Estratégia de controle com regulação da geração de energia e transição suave entre os modos de operação conectado e ilhado para sistemas de geração distribuída fotovoltaicos

Abstract

The world energy demand is expected to rise in the coming decades in a superior rate than the conventional energy sources availability. This forecast has driven the adoption of Renewable Energy Source Distributed Generation (RES-DG) systems in the power system. The trend is the organization of these RES-DG systems in the form of microgrids. The RES-DG based microgrids can serve local loads on an isolated system (islanded operation) or connected to the power grid (grid-connected operation). Ideally, these RES-DG systems should have the ability to transition smoothly between modes so that a continuous supply of power is achieved regardless of the grid state. This work proposes a local control strategy for a low-voltage RES-DG system capable of operating in islanded as well in grid-connected mode while achieving a smooth transfer between modes and beeing able to regulate the RES output power, foregoing the use of energy storage systems in islanded mode. The proposed control strategy is divided in three parts: (a) the VSI control, which constitutes the inner control loops of the Voltage Source Inverter (VSI) (current, voltage and power control loops), (b) operating mode management unit (DC link, voltage at the PCC and DG system angular frequency control loops) and (c) the synchronization islanding detection subsystem. The control strategy is validated through simulation of a three-phase RES-DG system. The proposed strategy presents a smooth transition between modes, with little perturbation on the PCC voltage, a fast synchronization process from islanded to grid-connected mode and mantains power balance inside the microgrid while operating in islanded mode. In addition, it also presents a fast DC link voltage control response time that is capable of maintaining the transitory small even for large power imbalances during mode transition.