Enhancing efficiency and robustness of a photovoltaic power system under partial shading

摘要

Photovoltaic (PV) power systems have been widely applied in commercial and domestic facilities. Electrical energy storage (EES) systems are mandatory in standalone PV systems for continuous power supply. In this paper the efficiency and robustness enhancement methods for PV systems under partial shading have been investigated. Partial shading due to moving clouds and shadows of nearby obstacles on a PV module array causes significant efficiency degradation, since shaded and non-shaded PV modules have large discrepancy in their maximum power points (MPPs). Use of Individual charger for each PV module may mitigate the negative effect from partial shading. However, this method alone may still face severe energy efficiency degradation caused by i) the energy loss due to parasitic effects in the EES elements under variable incoming power from the PV modules and ii) the energy loss in each charger incurred by potentially high imbalance between its input and output voltages. This paper proposes three methods to enhance the PV system efficiency and robustness under partial shading: i) incorporation of a HEES (hybrid electrical energy storage) system into the PV system, ii) extension of the MPTT (maximum power transfer tracking) approach, and iii) dynamic PV module reconfiguration. The three proposed methods can be effectively combined together, yielding a significant efficiency gain ranging from 17.1% to 53.3% compared with the baseline systems.