Optimisation and comparison of generators with different magnet materials for a 6MW offshore direct drive wind turbine

Abstract

This version is available at https://strathprints.strath.ac.uk/56794/ Strathprints is designed to allow users to access the research output of the University of Strathclyde. Unless otherwise explicitly stated on the manuscript, Copyright © and Moral Rights for the papers on this site are retained by the individual authors and/or other copyright owners. Please check the manuscript for details of any other licences that may have been applied. You may not engage in further distribution of the material for any profitmaking activities or any commercial gain. You may freely distribute both the url (https://strathprints.strath.ac.uk/) and the content of this paper for research or private study, educational, or not-for-profit purposes without prior permission or charge.Any correspondence concerning this service should be sent to the AbstractIn the past few years interest in the use of low speed permanent magnet generators for direct-drive wind turbine generator applications has increased significantly. The significant fluctuations in NdFeB magnet prices has encouraged designers to optimise magnet utilisation and to look at alternative magnet materials for wind turbine electrical generators. In this paper an analytical design model is developed for 6 MW offshore direct-drive wind turbine generators using different magnet materials (one with surface mounted NdFeB and another with flux concentrating ferrite magnet). Finite element method models are used to check key dependent variables calculated by the analytical models. The generator designs are optimised using a hybrid optimisation method incorporating a Genetic Algorithm and Pattern Search approaches. This is applied for four different objective functions, the first two which concentrate on maximising rated torque per unit magnet mass or unit of generator active material cost. They are simple and quick to execute but prioritise cost reduction and ignore lower efficiencies leading to lower turbine energy yields and hence poor cost of energy. A third objective function which seeks to minimise the sum of the generator active material cost and the costs of lost revenue over a finite number of operational years. This gives similar results to a fourth objective function which is an explicit turbine cost of energy calculation. The cost of NdFeB magnets affect the cost of energy of the surface mounted generator which tested with different cost €40/kg, €60/kg and €80/kg. The ferrite magnet generator being better when the NdFeB magnet price rises to €80/kg.

Optimization and comparison of flux-concentrating Nd-Fe-B generator considering variable power factor and wind conditions for a 6MW offshore wind turbine

“…The generators are modelled analytically in MATLAB. The magnetic properties of the chosen Nd-Fe-B magnet is given in [9]. Lumped parameter magnetic circuit models are used to calculate flux per pole.…”

Replacement of NdFeB by Ferrite Magnets

“…This can be achieved with improved design for cooling [30,31]. Even with some suggested ferrite projects [5,6], the industry of wind turbines prefer rare-earth based magnets. The most used wind turbine type, however, is the DFIG (Doubly Fed Induction Generator).…”

“…Ferrite magnets have been suggested even for wind turbines [5,6]. However, for this kind of application NdFeB magnets have many advantages, for example reducing weight in the structure.…”