CN107957560A - A kind of lithium ion battery SOC algorithm for estimating based on equivalent circuit - Google Patents

Abstract

The present invention provides a kind of lithium ion battery SOC algorithm for estimating based on equivalent circuit, including step:S1, at different temperature, obtains open-circuit voltage U_OCVWith the relation of SOC and temperature T, S2, establish equivalent-circuit model, obtains model parameter and the relation of SOC and temperature T, and S3, calculate SOC value under Current Temperatures T and time t, including simplifies voltage characteristic equation, and voltage characteristic equation is solved.The SOC methods of estimation of lithium ion battery provided by the invention, principle is simple, and estimated accuracy is high, is no more than 1% to the SOC estimated accuracies maximum deviation of lithium ion battery.

Description

An Algorithm for SOC Estimation of Li-ion Battery Based on Equivalent Circuit

technical field

The invention belongs to the detection field, and in particular relates to a method for estimating the state of charge of a lithium ion battery.

Background technique

In recent years, the number of automobiles in the world has risen sharply, the demand for energy is also increasing, and the pollution to the environment is also becoming more and more serious. New energy vehicles, especially electric vehicles, have become the development direction of future vehicles, but their development speed is still restricted by power batteries and their application technologies. How to prolong the service life of the battery and improve the energy efficiency and reliability of the battery is a problem that must be solved in the industrialization of electric vehicles. Therefore, it is of great significance to study battery management technology.

The state of charge of the power battery is referred to as SOC. The remaining power of a lithium-ion battery is one of the most important performance parameters during the operation of the battery, and the estimation of the remaining power is a link that cannot be ignored. For electric vehicles, accurately estimating the SOC of the battery can not only improve battery life, but also extend battery life and improve safety.

Contents of the invention

Aiming at the deficiencies in the art, the invention discloses a lithium-ion battery SOC estimation algorithm based on an equivalent circuit to accurately estimate the SOC of the battery.

Realize above-mentioned object technical scheme of the present invention is:

A kind of lithium-ion battery SOC estimation algorithm based on equivalent circuit, comprises steps:

S1. Obtain the relationship between open circuit voltage U _OCV , SOC and temperature T at different temperatures,

S2. Establish an equivalent circuit model to obtain the relationship between the model parameters and the SOC and temperature T. This step is specifically as follows

S21, establish a third-order equivalent circuit model, the equivalent circuit includes a series-connected ohmic resistor _R0 and three RC units, each RC unit is composed of parallel resistors and capacitors; determine the equivalent circuit terminal voltage U and open circuit The characteristic relationship of the voltage U _OCV ;

S22. Obtain the relationship between the ohmic internal resistance R ₀ , the SOC, and the temperature T in the equivalent circuit model: determine the voltage characteristic at the moment when the pulse discharge ends.

S222. Obtain the relationship between the ohmic internal resistance R ₀ and the SOC at the temperature T

S223. Obtain the relationship between ohmic internal resistance R ₀ and SOC at other temperatures

S23. Obtain the relationship between the RC unit parameters R ₁ , C ₁ , R ₂ , C ₂ , R ₃ , and C ₃ in the equivalent circuit model and the SOC and temperature T;

S231. Measuring the voltage U(t) of the equivalent circuit immediately after the end of the pulse discharge;

S232. Obtain the relationship between the RC unit parameters R ₁ , C ₁ , R ₂ , C ₂ , R ₃ , and C ₃ and the SOC at the same temperature.

S233. Obtain the relationship between the parameters R1, C1, R2, C2, R3, C3 and the SOC of the parallel RC units at other temperatures.

S3. Estimating the SOC value at the current temperature T and the battery running time t, including S31, simplifying the voltage characteristic equation, and S32, solving the voltage characteristic equation.

Wherein, in step S1, the relationship between the open circuit voltage U _OCV and SOC at a series of temperatures T is obtained, the temperature range of T is -10-50°C, and the SOC is at least 9 values within the range of 0.1-0.9.

Further, the relationship between open circuit voltage UOCV and SOC at temperature T is expressed by a fifth-order polynomial:

U _OCV ＝a ₀ +a ₁ SOC+a ₂ SOC ² +a ₃ SOC ³ +a ₄ SOC ⁴ +a ₅ SOC ⁵

Among them, Uocv represents the open circuit voltage of the battery, a0-a5 are polynomial coefficients and are constants, and SOC is the state of charge of the battery.

Optionally, a set of relationship between U _OCV and SOC is obtained every 4-8°C when T is lower than 10°C, and a set of relationship between U _OCV and SOC is obtained every 8-12°C when T is above 10°C.

Wherein, the step S21 is:

For the third-order equivalent circuit model, the characteristic equation of the battery model is established:

Wherein, U ₀ is the voltage at both ends of the ohmic internal resistance R ₀ , U ₁ to U ₃ are the voltages at both ends of the three RC units, and I is the current;

Solving equation (1), the expression of the equivalent circuit terminal voltage can be obtained as:

Wherein, U ₁ (0), U ₂ (0) and U ₃ (0) are the initial voltage values at both ends of the three RC units when the pulse discharge (HPPC) timing starts, respectively.

In step S22, pulse discharge (HPPC) is an existing test method, and pulse discharge time, current, etc. are all existing specifications (for example, according to the Freedom battery test manual).

According to the structure in Fig. 2, it can be seen that at the end of the pulse discharge, the voltage change is entirely caused by the ohmic internal resistance R ₀ . Therefore, the ohmic internal resistance R0 is obtained by the following formula _:

In the formula, U _L is the voltage mutation at the end of the pulse discharge, and I is the pulse discharge current value.

