CN110646741A - A kind of parameter acquisition method of lithium-ion battery equivalent circuit model - Google Patents

Abstract

The invention discloses a parameter acquisition method of an equivalent circuit model of a lithium ion battery, which adopts an improved HPPC method to acquire parameters of the equivalent circuit, can acquire all the parameters under one test, can adjust the test time according to objective conditions, adjust the complexity of the model according to the computing power of a simulation platform and select different parameter application methods according to the application scene of a battery cell: such as a data table or a functional expression. The parameter acquisition method of the lithium ion battery equivalent circuit model has the advantages of high test speed, accurate test result, customizability and the like, can be applied to the aspects of simulation, battery management and the like of electric vehicles, micro-grids and energy storage systems, and has wide application prospect.

Description

A kind of parameter acquisition method of lithium-ion battery equivalent circuit model

technical field

The invention relates to a method for obtaining parameters of a lithium ion battery, in particular to a method for obtaining parameters of an equivalent circuit model of a lithium ion battery, and belongs to the technical field of lithium ion batteries.

Background technique

Lithium-ion batteries, as the current energy storage technology with the highest energy density, are widely used in many fields such as mobile electronic devices, electric vehicles, and energy storage devices. The vigorous development of the application market and the increasing demand have also put forward higher requirements for many technical indicators such as energy density, capacity density, and power density of lithium-ion batteries.

The modeling of lithium-ion batteries plays a vital role in the simulation of lithium batteries, and is widely used in the research process of electric vehicles, microgrids, and optical storage systems. Accurate battery models are also the basis for methods such as battery state of charge estimation, state of health estimation, and remaining life estimation.

Commonly used lithium-ion battery models include electrochemical models and equivalent circuit models. The equivalent circuit model uses circuit components such as resistors and capacitors to simulate the state of the battery, and expresses the internal changes of the battery through the characteristics of external components. It has the advantages of intuitive visualization, few parameters, and easy simulation. In order to obtain various parameters in the equivalent circuit model, a series of test analysis and data processing are required for the battery. For this reason, various methods for obtaining parameters of equivalent circuits have been designed. For example, in the Chinese invention patent application document with the application number of 2017113765734, titled "An Equivalent Circuit-Based Lithium-ion Battery SOC Estimation Algorithm", a power battery state of charge of a lithium-ion battery based on an equivalent circuit is disclosed (SOC) estimation method, however, this method can only estimate one parameter of the battery, so the scope of application is limited. For this reason, it is necessary to invent a parameter acquisition method to acquire as much parameter information as possible in one test.

SUMMARY OF THE INVENTION

In order to solve the above technical problems, the present invention provides a method for obtaining parameters of an equivalent circuit model of a lithium ion battery, which can obtain a number of parameters of the battery in one test process.

For this reason, the present invention adopts following technical scheme:

A method for obtaining parameters of an equivalent circuit model of a lithium-ion battery, comprising the following steps:

S1: Connect the single cell into the cell test cabinet, and set multiple test temperatures;

S2: Carry out the constant current charge/discharge cycle N times under the standard working condition of the cell, obtain the charge/discharge curve of the cell, and analyze the rate of change of the battery voltage in each SOC segment, where N is an integer ≥ 2;

S3: Carry out an improved HPPC test, specifically: SOC segmentation is performed according to the charge/discharge curve in step S2, and the frequency of pulse charge/discharge in each segment is adjusted. 2.5% SOC for one pulse; in the stage of slow battery voltage change, one pulse for every 3-5% SOC; 1-3min rest after each pulse charge/discharge;

S4: Adjust the state of charge: According to the pulse charge/discharge situation in step S3, carry out constant current charge/discharge to adjust the state of charge, the amplitude is 1.5-5% SOC, and after the charge/discharge time expires, a short-term static charge is performed. set, such as 1-3min, to obtain the open circuit voltage corresponding to the state of charge;

