Analysis and design of tower motion estimator for wind turbines

The use of blade individual pitch control (IPC) provides a means of alleviating the harmful turbine loads that arise from the uneven and unsteady forcing from the oncoming wind. Such IPC algorithms, which mainly target the blade loads at specific frequencies, are designed to avoid excitations of other turbine dynamics such as the tower. Nonetheless, these blade and tower interactions can be exploited to estimate the tower movement from the blade load sensors. As a consequence, the aim of this paper is to analyse the observability properties of the blade and tower model and based on these insights, an estimator design is proposed to reconstruct the tower motion from the measurements of the flap-wise blade loads, that are typically available to the IPC. The proposed estimation strategy offers many immediate benefits, for example, the estimator obviates the need for hardware sensor redundancy, and the estimated signals can be used for control or fault monitoring purposes. We further show results obtained from high-fidelity turbine simulations to demonstrate the performance of the proposed estimator.