Transient and Steady-State Simulation Study of Decoupled d-q Vector Control in PWM Converter of Variable Speed Wind Turbines

Variable-speed wind turbines are attractive to the high performance and are commonly used by the wind turbine industry today. They are based on variable-speed operation with pitch control using either a direct driven synchronous generator (without gearbox) or a doubly-fed induction generator. For both, there is an AC/DC/AC PWM converter that is used for wind turbine control and grid interface. The AC/DC/AC converter usually consists of a machine-side converter and a grid-side converter. In order for effective control and integration of variable-speed wind turbines with the electrical grid, it is important to understand the power control characteristics of the two PWM converters. This paper focuses on the analysis of decoupled d-q vector control approaches applied to the grid-side converter control in variable-speed wind turbines and studies the power control characteristics of the PWM converters through both steady-state and transient simulation techniques. A typical decoupled d-q control concept that has been widely used in the grid-side converter control is reviewed in the paper. Deficiencies of conventional d-q control mechanisms are discovered and analyzed both analytically and through computer simulation. An extensive simulation-based study, in both steady-state and transient, is performed to examine the characteristics of the grid- side converter under different d-q control conditions in variable- speed wind turbines.