An Advanced PWM Method for Highly Efficient Power Train in Hybrid Electric Propulsion Aircrafts

This paper presents the application of a low-loss PWM method called 240° clamped space vector PWM (240CPWM) in hybrid electric propulsion (HEP) aircrafts. 240CPWM allows 85% reduction in switching loss at unity power factor which improves the inverter efficiency significantly as compared to conventional space vector PWM (CSVPWM). 240CPWM requires a unique six-pulse dynamically varying DC link voltage which is regulated by a close loop control in DC-DC converter. In HEP aircrafts, DC-DC converter is often implemented between battery packs and inverter to regulate the charging and discharging of the battery which allows the use of 240CPWM without adding any components or changing the powertrain architecture. Besides higher voltages and power in HEP aircrafts as compared to hybrid electric vehicles, the fundamental frequency is also very high which makes the control of dynamic DC link voltage challenging. PLECS simulation results of a HEP aircraft at 250 kW and fundamental frequency of 300 Hz are shown with power efficiency of 98.7% for DC-AC stage with 240CPWM. Experimental result at 5 kW and fundamental frequency of 300 Hz shows a precise control of six-pulse dynamic DC link voltage. The inverter efficiency from experimental prototype for 240CPWM is 98.5% whereas it reduces to 97% for CSVPWM. Hence, 240CPWM is a viable PWM method for HEP aircrafts that results in substantial savings in power losses in the DC-AC stage as compared to CSVPWM.