Design and Control Optimization of Surface-Mounted Permanent-Magnet Machines with High Torque and Low Ripples

This paper presents a systematic design and control procedure for the surface-mounted permanent-magnet (SPM) machine with high torque and low ripples. From the design perspective, the concentrated windings with similar slot and pole numbers may achieve many advantages, such as less power loss, high torque density, and very low torque ripple without stator and rotor skewing. The latter leads the design to a sinusoidal flux density for a ripple-free torque distribution. From the control perspective, an ideal current waveform and its shift angle for each phase are determined by aligning the current excitation with the back electromotive force. The design and control of the SPM machine are analyzed by the finite element method. An exampling machine with 48 slots and 44 poles and ideal current shift can achieve a maximum torque at 1034 N-m but only with 2.7% torque ripple.