Wherein, the step S22 is:

According to the voltage response curve obtained from the HPPC experiment of the battery at different SOCs at temperature T, the ohmic internal resistance R ₀ and R ₀ -SOC curves at different SOCs are calculated by using formula (4). The SOC value is at least 9 values within the range of 0.1-0.9. The R ₀ -SOC curve at this temperature is subjected to polynomial fitting, and the polynomial fitting formula is:

R ₀ ＝b ₀ +b ₁ SOC+b ₂ SOC ² +b ₃ SOC ³ +b ₄ SOC ⁴ +b ₅ SOC ⁵

Where R ₀ represents ohmic internal resistance, b ₀ to b ₅ are polynomial coefficients and are constants, and SOC is the state of charge of the battery.

At the moment when the pulse discharge ends, the current is zero, and the circuit structure shown in Figure 2 responds to zero input, and its voltage characteristic equation is:

Further, the step S231 is specifically:

It can be known from the circuit structure in Figure 2 that the voltage across the ohmic internal resistance becomes zero immediately after the pulse discharge ends, but the voltage across the three RC units does not become zero. So formula (3) becomes:

In principle, using the nonlinear fitting tool of mathematical software, the voltage response curve can be fitted directly according to formula (4), and the parameter values of the three RC units can be obtained. However, since there is an exponential function in formula (4), and the value of the capacitance in the structure in Figure 2 varies from tens to hundreds of kF, it is difficult to control the fitting process by using formula (5) for direct fitting. At the same time, since the fitting parameters are in the denominator position, truncation errors will be introduced for each iteration. The obtained results are less stable. Therefore, formula (5) can be written as:

Wherein, c ₁ -c ₃ and d ₁ -d ₃ are constants related to the parameters of the RC unit.

Wherein, in the step S231, the voltage characteristic equation after the end of the pulse discharge moment is determined as

Among them, t _s is the resting time after the pulse discharge, and c ₁ ~ c ₃ and d ₁ ~ d ₃ are constants related to the parameters of the RC unit.

The HPPC experiments consisted of pulse-discharging the battery followed by resting. The timing starting point of t _s is when the pulse ends, that is, the time after the pulse discharge ends.

Wherein, step S232 is:

According to the voltage response curves of the battery under different SOC after the pulse discharge of the HPPC experiment at temperature T, the values of c ₁ ~ c ₃ and d ₁ ~ d ₃ under different SOCs can be obtained by nonlinear fitting using formula (6) . The SOC value is at least 9 values in the range of 0.1 to 0.9, and then calculated according to the following formula to obtain the RC unit parameter values under different SOCs:

According to the Ri and Ci values obtained under different SOC, perform cubic spline interpolation on the parameter tables of R ₁ -SOC, R ₂ -SOC, R ₃ -SOC, C ₁ -SOC, C ₂ -SOC and C ₃ -SOC , to obtain the encrypted parameter tables of R ₁ -SOC, R ₂ -SOC, R ₃ -SOC, C ₁ -SOC, C ₂ -SOC and C ₃ -SOC.

Wherein, the step S233 specifically includes changing the temperature T, repeating S232, and obtaining encrypted R ₁ -SOC, R ₂ -SOC, R ₃ -SOC, C ₁ -SOC, C ₂ -SOC and C ₃ at other temperatures _- SOC parameter table, establish a two-dimensional parameter network of R ₁ , R ₂ , R ₃ , C ₁ , C ₂ and C ₃ with SOC and temperature

Further, in step S32, when calculating the SOC value under the current temperature T and time t, the non-linear equation solving tool of the mathematical software is not directly used to solve the highly nonlinear equation obtained by the equivalent circuit model, but the method of writing a program is used to solve it, include:

i) Set the initial value of SOC to 0.9, and calculate the terminal voltage value U of the battery;

ii) Calculate the relative deviation between the battery terminal voltage value U* and U at the current t

Δ=|U-U*|/U;

iii) If Δ≥0.001, decrease the SOC value by 0.001, and repeat i)~ii); if Δ<0.001, output the SOC value, which is the SOC value under the current temperature T and time t.

Since the values of formula (2) U _ocv , R ₀ , R ₁ , R ₂ , R ₃ , C ₁ , C ₂ and C ₃ at different SOCs and temperatures T have been obtained, step S31 is:

The expression for the terminal voltage of the equivalent circuit is written as:

For the current temperature T and time t, U(t), U ₁ (0), U ₂ (0), U ₃ (0) and I in formula (8) are all known quantities, and U _ocv , R ₀ , R ₁ , R ₂ , R ₃ , C ₁ , C ₂ and C ₃ are only related to SOC, then formula (8) can be written as

Solving formula (9), the SOC value at the current temperature T and time t can be obtained.

The beneficial effects of the present invention are:

The invention provides a method for estimating the SOC of a lithium ion battery. The principle of this method is simple and the estimation accuracy is high. Specifically include:

1. The SOC estimating method provided by the present invention has a maximum deviation of SOC estimating accuracy of lithium-ion batteries not exceeding 1%.

2. The SOC estimation method provided by the present invention changes the form of the fitting parameters when performing nonlinear fitting to the RC unit parameters of the equivalent circuit model, and can effectively improve the stability and speed of the fitting.

3. The SOC estimation method provided by the present invention does not adopt the polynomial fitting method when obtaining the relationship between the RC unit parameters and the SOC of the equivalent circuit model, but adopts the cubic spline interpolation technique to set up the parameter table, which can effectively avoid the polynomial fitting band coming deviation.

4. The SOC estimation method provided by the present invention does not directly solve the nonlinear equation when solving the voltage characteristic equation of the equivalent circuit, but uses the method of writing a program to solve it, which effectively improves the solution accuracy and reduces the solution time.

Description of drawings

Fig. 1 is the flowchart of the estimation method of battery SOC based on equivalent circuit of the present invention;

Fig. 2 is the circuit structure of equivalent circuit;

Figure 3 is a flow chart for solving formula (9) by writing a program.

