CN115267546A - Battery life model parameter fitting method - Google Patents
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- 125000004122 cyclic group Chemical group 0.000 claims description 10
- 238000005562 fading Methods 0.000 claims description 7
- 238000006243 chemical reaction Methods 0.000 claims description 6
- 238000012216 screening Methods 0.000 claims 1
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- G01R31/392—Determining battery ageing or deterioration, e.g. state of health
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Abstract
The invention relates to the technical field of power batteries, in particular to a battery life model parameter fitting method, which converts a nonlinear parameter fitting equation of a calendar capacity attenuation rate and a cycle capacity attenuation rate into a linear parameter fitting equation; dividing the data into two groups of data according to the battery capacity attenuation test data of standing and charging and discharging of the single battery; taking logarithms of two values of the two groups of data as an array for parameter solution; removing unreasonable values in the solved parameter array; and performing parameter solution by using a combined equation based on the minimum weighted sum of the absolute values of the errors. The invention can be used for Kcal、Eacal、Zcal、Kcyc、EacycAnd ZcycFast solution, rootAnd the bias of fitting data is ensured according to different requirements, so that the fitting parameters of the battery life model are closer to the test data.
Description
Technical Field
The invention belongs to the technical field of power batteries, and particularly relates to a battery life model parameter fitting method.
Background
With the increasing market of electric automobiles, the reserve capacity is increased explosively, and the indexes directly related to three packs of power batteries, warranty and quality assurance are involved, so that the state of health (SOH) of the batteries is more and more important, whether the state of health of the batteries of the power batteries can be quickly and accurately predicted is more and more critical, and a battery life prediction model provides a solution for the problem.
At present, a battery life prediction model is divided into a battery capacity decay rate prediction model and a battery internal resistance increase rate prediction model, and the rule is that the worse the battery health state is, the more the battery capacity is reduced relatively to the initial state or the more the battery internal resistance is increased relatively to the initial state, and the battery capacity decay rate is the current mainstream battery health state judgment evidence, so the battery capacity decay rate prediction model is the mainstream prediction model.
The equation of the battery capacity decay rate comprises two aspects:
(2) And rate of decay of cyclic capacityCapacity attenuation rate equation of battery in charging and discharging processes
t represents a battery temperature;
t represents the number of days the battery is left standing;
n represents the number of charge and discharge times of the battery;
Kcal、Kcycis a correction factor;
Eacal、Eacycis a temperature dependent coefficient;
Zcal、Zcycis a dimensionless constant;
to obtain a coefficient Kcal、Eacal、Zcal、Kcyc、EacycAnd ZcycAt present, the battery capacity fading test of battery standing and battery charging and discharging at different temperatures is generally adopted, wherein the test data of battery standing is data of the number of days of battery standing and the battery capacity, and the battery charging and discharging is data of the number of battery charging and discharging times and the battery capacity. However, the current method for testing the battery capacity attenuation by adopting battery standing and battery charging and discharging at different temperatures cannot ensure the bias of fitting data according to different requirements, so that the parameters of the battery life model fitting deviate from the test data.
Disclosure of Invention
In view of the above, the present invention provides a method for fitting parameters of a battery life model, which can match a coefficient K in a calendar capacity decay rate and a cyclic capacity decay ratecal、Eacal、Zcal、Kcyc、EacycAnd ZcycAnd fast solving, and ensuring the bias of fitting data according to different requirements, so that the parameters fitted by the battery life model are closer to the test data.
The invention solves the technical problems by the following technical means:
a battery life model parameter fitting method is based on test data of battery cell standing and charging and discharging, and data are converted and screened out; and performing parameter solution by adopting a combined equation based on the minimum weighted sum of the absolute values of the errors to obtain corresponding parameters of the battery life model.
Further, the battery life model parameter fitting method specifically comprises the following steps,
s1, converting a nonlinear parameter fitting equation of a calendar capacity attenuation rate and a cycle capacity attenuation rate into a linear parameter fitting equation to obtainAndwherein:the rate of decay of the calendar battery capacity is indicated,represents the attenuation rate of the charge and discharge capacity of the battery;
s2, dividing the data into two groups of data according to the battery capacity attenuation test data of standing and charging and discharging of the single batteryAndwherein: t represents the temperature of the battery, T represents the number of days for which the battery is left standing, and N represents the number of charge and discharge times of the battery;
s3, taking logarithms of two values of the two groups of data to serve as an array for parameter solution;
s4, removing unreasonable values in the solved parameter array;
and S5, solving parameters by adopting a combined equation with the minimum weighted sum based on the absolute values of the errors.
Further, in the step S1, logarithms are taken on both sides of the calendar capacity decay rate equation and the cycle capacity decay rate equation, and equations of the calendar capacity decay rate and the cycle capacity decay rate are converted.