S5: Process charge/discharge data, and obtain equivalent circuit parameters: according to the open-circuit voltage data obtained in step S4, and the resistance and capacitance data obtained in step S3; establish an equivalent circuit model, the equivalent circuit consists of an ideal controlled voltage The source, an ohmic resistor R ₀ and multiple RC units are connected in series to simulate a battery; each RC unit consists of a parallel polarized resistor and polarized capacitor; as shown in Figure 1;

S6: Fitting the charge/discharge curve piecewise. During the charge/discharge process, the function relationship between the voltage of the battery terminal and the time is:

After charging/discharging, the function relationship between the voltage of the battery terminal and the time is as follows:

Where: U is the battery terminal voltage, U _oc is the open-circuit voltage, R ₀ is the ohmic resistance, R _i is the polarization resistance, C _i is the polarization capacitance, and τ _i is the time constant (i=1, 2, 3);

S7: According to different temperatures and states of charge, corresponding equivalent circuit parameters are selected to perform simulation using the above equivalent circuit model, and data sets or fitting SOC-X curve functions are used according to different operating platforms.

Further, in step S5, the equivalent circuit model includes a first-order Thevenin model, a second-order RC model, and a third-order RC model.

Further, in step S7, the curve fitting method uses the least squares method.

Further, in step S5, the open-circuit voltage is represented by an ideal controlled voltage source in the equivalent circuit model, and each parameter changes with the change of the battery state of charge and the charge/discharge state.

Compared with the prior art, the present invention has the following beneficial effects:

The invention adopts the improved HPPC method to obtain the parameters of the equivalent circuit, all parameters can be obtained in one test, the test time can be adjusted according to the objective conditions, the model complexity can be adjusted according to the computing capability of the simulation platform, and the selection can be made according to the application scenario of the battery cell. Define different parameter application methods: such as data table or functional. The method for obtaining parameters of an equivalent circuit model of a lithium ion battery provided by the present invention has the advantages of fast test speed, accurate test results, customizability and the like, and can be applied to the simulation and battery management of electric vehicles, microgrids, energy storage systems, etc. , the application prospect is very broad.

Description of drawings

FIG. 1 is a circuit structure of an equivalent circuit in the present invention.

Detailed ways

The method for obtaining parameters of an equivalent circuit model of a lithium ion battery provided by the present invention includes the following steps:

S1: Connect the single cell into the cell test cabinet, and set multiple test temperatures. For example, in this embodiment, set -10°C, 0°C, 10°C, 25°C, 30°C, 40°C, and 45°C Wait for the test temperature, and test at different set temperatures;

S2: Perform constant current charge-discharge under the standard operating conditions of the cell, cycle 3 times, obtain the charge/discharge curve of the cell, and analyze the rate of change of the battery voltage in each SOC segment;

S3: Carry out an improved HPPC test, specifically: SOC segmentation is performed according to the charge/discharge curve in step S2, and the frequency of pulse charge/discharge in each segment is adjusted. 2.5% SOC for one pulse; in the stage where the battery voltage changes slowly, one pulse for every 3-5% SOC; after each pulse charge/discharge, a short period of standing, such as standing for 1-3 minutes;

S4: Adjust the state of charge: According to the pulse charge/discharge situation in step S3, perform constant current charge/discharge to adjust the state of charge, the amplitude is 1.5-5% SOC, and the charge/discharge time is over for a short period of time. standing for 1-3 minutes, to obtain the open circuit voltage corresponding to the state of charge;

S5: Process the charge/discharge data, and obtain the equivalent circuit parameters: according to the open-circuit voltage data obtained after standing in step S4, and by fitting the obtained "time-voltage" curve after the pulse-resting in step S3, and Obtain the resistance and capacitance data of each pulse process according to the constant term value of the obtained functional formula; establish an equivalent circuit model, which includes an ideal controlled voltage source in series, an ohmic resistance R ₀ and multiple RC units , each RC unit is composed of parallel polarization resistance and polarization capacitance; as shown in Figure 1; wherein, the equivalent circuit model mainly includes first-order Thevenin model, second-order RC model, third-order RC model and other models; In the equivalent circuit model, an ideal controlled voltage source is used to represent the open-circuit voltage, and each parameter changes with the battery state of charge and charge/discharge state.

