Robustness Analysis of Wind Turbine Control Systems

Abstract

In this thesis, a framework for robustness analysis of wind turbine control systems is proposed. This framework is employed to examine and compare the robustness of H_infinity and PI blade pitch controllers designed to maintain the turbine’s generated power at its rated value in Region 3 of the wind turbine operation. The L_2-induced norm of the closed-loop system is used as the performance metric. In this framework, a turbulent wind model based on the Kaimal spectrum is added to the closed-loop wind turbine model obtained by linearizing the nonlinear model at different operating wind speeds. This framework utilizes the theory of Integral Quadratic Constraints (IQCs), whereby IQCs and signal IQCs are used to incorporate the wind model into the wind turbine model. As a result, upper bounds on the L_2-induced norm of the system are obtained by solving semidefinite programs (SDPs). The proposed framework results in a better characterization of the system’s performance. The analysis results from the proposed framework are verified and validated via extensive high-fidelity simulations of the nonlinear wind turbine model.