Battery SOC Estimation Using Impedance-Triggered Model Updates
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Solution Overview
Problem
Current battery state estimation methods for hybrid electric vehicles and electric vehicles lack accuracy in calculating the state of charge (SOC) and state of health (SOH) of lithium-ion batteries, leading to potential safety and performance issues.
Innovation Solution
A battery state estimation device that employs a first SOC calculator using a Kalman filtering method, a second SOC calculator using a Coulomb counting method, and an AC impedance measurement unit to recalculate the SOC when the error between the two methods exceeds a threshold, thereby enhancing accuracy by updating battery model parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single SOC calculation method is used, then the device complexity is low, but the measurement precision of SOC is insufficient
Solution Approach 1:
The patent combines two different SOC calculation methods (first SOC calculation unit and second SOC calculation unit) into a unified system. The first unit uses a battery model parameter-based approach while the second unit uses an alternative calculation method. By merging these two approaches and comparing their results, the system achieves higher SOC calculation accuracy than either method could provide alone, while managing complexity through systematic integration.
Solution Approach 2:
The system implements a feedback mechanism where the difference between the first SOC and second SOC calculations is continuously monitored. When the absolute difference exceeds a predetermined threshold, the system triggers AC impedance measurement to recalculate the battery model parameter. This feedback loop ensures accuracy by automatically correcting deviations without requiring constant manual intervention or overly complex real-time processing.
2Measurement precision
If AC impedance measurement is performed continuously, then the measurement precision of battery model parameter is improved, but the use of energy increases
Solution Approach 1:
Instead of continuous AC impedance measurement, the system employs periodic measurement triggered only when necessary. The measurement is activated when the difference between the two SOC calculation methods exceeds a threshold, indicating potential parameter drift. This periodic approach maintains measurement precision when needed while significantly reducing energy consumption compared to continuous monitoring.
Solution Approach 2:
The system uses the discrepancy between the two SOC calculation methods as a self-diagnostic indicator. When this internal feedback shows a threshold exceedance, it automatically triggers the AC impedance measurement and parameter recalculation process. This self-service mechanism eliminates the need for external monitoring or scheduled maintenance, optimizing energy use by acting only when the system itself indicates a problem.
3Productivity
If threshold-based triggering is used, then the productivity is improved by reducing unnecessary measurements, but the measurement precision may be compromised when threshold is not exceeded
Solution Approach 1:
The system uses a dual-approach where the second SOC calculation method serves as a continuous reference check, while the AC impedance measurement provides excessive verification when needed. The threshold mechanism ensures that full measurement accuracy is maintained at critical moments (when divergence occurs) while accepting approximate accuracy during normal operation. This partial/excessive action strategy optimizes productivity without permanently compromising precision.
Data Source
AI summary
A battery state estimation device includes: a first state of charge (SOC) calculator that calculates a first SOC using a first method that uses the battery model parameter of a battery; a second SOC calculator that calculates a second SOC using a second method different from the first method; an alternating-current (AC) impedance measurement unit that measures the AC impedance of the battery when the error between the first SOC and the second SOC is greater than a predetermined threshold; and a battery model parameter calculator that calculates a battery model parameter using the measured AC impedance. The first SOC calculator recalculates the first SOC using the battery model parameter calculated.