Load Reduction in Wind Turbines with Bend-Twist Coupled Blades without Power Loss at Underrated Wind Speeds

Usage of composite materials in wind turbine blades is a passive mechanism to alleviate fatigue loads besides the reduction in the mass of the wind turbine system. Off-axis plies in bend-twist coupled (BTC) blades account for the passive fatigue load reduction by reducing the effective angle of attack of blade sections. Reduction in fatigue loads is generally represented by damage equivalent load ratios. In the present study, multibody aeroelastic analyses are performed for wind turbine systems for the underrated, rated and the overrated turbulent wind speeds. It is shown that load reduction can be achieved for the whole range of wind speeds with the usage of bend-twist coupled blades at the cost of power loss at underrated wind speeds which is unacceptable. Thus, the main concern of the present study is first to make performance study of wind turbines with bend-twist coupled blades at underrated wind speeds and then to overcome the power loss while still achieving reduction in damage equivalent loads by the proper modification of the pre-twist variation of the bend-twist coupled blades together with the generator torque curve across whole range of wind speeds. This study has been performed utilizing the same pitch control settings in region 2 to examine the mere effect of pretwist modification on the power performance of the wind turbine and on the damage equivalent loads.