Microgrid dynamic response during the pre-planned and forced islanding processes involving DFIG and synchronous generators

In this article, some important issues associated to the dynamic response of a microgrid system are addressed. In particular, issues related to the pre-planned islanding mode of operation, load shedding, loss of one generator and the failure to shed an unforeseen connected load are studied. In this context, the dynamic behavior results of a Doubly-Fed Induction Generator (DFIG) and two other synchronous sources (a diesel and a small hydro-generator) within a microgrid, are presented. The overloading condition can occur due to causes ranging from poor load schedule, inadequate switching of circuits within the microgrid, illegal connection of load by some low voltage consumers, etc. In most of the simulated conditions the microgrid generators resumed their operation after clearing the disturbance. However, under some critical conditions, like in the case of a considerably large load connected, the microgrid was unable to return to the pre-fault condition and even failed while trying to gain stability for this new load condition. Because microgrid systems normally have low equivalent inertia, it was also observed that very little to practically no overload can be accepted by the generators. (C) 2014 Elsevier Ltd. All rights reserved.