Design and Assessment of HVDC Off-shore Wind Turbine Generator

Abstract: 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 aninterior permanent magnet synchronous generator (IPMSG) as well as a permanent magnetassisted 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 barrierswith magnet material, in order to achieve high torque density and low torque ripple. The ironbridge 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 ofsegmenting the magnets and the risk of demagnetization are quantified. Assessing the averageannual efficiency using the two generating systems during different average wind conditionsshows that when the PMa-SynRG is used, the machine annual energy efficiency is higher. Thekey reason for this is the lower flux level in the PMa-SynRG which creates lower iron lossesat low wind speeds. In addition, the PMa-SynRG has 30% less magnet weight for the samegeometrical size and maximum power level.