Vehicle power battery charging SOC calibration method

Abstract

The invention relates to a vehicle power battery charging SOC calibration method. The method comprises the following steps: carrying out a battery characteristic experiment at different temperatures; establishing a corresponding relation table of the battery model parameters and the SOC at different temperatures; establishing a constant voltage stage current recursion formula through derivation; according to a current recursion formula and the CV stage charging data, current simulation in a constant voltage stage is carried out, a temperature-current-SOC corresponding table is established, and SOC calibration points at different temperatures when the current in the constant voltage stage drops to a specific value are recorded in the table; and writing the table into a battery management system, monitoring the current in real time at a constant voltage stage, and carrying out SOC calibration according to the corresponding table. According to the method, in the constant voltage stage, SOC calibration can be carried out by monitoring the current drop value in the charging process without waiting for the complete completion of the CCCV charging process.

Description

Technical Field

[0001] The present invention relates to the technical field of electric vehicle power battery applications, and in particular to a calculation method for calibrating the charging SOC of a vehicle power battery. Background Art

[0002] The state of charge (SOC) is the ratio of the remaining charge of the battery to its fully charged state capacity, and is a key parameter for energy management in electric vehicles. The accuracy of the battery SOC is crucial to the performance and range of the vehicle. However, due to the influence of many factors such as the variable vehicle operating conditions and battery capacity attenuation, SOC, as an invisible state quantity, is difficult to obtain its precise value, which in turn affects the user's judgment of the remaining range. Therefore, the battery SOC needs to be calibrated. The existing on-board power battery full charge calibration strategy is usually implemented through the CCCV (Constant Current Constant Voltage) charging process. However, in actual use, users are often unable to wait for the charging process to be completely completed, resulting in the inability to trigger the correction. The SOC cannot be calibrated through full charging, which in turn affects its accuracy.

[0003] Chinese Patent No. 202311812971.1 discloses a power battery SOC calibration method and device, while Patent No. CN 117183821A discloses a method and system for controlling SOC correction at the end of a charging cycle. Both patents perform SOC correction based on the battery charging voltage, relying on triggering under specific conditions and making it difficult to implement SOC correction during constant voltage charging. Summary of the Invention

[0004] This disclosure provides a calculation method for calibrating the SOC of a vehicle power battery during charging. During the constant voltage phase, this method calibrates the SOC based on the current when it drops to a specific value. This method calibrates the SOC in stages during the charging process, without waiting for CCCV to fully complete. This effectively reduces SOC cumulative error and improves SOC estimation accuracy, making it particularly suitable for practical use cases where a full charge cannot be achieved.

[0005] The method mainly includes the following steps:

[0006] S1, battery characteristics experiment: OCV (Open Circuit Voltage, open circuit voltage test after battery discharge, a commonly used test method in the battery field) test, HPPC (Hybrid Pulse Power Characteristic, hybrid power pulse characteristic) test and CCCV (Constant Current Constant Voltage, constant current constant voltage) charging test are performed at different temperatures;

[0007] S2: Establish the Thevenin model, use the offline parameter identification method based on genetic algorithm to determine the key parameters of the battery model, and establish the corresponding relationship table between the battery model parameters and SOC at different temperatures;

[0008] S3: Establish the recursive formula of current in constant voltage stage through deduction;

[0009] S4: Based on the current recursion formula and the constant voltage stage charging data, the current simulation of the constant voltage stage is performed to establish a temperature-current-SOC correspondence table. The table records the SOC calibration points when the current in the constant voltage stage drops to a specific value at different temperatures;

[0010] S5: Write the temperature-current-SOC correspondence table into the BMS battery management system. The BMS monitors the current in real time during the constant voltage stage and performs SOC calibration according to the corresponding table.

[0011] Compared with the prior art, the beneficial effects of the present disclosure are: ① This method can calibrate the SOC in stages during the charging process without waiting for CCCV to be completely completed, thereby effectively reducing the SOC cumulative error and improving the accuracy of SOC estimation; ② It can be applied to scenarios in actual use where users cannot wait for full charging; ③ It can accurately reflect the actual remaining power of the battery when full charging correction is not possible, which is conducive to improving the range estimation of electric vehicles and the reliability of the battery management system. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The above and other objects, features and advantages of the present disclosure will become more apparent through a more detailed description of exemplary embodiments of the present disclosure in conjunction with the accompanying drawings, wherein like reference numerals generally represent like components throughout the exemplary embodiments of the present disclosure.

[0013] Figure 1 This is a flow chart of a method for calibrating the SOC of a power battery charging terminal for disembarking from a vehicle in one embodiment;

[0014] Figure 2 : is a current simulation curve for SOC calibration obtained in the constant voltage stage in an exemplary embodiment. DETAILED DESCRIPTION

[0015] The preferred embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although preferred embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided to make the present disclosure more thorough and complete, and to fully convey the scope of the present disclosure to those skilled in the art.