S6: The function fitting performed on the "time-voltage" curve obtained from the charge/discharge test is piecewise fitting, that is, fitting is performed on each pulse-resting stage separately. During the charging/discharging process, the function relationship of the battery terminal voltage with time is:

After charging/discharging, the function relationship between the voltage of the battery terminal and the time is as follows:

Where: U is the battery terminal voltage, U _oc is the open circuit voltage, R ₀ is the ohmic resistance, R _i is the polarization resistance, C _i is the polarization capacitance, τ _i =R _i C _i is the time constant (i=1,2 , 3); the "time-voltage" curve is the curve in which the independent variable is t and the dependent variable is U.

S7: The properties of the battery, that is, the parameters of the equivalent circuit, are constantly changing with the battery temperature and the state of charge of the battery. During the application of the equivalent circuit model, the corresponding equivalent circuit needs to be selected according to different temperatures and states of charge parameters for model simulation. At the same time, according to the different operating platforms, it is necessary to select the data set or the SOC-X curve function formula obtained by fitting according to the computing power and data storage capacity of the platform, and apply the mathematical model; among them, the curve The fitting method uses the least squares method, and most of the curve functions obtained from fitting are polynomial functions.

Claims (4)

1. a parameter acquisition method of an equivalent circuit model of a lithium ion battery, is characterized in that: comprise the steps: S1: Connect the single cell into the cell test cabinet, and set multiple test temperatures; S2: Carry out the constant current charge/discharge cycle N times under the standard working condition of the cell, obtain the charge/discharge curve of the cell, and analyze the rate of change of the battery voltage in each SOC segment, where N is an integer ≥ 2; S3: Carry out an improved HPPC test, specifically: SOC segmentation is performed according to the charge/discharge curve in step S2, and the frequency of pulse charge/discharge in each segment is adjusted. 2.5% SOC for one pulse; in the stage of slow battery voltage change, one pulse for every 3-5% SOC; 1-3min rest after each pulse charge/discharge; S4: Adjust the state of charge: According to the pulse charge/discharge situation in step S3, perform constant current charge/discharge to adjust the state of charge, the amplitude is 1.5-5% SOC, and the charge/discharge time expires to stand for obtaining the open circuit voltage corresponding to the state of charge; S5: Process the charge/discharge data, and obtain equivalent circuit parameters: according to the open-circuit voltage data obtained in step S4, and the resistance and capacitance data obtained in step S3; establish an equivalent circuit model, and the equivalent circuit includes ohmic resistors connected in series R ₀ and two RC units, each RC unit is composed of parallel polarization resistance and polarization capacitance; as shown in Figure 1; S6: Fitting the charge/discharge curve piecewise. During the charge/discharge process, the function relationship between the voltage of the battery terminal and the time is: After charging/discharging, the function relationship between the voltage of the battery terminal and the time is as follows:

Where: U is the battery terminal voltage, U _oc is the open-circuit voltage, R ₀ is the ohmic resistance, R _i is the polarization resistance, C _i is the polarization capacitance, and τ _i is the time constant (i=1, 2, 3); S7: According to different temperatures and states of charge, corresponding equivalent circuit parameters are selected to perform simulation using the above equivalent circuit model, and data sets or fitting SOC-X curve functions are used according to different operating platforms. 2. The method for obtaining parameters of an equivalent circuit model of a lithium-ion battery according to claim 1, wherein in step S5, the equivalent circuit model comprises a first-order Thevenin model, a second-order RC model, and a third-order RC model. Model. 3 . The method for obtaining parameters of an equivalent circuit model of a lithium ion battery according to claim 1 , wherein in step S7 , the curve fitting method uses the least squares method. 4 . 4. The method for obtaining parameters of an equivalent circuit model of a lithium-ion battery according to claim 1, wherein in step S5, an ideal controlled voltage source is used to represent the open-circuit voltage in the equivalent circuit model, and each of the All parameters vary with the battery state of charge and charge/discharge state.