Stability Enhancement of Doubly Fed Induction Generator with Virtual Resistance for Grid Disturbances

Abstract

In a doubly fed induction generator the rotor is connected to the grid through the AC/DC/AC rotor converters. When a fault occurs in the grid, abnormal currents will be circulating in the rotor and rotor side converters. In olden days the grid stability maintained by crowbars but this method has few considerable limitations.In this paper virtual resistance is proposed to protect the rotor side converters increases the stability of the system. In keeping the requirements of the reactive power in wind farms, crowbars are not preferable they absorb the reactive power from grid whereas by virtual resistance system supplies the reactive power to the grid. In order to regulate the virtual resistance PI method and Fuzzy logic controller method are developed, outputs are compared. By using virtual resistance system stability is enhanced as the rotor demagnetizing currents are developed to cut off the dc and negative flux of the stator. The concept of virtual resistance for stabilizing the system during grid faults is opted by using a fuzzy logic controller the total harmonic distortion is reduced which are observed in the output waveform compared to PI controller.