Method for estimating battery health
Technical Field
The invention belongs to the technical field of power battery health assessment, and particularly relates to a method for estimating the health degree of a battery according to the service condition of the battery.
Background
The lithium ion battery is widely applied to various fields because of the advantages of high output voltage, long cycle life, high energy density, low self-discharge rate, wide working temperature range and the like, and the safety and reliability of the lithium ion battery are always important points of great attention.
Currently, the mainstream methods for estimating the health of the battery in the industry are mainly divided into the following methods:
1. Machine learning model method
The disadvantage of this method is that:
(1) A large amount of data with labels is needed, a large amount of experiments are needed, and the experiment cost is high;
(2) Migration from experimental data to actual conditions may result in reduced model accuracy because the experiment cannot cover all use cases.
2. Ampere-hour integration method
The disadvantage of this method is that:
(1) The error is relatively large;
(2) The accuracy of the health calculation is limited by the sensor accuracy;
(3) The calculated result fluctuates up and down.
3. Double Kalman filtering method
The disadvantage of this method is that:
(1) The calculation process is complex;
(2) It is necessary to establish a battery equivalent circuit diagram, and a device using a battery, such as a vehicle, is difficult to identify parameters in the equivalent circuit diagram in actual operation.
Therefore, the mainstream method is to evaluate the current state of health of the battery through the current battery performance, and the disadvantage is more.
Disclosure of Invention
The invention aims to provide a method for estimating the battery health, which has the advantages of limited required experiment times, easy expansion of application range, higher accuracy and lower complexity.
In order to achieve the above purpose, the invention adopts the following technical scheme:
A method of estimating battery health, comprising the steps of:
Step one, carrying out a cyclic charge-discharge attenuation experiment on N batteries with the same type, wherein N is an integer larger than 3, fitting an attenuation curve of the battery with the same type by using experimental data of the cyclic charge-discharge attenuation experiment to be used as an attenuation reference curve of the battery with the same type, wherein the attenuation curve represents the relation between the attenuation percentage P loss of the battery with the same type and the cycle number N of the battery with the same type, and the attenuation curve comprises three coefficients which are alpha sei、βsei、fd,1 respectively;
Step two, taking a plurality of batteries of the model to carry out cyclic attenuation experiments under different temperatures, different average SOCs and different discharge depths, solving a temperature correction form, an average SOC correction form, a discharge depth correction form and a calendar time correction form corresponding to the f d,1 by using experimental data of the cyclic attenuation experiments, correcting the f d,1 by using the temperature correction form, the average SOC correction form, the discharge depth correction form and the calendar time correction form to obtain a corrected f d,1, and correcting an attenuation reference curve of the battery of the model by using the corrected f d,1 to obtain a corrected attenuation curve of the battery of the model;
and thirdly, when the health degree of the battery to be estimated, which belongs to the battery of the model, is estimated, estimating the attenuation of each cycle of the battery to be estimated by using the use data of the battery to be estimated and the corrected attenuation curve of the battery of the model, so as to estimate the service life and the health degree of the battery to be estimated.
In the first step, the cyclic charge-discharge decay experiment is performed at a standard temperature t 0.
In the first step, according to the cycle number and the attenuation percentage of each battery model, fitting to obtain an attenuation curve corresponding to each battery model, thereby determining alpha sei、βsei and f d,1 corresponding to each battery model, and further obtaining the battery modelAndAnd by combiningAndAs alpha sei、βsei、fd,1 in the decay reference curve of the model battery.
In the first step, the attenuation curve is expressed as
In the second step, at least different temperatures, 2 different average SOCs and 4 different discharge depths are taken when the cyclic attenuation experiment is carried out.
In the second step, the temperature correction is as followsWherein k T is a temperature correction coefficient, T is a current temperature, and T ref is a reference temperature;
The average SOC correction formula is Wherein k σ is an average SOC correction coefficient, σ is a current average SOC, and σ ref is a reference average SOC;
the calendar time correction formula is S t(t)=kt t, wherein k t is a calendar time correction coefficient, and t is the current calendar time;
The depth of discharge correction is S δ(δ)=kδ,e1δexp(kδ,e2 δ), where k δ,e1、kδ,e2 is the depth of discharge correction coefficient, and δ is the current depth of discharge.
