Point-to-point two-level converter system fault analysis

Voltage-source converter (VSC) HVDC transmission is receiving significant attention as the UK is trying to meet its renewable energy targets. However, VSC-HVDC is more vulnerable to DC faults compared to more traditional current-source converter (CSC) HVDC transmission techniques, due to the low DC side impedances and sensitive power electronics within the converters. This presentation investigates the two-level converter system response under different fault scenarios, i.e. pole-to-pole and pole-to-ground faults. A point-to-point two-level VSC-HVDC system was developed in PSCAD/EMTDC to evaluate the system fault response and to verify the theoretical analysis. The study details the system response of the DC side and AC side to pole-to-pole and pole-to-ground faults. The paper details parameters which are considered to be fundamental in the design of a DC protection system.