Decoupled Direct Control of Natural and Power Variables of Doubly Fed Induction Generator for Extended Wind Speed Range Using Feedback Linearization

The electromagnetic torque, stator power, and the grid side converter power outputs of a doubly fed induction generator (DFIG) are differentiated to obtain a feedback linear relationship with the rotor voltage vectors serving as the control inputs. The derived model is such that can allow for a transition of DFIG to operate at low wind speed by shorting its stator terminal to one another. The torque and power quantities are the state variables of the system, which are insensitive to coordinate system orientation. Steady-state models are used to obtain optimal operating regimes with respect to minimal electrical losses. Decoupled torque control is developed by field orientation, while decoupled power control is derived from voltage orientation of the DFIG. Transients originating from transitioning into low wind speed operation are investigated. Robustness of each of the decoupled controllers against parameter variations is investigated by locating the poles of its closed-loop transfer function. The results for a 5-Hp machine are presented.