Figure 4 shows the relationship between the fitted open circuit voltage and SOC.

Figure 5 shows the relationship between the fitted ohmic internal resistance and SOC.

Figure 6 to Figure 11 are the parameter tables of R1-SOC, R2-SOC, R3-SOC, C1-SOC, C2-SOC and C3-SOC respectively.

Figure 12 is a comparison of the obtained SOC estimated value and the experimental value,

Figure 13 The deviation of the estimated results.

Detailed ways

The present invention is illustrated below through the preferred embodiments. It should be understood by those skilled in the art that the examples are only used to illustrate the present invention and not to limit the scope of the present invention.

In the examples, unless otherwise specified, the means used are conventional means in the art.

Example 1

In this embodiment, a battery whose cathode material is a ternary material is used as an example, and the SOC is estimated by using the following estimation method.

The specific process includes the following steps:

S1. Obtain the relationship between the open circuit voltage U _OCV and the SOC and temperature T

According to the open circuit voltage U _ocv of the battery at different SOCs obtained by constant current discharge at a temperature of 25° C., the SOC values are at least 9 values within the range of 0.1-0.9. A polynomial fit was performed on the U _ocv -SOC curve at 25 °C.

The polynomial fitting formula is:

U _OCV ＝a ₀ +a ₁ SOC+a ₂ SOC ² +a ₃ SOC ³ +a ₄ SOC ⁴ +a ₅ SOC ⁵

Among them, U _ocv represents the open circuit voltage of the battery, a ₀ to a ₅ are polynomial coefficients and are constants, and SOC is the state of charge of the battery.

Figure 4 is the fitting result, the relationship between the obtained open circuit voltage and SOC is:

U _OCV ＝3.3233+0.02455SOC-8.9131×10 ^-4 SOC ²

+1.6196×10 ^-5 SOC ³ -1.2246×10 ^-7 SOC ⁴ +3.3391×10 ^-10 SOC ⁵

S2. Establish an equivalent circuit model to obtain the relationship between the model parameters and the SOC and temperature T. This step includes the following sub-steps:

S21. Establish a third-order equivalent circuit model to clarify the characteristic relationship between the battery terminal voltage U and the open circuit voltage U _OCV .

According to the circuit diagram shown in Figure 2, the characteristic equation of the battery model is established:

U ₀ =IR ₀

U＝U _ocv -U ₀ -U ₁ -U ₂ -U ₃

Wherein, U ₀ is the voltage across the ohmic internal resistance R ₀ , U ₁ to U ₃ are the voltages across the three RC units, and I is the current.

Solving equation (1), the expression of terminal voltage can be obtained as:

Wherein, U ₁ (0), U ₂ (0) and U ₃ (0) are the initial values of the voltages at both ends of the three RC units when the timing starts, respectively.

S22. Obtain the relationship between the ohmic internal resistance R ₀ , the SOC, and the temperature T in the equivalent circuit model.

S221. Determine the voltage characteristic at the moment when the pulse discharge ends.

At the moment when the pulse discharge ends, the current is zero, and the circuit structure shown in Figure 2 responds to zero input, and its voltage characteristic equation is:

According to the structure in Fig. 2, it can be seen that at the end of the pulse discharge, the voltage change is entirely caused by the ohmic internal resistance R ₀ . Therefore, the ohmic internal resistance R0 is obtained by the following formula _:

Among them, U _L is the voltage mutation at the end of the pulse discharge, and I is the pulse discharge current value.

S222. Obtain the relationship between ohmic internal resistance R ₀ and SOC at the same temperature

According to the voltage response curve obtained from the HPPC experiment of the battery at different SOCs at a temperature of 25°C, the ohmic internal resistance R ₀ and R ₀ -SOC curves at different SOCs were calculated using the method described in S221. The SOC values are 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 and 0.9. The following polynomial fitting is performed on the R ₀ -SOC curve at 25°C:

R ₀ ＝b ₀ +b ₁ SOC+b ₂ SOC ² +b ₃ SOC ³ +b ₄ SOC ⁴ +b ₅ SOC ⁵

Where R ₀ represents ohmic internal resistance, b ₀ to b ₅ are polynomial coefficients and are constants, and SOC is the state of charge of the battery.

Figure 5 is the fitting result, the obtained relationship between ohmic internal resistance and SOC is:

R ₀ =2.5800-0.03058SOC-4.5770×10 ^-4 SOC ²

+1.6125×10 ^-6 SOC ³ -8.6662×10 ^-8 SOC ⁴ +5.0321×10 ^-10 SOC ⁵

S23. Obtain the relationship between the parameters R ₁ , C ₁ , R ₂ , C ₂ , R ₃ , and C ₃ of the parallel RC unit in the equivalent circuit model, and the SOC and temperature T. Contains the following sub-steps:

S231. Determine the voltage characteristic immediately after the end of the pulse discharge.

It can be known from the circuit structure in Figure 2 that the voltage across the ohmic internal resistance becomes zero immediately after the pulse discharge ends, but the voltage across the three RC units does not become zero. So formula (3) becomes:

In principle, using the nonlinear fitting tool of mathematical software, the voltage response curve can be fitted directly according to formula (4), and the parameter values of the three RC units can be obtained. However, since there is an exponential function in formula (4), and the values of the capacitors in the structure in Figure 2 range from tens to hundreds of kF, and because the fitting parameters are in the denominator position, each iterative operation will introduce a truncation error . Therefore, it is difficult to control the fitting process by using formula (5) for direct fitting, and the stability of the obtained results is poor. So, write formula (5) as:

Wherein, c ₁ -c ₃ and d ₁ -d ₃ are constants related to the parameters of the RC unit.

S232. Obtain the relationship between the parameters R ₁ , C ₁ , R ₂ , C ₂ , R ₃ , and C ₃ of the parallel RC units at the same temperature and the SOC.

