A hybrid pulse-width modulation technique for a modular multilevel converter with embedded energy sources

This paper presents a hybrid pulse-width modulation technique for a double-star chopper cell modular multilevel converter with embedded energy sources. The technique combines the advantages of the nearest level control as well as the carrier-based pulse-width modulation techniques for the modular multilevel converter. It mitigates the lower-order harmonics in the output voltage of the converter compared to the nearest level control technique while also reducing the switching frequency of the power electronic devices compared to the carrier-based modulation techniques. It does so with an acceptable total harmonic distortion in the output voltage waveform while keeping the undesirable component of the circulating current between the converter legs at zero. Simulation and experimental results are provided to verify the feasibility of the proposed techniques. Although the technique is proposed for a modular multilevel converter with embedded energy sources, it is equally applicable for the widely used double-star chopper cell converter with an input dc bus.