Investigation of the Rotor-Tower Instability of the KEWT Wind Turbine.

摘要

This report reassesses the dynamic instabilities of the KEWT ('Kosten Effective Wind Turbin') wind turbine prototype. The KEWT wind turbine was a two bladed wind turbine in the 1980s. During tests, violent vibrations were observed as the rotor angular velocity. This report further investigates the KEWT instabilities, concentrating on the case of tower second bending-blade edgewise instability. It is demonstrated that the 'advancing lag mode' is responsible for the coupling between the lead-lag and the second tower-bending mode. The generator supplies energy to the control system in order to keep the rotor rpm constant. The new contribution in this report concerns the demonstration that the lead-lag instability is in the advancing mode. To prove this, a method is used which can predict the couplings between the uncoupled rotor and tower dynamics. The method consists in essence of representing in the complex plane the uncoupled poles of different modes and defines critical regions in the complex plane.