Efficiency analysis and control of a grid-connected PEM fuel cell in distributed generation

•Coupling among the PEMFC, compressor and inverter is analyzed.•Efficient operation reference is modified based on the inverter constraint.•Constant power mode will lead to an initial inverse response in OER step response.•Flexibility of PEMFC is discussed in compensating the renewable intermittency. Proton Exchange Membrane Fuel Cell (PEMFC) is promising in distributed generation owing to its load reliability in complementing intermittent renewable energy sources. However, the existing PEMFC operational researches, usually developed based on the constant current (CC) mode, is not compatible with the grid-connected applications, which instead requires the PEMFC to operate under the constant net power (CP) mode. Some novel difficulties are revealed in association with the couplings caused by the CP operation. An iterative algorithm is developed to decouple the computational interactions so that the steady-state variables can be derived. The efficiency analysis gives the static references of the oxygen excess ratio (OER), which is, however, revealed as contradicting with the voltage requirement of the inverter. Thus, it results in the optimal OER reference modified. In dynamic operation, a peculiar initial inverse response of the OER is exhibited under the CP mode, which requires more cautious controller design than that under the CC mode. Moreover, a power profile governor is designed to prevent the stack voltage from decreasing below the lower bound during transient. Finally, the simulation demonstrates the feasibility and capability of the proposed method in compensating for the renewable intermittency, laying a foundation for the future work on the grid-connected PEMFC.