Three-level inverter based on direct power control connecting offshore wind farm

VSC-HVDC system based on voltage source converter connecting large-scale offshore wind farm is illustrated in the paper. To improve the transmission capacity and solve power quality problem, multilevel inverter is used in VSC-HVDC system. The simulation system is built on the basis of power control algorithm, implementing the independent control on bilateral sides. On wind turbine side, three are wind generators with respective converter, adopting the power control method based on hysteresis comparison and the three-level converter on system side adopts multi-level direct power control, achieved by three hysteresis control devices for active power, reactive power and midpoint voltage. The results on the simulation prove that under large transmission capacity, VSC-HVDC system connecting large-scale offshore wind farm and power system can operate under a normal and stable situation. Owing to the three-level inverter on system side, the power quality is better such as low harmonics and high power factor.