High power medium voltage DC/DC converter technology for DC wind turbines

Offshore HVDC-connected wind farms promise reduced electrical losses, lower bill-of material cost and undiminished functionality with the condition the wind plant MV collection network becomes DC, rather than MVAC. One dearly missed building block that would enable the transition to a DC voltage collection, is the DC/DC converter for high power & high voltage (megawatss and kilovolts).The main objective of this thesis was investigation and development of a turbine DC/DC converter proof of concept. The selected topology is based on a single phase series resonant converter, operated with a new modulation scheme, which permits regulation of power from nominal level to zero, in presence of variable input and output DC voltage levels. The circuit was rearranged so that the LC tank is located on the rectifier side of thehigh-turns ration transformer combined with frequency control and phase shifted inverter modulation. The modulation scheme was entitled pulse removal technique and it keeps the transformer flux constant from nominal frequency down to DC, always in sub-resonant continuous or discontinuous conduction mode. A design guide line, suitable for a given range of specifications, in the megawatt (5 to 15 MW), kilovolt (_35 to _50 kV) and kilohertz (0.5 to 5.0 kHz) range is introduced, while medium voltage experimental setups are implemented for characterization of losses, control and voltage sharing.