On orientation control of suspended blade during installation in wind turbines

This paper discusses problems involved in the procedure for offshore installation of blades in wind turbines, due to wind loads. In general the high winds at sea provides for nearly optimal conditions for harvesting energy via wind turbines due to the often high wind speeds and low turbulence intensity. However, the very same features also call for great difficulties during installation of the wind turbine blades, making this process extremely difficult, expensive and time consuming. Often the blades are hoisted to the wind turbine hub via cranes and sought held in appropriate positions by so-called taglines/wires, but still significant motion oscillations of blade root ends are experienced, even at rather low wind speeds. The paper considers the possibility to dampen the oscillating motions via control of the tagline lengths. The main control strategy considered, is the possibility to control the orientation of the blade, i.e. the pitch, yaw and roll angles via a decentralized control approach. An overall dynamic model structure of such systems is presented, and a system analysis and control design is presented based on various considerations on the system. In order to evaluate the proposed control design, a scaled test system has been established for this purpose, and results demonstrate the proposed features of the controlled system.