A Pulse Width Modulation technique for reducing switching frequency for modular multilevel converter

In this paper, a Pulse Width Modulation (PWM) technique for modular multilevel converter has been explored. The PWM technique is implemented using carrier based level shifted PWM strategy. It does not necessitate the calculation of duty cycles, and can be easily implemented in a DSP. With the proposed technique, harmonics in the phase voltage is shifted to twice the switching frequency. Thus, the devices of the converter can be switched at a reduced switching frequency to maintain the same output voltage quality. A detailed explanation of the carrier based level shifted PWM for implementing the proposed technique is included in the paper. This is verified by computer simulation on a 6.6 kV, 6 MW drive system.