New Voltage Balancing Technique Based on Carrier-Disposition Pulse Width Modulation for Modular Multilevel Converter

Various modulation schemes have been employed in literature for controlling the output voltage of Modular Multilevel Converters (MMCs). Among these techniques, carrier-disposition PWM method results in uneven distribution of voltage on the capacitors of different submodules (SMs), and therefore affects the output voltage harmonics and causes large magnitudes of circulating current. This paper presents a novel modified carrier deposition PWM technique with SM capacitor voltage balancing that does not need the number of output voltage levels and can be employed for any of the three carrier-deposition PWM methods (PD, POD, and APOD) without any modification. The proposed method is described, and simulation results are provided to verify the theoretical outcomes. Among the three mentioned PWM schemes, PD scheme generates around two times output voltage levels than POD and APOD, and hence has best output voltage harmonic performance.