Flying Capacitor Hybrid Modular Multilevel Converter with Thyristor Director Valves

This thesis focuses on the field of HVDC transmission systems, specifically exploring the modular multilevel converter (MMC) topology. A new variation, the Flying Capacitor Hybrid Modular Multilevel Converter (FCHMMC), is proposed. While the original topology utilizes IGBT devices, these components are prone to fail due to high voltage and current during turn-on, leading to latch-up or avalanche breakdown. In contrast, thyristors typically short due to physical or electrical abuse, with very few failing open. However, integrating thyristors into the FC-HMMC topology presents new challenges that require a thorough investigation into the commutation process. The significance of this work lies in its contribution to analyzing and proposing solutions to the problems. The project involves building a detailed simulation model of the FC-HMMC from the ground up using PSCAD, analyzing its operating principles, and proposing a modified control algorithm to enable the replacement of IGBTs with thyristors. The proposed method is implemented and validated through simulation, with results demonstrating its effectiveness. This work provides new insights into converter design and control, paving the way for future research and practical applications in high-voltage power electronics.