AC Fault Clearing within an MMC-Based DC Hub

Abstract

As the number of high voltage (HVDC) installations is increasing, there is a growing need for interconnection to create more efficient grids. To tackle the main challenges in HVDC grids, a multiport DC-DC converter, often referred to as DC hub, is considered a solution. This paper provides a methodology for the clearing of AC faults within the DC hub and the protection of the system during a fault. A methodology is also presented for the safe connection or disconnection of additional ports from the DC hub without affecting the operation of the other ports. A design based on modular multilevel converters (MMC) is chosen due to their inherent advantages and its control operation is described. A DC hub was modelled in Matlab/Simulink and was tested in a case study including the interconnection of three DC lines in symmetric monopolar configuration, operating at different voltage levels.