Permanent magnet motor with pole changing and variable magnetic force for variable speed

We developed a technique in which the number of poles in a permanent magnet (PM) motor is varied to reduce energy consumption. We propose a PM motor that can change the number of poles and vary the magnetic force in PM. The motor produces a PM torque at low speeds when it operates with eight poles, but it produces both PM torque and reluctance torque at high speeds when it operates with four poles. We explain the principle involved and the basic characteristics of the motor using a magnetic field analysis, which consists of a PM magnetized by a pulse d-axis current in the armature winding. Our results show that the proposed motor reduces iron loss by 46-55%, has triple the speed range than it would without pole changing and variable magnetic force, and has high efficiency over a wide speed range.