Battery SOC Estimation Correcting Aging OCV Variations
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Solution Overview
Problem
Existing methods for estimating the state of charge (SOC) of electrochemical battery elements are sensitive to current measurement errors and resistance estimation, and do not account for open circuit voltage (OCV) variations due to aging, leading to inaccurate SOC evaluations.
Innovation Solution
A method that corrects OCV variations linked to aging by using a calibration function to calculate the SOC, involving measurements of voltage and current during a charge or discharge cycle, and determining reference points with specific OCV and SOC values to estimate the overvoltage parameter, thereby updating the calibration function to improve SOC estimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If open circuit voltage measurements are used to estimate state of charge, then the estimation is simple, but the accuracy deteriorates due to aging-related OCV variations
Solution Approach 1:
The method performs preliminary identification of the OCV-SOC characteristic curve during initial battery calibration or manufacturing. This pre-established relationship is stored and used throughout the battery's operational life to correct OCV measurements for aging effects, enabling accurate SOC estimation without requiring real-time complex measurements
Solution Approach 2:
The method changes the parameter approach by transitioning from using fixed OCV-SOC lookup tables to dynamically adjusting the OCV-SOC relationship based on identified aging parameters. The OCV-SOC curve is modified according to measured voltage deviations and capacity fade, adapting the characteristic parameters to reflect the battery's current aged state
2Reliability
If Coulomb counting technique is used to estimate state of charge, then continuous monitoring is achieved, but accuracy deteriorates due to sensitivity to current measurement errors and capacity estimation
Solution Approach 1:
The method implements feedback by continuously comparing the OCV-based SOC estimation with the Coulomb counting result. The voltage deviation from the expected OCV-SOC curve serves as feedback to correct the accumulated errors in Coulomb counting, while the Coulomb counting provides continuous monitoring that complements the periodic OCV measurements
Solution Approach 2:
The method merges two complementary techniques: Coulomb counting provides continuous SOC tracking while OCV measurements provide periodic absolute reference points. By combining these approaches and using the OCV-SOC characteristic to correct Coulomb counting drift, the system achieves both continuous monitoring and high accuracy
3Device complexity
If aging effects are not considered in OCV-SOC relationship, then the calculation is simple, but SOC estimation accuracy deteriorates over time
Solution Approach 1:
The method makes the OCV-SOC relationship dynamic by introducing aging compensation that adapts to the battery's condition over time. The system transitions from a static lookup table to a dynamic model that updates the OCV-SOC curve based on measured voltage deviations and identified capacity fade, allowing the characteristic to evolve with battery aging
Data Source
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AI summary
The invention relates to a method for correcting the variation in open-circuit voltage due to aging of an electrochemical element exhibiting a state-of-charge - open-circuit-voltage characteristic with a flat portion comprising a reference point, the method comprising the steps of: - obtaining the voltage and the current of the element during charging or discharging; - calculating the overvoltage by calculating the state of charge according to two techniques, only one using a state-of-charge - open-circuit-voltage calibration function; - determining the measured value of the reference voltage for each reference point using the overvoltage; and - estimating the variation by comparing the reference value with the corresponding measured value.