Date of Award


Publication Type

Master Thesis

Degree Name



Electrical and Computer Engineering


Active distribution network, Balanced faults, Distributed generation, Optimal protection coordination, Renewable energy resources, Synchronverter


Maher A. Azzouz




The integration of distributed generators (DGs) into distribution networks leads to the emergence of active distribution networks (ADNs). These networks have advantages, such as deferring the network upgrade, lower power losses, reduced power generation cost, and lower greenhouse gas emission, DGs are classified due to their interface with the network as inverter-interfaced or synchronous-interfaced. However, DGs integration results in bidirectional power flow, higher fault current levels, deterioration of the protection coordination of the directional overcurrent relays (DOCRs) which are used in ADNs, reduced system stability due to the inverters’ lack of damping. The stability can be enhanced by controlling the inverters to behave as synchronous generators, which are known as synchronverters. In this thesis, a two-stage optimal protection coordination (OPC) scheme is proposed to guarantee reliable protection of ADNs while protecting synchronverters from overcurrent using virtual impedance fault current limiters (VI-FCLs). VI-FCLs provide a cost-effective way to protect synchronverters from overcurrent. The first stage integrates the fault current calculations of synchronverters in the fault analysis to find the parameters of VI-FCLs used to limit the synchronverter’s fault current. In the second stage, the fault current calculations, along with the designed VI-FCLs from the first stage, are employed to determine the optimal relays’ settings to minimize the total operating times for all the DOCR. It is found that fixed VI-FCLs can limit synchronverters’ fault currents but may make the OPC problem infeasible to solve. Thus, an adaptive VI-FCL is proposed to ensure a feasible OPC under various fault conditions, i.e., locations and resistances.