This paper appears in: Power Systems, IEEE Transactions on
Issue Date: May 2010
Volume: 25 Issue:2
On page(s): 894 - 905
This paper details a modeling procedure that incorporates composite loads in stand-alone microgrids in which, because of the low system inertia provided by inverter-interfaced generation units, the grid dynamics is not neglected. The paper introduces a methodology based on 1) separately treating the plants (RL grid elements) from reference frames and control systems; and 2) establishing a vector valued function to methodologically describe all plants in a similar way. Induction motors equations are rearranged to be integrated within the model, giving as a result a highly structured, compact system model. Next, bifurcation theory is adapted to the problem to show that composite loads are a need in the microgrid modeling if more realistic results about oscillations and mainly about load margin are pursued. Thanks to the modeling procedure, this is proven by means of a series of analyses conducted in a microgrid of considerable larger dimensions than those presented to date in the literature.