A multiplexing controllable line-commutated converter without commutation failures

• The paper proposes a new MLCC topology to address commutation failures in LCC-based HVDC systems. • MLCC reduces IGBT modules and surge arresters, improving the cost-effectiveness of retrofitting LCC-HVDC systems. • Simulation results show that MLCC achieves the same fault ride-through performance as CLCC, but with fewer auxiliary components. • The proposed MLCC shows great potential for engineering applications, offering a solution for commutation failure in HVDC systems. Conventional Line-Commutated Converter-based High Voltage Direct Current (LCC-HVDC) systems are widely used in long-distance, high-capacity power transmission, but they are prone to commutation failures due to the uncontrollable turn-off characteristics of thyristors, particularly during AC grid faults. To address this issue, several strategies have been developed, including the Controllable Line-Commutated Converter (CLCC) topology, which integrates fully controlled auxiliary branches. While CLCC successfully mitigates commutation failures, it introduces hardware redundancy that affects cost-effectiveness. This paper presents a novel solution in the form of the Multiplexing Controllable Line-Commutated Converter (MLCC). The MLCC reuses auxiliary branches across the upper and lower arms of the same phase, significantly reducing the number of required Insulated-Gate Bipolar Transistor (IGBT) modules and surge arresters while retaining the commutation failure immunity of CLCC. Simulation results based on a MATLAB/SIMULINK model of a ± 500 kV, 3000 A HVDC system under various fault conditions show that the MLCC achieves equivalent fault ride-through capabilities as CLCC but with a substantial reduction in auxiliary components. The results demonstrate the practical potential of MLCC for retrofitting existing LCC-HVDC systems.