MODULAR MULTILEVEL CONVERTER WITH CASCADED H-BRIDGES AND PHASE-SHIFTED TRANSFORMER GROUPS

摘要

A converter system (10) comprises a plurality of converter cells (26), each converter cell (26) being adapted for converting an AC cell input voltage into a cell output voltage and a transformer (18) with a plurality of secondary windings (22), each secondary winding (22) connected with one converter cell (26) and providing the AC cell input voltage of the one converter cell (26); wherein the secondary windings (22) are arranged into at least two groups (G₁, G₂, G₃) and the converter cells (26) connected to one group (G₁, G₂, G₃) are series-connected; wherein the transformer (18) is designed such that the secondary windings (22) of different groups (G₁, G₂, G₃) provide AC cell input voltages that are phase- shifted with respect to each other, such that higher order harmonics generated by the converter cells (26) cancel each other; and wherein the secondary windings (22) of one group (G₁, G₂, G₃) provide AC cell input voltages with at least two different phase-shifts (θ₁, θ₂, θ₃, θ₄, θ₅, θ₆).