Interior Type Permanent Magnet Synchronous Motor Analysis by Equivalent Circuits

The equivalent circuit of a non-salient pole synchronous machine is usually adopted to describe Permanent Magnet motors. Iron core losses are also commonly neglected in such representations. However for PM machines of the interior type, due to the particular configuration of their rotors, rotor saliency and iron core loss assume an important role in the motor operation, both at constant speed linE start applications and as the motor is used in a variable speed drive system. Experimental tests show a trend of core loss which is peculiar to this type of motor which is presented in Fig. 1. Unlike conventional machines, steady-state core loss exhibits a minimum as the terminal voltage is at its open circuit value and then increases as the voltage decreases. Based on experimental measurements performed on a tested PM machine, an equivalent circuit is deduced in the paper aiming to model the rotor saliency and the unusual core loss characteristic, while in the meantime accounting for flux path saturation and armature reaction influence on magnet flux demagnetization or magnetization.