Integration Aspects of Full Converter Wind Turbines and the Impact on Long-term Voltage Stability

This paper examines how various integration aspects of full converter wind turbines, such as grid code design, control aspects, and placement of turbines, impact the long-term voltage stability of a power system. The simulations are conducted on a modified version of the Nordic32 test system. Different cases have been analyzed and show, for example, that if over-dimensioning of converters is implemented, it is mainly the converters’ currentcapacity that should be increased since the voltage limitation of converters seldom is reached during voltage instability events. Furthermore, a restrictive reactive control scheme is tested, with the aim of minimizing the wear and maintenance of converter components. Although found to generally reduce the voltage stability, the proposed control scheme could be adopted during specific conditions where the local need of voltage support is low. The placement of larger wind farms was found to have the largest impact, both on long-term voltage stability of the system itself, and on the effect that the analyzed design and control aspects had on the system stability. Consequently, the placement of WFs is found be an important factor to consider when designing ancillary services and grid codes for wind power