Research on the Principle and Numerical Simulation of H-Bridge CLCC Converter Valve

The Controllable Line-Commutated Converter (CLCC) integrates fully controlled and semi-controlled devices to mitigate commutation failure. However, its application in large-capacity HVDC systems is constrained by the limited current-carrying capability of fully controlled valves in the main branch. To address the HVDC requirements under high-current conditions, this paper proposes a high-reliability cascaded H-bridge CLCC (H-CLCC) valve topology. The proposed topology employs a dual-path conduction mode for H-bridge sub-valves, reducing electrical stress on devices and enabling modular scalability. A redundant configuration, in which cascaded H-bridges are paralleled with bypass thyristors, allows faulty sub-modules to be rapidly bypassed, ensuring continuous operation. An analytical model based on the Laplace transform is developed to reveal the relationship between capacitor voltage and turn-off current, providing guidance for capacitance design. PSCAD/EMTDC simulations verify that the H-CLCC valve effectively suppresses commutation failure via active commutation, even under severe AC-side faults with currents up to 8 kA. Device-failure simulations further demonstrate strong self-healing capability, ensuring sustained forced commutation under local faults. This work provides a foundation for high-reliability UHVDC converter valve design.