CN107957560B - Lithium ion battery SOC estimation algorithm based on equivalent circuit - Google Patents

Lithium ion battery SOC estimation algorithm based on equivalent circuit Download PDF

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CN107957560B
CN107957560B CN201711376573.4A CN201711376573A CN107957560B CN 107957560 B CN107957560 B CN 107957560B CN 201711376573 A CN201711376573 A CN 201711376573A CN 107957560 B CN107957560 B CN 107957560B
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soc
voltage
temperature
equivalent circuit
lithium ion
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CN107957560A (en
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方彦彦
唐玲
云凤玲
栗敬敬
崔义
王琳舒
黄倩
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China Automotive Battery Research Institute Co Ltd
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
    • G01R31/367—Software therefor, e.g. for battery testing using modelling or look-up tables
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
    • G01R31/385—Arrangements for measuring battery or accumulator variables
    • G01R31/387—Determining ampere-hour charge capacity or SoC
    • G01R31/388—Determining ampere-hour charge capacity or SoC involving voltage measurements

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Abstract

The invention provides a lithium ion battery SOC estimation algorithm based on an equivalent circuit, which comprises the steps of S1, obtaining open-circuit voltage U at different temperaturesOCVAnd S2, establishing an equivalent circuit model, obtaining the relation between model parameters and the SOC and the temperature T, S3, calculating the SOC value under the current temperature T and the time T, simplifying a voltage characteristic equation, and solving the voltage characteristic equation. The SOC estimation method of the lithium ion battery provided by the invention has the advantages of simple principle and high estimation precision, and the maximum deviation of the SOC estimation precision of the lithium ion battery is not more than 1%.

Description

Lithium ion battery SOC estimation algorithm based on equivalent circuit
Technical Field
The invention belongs to the field of detection, and particularly relates to a method for estimating the state of charge of a lithium ion battery.
Background
In recent years, the number of global automobiles is rapidly increased, the demand for energy is also increased, and the pollution to the environment is also increased. New energy automobiles, especially electric automobiles, have become the development direction of future automobiles, but the development speed of the new energy automobiles is still limited by power batteries and application technologies thereof. How to prolong the service life of the battery and improve the energy efficiency and the reliability of the battery is a problem which needs to be solved in the industrialization of the electric automobile, so that the research on the battery management technology has great significance.
The State of Charge (State of Charge) of the power battery is called SOC for short. The residual capacity of the lithium ion battery is one of the most important performance parameters of the battery in the operation process, and the estimation of the residual capacity is a non-negligible link. For the electric vehicle, the SOC of the battery is accurately estimated, so that the cruising ability can be improved, the service life of the battery can be prolonged, and the safety is improved.
Disclosure of Invention
Aiming at the defects in the field, the invention discloses a lithium ion battery SOC estimation algorithm based on an equivalent circuit so as to accurately estimate the SOC of a battery.
The technical scheme for realizing the aim of the invention is as follows:
a lithium ion battery SOC estimation algorithm based on an equivalent circuit comprises the following steps:
s1, acquiring open-circuit voltage U at different temperaturesOCVThe relationship with the SOC and the temperature T,
s2, establishing an equivalent circuit model, and obtaining the relation between the model parameters and the SOC and the temperature T
S21, establishing a three-order equivalent circuit model, wherein the equivalent circuit comprises ohmic resistors R connected in series0Each RC unit consists of a resistor and a capacitor which are connected in parallel; determining the equivalent circuit terminal voltage U and the open circuit voltage UOCVThe characteristic relationship of (a);
s22, acquiring ohmic internal resistance R in the equivalent circuit model0Relation to SOC and temperature T: the voltage characteristic at the end instant of the pulse discharge is determined.
S222, acquiring ohmic internal resistance R at temperature T0Relation to SOC
S223, obtaining ohmic internal resistance R at other temperatures0Relation to SOC
S23, obtaining RC unit parameter R in the equivalent circuit model1，C1，R2，C2，R3，C3And SOC and temperatureThe relationship of T;
s231, measuring the voltage U (t) of the equivalent circuit after the pulse discharge finishing moment;
s232, obtaining RC unit parameter R at the same temperature1，C1，R2，C2，R3，C3Relation to SOC.
