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.     

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.     

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.     

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     

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.     

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.     

Torque-ripple minimization in switched reluctance motors usingadaptive fuzzy control

An adaptive fuzzy control scheme for the torque-ripple minimization of switched reluctance machines is presented. The fuzzy parameters are initially chosen randomly and then adjusted to optimize the control. The controller produces smooth torque up to the motor base speed. The torque is generated over the maximum positive torque-producing region of a phase. This increases the torque density and avoids high current peaks. The controller is robust toward errors in the rotor position information, which means inexpensive crude position sensors can be used. Detailed simulation and experimental results are presented. The controller shows good response in both cases     

无刷双馈电机直接转矩控制转矩脉动最小化

针对无刷双馈电机直接转矩控制系统转矩脉动大的问题,依据模糊控制理论,研究了基于模糊控制的无刷双馈电机直接转矩控制系统。将转矩误差、磁链误差、扇区作为模糊控制器的输入,采用模糊控制器自动合理地选择电压空间矢量,取代传统的开关矢量表,同时将磁链圆划分为24个扇区。Matlab环境下的仿真结果表明,与传统的无刷双馈电机直接转矩控制系统相比,有效地减小了稳态时的转矩脉动,并且改善了定子磁链渡形,使定子电流波形更接近于正弦。系统在启动、负载扰动等情况下仍然保持了良好的动态性能。在DSP控制系统中实现时。可经相应的离散化后通过查表运算实现模糊控制,实现算法简单,且具有良好的实时性。     

基于换相过程控制的开关磁阻电动机转矩波动最小化研究

转矩波动是开关磁阻电动机较为突出的问题，在对开关磁阻电动机转矩模型分析的基础上，提出了一种控制策略用于解决换相过程中转矩平滑过渡的问题，详细讨论了该控制策略的一种在线控制方案，理论分析表明该方法能减小转矩波动，且效果较好，通过对12／4极三相开关磁阻电动机的仿真和实验研究，验证了所提方案的可行性。     

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.     

Online optimal flux-weakening control of permanent-magnet brushless AC drives

An enhanced online optimal control strategy, which maximizes the flux-weakening performance of a brushless AC motor, is described, and applied to motors having different rotor topologies: interior (radial or circumferential), inset, and surface-mounted magnet. It enables the maximum inherent power capability of a brushless AC motor to be achieved independent of any variation in its parameters, and facilitates maximum efficiency over the entire speed range. It also results in good transient dynamic performance, since it is coupled with feedforward vector control based on optimal current profiles.     

A low-loss permanent-magnet brushless DC motor utilizing tape woundamorphous iron

An axial field permanent-magnet brushless DC motor that utilizes tape wound amorphous iron and an air gap winding is proposed. Simplified waveforms and performance equations for this type of machine are presented. The machine equations and waveforms are verified with a proof-of-concept machine. No-load iron losses are compared with manufacturer's data, and full-load iron losses are also presented. Output torque for rectangular and trapezoidal current waveforms are measured and compared. Machine designs from a computer program that demonstrate the possible benefits of this type of machine could be considerably more efficient than induction machines, and, additionally. cost competitive when a variable speed drive is already a system requirement     

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     

Issues in reducing the cogging torque of mass-produced permanent-magnet brushless DC motor

A variety of techniques are available to reduce cogging torque in permanent-magnet brushless DC motors. Theoretically, all the techniques are quite effective for minimizing the cogging torque. This paper presents the efficacy of these methods in mass production subject to manufacturing tolerances/variations. The cogging torque minimization becomes a challenging task when the requirement is very stringent in applications such as electric power steering and robotics. Some of the known techniques for reducing the cogging torque are the magnet pole design, skewing, step skewing, and dummy slots in the stator lamination. They will be discussed in this paper considering manufacturing tolerances/variations when used in mass production. Finite-element analysis is carried out to determine the worst case scenarios. The research demonstrates that the cogging torque amplitude and frequency are highly sensitive to magnet shapes, dimensions, locations and magnetization pattern, as well as slot/pole combination. In reality, the cogging torque may not be eliminated completely but minimized to a satisfactory level depending on the application requirements.     

80C196KC在永磁无刷直流电动机中的应用

介绍了80C196KC及其在永磁无刷直流电动机中的应用,在控制系统的基础上,分析了80C196KC的功能负控制系统主程序流程.     

Direct torque control for brushless doubly-fed machines

Work has illustrated the potential benefits of brushless doubly-fed machines in adjustable speed drive applications. While it has been shown that the drive is open-loop stable over a wide speed range, the resultant steady-state and dynamic performance characteristics are far from optimum. Thus, a closed-loop controller is desirable to achieve competitive drive performance. The controller proposed here is applicable for general purpose industrial drives in the medium to high power range. The nature of the doubly-fed machine, with two separate sources of excitation, only one of which is controllable, rules out field-oriented control strategies applied to conventional induction machines. However, the concept of direct torque control based on instantaneous error shows promise for this machine geometry. The present paper extends the concept of predictive torque control for induction machines to the doubly-fed machine. The controller calculates the value of converter voltage which leads to desired changes of flux and torque. Once the voltage is determined, conventional algorithms, such as space vector pulsewidth modulation (PWM), can be used to generate the inverter switching function     

Dual-rotor, radial-flux, toroidally wound, permanent-magnet machines

A novel machine family-dual-rotor, radial-flux, toroidally wound, permanent-magnet (RFTPM) machines-is proposed in order to substantially improve machine torque density and efficiency. After the principles of operation, configurations, and features are discussed, the machine design and optimization guidelines are given. A prototype has been designed, built, and tested. The measured torque density of the prototype, which well matches the design value, is almost three times of that of the induction machine with the same power of 3 hp and speed. Meanwhile the efficiency is still kept high and the material cost is kept low by using ferrite magnets. Three novel approaches are proposed to reduce the cogging torque in the RFTPM machines, whose validity is verified by finite-element analysis results and experimental measurements.     

Axial-flux modular permanent-magnet generator with a toroidalwinding for wind-turbine applications

Permanent-magnet (PM) generators have been used for wind turbines for many years. Many small wind-turbine manufacturers use direct-drive PM generators. For wind turbine-generators, the design philosophy must cover the following characteristics: low cost, light weight, low speed, high torque and variable-speed generation. The generator is easy to manufacture and the design can be scaled up for a larger size without major retooling. A modular PM generator with axial flux direction was chosen. The permanent magnet used is NdFeB or ferrite magnet with flux guide to focus flux density in the air gap. Each unit module of the generator may consist of one, two, or more phases. Each generator can be expanded to two or more unit modules. Each unit module is built from simple modular poles. The stator winding is formed like a torus. Thus, the assembly process is simplified and the winding insertion in the slot is less tedious. The authors built a prototype of one unit module and performed preliminary tests in their laboratory. Follow-up tests will be conducted in their laboratory to improve the design     

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.