Robust control using coprime factorizations, application to a flexible wind turbine

The author proposes a control design method based on a coprime factorization of the plant. The design method includes the synthesis of low-order H_∞ controllers and the generation of a robustness margin which is less conservative than a gap-metric bound. For a set of linear models the choice of nominal model is discussed. The developed control design method is used to design a robust linear low-order controller for a nonlinear flexible wind turbine model under full load conditions. The controller will have to stabilize a set of linear models representing the nonlinear wind turbine under various operating conditions. It is shown that using the new robustness test this controller stabilizes the whole set with the desired performance