With rapid development of wind power technologies and significant growth of wind power capacity installed worldwide, various wind turbine concepts have been developed. The wind energy conversion system is demanded to be more cost-competitive, so that comparisons of different wind generator systems are necessary. An overview of different wind generator systems and their comparisons are presented. First, the contemporary wind turbines are classified with respect to both their control features and drive train types, and their strengths and weaknesses are described. The promising permanent magnet generator types are also investigated. Then, the quantitative comparison and market penetration of different wind generator systems are presented. Finally, the developing trends of wind generator systems and appropriate comparison criteria are discussed. It is shown that variable speed concepts with power electronics will continue to dominate and be very promising technologies for large wind farms. The future success of different wind turbine concepts may strongly depend on their ability of complying with both market expectations and the requirements of grid utility companies.

Overview of different wind generator systems and their comparisons

The paper presents an accurate analytical subdomain model for computation of the open-circuit magnetic field in surface-mounted permanent-magnet machines with any pole and slot combinations, including fractional slot machines, accounting for stator slotting effect. It is derived by solving the field governing equations in each simple and regular subdomain, i.e., magnet, air-gap and stator slots, and applying the boundary conditions to the interfaces between these subdomains. The model accurately accounts for the influence of interaction between slots, radial/parallel magnetization, internal/external rotor topologies, relative recoil permeability of magnets, and odd/even periodic boundary conditions. The back-electromotive force, electromagnetic torque, cogging torque, and unbalanced magnetic force are obtained based on the field model. The relationship between this accurate subdomain model and the conventional subdomain model, which is based on the simplified one slot per pole machine model, is also discussed. The investigation shows that the proposed accurate subdomain model has better accuracy than the subdomain model based on one slot/pole machine model. The finite element and experimental results validate the analytical prediction.

An Accurate Subdomain Model for Magnetic Field Computation in Slotted Surface-Mounted Permanent-Magnet Machines

In this paper, the suitability of a class of electric machines for vehicle traction applications is discussed. These machines, which are known as hybrid excitation synchronous machines, combine permanent-magnet (PM) excitation with wound field excitation. The goal behind the principle of hybrid excitation is to combine the advantages of PM excited machines and wound field synchronous machines. It is shown that these machines have good flux weakening capability compared with PM machines, and that they constitute an energy-efficient solution for vehicle propulsion.

Hybrid Excitation Synchronous Machines: Energy-Efficient Solution for Vehicles Propulsion

This paper reviews the progress that has been made in the analysis and design of axial-flux permanent-magnet machines over the past decade, with particular attention to aspects such as electromagnetic and thermal modeling, materials, manufacturing, pulsating torque, and extended speed range. Comparisons with other machine types and applications are also reviewed.

Recent Advances in Axial-Flux Permanent-Magnet Machine Technology

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.

Modeling of axial flux permanent-magnet machines

Various techniques exist for reducing the cogging torque in radial-flux permanent-magnet (RFPM) machines. However, although some of these can be applied to axial-flux PM (AFPM) machines, the additional manufacturing complexity and cost may be prohibitive. Therefore, alternative low-cost techniques are desirable for use in AFPM machines. In this paper, the utility of employing cogging torque minimization techniques that have been developed principally for use in RFPM machines is examined by 3-D finite-element analysis, and several alternative cogging torque minimization techniques for AFPM machines are proposed.

Minimization of Cogging Torque in Axial-Flux Permanent-Magnet Machines: Design Concepts

In this paper, pulsating torque components of permanent magnet machines and pulsating torque minimization techniques are discussed for axial flux surface-magnet disc-type PM machines. The pulsating torque analysis describing general instantaneous electromagnetic torque equation and torque ripple factor is briefly provided in order to analyze torque ripple component. Detailed finite-element analyses focusing on the minimization of cogging and torque ripple components using several techniques are also given. A detailed comparison of the two techniques is also illustrated in this paper.

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Torque quality and comparison of internal and external rotor axial flux surface-magnet disc machines

This paper presents the design, analysis, control, and experimental evaluation of an innovative field-controlled axial-flux surface-mounted permanent-magnet machine. Topology and design equations, as well as an optimized design study, are attained. The machine is investigated in detail using finite-element analysis, and a prototype machine is built. In order to evaluate the new axial flux machine topology, an experimental system setup is devised and discussed. The experimental results of the prototype machine and a comparison between the analysis and test results are also presented.

Design, Analysis, and Control of a Hybrid Field-Controlled Axial-Flux Permanent-Magnet Motor

This paper presents a new axial flux surface mounted permanent magnet (PM) field controlled TORUS type (FCT) machine. Machine structure and principles are explored and the field weakening feature of the topology as well as the advantages of the machine are presented in the first part. The second section introduces the linear model and sizing analysis using generalized sizing equations. Optimization of the machine pole number and power density maximization for the optimum pole number is also achieved. In the third section, 3D finite element analyses (FEA) of the topology are illustrated for different field currents in order to accomplish the machine design and to determine the sizing of the optimum field winding. Furthermore, torque analysis of the FCT machine using 3D finite element analysis is also carried out and illustrated in the paper.

A new axial flux surface mounted permanent magnet machine capable of field control

Nonslotted and slotted external rotor internal stator TORUS type surface mounted permanent magnet (PM) machines (TORUS-NS and TORUS-S) have simple structures, relatively high efficiencies and low cost These machines can be used for the applications that require high power and torque density, high efficiency and low noise with the use of neodymium-iron-boron (NdFeB) magnets providing relatively small overall size and weight In this paper, sizing equations of the TORUS machines are derived using generalized sizing equations The optimum machine design is illustrated by choosing the magnet pole-arc ratio and the skew angle of the rotor magnets Using the optimum design data, field analysis of TORUS-NS and TORUS-S machines are investigated Pulsating torque analyses including the cogging torque and the ripple torque are carried out using a 3D finite element analysis (FEA) software Utilizing the techniques such as modifying the winding structure and skewing the rotor magnets, minimization of cogging torque and ripple torque for the TORUS-NS and TORUS-S machines are obtained and verified using 3D FEA Finally a comparison of the TORUS topologies in terms of torque quality is illustrated in the paper

Menşure Aydin

Papers

Minimization of Cogging Torque in Axial-Flux Permanent-Magnet Machines: Design Concepts

Torque quality and comparison of internal and external rotor axial flux surface-magnet disc machines

Design, Analysis, and Control of a Hybrid Field-Controlled Axial-Flux Permanent-Magnet Motor

A new axial flux surface mounted permanent magnet machine capable of field control

Design and 3D electromagnetic field analysis of non-slotted and slotted TORUS type axial flux surface mounted permanent magnet disc machines