And S233, obtaining the relation between the parameters R1, C1, R2, C2, R3 and C3 of the parallel RC units and the SOC at other temperatures.
S3, estimating the SOC value under the current temperature T and the battery operation time T, including S31, simplifying a voltage characteristic equation, and S32, solving the voltage characteristic equation.
In step S1, a series of temperatures T is obtained, and the open-circuit voltage U is obtainedOCVAnd the relation with SOC, wherein the temperature range of T is-10-50 ℃, and the SOC is at least 9 values in the range of 0.1-0.9.
Further, the relationship between the open-circuit voltage uov and the SOC at the temperature T is expressed by a fifth-order polynomial:
UOCV＝a0+a1SOC+a2SOC2+a3SOC3+a4SOC4+a5SOC5
wherein Uocv represents the open-circuit voltage of the battery, a 0-a 5 are polynomial coefficients and are constants, and SOC is the state of charge of the battery.
Alternatively, T is taken every 4-8 ℃ at less than 10 ℃ for a group of UOCVIn relation to SOC, a group of U is obtained every 8-12 ℃ when T is above 10 DEG COCVRelation to SOC.
Wherein the step S21 is:
aiming at a third-order equivalent circuit model, establishing a characteristic equation of a battery model:
Figure BDA0001514692300000031
wherein, U0Is the ohmic internal resistance R0Voltage across, U1～U3Is the voltage across the three RC units, I is the current;
solving equation (1), the expression of the equivalent circuit terminal voltage can be obtained as follows:
Figure BDA0001514692300000032
wherein, U1(0)、U2(0) And U3(0) The initial values of the voltages across the three RC cells at the beginning of the pulse discharge (HPPC) timing, respectively.
In step S22, the pulse discharge (HPPC) is an existing test method, and the pulse discharge time, the current, and the like are all in the existing specifications (e.g., according to the Freedom battery test manual).
As can be seen from the structure of FIG. 2, the voltage change at the end of the pulse discharge is completely determined by the ohmic internal resistance R0And (4) generating. Therefore, ohmic internal resistance R0Obtained using the following formula:
Figure BDA0001514692300000033
in the formula of ULThe voltage abrupt change at the end of the pulse discharge is denoted as I, and the pulse discharge current value is denoted as I.
Wherein the step S22 is:
according to a voltage response curve obtained by HPPC experiments of the battery under different SOCs under the temperature T, ohmic internal resistance R under different SOCs is obtained by calculation through a formula (4)0And R0-a SOC curve. The SOC value is at least 9 values within the range of 0.1-0.9. For R at that temperature0-fitting a polynomial to the SOC curve, the polynomial fitting being:
R0＝b0+b1SOC+b2SOC2+b3SOC3+b4SOC4+b5SOC5
wherein R is0Indicates the ohmic internal resistance, b0～b5Is a polynomial coefficient and is a constant, and SOC is the state of charge of the battery.
At the end instant of pulse discharge, the current is zero, the circuit structure shown in fig. 2 has zero input response, and the voltage characteristic equation is as follows:
Figure BDA0001514692300000041
further, step S231 specifically includes:
as can be seen from the circuit configuration of fig. 2, after the pulse discharge is completed, the voltages at both ends of the ohmic internal resistance become zero, but the voltages at both ends of the three RC units do not become zero. Thus, the formula (3) becomes:
Figure BDA0001514692300000042
in principle, the nonlinear fitting tool of mathematical software is adopted, and the voltage response curve can be directly fitted according to the formula (4) to obtain the parameter values of the three RC units. However, since the exponential function exists in the formula (4), and the numerical value of the capacitance in the structure of fig. 2 is different from tens to hundreds of kF, it is difficult to control the fitting process by using the direct fitting of the formula (5), and since the fitting parameter is at the denominator position, a truncation error is introduced in each iteration. The results obtained are less stable. Therefore, equation (5) can be written as:
Figure BDA0001514692300000043
wherein, c1～c3And d1～d3Is a constant related to the RC cell parameter.
