Modeling and characterization of an aircraft electric power system with a fuel cell-equipped APU paralleled at main AC bus

In this paper a More Electric Aircraft (MEA) electric power system is modeled and simulated with a fuel cell/battery hybrid Auxiliary Power Unit (APU). Fuel cell/battery hybrid power source is connected at the AC-load bus bar of 200-VAC and 400-Hz. Due to the DC output of the hybrid power source, a 12-pulse inverter is used at the output of the APU. The two output voltages of the generator-channel inverter and the hybrid-source inverter must be synchronized. The output of the fuel cell is controlled using a DC/DC boost converter to provide the aircraft DC bus voltage of 270-V. The battery is controlled by using a bidirectional DC/DC converter to provide the excess load when necessary and be charged from the fuel cell during normal operating conditions. To make the aircraft electric power system compatible with the aircraft standards, an active power filter (APF) is connected at the synchronous generator terminals. The APF reduced the total harmonic distortion (THD) of the generator voltage and current to be within the standard values. 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.