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Axial-flux permanent magnet (AFPM) machines are gaining popularity in low-speed and high torque applications due to their high torque density, high efficiency, and compact structure. In this article, a dual-rotor slotless AFPM (DRSAFPM) machine equipped with equidirectional toroidal winding (EDTW) is proposed and compared with that equipped with conventional single-layer and double-layer concentrated windings (CWs). First, the differences between the DRSAFPM machine with EDTW and that with conventional CWs in coil layout, electromotive force (EMF), and winding magnetomotive force are revealed. Considering the special coil layout of the EDTW, the coil factor and size equations of the DRSAFPM machines with EDTW and conventional CWs are presented. Second, the electromagnetic performance including air-gap field, back-EMF, torque, and efficiency of the DRSAFPM machines with EDTW and conventional CWs are analyzed based on the three-dimensional finite-element method. The simulation results validate the correctness of the coil factor and size equations and indicate the EDTW–DRSAFPM machine has superiority in back-EMF amplitude and torque density. Finally, a prototype of the EDTW–DRSAFPM machine is manufactured and tested, which validates the feasibility of the EDTW–DRSAFPM machine and the correctness of the analysis. [ABSTRACT FROM AUTHOR]

A 2-degree-of-freedom (2DoF) induction machine realizes rotary, linear, and helical motions, exhibiting the merits of integrated structure and high material utilization. Compared with traditional electric machines, one of the special factors affecting the electromagnetic performances is the helical motion coupling effect (HMCE). This article systematically investigates its production mechanism based on the proposed HMCE model first. Then, a comprehensive comparison of the torque performances between the rotary and linear motion parts is conducted to evaluate the HMCE in two motion parts, and then the results are verified by 3-D finite element model. Besides, resistant torque and force ratios are proposed and calculated to assess the extent of the HMCE. It can be concluded that the torque performances of the rotary motion component are weakened more than those of the linear motion component by the HMCE. Further, two methods to suppress the coupling effect, namely adjustment of linear motion slip ratio and change of linear motion frequency, are discussed. Experimental results have validated the analytical results and effectiveness of the suppression strategies. [ABSTRACT FROM AUTHOR]

The 2-degree-of-freedom direct drive induction motor (2DoFDDIM) is capable of implementing rotary linear or helical motion, which has the definite advantages of integrated structure, high material utilization, and so on. In this paper, the characteristics analysis of the three kinds of motions is presented. The air-gap magnetic field distributions and mechanical characteristics of the 2DoFDDIM with three motions are derived respectively. The results show that there is super synchronous speed or velocity phenomenon for rotary or linear motion. Moreover, the coupling effects between the rotating and travelling wave magnetic fields and that between the two mechanical motions will deteriorate the performance of the three-dimensional (3-D) helical motion compared with the two-dimensional (2-D) motion (rotary or linear). The expressions of the resistant torque and force caused by the coupling effect are derived, which are verified by 3-D finite-element models (FEMs). The results regarding the weakening of the output torque of helical motion and interacting magnetic field obtained from FEMs are then verified by experimental tests. Finally, the skewed slot method is applied to 2DoFDDIM, which successfully improves the performance of helical motion aiming to compensate the coupling resistant torque and force. [ABSTRACT FROM AUTHOR]

This paper investigates the influence of stator slots and rotor pole pairs combinations on torque performances in rotor permanent magnet flux switching (RPM-FS) machines. Based on a magnetomotive force (MMF) permeance model, the candidates of stator slots and rotor pole pairs combinations with higher torque capability can be determined by analyzing the PM-MMF and winding factor. Meanwhile, the candidates with a lower torque ripple can be obtained by referring to the cogging torque, which is related to the greatest common divisor of stator slots and rotor pole pairs. In addition, from the field modulation principle, the RPM-FS machines with the same fundamental magnetic loadings and winding factors exhibit identical fundamental harmonic torque, but different modulation harmonic components. Finally, four candidates with attractive torque performance are chosen, and the characteristics are verified by finite-element analysis and experiments. [ABSTRACT FROM AUTHOR]