The decentralized integration of medium-and small-capacity inverter-interfaced distributed generator（IIDG） makes a radial medium-voltage distribution network to become a scattered multi-source system

and the conventional overcurrent protection will not be applicable for this complex system.What is worse

the current external characteristics and fault transient characteristics of those distributed generators connected to power grid by coupling with power electronics interface are greatly different from conventional synchronous generators.Therefore

we established an equivalent model firstly for those grid-connected IIDG using PQ control strategy.The equivalent model can not only describe IIDG’s current output characteristics during normal operation

but also accurately characterize its fault transient characteristics under low voltage ride through operation.Then

we analyzed the profile characteristics of the positive-sequence voltages at points of common coupling（PCCs） in detail.Thereby

we proposed a novel two-terminal pilot protection scheme for distribution network with high penetration IIDG

in which additional protective equipment needed not to be added at both sides of PCC.The proposed scheme reduces the pilot channel requirements for multi-terminal pilot protection

and thus improves the economic efficiency for power grid.Finally

the accuracy of the IIDG equivalent model and the feasibility of the proposed protection scheme were both verified by the PSCAD/EMTDC simulation platform.The test results indicate that the relative calculation error of the IIDG current that is obtained by the equivalent model is less than 5%; and the proposed protection is widely applicable to various conditions involving different IIDG penetrations

fault locations

and fault types.