A Virtual Multi-Terminal Current Differential Protection Scheme for Distribution Networks With Inverter-Interfaced Distributed Generators

The deployments of inverter-interfaced distributed generators (IIDGs) in medium voltage distribution networks may cause undesirable trips or tripping failures of conventional two-terminal current differential protective relays. It is economically and technically unfeasible to reconfigure large numbers of time-synchronized sampling clocks and communication channels for each terminal inside the protected zone. In this paper, a more accurate IIDG mathematical equivalent model is established that considers the control strategies of IIDG, and the profile characteristics of the positive-sequence voltage at each point of common coupling are investigated. Then, a real-time estimation algorithm is introduced for the fault current contribution of grid-connected IIDGs. On this basis, this paper proposes a novel virtual multi-terminal current differential protection scheme. This scheme only necessitates exchanging the electrical quantities between the protective relays at both terminals via an existing two-terminal pilot channel, thus reducing the cost and requirements for communications. The feasibility of the proposed protection is demonstrated in both the PSCAD/EMTDC simulation platform and the RTDS hardware experimental laboratory. A comparison of the proposed protection alongside the conventional protection is also presented. Test results indicate that the proposed protection is widely applicable to various fault conditions, thereby improving the sensitivity and selectivity of conventional protection schemes.