Vector control of doubly-fed induction machine for stand-alone variable speed energy system

This paper describes the terminal voltage control of doubly-fed induction generator (DFIG), used for a variable speed energy conversion system. The system focuses on DFIG, feeding without any auxiliary source an isolated load, by means of three back-to-back converters connected between the machine and the load. This configuration ensures the power extract over wide range speed and offers the possibility of full control on both the sides (stator and rotor) of the machine to an equal extent. A stator flux-oriented vector control strategy is proposed to keep the terminal voltage constant irrespective of the rotational speed and the loading conditions. The DC bus capacitor is charged by a small initial voltage produced by the remanent magnetism of the machine core, provides a necessary reactive energy for self-excitation of the generator. The proposed configuration is modeled and simulated using MATLAB/Simulink and the dynamic simulation results for different transient conditions demonstrate the effectiveness of the proposed control strategy on both the sides.