Universal precharging method for dc-link and flying capacitors of four-level Flying Capacitor Converter

This paper investigates universal start-up procedure for Flying Capacitor Converter (FLC). Main part of this procedure is pre-charging of the dc-link and flying capacitors. This method is usable for voltage pre-charging in rectifier as well as inverter mode of the multilevel FLC converter. This specific feature is based on use of converter topology and modification of converter switching pulses control. The proposed control improvements are designed to control particularly multilevel converters. The control system is implemented in development platform Multi Level Converter (MLC) interface for a four-level multilevel converter with flying capacitors. Its performance is investigated and evaluated by selected experiments made on a developed converter prototype of the rated power of 30 kVA. This paper also discusses behaviour of converter on occurrence of safe restart and shut-down procedure.