Contribuição ao melhoramento da operação durante afundamentos de tensão de geradores de indução duplamente alimentados baseados em conversores modulares multinível

Abstract

One of the main features of the Doubly Fed Induction Generator (DFIG) based Wind Energy Conversion Systems (WECS) is its high sensitivity to electrical disturbances, especially voltage sags since the stator is directly connected to the grid. This feature highlights a fundamental challenge which is to provide fault support. Given this problem’s relevance, this thesis proposes improving DFIG supportability to a voltage sag in the grid through a recent multilevel converter topology, the Modular Multilevel Converter (MMC). The inherent MMC arm impedance and the number of levels to provide significant damping of DFIG transient rotor and stator fault currents under severe grid faults is proposed in this thesis, effectively contributing to maintaining the DFIG connection keeping the control and avoiding the protection activation. Neither additional hardware nor control loops are necessary. Results obtained through simulations under symmetrical and asymmetrical fault scenarios considering 20, 50, and 80% voltage sags demonstrate the effective MMC fault current limiting function with 3, 21, 51, and 101 levels to damping both DFIG’s stator and rotor fault currents, which provides DFIG low voltage ride through enhancement under several grid fault scenarios.