DC-DC converter for high granularity, sub-string MPPT in photovoltaic applications using a virtual-parallel connection

This paper focuses on fine-grained, sub-string MPPT in photovoltaic applications. An accurate energy forecasting analysis using 3D modeling of an urban PV installation site is used to show that performing MPPT at the sub-string level inside the panel can result in a substantial increase in the yearly energy yield. The virtual-parallel concept is used to exploit the robustness of parallel-connected PV modules to irradiance mismatches, while maintaining the wiring advantages of the physical series configuration. A power-efficient 300 kHz dc-dc converter prototype with three asymmetrical phases is implemented to demonstrate the benefits of DMPPT with substring voltage equalization within the panel. A variable interleaving scheme is used to reduce the output voltage ripple during shading conditions, which increases the output capacitor lifetime and improves the system reliability. The prototype is measured with a single PV panel under a variety of shading test cases to confirm the power benefit of the two auxiliary phases, which reaches up to 30%.