Weizhong Fei

A High-Performance Line-Start Permanent Magnet Synchronous Motor Amended From a Small Industrial Three-Phase Induction Motor

Small industrial three-phase induction motors (IMs) normally suffer from poor operational efficiency and power factor. This paper presents a high-performance line-start permanent magnet synchronous motor (LSPMSM) which is developed by simple modifications of an off-the-shelf small industrial three-phase IM with minimized additional costs. Two-dimensional (2-D) dynamic finite element analysis (FEA) models are employed to assess the machine performances, which are validated by comprehensive experimental results. The experimental comparisons between the amended LSPMSM and the original IM have indicated that significant improvements in efficiency and power factor can be achieved by the proposed LSPMSM.

Development of a Magnetic-Geared Permanent-Magnet Brushless Motor

High-torque and low-speed electrical drives are often employed for applications where mechanical gearing cannot be accommodated. On the other hand, permanent-magnet (PM) gear has drawn significant attention from both academies and industries due to the conspicuous merits, such as reduced acoustic noise, maintenance free, improved reliability, precise peak torque transmission capability, and inherent overload protection. In this paper, a magnetic-geared PM brushless motor is presented. It is a novel low-speed and high-torque motor which merges the advantages of conventional PM brushless motor and PM gear. Its topology and operation principle are introduced. Some techniques are employed to optimize and improve the motor performance, while the validity of the proposed techniques is verified with finite-element analysis. Moreover, an alternative operation condition, which can further reduce the motor speed and increase its output torque, is proposed and analyzed.

A Novel Permanent-Magnet Flux Switching Machine With an Outer-Rotor Configuration for In-Wheel Light Traction Applications

This paper proposes a novel permanent-magnet (PM) flux switching (PMFS) machine with an outer-rotor configuration for in-wheel light traction applications. The geometric topology of the outer-rotor PMFS machine is introduced, and the analytical sizing equations are derived to determine the main design parameters of the machine. Two-dimensional finite-element analysis (FEA) models are developed to investigate and optimize the machine performance. Furthermore, the flux-weakening capability of the machine is analyzed and further improved by segmental PMs with iron bridges. The machine performance predictions by 2-D FEA models are validated by experimental tests on the prototype machine. The suitability of the proposed outer-rotor PMFS machine for in-wheel light traction application is demonstrated.

A New Technique of Cogging Torque Suppression in Direct-Drive Permanent-Magnet Brushless Machines

In direct-drive electric propulsion systems, where there is no reduction gear to minimize and absorb the adverse effects of cogging torque generated by the permanent-magnet (PM) machine, minimization of cogging torque generation is of particular importance. In this paper, a novel axial pole-pairing method is proposed to minimize cogging torque generation in a special three-phase outer-rotor PM brushless machine, which uses uneven stator poles to enhance back electromotive force (EMF). Analytical formulas of the machines cogging torque are first derived. The new technique is compared with conventional cogging torque suppression methods by means of analytical models and comprehensive finite-element analysis (FEA). The FEA results show that the new method not only achieves effective cogging torque reduction, but also results in improved harmonic content of the back EMF. The validity of the FEA model is verified by experimental results from the prototype machines. Finally, the significance of optimizing both the load-independent machine design techniques and load-dependent driving techniques to achieve overall torque ripple minimization is discussed.

Torque Analysis of Permanent-Magnet Flux Switching Machines With Rotor Step Skewing

This paper investigates the torque characteristics of permanent-magnet flux switching (PMFS) machines with rotor step skewing. The cogging torque, torque ripple, and average output torque of a PMFS machine with a common stator and different rotor pole widths and rotor pole numbers are first established using two-dimensional (2-D) finite element analysis (FEA). A cost-effective rotor step skewing technique is then proposed to reduce the cogging torque and torque ripple of the machine with two different rotors. The results have revealed that the least step number and angle for optimal torque ripple mitigation of the PMFS machine are determined by the harmonic contents of the torque pulsation and the rotor pole number. The influences of load conditions on the machine torque characteristics are carried out by varying current excitations. The corresponding three-dimensional (3-D) FEA models are constructed and experimental prototypes are built for validations.

