A method for testing the SOC estimation accuracy of a power battery system

Abstract

The application discloses a kind of power battery system SOC estimation precision test method, test process simulates the charging and discharging mode of actual use process of battery and carries out charging and discharging;Discharge is carried out using the equivalent current of actual use condition, and the cumulative capacity of discharge is used as the real residual capacity;The total electric quantity is calculated with the cumulative capacity of battery from the highest SOC state to the lowest SOC state in test process;Optimization formula for calculating SOC estimation error covers the end SOC estimation error of discharge.

Description

Technical Field

[0001] This invention relates to the field of battery system testing technology, and in particular to a test method for estimating the SOC accuracy of a power battery system. Background Technology

[0002] The State of Charge (SOC) of a battery system is one of the most important and widely used parameters for users. Users can use the SOC to understand the expected battery usage in real time, thus determining whether charging is needed and making timely battery usage plans. Furthermore, functions such as State of Charge (SOH) estimation, State of Operation (SOP) estimation, and battery equalization all rely on the SOC value. Therefore, the accuracy of battery system SOC estimation directly impacts the user experience and is one of the most critical indicators in the product development process.

[0003] Currently, most mainstream battery systems have SOC estimation capabilities. The SOC estimation test method for battery systems mainly refers to the "SOC Cumulative Error Test Method" in GB / T 38661-2020. This method is for testing the SOC estimation accuracy of BMS components within the battery system, and its application to battery systems has the following shortcomings:

[0004] 1) The specified test temperature points do not fully conform to the battery's operating temperature range;

[0005] 2) Charging and discharging methods at different temperatures do not fully reflect the actual usage conditions of the battery;

[0006] 3) Before testing, the battery system needs to be calibrated at different temperatures. The testing steps are complicated and take too long. Furthermore, it is impossible to avoid the impact of battery capacity decay or fluctuations on the test results.

[0007] 4) The calibrated capacity value at different temperatures differs from the total discharge capacity under actual battery usage conditions;

[0008] 5) The remaining power calculated by subtracting the discharge capacity from the total capacity differs from the actual remaining power that can be discharged under actual operating conditions. Summary of the Invention

[0009] To address the technical problems existing in the background art, this invention proposes a test method for estimating the SOC accuracy of a power battery system.

[0010] The present invention proposes a test method for estimating the SOC accuracy of a power battery system. Before the test, it is necessary to determine the SOC range nm of the battery system (0≤n<m≤100), as well as the single cell voltage values ​​corresponding to the lowest and highest SOC. The target temperature T can be selected from multiple values ​​within the operating temperature range of the battery system for testing as needed. The test SOC state M can also be selected from multiple values ​​for testing as needed.

[0011] Perform the test according to the following test steps:

[0012] Includes the following steps:

[0013] S1: Place the battery system in the environmental chamber, and connect the high-voltage charging and discharging harness of the battery system to the high-voltage harness of the charging and discharging test cabinet, connect the low-voltage communication harness of the battery system to the low-voltage communication harness of the charging and discharging test cabinet, and connect the low-voltage power supply harness of the battery system to the output port of the DC regulated power supply.

[0014] S2: Adjust the ambient temperature to room temperature, and discharge the battery system to the lowest single-cell voltage corresponding to the lowest usable SOC=n;

[0015] S3: Adjust the ambient temperature to T, let the battery system stand until the temperature is within the range of T±2℃, and charge the battery system after S2 discharge to the highest single cell voltage corresponding to the highest SOC=m according to the actual use charging method.

[0016] S4: Adjust the ambient temperature to T, let the battery system stand until the temperature is within the range of T±2℃, and cycle discharge it to SOC=M according to the actual operating conditions, and record the discharge capacity Q1.

[0017] S5: Simulate actual usage scenarios, discharge at a constant current of I under actual usage conditions until the lowest single cell voltage corresponding to the lowest usage SOC = n, and record the discharge capacity Q2 and the estimated SOC value A at the discharge cutoff time.

[0018] S6: Perform the following calculations based on the test record values:

[0019]

[0020]

[0021]

[0022]

[0023] Preferably, the method further includes S7: adjusting the values ​​of T and M in S4-S6, repeating test steps S2-S6, and testing the estimation accuracy of the battery system for different SOC states under different temperature environments.

[0024] Preferably, before testing, it is necessary to determine the SOC range nm (0≤n<m≤100) of the battery system, as well as the single-cell voltage values ​​corresponding to the minimum SOC = n and the maximum SOC = m.

