Battery Capacity Estimation Using Voltage Knee Point During Charging
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Solution Overview
Problem
Existing battery capacity estimation methods, particularly for lithium iron phosphate batteries, suffer from inaccuracies due to errors in State of Charge (SOC) estimation, leading to ineffective capacity estimation, especially under severe working conditions and high temperature changes.
Innovation Solution
A method that involves acquiring a voltage-capacity curve in real time during charging, differentiating it to obtain a differential-capacity curve, identifying wave crests, calculating determination indices, and determining 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 battery capacity is estimated by fully charging and discharging the battery or by charging and discharging within a certain SOC range, then the battery capacity can be calculated based on total electric quantity, but the estimation accuracy depends entirely on SOC accuracy and cumulative SOC errors affect battery capacity estimation accuracy
Solution Approach 1:
The patent extracts the battery capacity estimation problem from the SOC estimation dependency by using a different measurement approach. Instead of calculating capacity through SOC changes (which propagates SOC errors), the method directly measures voltage-capacity relationships during charging, extracting capacity information independent of SOC estimation, thereby eliminating the harmful dependency on SOC accuracy
Solution Approach 2:
The patent introduces voltage as an intermediary measurement parameter between charging electric quantity and capacity estimation. By measuring the voltage-capacity curve during charging and using differentiation to find inflection points, the method creates an intermediate measurement path that bypasses SOC estimation, allowing capacity determination without directly relying on SOC accuracy
2Measurement precision
If laboratory benchmarking methods are adopted for battery capacity estimation, then reference capacity data can be obtained, but the method is very time-consuming, labor-intensive, and expensive
Solution Approach 1:
The patent creates a simplified copy of the laboratory benchmarking process that can be executed in real-world conditions. Instead of requiring complete discharge cycles and extensive laboratory testing, the method uses a charging-only protocol with voltage-capacity curve analysis, creating a practical copy of capacity estimation that maintains accuracy while dramatically reducing time and resource requirements
Solution Approach 2:
The patent applies partial action by performing only the necessary charging portion of the capacity estimation process without requiring complete discharge cycles. By using differentiation of the voltage-capacity curve during charging to identify inflection points, the method achieves capacity estimation with partial charging action, reducing the excessive time and labor required by traditional full-cycle benchmarking methods
3Measurement precision
If traditional capacity estimation methods are used, then battery capacity can be calculated, but the method cannot cover all working conditions and is too dogmatic when benchmarking against laboratory data
Solution Approach 1:
The patent applies dynamics by making the capacity estimation method adaptable to different working conditions through real-time voltage-capacity curve analysis. Instead of using fixed laboratory benchmark data, the method dynamically adjusts to actual battery behavior during charging, identifying inflection points that reflect the battery's true capacity characteristics under current conditions, thereby achieving versatility across different working conditions
Data Source
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AI summary
Disclosed are a battery capacity estimation method and apparatus, and a computer storage medium. The method includes: acquiring a voltage-capacity curve of a battery in real time in a battery charging process; performing differentiation on the voltage-capacity curve to obtain a voltage differential-capacity curve; determining a voltage knee point in the voltage-capacity curve according to the voltage differential-capacity curve; acquiring a pre-calibrated reference capacity value corresponding to the voltage knee point; acquiring charging electric quantity of the battery from the voltage knee point to a full-charge state; and obtaining actual capacity of the battery based on a sum of the reference capacity value and the charging electric quantity.