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A fault-tolerant permanent-magnet vernier (FT-PMV) machine is designed for direct-drive applications, incorporating the merits of high torque density and high reliability. Based on the so-called magnetic gearing effect, PMV machines have the ability of high torque density by introducing the flux-modulation poles (FMPs). This paper investigates the fault-tolerant characteristic of PMV machines and provides a design method, which is able to not only meet the fault-tolerant requirements but also keep the ability of high torque density. The operation principle of the proposed machine has been analyzed. The design process and optimization are presented specifically, such as the combination of slots and poles, the winding distribution, and the dimensions of PMs and teeth. By using the time-stepping finite element method (TS-FEM), the machine performances are evaluated. Finally, the FT-PMV machine is manufactured, and the experimental results are presented to validate the theoretical analysis.

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Interior permanent-magnet (IPM) motors are widely used in electric vehicles (EVs) for their high torque density, efficiency and extended flux weakening region. The aim of this paper is to compare two fault-tolerant IPM motors, in which fault-tolerant teeth (FTT) are adopted in both motors to offer fault tolerance. The first motor is spoke-type, and the PMs of the second one are embedded in the rotor with V-shape. For a fair comparison, the two motors are designed at the same phase current, current density, and dimensions including the stator outer diameter and stack length. The simulation models are built through two actual motor designs. The results show that the spoke-type motor has more trapezoidal back-EMF hence is more suitable for brush less DC (BLDC) operation, offering the advantages of low PMs and manufactory cost. By contrast, it suffers from the disadvantage such as high cogging torque and torque ripple as compared with the other one. 1.I NTRODUCTION Due to problems like the energy crisis and environmental pollution, the electric vehicles (EVs) and hybrid electric vehicles (HEVs) have been researched more and more extensively [1][2][3][4][5][6][7]. The electrical motors and drives are the key technology for the EVs and REVs, and the basic characteristics are desired of an electrical machine for traction applications as following [2,6]:(a) High torque density, power density and efficiency; (c) Wide operating speed range; (e) High reliability and reasonable cost; At present, many types of motor have been adopted in EVs, and permanent magnet (PM) motors provide the highest power density and highest efficiency among all types of motors. Tn the PM motors, various topologies have been proposed [6][7]. According to where the PM is placed inside the motor, they can be classified as "rotor-PM motors" and "stator-PM motors" [8]. There are four types of "rotor-PM motors", namely, surface-mounted, surface-inset, interior, and spoke-type [9-10]. Also, the PM motor can be classified as "inner-rotor motor" and "outer-rotor motor". The outer-rotor motor, tenned as in-wheel motor, can be fixed in the wheel easily, which is more suitable for EVs. Moreover, in order to improve the reliability of these PM motors, many effective methods have been employed. Tn the interior PM (TPM) motors, the effect of adjacent phases can be suppressed by optimal winding configuration [11]. However, this method suffers from the phase short-circuit because of the distribution winding. Hence, fault-tolerant teeth (FTT) and concentrated winding have been adopted in surface-mounted motors to reduce the effect of adjacent phases [12]. This method has been introduced in two in-wheel motors [13][14]. Tn Ref. 13, the radial PMs are embedded in the rotor, this motor can be termed as "spoke-type motor". Since the embedded PM shape of the motor proposed in Ref. 14 is similar to Toyota [15], which can be called as "V -shape motor".On the other hand, many articles focus to investigate the advantage and disadvantage of various motors [16][17][18][19]. T...