Family of transformerless pulse-width modulation converters integrating voltage equalisers for PV panels and energy storage modules

Abstract

In photovoltaic (PV) systems, partial shading on PV panels is known to decrease the energy yield significantly. In energy storage applications, voltage imbalance of series-connected energy storage devices may result in over-charging and over-discharging of some devices. Although these issues can be precluded by voltage equalisers, PV and energy storage systems are prone to complexity because, in addition to main converters, voltage equalisers are separately necessary. To simplify the PV and energy storage systems, four kinds of transformerless pulse-width modulation converters integrating voltage equalisers are proposed in this study. Four kinds of basic circuits, each containing a unique ‘switching cell’, are introduced as a foundation of integrated converters. Stacking multiple switching cells with respective basic circuit derives the proposed integrated converters. Fundamental operation analyses are performed for two representative topologies. Experimental verification tests were performed using prototypes for a PV panel and series-connected electric double-layer capacitors (EDLCs). With the integrated converters, the energy yield from the partially shaded PV panel was significantly increased, and EDLCs were charged with eliminating voltage imbalance. This study chiefly focuses on the generalisation, fundamental operation analysis, and experimental verification for the proposed circuit derivation concept rather than detailed analysis for individual topologies.