Fuel Cell Stack Broadband Excitation for Online Condition Monitoring Using Different Switch-mode DC-DC Topologies

There is a need for online condition monitoring of fuel cell systems through switch-mode dc-dc converters. Recent work has researched online condition monitoring using impedance spectroscopy for electrochemical systems through switch-mode dc-dc converters. For fuel cells, the non-linearity and complex dynamics of both the fuel cell system and the converter pose a challenge to online monitoring. Therefore, this study exhibits and assesses the feasibility and use of the buck-boost and boost converters to perform impedance spectroscopy. This is done by modelling and designing the converters for a linearised region of operation that can be controlled to achieve different operating conditions of the fuel cell system. A practical buck-boost converter has discontinuous input current, more switching harmonics, and noise compared to the boost converter. As such, the contribution and influence of these factors are explored in this paper with regard to impedance estimation. The tolerance of error brought about by the implementation of impedance spectroscopy through PRBS and single-sine(different frequencies) signals using these dc-dc converters are compared to the benchmarked theoretical results and Frequency Response Analyzer (FRA) results. This is exhibited by the simulation results, as the simulation of the theoretical results presents the results obtained from the FRA.