Fault Characteristic Analysis and Countermeasure Research for Novel CLCC DC System

With the development of high-voltage direct current (HVDC) transmission, commutation failures (CFs) in line commutated converters (LCC) become increasingly prominent. A controllable line commutated converter (CLCC) is proposed to effectively solve commutation failures in LCC. Forced commutation is achieved in CLCC by incorporating auxiliary branches. However, the added components introduce the risks such as open-circuit or short-circuit failures, impacting the reliability of converter. This paper analyzes the fault characteristics of key components in both the main and auxiliary branches of the CLCC, with focus on open-circuit and short-circuit faults. A fault location method based on fault voltage and current is then proposed. Finally, the fault characteristic analysis and the proposed location method are validated by simulation on the developed 500kV/1.2kA CLCC-HVDC model in PSCAD/EMTDC. The result shows that the proposed method enables accurate identification of the faulty valve location.