Comparative Analysis of Y- and Delta-Connected Windings in Line-Start Permanent Magnet Motors with Different Rotor Configurations

Abstract

A line-start permanent-magnet motor (LSPM) combines the direct-on-line starting capability of a squirrel-cage induction motor (IM) with permanent-magnet-assisted synchronous operation. Previous studies on LSPM winding connections have mainly focused on load-dependent efficiency and the power factor, while their effects on harmonics, torque ripple, and synchronization across different rotor configurations remain unclear. This study compares Y- and delta-connected windings in two 5.5 kW, four-pole LSPM models using transient finite-element analysis. Current and voltage harmonics, losses, efficiency, torque ripple, and synchronization response were evaluated. The Y-connected cases exhibited lower current harmonic distortion and stator copper loss, whereas the delta-connected cases reduced torque ripple and maximum speed overshoot but required slightly longer settling times. For LSPM-B, the Y connection achieved the highest efficiency of 92.92% with a stator copper loss of 137.81 W, while the delta connection reduced the torque ripple ratio from 43.8% to 39.5%. These results demonstrate that winding-connection effects depend on the rotor magnetic circuit and cage-assisted starting characteristics, requiring a trade-off among efficiency, harmonic loss, torque ripple, and synchronization response.