Further, in the step S1, the equation conversion of the calendar capacity fading specifically includes:
wherein: t represents the battery temperature, and T represents the number of days the battery was left to stand.
Further, in step S1, the equation conversion of the cyclic capacity fading specifically includes:
wherein: t represents the battery temperature, and N represents the number of charge and discharge of the battery.
further, in step S4, when solving the parameters, a weighting coefficient k is introduced based on the absolute value sum of the errors and the minimum, so as to distinguish important fitting points.
Further, the specific equation in step S4 is:solving a, b and c to minimize the value of f (a, b and c), and then inversely substituting the solved a, b and c into the equation to obtain the corresponding Kcal、Eacal、Zcal、Kcyc、EacycAnd ZcycThe value of (c).
The battery life model parameter fitting method has the following advantages:
the battery life model parameter fitting method is based on a combined equation with the minimum weighted sum of absolute error values to solve, and based on test data of battery cell standing and charging and discharging, data are transformed to remove unreasonable data, and then corresponding coefficients are solved according to the parameter solving method with the introduction of weighting coefficients; the method can distinguish the key fitting points, can ensure the bias of fitting data according to different requirements, but not treat all data equally, so that the fitting parameters of the battery life model are closer to the test data.
Drawings
FIG. 1 is a graph of decay rate of battery resting capacity according to the present invention;
FIG. 2 is a graph of the decay rate of the charge-discharge cycle capacity of a battery according to the present invention;
FIG. 3 is a comparison graph of a fitted surface and a transformed array for the battery life model parameter fitting method of the present invention;
FIG. 4 is a comparison graph of a fitted curve and measured data in the parameter fitting method of the present invention.
Detailed Description
The invention will be described in detail below with reference to the following figures and specific examples:
the following description of the embodiments of the present invention is provided by way of specific examples, and those skilled in the art will appreciate the advantages and utilities of the present invention from the disclosure herein. It should be noted that the drawings provided in the following embodiments are only for illustrative purposes, are schematic drawings rather than actual drawings, and are not to be construed as limiting the invention, and in order to better illustrate the embodiments of the invention, some components in the drawings may be omitted, enlarged or reduced, and do not represent the size of an actual product; it will be understood by those skilled in the art that certain well-known structures in the drawings and their descriptions may be omitted.
In the description of the present invention, it should be understood that if there are terms such as "upper", "lower", "left", "right", "front", "back", etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the drawings, it is only for convenience of describing the present invention and simplifying the description, but not for indicating or implying that the indicated device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore the terms describing the positional relationships in the drawings are only used for illustrative purposes and are not to be construed as limiting the present invention, and those skilled in the art can understand the specific meanings of the terms according to specific situations.
In the embodiment, the battery capacity attenuation test data of battery standing and battery charging and discharging of the battery core of the power battery of the actual mass-produced vehicle of Chongqing Changan new energy automobile technology limited company is adopted, and the result is solved by combining the method provided by the invention.
In order to better explain the technical content of the present invention, the theory applied by the present invention will be explained first. The method comprises the steps of firstly carrying out logarithmic transformation on a life attenuation rate equation and test data of battery standing capacity attenuation (shown in figure 1) at different temperatures and battery charging and discharging capacity attenuation (shown in figure 2) at different temperatures, then carrying out corresponding logarithmic transformation on the test data, removing unreasonable values, further solving corresponding parameter values through weighting sum of absolute values of errors, and finally comparing a fitted curve with actually measured data.
The lifetime decay rate equation adopted in this embodiment is as follows:
t represents a battery temperature;
t represents the number of days the battery is left standing;
n represents the number of charge and discharge times of the battery;
Kcal、Kcycis a correction factor;
Eacal、Eacycis a temperature dependent coefficient;
Zcal、Zcycis a dimensionless constant;
first, taking the cyclic capacity decay equation as an example, K is obtainedcyc、EacycAnd ZcycThe steps of the values are as follows:
a1, equation conversion of capacity attenuation rate:
taking logarithm on two sides of the cyclic capacity attenuation rate equation, converting the nonlinear parameter fitting equation into a linear parameter fitting equation,
wherein: x represents T +273.15;
y represents ln (N);
a represents ln (K)cyc);
b represents-Eacyc;
c represents Zcyc;
A2, data processing:
according to the battery capacity attenuation test data of the single battery charge and discharge, firstly combining the data into a wholeN is arranged from small to large, T is arranged from small to large,arranging from small to large; then N is addedTaking logarithm, and converting the array intoAnd finally, removing unreasonable values in the array.
