Estimation and control of wind turbine tower vibrations based on individual blade-pitch strategies

In this paper, we present a method to estimate the tower fore-aft velocity based upon measurements from blade load sensors. In addition, a tower dampening control strategy is proposed, based upon an individual blade pitch control architecture that employs this estimate. The observer design presented in this paper exploits the Coleman transformations that convert a time-varying turbine model into one that is linear and time-invariant, greatly simplifying the observability analysis and subsequent observer design. The proposed individual pitch-based tower controller is decoupled from the rotor speed regulation loop and hence does not interfere with the nominal turbine power regulation. Closed-loop results, obtained from high fidelity turbine simulations, show close agreement between the tower estimates and the actual tower velocity. Furthermore, the individual pitchbased tower damping controller achieves 45% reductions in the variance of the tower vibrations for a modest 5% increase in the variance of the pitch rates, with negligible impact upon the nominal turbine power output.