Power generation characteristic study of integrated DFIG and its frequency converter

The doubly-fed induction generator (DFIG) is a ´special´ variable speed induction machine widely used in modern large wind turbines. It is a standard, wound rotor induction machine with its stator windings directly connected to the grid and its rotor windings connected to the grid through a back-to- back PWM converter. The DFIG power generation consists of power delivered from two paths, one from the stator to the grid and the other from the rotor, through its frequency converter, to the grid. The DFIG power production characteristics, therefore, depend not only on the induction machine but also on the two back-to-back AC/DC converters as well as how they are controlled. This paper studies power generation characteristics of a DFIG system through computer simulation. Steady-state models in dq reference frame are developed for both the DFIG and its frequency converter. A simulation system is built by integrating the models of the two parts together with effective consideration of d-q control strategies applied to both rotor- and grid-side converters. An extensive analysis is conducted to examine power generation characteristics of the integrated DFIG and its frequency converter under different d-q control conditions.