A3, parameter solving:
the parameter solving process adopts a combined equation based on the weighted sum of the absolute values of the errors to carry out parameter solving, the mathematical principle is to introduce a weighting coefficient k on the basis of the absolute values of the errors and the minimum values, and important fitting areas are distinguished, and the equation is as follows:
the meters a, b, c are solved so that the value of f (a, b, c) is minimized. Comparison graph with fitting surface and transformation group (as shown in FIG. 3)
Then the solved a, b and c are inversely substituted into the equation to obtain the corresponding Kcyc、EacycAnd ZcycThe value of (c):
Kcyc=exp(a)
Zacyc=-b
a4, comparing and verifying;
k to be solvedcyc、EacycAnd ZcycThe method can distinguish key fitting points, can ensure the bias of fitting data according to different requirements, but does not treat all data equally, so that fitting parameters are closer to the test data.
Then, taking calendar capacity decay equation as an example, to obtain Kcal、Eacal、ZcalThe value of (c).
The parameter solution of the calendar capacity decay equation is consistent with the steps of the cyclic capacity decay equation, and the method specifically comprises the following steps:
a1, equation conversion of capacity attenuation rate:
taking logarithm on two sides of calendar capacity attenuation rate equation, converting nonlinear parameter fitting equation into linear parameter fitting equation,
wherein: x represents T +273.15;
y represents ln (t);
a represents ln (K)cal);
b represents-Eacal;
c represents Zcal;
A2, data processing:
according to the battery capacity attenuation test data of the standing battery single battery, firstly combining the data into a wholeT is arranged from small to large,from small to aligned; then sum t withTaking logarithm and converting the array intoFinally, unreasonable values in the array are removed.
A3, parameter solving:
the parameter solving process adopts a combined equation based on the weighted sum of the absolute values of the errors to carry out parameter solving, the mathematical principle is to introduce a weighting coefficient k on the basis of the absolute values of the errors and the minimum values, and important fitting areas are distinguished, and the equation is as follows:
solving for a, b, c so that the value of f (a, b, c) is minimum.
Then the solved a, b and c are inversely substituted into the equation to obtain the corresponding Kcal、Eacal、ZcalThe value of (c):
Kcal=exp(a)
Zacal=-b
a4, comparing and verifying;
k to be solvedcal、EacalAnd ZcalSubstituting into corresponding equation, and collecting corresponding curve to compare with test data.
Although the present invention has been described in detail with reference to the preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the true spirit and scope of the present invention, which is defined by the claims appended hereto. The techniques, shapes, and configurations not described in detail in the present invention are all known techniques.
Claims (8)
1. A battery life model parameter fitting method is characterized in that: based on the test data of battery cell standing and charging and discharging, converting and screening the data; and performing parameter solution by adopting a combined equation based on the minimum weighted sum of the absolute values of the errors to obtain corresponding battery life model parameters.
2. The method of claim 1, wherein the battery life model parameters are fitted to the model parameters: the method specifically comprises the following steps of,
s1, converting a nonlinear parameter fitting equation of a calendar capacity attenuation rate and a cycle capacity attenuation rate into a linear parameter fitting equation to obtainAndwherein:the calendar battery capacity decay rate is represented,represents the attenuation rate of the charge and discharge capacity of the battery;
s2, dividing the data into two groups of data according to the battery capacity attenuation test data of standing and charging and discharging of the single batteryAndwherein: t represents the temperature of the battery, T represents the number of days for which the battery is left standing, and N represents the number of charge and discharge times of the battery;
s3, taking logarithms of two values of the two groups of data to serve as an array for parameter solution;
s4, removing unreasonable values in the solved parameter array;
and S5, solving parameters by adopting a combined equation with the minimum weighted sum based on the absolute values of the errors.
3. The battery life model parameter fitting method of claim 2, wherein: in the step S1, logarithms are taken on both sides of the calendar capacity decay rate equation and the cycle capacity decay rate equation, and equations of the calendar capacity decay rate and the cycle capacity decay rate are converted.
4. A method of fitting parameters of a battery life model according to claim 3, characterized in that: in the step S1, equation conversion of calendar capacity fading specifically includes:
wherein: t represents the battery temperature, and T represents the number of days the battery was left to stand.
7. the battery life model parameter fitting method of claim 2, wherein: in the step S4, when the parameter is solved, a weighting coefficient k is introduced based on the absolute value and the minimum of the error, so as to distinguish important fitting points.
8. The method of claim 7, wherein the battery life model parameter fitting method comprises: the specific equation in step S4 is:solve a, b, c so that f (a,b, c) is minimum, then the solved a, b, c is inversely substituted into the equation to obtain the corresponding Kcal、Eacal、Zcal、Kcyc、EacycAnd ZcycThe value of (c).
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