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Suppression of grid fault-induced vibration in wind turbines using UPQC

In this paper an innovative approach based on the use of Flexible AC Transmission Systems (FACTS) devices is investigated to explore the possibility of suppressing mechanical vibrations in wind turbines subjected to grid faults. The numerical analysis performed highlights the capability of FACTS devices to counteract the mechanical and structural vibrations in wind turbines due to the occurrence of electrical faults. In particular, we study the application of Unified Power Quality Conditioner (UPQC) as an effective means of suppressing the vibrations. In order to study the effectiveness of UPQC, first of all a detailed model describing the dynamic interaction between the mechanical and the electrical subsystems of a wind turbine is formulated and presented in this paper. The key feature of the developed model is that it can capture the impact of grid faults on the mechanical vibrations of drive train, flexible rotor blades and tower. Subsequently, the use of FACTS devices in general, with particular emphasis on UPQC in mitigating these vibrations has been investigated. Results show that FACTS devices are successful in mitigating vibrations due to electrical faults and they can be conveniently applied to stabilize the generator shaft speed, drive train oscillations, edgewise blade vibrations and tower responses. Further, superior performances of the UPQC as compared to STATCOM are also observed under conditions with increased fault duration.