CN111308352A - Method for estimating battery attenuation of lithium ions - Google Patents
Method for estimating battery attenuation of lithium ions Download PDFInfo
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- CN111308352A CN111308352A CN201911191548.8A CN201911191548A CN111308352A CN 111308352 A CN111308352 A CN 111308352A CN 201911191548 A CN201911191548 A CN 201911191548A CN 111308352 A CN111308352 A CN 111308352A
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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
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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]
- G01R31/378—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC] specially adapted for the type of battery or accumulator
Abstract
The invention provides a method for estimating the attenuation of a lithium ion battery, which comprises the following steps: obtaining the external characteristic change of the lithium ion battery through a Thevenin equivalent model, and modeling the external characteristic; identifying parameters of the external characteristic model, obtaining an identified voltage discrete mathematical model through discretization, and constructing the mathematical model in a simulink environment; the mathematical model is based on data fitting of multiple groups of identification parameters to obtain an equation and a curve of each parameter changing along with time; the parameter comprises an open circuit voltage value; according to the mathematical model, obtaining voltage attenuation rates in different charge state intervals by differentiating different open-circuit voltage values with corresponding actual nominal voltage values; and estimating and obtaining the attenuation of the battery according to the voltage attenuation rate. The method of the present invention may be more accurate for battery degradation estimation.
Description
Technical Field
The invention relates to the technical field of new energy batteries, in particular to a method for estimating battery attenuation of lithium ions.
Background
The lithium battery is the most critical part of the electric automobile and the part with the highest cost ratio, and the accurate prediction and evaluation of the service life attenuation degree of the battery are more and more important. Accurate life assessment can improve vehicle performance and user experience on the one hand, and on the other hand, how to optimally configure spare part proportion in commerce and calculate asset residual value also needs battery life decay analysis as reference.
Currently, the lithium battery attenuation is generally analyzed from three dimensions, and how the whole attenuation process evolves is firstly analyzed from the perspective of the electrochemical reaction inside the battery. And secondly, performing different working condition tests on the battery in a laboratory, and analyzing the external characteristic changes such as voltage, internal resistance and the like of the battery. And a large amount of data actually operated at the vehicle end is collected and analyzed by utilizing a machine learning technology.
The current battery estimation methods are not highly accurate.
Disclosure of Invention
Based on the above, the invention provides a lithium ion battery attenuation estimation method, which can estimate the battery attenuation more accurately.
In order to achieve the purpose, the invention adopts the following technical scheme:
a method of estimating battery degradation of lithium ions, comprising the steps of:
obtaining the external characteristic change of the lithium ion battery through a Thevenin equivalent model, and modeling the external characteristic;
identifying parameters of the external characteristic model, obtaining an identified voltage discrete mathematical model through discretization, and constructing the mathematical model in a simulink environment; the mathematical model is based on data fitting of multiple groups of identification parameters to obtain an equation and a curve of each parameter changing along with time; the parameter comprises an open circuit voltage value;
according to the mathematical model, obtaining voltage attenuation rates in different charge state intervals by differentiating different open-circuit voltage values with corresponding actual nominal voltage values;
and estimating and obtaining the attenuation of the battery according to the voltage attenuation rate.
The further improvement of the scheme is as follows:
the step of calculating the voltage decay rate in different state of charge intervals by differencing different open circuit voltage values with corresponding actual nominal voltage values according to the mathematical model comprises:
calculating voltage attenuation rate according to the mathematical model and by using different open-circuit voltage values and corresponding actual nominal voltage values through a calculation formula; the calculation formula is as follows:
θx＝(Ex-E0)/E0*100％
wherein: thetaxRepresenting the voltage attenuation rate obtained by current calculation; ex represents the current open circuit voltage value; e0Representing the actual nominal voltage.
