Optimal Switching of Submodules in Modular Multilevel Converters

Abstract

This paper offers an inventive switching algorithm for MMC staircase-based modulation strategies in MVDC and HVDC applications. We propose a simplified mathematical formulation of MMC modulation, in the format of Quadratic Optimization (QP), which uses submodules switching history to make a minimization compromise between the submodules switching frequencies, the submodules capacitor voltage ripples, and the arm(s) reference voltage tracking errors. Simulation results, at both normal and faulty conditions, highlight that the MMC submodules switching can be reduced to the limit of minimum switching frequency; thus, switching losses, size of submodules, and footprints could be significantly reduced.