Increasing Energy Capture From Partially Shaded PV String Using Differential Power Processing

In photovoltaic (PV) strings based on series-connected PV modules, mismatches among the modules due to partial shading will cause power loss either due to series connection constraint or bypass diodes. This paper proposes a new distributed maximum power point tracking (DMPPT) scheme using multiwinding forward-based converter, which acts as a current balancing differential power processing converter. The converter is configured in the way that each converter port is connected in parallel with individual PV module to enable module-level maximum power extraction. The proposed architecture operates in two modes: local maximum power point tracking (MPPT) mode and current balancing mode. The new maximum power points (MPPs) at module levels are tracked in a local MPPT mode and then dispatched to start current balancing mode of operation. In the current balancing mode, this paper proposes a simple control approach to maximize the output power from partially shaded PV string by maintaining an effective MPPT at module levels and directly transferring the compensation currents toward the shaded modules from modules under normal conditions without any intermediary. The proposed DMPPT scheme is validated by the simulation and experimental results. The results show that using the proposed scheme, the system efficiency is significantly improved compared to other existing topologies.