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A simple system has been formulated for the operation of wind-driven stand-alone doubly fed induction generators (DFIGs) supplying isolated loads at stator terminals. The stator voltage magnitude and frequency are maintained constant by closed-loop control. The excitation of the rotor is established using a single inverter which is an sinusoidal pulse width modulation (SPWM) inverter supplied through set of batteries. This allows the proposed system to feed continuous power supply to the isolated load via charging/discharging of the batteries depending on excess/deficit power from the wind. The system operates in various modes depending upon the availability of wind and size of the load. All possible modes of operation have been identified and described in the present study. The magnitude and frequency control strategies proposed in this study have been implemented using TMS320LF2407A digital signal processor (DSP) controller and detailed procedure for such implementation is given. The proposed control strategy is free from machine parameter variation and so the co-ordinate transformations, rotor position detection, measurements of rotor currents are not required. Experimental results obtained on a three-phase DFIG together with the closed-loop controller confirm the usefulness of the proposed system and the validity of its analysis.
Date of Publication: March 2012