Determination of boundary values of excitation capacitance and minimum load impedance for Wind-driven SEIGs

A simple method involving only a quadratic equation has been developed for calculating the minimum and maximum values of excitation capacitance that will sustain self-excitation in an induction generator meant for isolated power supplies. This approach has also been further extended for the determination of maximum load of a given power factor that could be applied to the generator without losing self-excitation, while operating with a specified capacitance and rotor speed. Both ac loads directly connected across the generator and also dc loads supplied through controlled rectifiers have been considered. Details of the various control schemes, which could be adopted for the rectifier and the effect of varying the control angle in each case, are presented. Experimental results obtained on a 400V, 3-phase, 3.7 kW, induction machine run as a generator validates the derived expressions.