[0025] Preferably, in step S5, the equivalent current I is the root mean square of the process current under a complete actual operating condition. Preferably, in step S5, the constant current discharge method for the equivalent current I under the actual operating condition includes:

[0026] A. Discharge at a constant current of I down to the lowest single-cell voltage corresponding to the lowest usable SOC;

[0027] B. Let stand for 5 minutes, then discharge with constant current I to the lowest single-cell voltage corresponding to the lowest operating SOC;

[0028] C. Adjust the ambient temperature to T, let the battery system stand until the temperature is within the range of T±2℃, and discharge it with constant current I to the lowest single cell voltage corresponding to the lowest operating SOC;

[0029] D. Adjust the ambient temperature to 25℃, let the battery system stand until the temperature is within the range of 25±2℃, and discharge it with constant current I to the lowest single cell voltage corresponding to the lowest operating SOC.

[0030] Preferably, step S1 further includes connecting the water inlet and outlet of the battery system to the water outlet and return outlet of the water chiller, respectively, and keeping other various connecting components connected according to the actual usage status.

[0031] Preferably, T can be between -20℃ and 60℃.

[0032] Preferably, T can be -10℃, 0℃, 25℃, or 40℃.

[0033] Preferably, in step S4, during the discharge of the battery system according to the actual operating conditions, the water chiller is turned on according to the thermal management strategy, and other functions such as self-heating and equalization are also turned on normally. That is, during the discharge of the operating conditions, the battery system is heated or cooled according to the temperature of the battery system, thereby restoring the state of the battery system in the actual process.

[0034] Preferably, in step S5, during the discharge of the battery system according to the actual operating conditions, the water chiller is turned on according to the thermal management strategy, and other functions such as self-heating and equalization are also turned on normally. That is, the battery system is heated or cooled according to the temperature of the battery system during the discharge process.

[0035] The proposed method for testing the SOC estimation accuracy of a power battery system involves simulating the charging and discharging process of a battery during actual use.

[0036] Discharge using the equivalent current under actual operating conditions, and use the accumulated discharge capacity as the true remaining charge.

[0037] The total charge is calculated based on the cumulative capacity of the battery during the test, from the highest SOC state to the lowest SOC state.

[0038] The calculation formula for SOC estimation error has been optimized to cover the SOC estimation error at the discharge end.

[0039] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the method flow of the present invention. Detailed Implementation

[0041] Embodiments of the present invention are described in detail below. Examples of these embodiments are illustrated in the accompanying drawings, wherein the same or similar symbols denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0042] like Figure 1 This illustrates a test method for estimating the SOC (State of Charge) of a power battery system.

[0043] The battery system was tested for estimation accuracy at 80%, 50%, and 10% SOC under four temperature environments: -10℃, 0℃, 25℃, and 40℃. The actual usable SOC range of the battery system is 5%–95% (i.e., the usable SOC range of the battery system is determined in nm (0≤n<m≤100)), corresponding to cutoff cell voltages of 2.8V and 3.58V, respectively. The battery BMS is powered by a low-voltage 12V supply, and the battery system has an automatic end-of-life SOC calibration function. The battery system is cooled by liquid cooling and heated by electric heating. The specific implementation steps are as follows: Figure 1 As shown:

[0044] S1: The battery system is placed in the environmental chamber. The high-voltage charging and discharging harness of the battery system is connected to the high-voltage harness of the charging and discharging test cabinet. The low-voltage communication harness of the battery system is connected to the low-voltage communication harness of the charging and discharging test cabinet. The low-voltage power supply harness of the battery system is connected to the output port of the DC regulated power supply. The water inlet and outlet of the battery system are connected to the water outlet and water return of the water chiller, respectively. Other connecting components are kept connected according to the actual use.

[0045] S2: Adjust the ambient temperature to 25℃, let the battery system stand until the BMS temperature is within the range of 25±2℃, turn on the DC regulated power supply 12V, close the relay through the host computer, discharge at 1C until the BMS collects the lowest single cell voltage of 2.8V and then turn off the DC regulated power supply 12V.

[0046] S3: Adjust the ambient temperature to 25℃, allow the battery system to settle until the BMS temperature is within 25±2℃, turn on the 12V DC regulated power supply, send a vehicle message command to close the relay, and turn on the charge / discharge test cabinet to charge the battery system according to the fast charging matrix until the highest single-cell voltage is greater than 3.58V and the battery system's BMS reports SOC=95%. During the charging process, set the water chiller outlet temperature according to the thermal management strategy and turn the water chiller on and off. Turn off the DC regulated power supply.

[0047] S4: Adjust the ambient temperature to 25℃, let the battery system stand until the BMS collects the temperature within the range of 25±2℃, turn on the DC regulated power supply 12V, and run the WLTC condition cycle until the BMS reports the SOC value M=10. During the WLTC condition operation, set the water chiller outlet temperature according to the thermal management strategy and turn the water chiller on and off. The charge and discharge test cabinet records the cumulative discharge capacity as Q1.

