Impact of PWM Techniques in Efficiency and Power Density of a 70kVA Multilevel Inverter for More Electric Aircrafts

This paper proposes an optimization technique for weight reduction in the flying capacitor and output inductors of a 7-level inverter composed of three 3-level legs connected in parallel per phase. The target application belongs to the aircraft domain, which demands weight reductions as it is related to the aircraft operating costs. The optimized techniques proposed in this paper are named FCPWM (Flying Capacitor Pulse Width Modulation Technique) and ILPWM (Output inductors Pulse Width Modulation Technique), achieved through simulation, up to 17 % and 37 % on weight reduction, for the flying capacitors and output inductor, respectively. Those values are calculated considering the same modulation index and power factor and comparing the optimized techniques to the sinusoidal PWM technique. Several PWM techniques are compared with the optimized ones and are validated by experimental results that confirm these reductions. For lower current ripple application (∆I L = 35 % and ∆V FC = 5 %), in the given conditions, ILPWM reaches the best results of power density and efficiency (8.30 kW/kg and 98.94 %) compared to the traditional continuous and discontinuous methods, for example, 7.01 kW/kg and 98.76 % for the SPWM and 7.54 kW/kg and 98.88 % for the DPWM3.