Rare-earth Permanent Magnet Motors Research Articles

Computer numerical simulations for accelerated design of rare earth permanent magnet motors in renewable energy applications: A review

Rare earth permanent magnet (REPM) motors underpin various emerging fields in electronic and mechanical industries. The rapid growth of renewable energy industries requires the higher performance of the REPM motors, such as the high output torque (≥ 350 N·m), high power (≥ 200 kW), and low ripple torque (< ±5%). To achieve these performances, the fine design for the materials and structures of the REPM motor is required. Computer numerical simulations play important roles in shortening the period and reducing the cost of REPM motor design. Finite difference method (FDM) and finite element method (FEM) are common methods for motor design. Boundary element method (BEM) exhibits advantage in accuracy and efficiency but its commercialization is slower. These three methods have their own advantages and applications. This review discusses the principles and present applications of the FDM, FEM and BEM in details. At present, the electromagnetic and structural simulations are mainly realized by FDM and FEM, while the acoustics simulation is carried out by BEM or combined FEM-BEM. The advantages and limits of various simulation methods in different parts of motor design are comprehensively compared. The recent progress of computer numerical simulations in REPM motor design is summarized, including the simulations in permanent magnets, electromagnetics properties, structure and acoustics characteristics in REPM rotor. In particular, the design of material and electromagnetic structure for the cutting-edge Nd-Fe-B rotor is highlighted. The opportunity and future directions of computational simulations in REPM motor design are also discussed in this review.

Direct Drive Applications: Possible Replacement of Rare-Earth Permanent Magnet Motors

This paper deals with the possibility to replace rare-earth permanent magnet (PM) motors in direct drive applications. According to previous researches, there are alternatives such as surface-mounted PM motors and spoke-type motors adopting Ferrite PMs, synchronous reluctance motors, with or without the assistance of low-energy PMs. Few studies have been carried out to compare all models at once, thus it is hard to choose which type motor is to be preferred as a valid alternative of rare-earth PM motors in direct drive applications. In this paper, the representative candidates listed above are analyzed and the results are compared with that of a rare-earth PM motor, which is considered as a reference motor. Additionally, the demagnetization phenomenon of the motors with Ferrite PMs is deeply analyzed because this kind of PM may be easily demagnetized by the stator flux. Finally, both strengths and weaknesses of each alternative motors are highlighted.

Design and analysis of a novel spoke‐type motor to reduce the use of rare‐earth magnet materials

In this study, a novel design for a tilted spoke-type hybrid permanent magnet synchronous motor (TH-PMSM) that uses two types of permanent magnet (PM) materials is proposed to reduce the consumption of rare-earth PM materials. The key feature of this motor is securing space by tilting the permanent magnet, so that more PMs can be used in the limited rotor space. In addition, based on the centre axis of the rotor, the rare-earth magnets are positioned deeper inside than ferrite PMs to maximise the torque density and reduce the leakage magnetic flux that occurs around the centre of the rotor. Moreover, unlike ordinary spoke-type rotors, it is designed with an integral core like the rotor of the interior permanent magnet synchronous motor (IPMSM), so it is structurally safe even at high speeds. To ensure that the proposed motor is efficiently designed, the output torque, PM cost, cogging torque, and torque ripple were compared with those of the conventional rare-earth PM motors with the same overall dimensions. The validity of the proposed motor was verified by the results of a finite element method simulation and experiments on the fabricated motor.

Robust optimization design of low-cost spoke-type permanent magnet motors with auxiliary salient poles

Applying ferrite to spoke-type permanent magnet motors with flux-focusing ability is a low-cost process and can yield torque density comparable to that of rare-earth permanent magnet motors. To overcome the drawback of the high torque ripple associated with traditional spoke-type permanent magnet motors, a new rotor with auxiliary salient poles is proposed. These poles enhance the plasticity of the rotor and increase the number of optimized parameters. The multiobjective optimization method, which combines response surface analysis and multiobjective backbone particle swarm optimization algorithm, is used to improve the torque performance of the motor. The motor will inevitably be affected by uncertainties, such as errors and tolerances, during motor mass production. Therefore, the six sigma design method and Monte Carlo analysis method are combined for optimizing the robustness of the motor. A comparison of the pre- and post-optimization electromagnetic performance revealed that the proposed motor can effectively reduce torque ripple while increasing the output torque and significantly reducing the mass production failure rate of the motor. Finally, experimental results verify the accuracy and feasibility of the proposed new motor structure and its robust optimization design.

