New converter topology to improve performance of photovoltaic power generation system under shading conditions

Abstract

Module integrated converters focus many research because they are considered as most promising solutions for grid connection of photovoltaic power generation systems. Most of the proposed approaches relied so far on the use of series string of DC-DC converter to create a high voltage string connected to DC-AC inverter. The boost converter is better in this application. However, under inhomogeneous irradiation, the power generated from each PV module and output DC voltage of each boost becomes unbalanced so that the output currents of each boost are balanced and equal to the string current. In this case the boost converter cannot always deliver all the power from a mixture of shaded panels and those delivering full power. In this paper, a non-dissipative string current diverter is proposed to overcome this problem. One important feature of the proposed circuit herein is the ability to effectively decouple each converter from the rest of the string, making this insensitive to changes in the string current. Hence it is possible to obtain the maximum power from the PV module and allow it to operate at the optimum efficiency. The simulation and experimental results verify that the proposed topology exhibits good performance anyway of inhomogeneous irradiation. On the other hand, the string current diverter circuit does not operate if irradiation is homogeneous. So, in this last condition, the topology efficiency is improved.