A Fast Fuel Cell EIS Measurement Method Based on Square Wave Excitation and Modified Wavelets

Abstract

Electrochemical impedance spectroscopy (EIS) is an effective technique for real-time fault detection of vehicle-mounted proton exchange membrane fuel cell (PEMFC). In this study, a method to enable fast online measurements of the EIS for PEMFC is presented based on square excitation and modified Morlet wavelet transform (WT), which is validated experimentally. The Morlet wavelet function has been optimized to be more suitable for WT applications in impedance calculations. With this improvement, WT is able to cover the analysis frequency range of 1 Hz to 4 kHz by using a very short time-domain data, precisely at the moment of a square-wave signal jump. This results in a significant reduction in computational cost and allows efficient impedance calculations. The calculated impedance based on the modified Morlet WT has a maximum calculation error of 2.57%, as confirmed by comparing the theoretical impedance at different frequency points. Compared to the general fast Fourier transform EIS calculation method, the proposed method demonstrates significant advantages in terms of both calculation accuracy and test implementation.