Multi-Terminal DC Fault Identification for MMC-HVDC Systems based on Modal Analysis -- A Localized Protection Scheme

We propose a localized protection scheme based on modal analysis in multi-terminal modular multilevel converter (MMC) based high voltage DC (HVDC) systems. The paper addresses the issues of localized protection scheme based DC fault identification, such as differentiating between external and internal faults, classification of type of fault contingency i.e., pole to pole (\textit{PTP}) or pole to ground (\textit{PTG}) for high impedance faults (HIFs) in the system. The scheme works on equivalent network of multi-terminal MMC-HVDC system for a DC fault, using phase-modal transformation to analyse line-mode and zero-mode voltage across the current limiting reactor (CLR) for different possible contingencies in the presence of fault resistance. The protection scheme is validated to be reliable for HIFs and in the presence of White Gaussian Noise (WGN) in measurement. The scheme operation is validated to be intact for varying fault location, fault resistances and system transients.