Arwyn S. Thomas

Multiphase Flux-Switching Permanent-Magnet Brushless Machine for Aerospace Application

Flux-switching permanent-magnet (FSPM) brushless machines have attracted considerable interest as a candidate machine technology for applications requiring high torque density and robust rotors. To date, published findings have focused exclusively on single- and three-phase FSPM machines. This paper investigates FSPM brushless machines of higher phase numbers by means of a detailed comparison of the electromagnetic performances of three-, four-, five-, and six-phase variants within the specific context of aerospace machine. Machines having both all poles and alternate poles wound are investigated, with the latter offering scope to reduce mutual coupling between phases so as to achieve improved fault tolerance. The finite-element (FE)-predicted electromagnetic performances in both machines, such as electromotive force waveform, winding inductance, cogging torque, and static torque, are validated by the experiments made on a small-scale five-phase FSPM machine. The nature of the machine specification requires that consideration must be given to mechanical stress in the rotor and the tradeoff with electromagnetic design considerations, notably the degree of rotor saliency which can be incorporated. Therefore, a mechanical FE study of the rotor mechanical stresses of multiphase FSPM machines is also comparatively assessed.

Alternate Poles Wound Flux-Switching Permanent-Magnet Brushless AC Machines

Flux-switching permanent-magnet (FSPM) brushless machines have emerged as an attractive machine type by virtue of their high torque densities, simple and robust rotor structure, and the fact that permanent magnets and coils are both located on the stator. Both 2-D and 3-D finite element analyses are employed to compare the performance of a conventional all poles wound (double-layer winding) topology with that of three modular alternate poles wound (single-layer winding) topologies, in terms of output torque, flux-linkage, back EMF, and inductances. It is shown that the FSPM machine can be designed in this way without incurring a significant performance penalty, but that some degree of rotor skewing or a variation in stator and rotor pole combination may be required in order to maintain a sinusoidal back-EMF waveform and reduce the torque ripple. Experimental validation is reported for both conventional all poles wound and alternate poles wound FSPM machine topologies.

Multi-Phase Flux-Switching Permanent Magnet Brushless Machine for Aerospace Application

Flux-switching permanent-magnet (FSPM) brushless machines have attracted considerable interest as a candidate machine technology for applications requiring high torque density and robust rotors. To date, published findings have focused exclusively on single- and three-phase FSPM machines. This paper investigates FSPM brushless machines of higher phase numbers by means of a detailed comparison of the electromagnetic performances of three-, four-, five-, and six-phase variants within the specific context of aerospace machine. Machines having both all poles and alternate poles wound are investigated, with the latter offering scope to reduce mutual coupling between phases so as to achieve improved fault tolerance. The finite-element (FE)-predicted electromagnetic performances in both machines, such as electromotive force waveform, winding inductance, cogging torque, and static torque, are validated by the experiments made on a small-scale five-phase FSPM machine. The nature of the machine specification requires that consideration must be given to mechanical stress in the rotor and the tradeoff with electromagnetic design considerations, notably the degree of rotor saliency which can be incorporated. Therefore, a mechanical FE study of the rotor mechanical stresses of multiphase FSPM machines is also comparatively assessed.

Cogging Torque in Flux-Switching Permanent Magnet Machines

The influence of manufacturing tolerances on the cogging torque waveforms, as well as the back-EMF waveforms, in 3- and 5-phase flux-switching permanent magnet (FSPM) machines having different numbers of stator/rotor poles is investigated by finite element analyses and experiments. The cause of excessive cogging torque in the prototype FSPM machines has been identified. It is due to modular stator structure which makes it mechanically weak, leading to the intrusion of C-core into the airgap and an uneven inner stator bore. The analyses presented in the paper should be useful to the design and analysis of modular PM machines in general.

