Online Monitoring of Fuel Cell Electrochemical Impedance Spectrum with Multi-stages Multi-sine Signals Based on DC–DC Converter

Advanced sensors based on electrochemical impedance spectrum (EIS) are essential for fuel cell system state estimation, fault diagnosis, and health management. However, traditional EIS methods are unsuitable for real-time state management due to high costs, large sizes, and long acquisition times, limiting their online industrial application. To enhance onboard EIS application, this study proposes a novel multistage and multisine injection method to improve wideband frequency sweeping, balancing EIS quality, and measurement time using a four-phase floating-interleaving parallel dc–dc converter prototype with EIS injection functions. In addition, a fuel cell coupled with a four-phase floating-interleaving parallel dc–dc equivalent circuit model is established for comprehensive performance analysis in impedance calculation with different excitation methods. Experimental validation showed an impedance magnitude error within 3.2% from 1 kHz to 0.1 Hz, and the implementation reduces EIS measurement time from 900 s to approximately 150 s. Furthermore, a case study on fuel cell EIS sensitivity under dynamic conditions indicates that the proposed prototype can capture dynamic EIS variations using local multifrequency points.