Analysis Of DC-side Fault Response of MMCs with Controlled Fault Blocking Capability for Different Transmission Line Types

MMCs with controlled fault blocking capability retain control of their currents during a dc-side fault, thereby reducing the required interruption capabilities for switchgear. To design the dc-side control to achieve this capability, it is important to take into account the interaction between the converter control and the transmission line during a short-circuit on the transmission line. This paper uses a dc-side equivalent model to assess the interactions of the converter control for two types of converters, i.e., full-bridge and hybrid, with two main types of transmission lines, i.e., cable and overhead line, during dc-side faults. In general, the dc-side voltages and currents for a full-bridge MMC connected to an overhead line show more oscillatory behavior compared to an MMC connected to a cable. Furthermore, a hybrid MMC connected to an overhead line may provide a more damped dc-side fault response due to its limited negative voltage capability.