According to the voltage response curves of the battery at 25°C, after charging and discharging in the HPPC experiment at different SOCs, c ₁ ~ c ₃ and d ₁ ~ d ₃ at different SOCs are obtained through nonlinear fitting based on formula (6) value.

The SOC values are 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 and 0.9. Then calculate the parameter values of the RC unit under different SOCs according to the following formula. Said expression is:

According to the values of R ₁ ~R ₃ and C ₁ ~C ₃ under different SOC obtained in the steps above, for R ₁ -SOC, R ₂ -SOC, R ₃ -SOC, C ₁ -SOC, C ₂ -SOC and C _{3 -} Perform cubic spline interpolation on the parameter table of the SOC to obtain encrypted parameter tables of R ₁ -SOC, R ₂ -SOC, R ₃ -SOC, C ₁ -SOC, C ₂ -SOC and C _3- SOC.

The results of the parameters are shown in Figures 6-11.

S3. Estimate the SOC value at the current temperature T and time t

This step includes the following sub-steps:

S31. Simplify the voltage characteristic equation

Since the values of formula (2) U _ocv , R ₀ , R ₁ , R ₂ , R ₃ , C ₁ , C ₂ and C ₃ at different SOC and temperature T have been obtained, formula (2) can be rewritten as :

For the current temperature T and time t, U(t), U ₁ (0), U ₂ (0), U ₃ (0) and I in formula (8) are all known quantities, and U _ocv , R ₀ , R ₁ , R ₂ , R ₃ , C ₁ , C ₂ and C ₃ are only related to SOC, then formula (8) can be written as

Solve equation (9), and then the SOC value at the current temperature T and battery running time t can be obtained.

S32, solving the voltage characteristic equation

Equation (9) is a highly nonlinear equation, which can be solved directly by the nonlinear equation solving tool of mathematical software, which cannot obtain stable solution results and takes a long time to solve. Considering that the SOC value itself has upper and lower limits, formula (9) is solved by writing a program. The specific process is shown in Figure 3.

i) Set the initial value of SOC to 0.9, and calculate the terminal voltage value U of the battery according to formula (9);

ii) The relative deviation between the battery terminal voltage value U* and U at the current t

Δ=|U-U*|/U;

iii) If Δ≥0.001. Then reduce the SOC value by 0.001, and repeat i) to ii). If Δ<0.001, then output this SOC value, which is the SOC value under the current temperature T and time t.

The specific programming example is as follows (only the program for solving nonlinear equations is listed, and the program for the relationship between each parameter in the formula and SOC is not listed):

This embodiment describes in detail the whole process of the method from parameter acquisition to SOC estimation. In practical applications, for the same battery, all parameter acquisition processes, namely S1 and S2 and the expression simplification process S31 of the estimation process, only need to be executed once to obtain corresponding parameter values. When performing SOC estimation, only step S32 needs to be specifically executed.

Implementation Effect:

The comparison of the obtained SOC estimated value and the experimental value is shown in Figure 12. From the figure, it can be seen that the experimental test (experiment) and the predicted result (prediction) basically coincide completely, and the deviation is shown in Figure 13. The maximum deviation, both positive and negative, is about 0.6%.

Example 2

Adopt the same method as in Example 1, set the temperature at other values, obtain the relationship between a set of U _OCV and SOC every 5°C when T is lower than 10°C, and obtain a set of U _OCV every 10°C when T is above 10°C Relationship with SOC.

The obtained SOC estimation value is compared with the experimental value, and its maximum deviation does not exceed 1%.

The above embodiments are only descriptions of preferred implementations of the present invention, and are not intended to limit the scope of the present invention. On the premise of not departing from the design spirit of the present invention, various technical solutions of the present invention can be made by ordinary engineers and technicians in the field. Variations and improvements should fall within the scope of protection defined by the claims of the present invention.

Claims (10)

