Torque ripple suppression control for permanent magnet motors

Permanent magnet motors are largely employed due to their high performances in terms of efficiency, power factor and power density. However, non-uniformity into the generated torque may heavily limit their use. In this paper a novel approach is proposed to cancel torque ripple when motor parameters are unknown. The cancellation scheme is based on the frequencies estimation of periodic disturbances acting on the generated motor torque. The estimation process makes use of an adaptive frequency-locked loop system driven by speed measurements. A fractional-order controller is designed to guarantee the stability of the closed-loop system.