Field weakening of a surface mounted permanent magnet motor by winding switching

A new method for flux weakening in surface permanent magnet (SPM) machines is proposed in this paper. This method is called winding switching technique and can reliably double the field weakening speed range of PM motors. This is significant because extending the constant power speed ratio (CPSR) of SPM machines is usually challenging task due to the presence of low-permeability surface magnets and the resulting low machine inductance. In the new method of field weakening the usual three phase motor windings are separated into two portions and each portion is connected to an inverter. The paper discusses the stator winding arrangement which allows the normal and high speed operation of the machine along with the constant output power and reports simulation results taken from Finite Element Analysis.