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

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Analysis of Dynamic Behaviour of Electric Power Systems with Large Amount of Wind Power

This report presents a survey on generator concepts and power electronic concepts for wind turbines. The report is aimed as a tool for decision-makers and development people with respect to wind turbine manufactures, utilities, and independent system operators as well as manufactures of generators and power electronics. The survey is focused on the electric development of wind turbines and it yields an overview on: State of the art on generators and power electronics; future concepts and technologies within generators and power electronics; market needs in the shape of requirements to the grid connection, and; consistent system solutions, plus an evaluation of these seen in the prospect of market needs. This survey on of generator and power electronic concepts was carried out in co-operation between Aalborg University and Risoe National Laboratory in the scope of the research programme Electric Design and Control. (au)

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Conceptual survey of Generators and Power Electronics for Wind Turbines

This paper presents a unique axial-flux permanent-magnet synchronous generator (AFPMSG), which is suitable for both vertical-axis and horizontal-axis wind turbine generation systems. An outer-rotor design facilitates direct coupling of the generator to the wind turbine, while a coreless armature eliminates the magnetic pull between the stationary and moving parts. The design and construction features of the AFPMSG are reviewed. The flux-density distribution is studied, with the aid of a finite element software package, in order to predict the generated e.m.f. waveform. The performance equations of the AFPMSG are derived, and the condition for maximum efficiency is deduced, for both constant-speed and variable-speed operations. The experimental results, in general, confirm the theory developed

An Axial-Flux Permanent-Magnet Synchronous Generator for a Direct-Coupled Wind-Turbine System

Permanent-magnet generators have been used for wind turbines for many years. Many small wind turbine manufacturers use direct-drive permanent-magnet 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 permanent-magnet 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 the lab to improve the design.

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Axial flux, modular, permanent-magnet generator with a toroidal winding for wind turbine applications

The slotless toroidal-stator permanent-magnet machine 'TORUS' can be integrated with an engine to form a compact generating set, but the terminal voltage naturally reduces on load because the armature reaction MMF leads to reduced flux. However, if a stator core of reduced thickness is used, heavy saturation takes place on no-load so that, on load, the armature reaction MMF simply reduces the degree of saturation. The stator coils may then link the same rotating flux whether current is drawn or not, with the terminal voltage without being greatly affected by armature reaction. The design and analysis of the resulting machine with reduced voltage regulation are presented with supporting test results taken from two prototype machines. >

Design of slotless TORUS generators with reduced voltage regulation

The paper discusses the development of an axial-flux permanent-magnet generator for a gearless wind energy system which aims to demonstrate the feasibility of integrating wind and photovoltaic energy converters for the generation of electricity and to achieve optimum exploitation of the two energy sources. The merits of an axial-flux generator topology are discussed with reference to the particular requirements of an electrical generator for a direct-coupled wind turbine application. The design, construction and test results of a 5 kW, 200 RPM permanent-magnet generator, to form a 10 kW pilot power plant in combination with a 5 kW photovoltaic array, are presented.

B.J. Chalmers

Papers

Design of slotless TORUS generators with reduced voltage regulation

An axial-flux permanent-magnet generator for a gearless wind energy system