Stability studies of offshore wind farms

Wind energy is the most important type of renewable energy in Europe. The stability of system network operation with a large penetration of wind energy has become one of the most critical issues in the new structure of power systems with different types of generation. In this paper the HVDC and HVAC connection of the wind farm to grid is compared. The HVDC is more advantageous in maintaining the system stability. Nevertheless this study focuses on the HVAC connection of wind farms with regard to its lower costs and widely practical application. Based on the topology of the offshore wind farm Alpha Ventus, a simulation model is developed in software PSS/NETOMAC. Using this model the steady-state voltage and power factor at the wind farm connection point is analyzed and compared with the grid code requirement on reactive power exchange and voltage stability. The impact of the cable switching on voltage is investigated as well. The simulation results indicate that overvoltage will occur during cable switching if the cable is not sufficiently compensated, and the overvoltage will become more critical with as the operational voltage levels of the cable increases.