An adaptive virtual impedance fault current limiter for optimal protection coordination of islanded microgrids

Fault currents of inverter-interfaced distributed generators (IIDGs) depend on inverter controllers. Thus, IIDGs fault are different than those synchronous-based DGs, both from the magnitude and waveshape perspectives. In event short-circuit faults, droop-based switch between a voltage source current source, which increases complexity non-linearity calculation (SCC). This paper proposes new SCC algorithm that incorporates virtual impedance-fault limiters (VI-FCLs) to enable modelling as behind an impedance. The VI-FCL was implemented additional control loop in scheme limit IIDG achieve optimal protection coordination (OPC). Further, is adaptively adjusted enhance overcurrent sensitivity. A two-stage OPC for directional relays (DOCRs) developed. Stage I, value adaptive VI-FCLs relay calculated. II aims at obtaining DOCRs settings. Time-domain simulations used demonstrate effectiveness proposed accuracy algorithm. program successfully validated using islanded microgrid part Canadian distribution system.