The development of traditional permanent magnet synchronous machines (PMSMs) in electric vehicle (EV) industry is limited by the unalterable permanent magnet (PM) excitation field. Variable-flux PMSMs are considered as a good candidate for EV propulsion for their ability to operate in a wide speed range with high efficiency by manipulating the magnetization state dynamically. A novel hybrid-PM variable-flux PMSM with series-parallel magnetic circuits is proposed in this paper. The structure and operating principle of the proposed machine are introduced. The electromagnetic performances of the proposed machine are analyzed and compared with the series-connected and parallel-connected variable-flux machines, and the proposed machine combines the advantages of these two kinds of machines. The inductance characteristics of the proposed machine are analyzed by frozen permeability method (FPM), and the variation laws of inductance are quite different in different magnetization states and load conditions. The torque capacity of the proposed machine is analyzed. The torque ripple can be significantly reduced and the output torque can be improved by properly applying flux-weakening control.

This paper investigates the demagnetization characteristic and permanent-magnet (PM) minimization of the less-rare-earth interior PM synchronous machines (LRE-IPMSMs) used for the electric vehicles, which are featured with high power density, high efficiency, and low cost. First, the equivalent magnet circuit (EMC) of the investigated LRE-IPMSM in demagnetization case is established. Then, the effects of the PM width and the thickness on the machine demagnetization characteristic are investigated. After that, the no-load EMC of the investigated LRE-IPMSM is established. Finally, an analytical method is proposed to obtain the minimum PM volume scheme on the premise of providing the targeted no-load flux and taking the machine anti-demagnetization ability into consideration simultaneously.

The magnetic-field modulated brushless double-rotor machine (MFM-BDRM), getting rid of brush and slip ring, is a preferable selection for the power splitting device in hybrid electric vehicles (HEVs). In practical application, however, the MFM-BDRM is facing the challenge of low power factor owing to its special operating principle — the magnetic field modulation principle. Although some researchers dedicate themselves to improving the power factor of MFM-BDRM, the cause of low power factor in the MFM-BDRM is still not clear. This paper will investigate the power factor problem of MFM-BDRM systematically. Firstly, the inductance feature of MFM-BDRM based on the magnetic field modulation principle is investigated. Secondly, the fundamental cause of low power factor of MFM-BDRM is analyzed. Furthermore, three feasible attempts are made and investigated to improve the power factor of MFM-BDRM. Finally, a prototype of MFM-BDRM is manufactured, and parts of analysis are verified by experiments.

The compound-structure permanent-magnet synchronous machine (CS-PMSM) is a power-split device which can enable the internal combustion engine (ICE) to operate at optimum efficiency during all driving conditions by controlling its torque and speed. However, the CS-PMSM has more serious temperature rise and heat dissipation problems than conventional permanent-magnet (PM) machines, especially when the CS-PMSM is running at low speed and under full load conditions. As the thermal resistance of double-layer air gaps is quite big, the hot spot proves to be in the inner winding rotor. To ensure the safe operation of the CS-PMSM, the use of forced-air and water cooling in the inner winding rotor are investigated. The study shows that the water cooling can provide a better cooling effect, but require a complicated mechanical structure. Considering the complexity of the high efficiency cooling system, a real-time temperature monitoring method is proposed and a temperature measuring system which can accurately measure the real-time temperature of multiple key points in the machine is developed to promptly adjust the operating and cooling conditions based on the measured temperature results. Finally, the temperature rise experiment of the CS-PMSM prototype is done and the simulation results are partly validated by the experimental data.

Due to the rising price of rare-earth materials, permanent-magnet (PM) machines in different applications have a trend of reducing the use of rare-earth materials. Since iron-core poles replace half of PM poles in the consequent pole (CP) rotor, the PM machine with CP rotor can be a promising candidate for less rare-earth PM machine. Additionally, the investigation of CP rotor in special electrical machines, like hybrid excitation permanent-magnet PM machine, bearingless motor, etc., has verified the application feasibility of CP rotor. Therefore, this paper focuses on design and performance of PM machines when traditional PM machine uses the CP rotor. In the CP rotor, all the PMs are of the same polarity and they are inserted into the rotor core. Since the fundamental PM flux density depends on the ratio of PM pole to iron-core pole, the combination rule between them is investigated by analytical and finite-element methods. On this basis, to comprehensively analyze and evaluate PM machine with CP rotor, four typical schemes, i.e., integer-slot machines with CP rotor and surface-mounted PM (SPM) rotor, fractional-slot machines with CP rotor and SPM rotor, are designed to investigate the performance of PM machine with CP rotor, including electromagnetic performance, anti-demagnetization capacity and cost.

Owing to the low permanent magnet (PM) utilization in conventional transverse-flux machines, a novel tubular high-PM-utilization transverse-flux linear machine (HPMU-TFLM) is proposed in this article. The PM utilization ratio of the proposed machine is nearly 100% in theory. Thus, this machine presents a higher power factor and thrust density. First, the basic structure and operation principle of HPMU-TFLM are introduced. The flux-concentrating teeth and multi-unit concentrated winding are designed to improve PM utilization and reduce magnetic flux leakage. Then, the electromagnetic performances of HPMU-TFLM are investigated by the 3-D equivalent magnetic circuit model (EMCM) and the finite element analysis (FEA) method. Finally, its key performances of thrust density, power factor, and efficiency are compared with other typical transverse-flux linear machines (TFLMs). The superiority and feasibility of the proposed machine are verified.