A Start-Up Method for Flying Capacitor Topologies Using the Output Filter with few Additional Components

This paper presents a new method for precharging a flying capacitor and the DC link capacitor in a flying capacitor topology. The method uses an existing output filter for the precharging process, which is otherwise used to provide a sinusoidal output voltage. This minimizes the number of additional required components. A control scheme is presented, that enables a precharging process, which neither depends on the filter design nor on the number of levels of the flying capacitor topology. The precharge mechanism for a 3-phase inverter with the same configuration is introduced, as well. In addition, a shutdown mechanism is discussed. It allows the energy stored in the capacitors to be fed back into the system to increase efficiency. The presented concept is validated by simulations and measurement on a prototype system.