Battery SOC SOH Estimation Using Temperature-Compensated OCV Curves
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Solution Overview
Problem
Accurate state-of-charge (SOC) and state-of-health (SOH) estimation in battery packs is challenging due to variations in charge and discharge temperature, self-discharge rates, and environmental factors, leading to reduced battery service life and difficulty in characterizing battery health.
Innovation Solution
The method involves determining the SOC value using a relational expression between open circuit voltage, resting time, and battery temperature, and subsequently calculating the SOH value based on actual charge capacity and maximum charge capacity at specific temperatures, employing linear and moving average filtering techniques to ensure precise characterization of battery health.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional SOC estimation methods are used, then the estimation process is simple, but the accuracy of SOC and SOH estimation deteriorates due to temperature variations and self-discharge rates
Solution Approach 1:
The patent applies parameter changes by incorporating temperature as a variable parameter in the OCV-SOC relationship. Instead of using a fixed OCV-SOC curve, the method dynamically adjusts the curve based on measured battery temperature, selecting from multiple temperature-specific OCV-SOC curves. This resolves the contradiction by improving estimation accuracy through temperature compensation while maintaining reasonable system complexity through pre-established curve sets.
Solution Approach 2:
The patent implements dynamics by transitioning from static SOC estimation to a dynamic approach that accounts for time-dependent self-discharge. The method measures open circuit voltage at multiple time points after charging, calculates self-discharge rates, and dynamically adjusts SOC estimation based on the measured self-discharge characteristics. This dynamic approach improves accuracy by adapting to real-time battery behavior while managing complexity through systematic measurement protocols.
2Measurement precision
If multiple measurement parameters are used to improve estimation accuracy, then SOC and SOH estimation accuracy improves, but the measurement and calculation complexity increases
Solution Approach 1:
The patent applies preliminary action by pre-establishing multiple OCV-SOC correspondence relationships for different temperatures before actual SOC estimation. These pre-calibrated curves are stored in the system, eliminating the need for real-time complex calculations. During operation, the system only needs to measure temperature and select the appropriate pre-established curve, significantly reducing measurement and calculation difficulty while maintaining high estimation accuracy.
Solution Approach 2:
The patent segments the OCV-SOC relationship into multiple temperature-specific curves rather than using a single universal curve. By dividing the estimation problem into temperature-specific segments, the system simplifies the measurement process - each segment has its own calibrated characteristics that can be independently applied. This segmentation reduces the difficulty of detecting and measuring by allowing the system to focus on one temperature condition at a time.
3Measurement precision
If self-discharge compensation is implemented, then SOC estimation accuracy improves, but the charging time and measurement requirements increase
Solution Approach 1:
The patent implements continuity of useful action by performing self-discharge measurements during the natural resting period after charging, rather than requiring separate dedicated measurement time. The system continuously monitors open circuit voltage at multiple time points (e.g., 10 minutes, 30 minutes, 1 hour) as the battery naturally stabilizes, transforming the idle resting time into productive measurement opportunity. This approach improves SOC estimation accuracy through self-discharge compensation without adding extra charging time.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for accurate estimation of SOC and SOH, enabling effective battery management, extending battery life, and improving the characterization of battery attenuation, thus enhancing the reliability and performance of battery packs.
Implementation Method 1
a current resting time, a current battery temperature, and a current measured open circuit voltage corresponding to a current initial power-on time of the battery pack are obtained
Data Source
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AI summary
The disclosure provides state-of-charge (SOC) and state-of-health (SOH) estimation methods of a battery pack. The SOC estimation method of the battery pack includes the following steps. First, a current resting time, a current battery temperature, and a current measured open circuit voltage corresponding to a current initial power-on time of the battery pack are obtained. Next, an SOC value corresponding to the current initial power-on time is determined according to the obtained current resting time, current battery temperature, current measured open circuit voltage, and a relational expression between an open circuit voltage, a resting time, a battery temperature, and an SOC value at predetermined different battery temperatures, so that the battery pack can be characterized according to the obtained SOC value.