Modeling and characterization of an aircraft electric power system with a fuel cell-equipped APU connected at HVDC bus

A hybrid power source consisting from a fuel cell and a battery is proposed as an auxiliary power unit (APU) for the more electric aircraft (MEA) applications. The output of the fuel cell is controlled using a DC/DC boost converter to provide the voltage of the aircraft 270-VDC bus. The fuel cell and the battery are controlled by using DC/DC converters to provide 270-VDC at their outputs. The output of both fuel cell and battery are connected in parallel at the 270-VDC bus of the aircraft system. Connection at the 270-VDC bus provides several merits for the MEA system; it is simple, feeding DC loads and AC loads through the generator channel 12-pulse inverter, light weight and more economical. The fuel cell/battery hybrid system rating is chosen to be 60-kW to provide power for the aircraft loads in case of the main generator failure or maintenance. To comply with the aircraft standard of MIL-STD-704F and the IEEE Std. 519-1992, an active power filter (APF) is connected at the synchronous generator terminals to reduce or eliminate the harmonics generated from the power converters. The studied aircraft electric power system with the proposed fuel cell/battery hybrid system is simulated without and with the presence of the APF and it is found that the APF reduced the voltage and frequency transients of the system and improves the aircraft electric system performance.