Structural Flexibility of Large Direct Drive Generators for Wind Turbines

The trend in wind energy is towards large offshore wind farms. This trend has led to the demand for high reliability and large single unit wind turbines. Different energy conversion topologies such as multiple stage geared generators, single stage geared generators and gearless (direct drive) generators have been coupled to the wind turbine in the last decades. Direct drive generators based on permanent magnet technology have a high efficiency, less components and lower speeds that can translate to high energy yield and less maintenance demand. However, the mass of such direct drive generators can be significantly higher than of other geared generators. This thesis focuses on the issue of mass reduction of large direct drive generators in wind turbines. The main objective of this thesis is to investigate methods of mass reduction in large direct drive generators in wind turbines especially mass reduction by introducing structural flexibility in the generator. This allowance in structural flexibility is enabled by the use of magnetic bearing technology