Comparison of Two Possible Solution for Reducing Over-voltages at the Motor Terminals in High-Speed AC Drives

This paper addresses the overvoltage issue occurring at the motor terminals in high-speed AC drives. Such phenomenon is substantially due to the voltage wave reflections across the connection cable occurring in presence of PWM motor supply. Moreover, such over-voltages are strictly related to the steepness of the PWM pulse and hence are more evident and severe in case a high-frequency inverter based on wide band gap devices is used to feed an AC high-speed machine. The main effect consists in a more severe stress of the motor winding insulation system which in turn may result in a major failure deeply affecting the system reliability. Two possible solutions, based on different converter topologies, are analyzed and compared in this paper in terms of overvoltage level, efficiency, encumbrance and system complexity. In particular, a Cascaded H-Bridge multilevel converter is compared with a SiC MOSFET two-level inverter equipped with active gate drivers capable of dynamically changing the switching features of the power devices.