Multiterminal HVDC-VSC for offshore wind power integration

The different operation modes of multiterminal HVDC-VSC systems for large offshore wind farms are analyzed. Control schemes for each power converter are proposed. The wind farm VSCs inject the power to the HVDC grid and are controlled as ideal voltage sources that absorb all the incoming power in normal operation, and reduce the injected power whenever a fault occurs and the DC voltage rises. The grid-side VSC inject the power to the main grid and control the DC voltage using a droop control scheme. The proposed controllers are tested in a case study by means of dynamic simulations with a four terminal system. The results show good performance for changing wind speeds, a voltage sag and a loss of a converter.