Optimal trajectory tracking control for wind turbines during operating region transitions

Control systems for wind turbines have become an active area of research over the past decade as the wind industry has grown and more turbines are installed. Properly sited turbines experience many transitions between below rated operation, where the goal is to extract maximum energy from the wind, and rated speed operation, where the goal is to regulate the power capture to the rated power of the turbine. Many of the largest structural loads are induced during the transition between these operating regions. This paper focuses on using preview wind speed measurements to schedule, optimize, and track a desired trajectory of the wind turbine states and inputs during region transitions between below-rated and above-rated operation. The goal of this control system is to reduce the structural loading on the turbine components through smoother region transitions. The wind speed preview measurements are used to generate an initial desired trajectory of the turbine. This trajectory is optimized by finding a regulation trajectory that lies on the turbine trajectory manifold which is close to the desired trajectory in a weighted L₂ sense. The regulation trajectory is then used as a reference for a time-varying linear quadratic optimal controller.