Transformer-less Alternative Topologies of a Unified Power Quality Conditioner with Embedded Hybrid Energy Storage

This paper proposes alternative transformer-less topologies of a Unified Power Quality Conditioner with embedded hybrid energy storage, based on supercapacitors and Li-ion batteries for power condition in distribution grids. Existing transformer-based alternatives, analyzed in a previous contribution from the same authors, are able to compensate voltage sags and swells, current unbalances as well as operation in grid-forming mode when required. Nevertheless, due to the usage of shunt and series single-phase iron core transformers, the design is bulky, heavy and expensive. The main contribution of this paper is the study of alternative transformer-less topologies, which could be more efficient (less conduction losses), compact and cost convenient. The research included in here considers both half-bridge and full-bridge configurations, either with shared and independent dc-links. Control system design is analyzed and simulation results are used for the validation of the topology.