Control of doubly fed induction generator in standalone wind energy conversion system

This paper presents control of a doubly fed induction generator (DFIG) in a standalone wind energy conversion system (SWECS) to feed three-phase four-wire consumer loads. The voltage and frequency controller (VFC) is implemented using two voltage source converters (VSC´s) for a DFIG based SWECS. Two VSCs share common DC link and it is supported with battery energy storage system (BESS). The rotor-side converter (RSC) is controlled in field oriented mode to keep the stator terminal voltage, its frequency is regulated and to achieve maximum power point tracking (MPPT). The speed of a DFIG is estimated for sensor-less control. The stator-side converter (SSC) controls the stator currents to minimize stator winding losses. Furthermore, it also ensures load leveling, load balancing and harmonics elimination. In-between SSC and point of common coupling (PCC) a star-delta transformer is used to compensate neutral current and to facilitate suitable choice on DC-link BESS voltage. The proposed VFC for a SWECS is extensively investigated under varying speeds and loads.