Optimal Protection Coordination for Inverter-based Islanded Microgrids Utilizing an Optimized Time-Current-Voltage Characteristic

With the higher utilization of inverter-interfaced distributed generators (IIDGs) into the distribution networks, major protection challenges became more prevalent, as they are characterized by their low fault current contribution which results in a narrow coordination margin between primary and backup relays. This paper proposes an optimized time-current-voltage tripping characteristic for directional over-current relays (DOCRs). The goal is to minimize the overall operation time of relays as much as possible, and this is achieved by formulating the optimal protection coordination (OPC) problem as a constrained non-linear programming problem, which is then solved using the precise mathematical tools provided by the General Algebraic Modeling System (GAMS) optimization software. Lastly, the suggested relay characteristic is evaluated on a radial microgrid with nine buses, which is a component of the urban Canadian distribution network, to verify its effectiveness.