Mechanical-sensorless permanent-magnet motor drive using relative phase information of harmonic currents caused by frequency-modulated three-phase PWM carriers

This paper proposes a novel control strategy of a permanent-magnet motor drive without a rotor position sensor. The strategy is based on use of relative phase information of harmonic currents caused by frequency-modulated three-phase pulsewidth-modulation (PWM) carriers. In this system, the PWM carrier source is placed on an estimated rotor reference frame, and coordinate transformation is applied to the carrier source to generate the frequency-modulated three-phase PWM carriers on a stator reference frame. By modulating voltage references with the transformed carriers, a locus of the corresponding harmonic currents on the estimated rotor reference frame is observed as a stationary ellipse because of a rotor saliency. Since a long-diameter direction of the harmonic-current ellipse indicates a true d-axis direction, orienting the estimated d axis to the long-diameter direction makes the sensorless operation possible. The paper describes a theoretical aspect of the proposed method and, then, presents experimental results as well as computer simulation results. Consequently, not only excellent controllability over a wide speed range including zero speed has been verified, but also robustness to the motor parameter variations has been confirmed.