Permanent Magnet Vernier Machine: A Review

Permanent magnet vernier machines (PMVMs) gained a lot of interest over the past couple of decades. This is mainly due to their high torque density enabled by the magnetic gearing effect. This study will provide a thorough review of recent advances in PMVMs. This review will cover the principle of operation and nature of magnetic gearing in PMVMs, and a better understanding of novel PMVM topologies using different winding configuration as well as different modulation poles and rotor structures. Detailed discussions on the choice of gear ratio, slot-pole combinations, design optimisation and role of advanced materials in PMVMs will be presented. This will provide an update on the current state-of-the art as well as future areas of research. Furthermore, the power factor issue, fault tolerance as well as cost reduction will be discussed highlighting the gap between the current state-of-the art and what is needed in practical applications

A Review of Transverse Flux Machines Topologies and Design

High torque and power density are unique merits of transverse flux machines (TFMs). TFMs are particularly suitable for use in direct-drive systems, that is, those power systems with no gearbox between the electric machine and the prime mover or load. Variable speed wind turbines and in-wheel traction seem to be great-potential applications for TFMs. Nevertheless, the cogging torque, efficiency, power factor and manufacturing of TFMs should still be improved. In this paper, a comprehensive review of TFMs topologies and design is made, dealing with TFM applications, topologies, operation, design and modeling

Linear Machines for Long Stroke Applications: a review

This document reviews the current state of the art in the linear machine technology. First,the recent advancements in linear induction, switched reluctance and permanent magnet machines arepresented. The ladder slit secondary configuration is identified as an interesting configuration for linearinduction machines. In the case of switched reluctance machines, the mutually-coupled configuration hasbeen found to equate the thrust capability of conventional permanent magnet machines. The capabilities ofthe so called linear primary permanent magnet, viz. switched-flux, flux-reversal, doubly-salient and verniermachines are presented afterwards. A guide of different options to enhance several characteristics of linearmachines is also listed. A qualitative comparison of the capabilities of linear primary permanent magnetmachines is given later, where linear vernier and switched-flux machines are identified as the most interestingconfigurations for long stroke applications. In order to demonstrate the validity of the presented comparison,three machines are selected from the literature, and their capabilities are compared under the same conditionsto a conventional linear permanent magnet machine. It is found that the flux-reversal machines suffer froma very poor power factor, whereas the thrust capability of both vernier and switched-flux machines isconfirmed. However, the overload capability of these machines is found to be substantially lower than theone from the conventional machine. Finally, some different research topics are identified and suggested foreach type of machine

Design and analysis of novel asymmetric-stator-pole flux reversal PM machine

This paper proposes a novel flux reversal permanent magnet (FRPM) machine with asymmetric-stator-pole (ASP) configuration. Different from the conventional FRPM machine with uniform “NS-NS-NS” PM sequence, the proposed ASP-FRPM machine is characterized by a “NSN-S-NSN” magnet arrangement. Hence, the interpolar flux leakage is significantly reduced with the developed design, which can improve the torque capability. The machine topologies, features and operating principle are introduced, respectively. A simplified magnetic circuit model is established to reveal the underlying flux leakage reduction mechanism of the ASP design, and the rotor pole number is analytically optimized as well. The design parameters are then globally optimized so as to improve the torque quality. In addition, the electromagnetic characteristics of the ASP- and conventional FRPM machines are compared. Finally, experiments have been carried out to validate the theoretical results

Development of a Linear Vernier Hybrid Machine for direct drive wave energy converters

PhD ThesisThe work presented in this thesis concerns the development of linear electric machines for use with wave energy converters. The machine topology selected, the Linear Vernier Hybrid Machine, is extensively investigated, specifically looking at alternative magnet configurations. Topologies are evaluated by their generation capabilities at low velocities, as demanded by Direct Drive Wave Energy Converters. Attention is mainly focused on improving the electromagnetic performance and reducing the magnet mass. A new topology of the Linear Vernier Hybrid Machine is proposed for these purposes, known later as Inset Magnet Consequent Pole machine. Tapered ferromagnetic poles are employed in this topology, which have shown a great impact on minimising the inherent pole-to-pole leakage flux as well as the unwanted cogging force. Further investigation into the Inset Magnet Consequent Pole machine focuses on improving the power factor through modifications made to the machine structure with no increase in the mass magnet, steel or copper used. Two novel variants with the added benefit of flux concentration effect are proposed and described. Finite Element Analysis is used to optimize, analyse and compare the electromagnetic performances for the three investigated machines. Considering the complexity of manufacturing and number of components, two selected topologies are built and tested in the laboratory, the Inset Magnet Consequent Pole machine and V-shape Consequent Pole machine. The experimental results are compared to the simulation results to validate the design. In general, a good agreement is shown between the predicted and measured results. Afterwards, the experimental results obtained from the two prototypes are compared with each other. These results verify that the proposed V-shape Consequent Pole topology is superior in terms of no-load back EMF, force and power factor, while it exhibits lower cogging force in comparison with the Inset Magnet Consequent Pole topology. It is therefore concluded that the V-shape Consequent Pole machine is the best compromise between power factor, efficiency and ease of manufacture. It has half the number of components per pole of the best machine design presented, yet delivers 91% of the force density and 93% of the power factor. The last part of this thesis investigates the feasibility of using the proposed V-shape Consequent Pole machine as an alternative design for an existing wave energy device developed by Uppsala University to assess the effect of employing this sort of machine on Abstract ii the overall machine size and costs. Five variants of the V-shape Consequent Pole machine are described and comparedTechnical and Vocational Training Corporation, Saudi Arabi

