Analysis and Design of an Online Impedance Measurement System for Electric Vehicles Based on Wavelet Threshold Denoising

ABSTRACT Online electrochemical impedance spectroscopy (EIS) based on power converters has the obvious advantages of low cost and real‐time monitoring, and obtains wide applications in life evaluation and temperature monitoring of batteries. Instead of traditional full power converters, partial power processing is beneficial for low stress, high efficiency, and long‐term reliable operation of the system, facilitating EIS test. An online impedance measurement system based on a partial power voltage‐regulated DC‐DC converter is proposed in this paper. The duty cycle perturbation and closed‐loop reference perturbation test methods are analyzed based on the proposed system, which is evaluated from the perspectives of the test accuracy and bandwidth range. The EIS test of 0.5 Hz–1 kHz is achieved by the sawtooth signal disturbance at different frequencies, and the utilization of integer harmonic components improves the test efficiency further. The cross‐correlation algorithm is utilized for impedance calculation. Finally, the segment wavelet threshold denoising is conducted on the impedance results in the frequency domain, and the denoising performance can be improved by the wavelet parameters optimization. The mean relative errors (MRE) of the impedance results for different excitation amplitudes verified are about 1%.