Newly-Constructed Simplified Single-Phase Multistring Multilevel Inverter Topology for Distributed Energy Resources

TLDR

In microgrids, DER‑based single‑phase inverters are common, and reducing conversion losses is achieved by eliminating transformers and minimizing power devices. This work investigates a novel five‑level multistring inverter topology for DER‑based DC/AC conversion. The design incorporates a high‑step‑up front‑end converter to boost efficiency and stabilize DC from PV and fuel cells, and a simplified multilevel inverter that uses only six active switches—two operating at line frequency—rather than the eight required by conventional cascaded H‑bridge topologies. Simulations and experiments demonstrate that the proposed topology yields cleaner output waveforms, smaller filters, and reduced EMI and THD, confirming its effectiveness.

Abstract

In the microgrid system, the distributed energy resource (DER)-based single-phase inverter is usually adopted. In order to reduce conversion losses, the key is to save costs and size by removing any kind of transformer as well as reducing the power devices. The objective of this letter is to study a novel five-level multistring inverter topology for DERs-based dc/ac conversion system. In this study, a high step-up converter is introduced as a front-end stage to improve the conversion efficiency of conventional boost converters and to stabilize the output dc voltage of various DERs such as photovoltaic and fuel cell modules for use with the simplified multilevel inverter. The simplified multilevel inverter requires only six active switches instead of the eight required in the conventional cascaded H-bridge multilevel inverter. In addition, two active switches are operated at the line frequency. The studied multistring inverter topology offers strong advantages such as improved output waveforms, smaller filter size, and lower electromagnetic interference and total harmonics distortion. Simulation and experimental results show the effectiveness of the proposed solution.