Control of Magnetic Bearings in Wind Turbines

Control of Magnetic Bearings in Wind Turbines

Abstract

Direct drive generators applied to large wind turbines present some problems, such as very heavy and expensive price. The use of magnetic bearings has a possibility to reduce the weight of the direct drive generator. The control system for such magnetic bearings is considered.

In the beginning, the thesis discusses the problems of direct drive generators in large wind turbines, introduces a hybrid concept of active magnetic bearings, gives a demonstrator of magnetic bearings used in this project, and presents a basic control system of active magnetic bearings.

For the purpose of support such magnetic bearings in wind turbines, this thesis gives a complete control system. This control system includes electrical circuits and decentralized control method. The implementation of the electrical circuits is distributed into two PCBs. The decentralized control method is designed with six PID controllers.

Finally, in order to improve the stability of the system, the H-infinity control method is suggested to magnetic bearing system in wind turbine applications.

Introduction

Wind Energy

Wind energy is a kind of renewable energy, and we have used it for hundreds of years. The kinetic energy of wind can be converted into other useful forms of energy, such as electricity, using wind turbines. Nowadays, two kinds of wind turbines are used to transfer wind energy to electricity. Onshore wind energy is commonly used worldwide, but it takes a large land use. However, the offshore wind energy performs better than onshore energy. The higher wind speed on the sea makes the wind turbines produce more electricity. So there is an increased interest in offshore wind turbines.

Recently, wind energy has been growing faster than before in the world. Both onshore and offshore wind farms are being planed and built in the past few years. Until now the biggest offshore wind farm is Horns Rev 2 in Denmark with 209 megawatt (MW) of installated power [1].

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