Hybrid-excited system has been formulated for the operation of wind-driven Doubly-Fed Induction Generators (DFIGs) for stand-alone power supplies. Here, apart from the rotor side excitation of DFIG employing SPWM inverter supplied through set of batteries, the generator is partially excited by fixed capacitor at the stator terminals. The steady-state equivalent circuit and its analysis for the proposed system have been devised and presented. The selection of stator capacitor has clearly been brought out. An attempt is also made for sizing of various components such as inverter and battery for the given machine rating and other operating conditions. Phasor diagram representation of the proposed system for typical operating conditions is also furnished. The stator voltage magnitude and frequency are maintained constant by closed loop control developed using TMS320LF2407A Digital Signal Processor (DSP) controller. Efficacy of the proposed hybrid-excited stand-alone DFIG system has been demonstrated under steady-state and dynamic operating conditions with experimental results obtained on a 3-phase, 4-pole, 415 V, 50 Hz, 5 kVA generator in the laboratory.
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