1. a lithium-ion battery SOC estimation algorithm based on equivalent circuit, is characterized in that, comprises steps: S1. Obtain the relationship between open circuit voltage U _OCV , SOC and temperature T at different temperatures, S2. Establish an equivalent circuit model to obtain the relationship between model parameters, SOC and temperature T. This step is specifically as follows S21, establish a third-order equivalent circuit model, the equivalent circuit includes a series ohmic resistor _R0 and three RC units, each RC unit is made up of parallel resistors and capacitors, determine the equivalent circuit terminal voltage U and open circuit The characteristic relationship of the voltage U _OCV ; S22. Obtain the relationship between the ohmic internal resistance R ₀ and the SOC and temperature T in the equivalent circuit model: determine the voltage characteristic at the moment the pulse discharge ends, and obtain the relationship between the ohmic internal resistance R ₀ and the SOC at the temperature T; S23. Obtain the relationship between the RC unit parameters R ₁ , C ₁ , R ₂ , C ₂ , R ₃ , and C ₃ in the equivalent circuit model and the SOC and temperature T; S231. Measuring the voltage U(ts) of the equivalent circuit immediately after the end of the pulse discharge; S232. Obtain the relationship between RC unit parameters R ₁ , C ₁ , R ₂ , C ₂ , R ₃ , C ₃ and SOC at the same temperature; S3. Calculating the SOC value at the current temperature T and the operating time t of the battery, including simplifying the voltage characteristic equation and solving the voltage characteristic equation. 2. The lithium-ion battery SOC estimation algorithm according to claim 1, characterized in that in step S1, the relationship between the open circuit voltage U _OCV and SOC at a series of temperatures T is obtained, and the temperature range of T is -10 to 50°C, The SOC is at least 9 values within the range of 0.1 to 0.9. 3. lithium-ion battery SOC estimation algorithm according to claim 2, is characterized in that, the relation of open circuit voltage UOCV and SOC under the temperature T is expressed with fifth-order polynomial: U _OCV ＝a ₀ +a ₁ SOC+a ₂ SOC ² +a ₃ SOC ³ +a ₄ SOC ⁴ +a ₅ SOC ⁵ Among them, Uocv represents the open circuit voltage of the battery, a0-a5 are polynomial coefficients and are constants, and SOC is the state of charge of the battery. 4. lithium-ion battery SOC estimation algorithm according to claim 1, is characterized in that, described step S21 is: For the third-order equivalent circuit model, the characteristic equation of the battery model is established: <mrow><mtable><mtr><mtd><mrow><msub><mi>C</mi><mn>1</mn></msub><mfrac><mrow><msub><mi>dU</mi><mn>1</mn></msub></mrow><mrow><mi>d</mi><mi>t</mi></mrow></mfrac><mo>+</mo><mfrac><msub><mi>U</mi><mn>1</mn></msub><msub><mi>R</mi><mn>1</mn></msub></mfrac><mo>=</mo><mi>I</mi></mrow></mtd></mtr><mtr><mtd><mrow><msub><mi>C</mi><mn>2</mn></msub><mfrac><mrow><msub><mi>dU</mi><mn>2</mn></msub></msub>mrow><mrow><mi>d</mi><mi>t</mi></mrow></mfrac><mo>+</mo><mfrac><msub><mi>U</mi><mn>2</mn></msub><msub><mi>R</mi><mn>2</mn></msub></mfrac><mo>=</mo><mi>I</mi></mrow></mtd></mtr><mtr><mtd><mrow><msub><mi>C</mi><mn>3</mn></msub><mfrac><mrow><msub><mi>dU</mi><mn>3</mn></msub></mrow><mrow><mi>d</mi><mi>t</mi></mrow></mfrac><mo>+</mo><mfrac><msub><mi>U</mi><mn>3</mn></msub><msub><mi>R</mi><mn>3</mn></msub></mfrac><mo>=</mo><mi>I</mi></mrow></mtd></mtr><mtr><mtd><mrow><msub><mi>U</mi><mn>0</mn></msub><mo>=</mo><msub><mi>IR</mi><mn>0</mn></msub></mrow></mtd></mtr><mtr><mtd><mrow><mi>U</mi><mo>=</mo><msub><mi>U</mi><mrow><mi>o</mi><mi>c</mi><mi>v</mi></mrow></msub><mo>-</mo><msub><mi>U</mi><mn>0</mn></msub><mo>-</mo><msub><mi>U</mi><mn>1</mn></msub><mo>-</mo><msub><mi>U</mi><mn>2</mn></msub><mo>-</mo><msub><mi>U</mi><mn>3</mn></msub></mrow></mtd></mtr></mtable><mo>-</mo><mo>-</mo><mo>-</mo><mrow><mo>(</mo><mn>1</mn><mo>)</mo></mrow></mrow> Wherein, U ₀ is the voltage at both ends of the ohmic internal resistance R ₀ , U ₁ to U ₃ are the voltages at both ends of the three RC units, and I is the current; Solving equation (1), the expression of the equivalent circuit terminal voltage can be obtained as: <mrow><mi>U</mi><mrow><mo>(</mo><mi>t</mi><mo>)</mo></mrow><mo>=</mo><msub><mi>U</mi><mrow><mi>o</mi><mi>c</mi><mi>v</mi></mrow></msub><mo>-</mo><msub><mi>IR</mi><mn>0</mn></msub><mo>-</mo><msub><mi>U</mi><mn>1</mn></msub><mrow><mo>(</mo><mn>0</mn><mo>)</mo></mrow><msup><mi>e</mi><mrow><mo>-</mo><mfrac><mi>t</mi><mrow><msub><mi>R</mi><mn>1</mn></msub><msub><mi>C</mi><mn>1</mn></msub></mrow></mfrac></mrow></msup><mo>-</mo><msub><mi>U</mi><mn>2</mn></msub><mrow><mo>(</mo><mn>0</mn><mo>)</mo></mrow><msup><mi>e</mi><mrow><mo>-</mo><mfrac><mi>t</mi><mrow><msub><mi>R</mi><mn>2</mn></msub><msub><mi>C</mi><mn>2</mn></msub></mrow></mfrac></mrow></msup><mo>-</mo><msub><mi>U</mi><mn>3</mn></msub><mrow><mo>(</mo><mn>0</mn><mo>)</mo></mrow><msup><mi>e</mi><mrow><mo>-</mo><mfrac><mi>t</mi><mrow><msub><mi>R</mi><mn>3</mn></msub><msub><mi>C</mi><mn>3</mn></msub></mrow></mfrac></mrow></msup><mo>-</mo><msub><mi>IR</mi><mn>1</mn></msub><mrow><mo>(</mo><mn>1</mn><mo>-</mo><msup><mi>e</mi><mrow><mo>-</mo><mfrac><mi>t</mi><mrow><msub><mi>R</mi><mn>1</mn></msub><msub><mi>C</mi><mn>1</mn></msub></mrow></mfrac></mrow></msup><mo>)</mo></mrow><mo>-</mo><msub><mi>IR</mi><mn>2</mn></msub><mrow><mo>(</mo><mn>1</mn><mo>-</mo><msup><mi>e</mi><mrow><mo>-</mo><mfrac><mi>t</mi><mrow><msub><mi>R</mi><mn>2</mn></msub><msub><mi>C</mi><mn>2</mn></msub></mrow></mfrac></mrow></msup><mo>)</mo></mrow><mo>-</mo><msub><mi>IR</mi><mn>3</mn></msub><mrow><mo>(</mo><mn>1</mn><mo>-</mo><msup><mi>e</mi><mrow><mo>-</mo><mfrac><mi>t</mi><mrow><msub><mi>R</mi><mn>3</mn></msub><msub><mi>C</mi><mn>3</mn></msub></mrow></mfrac></mrow></msup><mo>)</mo></mrow><mo>-</mo><mo>-</mo><mo>-</mo><mrow><mo>(</mo><mn>2</mn><mo>)</mo></mrow></mrow> Wherein, U ₁ (0), U ₂ (0) and U ₃ (0) are the initial voltage values at both ends of the three RC units when the pulse discharge timing starts, respectively. 5. lithium-ion battery SOC estimation algorithm according to claim 1, is characterized in that, described step S22 is: According to the voltage response curve obtained from the HPPC experiment of the battery under different SOC at temperature T, the formula Among them, U _L is the voltage mutation at the end of the pulse discharge, I is the pulse discharge current value, The ohmic internal resistance R ₀ and R ₀ -SOC curves under different SOC are calculated. The SOC value is at least 9 values within the range of 0.1-0.9. The R ₀ -SOC curve at this temperature is subjected to polynomial fitting, and the polynomial fitting formula is: R ₀ ＝b ₀ +b ₁ SOC+b ₂ SOC ² +b ₃ SOC ³ +b ₄ SOC ⁴ +b ₅ SOC ⁵ Where R ₀ represents ohmic internal resistance, b ₀ to b ₅ are polynomial coefficients and are constants, and SOC is the state of charge of the battery. 6. Lithium-ion battery SOC estimation algorithm according to claim 1, is characterized in that, in step S231, the voltage characteristic equation after the end moment of pulse discharge is determined as <mrow><mi>U</mi><mrow><mo>(</mo><mi>t</mi><mi>s</mi><mo>)</mo></mrow><mo>=</mo><msub><mi>U</mi><mrow><mi>o</mi><mi>c</mi><mi>v</mi></mrow></msub><mo>-</mo><msub><mi>c</mi><mn>1</mn></msub><msup><mi>e</mi><mrow><mo>-</mo><msub><mi>d</mi><mn>1</mn></msub><msub><mi>t</mi><mi>s</mi></msub></mrow></msup><mo>-</mo><msub><mi>c</mi><mn>2</mn></msub><msup><mi>e</mi><mrow><mo>-</mo><msub><mi>d</mi><mn>2</mn></msub><msub><mi>t</mi><mi>s</mi></msub></mrow></msup><mo>-</mo><msub><mi>c</mi><mn>3</mn></msub><msup><mi>e</mi><mrow><mo>-</mo><msub><mi>d</mi><mn>3</mn></msub><msub><mi>t</mi><mi>s</mi></msub></mrow></msup><mo>-</mo><mo>-</mo><mo>-</mo><mrow><mo>(</mo><mn>6</mn><mo>)</mo></mrow></mrow> Among them, t _s is the resting time after the discharge of the pulse, and c ₁ ~ c ₃ and d ₁ ~ d ₃ are constants related to the parameters of the RC unit. 7. The lithium-ion battery SOC estimation algorithm according to claim 6, wherein step S232 is: According to the voltage response curves of the battery under different SOCs after the pulse discharge of the HPPC experiment at temperature T, the values of c ₁ ~ c ₃ and d ₁ ~ d ₃ under different SOCs can be obtained by nonlinear fitting using formula (6) , the SOC value is at least 9 values in the range of 0.1 to 0.9, and then the RC unit parameter values under different SOCs are calculated according to the following formula: <mrow><mtable><mtr><mtd><mrow><msub><mi>R</mi><mi>i</mi></msub><mo>=</mo><mfrac><msub><mi>c</mi><mi>i</mi></msub><mi>I</mi></mfrac><mo>,</mo><mi>i</mi><mo>=</mo><mn>1</mn><mo>,</mo><mn>2</mn><mo>,</mo><mn>3</mn></mrow></mtd></mtr><mtr><mtd><mrow><msub><mi>C</mi><mi>i</mi></msub><mo>=</mo><mfrac><mi>I</mi><mrow><msub><mi>c</mi><mi>i</mi></msub><msub><mi>d</mi><mi>i</mi></msub></mrow></mfrac><mo>,</mo><mi>i</mi><mo>=</mo><mn>1</mn><mo>,</mo><mn>2</mn><mo>,</mo><mn>3</mn></mrow></mtd></mtr></mtable><mo>-</mo><mo>-</mo><mo>-</mo><mrow><mo>(</mo><mn>7</mn><mo>)</mo></mrow></mrow> According to the obtained R _i and C _i values under different SOCs, the parameter tables of R ₁ -SOC, R ₂ -SOC, R ₃ -SOC, C ₁ -SOC, C ₂ -SOC and C ₃ -SOC were sampled three times. bar interpolation to obtain encrypted R ₁ -SOC, R ₂ -SOC, R ₃ -SOC, C ₁ -SOC, C ₂ -SOC and C ₃ -SOC parameter tables. 8. lithium ion battery SOC estimation algorithm according to claim 1, is characterized in that, The step S233 specifically includes changing the temperature T and repeating S232 to obtain encrypted R ₁ -SOC, R ₂ -SOC, R ₃ -SOC, C ₁ -SOC, C ₂ -SOC and C ₃ -SOC at other temperatures The parameter table of R ₁ , R ₂ , R ₃ , C ₁ , C ₂ and C ₃ is established as a two-dimensional parameter network with SOC and temperature. 9. The lithium-ion battery SOC estimation algorithm according to claim 1, wherein, in step S32, when calculating the SOC value under the current temperature T and time t, the method of writing a program is used to solve the problem, including: i) Set the initial value of SOC to 0.9, and calculate the terminal voltage value U of the battery; ii) Calculate the relative deviation between the battery terminal voltage value U* and U at the current t Δ=|U-U*|/U; iii) If Δ≥0.001, decrease the SOC value by 0.001, and repeat i)~ii); if Δ<0.001, output the SOC value, which is the SOC value under the current temperature T and time t. 10. lithium-ion battery SOC estimation algorithm according to claim 4, is characterized in that, in step S31, the expression of equivalent circuit terminal voltage is written as: <mrow><mtable><mtr><mtd><mrow><mi>U</mi><mrow><mo>(</mo><mi>t</mi><mo>)</mo></mrow><mo>=</mo><msub><mi>U</mi><mrow><mi>o</mi><mi>c</mi><mi>v</mi></mrow></msub><mrow><mo>(</mo><mi>T</mi><mo>,</mo><mi>S</mi><mi>O</mi><mi>C</mi><mo>)</mo></mrow><mo>-</mo><msub><mi>IR</mi><mn>0</mn></msub><mrow><mo>(</mo><mi>T</mi><mo>,</mo><mi>S</mi><mi>O</mi><mi>C</mi><mo>)</mo></mrow><mo>-</mo><msub><mi>U</mi><mn>1</mn></msub><mrow><mo>(</mo><mn>0</mn><mo>)</mo></mrow><msup><mi>e</mi><mrow><mo>-</mo><mfrac><mi>t</mi><mrow><msub><mi>R</mi><mn>1</mn></msub><mrow><mo>(</mo><mi>T</mi><mo>,</mo><mi>S</mi><mi>O</mi><mi>C</mi><mo>)</mo></mrow><msub><mi>C</mi><mn>1</mn></msub><mrow><mo>(</mo><mi>T</mi><mo>,</mo><mi>S</mi><mi>O</mi><mi>C</mi><mo>)</mo></mrow></mrow></mfrac></mrow></msup></mrow></mtd></mtr><mtr><mtd><mrow><mo>-</mo><msub><mi>U</mi><mn>2</mn></msub><mrow><mo>(</mo><mn>0</mn><mo>)</mo></mrow><msup><mi>e</mi><mrow><mo>-</mo><mfrac><mi>t</mi><mrow><msub><mi>R</mi><mn>2</mn></msub><mrow><mo>(</mo><mi>T</mi><mo>,</mo><mi>S</mi><mi>O</mi><mi>C</mi><mo>)</mo></mrow><msub><mi>C</mi><mn>2</mn></msub><mrow><mo>(</mo><mi>T</mi><mo>,</mo><mi>S</mi><mi>O</mi><mi>C</mi><mo>)</mo></mrow></mrow></mfrac></mrow></msup><mo>-</mo><msub><mi>U</mi><mn>3</mn></msub><mrow><mo>(</mo><mn>0</mn><mo>)</mo></mrow><msup><mi>e</mi><mrow><mo>-</mo><mfrac><mi>t</mi><mrow><msub><mi>R</mi><mn>3</mn></msub><mrow><mo>(</mo><mi>T</mi><mo>,</mo><mi>S</mi><mi>O</mi><mi>C</mi><mo>)</mo></mrow><msub><mi>C</mi><mn>3</mn></msub><mrow><mo>(</mo><mi>T</mi><mo>,</mo><mi>S</mi><mi>O</mi><mi>C</mi><mo>)</mo></mrow></mrow></mfrac></mrow></msup><mo>-</mo><msub><mi>IR</mi><mn>1</mn></msub><mrow><mo>(</mo><mi>T</mi><mo>,</mo><mi>S</mi><mi>O</mi><mi>C</mi><mo>)</mo></mrow><mrow><mo>(</mo><mn>1</mn><mo>-</mo><msup><mi>e</mi><mrow><mo>-</mo><mfrac><mi>t</mi><mrow><msub><mi>R</mi><mn>1</mn></msub><mrow><mo>(</mo><mi>T</mi><mo>,</mo><mi>S</mi><mi>O</mi><mi>C</mi><mo>)</mo></mrow><msub><mi>C</mi><mn>1</mn></msub><mrow><mo>(</mo><mi>T</mi><mo>,</mo><mi>S</mi><mi>O</mi><mi>C</mi><mo>)</mo></mrow></mrow></mfrac></mrow></msup><mo>)</mo></mrow></mrow></mtd></mtr><mtr><mtd><mrow><mo>-</mo><msub><mi>IR</mi><mn>2</mn></msub><mrow><mo>(</mo