Performance Comparison of Line-Start Permanent Magnet Synchronous Motors with Interior and Surface Rotor Magnets

Objectives: The aim is to undertake a comprehensive comparison of the dynamic and steady state performance of Permanent Magnet Synchronous Motors (PMSM) with interior and surface rotor magnets for line-start operation. Methods/Analysis: The dynamic model equations of the PMSM, with damper windings, are utilized for dynamic studies. Two typical loading scenarios are examined: Step and ramp loading. Emphasis was on the synchronization and load-withstand capabilities of the two motor classes. Also, the steady state torque performance was compared using the torque/torque angle relationship. Findings: The interior permanent magnet synchronous motor (IPMSM) showed superior asynchronous performance under no load, attaining faster synchronism compared to the Surface Permanent Magnet Synchronous Motor (SPMSM). With step load of 10Nm at 2 seconds the combined effect of the excitation and the reluctance torque forced the IPMSM to pull into synchronism faster than the SPMSM which lacks saliency. The ability of the motors to withstand gradual load increase, in the synchronous mode, was examined using ramp loading starting from zero at 2seconds. SPMSM lost synchronism at 12seconds under 11Nm load while the IPMSM sustained synchronism until 41seconds under 40Nm load. This clearly suggests that the IPMSM has superior load-withstand capability. The superiority is further buttressed with the steady state torque analysis where airgap torque in IPMSM is enhanced by the reluctance torque within 90º to 180º torque angle. Applications: The findings of this research will serve as guide in taking logical decisions in the design and operation of permanent magnet synchronous motors to achieve desired objectives in specific applications.