Resumo:
The growing concern related to the depletion of fossil fuels, the environmental effects of greenhouse gas emissions, and the low efficiency in transmitting large blocks of energy over long distances gave support to a new concept of energy systems, the microgrids. Thus, among the studies needed for these new systems, the voltage stability is cited. Therefore, this thesis proposes the analysis of static voltage stability in microgrids (islanded or isolated mode) and in transmission systems (considering the transmission-microgrid coupling) using the classical energy function method. The energy function allows the direct stability evaluation of the system operating points, taking into account the variation of loads, the intermittence of the photovoltaic sources and the charging/discharging of energy storage systems under pre-defined conditions. In addition, the auxiliary energy function is used to rank less robust buses in the microgrids and transmission systems. For microgrids, the auxiliary energy function indicates which buses are candidates for the insertion of intermittent sources. As for transmission systems, the auxiliary energy function indicates which microgrids connected to the main system are candidates for load shedding. Finally, considering the microgrid operation in islanded mode, it is evaluated which configuration is the most appropriate to supply critical loads within quality standards in the longest possible time. The results show the effectiveness of the voltage stability assessment using the energy function and the improvement of the energy-based voltage security index when using the auxiliary function technique to allocate intermittent sources and load shedding. The proposed methodologies are validated in a modified IEEE 37 node test feeder and IEEE 30 bus.