Design and Multi-Objective Stratified Optimization of a Less-Rare-Earth Hybrid Permanent Magnets Motor With High Torque Density and Low Cost

The price fluctuation and the unstable supply chain of rare-earth permanent magnet (PM) have posed potential risks for further application of rare-earth PM motors. To alleviate the consumption of rare-earth PM material, a less-rare-earth PM brushless motor with two types of PM materials is proposed in this paper. The key of this motor is that the rare-earth PM is purposely combined with a non-rare-earth ferrite PM, forming the hybrid PM excitation. To design the proposed motor efficiently, a multi-objective stratified optimization strategy is proposed, where the selected five optimization objectives of output torque, PM cost, cogging torque, torque ripple, and efficiency are divided into two levels. Then, different optimization methods are skillfully combined to meet the specific design requirements. The corresponding electromagnetic performances are analyzed and compared with the baseline rare-earth PM brushless motor. Finally, several experiments of the two motors are carried out for evaluation. Both theoretical analysis and experimental results verify the feasibility and validity of the proposed motor and the optimization method.

Sustainability of Permanent Rare Earth Magnet Motors in (H)EV Industry

It is clear that hybrid/electric vehicles [(H)EVs] are only as green as the materials and energy that they use. According to MIT, the production and processing of rare earth elements (REEs) found in (H)EVs come with their own hefty environmental price tag (K. Bourzac, Rare-Earth Crisis, MIT Technol. Rev., 114(3):58–63, 2011). These damages include radioactive wastewater leaks and ‘slash-and-burn processes’ required to manufacture and separate REEs. Some life cycle assessment (LCA) studies found that the carbon advantage of an electric vehicle over an internal combustion engine vehicle is small considering the production/manufacturing and end-of-life stages (C.-W. Yap, China Ends Rare-Earth Minerals Export Quotas, Wall Street Journal, updated 5 Jan. 2015; D.S. Abraham, War Over the Periodic Table, Bloomberg View, 23 Oct. 2015). However, sustainability is not only about environmental impacts, but also concerns other sustainable development principles such as economic viability and social well-being. Permanent magnet (PM) rare earth motors are most widely used in the (H)EV industry, but the price volatility of REEs does not make them an economically sustainable option. The research involving the potential social impacts of the extraction and use of rare earths for the automobile industry is examined. This review addresses the technical aspects of PM motors and how it contributes to or withdraws from the sustainability of (H)EVs. This paper undertakes a review of the literature and the present situation of sustainability of REEs in the electric vehicle industry. Furthermore, this paper highlights the areas of sustainability research considered by academic and industrial representatives to be essential for cleaning up the clean technology. The intention is not to declare rare earth PM motors sustainable, but to analyze their contribution to sustainability in terms of technical, social, environmental, and economic aspects. Ultimately, the potential opportunities toward a more sustainable rare earth PM motor are revealed.

Development of a Rare-Earth-Free SR Motor With High Torque Density for Hybrid Vehicles

The increased price and the limited supply of rare-earth materials have been recognized as a problem by the international clean energy community. Rare-earth permanent magnets are widely used in electrical motors in hybrid and pure electrical vehicles, which are prized for improving fuel efficiency and reducing carbon dioxide (CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) emissions. Such motors must have characteristics of high efficiency, compactness, and high torque density, as well as a wide range of operating speeds. So far, these demands have not been achieved without the use of rare-earth permanent magnets. Here, we show that a switched reluctance motor that is competitive with rare-earth permanent-magnet motors can be designed. The developed motor contains no rare-earth permanent magnets, but rather, employs high-silicon steel with low iron loss to improve efficiency. Experiments showed that the developed motor has competitive or better efficiency, torque density, compactness, and range of operating speeds compared with a standard rare-earth permanent-magnet motor. Our results demonstrate how a rare-earth-free motor could be developed to be competitive with rare-earth permanent-magnet motors, for use as a more affordable and sustainable alternative, not only in electric and hybrid vehicles, but also in the wide variety of industrial applications.

Comparison Study of Various Motors for EVs and the Potentiality of a Ferrite Magnet Motor

This paper presents a comparison study of various motors for application to an electric vehicle (EV) and the potentiality of a ferrite magnet motor as a candidate for rare-earth-less motor for an EV. The rotor shape of the proposed ferrite magnet motor is based on a spoke-type shape. Further, we developed two types of prototypes: one has a large magnetic torque equivalent to a conventional rare-earth permanent magnet motor for an equal volume, and another has a wide variable-speed range suitable for an EV.

Comparison of Test Result and Design Stage Prediction of Switched Reluctance Motor Competitive With 60-kW Rare-Earth PM Motor

A switched reluctance motor has been designed with identical outer dimensions, maximum torque, operating area, and maximum efficiency as rare-earth permanent-magnet motors used in the Toyota Prius. In this paper, a test machine has been constructed, and test results are presented over the entire speed range. The targets are torque of 207 N·m, a shaft output of 60 kW, and the maximum efficiency of 96%, as well as a speed range of 2768-13 900 r/min with an output of 60 kW and an outer diameter and an axial length of 264 and 112 mm, respectively. It is found that a shaft output of 100 kW is possible at high rotational speed under the voltage and current ratings. The possible operation area in a torque-speed plane is found to be enhanced. It is also found that the design stage prediction is close to the test results, except in two operation regions.

