With the rapid growth of new energy grid integration and High Voltage Direct Current (HVDC) transmission demand, Modular Multilevel Converter (MMC) valve as the core equipment of the transmission system, the performance and reliability of its sub-module is critical. This paper presents a compact and reliable MMC valve sub-module design using a novel 4.5kV/5kA domestic Controlled Punch-through Integrated Gate Commutator Thyristor (CP-IGCT) device. Through multi-stage bypass protection mechanism and clamp circuit optimization, the compactness, economy and fault tolerance of the module are significantly improved. In the topology design of sub-module, the constant voltage breakdown characteristics of CP-IGCT are innovatively used to realize the multi-stage bypass protection scheme. When the capacitor of sub-module is over-voltage, the device is passively breakdown, and the fast bypass of fault current is realized, which solves the problem of fault diffusion caused by bypass switch rejection. Concurrently, the clamp circuit required for IGCT application is optimized and selected. The sub-module based on 4.5kV/5kA domestic IGCT device is tested and verified, which proves the operation performance of the sub-module and the effectiveness of multi-stage bypass relying on passive breakdown of the device.
Li et al. (2026) studied this question.