Piezo based active vibration absorber for gear box noise reduction in wind turbines

Piezo Based Active Vibration Absorber for Gear Box Noise Reduction in Wind Turbines A. Illgen, V. Wittstock Fraunhofer Institute for Machine Tools and Forming Technology IWU Dresden, Germany In wind turbines the drive train, especially the gear box, is a significant source of noise. One reason is the tooth mesh of the gear wheels. The structure born noise generated by the tooth mesh propagates through the roller bearings to the gearbox and through the impact noise insulation to the nacelle bedplate and finally to the tower. The large surface area of the tower radiates the noise to the environment. The impact noise insulation is often insufficient. Single tones in the noise are especially problematic, since pure tone penalty to the maximum emission values is required by law if single tone components are in the noise spectrum. The Active Vibration Absorber (AVA) introduced in this paper based on Piezo Stack Actuators and allows active compensation of tonal components induced by the gear. It works with two commercial Piezo Stack Actuators in-phase opposition. They provide also the stiffness of the vibration absorber. Since wind turbines work with variable speed, adaptation in frequency is necessary. Depending on the special case different control laws could be chosen. If frequency is adapted by a variable position feedback of the actuator stroke the control law changes the effective stiffness of the system. The result is a tunable vibration absorber. Additionally, damping or increasing of the effective mass can be realized by the controller. Inferentially, the absorber works as an active system.