Experimental Study of the Operation of PV Strings at the MPP Closest to the Nominal MPP Voltage Instead of the Global MPP

Abstract

Under non-uniform operating conditions, photovoltaic (PV) generators can have multiple maximum power points (MPP) which may cause problems for MPP tracking. Since highly varying global MPP (GMPP) voltage causes large fluctuations in the inverter reference voltage, it would be beneficial to keep the operating point of the inverter all the time close to the nominal MPP voltage. In this way, operation of the PV system would be more predictable and straightforward. This paper presents an experimental study based on measured current–voltage curves of two PV strings of a scenario in which the MPP closest to the nominal MPP voltage is used all the time as the operating point instead of the GMPP. In total, 432000 I–U curves measured over 120 hours were analysed. The effects of inverter sizing on the selection of the operating point of the PV strings were also studied. The experimental results presented in this paper demonstrate that the wide operating voltage range when the GMPP is followed can be significantly reduced by operating at the MPP closest to the nominal MPP voltage at a cost of negligible energy losses.