Multi-Objective Optimization of Modular Multilevel Converter Systems

This paper investigates a multi-objective optimization method for modular multilevel converter systems. The method is applied to the AC-AC MMC topology, which connects the three-phase utility grid to the single-phase railway grid. The presented paper aims at a joint optimization of all system components providing a set of pareto-optimal system designs. The optimization space encompasses core system design parameters, such as the number of cells in a branch, the sizing of cell capacitor and branch inductance, but also the switching frequency and other parameters. The objectives studied in this paper are the overall system cost and losses. The considered constraints comprise limitations on system components as well as the power capability of the converter, compliance with grid codes and system efficiency. The obtained optimized design improved the total system cost by 7% compared to a manually derived benchmark design. It has been verified by offline and real-time simulations.