Photovoltaic to Virtual Bus Series-Parallel Differential Power Processing for Photovoltaic Systems

Abstract

Photovoltaic (PV) systems are frequently subject to voltage and current mismatches caused by various factors, such as partial shading, differing panel tilt angles, dust accumulation, and cell degradation among PV elements. These mismatches can significantly reduce the overall efficiency of PV systems by preventing individual modules or strings from operating at their maximum power point (MPP). This article introduces a novel architecture termed PV to virtual bus series-parallel differential power processing, which effectively mitigates mismatches in both series-connected PV modules (i.e., current mismatches) and parallel-connected PV strings (i.e., voltage mismatches). The proposed architecture employs a combination of string-level converters (SLCs) and module-integrated converters (MICs) that process only a fraction of the total power. Notably, the architecture leverages virtual buses on the primary side of both SLCs and MICs, leading to reduced voltage rating requirements for SLCs and lower power rating demands for MICs. This design reduces the stress on individual components, making the system more cost-effective and reliable. The article provides a comprehensive analysis of the requirements for SLCs and MICs, along with a detailed explanation of how the proposed architecture ensures that PV modules consistently operate at their respective MPPs. In addition, it explains how the virtual bus voltage is balanced through mathematical power flow equations, ensuring stable and efficient operation. Finally, the architecture's effectiveness is validated through real-time simulation results with two PLECS real-time (RT) boxes, which demonstrate its capability to address mismatch issues and optimize the performance of PV systems.