Experimental validation of wind turbine higher harmonic control using shaft loads measurements

In order to achieve reductions in wind turbine structural loads and to enable further increase of wind turbine rated power and dimensions, individual pitch control algorithms received significant portion of attention in the scientific community in the recent years. Individual pitch control typically reduces only the first loads harmonic, but as the wind turbines grow in size, it is expected that higher harmonics will have to be reduced as well. Instead of using blade loads, which is typical approach in the literature, this paper analyses the possibilities of reduction of higher harmonics from the wind turbine loads using the shaft measurements. To this aim, loads transformations capable of extracting information about higher loads harmonics from shaft measurements are derived. The controller for load reduction based on such transformations is implemented on a scaled wind turbine model and experimentally validated in the wind tunnel at Politecnico di Milano.