Algorithms and devices for the dynamical reconfiguration of PV arrays

Abstract

Shadowing, manufacturing tolerances and parametric drifts introduce mismatching effects in photovoltaic (PV) arrays. The consequent power drop can be faced by using power optimizers, which are module dedicated dc/dc converters, or micro-inverters. The main drawbacks of such devices are the high cost and the reduced plant efficiency during the day hours in which the PV array works under a uniform irradiation level. This usually happens in the middle of the day, just when the PV power reaches the peak. Moreover, both the dc/dc and the dc/ac module dedicated converters introduce further components that may reduce the system lifetime, e.g. large electrolytic capacitances. A recent alternative is represented by the dynamical re-configuration of the PV array by means of active switches: in this way, the efficiency under uniform irradiation conditions is preserved and, in presence of mismatching, the best series/parallel modules configuration is achieved. This solution is cheaper than the one involving power optimizers and, besides the possibility of plant monitoring, offers additional advantages in terms of safety in case of fire. An overview of the main reconfiguration algorithms and devices presented in literature and available on the market is given in this paper. Moreover, a novel approach to the PV string dynamical reconfiguration is sketched.