Grid-Connected Induction Generators Using Delta-Star Switching of the Stator Winding with a Permanently Connected Capacitor

Abstract

The delta-star switching proposed earlier for grid-connected induction generators has been modified to include a permanently connected capacitor across each phase winding of the stator of the generator. It has been shown that, with this capacitor addition, operating the generator in delta and star connections respectively at higher and lower wind speeds further reduces the reactive power taken by the generator from the grid. Moreover, such switchings do not cause any current harmonics in the supply lines. Test results on a 3-phase, 4-pole, 415 V, 50 Hz, 3.3 kW generator validate such advantages of the proposed scheme, apart from the simplicity of the switching controller involving only five sets of anti-parallel thyristors. The method of choosing a suitable value for the capacitor has also been illustrated. The superiority of proposed scheme, compared to the other single speed schemes of wind driven induction generators, has also been demonstrated through a case study carried out on a 400 V, 250 kW generator, using a typical annual wind data. Any further improvement in grid side power factor can be achieved by employing a STATCOM of reduced VAR rating.