Modelagem e controle de um conversor SEPIC isolado com célula dobradora de tensão para aplicação em microinversores fotovoltaicos

Abstract

With the increase in the installation of photovoltaic systems connected to the grid, several types of research have been carried out to develop and improve the electronic circuits used in the processing of energy supplied by these systems. Among the different configurations, microinverters have received a lot of attention due to their many advantages. In these systems, a control strategy composed of a proportional-integral (PI) controller and a Maximum Power Point Tracking Method (MPPT) is commonly used. Thus, this work has as main objectives to develop the dynamic modeling, the control, and the implementation of a DC-DC converter with high voltage gain to be applied as the first stage of a photovoltaic microinverter. To achieve a high voltage gain, which is necessary for this kind of system, but with low values of duty cycle and transformer turns ratio, a Greinacher voltage multiplier cell is applied at transformer secondary side. Thus, to obtain the dynamic model of the converter the state-space averaging technique is applied, considering an equivalent circuit with the parameters of the secondary side reflected for the primary side of the transformer. In addition, for this case, the Perturb and Observe method (P&O) is adopted. To validate the DC analysis, the dynamic model, and also the design of the control system, experimental results are presented considering open-loop and closed-loop analysis for a 310 W prototype. Finally, the efficiency curve considering different irradiance levels is presented, so that the weighted average European and Californian efficiencies are estimated, which presented values, respectively, of 96.54 % and 96.99 %, which can be considered high values for a converter that uses only one switch.