Wenliang Zhao

Material-Efficient Permanent-Magnet Shape for Torque Pulsation Minimization in SPM Motors for Automotive Applications

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.

Comparative Study on Novel Dual Stator Radial Flux and Axial Flux Permanent Magnet Motors With Ferrite Magnets for Traction Application

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.

Optimal Design of a Novel V-Type Interior Permanent Magnet Motor with Assisted Barriers for the Improvement of Torque Characteristics

This paper performs a study on the optimal design of V-type interior permanent magnet motors (VIPMMs), in which the rotor is equipped with assisted barriers for the improvement of average torque and torque ripple. The approach differs from the conventional interior permanent magnet motors, in which the reluctance torque due to saliency reaches a maximum value at a current phase angle located 45 electrical degrees with respect to the maximum value obtained from the magnetic torque produced by the rotor magnets. The adoption of assisted barriers is employed to improve the torque production by creating rotor asymmetry to allow the reluctance torque and the magnetic torque reach a maximum value near or 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. First, an iterative optimization is performed on a concept design of a 6/4 VIPMM for demonstrating the design principle based on finite element method. Then, the VIPMM is further optimized by algorithms, such as the kriging method and genetic algorithm for improving the torque characteristics and efficiency. As a result, the optimal VIPMM with assisted barriers shows the substantially improved performance compared with a conventional design.

Optimal Design of a Novel Asymmetrical Rotor Structure to Obtain Torque and Efficiency Improvement in Surface Inset PM Motors

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.

Design and analysis of a novel dual stator axial flux spoke-type ferrite permanent magnet machine

This paper proposes a novel dual stator axial flux spoke-type permanent magnet (DSAFSPM) machine for the purpose of improving torque (power) density and reducing cogging torque and torque ripple. This machine adopts low cost ferrite permanent magnets inserted into the rotor as a spoke-type array. Two stators with the same slot/teeth construction are arranged to be shifted by one stator tooth width. Three phase-group concentrated-coil windings are placed into the slots. In order to highlight the contribution of the novel configuration to the proposed DSAFSPM machine, the electromagnetic characteristics such as air-gap flux density, permanent magnet (PM) flux linkage, back EMF, cogging torque, torque ripple, and torque density are compared with those of a basic DSAPSPM machine with two axially aligned stators based on 3-D finite element method (FEM).

Dual airgap stator- and rotor- permanent magnet machines with spoke-type configurations using phase-group concentrated-coil windings

This paper presents an advanced design procedure for stator-based and rotor-based permanent magnet (PM) machines to improve the electromagnetic performance by incorporating the spoke-type magnet configurations, phase-group concentrated coil windings, and an unaligned arrangement of two rotors/stators. The dual-rotor switched flux PM machine (SFPMM), designated as the stator-PM machine, and the dual-stator spoke-type interior PM machine (S-IPMM), termed the rotor-PM machine, are designed by the proposed design procedure to obtain high torque density and low pulsating torques for direct-drive applications. A quantitative comparison is performed between the proposed SFPMM and S-IPMM, and a conventional SFPMM with concentrated windings is adopted as the referenced model to evaluate the contribution of the proposed design procedure. The machine performance including back electromotive force, cogging torque, and electromagnetic torque is first analyzed by a finite element method under the same operating conditions. Finally, a prototype of the dual-stator S-IPMM is manufactured, and some key simulation results are verified by the experimental tests.

Design of Ultrahigh Speed Axial-Flux Permanent Magnet Machine With Sinusoidal Back EMF for Energy Storage Application

This paper focuses on the design and the analysis of an ultrahigh speed axial-flux permanent magnet (AFPM) machine for an aerospace flywheel energy storage system. The superiority of the proposed AFPM machine is the material-efficient PM shape, which contributes to obtain a sinusoidal back electromotive force (back EMF) and, hence, reduces the torque pulsations of the machine such as torque ripple. The harmonics present in back EMF have a large influence on iron loss and torque pulsations, which are always unacceptable in the applications involving the speed as high as 1 000 000 r/min. Analytical modeling is first performed to determine the PM shape for the proposed models. Then, the advantages of the proposed models are verified by comparing with the basic model with the conventional ring-shaped PMs using the 3-D finite-element method. The results show that the proposed models have a nearly ideal sinusoidal back-EMF waveform that significantly reduces the torque ripples compared with the basic model.

Dual-stator, spoke-type ferrite permanent magnet motor with phase-group concentrated-coil windings using auxiliary inner stator

This paper proposes a dual-stator, spoke-type ferrite permanent magnet motor (FPMM) with phase-group concentrated-coil (PGCC) windings using an auxiliary inner stator to obtain high motor performance and improve the thermal conditions. In the proposed FPMM, the utilization of the PGCC windings, together with the spoke-type magnets and an unaligned arrangement of two stators, aims at improving torque density and suppressing torque pulsations. Since the inner stator suffers from thermal issues due to the relatively higher electric loading than the outer stator and difficult heat dispassion, the PGCC windings in the proposed FPMM are fed only on the outer stator, featuring an auxiliary inner stator with only iron core. Consequently, the proposed FPMM with PGCC windings could obtain high performance, including high torque density and low torque pulsations, and improve the thermal conditions as well as release manufacturing difficulties by removing windings from the inner stator. Furthermore, a quantitative comparison is carried out among the proposed FPMM with the auxiliary inner stator, the referenced FPMM with PGCC windings in both outer and inner stators, and the referenced FPMM with a single stator, by the aid of a finite element method (FEM). Finally, the operating range characteristics of the proposed FPMM is examined to satisfy the demand of applications with an over 3:1 speed range.

Cost-effective permanent magnet shape for reducing cogging torque and torque ripple in surface-mounted permanent magnet machines

This work was supported in part by the BK21PLUS Program through the National Research Foundation of Korea within the Ministry of Education, and in part by the Human Resources Program in Energy Technology through the Korea Institute of Energy Technology Evaluation and Planning within the Ministry of Trade, Industry and Energy, Korea, under Grant 20154030200730.

Dual rotor flux switching permanent magnet machines with phase-group concentrated-coil windings for high performance

This paper proposes a novel dual rotor radial field flux switching permanent magnet machine (FSPMM) with phase- group concentrated-coil (PGCC) windings and two misaligned rotors to obtain high performance, including high torque density and low cogging torque, as well as low torque ripple. The proposed FSPMM features a new combination of stator slots and rotor poles, which is determined by the winding configurations. The PGCC windings are adopted to obtain a unity displacement winding factor, and enhance the flux focusing effects together with the use of spoke-type PM constructions. The unaligned arrangement of two rotors will help to not only achieve further flux magnification by an alternate operating principle for PM flux concentration, but also suppress the cogging torque. To highlight the advantages of the proposed FSPMM, two conventional FSPMMs with typical machine configurations having concentrated windings are adopted for performance comparison based on a finite element method (FEM) using JMAG-Designer.