[0016] The present disclosure provides a calculation method for calibrating the SOC of a vehicle power battery during charging. The method calibrates the SOC by monitoring the current drop value during a constant voltage phase.

[0017] In an exemplary embodiment, the process of the vehicle power battery charging SOC calibration method is as shown in the attached Figure 1 As shown:

[0018] Step 1: Battery characterization test. Perform OCV, HPPC test and CCCV charge test at different temperatures.

[0019] Step 2: Establish the Thevenin model and use the offline parameter identification method based on genetic algorithm to determine the key parameters of the battery model, including open circuit voltage, ohmic internal resistance R i , polarization internal resistance R D , polarization capacitance C D wait;

[0020] Step 3: In the constant voltage stage, derive the current recursive formula and establish a mathematical model of current and SOC;

[0021] Step 4: Based on the derived formula and the CV (Constant Voltage) charging data, perform current simulation during the CV phase and create a temperature-current-SOC correspondence table. The table records the SOC calibration points when the current drops to a specific value during the CV phase at different temperatures.

[0022] Step 5: Write the temperature-current-SOC correspondence table into the battery management system. The BMS monitors the current in real time during the constant voltage phase and performs SOC calibration based on the corresponding table.

[0023] Application Examples

[0024] The battery positive electrode material used is nickel-cobalt-manganese ternary lithium, with a nominal capacity of 30Ah. The CCCV charging method is 1 / 3C constant current charging to 4.25V, and then constant voltage charging at 4.25V until the current drops to 0.05C.

[0025] The specific process of step 1 is:

[0026] Step S101: performing an OCV test at 25°C;

[0027] Step S102: performing an HPPC test and a CCCV charging test at temperatures of 25° C., 10° C., and 40° C., with the SOC of the pulse excitation sequence experiment of the HPPC test being 10% apart;

[0028] The specific process of step 2 is:

[0029] Step S201: Using the OCV test data, a relationship table between the OCV and SOC of the battery is established, and the corresponding open circuit voltage values when the SOC is 100%, 90% ... 10% are recorded;

[0030] Step S202: According to the Thevenin model, an offline parameter identification method based on a genetic algorithm is used to obtain parameter identification results of the battery under composite pulse test data at different temperatures, i.e., the battery ohmic internal resistance, polarization internal resistance, and polarization capacitance corresponding to SOC of 100%, 90%, ..., 10%;

[0031] Step S203: establishing a relationship table between battery model parameters and SOC at different temperatures based on the parameter identification results;

[0032] The specific process of step 3 is:

[0033] Step S301: According to the working equation of the Thevenin model, the terminal voltage U of the model can be obtained. t,k The expression is: U t,k =f(SOC k )-I k R i -U D,k , since the voltage remains constant during the constant voltage stage, U t,k+1 =U t,k , we can get:

[0034] f(SOCk +1 )-Ik +1 R i -U D,k+1 =f(SOCk)-IkR i -U D,k (1)

[0035] f(SOC k+1 )-I k+1 R i -U D,k+1 =f(SOC k )-I k R i -U D,k , where the subscript k represents t k time;

[0036] Step S302: Assuming that the SOC changes slowly during the constant voltage phase, it is approximately assumed that f(SOC k+1 )≈f(SOC k ), and substituting it into equation (1) we can get:

[0037] I k+1 R i +U D,k+1 =I kR i +U D,k (2)

[0038] Step S303: The recursive formula for polarization voltage in the Thevenin model is U D,k+1 =e -Δt / τ U D,k +R D (1-e -Δt / τ )I k+1 , where τ = R D C D , substituting the recursive formula into equation (2) yields:

[0039]

[0040] Step S304: The final recursive formula for the current in the constant voltage stage is:

[0041]

[0042] The current value corresponding to the SOC in the constant voltage charging phase can be calculated according to formula (4);

[0043] The specific process of step 4:

[0044] Step S401: Calculate the current value in the constant voltage phase according to the current recursive formula (4), and then use the constant voltage phase charging data to obtain the reference SOC, thereby obtaining a relationship table between the battery current and SOC in the constant voltage phase, and establish a current-SOC table at temperatures of 10°C, 25°C, and 40°C respectively;

[0045] Step S402: Based on the result of step 401, a temperature-current-SOC correspondence table is established. The table records the SOC calibration points when the current drops to a specific value during the constant voltage phase at different temperatures. The results of this case are as follows: Figure 2 As shown;

[0046] The specific process of step 5:

[0047] Step S501: writing the temperature-current-SOC table into the battery management system;

[0048] Step S502: During the actual vehicle charging process, when the charging reaches the constant voltage stage, the current-SOC calibration mode is entered:

[0049] When the constant current charging stage is not stopped, the SOC is calculated by time integration and no calibration is triggered;

[0050] When the constant current phase of charging ends and enters the constant voltage phase: If charging is terminated prematurely due to various unexpected factors or human intervention, the temperature-current-SOC calibration mechanism is triggered. The actual SOC is interpolated based on the temperature and current at the last moment before the end, triggering SOC calibration;

[0051] If the battery is fully charged normally and the current reaches the cut-off current, charging will automatically end (the end of charging is usually determined based on the current in the constant voltage section, which is usually given a value. When the current drops to this value, the battery is considered fully charged and charging is ended by default). This triggers full charge calibration and the SOC is calibrated to 100%.

