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

Abstract

Alternate arm converter (AAC) and hybrid cascaded multilevel converter (HCMC) are two promising hybrid multi-level converters (HMCs) for long-distance overhead line (OHL) based high voltage direct current (HVDC) transmission systems. This paper first outlines the basic operational principles of AAC and HCMC and based on their topological features, the initial required numbers of the H-bridge cells in the wave-shaping circuits and series connected insulated gate bipolar transistors (IGBTs) in the director switches of AAC and HCMC are calculated. Then considering the operational characteristics including the transient voltage stresses over IGBTs and diodes, the reliability of the individual semiconductor device in AAC and HCMC are initialized. Further, the reliability analysis of the two HMCs are carried out and the optimal redundancy configuration method of wave-shaping circuits and director switches are proposed and calculated by the first-order differences of the three-dimensional (3-D) surfaces, in which an objective function is established that reconciles reliability and investment of HMCs. Finally numerical calculations successfully validated the effectiveness of the proposed redundancy configuration method.