A permanent magnet motor capable of pole changing for variable speed drive

For reduction of energy consumption, we developed a technique that varies the number of magnetic poles in a permanent-magnet (PM) motor in accordance with speed. In this paper, we propose a novel PM motor that can change the number of magnetic poles and produce two types of torque. When the motor operates with 8 poles, it produces a PM torque at low speeds. When the motor changes to 4 poles, it produces both a PM torque and a reluctance torque at high speeds. We explain the principle and basic characteristics of the motor, which has a PM magnetized by the pulse d-axis current of the armature winding. The results show that the proposed motor reduces core losses by 50% and doubles the speed range of the motor.