Torque density

Abstract: Vernier permanent-magnet (VPM) machines are well known for high torque density but low power factor. This paper deals with the low power factor of VPM machines. The goal is not obtained by reducing the electrical loading or adjusting current advance angle but by proposing a novel vernier topology, i.e., a dual-stator spoke-array (DSSA) VPM topology. In this paper, the characteristics of the DSSA VPM topology, such as active part, auxiliary mechanical structure, and rotor anisotropy, are analyzed in detail. Performances are evaluated based on finite-element analysis, including power factor, torque density, and cogging torque. The results show that the DSSA VPM topology exhibits high power factor, viz., ~0.9, and significantly high torque capability. The verification of the mechanical structure scheme is also done in this paper. Finally, theoretical analyses are validated by the experimental results by a 44-rotor pole 24-slot DSSA VPM prototype.

Abstract: The use of six-phase induction motor for industrial drives presents several advantages over the conventional three-phase drive such as improved reliability, magnetic flux harmonic reduction, torque pulsations minimization and reduction on the power ratings for the static converter. For these reasons, six-phase induction motors are beginning to be a widely acceptable alternative in high power applications. A typical construction of such drives includes an induction machine with a dual three-phase connection, where two three-phase groups are spatially shifted thirty electrical degrees, a six-leg inverter and a control circuit. By controlling the machine's phase currents, harmonic elimination and torque ripple reduction techniques could be implemented. This paper describes a technique of injecting third harmonic zero sequence current components in the phase currents, which greatly improves the machine torque density. Analytical, finite element and experimental results are presented to show the system operation and to demonstrate the improvement on the torque density.

Abstract: This paper proposes a coaxial magnetic gear that offers higher torque density, lower cogging torque, and lower iron losses than its counterparts. The key is to newly employ a Halbach permanent-magnet (PM) array to constitute the PM poles in the inner rotor and a partial Halbach array (two segments per pole) for the outer rotor. The corresponding magnetic field distributions, torque transmission, and torque ripples are analytically discussed. Then, the corresponding performances are quantitatively assessed by using the finite-element method.

Abstract: A machine design of a switched reluctance motor having competitive torque and efficiency as well as compactness with respect to an interior permanent-magnet (IPM) synchronous motor (IPMSM) in a hybrid electric vehicle (Toyota Prius 2003) has been investigated. A torque of 400 N·m is set as a target with an outer diameter of 269 mm with an axial length of 156 mm, including coil end lengths. In addition, a 50-kW field weakening capability must be competitive to the IPMSM. The highest efficiency of 95% is also aimed. Stator and rotor structures and iron material are investigated. Test machines are built. Static and light load tests are carried out.