The controllable line-commutated converter (CLCC) features forced commutation capability. By leveraging its auxiliary branch to repeatedly interrupt large currents within a short time frame

it can broaden the regulation range of the firing angle

enabling short-term power support to the system and playing a vital role in enhancing system security. Firstly

the commutation characteristics of the CLCC and the stress endured by its components under different firing angles are analyzed. The feasibility of regulating the CLCC firing angle in a short period to generate reactive power is revealed

and the quasi-steady-state equations of the CLCC under multi-quadrant firing angle operation are established. Secondly

based on the sensitivity characteristics of CLCC power to firing angle and DC current under varying degrees of AC faults

considering the arrester residual voltage in the CLCC auxiliary branch and the inverter operation conditions of the CLCC

the regulation range of the CLCC firing angle is determined. Finally

this paper proposes a reactive power support control strategy for the CLCC based on firing angle compensation to maximize the CLCC’s DC transmission power maintenance

and develops an electromagnetic transient simulation model of the CLCC in PSCAD/EMTDC to verify the multi-quadrant power regulation capability of the CLCC and the effectiveness of the proposed reactive power support strategy. Compared with traditional control methods

the reactive power support capability of the CLCC during AC faults is significantly improved.