Measurement of inverter caused losses in permanent magnet synchronous machines using a modular multiphase multilevel converter

Current distortion of two-level converter-fed permanent magnet synchronous machines causes additional machine-side losses, which lead to a distinct reduction in the drive train efficiency of electric vehicles for instance. Determining these losses by measurement is still an ambitious task. On the one hand, there's a lack of adequate voltage sources. On the other hand, there is no accurate procedure to distinguish between the different loss components. In this publication, a 100 kVA seven-level multilevel converter is used to determine the losses of a 60 kW highly-utilized permanent magnet synchronous machine for automotive use. Due to the good voltage quality of the multilevel converter, the machine currents have very low harmonic distortion and the determined losses are considered as fundamental ones. In a second experiment, the machine is operated with a conventional two-level converter. Comparing machine losses in both experiments allows the determination of the additional machine losses in two-level operation.