This paper reviews motor techniques for reducing the cost of electric vehicles (EVs) and improving their range. In recent years, environmental issues, energy crises and the greenhouse effect have urged the popularization of clean energy EVs. In order to achieve this goal, it is necessary to overcome technical difficulties in vehicle cost and range. As a key component of an EV, the motor occupies a large proportion of the overall vehicle cost, and its efficiency directly affects the mileage. In this context, this article discusses the merits and challenges of three mainstream EV motors: permanent magnet synchronous motor (PMSM), induction motor (IM), and switched reluctance motor (SRM) in terms of vehicle cost and range. Then this paper compares the advanced techniques of these motors in terms of topology, material applications and control strategies. Finally, the development trends and opportunities of the three motors in EVs are predicted.

This paper proposes and implements the concept of time-division multiplexing (TDM) wireless power transfer (WPT) for separately excited dc motor drives. Essentially, the proposed WPT system has only one transmitter that can transfer power to multiple receivers simultaneously while the power transfer to individual receivers can be independently controlled. Thus, the armature and field currents of the separately excited dc motor can be independently controlled, hence achieving the desired constant torque operation and constant power operation. The key is to make use of the TDM scheme to simultaneously transfer powers to both the armature and field windings. Meanwhile, the burst firing control method is incorporated to independently regulate the power flows to the armature and field windings at the resonant frequency, hence retaining the maximum power transfer efficiency. Both finite element analysis and experimentation are given to verify the validity of the proposed system.

Vernier permanent-magnet (VPM) machines attract more and more attention recently because of the high-torque density and low-speed operation features. Due to the vernier structure for field modulation, its power factor (PF) usually is lower than that of the conventional PM machines. In this paper, a new linear VPM machine for improving the PF is proposed. By using an auxiliary dc field winding to provide an additional excitation, the air-gap flux excited by PMs is compensated. The proposed machine has a similar structure to the split-pole VPM machines with surface-mounted PMs. For implementing the auxiliary dc field winding, a parallel-hybrid excitation topology and consequent-pole PM machine structure are adopted. The machine topology, modeling, and operating principle are discussed. Both simulation and experimentation show that the PF of the machine can be improved by the auxiliary dc field excitation.

This paper presents the quantitative analysis for the optimal design of wireless power transmission (WPT) systems based on magnetic resonant coupling (MRC) mechanism. In this paper, the exemplified MRC-based WPT system adopts the series-series topology and one resonant coil, which shows that the energy efficiency and transferred power are both significantly affected by the mutual inductance of the primary-resonant coils and the resonant-secondary coils. In addition, the simulated and experimental results are both provided to illustrate the influence of the mutual inductance on the performance of MRC-based WPT systems regulating the relative displacement among coils. Thus, this quantitative analysis can offer the significant theoretical and experimental basis for the optimal design of MRC-based WPT systems in various application fields.

This article proposes and implements an output-controllable efficiency-optimized wireless power transfer scheme using hybrid modulation. The key is to combine pulse frequency modulation (PFM) and on-off keying (OOK) modulation and to utilize feedback control. Among them, PFM is used for the output voltage regulation of the inverter to adjust the rectified output voltage on the receiver side, while OOK modulation is adopted to convert the load resistance to be close to the optimal resistance value so that the system efficiency can be effectively optimized. When the relationship between the input and output voltages reaches a ratio related to system parameters, it can be considered that the load resistance has reached the optimal state. Hence, the feedback output voltage is utilized to help convert the load resistance into an optimal value and only one voltage acquisition circuit is needed. In this article, theoretical analysis and practical experimentation (using the LED lamp as a nonlinear load and the 102-Ω resistance as a linear load) are both given to verify that the proposed scheme can help to maintain high system efficiency during the output voltage regulation process.

A MW class direct-drive vernier motor for the elec-tric ship propulsion is proposed in this paper. The proposed ver-nier motor adopts the homopolar structure and utilizing the high-temperature superconducting wire for electrical excitation. The stator houses the superconducting field winding and the copper armature winding. The rotor consists of iron core without excitation sources. Thus, no cryo-moving components are re-quired. A dual-body Dewar for cooling the pancake HTS field winding is proposed. The motor performance is analyzed and evaluated using the 3-D finite element analysis. Both the brush-less AC (BLAC) and brushless DC (BLDC) operation modes for the proposed motor are assessed and compared.