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This study presents a detailed investigation on self-excitation of a squirrel-cage induction generator (SCIG) used in a wind energy conversion system. Air-gap flux of the SCIG is gradually built up through controlled current injection from a voltage source converter (VSC), connected directly across its stator terminals. Dc voltage of the VSC is ramped from a small initial value, which is the rectified output of the small terminal voltage developed because of remanent magnetism. Increase in air-gap flux increases generator terminal voltage and output power which further increases the dc bus voltage. The field-oriented control method is appropriately applied both for control of voltage build-up as well as dynamic transients. The critical factors deciding this collaborative excitation are analysed and sufficient conditions are derived analytically. System modelling and analytical results are validated through numerical simulation and verified on a 2.2 kW laboratory prototype.
Date of Publication: September 2011