A New Synchronization Method of Double Fed Induction Generator Wind Turbines to the Grid

Meeting grid code requirement creates an obligation to smart WTs disconnection following some electrical or mechanical events. Increasing the penetration level of wind turbines (WTs) in different voltage levels of the network have a major effect on this condition. In this regard, soft and rapid synchronization control of doubly fed induction generator (DFIG) to reduce the dynamic and transient effects of DFIG on a smart grid is very important. This paper gives a review on WTs power generation and a basic requirement to operate in a stable manner in connection to the network at first. After that, different startup and synchronization methods will be described. Then, a new synchronization method for grid connection of DFIG driven by WT is proposed. In this method, the rotor side converter is synchronized with the induced voltage at the rotor winding of DFIG while the stator windings have been connected to the grid and the rotor accelerates normally with the wind torque. This startup process is soft and the synchronization is carried out between two low voltages with very low frequency and may overcome some difficulties and limitations of previous methods since it uses the rotor side converter as power electronics switches instead of the mechanical circuit breaker at stator side and causes the synchronization to be more accurate and controllable. The proposed method is evaluated with EMTDC/PSCAD simulation to show the performance of soft starting synchronization with lower electrical transients in comparison with traditional methods.