S. L. Ho

Quantitative Comparison of Novel Vernier Permanent Magnet Machines

In this paper, a novel direct-drive double rotor Vernier panent magnet (DR-VPM) machine is proposed and analyzed. The key of the design is to incorporate two concentric rotors and the Vernier structure within one permanent magnet (PM) machine, while keeping the machine volume and slot number unchanged. The main merits of this proposed machine are its compact structure, improved torque density, reduced stator end winding length, and reduced copper loss. The operating principle of the machine is discussed and its steady and transient performances are analyzed using circuit-field-motion coupled time-stepping finite element method (CFM-TS-FEM). A dual-excitation PM Vernier (DE-VPM) machine and a single outer rotor PM Vernier (SR-VPM) machine are designed and compared with this proposed Vernier PM machine using CFM-TS-FEM. Comparison results as reported are used to confirm and validate the advantageous performance of the proposed machine.

Design and Comparison of Vernier Permanent Magnet Machines

Vernier permanent magnet (VPM) machines can be utilized for direct drive applications by virtue of their high torque density and high efficiency. The purpose of this paper is to develop a general design guideline for split-slot low-speed VPM machines, generalize the operation principle, and illustrate the relationship among the numbers of the stator slots, coil poles, permanent magnet (PM) pole pairs, thereby laying a solid foundation for the design of various kinds of VPM machines. Depending on the PM locations, three newly designed VPM machines are reported in this paper and they are referred to as 1) rotor-PM Vernier machine, 2) stator-tooth-PM Vernier machine, and 3) stator-yoke-PM Vernier machine. The back-electromotive force (back-EMF) waveforms, static torque, and air-gap field distribution are predicted using time-stepping finite element method (TS-FEM). The performances of the proposed VPM machines are compared and reported.

Ring-type electric current sensor based on ring-shaped magnetoelectric laminate of epoxy-bonded Tb0.3Dy0.7Fe1.92 short-fiber/NdFeB magnet magnetostrictive composite and Pb(Zr, Ti)O3 piezoelectric ceramic

A ring-type electric current sensor operated in vortex magnetic field detection mode is developed based on a ring-shaped magnetoelectric laminate of an axially polarized Pb(Zr, Ti)O3 (PZT) piezoelectric ceramic ring bonded between two circumferentially magnetized epoxy-bonded Tb0.3Dy0.7Fe1.92 (Terfenol-D) short-fiber/NdFeB magnet magnetostrictive composite rings. The electric current sensitivity of the sensor was evaluated, both theoretically and experimentally. The sensor showed a high nonresonance sensitivity of ∼12.6 mV/A over a flat frequency range of 1 Hz–30 kHz and a large resonance sensitivity of 92.2 mV/A at the fundamental shape resonance of 67 kHz, besides an excellent linear relationship between the input electric current and the output magnetoelectrically induced voltage. The power-free, bias-free, high-sensitive, and wide-bandwidth natures of the sensor make it great potential for real-time condition monitoring of engineering systems having electric current-carrying cables or conductors.

Application of a meshless method in electromagnetics

An improved meshless method is presented, with an emphasis on the detailed description of this new computational technique and its numerical implementations, by investigating the usefulness of a commonly neglected parameter. Two approaches to enforce essential boundary conditions are also thoroughly investigated. Numerical tests on a mathematical function are carried out as a means of validating the proposed method. It is seen that the proposed method is more robust than the conventional ones. Applications in solving electromagnetic problems are also presented.

Quantitative Design and Analysis of Relay Resonators in Wireless Power Transfer System

Wireless power transfer systems are finding increasing applications which can enhance the living standard of the general public. Typical examples are wireless charging of mobile phone batteries and car batteries. Thanks to the advent of power electronics in the past few decades, some wireless charging systems are now emerging in the commercial sector. However, the transfer efficiency and transfer distance of these chargers are limiting the technology to a few specific applications only. In order to increase the transfer distance, some researchers have successfully proposed to use relay coils to improve their wireless power transfer efficiency. In this paper, the role of relay resonator is examined critically. The reported findings indicate that it is not always desirable to have relay coils in wireless charger as the relay resonator may increase, or sometimes reduce, the overall power transfer efficiency. The findings also reveal that there is an optimal position for the designer to locate the relay resonator to maximize the power transfer efficiency.

