Maintaining a fuel cell system in correct operating conditions when subjected to fast load changes requires good system control. In order to design such a controller, a simple PEFC system model describing all the important system dynamics and cross couplings is required. The simple model shown here describes the fuel cell auxiliary systems in a state space approach, linking user input to fuel cell operating conditions. A steady state fuel cell stack model then describes the effect of those operating conditions on system performance. The model then allows implementation of advanced control strategies such as multivariable control with decoupling, actuator sensitivity analysis or maximum efficiency tracking algorithms.