Wind speed estimation using second-order sliding-mode observers: simulation and experimental validation on a floating offshore wind turbine

Abstract. Wind speed estimation is crucial for the control and performance optimization of floating offshore wind turbines (FOWTs). This paper introduces a robust estimation framework based on second-order sliding-mode observers (SOSMOs), developed in both constant-gain and adaptive versions. The observers are developed using a reduced-order dynamic model and validated in the OpenFAST simulation environment when all degrees of freedom are activated. Their performances are compared with the continuous-discrete extended Kalman filter (CD-EKF) used in the reference open-source controller (ROSCO). The proposed approach is assessed under stochastic wind/wave conditions through OpenFAST simulations and further validated experimentally using a scaled software-in-the-loop (SIL) setup. Simulation results indicate that the proposed observers perform comparably to the CD-EKF in terms of estimation accuracy, while offering robustness, simpler implementation, and reduced computational complexity.