Line-Start Permanent Magnet Motors with Variable Coil Turns

Line-start permanent magnet motors (LSPM) have significant advantages in efficiency and power factor compared to regular induction motors. However, the poor starting torque and synchronization capability are the key issues, and this influences LSPM motors used in many applications. In this paper, coil turns-changing method is proposed to relieve the contradiction between starting and steady-state performance, and improves starting torque and synchronization capability. In order to further remove the magnet braking torque, a novel coil turns-pole-changing method is also proposed to remove the contradiction. The permanent magnet braking torque can be eliminated, in additions, the starting-state and steady-state performance can be nearly decoupled totally. Furthermore, these two turns-changing methods can also start successfully even when network voltage is low. Finite element analysis is carried out to validate the big starting torque and strong synchronization capability.