Optimal Redundancy Configuration of Wave-shaping Circuits and Director Switches in Hybrid Multi-level Converters

Abstract

The alternate arm converter and hybrid cascaded multi-level converter are two promising hybrid multi-level converters for long-distance overhead-line-based high-voltage DC transmission systems. This article first outlines the basic topologies, mathematical equations, and switching patterns of both the alternate arm converter and hybrid cascaded multi-level converter; the initial required number of H-bridge cells in the wave-shaping circuits and series-connected insulated-gate bipolar transistors in the director switches of the alternate arm and hybrid cascaded multi-level converters are calculated. Then considering the operational characteristics, including the transient voltage stresses, the over-insulated-gate bipolar transistor and diode reliability of the individual semiconductor device in the alternate arm and hybrid cascaded multi-level converters are initialized. Further, the reliability analysis of the two hybrid multi-level converters is carried out, and the optimal redundancy configuration method of wave-shaping circuits and director switches is proposed and calculated by the first-order differences of the three-dimensional surfaces, in which an objective function is established that reconciles reliability and investment of hybrid multi-level converters. Finally, numerical calculations successfully validated the effectiveness of the proposed redundancy configuration method.