Superconducting electrical motorsMoteurs électriques supraconducteurs

Superconductors have always been very promising materials because they offer the possibility of building lighter and more efficient electrical machines than by any other conventional solution. These characteristics make superconducting motors very attractive drives for embarked equipment with low weight requirements. The historical development of superconducting machines is quickly reviewed. The high critical temperature superconductors have renewed the works about superconducting machines. Different motor options are presented (fully superconducting machine and permanent magnet superconducting motor). For each, the choice of the superconductor (low or high critical temperature) is discussed, according to their performance and technological problems, especially about cryogenics. The different solutions are compared through a preliminary electromagnetic design for a 10 MW–100 rpm torque motor. We carry out a research and development program on the permanent magnet superconducting motors. After a first 15 kW–750 rpm successfully tested model a second 150 kW–400 rpm demonstrator is under development.     

Modeling Magnet Length In 2-D Finite-Element Analysis of Electric Machines

Two-dimensional finite-element-method (2-D FEM) calculations are widely used in electric machine modeling instead of three-dimensional calculations because of their faster calculation time and simplicity. However, the 2-D calculations ignore end effects, causing a large error in calculating eddy currents in permanent magnets of synchronous machines. In this paper, we develop three analytical models and one curve-fitting model based on numerical calculations. The models improve the eddy-current loss calculation accuracy in 2-D FEM. The method adjusts the resistivity of a magnet material according to magnet dimensions. The adjustment takes into account the resistivity, the temperature dependence, and anisotropy of the resistivity of rare-earth magnet materials. We compare the models against FEM calculations in two and three dimensions and show that all the models improve the eddy-current loss calculation accuracy significantly, especially when the time-harmonic caused eddy-current losses in permanent magnets are considered.      

Performance improvement of permanent magnet machines by modular poles

Modular permanent magnet poles have recently been proposed to enhance the performance of permanent magnet machines and improve the exploitation of used magnet materials. An optimisation method for these poles is proposed for use in linear permanent magnet synchronous machines. The main objective of the optimisation is to select proper dimensions and material properties of modular permanent magnet poles to enhance the machine developed thrust. The optimisation is carried out based on a mathematical model of the machine obtained analytically. In particular, the developed thrust of linear permanent synchronous machines with modular poles is given by the model. Genetic algorithm is then employed to optimise pole parameters where the ratio of thrust ripples to average thrust is chosen as an objective function. Extensive investigations carried out by analytical and finite element methods confirm that substantial lower thrust ripples are produced with almost the same average thrust.     

Demagnetization Testing for a Mixed-Grade Dovetail Permanent-Magnet Machine

A dovetail machine is a novel design developed to solve the strength problems of traditional buried magnet machines. A mixed-grade construction can be easily applied to a dovetail machine, because a dovetail machine has several magnets in a single pole in different positions. The basic idea of the mixed-grade construction is to use high intrinsic coercivity material in the positions of the high demagnetization risk and high remanence material in the positions of low demagnetization risk. We have developed a demagnetization model that takes into account the temperature dependence of the properties of the permanent-magnet materials to model a dovetail permanent-magnet motor with mixed-grade construction. We compared the model with a real motor. By comparing the testing and the calculations, we show that our demagnetization model can predict the demagnetization of the permanent magnets with reasonable accuracy. We discuss the benefits of the mixed-grade construction in a dovetail machine.      

软磁复合材料铁芯电机特性的仿真研究

为了发挥软磁复合材料的高电阻率,低损耗,易于再利用的特点,仿真模拟将其应用在永磁电机的铁芯上.以12槽4极直流电机为仿真对象,把三维计算问题转化成二维模型,用JMAG软件对电机进行建模,阐述SMC与硅钢片铁芯差异,先用两种材料进行仿真,结果说明只靠替换铁芯材料对电机性能改进并不会产生很大改善,改进模型,得出不同延伸高度铁芯延伸长度增加引起的电流和转矩特性与功率变化的关系.利用所建模型将Somaloy500的软磁复合材料与50CS800的硅钢片制备的铁芯进行模拟实验,结果表明:相同条件下软磁复合材料铁芯的效率要更高一些.最低转速时效率增加5%,最高转速时效率增加10%;软磁复合材料铁芯模型抑制电流输出,各向同性的优势明显.结论为SMC材料在低转速电机的开发中依旧能够发挥优势,实现电机性能的提高.     

