Comparison of Different Types of Pole-Changing Line-Start Permanent Magnet Motors

Pole-changing line-start permanent magnet (LSPM) motors eliminate the braking torque during starting process. The pole-changing LSPM motors often starts with pole-decreasing way in order to synchronize successfully, however, the asynchronous torque in starting stage is reduced and winding factor in steady stage is also decreased. In this paper, a pole-increasing-start LSPM motor is studied. The asynchronous torque increases effectively by increasing pole pairs number during starting process but the speed cannot accumulate up to synchronous speed directly in starting stage. So the starting process should be divided into pole-increasing starting stage and steady pole pairs starting stage. The starting torque becomes larger effectively in early process and the synchronization capability even better compared with conventional LSPM motors. Furthermore, the starting performance and steady-state winding factor are compared between pole-increasing and pole-decreasing LSPM motors. Finite element analysis is carried out to show the performance differences of those two kinds of motors.