Wherein, in step S231, the voltage characteristic equation after the end moment of the pulse discharge is determined as
Figure BDA0001514692300000044
Wherein, tsIs the time of standing after pulse discharge, c1～c3And d1～d3Is a constant related to the RC cell parameter.
The HPPC experiment included pulsing the cell discharge and then standing. t is tsThe timing starting point of (2) is at the end of a pulse, i.e. a pulseTime after the end of discharge.
Wherein, step S232 is:
according to the voltage response curve of the battery standing after HPPC experiment pulse discharge under different SOCs under the temperature T, obtaining c under different SOCs by adopting the formula (6) through nonlinear fitting1～c3And d1～d3The value is obtained. The SOC value is at least 9 values within the range of 0.1-0.9, and RC unit parameter values under different SOCs are obtained through calculation according to the following formula:
Figure BDA0001514692300000051
according to the obtained Ri and Ci values under different SOC, R is subjected to1-SOC，R2-SOC，R3-SOC，C1-SOC，C2SOC and C3-performing cubic spline interpolation on the parameter table of SOC to obtain encrypted R1-SOC，R2-SOC，R3-SOC，C1-SOC，C2SOC and C3-a parameter table of SOC.
Wherein, the step S233 specifically includes changing the temperature T, repeating S232, and obtaining the encrypted R at other temperatures1-SOC，R2-SOC，R3-SOC，C1-SOC，C2SOC and C3-Parameter table of SOC, establishing R1、R2、R3、C1、C2And C3Two-dimensional parameter network with SOC and temperature
Further, in step S32, when calculating the SOC value at the current temperature T and time T, the method of writing a program instead of directly using a nonlinear equation solver of mathematical software to solve the highly nonlinear equation obtained by the equivalent circuit model includes:
i) setting an initial value of SOC to be 0.9, and calculating a terminal voltage value U of the battery;
ii) calculating the relative deviation of the terminal voltage value U and U of the battery at the current t
Δ＝|U-U*|/U；
iii) if the delta is more than or equal to 0.001, reducing the SOC value by 0.001, and repeating i) -ii); if delta is less than 0.001, the SOC value is output, namely the SOC value under the current temperature T and time T.
Since the formula (2) U is obtainedocv、R0、R1、R2、R3、C1、C2And C3At different values of SOC and temperature T, therefore, step S31 is:
the expression for the equivalent circuit terminal voltage is written as:
Figure BDA0001514692300000052
for the current temperature T and time T, U (T) in the formula (8), U1(0)、U2(0) And U3(0) And I are known amounts, and Uocv、R0、R1、R2、R3、C1、C2And C3Only SOC is relevant, equation (8) can be written
Figure BDA0001514692300000061
Solving the equation (9) to obtain the SOC value under the current temperature T and time T.
The invention has the beneficial effects that:
the invention provides a method for estimating the SOC of a lithium ion battery. The method has simple principle and high estimation precision. The method specifically comprises the following steps:
1. the maximum deviation of the SOC estimation precision of the SOC estimation method provided by the invention on the lithium ion battery is not more than 1%.
2. The SOC estimation method provided by the invention changes the fitting parameter form when carrying out nonlinear fitting on the RC unit parameters of the equivalent circuit model, and can effectively improve the fitting stability and speed.
3. According to the SOC estimation method provided by the invention, when the relation between the RC unit parameters of the equivalent circuit model and the SOC is obtained, a polynomial fitting method is not adopted, but a parameter table is established by adopting a cubic spline interpolation technology, so that the deviation caused by polynomial fitting can be effectively avoided.
4. When the SOC estimation method provided by the invention is used for solving the voltage characteristic equation of the equivalent circuit, the nonlinear equation is not directly solved, and the method of programming is adopted for solving, so that the solving precision is effectively improved, and the solving time is reduced.
