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In this paper, a robust anti-islanding algorithm for distributed fuel cell powered generation (DFPG) is proposed. Three different islanding scenarios are explored and presented based on analysis of real and reactive power mismatch. It is shown via analysis that the islanding voltage is a function of real power alone, whereas its frequency is a function of both real and reactive power. Following this analysis, a robust anti-islanding algorithm is developed. The proposed algorithm continuously perturbs (± 5%) the reactive power supplied by DFPG while simultaneously monitoring the utility voltage and frequency. If islanding were to occur, a measurable frequency deviation takes place upon which the real power of DFPG is further reduced to 80%; now a drop in voltage positively confirms islanding, and the DFPG is safely disconnected. This method of control is shown to be robust, able to detect islanding under resonant loads, and fast acting (operable in one cycle). Possible islanding conditions are simulated and verified with analysis. Experimental results on a 0.5 kW fuel cell inverter connected to 120 V 60 Hz utility are discussed.
Date of Publication: Sept. 2004