A method for estimating state of energy (SOE) of a battery

Abstract

The application relates to a battery residual energy SOE estimation method, which comprises the following steps: generating an SOC-OCV curve based on the correspondence between a battery residual capacity SOC and an open circuit voltage OCV and generating a temperature-capacity retention rate correspondence table under different temperatures; acquiring a voltage compensation factor VoltFactor and a rated voltage RatedVolt under different SOCs; estimating a battery residual energy SOE_nom under normal temperature, and then estimating a battery residual energy SOE under different temperatures according to a SOC freezing condition SOC_bottom and a capacity retention rate under a low-temperature environment. The application fully considers the influence of temperature, a battery residual capacity SOC and voltage on the battery residual energy SOE, converts the conventional parameter SOC of the battery into SOE, is convenient to realize, shortens the development cycle, and fully reflects the discharge capacity of the battery under different temperatures and different SOCs.

Description

Technical Field

[0001] This invention belongs to the field of battery management technology, and in particular relates to an estimation method for SOE generation based on SOC. Background Technology

[0002] As a core component of electric vehicles, the Battery Management System (BMS) has always been a key focus of electric vehicle research and development. State of Charge (SOC), State of Hypothesis (SOH), State of Operation (SOP), and State of Energy (SOE) are the most critical parameters of the BMS. During vehicle operation, lithium batteries undergo complex chemical reactions, and the relationships between parameters such as SOC, SOH, SOP, and SOE cannot be directly obtained. They can only be indirectly estimated by collecting battery voltage and temperature data through the BMS and using lithium battery models and estimation algorithms. While SOC is commonly used to represent the remaining discharge capacity of a battery, it has significant limitations. Firstly, SOC cannot represent the same change in SOC where higher battery voltage results in more discharged electricity and a longer driving range. Secondly, SOC also cannot represent the same change in SOC where higher temperature results in more discharged electricity and a longer driving range. Compared to SOC, SOE fully considers the impact of temperature and individual cell voltage on battery discharge capacity. SOE is analogous to the remaining fuel level in a gasoline vehicle; it is crucial for mileage calculation. Accurate SOE calculation provides a reliable reference for end-users' travel, improving the user experience. Summary of the Invention

[0003] The purpose of this invention is to provide a method for estimating the remaining energy (SOE) of a battery in order to solve the above-mentioned problems.

[0004] The present invention achieves the above objectives through the following technical solution: the method for estimating the remaining energy (SOE) of a battery according to the present invention includes the following steps:

[0005] S1. Generate SOC-OCV curves based on the relationship between battery remaining capacity SOC and open circuit voltage OCV, and generate a table of temperature-capacity retention rate based on different temperatures;

[0006] S2. Based on the SOC-OCV curve, obtain the voltage compensation factor VoltFactor and the rated voltage RatedVolt under different SOCs;

[0007] S3. Estimate the remaining energy SOE_nom of the battery at room temperature based on the voltage compensation factor VoltFactor, rated voltage RatedVolt, and nominal capacity Cap of the battery. Then estimate the remaining energy SOE of the battery at different temperatures based on the SOC freezing condition SOC_bottom under low temperature conditions and the capacity retention rate in the temperature-capacity retention rate correspondence table for different temperatures.

[0008] As a further preferred embodiment of the present invention, in step S1, the step of generating the SOC-OCV curve based on the relationship between the remaining battery capacity (SOC) and the open-circuit voltage (OCV) specifically involves:

[0009] a. Place the battery cells in a 25°C environment until the cell temperature reaches 25°C, and let them stand for 60 minutes;

[0010] b. Charge the battery to the charging cutoff voltage at a current of 1 / 3C, and then charge the battery to the charging cutoff voltage at a current of 0.1C.

[0011] c. After the temperature cools to 25℃, let it stand for 60 minutes, then discharge it at a current of 1 / 3C to 5%*. After letting it stand for 4 hours, record the current battery voltage as OCV and the current SOC. Repeat this step until the battery is discharged to its maximum capacity. Then stop, among which Indicates the discharge energy;

[0012] d. Record the correspondence between SOC and OCV, and generate an SOC-OCV curve showing the correspondence between the remaining battery capacity SOC and the open circuit voltage OCV.

