A Damping-Controllable-Commutated Converter for Mitigating Commutation Failure of LCC-HVDC

A damping-controllable-commutated converter (DCCC) is proposed to enhance the commutation failure (CF) mitigation capability of line-commutated converter-based high-voltage direct current (LCC-HVDC) systems. The DCCC comprises a main branch and an auxiliary branch, with the main branch consisting of thyristors and a few high-current capacity integrated gate-commutated thyristors (
i
-IGCTs) and the auxiliary branch composed of damping modules and a few high-voltage tolerance IGCTs (
v
-IGCTs). In normal operating conditions, the DCCC operates like the LCC for commutation. However, under fault conditions, the commutation process in the DCCC is decomposed into a current-limiting process and a forced commutation process. During the current-limiting process, the damping module transfers the valve current to the auxiliary branch, and the
i
-IGCTs actively block the main branch in the zero-current state. When the current reaches the turn-off value of the
v
-IGCTs, the forced commutation process is initiated, and the
v
-IGCTs actively turn off the current to complete the commutation. Operation strategy for DCCC and parameters for damping and snubber circuits are devised based on the preceding work modes. Simulations show that the DCCC can effectively enhance the CF mitigation capacity of the system, with the switching device maintaining reasonable electrical stress.