Steady-State Analysis of a Permanent Magnet Synchronous Motor Drive with Voltage-Source Inverter

A steady-state analysis of a permanent magnet (PM) synchronous motor drive with a voltage-source inverter (VSI) is presented. The torque-speed profile required of the drive is a constant torque region from zero to base speed and a constant power region above base speed. Assuming position feedback control from a shaft-position sensor, optimum strategies are obtained for the two regions of the torque-speed profile. Using these optimum strategies, performance curves of the drive are predicted and experimentally verified. The harmonic distortion in the motor is strongly dependent on the presence and configuration of dampers in the motor. An expression is obtained for the equivalent inductance seen by the harmonics for different damper configurations. A Fourier series approach is used to predict the line current waveforms. Since dampers are not otherwise essential to the operation of this type of drive and since the line current without dampers is nearly sinusoidal, it is concluded that it is advantageous not to have dampers in the motor.