Modeling and impact of gear train backlash on performance of DFIG wind turbine system

In this paper, the performance of a grid connected doubly fed induction generator based wind turbine (DFIG-WT) system is examined, in the presence of backlash in its gear-train. A detailed model of the backlash in its gear-train which couples the wind turbine to the DFIG, has been derived based on a two-mass drive-train model. The DFIG is equipped with the control for maximum power point tracking, terminal voltage, DC-link voltage and rotor reactive power minimization. In order to investigate the system dynamics, the modes of oscillations of the system with backlash have been characterized using a small-signal stability model. It has been found that the backlash has a pronounced impact on the system behaviour when subjected to a large wind disturbance, a fact that may have been overlooked in conventional controller design philosophies. It has also been observed that an electrical disturbance such as a voltage-sag at the point-of-common-coupling during varying winds may further deteriorate the available damping of the electro-mechanical oscillations, due to the backlash. The overall system performance has been investigated with the time-varying wind modelled by the Van der Hoven's spectral model with added turbulence using Kaimal spectrum.