[0013] As a further preferred embodiment of the present invention, the step of generating the temperature-capacity retention rate correspondence table at different temperatures in step S1 is specifically as follows:

[0014] Place the battery cells in a 25°C environment until the cell temperature reaches 25°C, and let them stand for 60 minutes.

[0015] Charge the battery with a current of 1C to the charging cutoff voltage, and then charge the battery with a current of 0.1C to the charging cutoff voltage.

[0016] After the cell temperature reaches 25℃, let it stand for 60 minutes.

[0017] Discharge continuously with a current of 1 / 3C until the discharge cutoff voltage is reached, and the discharge energy is recorded. ;

[0018] By adjusting the temperature, the discharge is continuously carried out at different temperatures until the discharge cutoff voltage is reached. The discharge energy at different temperatures is denoted as Q(T).

[0019] Based on the capacity retention rate calculation formula, the capacity retention rate at different temperatures is obtained. The capacity retention rate calculation formula is as follows:

[0020] ;

[0021] A table of temperature-capacity retention rate (η) is generated based on the capacity retention rate at different temperatures.

[0022] As a further preferred embodiment of the present invention, the step S2 of obtaining the voltage compensation factor VoltFactor and the rated voltage RatedVolt based on the SOC-OCV curve under different SOCs specifically includes:

[0023] Based on the SOC-OCV curve, the voltage compensation factor VoltFactor and the rated voltage RatedVolt at different SOCs are calculated using the following formulas:

[0024] ;

[0025] ;

[0026] In the formula, BatNum represents the number of batteries.

[0027] As a further preferred embodiment of the present invention, the step in S3 of estimating the remaining energy SOE_nom of the battery at room temperature based on the voltage compensation factor VoltFactor, the rated voltage RatedVolt, and the nominal capacity Cap of the battery, and then estimating the remaining energy SOE of the battery at different temperatures based on the SOC freezing condition SOC_bottom under low temperature conditions and the capacity retention rate in the temperature-capacity retention rate correspondence table at different temperatures, specifically involves the following steps:

[0028] S301. Calculate the battery's charging capacity cap, as follows:

[0029] ;

[0030] S302. The charging capacity cap is expressed using the remaining battery charge (SOC), the battery state of health (SOH), and the nominal capacity (Cap), as shown in the following formula:

[0031] ;

[0032] S303. Based on the voltage compensation factor VoltFactor and the rated voltage RatedVolt, the estimation formula for the remaining battery energy SOE_nom at room temperature can be expressed as follows:

[0033] ;

[0034] S304. Based on the SOC_bottom under low-temperature freezing conditions and the capacity retention rate in the table of temperature-capacity retention rate correspondence at different temperatures, the remaining energy SOE of the battery at different temperatures is estimated as follows:

[0035] ;

[0036] Wherein, the freezing condition Soc_bottom is represented as the difference between 100% and the capacity retention rate.

[0037] The beneficial effects of this invention are as follows: This invention fully considers the influence of temperature, SOC and voltage on SOE, and converts the SOC of the battery into SOE through the OCV-SOC correspondence table and the temperature capacity retention rate correspondence table, which simplifies the implementation and shortens the development cycle, and fully reflects the discharge capacity of the battery at different temperatures and different SOCs. Attached Figure Description

[0038] Figure 1 This is a flowchart of the method of the present invention.

[0039] Figure 2 This is a diagram illustrating SOC-OCV curves at different temperatures according to the present invention. Detailed Implementation

[0040] The present application will now be described in further detail with reference to the accompanying drawings. It should be noted that the following specific embodiments are only used to further illustrate the present application and should not be construed as limiting the scope of protection of the present application. Those skilled in the art can make some non-essential improvements and adjustments to the present application based on the above application content.

