Resilient Protection of Medium Voltage DC Microgrids Against Cyber Intrusion

Differential current protection has been a reliable approach for line protection in DC systems. However, due to its dependence on communication for terminal current information, resiliency of such a protection approach is poor against external cyber intrusions (ECI) of different types, i.e., false data injection (FDI) and time synchronization attacks (TSA). As a result of which, the system is prone to collapse due to line tripping in the presence of coordinated ECIs. The scope of this paper is to propose a resilient protection approach for medium voltage DC (MVDC) microgrids differentiating between the real faults and the ECIs in a system. The approach also detects ECIs on an adjacent line occurring simultaneous to a real fault where the system deploys current limiting reactors (CLR) which have the function of limiting the peak of fault current. Modal transformation is carried out to obtain the line-mode and zero-mode voltage across these CLRs. The mode voltages across the faulty mode networks are utilised along with differential current protection to propose a resilient protection approach against ECIs, which is sensitive to high impedance faults (HIFs), working well in the presence of White Gaussian Noise (WGN) in measurement. Further, a sensitivity function is formulated which gives the variation of decisive variables i.e., line-mode voltage and zero-mode voltage with respect to change in decisive parameters i.e., fault resistance and fault location in the system.