Fundamental study on voltage stability of induction generators for wind power generation — Voltage-power curves for various types of generators

Large-scale integration of wind power generation causes various concerns for its impacts on an electricity grid. One of the concerns is voltage stability of a power system because most wind power generators use an induction generator and the generator does not basically have a voltage supporting ability. Meanwhile, one of the authors has observed a phenomenon that limited variable speed machines kept a stable operation after a system disturbance with voltage level lower than that in a normal condition. However, operation of an induction generator in a low voltage solution is generally considered to be unstable. This paper analyzes voltage stability of wind power generations using the voltage-power curves (nose curves). Sensitivity studies are conducted for line impedance of fixed speed machine, for external resistance of a limited variable speed machine and for power factor of a variable speed machine. The results suggest the possibility for stable operation of a limited variable speed machine at a low voltage solution by controlling its external resistance.