[0041] like Figure 1 As shown, a method for estimating the remaining energy (SOE) of a battery includes the following steps:

[0042] S1: Generate SOC-OCV curves based on the relationship between battery remaining capacity (SOC) and open-circuit voltage (OCV), and generate a table of temperature-capacity retention rates based on different temperatures.

[0043] In this embodiment, the specific process is as follows:

[0044] Through experimental testing, the correlation between the battery's remaining charge (SOC) and open-circuit voltage (OCV), as well as the correlation between temperature and capacity retention rate, were obtained, and SOC-OCV curves and temperature-capacity retention rate correlation tables were generated.

[0045] The method for obtaining the SOC-OCV curves shown in Table 1 is as follows:

[0046] a. Place the battery cells in a 25°C environment until the cell temperature reaches 25°C, and let them stand for 60 minutes;

[0047] b. Charge the battery to the charging cutoff voltage at a current of 1 / 3C, and then charge the battery to the charging cutoff voltage at a current of 0.1C.

[0048] c. After the temperature cools to 25℃, let it stand for 60 minutes, then discharge it at a current of 1 / 3C to 5%*. After letting it stand for 4 hours, record the current battery voltage as OCV and the current SOC. Repeat this step until the battery is discharged to its maximum capacity. Then stop; d. Record the correspondence between SOC and OCV, and generate the SOC-OCV curve showing the correspondence between the remaining battery capacity SOC and the open circuit voltage OCV.

[0049] Table 1 SOC-OCV curves ;

[0050] The method for obtaining the temperature-capacity retention rate correspondence table shown in Table 2 is as follows:

[0051] a. Place the battery cells in a 25°C environment until the cell temperature reaches 25°C, and let them stand for 60 minutes;

[0052] b. Charge the battery pack to the charging cutoff voltage at a current of 1C, and then charge the battery to the charging cutoff voltage at a current of 0.1C.

[0053] c. After the battery cell temperature reaches 25℃, let it stand for 60 minutes;

[0054] d. Discharge continuously at 1 / 3C until the discharge cutoff voltage, and record the discharge energy. And conduct tests;

[0055] e. Adjust the temperature T sequentially to -20℃, -10℃, 0℃, 10℃, 25℃, and 45℃, record the capacity during the discharge process as Q(T), and perform the test;

[0056] f. According to The capacity retention rate η at different temperatures was calculated, and a temperature-capacity retention rate correspondence table was generated. Table 2: Temperature-Capacity Retention Rate Correspondence Table

[0057] Table 2 Temperature-Capacity Retention Rate Correspondence Table ;

[0058] S2. Based on the SOC-OCV curve, obtain the voltage compensation factor (VoltFactor) and the rated voltage (RatedVolt) under different SOCs. According to the SOC-OCV curve, obtain the open-circuit voltage (OCV) corresponding to different remaining battery capacity SOCs. Substitute the remaining battery capacity SOC and the corresponding open-circuit voltage (OCV) into the voltage compensation factor calculation formula to obtain the voltage compensation factor (VoltFactor) under different remaining battery capacity SOCs. The voltage compensation factor calculation formula is as follows:

[0059] ;

[0060] Generate the SOC-VoltFactor mapping table, as shown in Table 3:

[0061] Table 3. Correspondence between SOC and VoltFactor

[0062] ;

[0063] To obtain the battery's basic parameters at the current temperature, including the nominal capacity (Cap), the battery management system (BMS) basic parameters (remaining charge (SOC) and state of health (SOH), and to calculate the rated voltage (RatedVolt), the specific steps are as follows:

[0064] Get the number of batteries in the battery, BatNum;

[0065] Obtain the battery's remaining charge (SOC) at the current temperature; based on the SOC-OCV curve, obtain the open-circuit voltage (OCV) corresponding to the battery's remaining charge (SOC) at the current temperature. Substitute the number of batteries (BatNum), the battery's remaining charge (SOC) at the current temperature, and the open-circuit voltage (OCV) into the rated total voltage calculation formula to obtain the rated voltage (RatedVolt). The rated total voltage calculation formula is as follows: ;

