Dynamical electromechanical analysis of pole-piece rotors in pseudo direct-drive machines

Abstract

Wind energy has shown to be a great renewable energy source, with a possible penetration of 20% by 2040. In order to increase its competitiveness with fossil fuels, the LCOE should decrease further than it already has. Increasing the power rating of wind turbines has proven to be an effective way to achieve this. However, this results in impractical large nacelles which are hard to install offshore. Reducing the size can be done with a gearbox, but due to the gearbox being a high-risk component of offshore wind turbines, wind turbine manufacturers have moved to direct-drive topologies. The pseudo direct-drive topology, where a magnetic gear and direct-drive machine are combined, has shown great potential reducing the size of the generator while keeping the reliability of a direct-drive machine. However, due to the introduction of an extra rotor for the magnetic gearing, the mechanical complexity increases. Focusing on a particular 10 MW design, large deflections in this extra rotor of up to five times the air gap length have been observed during nominal operation. Simple modifications have been investigated, resulting in deflections of less than 1 mm. Each modification was then compared to identify the most promising one.