Analysis of a Hybrid Permanent Magnet Variable-Flux Machine for Electric Vehicle Tractions Considering Magnetizing and Demagnetizing Current

The overall driving cycle efficiency of conventional permanent magnet synchronous machines (PMSMs) for electric vehicle tractions in a wide speed range is constrained due to the large field weakening current and high iron loss in high speed. The series hybrid permanent magnet variable flux machines (HPM-VFMs) which employ both low coercive force (LCF) magnets and high coercive force magnets are proposed to obtain high torque density and flexible air-gap flux density simultaneously. The key of HPM-VFMs design is the accuracy of hysteresis model of LCF magnets and operating principle analysis. This article contributes to clarify operating principle based on hysteresis model of AlNiCo magnets and propose a novel design consideration to reduce magnetizing and demagnetizing current. Based on the theoretical analysis, this article proposes a novel series HPM-VFM, in which the NdFeB and AlNiCo magnets are arranged separately. Furthermore, flux paths are designed to achieve appropriate interaction between two kinds of magnets. The proposed machine has features of wide magnetization state (MS) variation range, low magnetizing and demagnetizing current, and low risk of unintentional demagnetization. By manipulating the MS of the proposed machine, the losses of a wide speed range operation could be reduced. The comparison of efficiency maps and the worldwide-harmonized light vehicles test cycle driving cycle losses between the proposed machine and a conventional interior PMSM proves that the proposed machine achieves higher efficiency for electric vehicle.