Analysis of Decoupled d-q Vector Control in DFIG Back-to-Back PWM Converter

The doubly-fed induction generator (DFIG) is a ´special´ variable speed induction machine and is widely used as modern large wind turbine generators. 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 an AC/DC/AC PWM converter. The AC/DC/AC converter normally consists of a machine-side converter and a grid-side converter, both of which are controlled by decoupled d- q control approaches. In order to gain proper control of a DFIG and appropriate DFIG integration with the grid, it is important to understand the power control characteristics of the two AC/DC converters. This paper focuses on the analysis of traditional decoupled d-q vector control approaches for control of DFIG wind turbines. A typical d-q control concept that has been used widely in DFIG converter control is reviewed in the paper. Then, detailed study is performed to investigate the power control characteristics of DFIG converter using decoupled d-q control approaches. Deficiencies of conventional d-q control mechanisms are discovered and analyzed both analytically and through computer simulation. An extensive simulation study is performed to examine the power control characteristics of DFIG PWM converter under different d-q control conditions.