Grid-Connected Symmetrical Cascaded Multilevel Converter for Power Quality Improvement

This paper discusses the use of a cascaded multilevel converter for flexible power conditioning in smart-grid applications. The main feature of the proposed scheme is the use of independent dc links with reduced voltages, which makes such a topology an ideal candidate for medium-and high-power applications with increased reliability. The developed control strategy regulates independent dc-link voltages in each H-bridge cell, and allows the selective and flexible compensation of disturbing currents under a variety of voltage conditions without requiring any reference frame transformation. The selective control strategies are based on the decompositions proposed in the conservative power theory, which result in several current-related terms associated with specific load characteristics. These current components are independent of each other and may be used to define different compensation strategies, which can be selective in minimizing particular effects of disturbing loads. Experimental results are provided to validate the possibilities and performance of the proposed control strategies, considering ideal and deteriorated voltage conditions.