Comparative Performance of Direct and Energy-based Controllers to Compensate Internal Currents of Modular Multilevel Converters

This paper presents a comparative study between direct and indirect, or energy-based, current controllers to compensate circulating currents of modular multilevel converters. Despite being easy to implement, direct suppression controllers can produce oscillations on the dc side current of the MMC during transients. On the other hand, energy-based controller allows complete control of the internal dynamics of the converter, attenuating the dc-current oscillations during transient. Digital simulation results obtained with a modular multilevel converter with 20 submodules per converter's arm, modeled in the PSCAD/EMTDC program, will be used to demonstrate the performance of each compensation technique.