Research of Halbach Array’s Influence on Permanent Magnet Synchronous Motor’s Performance

The present motors are required to high speed, high efficiency, high power density but low pulsating torque. Traditonal rare-earth permanent magnet motor shows its defect; Halbach Array is a new type of permanent magnet structure: magnet field presents unilateral with the sinusoidal distribution. The structure makes the magnetic density of motor’s air gap larger relatively while the magnetic density of rotor’s yoke smaller. And it can help to reduce the motor’s pulsating torque and its size, as well as to raise the power density of motor. The result of finite element analysis based on ANSYS shows that the above structure is able to decrease the mass of motor, to widen the width of air gap and obviously to improve the multi properties of motors.

Analysis of New Type Permanent Magnet Synchronous Motor Based on ANSYS

Modern motor needs high speed, high efficiency, high power density and low pulsating torque, traditional rare earth permanent magnet motor manifests its limitation. Halbach motor is a novel permanent magnet motor. Analysis of Halbach motor based on ANSYS proves its merits: sinusoidal field, higher air gap flux and lower rotor yoke flux, which can reduce pulsating torque and improve power density, efficiency of the motor, these merits can improve its dynamic characteristics greatly.

Structure and Characteristics of High‐Performance PMASynRM with Ferrite Magnets

SUMMARYRecently, the use of permanent magnet (PM) motors has risen markedly because of improvements in the performance of rare earth PM motors. However, the use of rare earth materials, which is an important aspect of the high‐performance PM motor, should be reduced because of the high cost and unpredictability associated with procuring such materials. The performance of motors that use rare earth materials has reached a very high level, one that will not be easy to match without such materials. In this paper, we propose a structure for a high‐power‐density PM‐assisted synchronous reluctance motor involving the use of a ferrite PM. The structure prevents irreversible demagnetization of the PM even in the presence of heavy flux‐weakening excitation or an inverter fault. It is shown that the proposed structure achieves high‐power and high‐efficiency performance. © 2014 Wiley Periodicals, Inc. Electr Eng Jpn, 187(1): 42–50, 2014; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22362

Comparison of the Test Result and 3D-FEM Analysis at the Knee Point of a 60 kW SRM for a HEV

The maximum torque values in computer analysis and experiment in the switched reluctance motor (SRM), having competitive torque density and efficiency with respect to the rare-earth permanent magnet motor employed in the 2009 Toyota Prius, have been compared. The SRM is highly saturated to provide the maximum torque for a short time; thus, the torque value tends to have considerable error of 15% even in the 3D FEM analysis with respect to experimental result because of the incomplete material setting. A comparison of the flux-linkage and current is also provided for consideration. The results of the 2D-FEM and 3D-FEM analysis as well as a test machine are presented. The maximum torque in the 3D-FEM analysis is shown to be within errors of 5.0% with respect to that in the test machine.

フェライト磁石を用いた高性能PMASynRMの構造と特性

SUMMARY Recently, the use of permanent magnet (PM) motors has risen markedly because of improvements in the performance of rare earth PM motors. However, the use of rare earth materials, which is an important aspect of the high-performance PM motor, should be reduced because of the high cost and unpredictability associated with procuring such materials. The performance of motors that use rare earth materials has reached a very high level, one that will not be easy to match without such materials. In this paper, we propose a structure for a high-power-density PM-assisted synchronous reluctance motor involving the use of a ferrite PM. The structure prevents irreversible demagnetization of the PM even in the presence of heavy flux-weakening excitation or an inverter fault. It is shown that the proposed structure achieves high-power and high-efficiency performance. © 2014 Wiley Periodicals, Inc. Electr Eng Jpn, 187(1): 42–50, 2014; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22362

Post Assembly Magnetization Patterns in Rare-Earth Permanent-Magnet Motors

This paper illustrates a method for verifying the full magnetization of a rare-earth permanent-magnet motor when it is magnetized using a post-assembly method. The usual method of manufacturing a rare-earth magnet machine is to premagnetize before assembly, however, the assembly can be cumbersome. It is possible to magnetize after assembly. This is a critical procedure. If the magnetizing current is too low, then incomplete magnetization occurs. If it is too high, then the winding will overheat and be damaged. A simple method can be used to ascertain the correct magnetization current and this is put forward here. The method is verified experimentally

A comparison of the magnetic properties of commercial HDDR powder with those of other commercial sintered rare-earth magnets

Rare-earth permanent magnet motors are being used increasingly in electrical machines and modern production methods frequently require in situ magnetization of the magnets. Magnetic measurements have been performed on magnetically anisotropic powder (Magnequench MQA-T), sintered and sintered and were compared in order to study the influence of the magnetizing field strength on the measured values of the remanence and intrinsic coercivity. For thermally de-magnetized material, the internal magnetic field necessary to obtain limiting values of the remanence and intrinsic coercivity varies with magnet type. For example, the and magnets studied have similar values of remanence and intrinsic coercivity , but the latter requires an internal magnetizing field three times larger than does the former in order for one to attain limiting values of the remanence and coercivity. Further insight into the magnetization processes in these three materials has been gained from the determination of the magnetic viscosity parameter, S, and the irreversible susceptibility, .