Battery Module SOC Estimation from Maximum Voltage-Difference Cell
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Solution Overview
Problem
Existing battery systems face challenges in accurately determining the state of charge, leading to potential over-charging or over-discharging, especially due to differences in cell deterioration and characteristics within a battery rack, which can result in errors when using average voltage as a representative value.
Innovation Solution
A method and apparatus that calculate the voltage difference between specific time points for each cell in a battery module, select a representative cell with the maximum voltage difference, and estimate the state of charge using its voltage, allowing for precise SOC estimation and control functions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If average voltage of all cells is used as representative value, then calculation is simple, but state of charge determination accuracy deteriorates due to cell deterioration differences
Solution Approach 1:
The patent applies local quality by selecting a specific cell (the one with maximum voltage difference between charging and discharging states) as the representative cell, rather than using an average of all cells. This localized selection accounts for individual cell characteristics and deterioration patterns, improving SOC determination accuracy while maintaining relatively simple calculation procedures.
2Measurement precision
If representative cell with maximum voltage difference is selected, then state of charge determination accuracy is improved, but calculation complexity increases
Solution Approach 1:
The patent implements preliminary action by pre-calculating and storing the open circuit voltage (OCV) values for each cell during charging periods. When a discharging period occurs, these pre-stored OCV values are immediately available for comparison with actual voltages, eliminating the need for complex real-time calculations and enabling rapid SOC determination with improved accuracy.
3Reliability
If voltage difference calculation is performed for all cells, then accurate representative cell selection is achieved, but computational load increases
Solution Approach 1:
The patent applies the taking out principle by extracting only the necessary information (voltage differences) from each cell during discharging periods and comparing them against pre-stored OCV values. This selective extraction and comparison approach identifies the representative cell with maximum voltage difference without requiring exhaustive analysis of all possible cell combinations, reducing computational energy consumption while maintaining reliable selection accuracy.
Data Source
AI summary
A method for determining a state of charge of a battery system, including calculating a voltage difference between a first voltage detected at a first time point and a second voltage detected at a second time point, for each of a plurality of cells included in a battery module, selecting a representative cell having a maximum voltage difference among the plurality of cells, and estimating a state of charge of the battery module by using a representative cell voltage of the representative cell.