A novel soft-switching seven-level converter topology with self-voltage balancing ability

One of the major limitations of the multilevel converters is the voltage unbalance between different levels. The techniques to balance the voltage between the different levels normally involve voltage clamping or capacitor charge and discharge control. However, traditional Flying Capacitor Converter (FCC) may be quite limited by the voltage unbalance of flying-capacitors that is the most serious problem. This paper describes operating principles of a new soft-switching seven-level converter topology based on FCC for self-voltage stabilization and balancing. By adding power electronic devices to the traditional FCC topology, the proposed topology regulates the DC bus voltage and balances the capacitors' voltages. To reduce switching losses and improve the converter efficiency, a soft-switching technique has been used. The soft-switching seven-level converter not only utilizes maximum switching operations without additional switching losses, but also it significantly reduces high voltage and current stresses compared with hard-switching converter. Simulation results demonstrate the validity of the new proposed converter topology.