Mitigation of PWM-Induced Losses in Electric Machines Using Multi-Level Converters

Abstract:
The efficiency of the drivetrain of an electric vehicle is one of the major factors influencing the range of the vehicle and battery size. With the advent of electric vehicles, this efficiency needs to be optimised on a system level to be as high as possible while also keeping the drivetrain cost in control. This paper explores the influence of PWM-based switching harmonics on the losses of a machine considering the machine design, inverter switching frequency and multi-level excitation. The effect of each of these changes are explored in detail using the measured impedances of two different in-wheel motors. It is shown that the use of multi-level excitation for an electric motor can significantly reduce the PWM-induced losses as well as enable simpler designs of the machine.