A Simple Modulation and Capacitor Voltage Balancing Method for Four-Level Single Flying Capacitor Converters

The four-level single flying capacitor (4L-SFC) converter is a novel and emerging multilevel topology, which has very high power density and the smallest device count compared with other four-level converters. However, due to the absence of sufficient redundant states, it is of great difficulty to achieve flying capacitor (FC) voltage balance objective. In this paper, a simple but effective modulation and its related FC voltage regulation strategy for 4L-SFC converters is presented. The modulation is based on a modified carrier-overlapped PWM (COPWM), which not only satisfies the volt-second balance principle but can also achieve the natural FC balancing objective. Compared with the conventional COPWM, the relationships between the overlapped carriers and switches are modified to cope with the operation principles of 4L-SFC converters. Simulation and experimental results are provided to show the validity of COPWM modulation and FC balancing method for 4L-SFC converters.