Initial Capacitor Charging in Grid-Connected Flying Capacitor Multilevel Converters

Abstract

This letter reports a method for the initial charging of capacitors in grid-connected flying capacitor (FC) multilevel converters. A resistor is inserted between each phase of the FC converter and the grid. A voltage balancing algorithm is activated from the beginning of the process and the FC converter generates proper output voltages to achieve balanced charging of both the dc-bus capacitor and the FCs. The proposed initial charging method achieves low voltage and current stress on the power devices and the passive components. The method is simple to implement and can be applied to an FC with any number of levels. Experimental results demonstrate the effectiveness of the proposed method.