Offshore Wind Park Connection to an HVDC Platform, without using an AC Collector Platform

Sammanfattning: This thesis investigates the comparison between two different alternating current topologies of an offshore wind farms connection to an offshore high voltage direct current (HVDC) converter platform. The offshore high voltage direct current converter platform converts alternating current into direct current. Two different topologies will be investigated. In the first topology, the offshore wind farms are connected to an HVDC converter platform through offshore AC collector platform. An offshore AC collector platform is used to collect energy from the wind farm and step up the voltages for transmission to HVDC convertor platform. The offshore AC collector platforms contribute significantly in the total cost and technical complexity of the HVDC connection. In the second topology, the offshore AC collector platform is removed from the circuit and the offshore wind farms are connected directly to offshore HVDC converter platform. In this thesis, short circuit analysis and loss analysis of an offshore wind farm cluster connected to an offshore HVDC converter platform is conducted for the two topologies described above. Two wind turbine generator types i.e. doubly fed induction generator and full conversion generator is compared for two different topologies. The effect of changing the distance between wind farms and offshore HVDC converter platform on short circuit currents in the absence of AC collector platform is presented for the second configuration. Two internal voltage levels i.e. 33 kV and 66kV of wind farms are compared for short circuit currents in the absence of AC collector platform. DIgSILENT software is used to perform short circuit calculations. The thesis is done in collaboration with “Offshore Wind Connections” department ABB, Sweden. The idea is still under development however this study will serve as good starting point to figure out the cost efficient AC topology of an offshore wind park HVDC connection.