New multilevel Flying-Capacitor inverters with coupled-inductors

Abstract

In the paper a new five-level (5L) inverter based on unidirectional Flying-Capacitor switching cells is presented. It is named 5L-Flying-Capacitor with Coupled-Inductor (5L-FC-CI) and consists in parallel connection of two unidirectional (P and N) three-level (3L) Flying-Capacitor switching cells with a coupled-inductor. The PWM output voltage is vastly improved and the switch control dead times is eliminated, particularly when compared with the 3L inverter obtained with bidirectional Flying-Capacitor cells. The phase-shifted carrier (PSC) modulation is used to control the new 5L topology. Thus, the proposed structure ensures an apparent switching frequency in each winding of coupled-inductors twice of switching frequency. The analysis of the new inverter is verified by numerical simulations both for single- and for three-phase topologies and their features are generalized for N odd voltage-levels (NL).