Drawings
FIG. 1 is a flow chart of a method for estimating battery SOC based on an equivalent circuit according to the present invention;
FIG. 2 is a circuit configuration of an equivalent circuit;
fig. 3 is a flowchart for solving equation (9) by writing a program.
Fig. 4 is a relationship between the open-circuit voltage and the SOC obtained by the fitting.
Fig. 5 is a relationship between the ohmic internal resistance and the SOC obtained by fitting.
FIGS. 6 to 11 are parameter tables for R1-SOC, R2-SOC, R3-SOC, C1-SOC, C2-SOC and C3-SOC, respectively.
Figure 12 compares the resulting SOC estimate with experimental values,
FIG. 13 estimates the deviation of the results.
Detailed Description
The present invention is illustrated by the following preferred embodiments. It will be appreciated by those skilled in the art that the examples are only intended to illustrate the invention and are not intended to limit the scope of the invention.
In the examples, the means used are conventional in the art unless otherwise specified.
Example 1
In this example, in combination with a battery in which the positive electrode material is a ternary material, the SOC is estimated by using the following estimation method with T ═ 25 ℃.
The specific process comprises the following steps:
s1, obtaining the open circuit voltage UOCVRelation with the SOC and the temperature T
According to the open-circuit voltage U of the battery obtained by constant current discharge at the temperature of 25 ℃ under different SOCocvAnd the SOC value is at least 9 values in the range of 0.1-0.9. For U at 25 DEG Cocv-fitting a polynomial to the SOC curve.
The polynomial fitting formula is:
UOCV＝a0+a1SOC+a2SOC2+a3SOC3+a4SOC4+a5SOC5
wherein U isocvRepresents the open circuit voltage of the battery, a0～a5Is a polynomial coefficient and is a constant, and SOC is the state of charge of the battery.
Fig. 4 shows the fitting results, and the relationship between the open-circuit voltage and the SOC is obtained as follows:
UOCV＝3.3233+0.02455SOC-8.9131×10-4SOC2
+1.6196×10-5SOC3-1.2246×10-7SOC4+3.3391×10-10SOC5
s2, establishing an equivalent circuit model, and obtaining the relation between the model parameters and the SOC and the temperature T, wherein the step comprises the following substeps:
s21, establishing a three-order equivalent circuit model to determine the battery terminal voltage U and the open circuit voltage UOCVThe characteristic relationship of (1).
For the circuit diagram shown in fig. 2, a characteristic equation of the battery model is established:
Figure BDA0001514692300000081
Figure BDA0001514692300000082
Figure BDA0001514692300000083
U0＝IR0
U＝Uocv-U0-U1-U2-U3
wherein, U0Is the ohmic internal resistance R0Voltage across, U1～U3Is the voltage across the three RC cells, I is the current。
Solving equation (1), the expression of the available terminal voltage is:
Figure BDA0001514692300000084
wherein, U1(0)、U2(0) And U3(0) The initial voltage values at two ends of the three RC units are respectively when the timing is started.
S22, acquiring ohmic internal resistance R in the equivalent circuit model0The relation with SOC and temperature T.
And S221, determining the voltage characteristic at the pulse discharge ending moment.
At the end instant of pulse discharge, the current is zero, the circuit structure shown in fig. 2 has zero input response, and the voltage characteristic equation is as follows:
Figure BDA0001514692300000085
as can be seen from the structure of FIG. 2, the voltage change at the end of the pulse discharge is completely determined by the ohmic internal resistance R0And (4) generating. Therefore, ohmic internal resistance R0Obtained using the following formula:
Figure BDA0001514692300000086
wherein, ULThe voltage abrupt change at the end of the pulse discharge is denoted as I, and the pulse discharge current value is denoted as I.
