Ultracapacitor storage enabled global MPPT for photovoltaic central inverters

Abstract

In most large-scale grid-tied photovoltaic (PV) plants, central inverter configurations are used, mainly due to higher converter efficiency and lower cost per kW. However, compared to other configurations, its Maximum Power Point Tracking (MPPT) efficiency is the lowest since it is the less distributed configuration. Under non-uniform conditions, as mismatch caused by aging and/or partial shading, several local maxima may arise in the PV curve, hence requiring additional actions to maximize the output power of the PV plant. Moreover, tighter grid codes have appeared, requiring for PV systems to limit power fluctuations. This paper presents an alternative to perform Global MPPT (GMPPT) while complying with stiffer grid code limitations. The proposed alternative adds an Energy Storage System (ESS) at inverter level, consisting of an ultracapacitor (UC) bank connected to the DC-link of a PV central inverter through interleaved DC-DC power converters. The proposed configuration is preliminary validated through simulations and tested under extreme conditions. The performance of the system is analyzed and compared to other existing solutions.