Load reducing control for wind turbines: Load estimation and higher level controller tuning based on disturbance spectra and linear models

In wind turbine engineering, it is a well-known fact that mechanical loading of the structural components, as tower and blades, can be heavily influenced by means of control. This work provides a comprehensive discussion on systematic control design for active load reduction. A review of the established approaches for load reducing pitch control is given. The basic idea is to adjust the blade pitch angles to provide active damping of structural loads or to compensate for periodic load components. A survey on rating and cost of wind turbine structural components is given to sketch the potential impacts of control design on Cost-of-Energy. Special focus in a separate chapter is given to the major trade-off between load reductions and rating of the pitch actuator system. In the main part, a pragmatic approach to systematic control design by use of modern multi-variable control design methods is introduced. Linear models in combination with disturbance spectra are applied to allow for fast and transparent optimization of the controllers. Exemplarily, this hierarchical control design / controller tuning approach is demonstrated for two different types of load reducing pitch controllers