Analytical approach and solution for start-up behavior of line-start permanent magnet synchronous machines (LSPSM)
This paper presents a derivation for the maximum transient current and torque peak values for small non-salient line starting permanent magnet synchronous machine (LSPSM) on base of permissible approximations. First the equations for locked rotor operation and secondly for constant speed operation are deduced. This paper is focused on derivation of the analytical calculation process to get an approach for transient current and torque. Saturation and speed dependency of parameters are not considered. With the derived equations, effects of parameters on the peak values of torque and current at starting can be shown.
Transient Starting Torques in Induction Motors
A transient fundamental-frequency torque is shown to occur in the starting of all induction motors. For full-voltage starting on a general-purpose squirrel-cage motor, this torque may be as high as two or three times the pull-out torque. A consideration of such torques is particularly advisable for cases where induction motors are started and stopped frequently or continuously, since under such conditions mechanical failure of the motor or associated parts, gearing, couplings, etc., may occur if the stresses exceed the endurance limit of the material. A method of analysis is given for calculating the transient electrical torques acting in the case of a locked rotor; the results obtained by means of this analysis are compared with test data obtained on a special locked-rotor test setup. A method is also given for calculating shaft torque from the electrical torque in the usual application. Test results also indicate that this method is satisfactory for practical use.
Line-Start Permanent-Magnet Motors: Significant Improvements in Starting Torque, Synchronization, and Steady-State Performance
We present a new scheme to improve the starting torque and synchronization capability of line-start permanent-magnet motors based on pole changing winding. Pole changing at start-up neutralizes the magnetic influence of permanent magnets and, therefore, leads to the elimination of braking and pulsating torques, and enhances the starting torque. Our scheme also solves the synchronization problem. We used finite-element analysis to validate the scheme. The simulation results show that the method leads to a high starting torque, good synchronization, and excellent steady-state performance.