Magnetic Gears and Magnetically Geared Electrical Machines with Reduced Rare-Earth Materials

This thesis covers a new emerging class of electrical machines, namely, Magnetic Gears (MGs) and Magnetically Geared Machines (MGMs). This particular kind of gears/machines are able of either scaling up or down the revolution-per-minute to meet various load profiles as in the case of mechanical gearboxes. Mechanical gearboxes have historically dominated various applications due to their relatively high torque density. However, mechanical gearboxes require physical contact between the rotational components, whereas MGs and MGMs accomplish fundamentally the same function via a contactless mechanism. This physical isolation between the rotational components lead to several advantages in a favor of MGs and MGMs over mechanical gearboxes. Although MGs and MGMs can potentially provide a solution for some of the practical issues of mechanical gears, MGs and MGMs have two major challenges that researchers have been trying to address. Those challenges are the high usage of rare-earth Permeant Magnet (PM) materials and the relatively complex mechanical structure of MGs and MGMs both of which are a consequence of the multi-airgap design. As in any engineering field, materials play a significant role and present a trad-off between the performance and cost. In addition to the previous trad-off, the concern with rare-earth PM materials is sustainability as well as price fluctuations. Current research in electrical machines demonstrate real initiatives to reduce the cost of electrical machines by reducing/eliminating the PM rare-earth content while attempting to maintain a competitive electromagnetic performance. Most advanced electrical machines use Dy-NdFeB PM with high energy product at elevated temperatures. Dysprosium (Dy) is one of heavy rare-earth elements and the key source of the price volatility. As a consequence, this thesis aims to address foregoing PM material challenges and investigate the electromagnetic performance of designs that blend different PM types in the context of MGs and MGMs. In addition, practical designs will be proposed in order to reduce the complexity related to the nature of MGs and MGMs

Vernier hybrid wind turbine generators

A great deal of research is currently being undertaken in the field of renewable energy, much of it dedicated to wind power conversion and focussing on a machine topology that increases efficiency. The vernier hybrid machine, VHM, is one topology considered and has promising features for use in direct drive and variable speed operation. Using the VHM topology, two prototype generators were built and tested. The machines use magnets that are buried within the stator and orientated in a flux concentration arrangement. The flux paths in the machines are inherently 3D in nature and thus require complicated modelling methods to achieve sufficient design accuracy. Various tests were conducted in an effort to find results that will describe the machines characteristics and operating mechanisms. It was found that increased torque handling capabilities can be observed at the detriment of power factor and construction complexity. With the use of power factor correction and suitable construction techniques the VHM is a viable wind turbine generation technique. To determine whether it is suitable for renewable energy applications would require an in depth economic feasibility study over the operating lifetime of the machine

Comparative analysis of partitioned stator flux reversal PM machine and magnetically geared machine operating in Stator-PM and Rotor-PM modes

In this paper, the partitioned stator flux reversal permanent magnet (PM) (PS-FRPM) machine and the conventional magnetically geared (MG) machine operating in both stator-PM (SPM) and rotor-PM (RPM) modes are comparatively analyzed in terms of electromagnetic performance to provide design guides for a MG machine regarding: (a) a SPM or RPM type machine and (b) a higher or lower gear ratio machine. It is found that a SPM type machine is recommended, since both PS-FRPM and MG machines operating in SPM modes have a higher phase back-EMF and hence torque than their RPM counterparts, respectively, as a result of a similar phase flux-linkage but a higher electric frequency since the iron piece number is larger than the PM pole-pair number. Moreover, a smaller gear ratio machine is preferred from the perspective of a higher power factor and hence a lower inverter power rating, as the conventional MG machines with higher gear ratios suffer from larger flux-leakage, higher synchronous reactance and hence lower power factors, as well as higher iron losses, than the PS-FRPM machines. However, higher gear ratio machines feature lower cogging torques and torque ripples due to the smaller difference between the PM pole-pair number and iron piece number. Both prototypes of PS-FRPM machine operating in SPM mode and MG machine operating in RPM mode are built and tested to verify the FE predicted results