Battery Capacity Estimation Using Voltage Knee Point Detection
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Solution Overview
Problem
Existing battery capacity estimation methods, particularly for lithium-ion batteries, suffer from inaccuracies due to errors in State of Charge (SOC) estimation, leading to ineffective battery capacity estimation, especially for lithium iron phosphate batteries, and are labor-intensive and time-consuming in laboratory settings.
Innovation Solution
A method involving the acquisition of a voltage-capacity curve during charging, differentiation to obtain a differential-capacity curve, identification of wave crests, calculation of a determination index, and determination of a voltage knee point to estimate battery capacity without requiring full discharge, using a pre-calibrated reference capacity value.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If full charge and discharge testing is performed to calculate battery capacity, then capacity estimation accuracy can be improved, but testing time and labor costs increase significantly
Solution Approach 1:
The patent performs preliminary differentiation and wave crest identification on the voltage-capacity curve during the charging process to locate the voltage knee point in advance. This preliminary analysis enables capacity estimation without requiring complete charge-discharge cycles, significantly reducing testing time while maintaining accuracy through pre-calibrated reference capacity values.
2Device complexity
If SOC-based capacity calculation methods are used, then the calculation process is simplified, but estimation accuracy deteriorates due to cumulative SOC errors
Solution Approach 1:
The patent extracts the voltage knee point information from the voltage-capacity curve through differentiation and wave crest analysis, obtaining capacity estimation data independent of SOC calculations. This extraction method removes the dependency on cumulative SOC errors while maintaining relatively simple calculation procedures through direct curve analysis.
3Measurement precision
If laboratory benchmarking methods are adopted for capacity testing, then measurement accuracy can be improved, but the method becomes too dogmatic and cannot estimate actual battery capacity under practical conditions
Solution Approach 1:
The patent enables the battery management system to perform self-diagnosis and capacity estimation using real-time voltage-capacity data from actual charging processes. The method uses pre-calibrated reference values combined with real-time curve analysis, allowing the system to adapt to practical operating conditions while maintaining accuracy comparable to laboratory methods.
4Measurement precision
If the battery is discharged to estimate capacity, then accurate baseline measurement can be obtained, but user convenience deteriorates as users prefer not to discharge their batteries
Solution Approach 1:
The patent performs preliminary differentiation and wave crest identification on the voltage-capacity curve during the charging process to locate the voltage knee point in advance. This preliminary analysis enables capacity estimation without requiring complete charge-discharge cycles, significantly reducing testing time while maintaining accuracy through pre-calibrated reference capacity values.
Data Source
AI summary
A method of obtaining battery capacity, includes: acquiring a voltage-capacity curve of a battery; performing differentiation on the voltage-capacity curve to obtain a voltage differential-capacity curve; identifying wave crests in the voltage differential-capacity curve; calculating heights and widths between each wave crest and the adjacent wave trough on the left and the right; calculating a determination index p according to the heights and the widths; determining a voltage knee point in the voltage-capacity curve according to a wave crest with a minimum determination index; acquiring a reference capacity value corresponding to the voltage knee point in the voltage-capacity curve; after the battery reaches a full-charge state, acquiring charging electric energy of the battery for charging from the voltage knee point to the full-charge state; and obtaining a capacity of the battery based on a sum of the reference capacity value and the charging electric energy.