Permanent magnet motor capable of pole changing for high efficiency

To reduce energy consumption, we developed a technique that varies the number of magnetic poles in a permanent magnet (PM) motor. We propose a PM motor that can change the number of magnetic poles and produce two types of torque. When the motor operates with eight poles, it produces a PM torque at low rotational speeds. When the motor changes to four poles, it produces both PM torque and reluctance torque at high speeds. We explain the principle and basic characteristics of the motor by using a finite element method magnetic-field analysis, which consists of a PM magnetized by a pulse d-axis current of the armature winding. The results of our experiment show that the proposed motor reduces core loss by 49% and 33% under no-load and load conditions, respectively, and doubles the speed range of the motor.