Adaptive shutdown drying of automotive PEM fuel cell systems using embedded impedance-based control

Residual water remaining in polymer electrolyte membrane (PEM) fuel cell stacks after shutdown can freeze during cold soak, leading to impaired freeze start performance and accelerated degradation. Conventional shutdown drying strategies rely on fixed parameter settings, which do not account for variability in operating conditions, stack aging, or ambient humidity. This article presents an adaptive shutdown drying strategy for automotive PEM fuel cell systems using an embedded impedance-based control approach. A resistance proxy derived from fixed-frequency electrochemical impedance measurements is employed as a supervisory state to guide drying actuation and termination. Experimental investigations on a fully integrated 70 kW automotive fuel cell power module demonstrate that resistance evolution correlates with cathode humidity gradients and correlates quantitatively with net water removal from the stack. An envelope-based resistance threshold combined with slope-guarded actuation enables robust drying termination across variations in air humidity, airflow, and coolant temperature, while avoiding excessive drying conditions associated with membrane stress. The proposed approach improves freeze-readiness robustness and provides a control-relevant alternative to fixed-time shutdown drying strategies suitable for automotive fuel cell applications. • Adaptive shutdown drying using an embedded impedance proxy in PEM fuel cells. • Resistance evolution correlates with humidity gradients and water removal. • Envelope-based resistance threshold enables robust drying termination. • Slope-guarded supervision adapts air flow and coolant temperature. • Enhances robustness of shutdown preparation across varying operating conditions.