Battery Cell SOC Estimation Using Model Validation and Charge Integration
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Solution Overview
Problem
Existing methods for determining the state of charge (SOC) of battery cells, particularly in electric and hybrid transportation vehicles, face challenges in accuracy and reliability due to measurement errors and fluctuations, which can lead to invalid SOC estimates.
Innovation Solution
A method and apparatus that measure voltage and current across a battery cell to estimate parameters using a second-order equivalent circuit model, with online parameter identification via a variable-forgetting-factor recursive least-squares method, and validate SOC estimates using a predefined lookup table or characteristic curve, incorporating charge integration as a fallback for increased accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If model-based SOC estimation is used, then response speed is improved, but measurement precision deteriorates due to measurement errors and fluctuations
Solution Approach 1:
The patent combines model-based SOC estimation with charge integration-based SOC determination into a hybrid system. The model-based estimator provides fast response, while the charge integration method provides accurate reference values for validation and correction, merging the advantages of both approaches to achieve both speed and precision.
Solution Approach 2:
The patent implements a feedback mechanism where the charge integration-based SOC determination serves as a reference to validate and correct the model-based SOC estimation. The system continuously compares the model-based estimate with the charge integration reference and uses the checking criteria to provide feedback for correction when discrepancies are detected.
2Measurement precision
If charge integration is used for SOC determination, then measurement precision is improved, but loss of time increases due to integration over time
Solution Approach 1:
The patent uses charge integration not continuously but partially - specifically when validation of the model-based estimate is required or when checking criteria are not met. This partial application of charge integration maintains accuracy while minimizing time loss by avoiding continuous integration calculations.
Solution Approach 2:
The system performs charge integration in advance to establish accurate reference SOC values and capacity information that can be stored and used for future validations. This preliminary action allows the system to have accurate reference data ready without performing time-consuming integration calculations in real-time operation.
3Reliability
If validation with checking criteria is implemented, then reliability is improved, but device complexity increases
Solution Approach 1:
The patent implements validation by monitoring changes in SOC values and comparing them against predefined checking criteria (maximum change thresholds). This parameter-based validation approach provides reliable error detection without requiring complex additional hardware or sophisticated algorithms, maintaining simplicity while improving reliability.
Data Source
AI summary
A method for providing a state of charge of a battery cell, measuring a voltage and a current across the battery cell that are the basis for estimating parameters of a battery cell model, using the estimated parameters and the battery cell model as a basis for estimating an open-circuit voltage of the battery cell which is used as a basis for determining a first state of charge of the battery cell by using a predefined lookup table and/or a predefined characteristic curve, determining a second state of charge by charge integration over time, the determined first state of charge is checked based on at least one checking criterion, and the determined first state of charge is the basis for providing the state of charge of the battery cell, and the determined second state of charge is the basis for providing the state of charge.