An HVDC Off-shore Wind Generation Scheme with High Voltage Hybrid Generator

Abstract

This thesis proposes a high voltage DC generation system for off-shore wind applications. The proposed scheme consists of a high voltage (HV) hybrid generator, a passive rectifier, DC/DC converters and HVDC interconnection and transmission. The HV hybrid generator prime mover is a wind turbine that may incorporate a gear-stage or be a direct drive system. Two regions of operation for the wind turbine are proposed; a limited speed region and a high speed operation region. The proposed system is studied and compared with a commercial off-shore wind system installed in the UK. The analyses are carried out considering system steady-state operation to identify system envelope specification requirements, key technology gaps, benefits and system performance and deduce component ratings. The proposed system results in higher efficiency, lower mass for the turbine power-train and also interconnections and transmission cables. The hybrid generator in this thesis is a high voltage machine with two rotor components namely a wound field (WF) and a permanent magnet rotor. Two designs for the HV hybrid generator are proposed; a surface PM rotor and an embedded PM rotor design. The DC wound field is the same for both designs while both design have a 9-phase stator winding. Finite element analysis (FEA) is used to study the machine electro-magnetic performance and MATLAB to process the results data. Machine losses including copper, windage and friction are calculated while the iron losses are predicted analytically from the machine field solution information and materials characteristics. Different insulation systems for the HV winding are studied based on commercial high voltage winding practice with the conclusion that the winding scheme is highly practicable.