Battery Pack Full-Charge Capacity Estimation Using Voltage-Capacity Curves
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Solution Overview
Problem
Current methods for determining the full-charge capacity of battery packs are inaccurate due to the limitations of real-time state of charge estimation and the broad flat areas in open circuit voltage-state of charge curves, which restrict opportunities for SOC correction, especially in battery packs with individual cell differences.
Innovation Solution
A method that calculates the full-charge capacity by obtaining first and second state of charge values, using voltage-capacity curves to determine capacity differences, and calculating state of charge variations, allowing for more accurate and frequent updates of the full-charge capacity without requiring batteries to stand twice, even in flat areas of the OCV-SOC curve.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If static OCV-SOC curve correction is used, then accurate SOC can be obtained, but the broad flat areas in the curve reduce the number of correction opportunities
Solution Approach 1:
The patent applies dynamics by transitioning from static OCV-SOC curve correction to dynamic voltage-capacity curve analysis during charge termination phase. Instead of relying solely on static rest conditions, the method dynamically tracks voltage changes and corresponding capacity variations as the battery charges, enabling SOC correction opportunities even when the battery is not at complete rest.
Solution Approach 2:
The patent introduces another dimension by adding the time dimension to SOC correction. Rather than relying only on the voltage-SOC relationship at static points, it incorporates the temporal evolution of voltage and capacity during charge termination. This dimensional expansion creates additional correction opportunities by utilizing the dynamic trajectory of voltage-capacity relationships.
2Measurement precision
If individual cell differences in battery packs are addressed using traditional methods, then accurate full-charge capacity can be determined for cells at correction opportunities, but cells in flat areas of OCV-SOC curve cannot be corrected
Solution Approach 1:
The patent applies universality by creating a voltage-capacity curve analysis method that works for all cells regardless of their individual characteristics or position in the OCV-SOC curve. The dynamic voltage-capacity relationship approach during charge termination phase provides a universal correction mechanism that adapts to each cell's specific voltage trajectory, enabling consistent full-charge capacity determination across all cells in the battery pack.
Data Source
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AI summary
The present invention relates to a method for determining a full-charge capacity of a battery pack, including: obtaining first state of charge values of cells at a first state of charge correction moment; calculating a net cumulative charge capacity from the first state of charge correction moment to a full-charge moment; obtaining a voltage-capacity curve of a fully charged cell from start of a charge termination phase to the full-charge moment, where the fully charged cell reaches a first full-charge voltage at the full-charge moment; obtaining a second voltage of a not fully charged cell at the full-charge moment; obtaining a capacity difference between the not fully charged cell at the full-charge moment and the not fully charged cell at the first full-charge voltage based on the voltage-capacity curve and the second voltage; calculating a state of charge difference by dividing the capacity difference by an actual full-charge capacity; calculating a second state of charge value of the not fully charged cell at the full-charge moment by subtracting the state of charge difference of the not fully charged cell from a second state of charge value of the fully charged cell; obtaining state of charge variations; calculating full-charge capacities; and obtaining a full-charge capacity of the battery pack based on the calculated full-charge capacities.