Modular Differential Power Processing Architecture Utilizing Isolated Bus to Virtually Unify Photovoltaic Panel Characteristics in Large-Scale Systems

The characteristic mismatch due to partial shading in photovoltaic (PV) strings comprising multiple panels triggers not only a significant reduction in energy yield but also a malfunction of maximum power point tracking. Differential power processing (DPP) converters have been proposed to prevent negative influences of characteristic mismatch. In large-scale systems, however, conventional DPP converters face various challenges, such as poor extendibility and increased cumulative power conversion loss. This paper proposes a modular DPP architecture with an isolated bus for large-scale systems. Several panels are grouped as a module, each having a DPP converter, and the system can be flexibly scaled up by adding modules without redesigning the DPP converter. Power from unshaded high-voltage modules is directly transferred to shaded low-voltage ones through the isolated bus, reducing the cumulative power conversion loss. A field testing using a prototype for a 1-kW module demonstrated the energy yield enhancement of 5.6% by the proposed DPP converter.