Interfacing constraints of distributed maximum power point tracking converters in photovoltaic applications

Long strings of photovoltaic (PV) modules have been observed to be prone 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 maximum power extraction out of the PV modules. The output terminals of these converters are connected either in series or in parallel, followed by a grid-connected inverter. The series concept has been under intensive study with novel topologies and control schemes, yet operational problems compromising its feasibility have been widely reported. The parallel concept does not contain similar operational limitations, but suffers mainly from higher voltage levels. This paper discusses the feasibility of the series and the parallel schemes and introduces fundamental constraints governing the operation of DMPPT converter systems. These constraints have not been truly recognized to be key issues in designing high-performance, high-efficiency photovoltaic systems.