In the second step, when the current temperature t=t A,F d,t[T=TA is f d,1 data obtained through the cyclic attenuation experiment when the current temperature is T=T A, f d,t[T=Tref is f d,1 data obtained through the cyclic attenuation experiment when the current temperature is T=T ref, and the temperature correction coefficient k T is solved by combining the temperature correction type, so that the temperature correction type is obtained;
when the current average SOC sigma=sigma A, F d,t[σ=σA is f d,1 data obtained through the cyclic attenuation experiment when the current average SOC sigma=sigma A, f d,t[σ=σref is f d,1 data obtained through the cyclic attenuation experiment when the current average SOC sigma=sigma ref, and the average SOC correction coefficient is solved by combining the average SOC correction coefficients, so that the average SOC correction formula is obtained;
The calendar time correction factor Wherein f d,t[T=TA,σ=σA is f d,1 data obtained by the cyclic decay experiment when the current temperature t=t A and the current average SOC σ=σ ref;
When the current depth of discharge δ=δ A, Wherein f d,1[δ=δA,σ=σA,T=TA,t=tp,A is f d,1 data obtained through the cyclic attenuation experiment when the current depth of discharge δ=δ A, the current average SOC σ=σ ref, the current temperature t=t A, and the current calendar time t=t p,A, and then the depth of discharge correction coefficient k δ,e1、kδ,e2 is solved in combination with the depth of discharge correction, thereby obtaining the depth of discharge correction formula.
In the second step, the corrected f d,1=[Sδ(δ)+St(t)]Sσ(σ)ST (T).
And thirdly, counting the use data of the battery to be estimated according to a rain flow counting method.
Due to the application of the technical scheme, the invention has the advantages of strong expansibility, high precision and simple calculation, and can be realized only by limited experiments.
Drawings
FIG. 1 is a flow chart of a method for estimating battery health according to the present invention.
Detailed Description
The invention will be further described with reference to examples of embodiments shown in the drawings.
In a first embodiment, as shown in fig. 1, a method for estimating the health of a battery includes the following steps:
Step one, solving an attenuation reference curve of a battery through a cyclic charge-discharge attenuation experiment
And (3) taking N (N is an integer larger than 3) batteries (lithium ion batteries) of the same type, carrying out a cyclic charge-discharge attenuation experiment, fitting an attenuation curve of the battery of the type by using experimental data of the cyclic charge-discharge attenuation experiment as an attenuation reference curve of the battery of the type, wherein the attenuation curve represents the relation between the attenuation percentage P loss of the battery of the type and the cycle number N of the battery of the type, and the attenuation curve comprises three coefficients which are alpha sei、βsei、fd,1 respectively.
1. N (n > 3) batteries with the same type are taken, and a cyclic charge-discharge attenuation experiment is carried out at a standard temperature t 0(t0 which is generally 25 ℃. In the cyclic charge-discharge attenuation experiment process, the cyclic range of the battery SOC is 0% -100%. The number of cycles N of each cell is recorded separately as a percentage of decay P loss corresponding to each cycle.
2. According to the cycle times N of each battery and the attenuation percentage P loss corresponding to each cycle, respectively fitting attenuation curves corresponding to the batteries according to a formula:
3. Alpha sei in the above formula is related to the first effect of the battery and represents the early duty cycle of lithium ions consumed by the battery to form a stable sei film.
4. And according to the cycle times and the attenuation percentages of each type of battery, determining alpha sei、βsei and f d,1 corresponding to each type of battery after fitting to obtain an attenuation curve corresponding to each type of battery, namely obtaining n alpha sei, n beta sei and n f d,1 in total. Averaging n alpha sei, n beta sei and n f d,1 to obtain the batteryAndAnd will be as followsAndAlpha sei、βsei、fd,1 in the attenuation reference curve of the battery of the model is used as the attenuation reference curve of the battery of the model to finally obtain the attenuation curve of the battery of the modelThis was used as a reference curve for attenuation of the battery of this model.
Step two, parameter correction under different conditions
And (3) dividing a plurality of batteries of the model into n z groups, carrying out cyclic attenuation experiments under different temperatures, different average SOCs and different discharge depths, obtaining a temperature correction formula, an average SOCs correction formula, a discharge depth correction formula and a calendar time correction formula corresponding to f d,1 by using experimental data of the cyclic attenuation experiments, correcting f d,1 by using the temperature correction formula, the average SOCs correction formula, the discharge depth correction formula and the calendar time correction formula to obtain a corrected f d,1, and correcting an attenuation reference curve of the battery of the model by using the corrected f d,1 to obtain a corrected attenuation curve of the battery of the model.
