Effects of pre-insertion resistor on energization of MMC-HVDC stations

With the development of power electronics technology, the modular multilevel converter (MMC) based HVDC has become one of the optimal solutions for large-scale renewable energy integration and network interconnections. When a MMC-HVDC station is in the status of energization, all the controllable switches in the MMC converter need to be switched off. It makes the converter become a three-phase uncontrollable diode bridge. Its electromagnetic transient model has been proposed in this paper. In addition, the generic model of a MMC-HVDC station has been developed on the Siemens PTI software PSS
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NETOMAC, in order to study the energization transients of a MMC-HVDC station, say, Siemens HVDC PLUS. The simulation results show that the pre-insertion resistor (PIR) can effectively suppress inrush currents of the converter transformer, and alleviate the effects of converter harmonics on the HVDC-connected network In the energization circuit, the PIR is bypassed after a selected insertion time, usually a few seconds. The resulting transient current involves a dc component that can result in current zero-crossing missing phenomena and endanger security of power system devices Therefore, it is significant to determine an appropriate PIR to avoid dangerous inrush currents and possible current zero-crossing missing issues.