Design and Assessment of HVDC Off-shore Wind Turbine Generator

Doktorsavhandling, 2015

In this work, design and assessment of a 5 MW wind energy generator with a gearbox is performed to find an energy-efficient generator for HVDC offshore wind turbines, studying an interior permanent magnet synchronous generator (IPMSG) as well as a permanent magnet assisted synchronous reluctance generator (PMa-SynRG). Quantities such as torque density, torque ripple, losses and amount of magnet material are studied. The investigation includes dif- ferent numbers of air barriers of the PMa-SynRG rotor; up to 6, as well as how to fill the barriers with magnet material, in order to achieve high torque density and low torque ripple. The iron bridge thickness is checked from a mechanical perspective in order to ensure good electromag- netic performance while still keeping the needed mechanical strength. Moreover, the impact of segmenting the magnets and the risk of demagnetization are quantified. Assessing the average annual efficiency using the two generating systems during different average wind conditions shows that when the PMa-SynRG is used, the machine annual energy efficiency is higher. The key reason for this is the lower flux level in the PMa-SynRG which creates lower iron losses at low wind speeds. In addition, the PMa-SynRG has 30% less magnet weight for the same geometrical size and maximum power level.