Steady-state analysis of a self-excited induction generator including transformer saturation

Due to speed fluctuations of unregulated wind-turbines, the terminal voltage may increase to dangerously high levels which have been reported to cause capacitor failure at windfarms. This paper examines the steady-state analysis and performance characteristics of a stand-alone self-excited induction generator (SEIG) when a transformer is connected to its terminals to supply the load at a different voltage level or to step-up the terminal voltage for transmission. The transformer tends to saturate at higher speeds, and thus absorbs the excess reactive power and limits the increase in terminal voltage and improves voltage regulation. Transformer saturation introduces an additional nonlinearity which complicates the analysis considerably. A technique for formulating and solving the system's equations including transformer saturation is presented. The same technique is also applicable when the load itself is nonlinear. Experimental investigation has confirmed the accuracy of the proposed technique.