Influence of the control system on wind turbine reliability in extreme turbulence

One of the critical design driving load cases for modern large onshore/offshore wind turbines is power production in extreme turbulence. According to the IEC 61400-1 edition 3 design standard, the normal production extreme loads are extrapolated and compared to the extreme loads obtained under extreme turbulence input. This study shows that using a probabilistic approach and the first order reliability method, wind turbine structural reliability can be assessed when the extreme turbulence model is uncertain. The structural reliability is assessed for a wind turbine with/without structural load alleviation control features. It is shown that large uncertainties in inflow conditions and turbulence can be significantly reduced while maintaining an acceptable structural reliability through the use of advanced structural load alleviation control features. However, that comes at a cost of increased controller complexity and loss in annual energy production.