Effects of PWM excitations on iron loss in electrical steels and machines

Abstract

The iron loss in the ferromagnetic cores of electrical machines under PWM excitations could be many times higher than the loss under sinusoidal excitation. Therefore, the effects of the PWM waveforms, and their various characteristics (modulation index, switching frequency, and topology, etc.), on the iron loss must be understood and the ability to model these effects in the electrical machine design process is highly desired. In this work, the iron loss is reported for various electrical steels under PWM excitations and the effects of PWM waveform characteristics are studied. The iron loss measurements in a surface mounted permanent magnet motor under PWM excitations are also presented and are in agreement with the measured iron losses in electrical steels. The effect of the iron loss variations on the operating point of the machine is also discussed from the electric vehicle point of view. In the end, a computationally efficient approach based on the static Preisach model is presented to predict the iron loss in electrical steels. The proposed approach can model the effects of changing switching frequency, switching topology and modulation index on the iron loss with a reasonable accuracy.