Design of a nonlinear multi-input-multi-output sliding mode pitch angle and plunge controller for a 5MW wind turbine blade tip

Traditionally, wind turbine blades are primarily controlled by varying the pitch angle of the full blade. The primary motivation of this article is to develop a design of a nonlinear multi-input-multi-output sliding mode controller for tracking the pitch angle and the plunge of the wind turbine blade tip instead of controlling the entire blade. The hypothesis is that controlling the pitch and plunge for a portion of blade tip length can be an alternate control strategy. A method was adopted wherein a separated pitch angle control at the tip (SePCaT) was modeled and tested in a digital environment and controller response was realized by modeling desired pitch angle and plunge trajectories to abate power generated by the wind turbine to rated power at high wind speeds. From the comparative results with the desired trajectory, it was observed that the sliding mode controller exhibited excellent trajectory tracking for controlling the blade pitch angle and plunge. It can be concluded that controlling blade plunge is essential to maintaining desired blade pitch angle trajectories. This technology offers significant improvement over other technologies as desired pitch and plunge control is achieved over a shorter blade length.