Patrick Chi-Kwong Luk

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.

Electronic Tuning of Misaligned Coils in Wireless Power Transfer Systems

The misalignment and displacement of inductively coupled coils in a wireless power transfer system (WPT) can degrade the power efficiency and limit the amount of power that can be transferred. Coil misalignment leads the primary coil driver to operate in an untuned state which causes nonoptimum switching operation and results in an increase in switching losses. This paper presents a novel method to electronically tune a Class-E inverter used as a primary coil driver in an inductive WPT system to minimize the detrimental effects of misalignment between the inductively coupled coils which may occur during operation. The tuning method uses current-controlled inductors (saturable reactors) and a variable switching frequency to achieve optimum switching conditions regardless of the misalignment. Mathematical analysis is performed on a Class-E inverter based on an improved model of a resonant inductive link. Experimental results are presented to confirm the analysis approach and the suitability of the proposed tuning method.

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.

Tuning Class E Inverters Applied in Inductive Links Using Saturable Reactors

This paper investigates the performance of Class E inverters used in wireless power transfer applications based on resonant inductive coupling. The variations in the load and the distance between the coils cause Class E inverters to operate under nonoptimal switching conditions, which result in inefficient operation and can lead to permanent damage to its switching transistor. Therefore, a novel approach to tune Class E inverters electronically is proposed. The tuning method relies on saturable reactors to ensure that the inverter operates under optimal switching conditions regardless of variations in the load and the distance between the coils. In addition, a more accurate model of inductive links is presented in order to provide a better understanding of the major power losses in resonant inductive links. Experimental results are presented to confirm the improved accuracy of the inductive link model and the validity of the tuning method.

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.

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.

Wireless Power Transfer Using Class E Inverter With Saturable DC-Feed Inductor

Resonant converters used as coil drivers in inductive links generally operate efficiently at optimum switching conditions for constant load values and ranges. Changes in load and range can shift the operation of the coil driver to a nonoptimum switching state which results in higher switching losses and reduced output power levels. This paper presents a method to adapt to variations in range for a Class E inverter used as a coil driver in a wireless power transfer (WPT) system based on resonant inductive coupling. It is shown that by controlling the duty cycle of the inverters switch and the value of the DC-feed inductance, the Class E inverter can be tuned to operate at optimum switching conditions as the distance between the resonant coils of the WPT system changes. Mathematical analysis is presented based on a linear piecewise state-space representation of the inverter and the resonant inductive link. Extensive experimental results are presented to verify the performed analysis and validity of the proposed tuning procedure.