Multilevel DC-link converter-based photovoltaic system with integrated energy storage

This paper presents a multilevel topology of photovoltaic (PV) system with integrated energy storage system (ESS). In this proposed topology, half of the cells are connected to PV panels, the rest are connected to batteries. The sum of the cells are connected in series to form a dc-link, which is then connected to an H-bridge to convert the dc voltage to an ac one. The advantage of the proposed topology compared to the modular multilevel converter (MMC) as well as compared to the cascaded H-bridge converter is that less active switches are needed here. More switches are saved as the level of the output voltage increases, which results to a cheaper and less sizable converter. A local maximum power point tracking (MPPT) algorithm is proposed for this converter, which requires the voltage and current of each sub-module. Hence, there are no losses related to partial shading effect here. The excess of power in case of high irradiation levels is stored in the batteries, and is recovered when needed. A detailed simulation program has been built to test the effectiveness of the proposed converter; the obtained results are shown in the paper.