Newly-constructed single-phase multistring multilevel inverter for fuel-cell microgrid

The objective of this paper is to construct a novel transformerless five-level multistring inverter topology for fuel-cell microgrid 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 PV 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 H-bridge cascaded multilevel inverter. In addition, two active switches are operated under line frequency. The presented multistring inverter offers strong advantages such as improved output waveforms, smaller filter size, and lower EMI and THD. Experimental results show the effectiveness of the proposed solution.