S222, acquiring ohmic internal resistance R at certain same temperature0Relation to SOC
According to the voltage response curve obtained by HPPC experiments of the battery under different SOC at the temperature of 25 ℃, ohmic internal resistance R under different SOC is obtained by adopting the method S2210And R0-a SOC curve. The SOC values are 0.1,0.2,0.3,0.4,0.5,0.6,0.7,0.8 and 0.9. For R at 25 DEG C0-the SOC curve is fitted with a polynomial as follows:
R0＝b0+b1SOC+b2SOC2+b3SOC3+b4SOC4+b5SOC5
wherein R is0Indicates the ohmic internal resistance, b0～b5Is a polynomial coefficient and is a constant, and SOC is the state of charge of the battery.
Fig. 5 is a fitting result, and the obtained relationship between the ohmic internal resistance and the SOC is:
R0＝2.5800-0.03058SOC-4.5770×10-4SOC2
+1.6125×10-6SOC3-8.6662×10-8SOC4+5.0321×10-10SOC5
s23, obtaining parallel RC unit parameter R in the equivalent circuit model1，C1，R2，C2，R3，C3The relation with SOC and temperature T. Comprising the following substeps:
and S231, determining the voltage characteristic after the pulse discharge finishing moment.
As can be seen from the circuit configuration of fig. 2, after the pulse discharge is completed, the voltages at both ends of the ohmic internal resistance become zero, but the voltages at both ends of the three RC units do not become zero. Thus, the formula (3) becomes:
Figure BDA0001514692300000091
in principle, the nonlinear fitting tool of mathematical software is adopted, and the voltage response curve can be directly fitted according to the formula (4) to obtain the parameter values of the three RC units. However, since the exponential function exists in the formula (4), and the value of the capacitance in the structure of fig. 2 varies from tens to hundreds of kF, a truncation error is introduced in each iteration operation because the fitting parameter is at the denominator position. Therefore, the direct fitting of the formula (5) is difficult to control, and the obtained result has poor stability. Therefore, equation (5) is written as:
Figure BDA0001514692300000092
wherein, c1～c3And d1～d3Is a constant related to the RC cell parameter.
S232, obtaining a parameter R of the parallel RC unit at a certain same temperature1，C1，R2，C2，R3，C3Relation to SOC.
Obtaining c under different SOC through nonlinear fitting based on formula (6) according to a voltage response curve of the battery standing after the HPPC experiment under different SOC is charged and discharged at the temperature of 25 DEG C1～c3And d1～d3The value is obtained.
The SOC values are 0.1,0.2,0.3,0.4,0.5,0.6,0.7,0.8 and 0.9. And calculating to obtain RC unit parameter values under different SOCs according to the following formula. The expression is:
Figure BDA0001514692300000101
Figure BDA0001514692300000102
according to the R obtained in the step under different SOC1～R3And C1～C3Value, for R1-SOC，R2-SOC，R3-SOC，C1-SOC，C2SOC and C3-Carrying out cubic spline interpolation on the parameter table of the SOC to obtain the encrypted R1-SOC，R2-SOC，R3-SOC，C1-SOC，C2SOC and C3-Parameter table of SOC.
The results of the parameters are shown in FIGS. 6-11.
S3, estimating the SOC value at the current temperature T and the time T
The step comprises the following substeps:
s31 simplified voltage characteristic equation
Since the formula (2) U is obtainedocv、R0、R1、R2、R3、C1、C2And C3The values at different SOCs and temperatures T, therefore, equation (2) can be rewritten as:
Figure BDA0001514692300000103
for the current temperature T and time T, U (T) in the formula (8), U1(0)、U2(0) And U3(0) And I are known amounts, and Uocv、R0、R1、R2、R3、C1、C2And C3Only SOC is relevant, equation (8) can be written
Figure BDA0001514692300000104
Solving the equation (9) to obtain the SOC value under the current temperature T and the battery operation time T.
