Abstract

Electrical machines account for about 60% of the electricity consumption in industrial countries; hence a huge energy savings could be achieved by even a small increment in the machine efficiency. Improving the designs of electrical machines requires accurate quantification of the machine losses. A significant portion of the losses in electrical machines is caused by the core loss in the magnetic material. The physical mechanism of core losses is still an open problem, and most of the available core loss models are based on limited curve fitting techniques, instead of a physical understanding of magnetic material behaviour.
In this thesis, a new method is proposed to separate the core loss components in laminations exposed to high frequency excitations. Accurate separation of core losses is achieved by calculating the hysteresis energy loss at each frequency, taking into account the flux density distribution. The results highlight that the conventional assumption of constant hysteresis energy loss per cycle is only valid at low frequencies, where skin effect is negligible. In addition to the new separation method, a physics based core loss model is developed to estimate core losses in electrical machine laminations exposed to non-sinusoidal flux. The developed model accounts for the effects of the non-uniform flux density inside the lamination. The model results are verified experimentally by comparing with the measured core losses in laminations exposed to the flux waveforms in different sections of permanent magnet (PM) and switched reluctance (SR) machines.