[0052] Experimental results show that the SOC calibration method in this embodiment can accurately reflect the actual remaining capacity of the battery when full charge calibration is not possible.

[0053] The above technical solutions are only exemplary embodiments of the present invention. For those skilled in the art, it is easy to make various types of improvements or modifications based on the application methods and principles disclosed in the present invention, and are not limited to the methods described in the above specific embodiments of the present invention. Therefore, the methods described above are only preferred and do not have a restrictive meaning.

Claims

1. A method for calibrating the SOC of a vehicle power battery charge, comprising the following steps: S1, battery characterization experiment: OCV test, HPPC test and CCCV charge test at different temperatures; S2: Establish the Thevenin model, use the offline parameter identification method based on genetic algorithm to determine the key parameters of the battery model, and establish the corresponding relationship table between the battery model parameters and SOC at different temperatures; S3: Establish the recursive formula of current in constant voltage stage through deduction; S4: Based on the current recursion formula and the constant voltage stage charging data, the current simulation of the constant voltage stage is performed to establish a temperature-current-SOC correspondence table. The table records the SOC calibration points when the current in the constant voltage stage drops to a specific value at different temperatures; S5: Write the temperature-current-SOC correspondence table into the BMS battery management system. The BMS monitors the current in real time during the constant voltage stage and performs SOC calibration according to the corresponding table.

2. The method according to claim 1, characterized in that The step S1 specifically includes: S11: OCV test at 25°C; S12: HPPC test and CCCV charging test are performed at temperatures of 25° C., 10° C., and 40° C. in sequence, with the SOC of the pulse excitation sequence experiment of the HPPC test being 10% apart.

3. The method according to claim 1, characterized in that The step S2 specifically includes: S21: Using the OCV test experimental data, establish a relationship table between the OCV and SOC of the battery used, and record the corresponding open circuit voltage values when the SOC is 100%, 90%...10%; S22: According to the Thevenin model, the offline parameter identification method based on genetic algorithm obtains the parameter identification results of the composite pulse test data of the battery used at different temperatures, that is, the battery ohmic internal resistance R corresponding to SOC of 100%, 90%...10% i , polarization internal resistance R D , polarization capacitance C D ; S23: Based on the parameter identification results, a corresponding relationship table between the battery model parameters and the SOC at different temperatures is established.

4. The method according to claim 3, characterized in that The step S3 specifically includes: S31: According to the working equation of the Thevenin model, the terminal voltage U of the model is obtained t,k The expression is: The t,k =f(SOC k )-I k R i -U D,k , Wherein, the subscript k represents t k time; U D,k represents the polarization voltage at time k; In the constant voltage stage, since the voltage is kept constant, that is, U t,k+1 =U t,k ,get: f(SOC k+1 )-I k+1 R i -U D,k+1 =f(SOC k )-I k R i -U D,k (1) S32: In the constant voltage stage, SOC changes slowly, and it is approximately considered that f(SOC k+1 )≈f(SOC k ), and substituting it into equation (1) we get: I k+1 R i +U D,k+1 =I k R i +U D,k (2) S33: The recursive formula for polarization voltage in the Thevenin model is U D,k+1 =e -Δt / τ U D,k +R D (1-e -Δt / τ )I k+1 , where τ = R D C D , put the recursive formula into equation (2) to get: R D is the polarization internal resistance, C D is the polarization capacitance, Δt=t k+1 -t k ; S34: The recursive formula for the current in the constant voltage stage is obtained as follows:

5. The method according to claim 1, characterized in that The step S4 specifically includes: S41: Calculating the current value in the constant voltage phase according to the current recursive formula; then using the relationship table between the battery model parameters and SOC at different temperatures established in step S2, obtaining a reference SOC based on the charging data in the constant voltage phase, thereby obtaining a relationship table between the battery current and SOC in the constant voltage phase; S42: Based on the result of step S41, a temperature-current-SOC correspondence table is established, where the table records the SOC calibration points when the current drops to a specific value during the constant voltage phase at different temperatures.

6. The method according to any one of claims 1 to 5, characterized in that: The step S5 specifically includes: S51: Writing the temperature-current-SOC table into the battery management system; S52: During the actual charging process of the vehicle, When the constant current charging stage is not stopped, the SOC is calculated by time integration and no calibration is triggered; When the constant current phase of charging ends and enters the constant voltage phase, if charging is terminated prematurely due to various unexpected factors or human factors, the temperature-current-SOC calibration mechanism is triggered. The actual SOC is interpolated and calculated based on the temperature and current at the last moment before the end, triggering SOC calibration. If the battery is fully charged normally and the current reaches the cut-off current, charging ends automatically, triggering full charge calibration, and the SOC is calibrated to 100%.

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