Abstract
This paper presents an analytical estimation approach for PWM carrier loss on the rotor in the design stage of slotless permanent magnet motors. The experimental studies using 400W, 3000r/min test motor show that the eddy current on the rotor surfaced by rare-earth magnets decreases the winding inductance and increases the winding resistance as the supplied frequency rises. The resultant lower inductance for high frequency over 10kHz produces a large amount of current harmonics caused by voltage PWM as well as the carrier loss combined with the resistance increment.
At first, the frequency dependent winding inductance and resistance of test motor are estimated by 3D-finite element method considering the eddy current on the rotor. The current spectrum is subsequently calculated from the obtained frequency dependent winding impedance and the simulated voltage spectrum. The carrier loss is finally derived from the current spectrum and the calculated resistance increment. The effectiveness of the proposed estimation approach for PWM carrier loss on the rotor is experimentally verified using test motor.