[0066] Based on the battery remaining capacity SOC, the SOC-VoltFactor correspondence table and the temperature-capacity retention rate correspondence table, the voltage compensation factor VoltFactor and capacity retention rate η under different SOCs are obtained;

[0067] S3. Estimate the remaining energy SOE_nom of the battery at room temperature based on the voltage compensation factor VoltFactor, rated voltage RatedVolt, and nominal capacity Cap of the battery. Then estimate the remaining energy SOE of the battery at different temperatures based on the SOC freezing condition SOC_bottom under low temperature conditions and the capacity retention rate in the temperature-capacity retention rate correspondence table for different temperatures.

[0068] In this embodiment, the remaining usable energy SOE_nom at room temperature of the battery is calculated using the following formula: (1);

[0069] Where V represents the total battery voltage, I represents the current, and t represents the charging time;

[0070] The expression for the total battery voltage V is:

[0071] (2); where BatNum represents the number of batteries and OCV represents the open circuit voltage;

[0072] Substituting formula (2) into formula (1) yields:

[0073] (3);

[0074] The formula for calculating the battery's charging capacity (cap) is as follows: (4);

[0075] Substituting formula (4) into formula (3) yields:

[0076] (5);

[0077] The charging capacity cap can also be expressed as: (6);

[0078] Where Cap represents the nominal capacity;

[0079] Substituting formula (6) into formula (5) yields:

[0080] (7);

[0081] The formula for calculating the rated voltage RatedVolt is as follows: (8);

[0082] Formula (8) is transformed to obtain formula (9): (9);

[0083] Substituting formula (9) into formula (7) yields: (10);

[0084] The voltage compensation factor VoltFactor is calculated using the following formula: (11);

[0085] Substituting formula (11) into formula (10) yields: (12);

[0086] Because of the low temperature environment, some of the charge cannot be released due to freezing. The SOC at room temperature discharges to the frozen SOC, and the SOC at low temperature is... The remaining usable energy SOE is 0 kWh. Through testing, the freezing conditions SOC_bottom at different temperatures are obtained as 100% - capacity retention rate, and the corresponding relationship table of "Temperature ~ Freezing SOC Table" is obtained.

[0087] ;

[0088] In low-temperature environments, due to battery polarization, some charge cannot be released, resulting in a frozen portion of the State of Charge (SOC). The frozen SOC is defined as soc_bottom. Figure 2 As shown, only the amount of electricity represented by ① in the diagram can be released. The remaining usable electricity at different temperatures is shown below:

[0089] (14).

[0090] This invention uses the battery temperature collected by the BMS to linearly interpolate the value from the "Temperature ~ Freeze-off SOC Table" to obtain the freeze-off SOC corresponding to the current temperature. Based on the current SOC, use linear interpolation from "SOC~VoltFactor" to obtain the VoltFactor corresponding to different SOCs. Then, freeze the SOC corresponding to the current temperature. Substituting VoltFactor and SOH into the formula, SOC can be converted to SOE. By using the OCV-SOC correspondence table and the temperature capacity retention rate correspondence table, the SOC of the battery's conventional parameters can be converted to SOE, simplifying the process and shortening the development cycle. The influence of temperature, SOC, and voltage on SOE is fully considered, accurately reflecting the battery's discharge capacity at different temperatures and SOCs. Furthermore, by separating the voltage compensation factor... This can effectively reflect the battery's discharge capacity within different discharge voltage ranges. The above embodiments only illustrate several implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. A method for estimating the remaining energy (SOE) of a battery, characterized in that, Includes the following steps: S1. Generate SOC-OCV curves based on the relationship between battery remaining capacity SOC and open circuit voltage OCV, and generate a table of temperature-capacity retention rate based on different temperatures; S2. Based on the SOC-OCV curve, obtain the voltage compensation factor VoltFactor and the rated voltage RatedVolt under different SOCs; The specific steps in step S2 of obtaining the voltage compensation factor VoltFactor and the rated voltage RatedVolt under different SOCs based on the SOC-OCV curve are as follows: Based on the SOC-OCV curve, the voltage compensation factor VoltFactor and the rated voltage RatedVolt at different SOCs are calculated using the following formulas: ； In the formula, BatNum represents the number of batteries; S3. Estimate the remaining energy SOE_nom of the battery at room temperature based on the voltage compensation factor VoltFactor, the rated voltage RatedVolt, and the nominal capacity Cap of the battery. Then, estimate the remaining energy SOE of the battery at different temperatures based on the SOC freezing condition SOC_bottom under low temperature conditions and the capacity retention rate in the temperature-capacity retention rate correspondence table for different temperatures. Wherein, the SOC freezing condition SOC_bottom = 100% - capacity retention rate.

