Utilization of blade pitch control in low wind speed for floating offshore wind turbines

This paper investigates a potential advantage of utilizing blade pitch control over the conventional fixed blade pitch strategy in low wind speed for horizontal-axis offshore floating wind turbines mounted on a barge platform. To examine the advantage, simulation studies with a 5MW wind turbine model in the software FAST are conducted. The generated power and the platform pitch movement are compared among closed-loop systems with three feedback controllers, that is, a baseline controller with fixed blade pitch, a linear-parameter-varying (LPV) controller with fixed blade pitch, and an LPV controller with varying blade pitch. The LPV controllers are gain-scheduled in terms of wind speed. For the design of LPV controllers, an LPV model which represents a family of linearized models of the nonlinear model in FAST over the low wind speed range is employed, and a well-known LPV controller design technique is applied to the LPV model. Simulation results demonstrate that the utilization of blade pitch control can reduce the platform pitch oscillation by more than 5 percent compared to fixed blade pitch strategies, possibly by slight reduction in power capture. This suggests the usage of blade pitch control in low wind speed when the cost decrease due to the load reduction outweighs the cost increase caused by the loss of power generation.