Module-to-Panel Modular Differential Power Processing Converter With Isolated DC Bus for Photovoltaic Systems Under Partial Shading

The occurrence of partial shading is known to significantly reduce the energy yield of photovoltaic (PV) panels. Differential power processing (DPP) converters can prevent negative influences of partial shading at a substring level. For PV strings comprising numerous series-connected panels, however, conventional DPP converters face various issues, such as increased converter count, poor extendibility, and cumulative power conversion loss. This article proposes a modular DPP converter with an isolated dc bus for PV strings. The proposed DPP converter is the integration of panel- and module-level DPP converters. Four panels are grouped as a module having a DPP converter, and each DPP converter can handle four panels. PV systems can be scalable with no need to redesign the DPP converter as all modules are connected through the isolated dc bus. The isolated dc bus allows the direct power transfer from unshaded high-voltage modules to shaded low-voltage ones, reducing the cumulative power conversion loss. A field testing for a three-module PV string was performed using a prototype for a four-panel 1-kW module. The experimental results demonstrated 5.6% energy yield enhancement by the proposed DPP converter.