A Novel Capacitor Voltage Balancing Method in Modular Multilevel Converters

Modular multilevel converters (MMC) are used in the applications such as medium voltage multi-megawatt drives and in HVDC power transmission. The converter has several sub-modules connected in series that are switched appropriately to regulate the pole voltage. Besides regulation of output voltage, it is also essential to regulate the individual sub-module capacitor voltages. In this paper, a novel modulation scheme for an MMC converter based on carrier phase shifted PWM is proposed. The proposed modulation scheme balances the sub-module capacitor voltages without distortions in output voltage. The scheme combines the best features of the two well-known modulation approaches, namely, carrier-based modulation approach and sub-module insertion approach. Real-time simulation results modeling a single leg MMC converter using a Typhoon HIL system are presented to validate the performance of the proposed modulation scheme.