S32, solving the voltage characteristic equation
The formula (9) is a highly nonlinear equation, and a nonlinear equation solving tool of mathematical software is directly adopted for solving, so that a stable solving result cannot be obtained, and the solving time is long. Considering that the SOC value itself has upper and lower limits, equation (9) is solved by writing a program, and the specific flow is shown in fig. 3.
i) Setting an initial value of SOC to be 0.9, and calculating a terminal voltage value U of the battery according to the formula (9);
ii) the relative deviation of the terminal voltage values U from U at the present time t
Δ＝|U-U*|/U；
iii) if Delta is not less than 0.001. The SOC value is reduced by 0.001 and i) -ii) are repeated. If delta is less than 0.001, the SOC value is output, namely the SOC value under the current temperature T and time T.
Specific programming examples are as follows (only programs for solving the non-linear equations are listed, and programs for relating parameters to SOC in the equations are not listed):
Figure BDA0001514692300000111
the embodiment describes the whole process of acquiring the SOC estimation from the parameters by the method in detail. In practical applications, all the parameter obtaining processes, i.e., S1 and S2 and the expression simplification process S31 of the estimation process, need to be performed only once for the same battery to obtain the corresponding parameter values. The SOC estimation only needs to be performed specifically at step S32.
The implementation effect is as follows:
the resulting SOC estimation is compared to the experimental values in FIG. 12, where the experimental test (experiment) and prediction (prediction) are essentially completely coincident, and the deviation is shown in FIG. 13. The maximum deviation of both positive and negative is about 0.6%.
Example 2
Using the same method as in example 1, other values of temperature were set, and T was taken every 5 ℃ at a temperature below 10 ℃ for a set of UOCVIn relation to SOC, T is above 10 ℃ and a group of U is obtained every 10 DEG COCVRelation to SOC.
Compared with the experimental value, the maximum deviation of the obtained SOC estimated value is not more than 1%.
The above examples are only for describing the preferred embodiments of the present invention, and are not intended to limit the scope of the present invention, and various modifications and improvements made to the technical solution of the present invention by those skilled in the art without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims (10)

1. A lithium ion battery SOC estimation algorithm based on an equivalent circuit is characterized by comprising the following steps:
s1, acquiring open-circuit voltage U at different temperaturesOCVThe relationship with the SOC and the temperature T,
s2, establishing an equivalent circuit model, and obtaining the relation between model parameters and SOC and temperature T
S21, establishing a three-order equivalent circuit model, wherein the equivalent circuit comprises ohmic resistors R connected in series0And three RC units, each RC unit consists of a resistor and a capacitor which are connected in parallel, and the voltage U of the equivalent circuit end and the open-circuit voltage U are determinedOCVThe characteristic relationship of (a);
s22, obtaining theOhmic internal resistance R in equivalent circuit model0Relation to SOC and temperature T: determining the voltage characteristic at the moment of pulse discharge ending to obtain ohmic internal resistance R at temperature T0Relation to SOC;
s23, obtaining RC unit parameter R in the equivalent circuit model1，C1，R2，C2，R3，C3Relation to SOC and temperature T;
s231, measuring the voltage U (ts) of the equivalent circuit after the pulse discharge finishing moment;
s232, obtaining RC unit parameter R at the same temperature1，C1，R2，C2，R3，C3Relation to SOC;
and S3, calculating the SOC value under the current temperature T and the battery operation time T, simplifying a voltage characteristic equation, and solving the voltage characteristic equation.
2. The lithium ion battery SOC estimation algorithm of claim 1, wherein in step S1, a series of temperatures T is obtained and a switching voltage U is obtainedOCVAnd the relation with SOC, wherein the temperature range of T is-10-50 ℃, and the SOC is at least 9 values in the range of 0.1-0.9.
3. The lithium ion battery SOC estimation algorithm of claim 2, wherein the relationship of the open-circuit voltage Uocv at temperature T to SOC is expressed as a fifth order polynomial:
UOCV＝a0+a1SOC+a2SOC2+a3SOC3+a4SOC4+a5SOC5
wherein Uocv represents the open-circuit voltage of the battery, a 0-a 5 are polynomial coefficients and are constants, and SOC is the state of charge of the battery.
