Excitation sharing between the grid and the rotor excitation source of a doubly-fed induction generator in the presence of distribution system transients

Doubly-fed induction generator is an effective solution when there are distributed energy resources of variable availability. These generators have their excitation provided through the rotor as well as the stator. The objective of the present work is to investigate the way in which the transient or permanent excitation is distributed. It was experimentally studied by using wound rotor induction machines propelled by an AC machine with adjustable speed drive control. The behavior was studied when one of three perturbations takes place: terminals near a short circuit, electric load abrupt variation, and sudden change in the mechanical power supplied to the machine shaft. Such perturbations break the balance existing between the machine emf and the grid voltage. The study was completed by modeling of the tested machines using MATLAB/SIMULINK software.