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Zhao, Wenliang,Lipo, Thomas A.,Kwon, Byung-Il IEEE 2015 IEEE transactions on magnetics Vol.51 No.11
<P>This paper presents two types of novel dual-stator two-phase permanent magnet synchronous machines (PMSMs) equipped with an advanced phase-group concentrated-coil winding and a spoke-type PM array for direct-drive applications. The key advantage of the proposed two-phase PMSMs is its superior flux-focusing effects, which greatly enhance the torque, benefiting from the whole machine configuration. To highlight the advantages of the proposed two-phase PMSMs, one three-phase PMSM and one two-phase PMSM with the conventional stator and winding configurations are adopted for comparison. All relevant machine characteristics, including the air-gap flux density, back electromotive force, and electromagnetic torque, are predicted by a 2-D finite-element method. Finally, one of the proposed dual-stator two-phase PMSMs is optimized to minimize cogging torque and torque ripples using the Kriging method and a genetic algorithm.</P>
Zhao, Wenliang,Chen, Dezhi,Lipo, Thomas A.,Kwon, Byung-Il IEEE 2015 IEEE transactions on magnetics Vol.51 No.11
<P>This paper proposes novel ferrite-assisted synchronous reluctance machines (FA-SynRMs) having the merit of highly improved machine performance including torque, efficiency, and power factor. The particular superiority of the proposed FA-SynRMs is the utilization of an asymmetrical rotor configuration that contributes to the full use of torque components by allowing the magnetic and reluctance torques to reach their maximum values near or at the same current phase angles. To provide visible insights into the contribution, a frozen permeability method is utilized to separate the torque into the reluctance torque and the magnetic torque based on a 2-D finite-element method by the aid of JMAG-Designer. For highlighting the advantages of the proposed models, a conventional FA-SynRM with symmetrical rotor configurations is adopted for comparison under the same operating conditions. As a result, it is demonstrated that the proposed design is effective in improving the performance of FA-SynRMs.</P>
Wenliang Zhao,Lipo, Thomas A.,Byung-Il Kwon IEEE 2015 IEEE transactions on magnetics Vol.51 No.3
<P>This paper proposes an optimal design of a novel asymmetrical rotor structure for surface inset permanent magnet (PM) motors to obtain torque and efficiency improvement. Different from the conventional approach, the proposed design of asymmetrical rotor structures is employed to improve the torque production by creating rotor asymmetry to allow the reluctance torque and the magnetic torque to reach a maximum at the same current phase angle. To evaluate the contribution, the frozen permeability method is utilized to segregate the torque into its reluctance and magnetic torque components. For demonstrating the design concept and obtaining a criterion for improving torque by making full use of torque components, an optimal design by iterative computation is first to be performed utilizing the finite-element method. Based on the obtained criterion, the optimal design by algorithms, such as the Kriging method and genetic algorithm, is applied to further improve the torque and efficiency. As a result, the performance of the proposed surface inset PM motor by two-step optimization is dramatically improved compared with that of the conventional surface inset PM motor. Furthermore, a comparison between the optimized surface inset PM motor and a conventional surface-mounted PM (SPM) motor is also performed under the same operating condition, which demonstrates that the optimized surface inset PM motor can significantly save the magnet amount compared with the conventional SPM motor for producing the same output torque.</P>
Wenliang Zhao,Lipo, Thomas A.,Byung-Il Kwon IEEE 2014 IEEE transactions on industrial electronics Vol.61 No.10
<P>This paper focuses on the design and analysis of a novel material-efficient permanent-magnet (PM) shape for surface-mounted PM (SPM) motors used in automotive actuators. Most of such applications require smooth torque with minimum pulsation for an accurate position control. The proposed PM shape is designed to be sinusoidal and symmetrical in the axial direction for minimizing the amount of rare earth magnets as well as for providing balanced axial electromagnetic force, which turns out to obtain better sinusoidal electromotive force, less cogging torque, and, consequently, smooth electromagnetic torque. The contribution of the novel PM shape to motor characteristics is first estimated by 3-D finite-element method, and all of the simulation results are compared with those of SPM motors with two conventional arched PM shapes: one previously reported sinusoidal PM shape and one step skewed PM shape. Finally, some finite-element analysis results are confirmed by experimental results.</P>
Wenliang Zhao,Lipo, Thomas A.,Byung-Il Kwon IEEE 2014 IEEE transactions on magnetics Vol.50 No.11
<P>This paper proposes two novel traction motors with ferrite magnets for hybrid electric vehicles (HEVs), which have competitive torque density and efficiency as well as operating range with respect to a referenced rare earth magnet motor employed in the third-generation Toyota Prius, a commercialized HEV. The two proposed traction motors, named as dual stator radial flux permanent magnet motor (DSRFPMM) and dual stator axial flux permanent magnet motor (DSAFPMM), adopt the same design concept, which incorporates the unaligned arrangement of two stators together with the use of spoke-type magnet array and phase-group concentrated-coil windings for the purpose of increasing torque density and reducing torque ripple. A finite element method is utilized for predicting the main characteristics, such as back electromotive force, cogging torque, electromagnetic torque, iron loss, and efficiency in both of the proposed motors. Moreover, a comparative study between the proposed DSRFPMM and DSAFPMM is performed under the same operating condition. As a result, it is demonstrated that both of the proposed ferrite permanent magnet motors could be good alternatives for traction application, replacing the rare earth magnet motors.</P>
Zhao, Wenliang,Lipo, Thomas A.,Kwon, Byung-Il IEEE 2015 IEEE transactions on magnetics Vol.51 No.11
<P>This paper proposes two approaches to minimize torque pulsations, including cogging torque and electromagnetic torque ripple, for spoke-type interior permanent magnet (IPM) motors. The first approach is an improved skewing method, in which the rotor PMs are skewed by being symmetrical in the axial direction within one magnet pole pitch for not only reducing torque pulsations but also maintaining maximum available torque and eliminating unbalanced axial electromagnetic forces. The second one is a sinusoidal PM-shaping method with the aim of achieving the same advantageous effects as the proposed skewing method. Both the proposed methods adopt stepped rotor-PM schemes, and the effects of the rotor-PM step numbers on motor performance are investigated. To highlight the advantages of the proposed approaches, a spoke-type IPM motor with the conventional PM configuration is adopted as the basic model. All the motor characteristics, such as back electromotive force, cogging torque, and electromagnetic torque, are predicted by a 3-D finite-element method with the aid of JMAG-Designer.</P>