Online Condition Monitoring of Fuel Cells (FC) by Implementing Electrical Impedance Spectroscopy using a Switch-Mode DC-DC Converter

Online condition monitoring of fuel cell systems without the need for additional hardware is desired. Recent work has explored the use of online impedance spectroscopy for lithium-ion cells using multi-sine signals through a single dc-dc converter. However, for fuel cells, the non-linearity of both the converter and the fuel cell poses a challenge on the online monitoring process. This study demonstrates the use of the pseudo-random binary sequence (PRBS) to perform impedance spectroscopy. This is done by modeling and designing the converter for a linearized region of operation to accommodate different operating conditions of the fuel cell. PRBS is a faster and easier technique to implement compared to the multi-sine signals used in the condition monitoring of batteries. The tolerance of error brought by the implementation of impedance spectroscopy through PRBS and multi-sine signals through a dc-dc converter is compared to the benchmarked theoretical results. This is demonstrated in simulation and experimentally. Results obtained from the Frequency Response Analyzer (FRA) are compared to the results obtained through a DC-DC converter using PRBS and Electrochemical Impedance Spectroscopy (EIS) as testing signals.