DESIGN, OPERATION AND CONTROL OF SERIES-CONNECTED POWER CONVERTERS FOR OFFSHORE WIND PARKS

Abstract

OFFSHORE wind farms need to develop technologies that fulfill three main objectives:Efficiency, power density and reliability. The purpose of this thesisis to study an HVDC transmission system based on series connection of the turbineswhich theoretically meet these three objectives. A new topology of matrixconverter operated at high frequency is proposed. This converter is studied usingdifferent modulation algorithms. Simulation and experimental results demonstratedthat the converter can be operated as a current source converter with highefficiency. An optimal control based on a linear quadratic regulator is proposedto control the matrix converter as well as the converter placed on shore. Resultsdemonstrated the high performance of this type of control and its simplicity forimplementation. An stationary state study based on non-linear programming andMontecarlo simulation was carried out to determine the performance of the conceptfor long-term operation. Series connection is an efficient technology if and only ifthe differences in the effective wind velocity are small. This aspect limits the numberof wind turbines that can be connected in series, since a numerous number ofturbines will lead to high covariances in the distribution of the wind. A complementarystudy about active filter and reactive power compensation was carried outusing an optimization-based algorithm.