Mechanical-sensorless permanent-magnet motor drive using 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 a harmonic current vector caused by frequency-modulated three-phase pulsewidth-modulation (PWM) carriers. In this system, the PWM carrier source is located on a reference frame rotating synchronously with an estimated rotor position, and coordinate transformation is applied to the carrier source to generate the frequency-modulated three-phase PWM carriers on a stator reference frame. By using the transformed carriers for pulsewidth modulation of voltage references, a locus of the corresponding harmonic current vector on the estimated synchronous reference frame is observed as a stationary ellipse because of the rotor saliency. Since a long diameter of the harmonic-current ellipse indicates a true d-axis direction, orientation of the estimated d-axis to the long-diameter direction makes 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 motor parameter variation has been confirmed.