Design and parameter effect analysis of dual-rotor, radial-flux, toroidally wound, permanent-magnet machines

A novel machine family-the dual-rotor, radial-flux, toroidally wound, permanent-magnet (RFTPM) machine-has been proven in a previous paper to be able to improve the machine efficiency and boost the torque density. This paper will present the key design equations and design procedure of the RFTPM machines, analyze parameter effects on machine performance, and give design guidelines to achieve specific design objectives. In addition, finite-element analysis is employed to prove the effectiveness of the design equations and find the machine overload capability. Experimental measurements of a prototype, which match the design specifications well, verify the effectiveness of the design equations.     

Pole-changing permanent-magnet machines

Electric drives in which discrete speed control is required are today equipped exclusively with squirrel-cage induction motors, due to the property of the squirrel cage to always have the same number of poles as the stator winding. Conventional permanent-magnet (PM) machines have a constant number of poles and can be operated from a constant frequency source only at one speed. If a PM machine is built after the principles of memory motors, one can change its number of poles as simply as in a squirrel-cage machine. In this paper, the principles of. operation of a pole-changing memory motor are described, and its measured performance is presented and discussed.     

Modeling of axial flux permanent-magnet machines

In modeling axial field machines, three-dimensional (3-D) finite-element method (FEM) models are required in accurate computations. However, 3-D FEM analysis is generally too time consuming in industrial use. In order to evaluate the performance of the axial flux machine rapidly, an analytical design program that uses quasi-3-D computation is developed. In this paper the main features of the developed program are illustrated. Results given by the program are verified with two-dimensional and 3-D finite element computations and measurements. According to the results, it is possible to evaluate the performance of the surface-mounted axial flux PM machine with reasonable accuracy via an analytical model using quasi-3-D computation.     

Rotor loss in permanent-magnet brushless AC machines

The eddy-current loss in the permanent magnets of brushless AC machines is usually neglected, since the fundamental air-gap field usually rotates in synchronism with the rotor, and time harmonics in the current waveform and space harmonics in the winding distribution are generally small. However, an important category of brushless AC machine design is emerging in which the fundamental component of the stator MMF has fewer poles than the rotor, the torque being developed by a higher order MMF harmonic. The fundamental and lower order MMF harmonics can then give rise to significant rotor eddy currents. An analytical model is developed to predict rotor-induced eddy currents in such machines, and to quantify the effectiveness of circumferentially segmenting the permanent magnets in reducing the rotor loss.     

Torque-ripple minimization in modular permanent-magnet brushless machines

This paper discusses the suitability of four-phase, five-phase, and six-phase modular machines, for use in applications where servo characteristics and fault tolerance are key requirements. It is shown that an optimum slot number and pole number combination exists, for which excellent servo characteristics could be achieved, under healthy operating conditions, with minimum effects on the power density of the machine. To eliminate torque ripple due to residual cogging and various fault conditions, the paper describes a novel optimal torque control strategy for the modular permanent-magnet machines operating in both constant torque and constant power modes. The proposed control strategy enables ripple-free torque operation to be achieved, while minimizing the copper loss under voltage and current constraints. The utility of the proposed strategy is demonstrated by computer simulations on a four-phase fault-tolerant drive system.     

Rotor resonances of high-speed permanent-magnet brushless machines

For high-speed machines, in particular, it is very important to accurately predict natural frequencies of the rotor at the design stage so as to minimize the likelihood of failure. Finite-element analysis and experimental measurements are used to establish the natural frequencies and modes of the rotor of a high-speed permanent-magnet brushless motor, and to assess the influence of leading design parameters, such as the active length, the shaft diameter and extension, the bearings, and the material properties.     

