Battery State of Charge Estimation Using Full Charge Capacity Correction
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Solution Overview
Problem
Existing methods for estimating the state of charge (SOC) of secondary batteries, such as current integration, become inaccurate as the charge cycle count increases, leading to rapid SOC drops near the end of discharge, causing users to underestimate remaining battery life and fail to manage full discharge effectively.
Innovation Solution
A method that calculates the full charge capacity (FCC) using voltage and current measurements, estimates the self-discharge rate, and determines the capacity deterioration rate to correct the SOC estimation, ensuring accurate SOC information even near the end of discharge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If current integration method is used to estimate SOC, then initial SOC estimation accuracy is improved, but SOC estimation accuracy deteriorates as charge cycle count increases due to SOC drop phenomenon
Solution Approach 1:
The patent implements a feedback mechanism where the estimated SOC is continuously monitored and compared against actual battery behavior. When SOC drop phenomenon is detected (discrepancy between integrated current-based SOC and actual voltage-based SOC), the system adjusts the full charge capacity value accordingly. This feedback loop ensures that SOC estimation remains accurate over multiple charge cycles by continuously correcting for capacity deterioration and self-discharge effects.
Solution Approach 2:
The patent dynamically changes the full charge capacity parameter based on charge cycle count and detected SOC drop. Instead of using a fixed full charge capacity value, the system updates this parameter to reflect actual battery degradation. By adjusting the full charge capacity parameter downward as the battery ages and experiences capacity loss, the SOC estimation formula (SOC = (integrated current) / (full charge capacity)) maintains accuracy even as the battery's actual capacity decreases over time.
2Device complexity
If full charge capacity is not corrected for self-discharge and capacity deterioration, then calculation complexity is reduced, but SOC estimation accuracy near end of discharge deteriorates
Solution Approach 1:
The patent performs preliminary measurements and calculations during the charging phase to prepare for accurate SOC estimation during discharge. Specifically, the system measures and records the full charge capacity, self-discharge rate, and capacity deterioration rate while the battery is being charged or at rest. These pre-determined parameters are then used in the SOC calculation formula during discharge, eliminating the need for complex real-time adjustments and simplifying the discharge-phase calculations while maintaining accuracy.
3Ease of operation
If SOC estimation does not account for capacity deterioration, then usability information provided to user is simplified, but user awareness of remaining battery life is reduced
Solution Approach 1:
The system provides feedback to the user about actual battery status by continuously monitoring SOC and comparing it against the full charge capacity that accounts for deterioration. This feedback mechanism allows the device to display accurate remaining battery life information without requiring complex user-facing calculations. The simplified user interface continues to show percentage-based SOC, but the underlying calculations incorporate capacity deterioration corrections, ensuring users receive accurate information about remaining battery life while maintaining ease of use.
Data Source
AI summary
Disclosed is a method for estimating a state of charge (SOC) of a secondary battery using a full charge capacity (FCC) of the battery, the method including (S1) measuring voltage and current of the battery, (S2) calculating the FCC using a voltage change and a current integral of the battery during a specific time, (S3) estimating a time remaining until the battery is fully discharged using the calculated FCC and the measured voltage and current to calculate a self-discharge rate, (S4) calculating a capacity deterioration rate of each charge cycle of the battery, and (S5) applying the calculated self-discharge rate and the calculated capacity deterioration rate to estimate the SOC of the battery.