STUDY ON ENHANCEMENT AND WEAKENING OF

Abstract–In a conventional permanent magnet (PM) machine, the air-gap flux produced by the PMs is fixed. It is difficult to enhance the air-gap flux density because of limitations of the PMs in a series magnetic circuit. However, the air-gap flux density can be weakened by using power electronics to weaken the field, up to the limit of demagnetization of the PMs. This paper presents an analytical study for controlling the PM air-gap flux density through a stationary brushless excitation coil. The air-gap flux density can be either enhanced or weakened. There is no concern with demagnetizing the PMs during field weakening. The leakage flux of the excitation coil through the PMs is blocked. The prototype motors built on this principle confirm the concept and verify the capability to significantly flux enhance and weaken the magnetic fiel