As a wheel traction motor used for electric vehicles (EVs), due to the requirement of high power/torque density and the poor working condition, it is more prone to cause severe inter- turn short circuit (ITSC) faults. In this paper, the ITSC faults characteristics of a permanent magnet synchronous machine (PMSM) used for wheel traction motors in EVs are deeply and comprehensively researched. The influence of fault intensity on machine's parameters and performance are researched at different fault resistances through finite element method (FEM). Besides, factors that affect the amplitude of short circuit current are researched by mathematic formula and simulation, including load state, rotation speed, fault position and branch inductance. Then, the loss and thermal characteristics of the PMSM under different conditions are analyzed. In the last, experiments are conducted to validate the simulation results.

The cogging force is a main component of the detent force in the permanent magnet linear synchronous motor (PMLSM). It will lead to the thrust ripple and deteriorate the control characteristics, which cannot be neglected especially in precision machine tools. In order to minimize the cogging force, a novel double-sided PMLSM structure with reversed slots is proposed and compared with a conventional PMLSM in this paper. Two novel windings are further added to compensate the unbalanced back electromotive force (EMF) caused by the reversed slots. With this suggested structure, an 8-pole 9-slot double-sided PMLSM is designed. And its detent force and back EMF are evaluated with the help of the 2-D finite element analysis. Finally, a prototype of the double-sided PMLSM with reversed slots is developed, and experiments are carried out to verify the analytical and simulated results.

This paper investigates the comparative design optimizations of a five-phase outer-rotor flux-switching permanent magnet (FSPM) machine for in-wheel traction applications. To improve the comprehensive performance of the motor, two kinds of large-scale design optimizations under different operating conditions are performed and compared, including the traditional optimization performed at the rated operating point, and the optimization targeting over the whole driving cycles. Three driving cycles are taken into account, namely, the Urban Dynamometer Driving Schedule (UDDS), the Highway Fuel Economy Driving Schedule (HWFET), and the combined UDDS/HWFET, representing the city, highway, and combined city/highway driving, respectively. Meanwhile, the computationally efficient finite-element analysis (CE-FEA) method, the cyclic representative operating points extraction technique, as well as the response surface methodology (in order to minimize the number of experiments when establishing the inverse machine model), are presented to reduce the computational effort and cost. From the results and discussion, it will be found that the optimization results against different operating conditions exhibit distinct characteristics in terms of geometry, efficiency, and energy loss distributions. For the traditional optimization performed at the rated operating point, the optimal design tends to reduce copper losses but suffer from high core losses; For UDDS, the optimal design tends to minimize both copper losses and PM eddy-current losses in the low-speed region; For HWFET, the optimal design tends to minimize core losses in the high-speed region; For the combined UDDS/HWFET, the optimal design tends to balance/compromise the loss components in both the low-speed and high-speed regions. Furthermore, the advantages of the adopted optimization methodologies versus the traditional procedure are highlighted.

This paper investigated a 12-slot/11-pole flux switching permanent magnet (FSPM) machine used for electric vehicles (EVs). Five novel rotor teeth shapes are proposed and researched to reduce the cogging torque and torque ripple of the FSPM machine. These rotor teeth shapes are notched teeth, stepped teeth, eccentric teeth, combination of notched and stepped teeth, and combination of notched and eccentric teeth. They are applied on the rotor and optimized, respectively. The influences of different rotor teeth shapes on cogging torque, torque ripple and electromagnetic torque are analyzed by the 2-D finite-element method (FEM). Then, the performance of FSPMs with different rotor teeth shapes are compared and evaluated comprehensively from the points of view of cogging torque, torque ripple, electromagnetic torque, flux linkage, back electromotive force (EMF), and so on. The results show that the presented rotor teeth shapes, especially the combination of stepped and notched teeth, can greatly reduce the cogging torque and torque ripple with only slight changes in the average electromagnetic torque.

The modular multilevel converter (MMC) has been proven to be an effective solution for grid-tied applications with medium/high voltage ratings. The MMC contains a large amount of floating capacitors, which require the voltage balancing control. The voltage balancing control complexity is normally increased with the number of floating capacitors. As a result, the computation burden of the controller as well as the corresponding hardware cost will be high. This paper proposed a novel Z-type MMC, which can achieve capacitor voltage self-balancing without any balancing control. Therefore, the overall control of the converter is significantly simplified. Both mathematical analysis and experimental results have confirmed the effectiveness of the proposed method.