Low voltage ride-through and performance improvement of a grid connected DFIG system
In this paper, analytical study on the impact of voltage sag in the internal dynamics of a grid connected Doubly Fed Induction Generator (DFIG) system is presented. A common dc-link of the rotor side converter (RSC) and grid side converter (GSC) supported static compensator (STATCOM) is proposed for the voltage ride through capability. The proposed system is connected to a small transmission network, where many types' loads are connected. It is observed that the voltage sag at the PCC of the grid affects the internal dynamics of DFIG such as flux demagnetization of the stator flux, high transients in the developed electromagnetic torque, and abnormal rotor current spikes. This affects the performance of the DFIG during transient conditions and this may leads to the malfunctioning of the power electronics converters. This topology will also support the reactive power requirement of the grid without affecting the performance of the dc-link voltage. Hence, this structure is useful in improving the transient stability, power oscillation damping, voltage stability and increase in power transfer limit of the connected power system. The proposed DFIG system along with its controller is modeled and simulated in MATLAB using Simulink and power system block-set toolboxes. The simulation results are presented to validate the performance of the proposed system.