In the foregoing solution, preferably, the step of obtaining the change in the external characteristics of the lithium ion battery through the thevenin equivalent model includes:
obtaining the external characteristic change of the lithium ion battery through a Thevenin equivalent model terminal voltage calculation formula; wherein the end voltage calculation formula is as follows:
U＝E-I*R0-Uc*e-1/τ，τ＝R1*C
wherein: e is an ideal voltage source and represents the open-circuit voltage of the battery; u is terminal voltage; r0Representing the internal resistance of the battery; r1Resistance in first order RC; c is the polarization capacitance in the first order RC; i is the current flowing through the model.
In the foregoing solution, preferably, the step of identifying the parameters of the external characteristic model further includes:
and obtaining a battery capacity interval according to the battery charge state and the open-circuit voltage.
In the foregoing solution, preferably, after the step of obtaining the attenuation of the battery according to the voltage attenuation rate estimation, the method further includes:
and storing corresponding data values of electric quantity, voltage and voltage attenuation rate in a preset area according to the charging and discharging process of the battery, and comparing the corresponding data stored in the preset area with corresponding error data when the estimated battery attenuation rate has an error.
According to the scheme, the lithium ion battery attenuation estimation method obtains the external characteristic change of the lithium ion battery through the Thevenin equivalent model, identifies the parameters of the external characteristic model, constructs a mathematical model about the open-circuit voltage, obtains the voltage attenuation rates in different charge state intervals through calculation, estimates the attenuation rate of the battery and enables the estimated battery attenuation rate to be more accurate.
Drawings
Fig. 1 is a schematic flow chart of a method for estimating battery degradation of lithium ions according to an embodiment of the present invention.
Detailed Description
The technical solution of the present invention is further described with reference to the accompanying drawings and specific embodiments.
The method of the invention is first described in the following as a particularly advantageous embodiment. The estimation method of the embodiment of the invention is realized on the basis of 32-bit battery management system hardware.
As shown in fig. 1, considering that the service life of a lithium ion battery is generally related to electrode materials, charge/discharge rate, discharge depth, discharge interval, use environment temperature, and other factors, the process of the embodiment of the present invention first finds out the influence of the SOC (state of charge) interval on the capacity fading of the battery by studying: the battery capacity in the high SOC interval decays faster than in the low SOC interval. The decay rate of the battery in the discharge region of 1.0-0.5 is about one time faster than that of the battery in the discharge region of 0.5-0.2, and about two times faster than that of the battery in the discharge region of 0.2-0. Therefore, in the subsequent strategy development, the SOC value is used as a prejudgment condition, the voltage value change in different SOC intervals is analyzed, and the attenuation rate is calculated by subtracting the actual nominal voltage value.
θx＝(Ex-E0)/E0*100％
Wherein: thetaxRepresenting the voltage attenuation rate obtained by current calculation; exRepresenting a current open circuit voltage value; e0Representing the actual nominal voltage.
Because the direct current internal resistance of the lithium ion battery is the sum of the internal ionic resistance and the electronic resistance of the battery, the direct current internal resistance determines the power characteristics of the lithium ion battery, and can reflect the aging condition and consistency of the battery, the external characteristic change of the lithium ion battery is obtained through the Thevenin equivalent model, and a foundation is laid for external characteristic modeling in a subsequent algorithm. The terminal voltage formula of the Thevenin equivalent model is as follows:
U＝E-I*R0-Uc*e-1/τ，τ＝R1*C
wherein: the lithium ion battery pack is equivalent to an ideal voltage source, an internal resistance and a first-order RC circuit; e is an ideal voltage source and represents the open-circuit voltage of the battery; u is terminal voltage; r0Representing the internal resistance of the battery; the first-order RC represents the polarization capacitance and resistance of a polar plate in the charging and discharging process of the battery; i represents the current flowing through the model.
Secondly, after understanding the battery attenuation mechanism and the change of the external characteristics of the battery, identifying model parameters in the first step, mainly aiming at identifying the OCV (open circuit voltage E), and obtaining a battery capacity interval through a table look-up of the relationship between the battery charge state and the OCV. And secondly, obtaining a discrete mathematical model of each voltage in the improved model by a discretization means, constructing the mathematical model in a simulink environment, and further analyzing the voltage E attenuation rate of different SOC intervals through the model. The mathematical model is mainly built on the basis of obtaining an equation and a curve of each parameter changing along with time by performing data fitting on a plurality of groups of identification parameters.