Torque Ripple Reduction of a Direct-Drive Permanent-Magnet Synchronous Machine by Material-Efficient Axial Pole Pairing

This paper investigates a material-efficient axial pole pairing method for torque ripple reduction in a direct-drive outer-rotor surface-mounted permanent-magnet synchronous machine. The effects of the magnet pole arc width on the torque ripple characteristics of the machine are first established by both analytical and 2-D finite element approaches. Furthermore, the effectiveness of the axial pole pairing technique in mitigating the machine cogging torque, back electromotive force harmonics, and overall torque quality is comprehensively examined. Finally, 3-D finite element analysis and experiments are carried out to validate the proposed approach, and the results show that axial pole pairing can be cost efficiently implemented in terms of magnet material usage and assembly.

Study of Retaining Sleeve and Conductive Shield and Their Influence on Rotor Loss in High-Speed PM BLDC Motors

Rotor eddy-current loss is usually significant in high-speed permanent magnet brushless dc (PM BLDC) motors. On the other hand, the rotor is usually protected with a nonmagnetic retaining sleeve. The influence of the conductivity of the retaining sleeve on the rotor eddy-current loss is analyzed in this paper. Furthermore, utility of a conductive copper shield between the sleeve and magnets is demonstrated. Although eddy current is induced in the copper shield, causing additional loss, its magnetic field can smooth the varying field in the rotor and reduce the overall eddy-current loss dramatically. The relationship between the thickness of copper shield and the rotor eddy-current loss is also examined

A new axial flux permanent magnet Segmented-Armature-Torus machine for in-wheel direct drive applications

A novel axial flux permanent magnet (AFPM) machine with a segmented-armature torus (SAT) topology is investigated. The machines key feature rests on a new and simple configuration of laminated stator poles, which allows high flux density similar to that of the radial flux machines to be established. A full analytical model of the proposed AFPM machine is first developed. To overcome the analytical complexity arising from the novel stator configuration, an efficient and yet realistic approximation is used. Then a three-dimensional (3-D) finite element analysis (FEA) model of a 6 kW AFPM machine is developed for the validation of the analytical model. Finally, experimental results are obtained from an AFPM prototype motor, which has been designed by the sizing equations developed in the analytical model. The results from the analytical model are then compared with those from the FEA model and the tests of the prototype motor. The validity of the analytical model and the viability of the proposed AFPM machine as a leading contender for in-wheel direct drive traction applications are then confirmed.

Permanent-Magnet Flux-Switching Integrated Starter Generator With Different Rotor Configurations for Cogging Torque and Torque Ripple Mitigations

This paper investigates the cogging torque and torque ripple features of a permanent-magnet flux-switching integrated starter generator. The effects of the rotor pole arc width on the cogging torque, torque ripple, and output torque are first established using finite-element analysis (FEA). Three torque ripple reduction techniques based on the optimization of three different rotor pole configurations, namely, uniform, step skewed, and axial pairing, are then proposed. The torque characteristics of each rotor configuration at varying load currents and phase angles are studied in detail. A prototype machine with a common stator and the three optimized rotor configurations are built for experimental validation. Both the FEA results and the experimental tests show that the step skewed and axial pairing techniques can alleviate the cogging torque significantly, but the latter is less effective than the former in reducing the overall torque ripple.

An Improved Model for the Back-EMF and Cogging Torque Characteristics of a Novel Axial Flux Permanent Magnet Synchronous Machine With a Segmental Laminated Stator

An improved model for the back-electromagnetic-force (back-EMF) and cogging torque characteristics of a novel axial flux permanent magnet (AFPM) synchronous machine with a segmental laminated stator is presented. Based on a 3-D finite-element analysis (FEA) modeling approach that takes into the anisotropic properties of the machines laminated cores, the proposed model provides superior performance prediction to existing isotropic models, in which lamination effects are not considered. An anisotropic model has been developed to predict the back-EMF and cogging torque of an existing prototype AFPM machine with optimized rotor magnets. Experimental results of the AFPM machine are compared against the results from the FEA models based on anisotropic and isotropic modeling, respectively. The results show that anisotropic modeling provides more accurate performance prediction of the AFPM machine with laminated cores.