Origin of Cross-Coupling Effects in Distributed DC-DC Converters in Photovoltaic Applications

Long strings of photovoltaic (PV) modules are found to be vulnerable to shading effects, causing significant reduction in the system power output. To overcome this, distributed maximum power point-tracking (DMPPT) schemes have been proposed, in which individual dc-dc converters are connected to each PV module to enable module-wise maximum power extraction. There are two main concepts to implement DMMPT systems: series and parallel configuration, describing the connection of the output terminals of the converters. Both systems are studied intensively, with innovative solutions to encountered operational challenges and novel control methods. However, a comprehensive dynamic model for neither system has been presented so far. This paper fills the gap by presenting small-signal models for both configurations, explaining the observed operational peculiarities. The analytical claims are verified with a practical system comprising two maximum power point-tracking buck-boost converters.