Grid connection of doubly-fed induction generators in wind energy conversion system

This paper presents a new synchronization algorithm for grid connection of a doubly fed induction generator (DFIG) in wind generation system. A stator fluxoriented vector control is used for the variable speed DFIG operation. By controlling the generator excitation current the amplitude of the stator EMF is adjusted equal to the amplitude of the grid voltage. To set the generator frequency equal to the grid one, the turbine pitch angle controller accelerates the turbine/generator until it reaches the synchronous speed. A slight difference of stator and grid frequencies may cause the large phase difference between the two voltages. To compensate for this phase difference, a PLL algorithm is used. After the synchronization is achieved, the generator is connected to the grid and is controlled to extract the maximum power. The effectiveness of the proposed synchronization algorithm is verified by simulation results using PSCAD.