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Control of VSC During Unsymmetrical AC Faults in Offshore Wind Farms
Norwegian University of Science and Technology, Faculty of Information Technology, Mathematics and Electrical Engineering, Department of Electrical Power Engineering.
2013 (English)MasteroppgaveStudent thesis
Abstract [en]

This master thesis has analyzed the eects of unbalanced faults in the AC grid of an oshore wind farm. The wind farm is connected to shore with a Voltage Source Converter (VSC) HVDC link, and the wind turbine genera- tors employs VSC technology in full scale converters. The oshore wind farm have been modelled in Matlab SIMULINK, and there have been performed dierent short circuit simulations at various places in the oshore AC grid. A control method designed to control positive and negative sequence currents in parallel have been tested and compared to a standard control system dur- ing these short circuit simulations. The theory behind the modelled negative sequence current controller is that it can be used to control active power oscillations, thus limiting DC voltage oscillations caused by this pheonmena. The simulation model built in Matlab SIMULINK could be further op- timized, and many challenges were faced to obtain a functioning and stable control system. Due to this, the negative sequence current controller is only enabled in the wind turbine converter, and not in the HVDC link oshore converter. Still it should be able to dampen out the oscillations in the HVDC link. The results obtained from the simulations show that in general the negative sequence current controller does not improve the oscillations on the HVDC link DC voltage signicantly. When it is enabled, it performs worse than the standard controller during a three phase fault, which in theory should give equal results with the two control systems. This means that the problem is probably not the theory of the negative sequnce current controller, but rather the implementation of the controller in the modelled system. It is therefore recommended further work to obtain a more credible simulation model with better tuned controller parameters. This thesis has resulted in a Matlab SIMULINK model based on the NOWITECH reference turbine, and there are many possibilities for further research on the reference turbine, as well as general research on control of oshore wind farms during fault ride throughs and other transient conditions. A brief overview over challenges and pitfalls when building a large simulation model in Matlab SIMULINK is available in Appendix A, this is very much recommended for students undertaking their rst large project in Matlab SIMULINK.

Place, publisher, year, edition, pages
Institutt for elkraftteknikk , 2013. , 97 p.
URN: urn:nbn:no:ntnu:diva-22585Local ID: ntnudaim:9193OAI: diva2:649830
Available from: 2013-09-19 Created: 2013-09-19 Last updated: 2013-09-19Bibliographically approved

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