[0048] S5: Calculate the equivalent current value I under WLTC operating conditions, discharge at a constant current of I until the minimum single-cell voltage collected by the BMS is 2.8V, set the water chiller outlet temperature according to the thermal management strategy and turn the water chiller on and off, the charge and discharge test cabinet records the cumulative discharge amount as Q2, and the BMS reports SOC=A at the discharge cutoff time; here, the continuous discharge scenario simulating actual use is selected for testing, but other discharge methods can also be selected for testing according to requirements;

[0049] S6: Calculate the SOC estimation error based on the test record values:

[0050]

[0051]

[0052]

[0053]

[0054] When the calculated SOC estimation error is within 5%, the SOC value reported by the BMS of the battery system is qualified. Preferably, the calculated SOC estimation error is within 3%.

[0055] S7: Adjust T in S3-S5 to -10, 0, and 40 respectively, and M in step S4 to 80 and 50 respectively. Repeating steps S2-S6 can test the estimation accuracy of the battery system for different SOC states under different temperature environments.

[0056] The above improvements make the testing method more consistent with the actual use of batteries. The optimization of the SOC estimation error calculation method can obtain a more accurate SOC that is closer to the actual use, thus making the SOC estimation error obtained from the test more reflective of the deviation from the actual use. There is no need to perform battery capacity calibration at different temperatures, avoiding the difference between the battery capacity calibration value and the actual discharge capacity value, as well as the impact of battery capacity decay or fluctuation on the test results, which greatly reduces the testing time and shortens the product development testing cycle.

[0057] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A test method for estimating the SOC (State of Charge) of a power battery system, characterized in that, Includes the following steps: S1: Place the battery system in the environmental chamber, and connect the high-voltage charging and discharging harness of the battery system to the high-voltage harness of the charging and discharging test cabinet, connect the low-voltage communication harness of the battery system to the low-voltage communication harness of the charging and discharging test cabinet, and connect the low-voltage power supply harness of the battery system to the output port of the DC regulated power supply. S2: Adjust the ambient temperature to room temperature, and discharge the battery system to the lowest single-cell voltage corresponding to the lowest usable SOC=n; S3: Adjust the ambient temperature to T, let the battery system stand until the temperature is within the range of T±2℃, and charge the battery system after S2 discharge to the highest single cell voltage corresponding to the highest SOC=m according to the actual use charging method. S4: Adjust the ambient temperature to T, let the battery system stand until the temperature is within the range of T±2℃, and cycle discharge it to SOC=M according to the actual operating conditions, and record the discharge capacity Q1. S5: Simulate actual usage scenarios, discharge at a constant current of I under actual usage conditions until the lowest single-cell voltage corresponding to the lowest usage SOC=n, and record the discharge capacity Q2 and the estimated SOC value A at the discharge cutoff time. S6: Perform the following calculations based on the test record values: 。 2. The test method for estimating the SOC of a power battery system according to claim 1, characterized in that, It also includes S7: Adjust the values ​​of T and M in S4-S6, repeat test steps S2-S6, and test the estimation accuracy of the battery system for different SOC states under different temperature environments.

3. The test method for estimating the SOC of a power battery system according to claim 1, characterized in that, Before testing, it is necessary to determine the SOC range of the battery system, n-m, and the individual cell voltage values ​​corresponding to the minimum SOC=n and the maximum SOC=m, where 0≤n<m≤100.

4. The test method for estimating the SOC of a power battery system according to claim 1, characterized in that, In step S5, the equivalent current I is the root mean square of the process current under a complete actual operating condition.

5. The test method for estimating the SOC of a power battery system according to claim 1, characterized in that, In step S5, the equivalent current I constant current discharge method under actual operating conditions includes: A. Discharge at a constant current of I down to the lowest single-cell voltage corresponding to the lowest usable SOC; B. Let stand for 5 minutes, then discharge with constant current I to the lowest single-cell voltage corresponding to the lowest operating SOC; C. Adjust the ambient temperature to T, let the battery system stand until the temperature is within the range of T±2℃, and discharge it with constant current I to the lowest single cell voltage corresponding to the lowest operating SOC; D. Adjust the ambient temperature to 25℃, let the battery system stand until the temperature is within the range of 25±2℃, and discharge it with constant current I to the lowest single cell voltage corresponding to the lowest operating SOC.

6. The test method for estimating the SOC of a power battery system according to claim 1, characterized in that, Step S1 also includes connecting the water inlet and outlet of the battery system to the water outlet and return outlet of the water chiller, respectively.

7. The test method for estimating the SOC of a power battery system according to claim 1, characterized in that, T is set at -20℃ to 60℃.

8. The test method for estimating the SOC accuracy of a power battery system according to claim 7, characterized in that, T is set at 25℃.

9. The test method for estimating the SOC of a power battery system according to claim 1, characterized in that, In step S4, the battery system is heated or cooled according to its temperature during the operating condition discharge process.

10. The test method for estimating the SOC of a power battery system according to claim 1, characterized in that, In step S5, the constant current discharge process heats or cools the battery system according to its temperature.

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