Battery Cell SOH Estimation Using Endpoint Voltage Interpolation
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Solution Overview
Problem
Existing methods for estimating the state of health (SOH) of battery cells require memorizing voltage evolution across each cell during discharge or charging, which becomes impractical with large battery sizes due to the high quantity of data needed, especially when identifying aging cells in complex applications.
Innovation Solution
A method that calculates the capacity of each cell using a formula based on interpolation coefficients derived from a single complete discharge or charge phase, allowing for SOH estimation without storing discharge or charge curves, and includes steps for balancing cells and selecting healthy cells for reassembly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If voltage evolution across each cell is recorded during discharge or charge phase, then SOH estimation accuracy is improved, but data storage requirements and device complexity increase significantly
Solution Approach 1:
The patent extracts only the essential information needed for SOH estimation - specifically the voltage of the limiting cell at the end of discharge or charge phase - while discarding the unnecessary continuous voltage evolution data. This extraction approach maintains measurement precision by capturing the critical data point that determines cell capacity, while dramatically reducing data storage requirements from continuous curves to single voltage values.
Solution Approach 2:
Instead of recording complete voltage evolution curves for all cells (excessive action), the patent uses only the voltage measurement at the critical endpoint when the limiting cell reaches its threshold (partial action). This partial measurement approach is sufficient for accurate SOH estimation while minimizing data storage needs.
2Measurement precision
If complete discharge or charge phases are used for SOH estimation, then measurement accuracy is improved, but time consumption and productivity are reduced
Solution Approach 1:
The patent performs preliminary balancing of all battery cells before the discharge or charge phase to ensure they start from the same voltage level. This preliminary action ensures that the limiting cell identification is accurate and that the endpoint voltage measurement truly reflects the cell's capacity, maintaining high measurement precision while enabling the use of complete phases for diagnostic purposes.
3Reliability
If individual cell monitoring is implemented, then reliability of battery system is improved, but device complexity and cost increase
Solution Approach 1:
The patent makes the voltage measurement system universal by using the same voltage sensors and measurement circuitry for both normal battery management operations and SOH estimation diagnostics. The existing voltage monitoring infrastructure serves multiple functions: real-time cell voltage monitoring during operation and endpoint voltage measurement for capacity estimation, eliminating the need for separate dedicated monitoring hardware and reducing overall system complexity.
Data Source
Figure 1
AI summary
The present description concerns a method for determining the state of health of the cells (Ci) of a battery, comprising: a) during a discharge phase (101) of the battery, measuring the voltage Ui at the terminals of each cell (Ci); b) when a first cell (Ci_lim) reaches a predefined end-of-discharge condition, interrupting (102) the discharge and storing the end-of-discharge voltage Ui of each cell; c) determining (103) a value QCi_lim representative of the capacity of the first cell; d) calculating (104), for each other cell, an interpolation coefficient C_interp_i; and e) determining (105), for each other cell, from the value QCi_lim and the interpolation coefficient C_interp_i calculated for the cell, a value QCi representative of the capacity of the cell.