4. The lithium ion battery SOC estimation algorithm of claim 1, wherein the step S21 is:
aiming at a third-order equivalent circuit model, establishing a characteristic equation of a battery model:
Figure FDA0002251771570000021
wherein, U0Is the ohmic internal resistance R0Voltage across, U1～U3Is the voltage across the three RC units, I is the current;
solving equation (1), the expression of the equivalent circuit terminal voltage can be obtained as follows:
Figure FDA0002251771570000022
wherein, U1(0)、U2(0) And U3(0) When the pulse discharge timing is started, the initial voltage values at two ends of the three RC units are respectively.
5. The lithium ion battery SOC estimation algorithm of claim 1, wherein the step S22 is:
according to a voltage response curve obtained by HPPC experiments of the battery under different SOC under the temperature T, adopting a formula
Figure FDA0002251771570000023
Wherein, ULThe voltage abrupt change of the pulse discharge end is shown, I is the pulse discharge current value,
ohmic internal resistance R under different SOC is obtained through calculation0And R0-a SOC curve, said SOC values being at least 9 values in the range of 0.1-0.9, R for said temperature0-fitting a polynomial to the SOC curve, the polynomial fitting being:
R0＝b0+b1SOC+b2SOC2+b3SOC3+b4SOC4+b5SOC5
wherein R is0Indicates the ohmic internal resistance, b0～b5Is a polynomial coefficient and is constant, SOC is of the batteryState of charge.
6. The lithium ion battery SOC estimation algorithm of claim 1, wherein the voltage characteristic equation after the end moment of the pulse discharge is determined as
Figure FDA0002251771570000031
Wherein, tsIs the rest time after the pulse has ended the discharge, c1～c3And d1～d3Is a constant related to the RC cell parameter.
7. The lithium ion battery SOC estimation algorithm of claim 6, wherein step S232 is:
according to the voltage response curve of the battery standing after HPPC experiment pulse discharge under different SOCs under the temperature T, obtaining c under different SOCs by adopting the formula (6) through nonlinear fitting1～c3And d1～d3The SOC value is at least 9 values within the range of 0.1-0.9, and RC unit parameter values under different SOCs are obtained through calculation according to the following formula:
Figure FDA0002251771570000032
according to the obtained R under different SOCiAnd CiValue, for R1-SOC，R2-SOC，R3-SOC，C1-SOC，C2SOC and C3-performing cubic spline interpolation on the parameter table of SOC to obtain encrypted R1-SOC，R2-SOC，R3-SOC，C1-SOC，C2SOC and C3-a parameter table of SOC.
8. The lithium ion battery SOC estimation algorithm of claim 1,
the step S23 is specifically to change the temperature T, repeat S232, and obtain the temperature at other temperaturesEncrypted R1-SOC，R2-SOC，R3-SOC，C1-SOC，C2SOC and C3-Parameter table of SOC, establishing R1、R2、R3、C1、C2And C3Two-dimensional parametric networks with SOC and temperature.
9. The SOC estimation algorithm for lithium ion batteries according to claim 1, wherein the step S32 of solving in a programmed manner when calculating the SOC value at the current temperature T and time T includes:
i) setting an initial value of SOC to be 0.9, and calculating a terminal voltage value U of the battery;
ii) calculating the relative deviation of the terminal voltage value U and U of the battery at the current t
Δ＝|U-U*|/U；
iii) if the delta is more than or equal to 0.001, reducing the SOC value by 0.001, and repeating i) -ii); if delta is less than 0.001, the SOC value is output, namely the SOC value under the current temperature T and time T.
10. The lithium ion battery SOC estimation algorithm of claim 4, wherein in step S31, the expression of the equivalent circuit terminal voltage is written as:
Figure FDA0002251771570000041
for temperature T and time T, U (T), U in formula (8)1(0)、U2(0) And U3(0) And I are known amounts, and Uocv、R0、R1、R2、R3、C1、C2And C3Only SOC is relevant, equation (8) can be written
Figure FDA0002251771570000042
Solving the equation (9) to obtain the SOC value under the current temperature T and time T.
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