Semi-active control of a wind turbine via magnetorheological dampers

This paper investigates the use of magnetorheological (MR) dampers to semi-actively control wind induced vibrations of a 1/20 scaled wind tower model. The idea consists in realizing a variable restraint at the base of the model, able to modify in real time its mechanical properties according to the instantaneous response of the tower. The restraint is made up of a cylindrical hinge, two springs and two prototype MR devices, the behavior of the latter being driven by control algorithms aiming to reduce the structural demand imposed to the steel tower. The demand is expressed in terms of base bending stress and top displacement.The model has been tested on a shaking table facility at the Denmark Technical University in Copenhagen imposing two different types of accelerograms at the base, equivalent to an extreme short operating gust and a longer high wind speed excitation, respectively. Two distinct control algorithms, each designed according to different philosophies and goals have been adopted to drive the semi-active devices.The results show the effectiveness of the proposed control technique in reducing the stress demand at the base, this at the cost, in the worst case, of a slight increase of top displacement. They encourage investigating further in this direction in order to promote the use of such strategy for a cost effective design of high wind towers.