Control system of a single-phase grid-connected cascaded H-bridge inverter based on energy regulation of DC-link capacitors

Photovoltaic (PV) systems are frontrunners in ever-growing renewable energy industry due to their clean nature and reliability. In this paper, a control method for a seven level photovoltaic cascaded H-bridge (CHB) is analyzed. Multilevel inverters offer the benefit of improved power quality and lower switching frequency while the nature of CHB makes it a very interesting prospect in PV applications. Independent control of each dc link voltage by means of a conventional MPPT algorithm enables the maximum power extraction from each PV module. The proposed control system regulates the voltage of dc link capacitors to their reference value by controlling the energy stored in them and energy extracted from PV modules. It also considers the effect of power circulating through the inverter to improve the inverter's performance, especially under unbalanced conditions. Behavior of the inverter is analyzed in different testing conditions through simulation.