Battery Equivalent Circuit Model Parameter Estimation

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Solution Overview

Problem

Existing battery equivalent circuit models struggle to accurately simulate nonlinear voltage characteristics, leading to lower accuracy in state of charge (SOC) estimation, especially when nonlinear characteristics dominate.

Innovation Solution

A method to extract the linear change range from a pulse discharge profile and estimate parameters of a battery equivalent circuit model using a least square algorithm, based on data from the extracted linear range, including resistance values of resistors and capacitance, which are then associated with specific temperature, SOC, and constant current conditions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If the battery equivalent circuit model is used to simulate battery voltage characteristics, then the linear voltage characteristics can be simulated accurately, but the nonlinear voltage characteristics cannot be simulated accurately

Engineering Contradiction:

Improveaccuracy of SOC estimationVSAvoidability to simulate nonlinear voltage characteristics

Core Design Contradiction:

Measurement precisionVSAdaptability or versatility

Solution Approach 1:

The pulse discharge profile is segmented into a linear change range and a nonlinear change range. The linear change range is extracted to estimate the equivalent circuit model parameters, while the nonlinear change range is excluded from this estimation process. This segmentation allows the model to accurately simulate linear characteristics without being compromised by nonlinear characteristics.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The linear change range is extracted from the pulse discharge profile by determining a threshold voltage and selecting terminal voltages between the OCV and the threshold voltage. This extraction isolates the portion of the discharge profile that exhibits linear characteristics, which is then used to estimate the equivalent circuit model parameters.

Inventive Principle:

Principle #2Taking out (Extraction)

2Measurement precision

If the extended Kalman filter is used to improve SOC estimation accuracy, then accuracy improves when linear characteristics dominate, but accuracy decreases when nonlinear characteristics dominate

Engineering Contradiction:

Improveaccuracy of SOC estimationVSAvoidperformance under nonlinear characteristics

Core Design Contradiction:

Measurement precisionVSAdaptability or versatility

Solution Approach 1:

The equivalent circuit model parameters (resistance values of first and second resistors, and capacitance value) are estimated by changing the selection criteria for data points. Instead of using all terminal voltages from the pulse discharge profile, only terminal voltages from the linear change range (between OCV and threshold voltage) are used for parameter estimation.

Inventive Principle:

Principle #35Parameter changes

3Ease of manufacture

If all terminal voltages from pulse discharge profile are used to estimate equivalent circuit model parameters, then the estimation process is simple, but the accuracy is reduced due to inclusion of nonlinear characteristic data

Engineering Contradiction:

Improvesimplicity of parameter estimation processVSAvoidaccuracy of equivalent circuit model parameters

Core Design Contradiction:

Ease of manufactureVSMeasurement precision

Solution Approach 1:

The pulse discharge profile is segmented into linear and nonlinear regions based on voltage characteristics. The linear change range is identified by determining a threshold voltage and extracting terminal voltages between the OCV and this threshold. This segmentation allows selective use of only relevant linear characteristic data for parameter estimation.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The linear change range is extracted from the complete pulse discharge profile by identifying and isolating terminal voltages that exhibit linear characteristics. This extraction removes the nonlinear characteristic data from the estimation process, ensuring that only appropriate data is used for parameter estimation.

Inventive Principle:

Principle #2Taking out (Extraction)

Data Source

PatentEP3627167B1Method, apparatus, and recording medium for estimating parameter of battery equivalent circuit model

Publication Date: 2023.04.26 LG ENERGY SOLUTION LTD

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AI summary

Disclosed is a method and apparatus for estimating parameters of a battery equivalent circuit model. The battery equivalent circuit model includes a first resistor, a second resistor and a capacitor. The method according to an embodiment of the present disclosure includes reading a pulse discharge profile corresponding to a parameter estimation condition from a plurality of pre-stored pulse discharge profiles, wherein the pulse discharge profile includes a first number of terminal voltages sequentially measured from a battery having a specific SOC in a predetermined cycle while the battery is discharged with a specific constant current from an OCV corresponding to the specific SOC to a lower limit of discharge voltage at a specific temperature, extracting a second number of terminal voltages between the OCV and a threshold voltage from the first number of terminal voltages, and estimating a resistance value of the first resistor and a resistance value of the second resistor based on the OCV, the constant current and the second number of terminal voltages.