Proximity Loss Study In High Speed Flux-Switching Permanent Magnet Machine

High speed flux-switching permanent magnet (FSPM) machines have been identified as key technologies for aerospace and hybrid electric vehicle applications. The open slot geometry, high stator flux densities and high operating frequencies result in high variable cross slot leakage and proximity losses within the armature windings. The aim of this study is to reduce AC losses in the armature of a high speed FSPM machine by stranding the conductors. The influence of rotor movement across the slot opening is investigated using 2-D finite element analysis. A simple 1-D analytical model is developed and validated by the finite element analysis to accurately estimate the level of proximity losses and then used to determine the optimal number and diameter of conductors.

Fault-Tolerant Flux-Switching Permanent Magnet Brushless AC Machines

Flux-switching permanent magnet (FSPM) brushless machines have emerged as an attractive machine type by virtue of their high torque densities, simple and robust rotor structure and the fact that permanent magnets and coils are both located on the stator. Both 2D and 3D finite element analyses (FEA) are employed to compare the performance of a standard topology with three modular, fault-tolerant designs in terms of output torque, flux-linkage, back-EMF and inductances. It is shown that the FSPM machine can be designed to be fault-tolerant without incurring a significant performance penalty, but that some degree of rotor skewing may be required in order to maintain a sinusoidal back-EMF waveform and reduce the torque ripple. Experimental validation is reported for both standard and fault-tolerant FSPM machine topologies.

Novel Modular-Rotor Switched-Flux Permanent Magnet Machines

Switched-flux permanent magnet (PM) (SFPM) machines have attracted considerable interest in recent years, since the flux focusing can be utilized, both armature windings and PM excitation sources are on the stator, while the salient pole rotor is very simple and robust. In SFPM machines, the high variable flux densities throughout the stator core result in iron loss being a significant proportion of the total losses. This paper presents a novel modular-rotor SFPM machine that facilitates a reduction in iron loss for a marginal reduction in output torque. The modular rotor also offers a reduction in rotor mass over the conventional-rotor topology. The electromagnetic performance of both conventional- and modular-rotor SFPM machines is analyzed by 2-D finite element analyses and is verified by measurements on small-scaled prototype SFPM machines.

Thermal modelling of switched flux permanent magnet machines

This paper presents the electromagnetic loss and thermal modelling of a switched flux permanent magnet (SFPM) machine. A 2D finite element method is first used to calculate the stator and rotor iron losses as well as PM eddy current losses. Then, 3-D thermal modelling has been performed for analysing the temperature distribution within the SFPM machine, the calculated power losses have been applied to different machine components as heat sources to predict the temperature distributions throughout the SFPM machine. A prototype of 50 kW SFPM machine has been used for thermal tests under both open-circuit and on-load conditions. Good agreement between measured and simulated results has been achieved.

Electromagnetic loss investigation and mitigation in switched flux permanent magnet machines

This paper presents the electromagnetic loss analysis and mitigating methods of switched flux permanent magnet (SFPM) machines. The 2-dimentional finite element (2-D FE) method is used to calculate the flux density in all the mesh elements within stator and rotor iron cores, then the stator and rotor hysteresis, eddy current and excess losses are calculated. The PM eddy current losses have been calculated as well by using 2-D FE method. The methods such as segmenting (either radially or axially) the permanent magnets or modifying the ratio of rotor pole to pole pitch have been employed for eddy current reduction. The FE results have shown that the proposed methods are very effective in reducing PM eddy current losses without sacrificing the average torque of the investigated SFPM machines.

Influence of pole number and stator outer diameter on volume, weight, and cost of superconducting generators with iron-cored rotor topology for wind turbines

This paper investigates the influence of pole number and stator outer diameter on the performance of superconducting (SC) generators. The SC generator has an iron-cored rotor topology. First, the generator structure is introduced and the optimization procedure is described. Then, the influence of design parameters on performance, in terms of generator volume, weight, SC wire utilization, active material cost, etc., is presented. Some relationships for the optimal combinations for different performance attributes are established. In addition, the influence of SC material price on the determination of optimal stator outer diameter and pole number is discussed. Finally, the influence of SC coil area per pole on performance is also investigated.