Pull out torque computation for line start permanent magnet motor

A combined method of stationary finite element method (FEM) and time-stepping FEM is proposed to calculate the pull out torque of line start permanent magnet motor accurately and efficiently. The power angle characteristic was obtained with stationary FEM, and then the critical step-out power angle and the field-circuit result corresponding to the critical condition can be acquired. On the basis of the result, time-stepping FEM was used to calculate the pull out torque while keeping the rotor synchronous. When the average electromagnetic torque in each period tends to be stable, the torque of the final period can be assumed as pull out torque. Application shows that the method has enough accuracy as well as efficiency.