The influence of the inverter switching frequency on rotor losses in high-speed permanent magnet machines: An experimental study

Abstract

Harmonic content of the output voltage of pulse width modulated voltage source inverters (PWM VSI) is determined by the switching frequency. On the other hand, rotor losses in high-speed permanent magnet (PM) machines are caused, among other factors, by harmonics in stator currents. These harmonics are determined by the harmonics in the inverter output voltage, and therefore dependent on the switching frequency. In high-speed PM machines, due to the high fundamental frequency, harmonics in the stator currents caused by PWM are located at very high frequencies. Measurement of rotor losses caused by these harmonics in a structure with a conductive retaining sleeve on the rotor which is prone to eddy currents might be very challenging. This paper investigates issues related to this measurement and presents a measurement method which results are compared with results from a 2D analytical model that takes into account eddy currents in the rotor.