Design of a highly reliable three-phase four-leg inversion power supply for more electric aircraft

In a more electric aircraft (MEA), there are always needs of inversion power supplies to power a bunch of legacy loads that need 115VAC/400Hz electric power. Space vector pulse width modulation (SVPWM) controlled three-phase three-leg inverter is usually adopted as the inversion power supply at present. The drawback of such inverter is that it does not have the ability to operate under unbalanced load conditions, especially under short-circuit condition, which makes it hard to be implemented in future commercial and especially military MEAs. Sinusoidal pulse width modulation (SPWM) controlled three-phase four-leg inverter may be a solution to such a problem, however, its DC voltage utility is low compared to the SVPWM controlled inverters. As a result, higher input DC voltage is required, which not only increases the voltage stresses of power switches but also deteriorates the system efficiency. Therefore, in this paper, a new saddle pulse width modulation (SAPWM) method is proposed and applied to a three-phase four-leg inverter to form a highly reliable inversion power supply which is very suitable for future MEAs. The way to generate the saddle pulse width modulation waveform using analog circuits, the system control method and the operational principle of the inversion power supply are elaborated. A 6kVA simulation platform is designed in Saber. The validity of the proposed inversion power supply is verified by simulation results.