Battery SOH Estimation from Pause-Period Voltage Derivatives
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Solution Overview
Problem
Existing battery state estimation methods assume uniform battery temperature and require complex circuit configurations for impedance measurement, failing to accurately estimate the state of health (SOH) distribution across battery cells, which leads to uneven degradation and reduced system performance.
Innovation Solution
A battery state estimation device that calculates the state of health (SOH) of individual cells using the time derivative of output voltage during pause periods and temperature, allowing for the estimation of the entire battery system's deterioration state by considering the SOH distribution across multiple cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If impedance measurement using sine wave or rectangular wave is used to estimate battery state, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent extracts only the necessary measurement capability by using simple voltage monitoring during pause periods instead of complex impedance measurement circuits. The voltage change during pause periods contains sufficient information for SOH estimation, allowing removal of sine wave generators, rectangular wave generators, and frequency response analysis equipment.
Solution Approach 2:
The battery system uses its own operational characteristics (voltage changes during pause periods) for self-diagnosis. The pause periods that naturally occur in battery operation are utilized for measurement, eliminating the need for external test equipment or dedicated measurement circuits.
2Measurement precision
If frequency response processing is used to measure temperature characteristic of impedance, then measurement precision is improved, but difficulty of detecting and measuring increases
Solution Approach 1:
The patent extracts the essential temperature-characteristic information directly from voltage changes during pause periods, eliminating the need for frequency response processing. The voltage derivative during pause periods directly reflects temperature-dependent battery state without requiring complex spectral analysis.
3Device complexity
If average SOH measurement is used without measuring SOH distribution, then device complexity is reduced, but reliability decreases
Solution Approach 1:
The patent segments the battery system into individual cell measurements, calculating SOH for each cell separately based on its voltage characteristics during pause periods. This allows identification of the lowest SOH cell that limits overall system performance, rather than relying on average values that mask individual cell degradation.
4Device complexity
If uniform temperature assumption is used for SOH estimation, then device complexity is reduced, but measurement precision decreases
Solution Approach 1:
The patent applies local quality by estimating SOH for each individual battery cell based on its local voltage characteristics during pause periods. Each cell's temperature and state are treated independently, allowing accurate SOH estimation that reflects local conditions rather than assuming uniform temperature across the entire battery system.
Data Source
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AI summary
An object of the present invention is to provide a battery state estimation device capable of accurately estimating a deterioration state of an entire battery system in consideration of an SOH distribution of battery cells. The battery state estimation device according to the present invention estimates an SOH of a battery cell by using a correspondence between a time derivative of an output voltage during a pause period of the battery cell and a battery temperature, and estimates a deterioration state of an entire battery system by using the SOHs of a plurality of battery cells (see FIG. 1).