Stability Control of Wind Turbines for Varying Operating Conditions Through Vibration Measurements

Abstract

Wind turbines have very specific characteristics and challenging operating conditions. Contemporary MW-scale turbines are usually designed to be operational for wind speeds between 4 and 25 m/s. In order to reach this goal, most turbines utilize active pitch control mechanisms where angle of the blade (pitch angle) is changed as a function of wind speed. Similarly, the whole rotor is rotated toward the effective wind direction by using the yaw mechanism. The ability of the turbine to adapt to the changes in operating conditions plays a crucial role in ensuring maximum energy production and the safety of the structure during extreme wind loads. This, on the other hand, makes it more difficult to investigate the system from dynamic analysis point of view. Unexpected resonance problems due to dynamic interactions among aeroelastic modes and/or excitation forces can always be encountered. Therefore, within the design wind speed interval, for each velocity increment, it has to be proven that there are no risks of resonance problems and that the structure is dynamically stable. This work aims at presenting the results of the dynamic stability analyses performed on a 2.5-MW, 80-m-diameter wind turbine. Within the scope of the research, the system parameters were extracted by using the in-operation vibration data recorded for various wind speeds and operating conditions. The data acquired by 8 strain gauges (2 sensors on each blade and 2 sensors on the tower) installed on the turbine were analyzed by using operational modal analysis (OMA) methods, while several turbine parameters (eigenfrequencies and damping ratios) were extracted. The obtained system parameters were then qualitatively compared with the results presented in a study from the literature, which includes both aeroelastic simulations and in-field measurements performed on a similar size and capacity wind turbine.