DC microgrid with bi-directional multistring solar inverter performing active power injection into the AC grid and DC bus voltage stabilization

This paper presents the preliminary results concerning the development of a multistring solar inverter system for dc microgrids. The proposed system is composed of two dc-dc converters as the dc input stage and an ac grid-tied bi-directional full-bridge inverter. Each input dc-dc converter operates with independent MPPT algorithms which are capable of extracting the maximum power even under shading and rapid fluctuations of solar irradiation. Regarding the ac grid-tied inverter, one can outline that it is responsible for the injection of the extra amount of dc power provided by the photovoltaic panels to the ac grid. Besides, in order to assure a tight dc bus voltage, it is also capable of extracting, from the ac grid, the amount of energy that is not provided by the photovoltaic panels due to the inherent characteristic of the solar energy. A digital signal processor (DSP 28335) performs the control of the entire system. In this paper, the authors present preliminary experimental results that demonstrate the MPPT performance even under shading conditions. In addition, simulation analysis demonstrate the bi-directional operating mode of the grid-tied inverter.