Modified Phase-Shift PWM to Achieve Voltage Balancing in a Five-Level DC-DC Converter

Multilevel converters that contain multiple capacitorswitching network structures may suffer from capacitor voltage imbalances. To avoid threats to safe operation, capacitor voltages need to be kept in balance either by active control or passive control. While conventional phase-shifted PWM (PS-PWM) possesses limited inherent balancing capabilities, these are often insufficient and unreliable. In this paper, a new PS-PWM method is proposed for a five-level DC-DC converter, which incorporates both series capacitors and flying capacitors into the calculation of the natural balancing mechanism and can achieve faster voltage balancing. This modified PS-PWM method considers the coupling relationship between the series capacitors and the flying capacitors in the natural balancing process, the trends of the capacitor voltage changes in different carrier orders are obtained. Finally, it is experimentally proved that this modified PS-PWM scheme has faster voltage balancing speed and stronger natural balancing ability.