Optimization method based on simplex algorithm for current control of modular multilevel converters

Abstract

The paper proposes an optimization formulation of the control problem for modular multilevel converter (MMC). The main control stage computes arm voltages on average over a fixed switching period by minimizing control errors in order to satisfy as best as possible the desired references of input, circulating and output currents, while taking into account arm voltage limits. Then, mean-values of required arm voltages are achieved by phase shift pulse-width modulation (PSPWM) by computing duty cycles for each submodule while taking into account the issue of active balancing of the capacitor voltages in a secondary control stage. The proposed optimization problems are solved by using a numerical method based on the simplex algorithm and simulation results are shown in order to support the validity of the approach.