Optimization of Permanent Magnet Surface Shapes of Electric Motors for Minimization of Cogging Torque Using FEM

A novel algorithm which minimizes the cogging torque of surface-mounted permanent magnet (SPM) brushless motors by optimizing the surface profile of PM is presented. An efficient strategy for using finite element method (FEM) is proposed to calculate the cogging torque of PM motors with different PM shape designs. Compared with the use of general FEM, the computing time with this proposed method is significantly reduced, which is only 0.017% of that required by the former. Because of the considerable reduction of computing time in the magnetic field analysis of PM motors, it becomes feasible to use genetic algorithm (GA) to optimize the PM shape in order to realize cogging torque minimization. A numerical experiment is used to validate the proposed method.

A Quantitative Comparative Analysis of a Novel Flux-Modulated Permanent-Magnet Motor for Low-Speed Drive

A novel low-speed flux-modulated (FM) permanent-magnet (PM) motor that breaks the traditional design rule, which stipulates that the number of stator pole pairs and the number of rotor pole pairs must be the same, is proposed. The FM motor has a special physical structure with iron segments in the air gap to modulate the magnetic field. In the design, the free space between adjacent stationary iron segments also acts as ventilating ducts to help improving the heat dissipation and ventilation of the motor. Its cogging torque is very small. In this paper, a rule for comparing the power density of electric motors is proposed. The performance of the FM motor is compared with those of a magnetic-geared PM motor, a traditional PM motor, and a fractional-slot PM motor by using magnetic field finite-element analysis.

Eddy Current Reduction in High-Speed Machines and Eddy Current Loss Analysis With Multislice Time-Stepping Finite-Element Method

The significance of eddy-current in high-speed permanent magnet machines cannot be underestimated in that it has serious implications on the machines efficiency or even demagnetizes the PMs because of an overheating problem. It is necessary to accurately estimate the eddy-current losses and find an optimal design to minimize the losses and improve the machines performance. In this paper, the axial segmentation of the PMs is first employed to cut off the eddy-current axial paths. Then, a conductive shield is introduced to smooth the time varying magnetic field in the conductive sleeve and the PMs in order to reduce the eddy-current losses. A nodal method based network-field coupled multislice time-stepping finite element method (TS-FEM) is proposed to analyze the steady-state and dynamic characteristics of the high-speed PM machine; its merit is that sub-block matrixes of the circuit equations are more convenient to be established compared with that of mesh method. Analysis of eddy-current losses in the rotor is reported.

Transient Analysis of a Magnetic Gear Integrated Brushless Permanent Magnet Machine Using Circuit-Field-Motion Coupled Time-Stepping Finite Element Method

In this paper, a novel magnetic gear integrated brushless permanent magnet machine is studied. The main merit of the machine is that the torque produced by the stator windings can be transmitted between the low-speed rotor and the high-speed rotor through the modulation of ferromagnetic pole pieces; hence it can output a large torque at a low speed. The operating principle of the machine is discussed and its steady-state and transient performances are analyzed using circuit-field-motion coupled time-stepping finite element method. Detailed analysis about its gear ratio, cogging torque, core losses, and power factor are reported. Theoretical analysis agrees well with the FEM computation results.

Analytical Design Study of a Novel Witricity Charger With Lateral and Angular Misalignments for Efficient Wireless Energy Transmission

Detailed theoretical and numerical analysis reveals that Witricity, which was first reported by a research team at the Massachusetts Institute of Technology, is efficient and practical for mid-range wireless energy exchange to transmit nontrivial amount of power wirelessly over a long distance. This paper presents an analytical model, based on Witricity technology, for resonant magnetic coupling to address misalignments between the transmitter and receiver of this advanced system. The relationships among the energy transfer efficiency and several key parameters of the system are analyzed using finite element method (FEM). Formulae are derived for the magnetic field of the receiver coil when it is laterally and angularly misaligned from the transmitter. A resonant near-field power transfer formula is suggested to incorporate the coil characteristics and misalignments. Experiments have also been carried out to facilitate quantitative comparison. It is shown that a maximum degree of misalignment can be defined in a given application. The analysis reported allows a formal design procedure to be established for the optimization of Witricity for a given application.