New Multilevel Converter Based on Cascade Connection of Double Flying Capacitor Multicell Converters and Its Improved Modulation Technique

This paper proposes a new multilevel converter based on the cascade connection of double flying capacitor multicell (DFCM) converters, as multilevel modules, to decrease the voltage diversity of the flying capacitors. Furthermore, a new switching pattern based on the phase-shifted pulse-width modulation technique is proposed to reduce the voltage ripple across the flying capacitors. Moreover, the proposed modulation technique reduces the rms value of the current flowing through flying capacitors. This results in an increase in the life time of flying capacitors and a decrease in the capacitance of the flying capacitors, to keep the same amount of the ripple, meaning a reduction in the physical size of the converter. In addition, this paper presents an analytical approach to calculate the average and rms currents of the insulated gate bipolar transistors (IGBTs)/diodes in the DFCM converter in a closed-form expression. The derived closed-form equations to calculate the average and rms currents of the IGBTs/diodes are utilized to investigate the conduction power losses in a DFCM converter and the proposed multilevel converter. Numerical results of the derived closed-form equations match the simulation results well, which validates the derived equations. Furthermore, simulation results and experimental measurements of the proposed multilevel power converter, configured by cascading two two-cell five-level DFCM converters, are presented to validate the performance of the proposed converter as well as the suggested modulation technique.