An encoder-free grid synchronization method for a Doubly-fed Induction Generator

In order to transfer energy generated through the stator winding of a doubly-fed induction generator (DFIG) to an electric power grid, we first need to synchronize the generated voltage vector with the grid voltage vector. However, the existing synchronization methods work only when the encoder is installed at a specific position and the system parameters are correct. In order to solve these problems, a new synchronization method has been proposed and a way of applying the method to the existing doubly-fed induction generator control algorithm has been suggested also. The validity of the proposed methods were verified by using a prototype converter for a MW-class doubly-fed induction generator and experimental results showed robust synchronization characteristics against variation of encoder positions, generator parameters, and grid voltages.