Performance and material advantages of VFPM over IPM in flux weakening region

Permanent magnet synchronous machines (PMSM) are attractive in many applications. Some of the applications require these machines to be operated beyond base/rated speed. This is achieved by weakening of flux through injection of negative direct axis current. However, the injection of this additional current contributes an additional copper loss and reduces the quadrature axis current component thereby reducing the torque. There is also the risk of permanent demagnetization in rotor poles. An alternative method for flux weakening (FW), a variable flux permanent magnet arrangement (VFPM) is analyzed in this paper. Further, a comparative study between a conventional interior permanent magnet machine (IPM) (which has a high constant power speed range (CPSR)) and a VFPM is done.