Electrical Machine Rotor Shielding for Low Cost Electrical Drive

Electrical machine rotor shielding has been proposed for high-speed electrical machines, i.e., ≥50krpm, where a smooth current waveform becomes difficult and costly to generate due to the required high switching frequency. The rotor shielding is used to suppress the unsynchronized low order high amplitude current harmonics and consequently reduces the induced eddy-current losses in rotor. For moderate speed machines, 10-40krpm, generally suited for automotive applications, a smooth current waveform is possible to generate, however, fast switching devices are required that increases the overall drive cost. In the paper, a feasibility study of low cost electrical drive is presented. The electrical drive consists of low cost, low switching frequency modules to generate a pulse width modulation (PWM) current waveform with a few switching pulses, and a rotor with electromagnetic shield to reduce the losses to an acceptable level. The feasibility study includes two permanent magnet machines (PMMs) with different rotors. Multi-physics results are obtained and compared to illustrate the feasibility of the proposed drive.