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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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A control strategy has been proposed for minimising the machine loss by optimally sharing the reactive power at the stator and rotor terminals of stand-alone doubly fed induction generator. For achieving this, fixed capacitor along with static synchronous compensator at the stator terminals has been employed apart from battery inverter system at the rotor terminals. A TMS320LF2407A digital signal processor-based controller has been developed for maintaining the stator voltage magnitude and frequency. A method has been developed for calculating the optimal reactive power at the stator terminals using the steady-state equivalent circuit of the proposed system. An analogue circuit-based optimal reactive power controller has been designed and fabricated in the laboratory for supplying this optimal reactive power at the stator terminals for all operating conditions. The salient feature of the proposed optimal reactive power controller is that it needs to monitor only the reference value of reactive power at the stator terminals for any operating conditions. The successful working of the proposed controller has been amply demonstrated through extensive analytical and experimental results obtained on a three-phase, four-pole, 415 V, 50 Hz, 5 kVA doubly fed induction generator.

In this paper, state space model of the complete Wind Energy Electric Conversion System (WEECS) comprising of wind turbine, Permanent Magnet Synchronous Generator (PMSG), uncontrolled rectifier, DC-DC boost converter, and SPWM inverter feeding a standalone load has been formulated. The derived state space model is then simulated using Matlab/Simulink to test the model. As the standalone three phase load connected to the inverter demands constant output voltage irrespective of intermittent wind pattern, a PI controller is used to control the duty ratio of DC-DC boost converter to maintain constant output voltage at the inverter end.