Design and analysis of full pitch winding and concentrated stator pole winding three-phase flux reversal machine for low speed application

The flux reversal machine (FRM) is a doubly-salient stator permanent magnet machine with flux linkage reversal in the stator concentrated winding. The existing machines at low speed, low power (2·4 kW, 300 rpm) range are not economical. FRM topology is best suited for this application. An attempt has been made to improve the power density of machine by introducing full pitch winding. Full pitch winding FRM (FPFRM) has higher power density than the conventional concentrated stator pole winding FRM (CSPFRM). Design and comparative analysis of FPFRM and CSPFRM are made. Both machines are designed for 88·58 Nm and 300 rpm. Design details of both machines are presented. Finite Element Method (FEM) analysis is carried out to evaluate and compare the performance of CSPFRM and FPFRM. Series capacitive compensation is provided for better voltage regulation of both machines.     

Vector control application of a novel PM motor

This study introduces a new type of dual-stator permanent magnetic propulsion motor: the dissimilar frequency supplied permanent magnet synchronous motor (DFPMSM). The main advantage of the motor is its improved torque density and fault tolerance, which is well suited for electric propulsion at low speed. The vector control of the DFPMSM is presented. A torque current decoupling method is proposed to maintain the torque output while changing the torque distribution. A power loss model is derived for the power distribution strategy to achieve optimum efficiency of this motor. Simulation and experimental results are presented to verify the effectiveness of the proposed machine and control strategy.     

变频空调用无稀土磁阻电机的退磁仿真及验证

在以往的变频空调中,压缩机电机常采用高效节能的稀土永磁同步电机,但稀土价格的上涨使其在空调中的继续应用受到限制。无稀土磁材的永磁辅助式同步磁阻电机（无稀土磁阻电机）成本低廉,性能可与稀土永磁同步电机相媲美,在空调上具有很好的应用前景,但因无稀土磁材磁性能较弱,电机抗退磁能力较差而难以系列化生产。本文借助Ansoft软件对无稀土磁阻电机的退磁情况进行仿真,并与等效磁路法计算结果及实测结果进行对比。结果表明,采用三维瞬态场的动态退磁仿真结果与实测值很接近,该仿真方法能够很好地反映电机实际的抗退磁能力,在缩短开发周期、降低开发成本方面效果显著。     

Determination of winding inductances in ferrite type permanent magnet electric machinery by finite elements

A key design factor in ferrite type permanent magnet machines is the accurate knowledge of the values of machine winding inductances during the design stage. In the present paper, a method which is based on perturbation of the energy stored in the magnetic field, and on numerical models of simulation of such permanent magnets is used in calculating machine inductances. The effect of change in the values of these winding inductances with magnet position throughout the cycle of operation of such machines is given. These inductances also include the apparent and incremental values, whose definition is directly related to the choice of apparent or incremental reluctivities in the energy perturbation process. Results of application of this method to the calculation of inductances in a 15 hp 6-pole ferrite type electronically operated permanent magnet machine are given. These calculated values of inductances are in good agreement with the measured values.     

The computations of 3D magnetostatics of REPM synchronous generators using GTFM and two scalar potentials

This paper presents two methods, graph-theoretic field model (GTFM) and two scalar potentials, for computing 3D magnetostatic fields of electrical machines with permanent magnets. The 3D fields of a 60kVA and a 3kW rare earth permanent magnet (REPM) synchronous generators are computed by these two methods with 3D automatic mesh generation and incomplete Cholesky Conjugate Gradiant (ICCG) procedure. These computations are validated through the test results.     

