Impact of Partial De-blocking of MTDC Link during DC Fault

Abstract

This paper analyzes the transient response of a multiterminal HVDC link during dc line fault and partial de-block of the inverter station. A simplified model of a four-terminal system was analyzed for current order control settings. Then, a parallel four-terminal LCC based converter system was modelled and analyzed on PSCAD. A dc line fault was applied at the middle of the transmission line. The waveforms showed a transient over-current at the rectifier station. A partial de-blocking measure was introduced to reduce the inflow of fault current into the inverter station. This resulted in a reduced active power transfer at the rectifier station. The system was able to maintain its steady state operating state after the fault period without any occurrence of commutation failure. The results validate the viability of MTDC for bulk power transfer and the fault ride through capability of the controller.