Conversor modular multiníveis para usinas solares fotovoltaicas: projeto da célula de potência c.c./c.a. baseada no transformador eletrônico

Abstract

This work presents the design of a DC/AC single-phase converter with high-frequency isolation, based on Solid-State Transformers. This converter constitutes the power-cell of a three-phase DC/AC Modular Multilevel Converter for large-scale photovoltaic solar powerplants,which was proposed in a previous work on the same research project. Initially the power cell is characterized in its topology and functions. Then the design of a downscaled prototype of the power-cell is displayed. Some goals for the converter prototyping are: to demonstrate the size reduction of the required transformer over conventional low-frequencytransformer found in power-plants, by means of performing the galvanic isolation at highfrequency using silicon carbide devices; to layout a power-cell with small volume and a modular form-factor in order to enable the demonstration of the concept of increased availability. Therefore, much effort was made aiming to obtain a reduced volume for the converter. Throughout the project, it was sought to minimize the parasitic inductances of the connections between the semiconductor devices and the DC-link, due to high-frequency nature of this power application. Analysis of Dual Active Bridge employed in the AC linkresulted in the definition of the operating point for displacement power factor and a very high true power factor in the transformer, which allowed a further reduction in high-frequency transformer, due to lower thermal stress and minimization of the coupling inductance.