基于新型光电材料PLZT的光电机研究

本文提出一种基于新型光电材料PLZT的电机——光电机。针对国内外的研究现状,重点分析光电机的驱动原理,光电机通过新型功能材料PLZT在紫外光照下产生光生伏特效应这一特性,借助电场力推动电机运动,实现从光能到机械能的转换。在此基础上结合有关数学推导,得出了光电机的驱动力表达式,给出简易的电机结构模型。本文将光电机与传统电机进行全面比较,得出其优势和存在的不足;在介绍国外研究的基础上,深入分析光电机研究过程中面临的难题,指出光电机研究未来的发展方向和光电机应用领域。     

Research and development of Ce-containing Nd_2Fe_(14)B-type alloys and permanent magnetic materials

Much demanded and overused are the critical rare-earth elements such as Pr, Nd, Dy, and Tb with increasing need of Nd Fe B-type rare-earth permanent magnets in the enlarging application areas, developing new high-tech industries, and emerging cutting-age frontiers. The balance and efficient use of rare-earth resources comes into being the national strategy, national defense, and border safety for many major countries and regions in the world.(Nd,Ce)Fe B-based permanent magnetic materials, which can not only reduce cost but also offer a feasible way for integrated and effective utilization of rare earth resources,have received much attention in recent years. The existence of CeFe_2 and the mixed valence state of Ce in Ce Fe B compound, the different metallurgy behavior and the particular processing as well as potential various magnetic-hardening mechanisms, however, make it quite different from Nd-based alloys.For instance, the coercivity of Ce-containing magnets in some certain composition range, is even higher than that of the counterpart pure Nd-based magnets though the Ce-containing magnets possess inferior intrinsic properties. Consequently, it is very important to design proper composition and structure, optimize processing, and analyze the mechanisms in depth for this kind of magnet. High performance and cost-effective magnets can be fabricated if we can make full use of the composition's inhomogeneous and abnormal coercivity variation of the Ce-containing permanent magnets. In this paper, we have summarized the phase structures, magnetic properties and microstructures of(Nd,Ce)Fe B-based permanent magnetic materials to shed light on further research and development of this type of so-called "gap magnet".     

Parametric variance consideration in speed control of single-phase flux reversal machine

The new flux reversal machine (FRM) has a simple robust rotor with a permanent magnet installed stator. However, the parameters of the FRM are dependant on the position of the rotor, operating temperature and magnetic saturation of the motor core. To obtain a robust performance in the speed control of the single-phase FRM, a control method that introduces an internal model of the motor is suggested for robustness against parameter variance and disturbance. The suggested control method is verified by both computer simulation and experiments and it is applied for popular AC induction/synchronous machines for their robust performance.     

Thermal-fluid and electromagnetic coupling analysis and test of a traction motor for electric vehicles

This paper proposes a multi-phasic coupling analysis and test of a 50 kW traction motor for electric vehicles. The temperature-dependent properties of the electrical and magnetic materials of the interior permanent magnet traction motor are not negligible over a wide operation range of the vehicle. The heat produced by the electromagnetic power loss changes the motor’s properties, and in turn the motor performance changes to produce a different power loss. This two-way coupled electromagnetic and thermal-fluid analysis of the torque and speed curve and the transient thermal response at a rated operation point are simulated and compared with the traditional one-way coupling analysis. The simulation results are also compared with and proved by experiments on a prototype motor. The experimental results show that it is critical and necessary to predict the motor performance by means of the proposed two-way coupling analysis that provides more accurate information than the traditional one-way coupling analysis.     

A Compact Superconducting Motor with Novel Stator Windings for Vehicle Applications

The aim of this paper is to investigate how compact a superconducting motor can achieve the same performance as a conventional permanent magnet (PM) motor. A design of superconducting motor is proposed and the performance is calculated to meet the specifications of a conventional PM machine while keeping the size of the superconducting motor as compact as possible. The proposed superconducting motor uses YBCO racetrack coil on the stator and bulk superconductors on the rotor. The operating temperature is 22 K and liquid hydrogen is chosen as the agent. A numerical model is developed to calculate the performance of this motor and the results show that it is able to deliver a power at 118 kW and a torque at 622 N m with a total volume as compact as 1.5 liter. The torque and power densities of this superconducting motor are compared with those of the PM motor and the boundary performance of volume reduction that can be achieved by substituting conventional copper and permanent magnets by superconducting materials is discussed.     