Performance comparisons of radial and axial field,permanent-magnet, brushless machines

The objective of this paper is to provide a comparison between the traditional radial field permanent-magnet brushless machine and four unique configurations of axial field permanent-magnet brushless DC machines. These consist of a single-gap slotted axial field machine, a dual-gap slotted axial field machine, a single-gap slotless axial field machine, and a dual-gap slotless axial field machine. The comparison is done at five power levels ranging from 0.25 to 10 kW. A rated speed of 2000 r/min is chosen for the 0.25-kW designs while 1000 r/min is chosen for the rest of the designs. The trends in performance and sizing for the different power outputs are obtained to get an understanding of the capability of various machine configurations. The comparison consists of required copper, steel, and magnet weights, copper and iron loss, moment of inertia, torque per unit moment of inertia, power per unit active weight, and power per unit active volume for five different power levels. For a given application, the results provide an indication of the machine best suited with respect to performance and size. The basis for the comparison is described with details on the design procedure     

Design and analysis framework for linear permanent-magnet machines

This paper presents a design and analysis framework for the general class of permanent magnet electric machines. In the authors' analysis, surface-mounted linear motors consisting of permanent magnets and ironless current-carrying coils are treated in a uniform way via the magnetic vector potential. This analysis is developed to design novel linear magnetic levitators for driving precision motion control stages such as those used in wafer steppers. For one such motor structure, they give analytical formulae for its magnetic field, force, flux linkage, inductance of the winding, and back electromotive force. They provide experimental results with a six degree-of-freedom magnetic levitator. These results are in good agreement with analytical estimations. The levitator uses a permanent-magnet Halbach array in order to improve its power efficiency. By analogy, there also exists an electromagnetic dual of the Halbach array. One such dual utilizes a triangular winding pattern in order to achieve a primarily single-sided magnetic field     

Fixation of buried and surface-mounted magnets in high-speed permanent-magnet synchronous machines

High-speed applications involve technical and economical advantages because, as direct drives, they avoid the gear as an additional mechanical drive component. Permanent-magnet synchronous machines (PMSMs) are attracting growing attention for high-speed drives. Surface-mounted PMSMs request a glass- or carbon-fiber bandage to fasten the magnets to the rotor surface at high speed. At rotors with "buried" magnets, the rotor iron itself fixes the magnets. This paper presents simple calculation strategies and discusses their limits for the mechanical design of high-speed machines with either surface-mounted or buried magnets. The results of the calculations are compared with finite-element calculations.     

A study on eddy-current losses in rotors of surface permanent-magnet synchronous machines

In this paper, we investigate the Eddy current (EC) losses in the rotors of surface permanent-magnet (PM) synchronous machines, which have concentrated armature windings. By the finite-element method (FEM) analysis, it is clear that the EC losses in rotors are apparently different at rated currents if the pole and slot combinations are different. The distribution of the EC density in the rotor is closely related with the asynchronous components of the armature magnetomotive force (MMF). If the armature MMF has a low order of spatial harmonic components, which is not synchronous with the rotor, the EC losses are of large amounts.     

Sensorless flux-weakening control of permanent-magnet brushless machines using third harmonic back EMF

The sensorless control of brushless machines by detecting the third harmonic back electromotive force is a relatively simple and potentially low-cost technique. However, its application has been reported only for brushless dc motors operating under normal commutation. In this paper, the utility of the method for the sensorless control of both brushless dc and ac motors, including operation in the flux-weakening mode, is demonstrated.     

三段Halbach磁铁阵列永磁同步电机铁心的优化设计

Halbach磁铁阵列和集中绕组的分数槽绕组应用于永磁同步电机可提高输出转矩并降低转矩波动,满足伺服系统快速性和高精确度的要求,但需要对电机铁心进行再设计。依据Halbach磁铁阵列的理论建立了每极三段Halbach磁铁阵列永磁同步电机磁场的模型,并分析了气隙磁场特点,提出采用集中绕组的分数槽绕组削弱齿谐波。分析电机铁心的结构特点,确定多个关键尺寸为设计变量,以一定电流的最大转矩平均值和最小转矩波动为主要优化目标,采用Taguchi方法简化优化设计的计算,并建立了双层的优化模型。以一台8极9槽的伺服电动机为例,采用有限元计算,阐述了每极三段Halbach磁铁阵列永磁电机多变量、多目标的优化过程。     

Assessment of torque components in brushless permanent-magnet machines through numerical analysis of the electromagnetic field

For the calculation of torque in brushless (BL) alternating current motors a local method is proposed, based on the Maxwell stress theory and the filtered contributions due to the harmonics of the magnetic vector potential in the motor air gap. By considering the space fundamental field only, the method can efficiently estimate the average synchronous torque for a variety or motor topologies, including concentrated winding designs. For BL direct current motor analysis a global method is introduced, based on the virtual work principle expressed in terms of energy components in various motor regions. The method leads to simplifications in the average torque calculation and enables the direct identification of the cogging and ripple components. The mathematical procedures have been validated against experiments and other numerical techniques.     

