Single blade installation using jack-up vessels is a commonly used blade installation setup for offshore wind turbines. During this operation, each blade is lifted by the main crane from the deck, moved, and then bolted to the rotor hub at the top of the turbine tower. Tugger lines from the crane boom are connected to the suspended blade to reduce the blade's pendulum motions. Lately, much research has been conducted to reduce the blade motion by actively controlling the tension force in the tugger lines. Since the tugger lines can only provide positive tension, pretension is needed before the mating process. In this paper, an active PID control strategy with a three-tugger-line configuration is proposed to reduce the blade motion by controlling the tugger line forces acting on the blade. The placement of the additional 3rd line is discussed. The control allocation is achieved by convex programming with an auto-generation solver using CVXGEN. Simulations under turbulent wind conditions are conducted to verify the active control scheme in HAWC2. The results shows that the active control scheme effectively reduces the translational motion of the blade root relative to the hub in the mean wind direction.
Offshore wind turbines (OWTs) have attracted increasing global attention due to advantages, such as saving land resources and a superior energy quality. However, the price of electricity from offshore wind in 2016 is still approximately 3-4 times greater than that of electricity from onshore wind. During an OWT installation, much time is spent on waiting for the allowable weather window. Hence, OWT assembly and installation are expensive, accounting for more than 10% of the OWT overall capital expenditures (Moné et al. 2017).
As the blade span exceeds 60 m, lifting an entire rotor assembly offshore may face more challenges in addition to transportation issues. Single blade installation is one of many OWT blades installation approaches, where one blade is lifted by the main crane and attached to the hub on the top of the turbine tower. The suspended blade and the crane boom are connected by tugger lines, typically without any active control. State-of-the-art single blade installation is limited to a mean-wind speed of 8-12 m/s (Gaunaa et al. 2014). The benefits of the single blade installation are a wider range of installation vessels, lower crane capacity, and higher deck usage. On the other hand, it requires a higher number of the offshore lifts.