Dual Converter Connecting Open-End Doubly Fed Induction Generator to a DC-Microgrid

This article presents a novel system to connect a three-phase doubly fed induction generator (DFIG) to a dc-microgrid. The proposed system uses a three-leg rectifier at each side of the stator windings, in an open-end winding configuration. Usually, these legs are composed of insulated gate bipolar transistors (IGBTs). To reduce the number of controlled switches and costs, one of the rectifiers has its IGBT switches replaced by diodes. The converters operating principles, pulsewidth modulation, power control, and zero-sequence current minimization strategies are discussed. The proposed system is compared with two conventional systems in terms of current harmonic distortion, torque ripple, and semiconductor losses. Simulations and experiments were also performed, showing steady-state and transient results for a 0.56-kW DFIG operating at constant torque. Finally, it was verified that the proposed system maintains balanced voltages and currents over the DFIG stator windings, with no significant torque oscillations.