Controle droop: análise de inversores trifásicos em paralelo tanto no modo conectado à rede quanto no modo ilhado

Abstract

Distributed microgeneration and minigeneration have grown in recent years due to the increase in renewable energies, such as photovoltaic panels and wind turbines. However, it is essential to discuss control methods, as these sources are intermittent and require proper dispatch to avoid instantaneous generation overproduction. Thus, the use of intelligent interfaces, such as DC/AC converters, becomes necessary to connect generation to the grid. In addition, with the increasing demand for electrical energy, the parallel interconnection of inverters stands out to expand system capacity and control the injected power. In this context, droop control, combined with current and voltage control in the DQ axis, enables efficient sharing of active and reactive power among inverters. Furthermore, distributed generation can supply energy to remote areas or unstable grids, requiring proper control for the islanded mode. In this way, droop control ensures efficient performance, maintaining constant voltage and frequency in the load. Thus, the objective of this work is to develop and analyze droop control techniques in three-phase inverters operating in parallel in both grid-connected and islanded modes, focusing on the efficient sharing of active and reactive power in AC microgrids. To achieve this, a literature review was conducted based on articles and books. From these reviews, droop control techniques based on DQ-axis control were implemented, modeled, and designed. Additionally, two simulations were carried out in MATLAB/SIMULINK, the first with inverters operating in parallel in islanded mode and the second in grid-connected mode. The results showed that, in frequency-controlled mode, the inverters maintain constant load voltage and frequency. In the mode where the frequency is imposed by the grid, the inverters operate to control active and reactive power, sharing power among them proportionally to their nominal capacities. It is inferred, then, that droop control, combined with voltage and current loops, can not only control the dispatch of active and reactive power from alternative energy sources but also operate efficiently in AC microgrids without an electrical grid. All of this is achieved while maintaining power quality aspects, including voltage and current harmonics and frequency variation.