Avaliação da impedância virtual no problema do compartilhamento de potência em microrredes

Abstract

Reactive power sharing is a common problem in a microgrid (MG), which may result in undesired events such as overloading of converters and feeders, higher thermal losses, voltage sags and consequent deterioration of the MG stability. One of the most consolidated control techniques in the literature to correct this problem has been the virtual impedance, which simulates the insertion of an impedance between the converter and the feeder, manipulating the reference voltage of the converter control. However, in addition to the difficulty of adjusting the impedance values to be inserted, whose depend on the size and topology of the MG, the implementation of fixed virtual impedance values does not take into account the dynamics of the MG loads, which can make worse the power sharing issue depending on the load scenario or MG topology reconfiguration. In this context, this work studied real-time virtual impedance adjustment techniques to correct the reactive power-sharing issue in MGs, and classified them according to their communication scheme. Three of these techniques were selected and implemented in two MGs with generation based on power electronic converters, one with a central bus topology and another with a distributed buses topology, and the performances of the techniques were compared. Also, it was proposed a combined operation of a centralized technique as the main technique and a decentralized one as backup of the first one in case of communication failure and its operation was evaluated in a radial topology MG. The simulations showed that, although centralized techniques perform better than decentralized ones, due to the reliability problem of techniques that use communication, the best result can be achieved with a combination of techniques.