Battery SOC Determination via Analytical Electrochemical Model
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Solution Overview
Problem
Current battery management systems face inaccuracies in determining the charging state and state of power of battery cells due to tolerances in cell capacities and aging, leading to increased costs and limited accuracy, especially in low SOC ranges, which are not economically viable for series production.
Innovation Solution
An analytical solution is developed using a reduced electrochemical model with a Butler-Volmer equation and a Kalman filter, allowing for precise determination of charging states and internal resistance, even at low SOC values, with reduced hardware requirements and improved memory and calculation efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If standard electrochemical models with extended Kalman filter are used for SOC correction, then SOC accuracy is improved, but computation and memory requirements increase significantly
Solution Approach 1:
The patent divides the SOC determination into two distinct methods: an analytical solution for low SOC ranges (0-20%) and equivalent circuit models for other ranges. This segmentation allows the computationally intensive analytical method to be applied only where needed (low SOC), reducing overall computation and memory requirements while maintaining high accuracy in the critical low SOC range.
Solution Approach 2:
The patent transforms the complex electrochemical model into an analytical solution by changing the mathematical parameters and approach. Instead of using numerical integration and extended Kalman filters, the patent derives closed-form analytical expressions for SOC determination in low SOC ranges, significantly reducing computational complexity while maintaining accuracy.
2Measurement precision
If more accurate measuring chips and cell selection are used to improve SOC determination, then measurement precision is improved, but manufacturing costs increase
Solution Approach 1:
The patent changes the mathematical approach from requiring high-precision hardware to using analytical solutions that compensate for measurement inaccuracies through sophisticated calculation methods. The analytical solution for low SOC ranges achieves high accuracy using standard measuring chips by transforming the underlying mathematical model.
Solution Approach 2:
The patent creates a mathematical model (analytical solution) that replicates the behavior of complex electrochemical processes without requiring expensive hardware. The analytical expressions serve as a computational copy of the battery's electrochemical behavior, enabling accurate SOC determination with standard components.
3Productivity
If equivalent circuit models are used for SOC calculation, then computation requirements are reduced, but accuracy in low SOC ranges deteriorates
Solution Approach 1:
The patent segments the SOC range into low SOC (0-20%) and other ranges, applying different methods to each. In the low SOC range where equivalent circuit models fail, the patent uses an analytical solution based on electrochemical principles. In other ranges, the computationally simpler equivalent circuit models are used, achieving both accuracy and efficiency.
4Adaptability or versatility
If the validity range of the analytical solution is extended to higher SOC values, then the application range is improved, but determination accuracy in that range deteriorates
Solution Approach 1:
The patent maintains a clear segmentation between low SOC range (0-20%) where the analytical solution is applied, and other ranges where equivalent circuit models are used. This segmentation ensures that each method is applied within its optimal validity range, preventing accuracy deterioration while maintaining overall system versatility.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution provides high accuracy in charging state and power prediction, extending the validity range and reducing hardware costs, enabling more complex algorithms on existing hardware and improving the battery management unit's performance.
Implementation Method 1
an analytical solution of a function (110), which specifies a connection between the open-circuit voltage and the charging state (121) of the battery cell
Data Source
AI summary
An electronic circuit for determining a charging state of a battery cell of a battery system. The electronic circuit is configured for obtaining a plurality of measured values of an open-circuit voltage of the battery cell with corresponding time values for which the measured values of the open-circuit voltage have been measured. The electronic circuit is further configured for determining a time up until which a charging state corresponding to an end point voltage of the battery cell is reached on the basis of an analytical solution of a function, which specifies a connection between the open-circuit voltage and the charging state of the battery cell. The electronic circuit is further configured for determining the charging state of the battery cell based on a reverse function of the charging-state dependent time.