N-version programming-based protection scheme for microgrids: A multi-agent system based approach

Islanded mode and grid-connected mode are the two operational modes of a microgrid (MG). It is essential to develop a suitable protection scheme for an MG network to protect it against all types of faults in both of the modes. The fault current in an inverter-dominated MG is limited by the ratings of the semiconductor devices. Only traditional over-current protection schemes are not adequate for such inverter-based grids. In order to cover the drawbacks of conventional protection schemes, an N-version programming-based protection scheme has been proposed in this paper. An N-version software unit with N = 3 has been developed in MATLAB Simulink and all the agents in the developed multi-agent scheme have been equipped with this unit. The three developed protection versions are Clark's transformation-based current protection, positive sequence phase differential-based protection and conventional over-current-based protection scheme. The software unit makes the final decision about the fault through a polling process. Different types of faults have been tested in both the islanded and grid-connected modes. The proposed protection scheme has given desired results in all the tested cases and hence proved to be a reliable and accurate method for fault identification in microgrid networks. Finally, a framework has been presented for possible realization of the proposed protection scheme through existing IEC 61850-based intelligent electronic devices (IEDs). (C) 2016 Elsevier Ltd. All rights reserved.