><mi>T</mi><mo>,</mo><mi>S</mi><mi>O</mi><mi>C</mi><mo>)</mo></mrow><mrow><mo>(</mo><mn>1</mn><mo>-</mo><msup><mi>e</mi><mrow><mo>-</mo><mfrac><mi>t</mi><mrow><msub><mi>R</mi><mn>2</mn></msub><mrow><mo>(</mo><mi>T</mi><mo>,</mo><mi>S</mi><mi>O</mi><mi>C</mi><mo>)</mo></mrow><msub><mi>C</mi><mn>2</mn></msub><mrow><mo>(</mo><mi>T</mi><mo>,</mo><mi>S</mi><mi>O</mi><mi>C</mi><mo>)</mo></mrow></mrow></mfrac></mrow></msup><mo>)</mo></mi>mrow><mo>-</mo><msub><mi>IR</mi><mn>3</mn></msub><mrow><mo>(</mo><mi>T</mi><mo>,</mo><mi>S</mi><mi>O</mi><mi>C</mi><mo>)</mo></mrow><mrow><mo>(</mo><mn>1</mn><mo>-</mo><msup><mi>e</mi><mrow><mo>-</mo><mfrac><mi>t</mi><mrow><msub><mi>R</mi><mn>3</mn></msub><mrow><mo>(</mo><mi>T</mi><mo>,</mo><mi>S</mi><mi>O</mi><mi>C</mi><mo>)</mo></mrow><msub><mi>C</mi><mn>3</mn></msub><mrow><mo>(</mo><mi>T</mi><mo>,</mo><mi>S</mi><mi>O</mi><mi>C</mi><mo>)</mo></mrow></mrow></mfrac></mrow></msup><mo>)</mo></mrow></mrow></mtd></mtr></mtable><mo>-</mo><mo>-</mo><mo>-</mo><mrow><mo>(</mo><mn>8</mn><mo>)</mo></mrow></mrow> For temperature T and time t, U(t), U ₁ (0), U ₂ (0), U ₃ (0) and I in formula (8) are all known quantities, and U _ocv , R ₀ , R ₁ , R ₂ , R ₃ , C ₁ , C ₂ and C ₃ are only related to SOC, then formula (8) can be written as <mrow><mtable><mtr><mtd><mrow><mi>U</mi><mrow><mo>(</mo><mi>t</mi><mo>)</mo></mrow><mo>=</mo><msub><mi>U</mi><mrow><mi>o</mi><mi>c</mi><mi>v</mi></mrow></msub><mrow><mo>(</mo><mi>S</mi><mi>O</mi><mi>C</mi><mo>)</mo></mrow><mo>-</mo><msub><mi>IR</mi><mn>0</mn></msub><mrow><mo>(</mo><mi>S</mi><mi>O</mi><mi>C</mi><mo>)</mo></mrow><mo>-</mo><msub><mi>U</mi><mn>1</mn></msub><mrow><mo>(</mo><mn>0</mn><mo>)</mo></mrow><msup><mi>e</mi><mrow><mo>-</mo><mfrac><mi>t</mi><mrow><msub><mi>R</mi><mn>1</mn></msub><mrow><mo>(</mo><mi>S</mi><mi>O</mi><mi>C</mi><mo>)</mo></mrow><msub><mi>C</mi><mn>1</mn></msub><mrow><mo>(</mo><mi>S</mi><mi>O</mi><mi>C</mi><mo>)</mo></mrow></mrow></mfrac></mrow></msup></mrow></mtd></mtr><mtr><mtd><mrow><mo>-</mo><msub><mi>U</mi><mn>2</mn></msub><mrow><mo>(</mo><mn>0</mn><mo>)</mo></mrow><msup><mi>e</mi><mrow><mo>-</mo><mfrac><mi>t</mi><mrow><msub><mi>R</mi><mn>2</mn></msub><mrow><mo>(</mo><mi>S</mi><mi>O</mi><mi>C</mi><mo>)</mo></mrow><msub><mi>C</mi><mn>2</mn></msub><mrow><mo>(</mo><mi>S</mi><mi>O</mi><mi>C</mi><mo>)</mo></mrow></mrow></mfrac></mrow></msup><mo>-</mo><msub><mi>U</mi><mn>3</mn></msub><mrow><mo>(</mo><mn>0</mn><mo>)</mo></mrow><msup><mi>e</mi><mrow><mo>-</mo><mfrac><mi>t</mi><mrow><msub><mi>R</mi><mn>3</mn></msub><mrow><mo>(</mo><mi>S</mi><mi>O</mi><mi>C</mi><mo>)</mo></mrow><msub><mi>C</mi><mn>3</mn></msub><mrow><mo>(</mo><mi>S</mi><mi>O</mi><mi>C</mi><mo>)</mo></mrow></mrow></mfrac></mrow></msup><mo>-</mo><msub><mi>IR</mi><mn>1</mn></msub><mrow><mo>(</mo><mi>S</mi><mi>O</mi><mi>C</mi><mo>)</mo></mrow><mrow><mo>(</mo><mn>1</mn><mo>-</mo><msup><mi>e</mi><mrow><mo>-</mo><mfrac><mi>t</mi><mrow><msub><mi>R</mi><mn>1</mn></msub><mrow><mo>(</mo><mi>S</mi><mi>O</mi><mi>C</mi><mo>)</mo></mrow><msub><mi>C</mi><mn>1</mn></msub><mrow><mo>(</mo><mi>S</mi><mi>O</mi><mi>C</mi><mo>)</mo></mrow></mrow></mfrac></mrow></msup><mo>)</mo></mrow></mrow></mtd></mtr><mtr><mtd><mrow><mo>-</mo><msub><mi>IR</mi><mn>2</mn></msub><mrow><mo>(</mo><mi>S</mi><mi>O</mi><mi>C</mi><mo>)</mo></mrow><mrow><mo>(</mo><mn>1</mn><mo>-</mo><msup><mi>e</mi><mrow><mo>-</mo><mfrac><mi>t</mi><mrow><msub><mi>R</mi><mn>2</mn></msub><mrow><mo>(</mo><mi>S</mi><mi>O</mi><mi>C</mi><mo>)</mo></mrow><msub><mi>C</mi><mn>2</mn></msub><mrow><mo>(</mo><mi>S</mi><mi>O</mi><mi>C</mi><mo>)</mo></mrow></mrow></mfrac></mrow></msup><mo>)</mo></mrow><mo>-</mo><msub><mi>IR</mi><mn>3</mn></msub><mrow><mo>(</mo><mi>T</mi><mo>,</mo><mi>S</mi><mi>O</mi><mi>C</mi><mo>)</mo></mrow><mrow><mo>(</mo><mn>1</mn><mo>-</mo><msup><mi>e</mi><mrow><mo>-</mo><mfrac><mi>t</mi><mrow><msub><mi>R</mi><mn>3</mn></msub><mrow><mo>(</mo><mi>S</mi><mi>O</mi><mi>C</mi><mo>)</mo></mrow><msub><mi>C</mi><mn>3</mn></msub><mrow><mo>(</mo><mi>S</mi><mi>O</mi><mi>C</mi><mo>)</mo></mrow></mrow></mfrac></mrow></msup><mo>)</mo></mrow></mrow></mtd></mtr></mtable><mo>-</mo><mo>-</mo><mo>-</mo><mrow><mo>(</mo><mn>9</mn><mo>)</mo></mrow></mrow> Solving formula (9), the SOC value at the current temperature T and time t can be obtained.