Enhanced Control of DFIG Based Wind Energy Conversion System Under Unbalanced Grid Voltages Using Mixed Generalized Integrator

The operation of a wind energy conversion system based on a doubly fed induction generator (DFIG) is found to be extremely sensitive to unbalanced grid voltages. In this context, this article presents an enhanced control strategy for a DFIG operating under unbalanced grid voltages, using a mixed generalized integrator (MGI). The MGI is a hybrid form of the second and third-order generalized integrators and is employed for positive and negative sequence calculation. The MGI-based enhanced control strategy utilizes the hysteresis band control of rotor currents and grid currents, to generate switching sequences for rotor side converter and grid side converter, respectively. In addition to superior dynamic tracking of reference currents, this scheme eliminates the need for implementation and careful tuning of eight distinct proportional-integral inner current regulators, as is the case with conventional control strategy for the DFIG operating at unbalanced grid voltages. Furthermore, MGI improves the grid synchronization in DFIG system amidst the presence of dc offset and unbalance in the supply voltages. The overall coordinated control strategy is designed to realize seven separate control objectives, and its effectiveness is verified through simulation and experimental results.