Converter-Based Electrochemical Impedance Spectroscopy for High-Power Fuel Cell Stacks With Resonant Controllers

Impedance spectrum is a key signature of a fuel cell stack (FCS). The variations of the impedance spectrum reflect the internal status of an FCS. Enabling electrochemical impedance spectroscopy (EIS) with the onboard power conditioning converter (PCC) provides an attractive approach for in situ diagnostics and condition monitoring of an FCS in end applications, such as heavy-duty vehicles. Although a few previous attempts were made with the PCC being controlled as the source of ac perturbations, the issue of how to properly produce a wide frequency range of perturbations to a high-power FCS has not been well recognized and addressed. In particular, the high-frequency portion is limited by the converter switching frequency and controller bandwidth. Different from existing approaches that fall short of being practical solutions for a high-power FCS, this article proposes the use of PI plus resonant controllers for the PCC to generate quality high-frequency perturbations without any additional hardware. Enabled by the proposed EIS method, an example application showing the effective detection of the impedance changes of an emulated FCS is also presented. The design and implementation of the scheme and the considerations of response measurement and impedance calculation are given in detail. Experimental verifications on a scaled-down laboratory setup demonstrate the validity and possibility of the proposed methods.