Dynamic Thermal Model of PEM Fuel Cells for MIMO Control Design

This paper discusses the development of a PEM fuel cell stack model that takes into account dynamic thermal and humidity effects. The outputs of the model are in good agreement with experimental results in literature. This nonlinear MIMO system is linearized and then analyzed by using the Relative Gain Array. The objectives are to understand the coupling between the control loops, and to pair the inputs to the outputs to achieve decentralized SISO control. The control inputs for the RGA are the compressor voltage and coolant flow rate. The performance indices are the net power output and fuel cell temperature. Analysis suggests that in most cases the stack temperature is strongly affected by the coolant flow rate, and the net power output is influenced by the compressor voltage. The coupling of the two loops is caused by the coupling of the heat and mass transfer dynamics during the fuel cell operation. When the fuel cell operates at high temperature and high current demand, the coupling of the two loops attenuates. Therefore, the decentralized SISO control is applicable when the temperature and current are high.