1. Since f d,1 in the attenuation reference curve of the battery of this model varies depending on the temperature, SOC, and depth of discharge, it is necessary to correct the attenuation reference curve for different conditions.
2. And (3) taking a plurality of batteries of the model, dividing the batteries into n z groups, and carrying out cyclic attenuation experiments on the batteries at different temperatures, different average SOCs and different depths of discharge by adopting a controlled variable method, namely at least taking different temperatures, 2 different average SOCs and 4 different depths of discharge during the experiment.
3. Corrected f d,1=[Sδ(δ)+St(t)]Sσ(σ)ST (T).
4. In the above formula, S δ (δ) is a depth of discharge correction type, S t (T) is a calendar time correction type, S σ (σ) is an average SOC correction type, and S T (T) is a temperature correction type.
5. In the case of the temperature correction type,Where k T is a temperature correction coefficient, T is the current temperature, T ref is a reference temperature, when the current temperature t=t A,Wherein f d,t[T=TA is f d,1 data obtained through a cyclic attenuation experiment when the current temperature T=T A, f d,t[T=Tref is f d,1 data obtained through the cyclic attenuation experiment when the current temperature T=T ref, and then the temperature correction coefficient k T is solved by combining the temperature correction, so that a temperature correction type is obtained. Reference temperature T ref in this equation, if the temperature of the reference curve is the reference temperature, T ref=t0.
6. In the case of the average SOC correction type,Where k σ is an average SOC correction coefficient, σ is a current average SOC, σ ref is a reference average SOC, when the current average SOC σ=σ A,Wherein, f d,t[σ=σA is f d,1 data obtained by a cyclic attenuation experiment when the current average SOC σ=σ A, and f d,t[σ=σref is f d,1 data obtained by a cyclic attenuation experiment when the current average SOC σ=σ ref, then the average SOC correction coefficient is solved in combination with the average SOC correction formula, and the average SOC correction formula is obtained. If the average SOC of the reference curve is taken as a reference, the average SOC σ ref=avg(SOCcycle is referred to).
7. For the calendar time correction type, S t(t)=kt t, wherein k t is a calendar time correction coefficient, t is the current calendar time, and the calendar time correction coefficientWherein f d,t[T=TA,σ=σA is f d,1 data obtained by a cyclic decay experiment when the current temperature t=t A and the current average SOC σ=σ ref. From this, a calendar time correction coefficient k t is calculated.
8. For depth of discharge correction, S δ(δ)=kδ,e1δexp(kδ,e2 delta), where k δ,e1、kδ,e2 is the depth of discharge correction factor, delta is the current depth of discharge, when the current depth of discharge delta = delta A,Wherein f d,1[δ=δA,σ=σA,T=TA,t=tp,A is f d,1 data obtained through a cyclic attenuation experiment when the current depth of discharge δ=δ A, the current average SOC σ=σ ref, the current temperature t=t A, and the current calendar time t=t p,A, and then the depth of discharge correction factor k δ,e1、kδ,e2 is solved in combination with the depth of discharge correction formula, thereby obtaining the depth of discharge correction formula.
Step three, estimating the actual battery
When the health degree of the battery to be estimated, which belongs to the type battery, is estimated, the use data of the battery to be estimated, including the cycle times, the average temperature, the discharge depth, the average SOC and the like in the use of the battery, are counted according to a rain flow counting method, and the use data of the battery to be estimated and the corrected attenuation curve of the type battery are utilized to estimate the attenuation of each cycle of the battery to be estimated, so that the service life and the health degree of the battery to be estimated are estimated.
The advantages of the above scheme are:
1. the expansibility is strong, and the batteries of the same model can be used universally only by carrying out limited experiments;
2. Considering and being compatible with different conditions, the device is used in different environments;
3. The precision is high;
4. The electrochemical characteristics of the battery are fused;
5. the concept of cumulative damage is incorporated.
Compared with the existing machine learning model method, the scheme only needs limited experiments, can be suitable for other batteries of the same model, is high in accuracy, free of up-and-down fluctuation and insensitive to sensor accuracy, does not need an equivalent circuit diagram and parameter identification, and reduces algorithm complexity.
The above embodiments are provided to illustrate the technical concept and features of the present invention and are intended to enable those skilled in the art to understand the content of the present invention and implement the same, and are not intended to limit the scope of the present invention. All equivalent changes or modifications made in accordance with the spirit of the present invention should be construed to be included in the scope of the present invention.