Design and control of an offshore wind farm connected to main grid with high voltage direct current transmission

One of the fastest growing renewable energy sources in the present day technology is the wind energy that has many benefits such as being clean and sustainable. Offshore wind locations are the best option for wind energy production due to the fact that onshore locations are already occupied or planned as new wind farm locations. Also, higher wind speed up to twenty percent are available on sea than on land locations, as a result, more power can be extracted in offshore locations. Furthermore, the absence of obstacles such as hills and smooth surface of the sea makes offshore wind energy more reliable than onshore. Offshore wind farms inherently need AC grid connection with undersea cables. However, this requires high reactive power compensation equipment that is not practical and difficult for stable operation. For this reason, high voltage direct current (HVDC) transmission is a promising solution because no reactive power is needed. Moreover, the DC power flow between offshore and onshore locations can easily be controlled by means of voltage source converters. In this thesis an offshore wind farm connected to onshore main grid through undersea cables were designed and the power transfer was in the form of HVDC. The overall system including wind farm, offshore and onshore converters, HVDC transmission and main grid side were designed and tested in simulation program. The designed control systems of the HVDC converters were tested by various case studies.