(215c) Pspice Simulation Via Ac Impedance for a PEM Stack at Operational Loads

The PEFC stacks in the
HCore-500 and Nexa^TM power systems were operated with room air and
pure hydrogen (99.99%). Some of the fuel cells or the whole PEFC stack were
separated from the embedded control system for AC impedance measurements. A 24 V
rechargeable battery or another PEFC system was applied to power the electronic
devices in the control system. Single MEAs, multiple MEA cell groups, and full
fuel cell stacks were examined at various operational currents using an EG&G Model 273A/5210 system and a Gamry FC350^TM/TDI
electronic load. The in-situ impedance data for separated cells and stacks were
fitted to equivalent circuits by the non-linear least squares method (NLLS). AC
impedance data were successfully measured at a high current of 35 A (ca.
291.7 mA/cm²) for the PEFC stack in its Nexa^TM system
using the Gamry/TDI system without embedded system controls. PSpice
simulated curves were obtained from equivalent circuit elements demonstrating
good agreement with the experimental pulse data measured from the PEFC power
system. AC impedance and PSpice simulation prove to be simple and trouble-free
methods to implement real time diagnostic capability suitable for evaluating
the peak pulse performance and the state-of-health of the fuel cells in the
PEFC stack.