2. The method for estimating the remaining energy (SOE) of a battery according to claim 1, characterized in that, In step S1, the step of generating the SOC-OCV curve based on the relationship between the remaining battery capacity (SOC) and the open-circuit voltage (OCV) is specifically as follows: a. Place the battery cells in a 25°C environment until the cell temperature reaches 25°C, and let them stand for 60 minutes; b. Charge the battery to the charging cutoff voltage at a current of 1 / 3C, and then charge the battery to the charging cutoff voltage at a current of 0.1C. c. After the temperature cools to 25℃, let it stand for 60 minutes, then discharge it with a current of 1 / 3C until... After letting it stand for 4 hours, record the current battery voltage as OCV and the current SOC. Repeat this step until the battery is discharged to its maximum capacity. Then stop, among which Indicates the discharge energy; d. Record the correspondence between SOC and OCV, and generate an SOC-OCV curve showing the correspondence between the remaining battery capacity SOC and the open circuit voltage OCV.

3. The method for estimating the remaining energy (SOE) of a battery according to claim 1, characterized in that, The specific steps in step S1 for generating the temperature-capacity retention rate correspondence table at different temperatures are as follows: Place the battery cells in a 25°C environment until the cell temperature reaches 25°C, and let them stand for 60 minutes. Charge the battery with a current of 1C to the charging cutoff voltage, and then charge the battery with a current of 0.1C to the charging cutoff voltage. After the cell temperature reaches 25℃, let it stand for 60 minutes. Discharge continuously with a current of 1 / 3C until the discharge cutoff voltage is reached, and the discharge energy is recorded. ; By adjusting the temperature, the discharge is continuously carried out at different temperatures until the discharge cutoff voltage is reached. The discharge energy at different temperatures is denoted as Q(T). Based on the capacity retention rate calculation formula, the capacity retention rate at different temperatures is obtained. The capacity retention rate calculation formula is as follows: ； A table of temperature-capacity retention rate (η) is generated based on the capacity retention rate at different temperatures.

4. The method for estimating the remaining energy (SOE) of a battery according to claim 1, characterized in that, The steps in S3, which involve estimating the remaining battery energy SOE_nom at room temperature based on the voltage compensation factor VoltFactor, rated voltage RatedVolt, and nominal battery capacity Cap, and then estimating the remaining battery energy SOE at different temperatures based on the SOC_bottom under low-temperature freezing conditions and the capacity retention rate in the temperature-capacity retention rate correspondence table, are as follows: S301. Calculate the battery's charging capacity cap, as follows: ； S302. The charging capacity cap is expressed using the remaining battery charge (SOC), the battery state of health (SOH), and the nominal capacity (Cap), as shown in the following formula: ； S303. Based on the voltage compensation factor VoltFactor and the rated voltage RatedVolt, the estimation formula for the remaining battery energy SOE_nom at room temperature can be expressed as follows: ； S304. Based on the SOC_bottom under low-temperature freezing conditions and the capacity retention rate in the table of temperature-capacity retention rate correspondence at different temperatures, the remaining energy SOE of the battery at different temperatures is estimated as follows: ； Wherein, the SOC freezing condition is SOC_bottom = 100% - capacity retention rate. To check based on the current SOC The linear interpolation in the correspondence table yields different SOCs. ; Freezing conditions corresponding to the current temperature The corresponding VoltFactor.

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