An adaptive control strategy for wound rotor synchronous machines

This paper addresses the problem of controlling wound rotor synchronous motors in association with their power conversion components, i.e. AC/DC rectifiers and DC/AC inverters. Considering the whole association, ‘converter‐motor’ makes it possible to account, in addition to motor speed regulation, four other important control objectives such as power factor correction with respect to the supply net and DC link voltage regulation. To achieve these objectives, an adaptive control strategy is developed, based on a nonlinear model of the whole ‘converter‐motor’ association. Adaptation is motivated by the uncertain nature of some motor characteristics, especially the mechanical parameters. The closed‐loop system stability and performances are formally described using averaging theory. Copyright © 2012 John Wiley & Sons, Ltd.     

Experimental study on reducing cogging torque and no-load power loss in axial-flux permanent-magnet machines with slotted winding

The axial-flux permanent-magnet machine (AFPM) topology is suited for direct-drive applications and, due to their enhanced flux-weakening capability, AFPMs having slotted windings are the most promising candidates for use in wheel-motor drives. In consideration of this, this paper deals with an experimental study devoted to investigate a number of technical solutions to be used in AFPMs having slotted windings in order to achieve substantial reduction of both cogging torque and no-load power loss in the machine. To conduct such an experimental study, a laboratory machine was purposely built incorporating facilities that allow easy-to-achieve offline modifications of the overall magnetic arrangement at the machine air gaps, such as magnet skewing, angular shifting between rotor discs, and accommodation of either PVC or Somaloy wedges for closing the slot openings. The paper discusses experimental results and gives guidelines for the design of AFPMs with improved performance.     

Modeling, simulation, and analysis of permanent-magnet motordrives. I. The permanent-magnet synchronous motor drive

The application of vector control to the PMSM (permanent-magnet synchronous motor) is described, and complete modeling, simulation, and analysis of the drive system are presented. State-space models of the motor and speed controller and real-time models of the inverter switches and vector controller are included. Performance differences due to the use of pulsewidth-modulation (PWM) and hysteresis current controllers are also examined. Particular attention is paid to the motor torque pulsations and speed response. Some experimental verification of the drive performance is also given     

低开关频率的五相永磁同步电机有限集模型预测电流控制算法

多相电机广泛应用于航空与船舶推进等领域,具有容错性能强、功率密度高等显著优点.本文以五相永磁同步电机(P MSM)为研究对象,提出了一种适用于大功率应用场合的低开关频率FCS-MPCC算法.首先,深入分析了电流轨迹的变化规律,并结合电流参考值设计给定电流区域,根据电流预测值对电压矢量进行初步筛选.接着,在电流预测中引入...     

Five-phase permanent-magnet motor drives

A five-phase brushless permanent-magnet (PM) motor is introduced. The proposed motor has concentrated windings such that the produced back electromotive force is almost trapezoidal. The motor is supplied with the combined sinusoidal plus third harmonic of currents. This motor, while generating the same average torque as an equivalent PM brushless dc motor (BLDC), overcomes its disadvantages. The motor equations are obtained in the d/sub 1/q/sub 1/d/sub 3/q/sub 3/0 rotating reference frame. Therefore, the so-called vector control is easily applicable to this kind of motors and the motor has the same controllability as a PM synchronous motor (PMSM). For presenting the superior performance of the proposed five-phase motor, its three and five-phase PMSM and BLDC counterparts are also analyzed. Finite element method is used for studying the flux density and calculating the developed static torque. Also, the developed torque is obtained using the mathematical model in the d-q reference frame. The average torque and the torque ripple for all cases are calculated and compared. Experimental results are in good agreement with the simulation results.     

双转子永磁同步风力发电机设计与应用

近年,风力发电得到了迅速的发展;双转子发电机推动了风力发电技术的发展.提出了一种能显著提高风能利用系数的新型双转子永磁同步风力发电机.介绍了其应用范围,并以普通永磁同步电机为基础提出了其数学模型,为以后对其控制系统研究提供了一定理论基础.