Design and analysis of a high step-up interleaved modified Y-source DC-DC converter for grid-connected PV inverters

In recent years, the total installed power capacity of renewable energy plants worldwide has been steadily increasing. Photovoltaic (PV) plants, in particular, have been rapidly rising within renewable energy technologies. The widespread adoption of this technology can be attributed to advancements in PV cells as well as significant developments in power electronics converters. Especially for residential applications, there has been a growing interest in micro-inverters due to their high-efficiency maximum power point tracking (MPPT) capability compared to other types of inverters. However, to transfer energy from a low-voltage PV module to the grid or a load, high step up DC-DC converters are required. Unlike conventional high step up DC-DC converters, impedance-source DC-DC converters can easily perform the necessary voltage step-up operation for the inverter input. Therefore, impedance-source converters are attracting increasing attention, especially for low-voltage PV systems. In this study, an interleaved modified Y-Source (i m-Y) DC-DC converter topology was developed for the first stage of a two-stage grid-connected PV inverter. After thoroughly detailing the design phases of this topology, its suitability for grid-connected residential PV applications was tested. Due to the interleaved structure in the proposed topology, lower voltage and current stress on the switching elements compared to other conventional high-voltage gain Y-source topologies allowed for the selection of lower-rated switching elements and smaller volume circuit components. Additionally, input current ripple and current stress on all circuit components were reduced. The proposed i m-Y source DC-DC converter was used in the voltage boosting stage of the H-bridge inverter. The dynamic performance of the proposed topology was tested under varying solar irradiance and ambient temperature conditions, and stable power production was demonstrated. The solar efficiency of the system was improved using the perturb and observe (P&O) MPPT algorithm. Outer loop DC link voltage control and internal loop proportional resonant current (PR) control were employed to achieve active power control on the grid. Moreover, a selective harmonic compensator (HC) was used to suppress harmonic components in the injected grid current. According to the obtained results, the proposed two-stage i m-Y source PV inverter achieved active power transfer to the grid with a total harmonic distortion (THD) below 5% even during sudden changes in environmental conditions. Consequently, the proposed two-stage i m-Y Source PV inverter can be a good option for PV micro-inverter applications where the low PV input voltage varies over a wide range.