding the changes in the no-load voltage 104 and the state of charge value 204 plotted on time axis 402, the changes in the state of charge value are determined by... Figure 1 The diagram shows the corresponding charging curve 302 and the corresponding discharging curve 304. The corresponding deviations are obtained at the initial state of charge value 112 or the final state of charge value 114.

[0040] In onboard batteries used in electric vehicles, such as those in electric motors, the maximum state of charge (SOC) that can be controlled by a DC / DC converter is limited. Therefore, in the case of four individual battery cells, the maximum voltage U... max For example, 15.5 volts, from which the maximum value of the state of charge (SOC) of 102 is derived. max The minimum state of charge (SOC) is 70%. The minimum SOC 102 is limited by battery availability requirements; for example, the minimum SOC 102 cannot be lower than 30%. This limitation restricts the range of starting and ending points used to measure capacity. More importantly for 12-volt battery systems, it is crucial to achieve good capacity estimation even with small SOC offsets (SOC-Hub). By using the method proposed according to the invention, the error in obtaining the SOC 102, i.e., the error in obtaining the SOC value for relatively close SOC offsets, is minimized, and the robustness of capacity estimation is significantly improved.

[0041] The accuracy of determining the remaining capacity of a vehicle battery or traction battery can be improved by generating the same or as similarly identical state-of-charge (SOC) open-circuit voltage hysteresis (SOC-OCV hysteresis) at both the initial and final SOC measurement points. This is achieved according to the formula: When determining capacity, SOC-OCV hysteresis is eliminated by forming the SOC difference.

[0042] The same or highly similar SOC-OCV hysteresis can be generated by using the same systematic approach and controlling the initial and final state-of-charge points in a defined manner, or by charging or discharging only at 1 C. The no-load current profile is obtained, for example, in a laboratory setting with a 1 C charging or discharging current, thus achieving charging to the voltage value at 1 C, followed by relaxation, and then continuing charging to the next voltage value at 1 C, followed by relaxation, and so on. If this approach is also used in vehicles, the resulting errors are minimized.

[0043] Thus, a single cell of the battery is relaxed to a known and uniform open-circuit voltage (OCV) curve, which can be determined in a series of measurements in the laboratory.

[0044] Ideally, it is also possible to use a state-of-charge point (SOC point) with the same SOC-OCV hysteresis. Regarding Figure 2 Here we will list the initial SOC value at 20% and the final SOC value at 50%. Therefore, the SOC-OCV hysteresis effect follows the relationship described above: The capacity estimation is continuously compensated and is no longer visible in the calculation.

[0045] In voltage-regulated systems, such as the onboard battery of a vehicle, the battery can be pre-set to a battery pack voltage and communicate this voltage to a DC / DC converter. If the set voltage is greater than or less than the battery pack's quiescent voltage, current flows into or out of the battery. This characteristic can be advantageously utilized when determining capacity, for example, during measurements in a vehicle. Figure 4.1 and Figure 4.2 The diagram shows the battery being discharged to below the initial SOC point, for example, 5% lower, and then charged to the initial SOC value with a defined current, plus a relaxation allowance. Subsequently, the battery is charged with a defined current, wherein the same magnitude 404 is set as when charging the battery to the final SOC value plus relaxation. Then, using the formula: Implement capacity calculation.

[0046] As an alternative, the measurement process in the vehicle can also be performed in the opposite direction.

[0047] Therefore, the battery is charged to a value above a starting point, which is, for example, chosen to be 5% higher, and then discharged to the starting state of charge (SOC) plus relaxation value using a defined current. The battery is then discharged again using a defined current having an amplitude 404 corresponding to the amplitude of the previously defined current. This is then achieved using the following relationship: Perform capacity calculation.

[0048] Using the method proposed according to the present invention, the SOC-OCV hysteresis error is decisively minimized and ideally completely eliminated because the initial SOC value and the final SOC value are always applied on the same charge and discharge open-circuit voltage curves 302 and 304 during capacity measurement. The open-circuit voltage hysteresis error (OCV hysteresis error) is determined according to the aforementioned method for Q. est,cell The subtraction operation performed by the relation can be partially or, ideally, completely eliminated within the framework of the relation.

[0049] For the control, the initial SOC value and the final SOC value have the same SOC-OCV hysteresis amplitude (e.g., in Figure 2 In the case of selecting an exemplary initial SOC value of 20% and a final SOC value of 45%, the SOC-OCV hysteresis effect can be completely eliminated. In this situation, following the previous approach for Q... est,cell The formula completely eliminates hysteresis error when calculating the remaining single-cell capacity of the battery.

[0050] The present invention is not limited to the embodiments described herein and the aspects highlighted therein. Rather, numerous variations are possible within the scope of the claims and are within the practice of those skilled in the art.

Claims

1. A method for optimizing capacity estimation using battery charging characteristics (406) or discharging characteristics (408), wherein, Creating the charging feature (406) includes at least the following steps: i) Discharge the battery to below its initial state of charge value (112), ii) Charge the battery to its initial state of charge (112) with a first current and combine with relaxation, iii) Charging the battery to its initial state of charge (112) with a second current combined with relaxation, wherein the second current has an amplitude (404) that is the same as the amplitude (404) of the first current, and iv) Determine the capacity, Creating the discharge feature (408) includes at least the following steps: a) Charge the battery to a level above the initial state of charge value (112), b) Discharge the battery to its initial state of charge value (112) with a third current, combined with relaxation, c) Discharging the battery to its initial state of charge (112) with a fourth current combined with relaxation, wherein the fourth current has the same amplitude (404) as the first current, and d) Determine the capacity.

2. The method according to claim 1, wherein, In step i), the battery is discharged to 5% below the initial state of charge value (112).

3. The method according to claim 1, wherein, In step a), the battery is charged to 5% above the initial state of charge value (112).

4. The method according to claim 1 or 3, wherein, In step ii), the battery is charged with the first current, wherein the first current is in the range of 1 C to 10 C, preferably in the range of 1 C to 5 C, and particularly preferably 1 C.

5. The method according to claim 1 or 3, wherein, In step b), the battery is discharged with the first current, wherein the first current is in the range of 1 C to 10 C, preferably in the range of 1 C to 5 C, and particularly preferably 1 C.

6. The method according to any one of the preceding claims, wherein, A first formula is used to determine the capacity, which takes into account the initial state of charge value (112), the final state of charge value (114), and the change in charge (116).

7. The method according to claim 6, wherein, The initial state of charge (112) is in the range of 10% to 30%, preferably in the range of 15% to 25%, and particularly preferably 20%.

8. The method according to claim 6 or 7, wherein, The final state of charge (114) is in the range of 45% to 60%, preferably in the range of 45% to 50%, and particularly preferably 50%.

9. The method according to claim 7, wherein, The charge change error is taken into account when the charge changes.

10. The method according to any one of the preceding claims, characterized in that, Eliminate state-of-charge hysteresis when determining capacity.

11. Use of the method according to any one of the preceding claims in a voltage-regulated system.

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