Battery Cell SOC Estimation from Partial Discharge Voltage
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Solution Overview
Problem
Existing methods fail to accurately determine the state of charge (SOC) of individual cells in a battery, which is crucial for identifying defective cells and optimizing battery performance, particularly in applications where SOC differences between cells are significant.
Innovation Solution
A method that measures voltage across each cell after a partial discharge phase, calculates an interpolation coefficient using measured voltages and discharge rate, and determines the charge stored in each cell using this coefficient, allowing for the estimation of SOC without requiring discharge curves or characterization libraries.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional methods are used to determine SOC of individual cells, then the process becomes complex and time-consuming, but the accuracy of SOC determination remains insufficient
Solution Approach 1:
The patent transforms the SOC determination problem from requiring complex discharge curves to using simple voltage measurements combined with interpolation coefficients. By changing the measurement parameters from complex temporal discharge profiles to simple voltage snapshots at specific states, the method achieves both accuracy and simplicity.
Solution Approach 2:
The patent creates a simplified mathematical model (interpolation coefficient) that copies the essential relationship between voltage and SOC without requiring the full complexity of actual discharge curves. This allows accurate SOC estimation using basic voltage measurements rather than complete discharge characterization.
2Measurement precision
If discharge curves or characterization libraries are used to estimate SOC, then more accurate information can be obtained, but the process requires more time and resources
Solution Approach 1:
The patent pre-calculates interpolation coefficients based on voltage measurements at specific states (fully charged, fully discharged, and intermediate states) and stores these coefficients for rapid lookup. This preliminary action eliminates the need for real-time discharge curve analysis, enabling fast SOC determination without sacrificing accuracy.
Solution Approach 2:
Instead of requiring complete discharge curves from 100% to 0% SOC, the patent uses partial discharge information combined with interpolation coefficients to estimate SOC. This partial action approach provides sufficient accuracy for practical applications while dramatically reducing the time and resources needed compared to full discharge characterization.
Data Source
AI summary
A method of determining, for each cell of a battery of series-coupled cells, an indicator QCi representative of the charge stored in the cell, this method comprising: a) at the end of a phase of partial discharge or charge of the battery, measuring the voltage Ui across each cell of the battery; b) calculating, for each cell, an interpolation coefficient Xi from a value C_rate representative of the discharge or charge rate of the battery during said partial discharge or charge phase, and from the voltages Ui measured at step a); and c) determining, for each cell, from the interpolation coefficient Xi calculated for the cell at step b) and from a quantity Qcm representative of the charge stored in the battery, said indicator QCi representative of the charge stored in cell.