<p>To improve the ability of a line-commutated converter (LCC) to mitigate commutation failures, a converter topology based on a novel fully controlled resistor capacitor sub-module (RCSM) is proposed in this paper. The topology, working principle, and the control strategy of RCSM are introduced in detail. When compared to the full-bridge structure adopted by other strategies, the proposed sub-module topology is effective and uses fewer power devices. The principle of a RCSM-based LCC for mitigating commutation failures is studied when a single-phase alternating current fault occurs. Through flexible control of the resistor and capacitors in the RCSM, the proposed converter provides additional auxiliary commutation voltage time for the commutating valve and accelerates the decaying of the closing-valve current during the commutation process, enabling the system to mitigate commutation failures. In addition, the thyristor has better blocking ability recovery characteristics. The parameter design of the RCSM under the proposed strategy is analyzed. The MATLAB/Simulink simulation results show that the RCSM-based LCC quickens the commutation process, promoting commutation performance and enhancing the immunity of LCC-HVDC to commutation failures.</p>