Multifunctional UPQC operating as an interface converter between hybrid AC-DC microgrids and utility grids

Abstract

This paper proposes a multifunctional hybrid unified power quality conditioner (UPQC-H), adapted to operate as an interface converter between utility grids and hybrid microgrids (H-MG). In addition to the generation of both ac and dc buses to the H-MGs, the main structure of the UPQC-H can also integrate distributed generation (DG) systems and energy storage systems (ESS) without the need for changing any control strategy. The proposed UPQC-H is built by including two additional power switches to the conventional three-phase UPQC power circuit, which in its traditional configuration is composed of two three-phase inverters used to operate as series and parallel converters. Some advantages related to the proposed UPQC-H configuration can be highlighted, as follows: 1) versatile application to any H-MG configuration; 2) natural power exchange between the H-MG ac and dc buses of both grid-connected and islanded operating modes; 3) seamless transitions between the islanded and grid-connected operating modes, and vice versa; and 4) smoothing of intermittency issues associated to renewable energy sources. Extended static and dynamic experimental results are presented to evaluate the UPQC-H performance and explore its functionalities when interfacing a 3-phase utility grid and an H-MG with integrating photovoltaic-based DG and ESS.