Quasi-Z-Source-Fed Switched-Capacitor Multilevel Inverters Without Inrush Charging Current

In switched-capacitor (SC) based multilevel inverters (MLIs), capacitors are usually replenished by a dc voltage source or other capacitors, inrush charging current are found at switching instants. In order to solve this issue, this article presents a new type of step-up MLIs, which is implemented by using a front-side quasi-Z-source unit to feed SC-based multilevel circuits. As a result, the charging current variation of capacitors is effectively limited by the quasi-Z-source impedance. Moreover, the charging voltage can be regulated by controlling the duty ratio of shoot-through states of the quasi-Z-source unit, and the total voltage gain of the new MLI is enhanced as both SC and quasi-Z-source units have boost capability. Structurally, the two units share a common switch network so that the new MLI has simple structure. Topologies for single- and three-phase configurations, operation, and modulation, as well as the parameter design are analyzed in detail. Finally, the feasibility of the new MLI is verified experimentally by a downscale three-phase prototype.