Modeling and simulation of a coupled double-loop-cooling system for PEM-fuel cell stack cooling

PEM (Polymer electrolyte membrane) fuel cell systems are very efficient energy converters. They generate electrical power, low oxygen concentration cathode exhaust gas, water as well as heat. The fuel cell technology has become very attractive for the use on aircraft where it may serve as a replacement for the auxiliary power unit currently being used for generating electrical power. For the use on aircraft coupled double-loop-cooling systems are investigated as different coolants can be used for inner and outer cooling system. As fuel cell electrical power is nonlinearly dependent on stack temperature and current, a cooling temperature control is required. In this study a nonlinear simulation model of a coupled double-loop-cooling system is presented. The effectiveness-NTU method is used to model the intercooler that couples inner and outer cooling loop. This method has the advantage that outlet temperatures are obtained explicitly based on inlet coolant temperatures and cooling mass flows. The model is valid over the entire operating range of the hydrogen fed fuel cell system. Subsequently, a linear controller with feedforward control is proposed to control for the stack inlet cooling temperature.