Battery SOC Estimation via OCV and Current Accumulation
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Solution Overview
Problem
Existing methods for determining the state of charge (SOC) of secondary batteries, particularly those using open-circuit-voltage-to-charging-condition characteristics, may not provide accurate results due to battery degradation, leading to errors in capacity calculations.
Innovation Solution
A secondary battery state of charge determination apparatus that measures open circuit voltages, accumulates charge or discharge currents, and stores relationships between capacity decreases and OCV-SOC characteristics, allowing for accurate SOC determination by estimating battery capacity decrease and specifying appropriate OCV-SOC characteristics based on degradation levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the SOC is determined simply based on the OCV using the OCV-SOC characteristics, then the measurement method is simple, but the measurement precision deteriorates because accurate SOC cannot be obtained in some cases
Solution Approach 1:
The invention changes the parameters used for SOC determination from only OCV-based methods to a combined approach using both OCV and accumulated current. By introducing current accumulation as an additional parameter and combining it with OCV measurements, the system achieves more accurate SOC determination while maintaining operational simplicity through automated calculation.
2Device complexity
If the initial total capacity is used as the denominator in SOC calculation, then the calculation is simple, but the measurement precision deteriorates because the calculated SOC includes errors when battery capacity decreases due to degradation
Solution Approach 1:
The invention implements a feedback mechanism where the system continuously monitors battery capacity degradation and adjusts the total capacity value used in SOC calculations accordingly. By feeding back the actual capacity information and using it to update the denominator in SOC calculations, the system maintains high accuracy even as the battery degrades over time.
Solution Approach 2:
The system performs preliminary measurements to determine the actual battery capacity before using it in SOC calculations. By预先 obtaining accurate capacity information through measurement rather than relying on initial factory values, the system prepares the correct parameters in advance for accurate SOC computation throughout the battery's lifecycle.
3Device complexity
If the OCV-SOC characteristics are assumed not to change due to battery degradation, then the measurement method is simple, but the reliability deteriorates because this assumption may not hold true for all batteries
Solution Approach 1:
The invention transitions from a static assumption that OCV-SOC characteristics remain unchanged to a dynamic approach that adapts to actual battery conditions. By continuously measuring capacity degradation and adjusting the SOC determination based on actual battery state, the system maintains reliability even as battery characteristics change over time due to degradation.
Data Source
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AI summary
A technology described herein is for accurately determining the SOC of a secondary battery. An open-circuit-voltage-to-state-of-charge (OCV-SOC) characteristic has a capacity decrease estimation OCV region in which a relationship between the OCV and the SOC is assumed not to change due to degradation of the secondary battery 1a since a reference time point. Charge currents or discharge currents in the capacity decrease estimation OCV region are accumulated in a process in which the secondary battery SOC changes among OCVs. From the accumulation, an accumulated current is obtained. A secondary battery capacity decrease is estimated based on the accumulated current. An OCV-SOC characteristic is specified based on the estimated secondary battery capacity decrease and a predetermined relationship between the battery capacity decrease of the secondary battery since the reference time point and the OCV-SOC characteristic. A secondary battery SOC is determined based on the OCV and the specified OCV-SOC characteristic.