Dynamics-Based Health Monitoring and Control of Wind Turbine Rotors

Automatic control and condition monitoring of wind turbines are usually treated as two distinct technical areas because control has a short-term focus, whereas condi- tion monitoring has a long-term focusIn practice, energy capture and condition monitoring actually have interrelated objectivesThe structural dynamic behav- iour of the rotor system is the link between control and condition monitoringThe aerodynamic loads that govern energy capture are converted by the dynamics of the rotor into drive train loads, which govern many of the failure modes in the turbineThis chapter will discuss two ways in which these rotor structural dynam- ics can be used to improve decision making in operation and maintenance of wind turbinesA horizontal axis wind turbine test bed is used to experimentally simulate the rotor structural dynamic response to uniform flow as well as horizontal and vertical shear flow across the rotor planeFirst, the vibrational characteristics of the rotor system are described in the context of modal analysis where each mode of vibration occurs at a particular frequency with a particular modal deflection shapeThese shapes dictate the effectiveness with which a given aerodynamic load couples into the rotor to produce mechanical power in addition to vibrations of the rotorIt is shown using operational modal analysis that changes in yaw and pitch set points change the degree to which the rotor modes of vibration are excited and, consequently, the energy that is captured from the wind and the fatigue loads that act on the turbineBy analysing the changes in rotor response in the flap, edge - wise and span directions, the source of power loss is classified so that corrective action can be taken in the form of rotor controlSecond, the effects of changes in the wind state on the sensitivity of condition monitoring data to damages in the turbine rotor are discussedIt is shown using modal filters that certain frequencies in the measured response of the wind turbine are sensitive to a change in condition of the rotor in the form of ice accretion or blade root damage for use in detecting