Analysis of the Impact of Non-Zero Crossing Switching of AC Filters on Controllable Line Commutated Converter

High Voltage Direct Current (HVDC) technology based on Line Commutated Converter (LCC) is widely used in long-distance power transmission due to high efficiency and low power loss. AC filters are equipped in HVDC project to eliminate the harmonics and support reactive power for converter units, but the non-zero cross switching of the filters may lead fluctuations and distortions in the AC bus voltage, causing HVDC power disturbances, and even commutation failure. To address this issue, phase-selective breaker controller, commutation failure prevention, Gamma-kick control, and low voltage current limiting (VDCOL) strategies are applied, while those methods can only reduce the risk and cannot completely avoid commutation failure. The literature proposes a Controllable Line Commutated Converter (CLCC) based on fully controlled IGBT and semi-controlled thyristor hybrid connection, which avoids commutation failure through topological innovation. The related research mainly focus on the commutation failure caused by AC faults, while lack of corresponding research on the impact of the AC filter switching on CLCC. This paper analyzes the structure and working principle of CLCC, and discusses the system impact of LCC and CLCC when the AC filter is switching at the non-zero point. The performance of CLCC in resisting filter switching disturbances is verified by PSCAD, revealing the influence mechanism of non-zero point closure on the commutation process, and proposing optimization strategies, providing guidance for the safe and stable operation of high voltage transmission systems.