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Nonslotted and slotted external rotor internal stator TORUS type surface mounted permanent magnet (PM) machines (TORUS-NS and TORUS-S) have simple structures, relatively high efficiencies and low cost. These machines can be used for the applications that require high power and torque density, high efficiency and low noise with the use of neodymium-iron-boron (NdFeB) magnets providing relatively small overall size and weight. In this paper, sizing equations of the TORUS machines are derived using generalized sizing equations. The optimum machine design is illustrated by choosing the magnet pole-arc ratio and the skew angle of the rotor magnets. Using the optimum design data, field analysis of TORUS-NS and TORUS-S machines are investigated. Pulsating torque analyses including the cogging torque and the ripple torque are carried out using a 3D finite element analysis (FEA) software. Utilizing the techniques such as modifying the winding structure and skewing the rotor magnets, minimization of cogging torque and ripple torque for the TORUS-NS and TORUS-S machines are obtained and verified using 3D FEA. Finally a comparison of the TORUS topologies in terms of torque quality is illustrated in the paper.
Aydin et al. (Wed,) studied this question.