Fast dynamical reconfiguration algorithm of PV arrays

Abstract

In case of mismatch (due to clouds, shadows, dirtiness, manufacturing tolerances, aging, different orientation of parts of the PV field, thermal gradients, etc.), the Power versus Voltage (P-V) characteristic of a PV field may exhibit more than one peak, because of the adoption of bypass diodes, therefore Centralized Maximum Power Point Tracking (CMPPT) algorithms can fail. The consequent power drop can be avoided 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. In this paper a novel approach to the PV string dynamical reconfiguration is presented and discussed.