Note: the model realizes that the lithium ion battery of a related platform, such as a new type battery of a new vehicle type, needs to be modeled again according to the two steps.
And finally, according to the charging and discharging process of the battery, dividing a designated area to store corresponding data values, including related data such as open-circuit voltage values and voltage attenuation rates calculated each time, and estimating the attenuation rate of the battery by analyzing the voltage E attenuation rates of different SOC intervals for multiple times according to actual conditions on the basis of a mathematical model.
The main purpose is to store the key data in the calculation process, so that the subsequent direct reference can be conveniently compared with the attenuation value calculated at the current time, and if a large error occurs, whether an abnormal phenomenon occurs needs to be judged. Besides, the program space utilization rate can be well realized through region division.
According to the scheme, the lithium ion battery attenuation estimation method obtains the external characteristic change of the lithium ion battery through the Thevenin equivalent model, identifies the parameters of the external characteristic model, constructs a mathematical model about the open-circuit voltage, obtains the voltage attenuation rates in different charge state intervals through calculation, estimates the attenuation rate of the battery and enables the estimated battery attenuation rate to be more accurate.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.
Claims (5)
1. A method for estimating battery degradation of lithium ions, comprising the steps of:
obtaining the external characteristic change of the lithium ion battery through a Thevenin equivalent model, and modeling the external characteristic;
identifying parameters of the external characteristic model, obtaining an identified voltage discrete mathematical model through discretization, and constructing the mathematical model in a simulink environment; the mathematical model is based on data fitting of multiple groups of identification parameters to obtain an equation and a curve of each parameter changing along with time; the parameter comprises an open circuit voltage value;
according to the mathematical model, obtaining voltage attenuation rates in different charge state intervals by differentiating different open-circuit voltage values with corresponding actual nominal voltage values;
and estimating and obtaining the attenuation of the battery according to the voltage attenuation rate.
2. The method of claim 1, wherein the step of calculating voltage decay rates within different state-of-charge intervals by differencing different open circuit voltage values with corresponding actual nominal voltage values according to the mathematical model comprises:
calculating voltage attenuation rate according to the mathematical model and by using different open-circuit voltage values and corresponding actual nominal voltage values through a calculation formula; the calculation formula is as follows:
θx＝(Ex-E0)/E0*100％
wherein: thetaxRepresenting the voltage attenuation rate obtained by current calculation; ex represents the current open circuit voltage value; e0Representing the actual nominal voltage.
3. The method according to claim 1, wherein the step of obtaining the change in external characteristics of the lithium ion battery through the Thevenin equivalent model comprises:
obtaining the external characteristic change of the lithium ion battery through a Thevenin equivalent model terminal voltage calculation formula; the terminal voltage calculation formula is as follows:
U＝E-I*R0-Uc*e-1/τ，τ＝R1*C
wherein: e is an ideal voltage source and represents the open-circuit voltage of the battery; u is terminal voltage; r0Representing the internal resistance of the battery; r1Resistance in first order RC; c is the polarization capacitance in the first order RC; i is the current flowing through the model.
4. The method of claim 1, wherein the step of identifying parameters of the external characteristic model is preceded by the step of:
and obtaining a battery capacity interval according to the battery charge state and the open-circuit voltage.
5. The method of claim 1, wherein the step of obtaining the battery decay based on the voltage decay rate estimate further comprises:
and storing corresponding data values of electric quantity, voltage and voltage attenuation rate in a preset area according to the charging and discharging process of the battery, and comparing the corresponding data stored in the preset area with corresponding error data when the estimated battery attenuation rate has an error.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN111929596A (en) * | 2020-07-31 | 2020-11-13 | 蜂巢能源科技有限公司 | Method and device for acquiring battery capacity, storage medium and electronic equipment |
| CN112130087A (en) * | 2020-09-24 | 2020-12-25 | 上海空间电源研究所 | Method for estimating health state of lithium ion storage battery |
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