Fluctuation of PV array global maximum power point voltage during irradiance transitions caused by clouds

Abstract

In well-designed photovoltaic (PV) power plants, such as in typical utility-scale PV plants, operational conditions are quite stable and homogeneous apart from the fast irradiance transitions caused by cloud shadings. These partial shading events cause fast power fluctuations leading even to stability and quality problems in power networks. Fast non-homogeneous irradiance transitions cause also mismatch losses in PV generators and the occurrence of multiple maximum power points (MPPs), which appear in a wide voltage range of the PV generator. In consequence, the global MPP can fluctuate in a wide voltage region causing possible MPP tracking problems and power losses. This article presents a study of the behaviour of the global MPP voltage of various PV arrays during irradiance transitions caused by clouds. The global MPP voltage, its rate of change and the differences in voltage and available energy between the global MPP and the MPP with the highest voltage of the PV generators have been analysed comprehensively, for the first time, by using the characteristics of around 8000 measured irradiance transitions. The global MPP voltage was found to vary between 28 and 112% of the nominal MPP voltage of the array.