Structural loads reduction in wind turbines via set-based control

The paper is focussed on set-based correction of the wind turbine controls in order to evade high mechanical loads on structural components of a wind turbine during transients. A set in the state space of the wind turbine model is constructed where all accounted mechanical loads are within the prescribed limits. The approach is universal in a way that mechanical loads on different components, which are expressed as functions of the wind turbine states and inputs, can be blended together in that set description. A procedure is proposed to determine a non-conservative polytopic under-approximation of the mentioned set. Following that, a controlled invariant set methodology is used to compute a controlled invariant subset of the polytopic set. It is applied in on-line controls for a minimalistic correction of outputs of any wind turbine control algorithm that assures all the observed mechanical loads on different components are within boundaries. The approach is illustrated for mechanical loads on the axle pin and controls in an operating area above the nominal wind speed.