Dynamic performance of a brushless DC tubular drive system

The authors describe the computer-aided analysis of the dynamic performance of a tubular linear machine system with permanent magnetic cogging forces. These forces include not only the conventional tooth cogging force apparent in both linear and rotary machines but also a force unique to permanent magnet linear machines that is due to the finite length of the stator. System equations which describe both the machine and the inverter supply are solved by a step-to-step numerical method to find the dynamic performance of the machine in an oscillator mode. The work is verified by experimental results obtained for a practical model     

Comparison of synchronous PM machine types for wide constant-power speed operation: converter performance

A thorough comparison of the converter performance characteristics for four permanent magnet (PM) synchronous machine configurations is presented. Two versions of an interior PM (IPM) machine with distributed windings are included. One version has a maximum back-EMF limit at the top speed while the second does not have any constraint on back-EMF amplitude. Two types of surface PM (SPM) machines are also considered, one with fractional-slot concentrated windings, and another with conventional distributed windings. The target application is an automotive direct-drive starter/alternator requiring a very wide 10:1 constant power speed ratio (CPSR). Detailed comparisons of the converter performance below and above the base speed are presented, evaluating significant issues, including the converter switching and conduction losses, output ripple current, and DC-link current ripple. Study results show that the higher excitation frequencies required by PM machines with high pole numbers have only a modest impact on converter efficiency for comparable output current waveform quality. In constrast, the imposition of maximum back-EMF amplitude constraints at top speed raise the machine rated current, resulting in elevated converter losses and larger DC-link capacitors     

稀土永磁材料辐照效应研究进展

稀土永磁材料以其优异的磁性能而日益得到广泛的应用,人们对其在各种环境下的磁性能稳定性,包括辐照环境下的性能越来越关注.本文对稀土永磁材料的辐照效应研究进行了回顾,包括质子、中子、电子、γ-射线与X-射线辐照的影响,并总结了稀土永磁材料辐照损伤机理方面的研究,指出为提高稀土永磁材料的抗辐照能力,还需深入研究以揭示辐照损伤机理.     

Magnetism of rare-earth elements, alloys, and compounds

The magnetic properties of the rare-earth metals and a number of the alloy and compound systems formed with rare earths are discussed. Emphasis is placed on current experimental results of bulk magnetic measurements and related transport phenomena and their bearing on theoretical studies. Topics covered include exchange interactions, magnetization processes, crystal field effects and anisotropy, magnetostriction, spin structures and their field dependence, specific heat, optical effects, resistivity, magnetoresistivity, and other transport properties affected by the magnetic order. Examples are drawn from a number of material systems including ionic compounds, solid solution compounds (e.g., rare-earth magnetic semiconductors), intermetallic compounds (permanent magnet materials, etc.), and bubble domain materials in addition to the rare-earth elements and intra-rare-earth alloys. Tables are presented giving the spin structures, ordering temperatures, saturation and effective moments, and other properties of the elements and specific compounds.     

Power density improvement of three phase flux reversal machine with distributed winding

The three phase flux reversal machine (FRM) is a doubly salient permanent magnet machine with concentrated windings. This study proposes the distributed winding for this machine. This winding (i.e. full pitch winding) offers high-power density and improves the efficiency. The permanent magnet (PM) flux linking the stator winding has effectively two or four pole flux pattern, which depends on the number of stator poles and independent of number of rotor poles. Finite element method (FEM) analysis is performed on the concentrated stator pole winding FRM (CSPFRM) and proposed full pitch winding FRM (FPFRM) to obtain induced EMF, flux linkages and inductance of the winding. The inductance of both machines is also obtained using winding function approach and compared with FEM results. The effect of armature reaction is compensated by capacitive series compensation to improve the voltage regulation. FEM analysis is also carried out on both the compensated generators to evaluate the power density. Speed of the flux pattern and that of the rotor is different in FRM. The ratio of these two speeds is termed as fictitious 'electrical gear'. FRM and permanent magnet synchronous machine (PMSM) have sinusoidal terminal voltage and surface mounted PMs. The power density of both machines is compared using the concept of fictitious `electrical gear?. To verify the above analysis, a 6/14 pole FRM with distributed and concentrated winding is designed and fabricated. The experimental results are in close agreement with simulated results.