Bifurcation study of wind energy generation systems

Wind energy generation systems are major components of distributed generation units or micro-grids. Application of the doubly fed induction generator (DFIG) in wind energy generation systems allows variable speed operation by using partially rated back-to-back quadruple active and reactive power PWM converters. The control of the system is very complex. Many new control schemes reported in the literature are designed to solve some specific control problems and have not thoroughly been tested for general stability with local loading which is common in micro-grids. In this paper, the oscillation boundaries of the system in the presence of an unbalanced three-phase reactive load are studied. Specifically, we report the system stability in terms of the amplitude modulated oscillatory magnitude of the three-phase voltage and current of the generator under a local reactive three phase load. The oscillation can also be observed as a linear modulated oscillation of the voltage link capacitor inside the wind energy generator. Oscillation boundaries of the system are collected using various damping component values of the three phase load, illustrating the potential instability problems that may be caused by imbalanced reactive loads.