A Novel Integrated Switching Strategy for Reliable Starting of Two Terminal MMC HVDC Transmission System

Abstract

If the initialization protocol of the Modular Multilevel Converter (MMC) system is not adhered to, the primary winding of the system transformer will experience a surge in inrush current, while the secondary winding on the converter side will exhibit significant starting current draw to charge the capacitors of the MMC-H-bridge. This pronounced initial current surge can trigger the activation of protective measures, leading to the disconnection of the High Voltage Direct Current (HVDC) line and thereby engendering power system reliability and stability concerns. This paper presents a starting methodology for a two-terminal MMC HVDC system. The proposed approach entails employing controlled switching techniques to mitigate inrush currents in the HVDC converter transformer, coupled with the utilization of pre-insertion resistance circuit breakers to diminish starting currents on the converter side. The efficacy of the aforementioned strategy is validated through simulations conducted on a two-terminal MMC HVDC system modeled using PSCAD/EMTDC, with the results confirming its effectiveness.