Desenvolvimento de sistemas fotovoltaicos multifuncionais de único e duplo estágios conectados à rede elétrica trifásica

Abstract

This paper presents the study and practical implementation involving the comparison between two photovoltaic (PV) systems. The first has a single and the second has a double power conversion stages, in which both of them are connected to a three-phase four-wire utility system. The single-stage PV system is composed of a four-leg inverter (4L), while the double-stage PV system contains a DC-DC boost converter placed between the PV array and the 4L inverter. The 4L inverter is connected to the grid by means of coupling filters. Three different coupling filters are employed in this work, such as the L, LC and LCL, so that a comparative analysis between them are performed. The modeling of the 4L inverter is performed into the two-phase stationary reference frame (αβ0-axes), in order to avoid the current coupling between the phases. From the obtained models, it is possible to obtain the gains of the controllers. Furthermore, in order to inject currents into the grid with low harmonic distortion, to meet national and international standards, control techniques, which are implemented through tuned controllers, are employed. Both PV systems, besides the active energy injection into the grid, can also operate as shunt active power filter performing active power line conditioning by means of harmonic currents suppression and reactive compensation of the loads. In both PV systems, feed-forward control loops (FFCLs) are used to improve the dynamic responses of the DC-bus voltages, as well as the inverter currents injected into the grid, when abrupt solar irradiation changes occur. Besides the performance analysis involving the three types of coupling filters and the FFCLs, a comparative analysis between the two PV system topologies is carried out, taking into account the efficiency.