SOC Estimation Correction for Battery Safety
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Solution Overview
Problem
Existing methods for estimating the remaining amount of a secondary battery, particularly near upper and lower limit values in the SOC management range, suffer from inaccuracies due to errors in current integration and self-discharge, leading to potential excessive charging or discharging.
Innovation Solution
A device and method that includes a first estimation unit for calculating a remaining amount based on charging/discharging current, a second estimation unit based on battery state, and a correction unit that adjusts the first estimation using a correction value calculated from the deviation between the last calculated value and the second estimation value, considering the magnitude and relationship between these values to enhance accuracy and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the correction value is determined such that the estimated SOC based on current integration approaches the estimated SOC based on electromotive voltage, then the estimation accuracy is improved, but the stability near management limit values deteriorates
Solution Approach 1:
The patent applies local quality by differentiating the correction strategy based on the SOC range. When SOC is within a predetermined range from management limit values, a first correction value (smaller magnitude) is applied to maintain stability. When SOC is outside this range, a second correction value (larger magnitude) is applied to improve accuracy. This localized adjustment resolves the contradiction by adapting the correction strength to the specific operational context.
Solution Approach 2:
The patent implements dynamics by making the correction value adaptive rather than fixed. The correction amount dynamically changes based on the current SOC level relative to management limits. This dynamic adjustment allows the system to prioritize stability near limits while maintaining accuracy in intermediate ranges, resolving the contradiction between these two opposing requirements.
2Measurement precision
If the SOC correction parameter is set to be larger in the vicinity of upper and lower limit values to improve estimation accuracy, then the measurement precision is improved, but the risk of excessive charging or discharging increases
Solution Approach 1:
The patent applies preliminary anti-action by preemptively reducing the correction amount when SOC approaches management limit values. This preventive measure counteracts the potential harmful effect of large corrections that could push the estimated SOC beyond safe boundaries. By anticipating the risk of excessive charging/discharging and applying a dampened correction in advance, the system maintains both accuracy and safety.
3Device complexity
If the current integration scheme is used to estimate SOC, then the device complexity is reduced, but the measurement precision deteriorates due to error accumulation and self-discharge effects
Solution Approach 1:
The patent introduces an intermediary correction mechanism that bridges the simple current integration method and the more accurate electromotive voltage method. Instead of directly using complex voltage-based estimation, the system uses voltage information to generate a correction value that adjusts the current integration result. This intermediary approach improves accuracy while maintaining the simplicity of the primary estimation method.
Data Source
AI summary
An SOC-estimation-value-depending gain selection unit multiplies the deviation of an SOC estimation value (last calculated value) relative to an estimated SOC by a correction gain G1 to calculate a correction value. The SOC-estimation-value-depending gain selection unit selects a relatively small correction gain G1 when the SOC estimation value lies in the range in proximity to excessive charging and the SOC estimation value is corrected to a smaller value (toward the SOC control center), and when the SOC estimation value lies in the range in proximity to excessive discharging and the SOC estimation value is corrected to a larger value (toward the SOC control center). Thus, the correction is performed so as to indicate the safe side value for the secondary battery in charge/discharge control when the SOC estimation value is in proximity to excessive charging or excessive discharging.