Magnetization and performance analysis of a variable-flux flux-intensifying interior permanent magnet machine

This paper mainly investigates the magnetization process and the performances of a variable-flux flux-intensifying interior permanent magnet machine (VFI-IPM). In conventional permanent magnet synchronous machine (PMSM), large flux-weakening current is needed to achieve a wide speed range, resulting in extra copper loss and limited power capacity. Recently, the VFI-IPM has been studied due to its feature of variable flux controllability in order to extend the speed range and obtain high efficiency at the entire torque-speed rang. Although design methodology of the VFI-IPM has been reported in literatures, investigation of the magnetization process in VFI-IPM has not been published, however, proper magnetization ratio should be recommended as the criteria to give the pulse current and design VA capability of the inverter. In this paper, principle and finite-element (FE) method of the magnetization process are discussed based on a tangentially magnetized VFI-IPM using Alnico magnet. Moreover, the performances of the machine after the PMs magnetized to different magnetization states are investigated. By comparing the efficiency maps, an optimal efficiency map and the corresponding magnetization ratio map are obtained, based on which the highest efficiency can be achieved at the entire torque-speed region.