Characteristics of a permanent magnet motor capable of changing poles by a factor of three

To reduce energy consumption, we developed a technique that varies the number of magnetic poles in a permanent-magnet (PM) motor. In this paper, we propose a novel PM motor that can change the number of magnetic poles by a factor of three. The motor has a rotor embedded with PMs that have both high and low coercive forces. When the motor operates with six poles, it produces mainly a PM torque at low speed. If the field due to the d-axis current reverses only four PMs with low coercive force, the motor changes to two poles at a high speed. We describe the principle and basic characteristics of the motor. The results of our analysis show that the proposed motor reduces core loss by 46% and 41% under no-load and load conditions, respectively, and triples the speed range of the motor.