An improved seven-level switched-capacitor-based neutral-point clamped inverter

Abstract

Multilevel inverters (MLIs) have seen significant growth in a variety of medium- to high-power industrial applications and have become a mature and viable solution for renewable energy systems over the past decade. The major concerns of MLIs are the high component count and the buck-type feature of the ac output voltage when used for grid-connected renewable-energy-based sources such as solar photovoltaic (PV) panels. As another option, a switched-capacitor (SC)-based inverter possessing the feature of boost ability is a prime solution to meet the requirements of ac power applications. Integrating an SC network with a neutral-point clamped (NPC) structure makes leakage current alleviation viable for transformerless PV grid-connected systems. In this article, an improved SCMLI based on the NPC structure is proposed to reduce the number of active switches and the number of switches in the charging loop, significantly reducing the power loss. It can generate seven voltage levels with voltage boosting and self-balancing of capacitors within a single-stage power conversion. The working principle of the proposed topology, circuit description, and control technique are presented. Further, the proposed inverter was compared with other recent SC topologies to show its superiority. In the end, a laboratory prototype was developed and tested for the seven-level module under steady-state and dynamic conditions to validate the practical viability of the proposed configuration. The proposed inverter’s maximum efficiency was 97.5% at 1.2 kW rated power.