PROJECT TITLE :

Optimal Pulsewidth Modulation of Medium-VoltageModular Multilevel Converter - 2016

ABSTRACT:

Modular multilevel converter (MMC) is now the state-of-the-art converter topology for top-voltage dc transmission (HVDC) systems. Another potential application for MMC is medium-voltage (MV) high-power industrial ac drives. In high-power applications, thermal constraints of power semiconductor devices limit device switching frequency to a few hundred hertz. However, there exists a tradeoff between device switching frequency and harmonic distortion of converter output currents. Synchronous optimal pulsewidth (SOP) modulation is an rising low-device switching-frequency-modulation technique for high-power converters, which maintains the quality of converter output currents. SOP technique has been successfully demonstrated for classical multilevel topologies and it's been proved that maximum-device switching frequency can be restricted to rated elementary frequency for seven or higher level inverters while not compromising on the quality of output currents. However, implementation of SOP technique for MMC topology remains pending. One among the main challenges for management of MMC is to take care of floating-capacitor voltages around their nominal value. The goal of our study is to propose, analyze, and implement enhanced SOP technique for MMCs to realize low-device switching-frequency operation, higher quality of converter output currents, and maintain capacitor voltages around their nominal price. The proposed technique has been validated using low-power prototype of 5-level MMC feeding an one.5-kW induction motor.