Converter-Based Online Battery Impedance Spectrum Measurement Using a Random Low-Frequency-Modulated Multisine Excitation

Electrochemical impedance spectroscopy (EIS) can access intrinsic information on various physical and chemical processes within batteries and thus has become popular for battery state estimation and fault diagnosis. Impedance spectrum measurements based on power converters with battery management systems facilitate the practical deployment of this method. However, existing excitation signals have shortcomings, such as low measurement accuracy or difficulty in being implemented to converters. In view of this, this article proposes a random low-frequency-modulated multisine (RLMMS) excitation, which is free of higher-order harmonics and exhibits a relatively low frequency of level switching. The RLMMS excitation is applied to measure the impedance spectrum of individual cells in series-connected battery packs based on a dual-active bridge (DAB) converter. The experimental results demonstrate that this excitation is easy to generate and exhibits superior measurement accuracy compared to existing excitation signals across different battery types, even under varying temperature conditions.