Analytical Method Using Impedance of Permanent Magnet Motor for Calculation of Rotor Eddy-Current Losses Caused by Carrier Harmonics

Abstract

In this paper, an analytical method using the impedance for calculating rotor eddy-current losses caused by inverter carrier harmonics in a permanent magnet motor is investigated. With respect to different types of motors, the accuracy of the proposed method is compared with direct calculation by finite element analysis (FEA) using pulse width modulation (PWM) voltage waveforms. First, the two-phase and three-phase current circuits are investigated for calculation of the impedance. Next, impedance and eddy-current losses of six types of motor are calculated in order to investigate the influences of the motor structure and stator magnetomotive force (MMF) on the rotor eddy-current losses. Because the magnetic saturation of the motor core decreases the accuracy of the calculation, an estimation method is proposed that takes the magnetic saturation into account in order to improve the accuracy. The validity of the proposed method is verified by a comparison with the results of direct calculation by FEA using PWM voltage waveforms. Moreover, the effect of the calculation time reduction obtained by the proposed method is also compared with the case where it is calculated directly by FEA.