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Active vibration absorber for gear box noise reduction in wind turbines

 
: Illgen, A.; Drossel, W.-G.; Wittstock, V.; Schirmer, W.; Wiedemann, L.

ERAS GmbH:
Active systems for dynamic markets. Conference proceedings. CD-ROM : 23./24.05.2007, Göttingen, Adaptronic Congress 2007
Göttingen: Adaptronic Congress Veranstaltungs GbR, 2007
Adaptronic Congress <11, 2007, Göttingen>
Englisch
Konferenzbeitrag
Fraunhofer IWU ()
active vibration absorbtion; vibration control; noise control; piezo stack actuator; wind turbine; adaptronic

Abstract
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. Most gearboxes consist of a planetary and a one or two-stage spur gear stage. Typical tooth mesh frequencies are 100 Hz and 600 Hz (tones in the noise). 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.
Introduction
Single tone components in noise Wind turbines have a rising share in energy supply and contribute to climate protection and saving of resources. With an ever increasing number of wind turbines also in densely populated areas the sound emissions are not be disregarded. There are two main sound sources: the rotor blades and the drive train. Over the past years the aerodynamic noise induced by the rotor blades could successfully be reduced. Now, the focus lies on the sound generated by the drive train, especially by the gear box inside. A significant sound source is the tooth mesh of the gear wheels [1]. Most gearboxes consist of a planetary and a one or two-stage spur gear stage [1]. Typical tooth mesh frequencies are in the range of 100 Hz to 600 Hz (tones in the noise). The noise generated by the tooth mesh propagates through the roller bearings to the gearbox and through.

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