Behaviour of Modular Multilevel DC/DC ConverterWith DC Voltage Control Integrated in a Multi-terminal DC System Under Fault Conditions

Abstract

The development of multi-terminal DC (MTDC) networks has various challenges as interconnecting grids of different voltages and grounding schemes, DC grid protection and power flow. DC/DC converter has emerged as the solution for interconnecting HVDC links with different specifications. In this paper, the Front-to-Front Modular Multilevel Converter (F2F-MMC) topology is adopted for DC/DC converter, which can act as a firewall between the healthy and faulty grid during DC faults. Along with this, DC/DC converters when operated in DC voltage control mode can provide supplementary functionalities such as participating in DC grid voltage management and increasing the reliability of the system. In this study, the F2F-MMC converter is operated with a virtual resistance DC voltage controller integrated into an MTDC system. A pole-to-pole DC fault is applied on the MTDC grid and the influence of the virtual resistance controller associated with the DC/DC converter is studied for re-establishing the power flow after DC faults.