Contents I. Introduction
Emergence of fuel cell system is one of the promising solutions for meeting the power demand for residential and industrial users. Fuel cell systems are characterized by various advantageous features [1] like high efficiency, pollution free operation (for systems without reformer), modularity, portability, noise free operation etc., hence design and modeling of a fuel cell system especially PEMFC motivates to take up the present work. Operation of a fuel cell based DG systems demands for reliable operation since, any form of electrical load transients or balanced and unbalanced faults (referred as contingency) can lead to damage in PEMFC module especially the costly membrane responsible for splitting of the hydrogen proton and electron. Further, if the above contingencies are not handled then there might be high current flow through the inverter which could be above the rated limit, resulting in damage of inverter switches [2], [3]. Thus, investigation of a PEMFC based DG system (Fig. 1) under contingency is another motivating objective in the work presented. It is well known, for situations where access to utility grid is a major constrain, their stand alone systems are preferred [2], [4]. For conditions when power generated from DG sources is abundant, then surplus power is fed to utility grid resulting for requirement of grid connected operation [5], [7]. Hence, the paper considers two operating modes namely, stand alone mode and grid connected mode for investigation purpose.
