Experimental Study of the Behaviour of the Global MPP of Partially Shaded PV Strings

Abstract

Under uniform operating conditions, a photovoltaic (PV) array has only one maximum power point (MPP) and successful MPP tracking is simple to implement. However, under non-uniform operating conditions, such as partial shading, multiple MPPs can exist on the characteristic of the PV array and the global MPP can vary over a wide voltage range. When multiple MPPs exist, conventional MPP tracking algorithms can be trapped to operate at a local MPP instead of the global one, and consequently the energy yield of the array can be considerably reduced. It is essential to know the operational MPP voltage range of the installed PV array in order to adjust the voltage range of the inverter properly. In this article, the behaviour of the global MPP of partially shaded PV strings is studied experimentally based on measured current–voltage curves of two strings consisting of 17 and 6 series-connected PV modules. The results of this study show that the voltage of the global MPP varies over a wide voltage range and changes in the voltage and power of the global MPP can be very fast. The largest measured changes in the GMPP voltage and power during one second were 60% and 32%, respectively.