Optimal Protection Coordination for Microgrid Considering DG and Line Outages Using IWO-ILP Technique

Abstract

Microgrids incorporated with synchronous distributed generators (SDGs) contribute to the significant amount of fault currents compared to inverter-based DGs. During islanded mode also, the fault magnitudes are significant and call for efficient and fast protection schemes. The coordination protection devices, especially, directional overcurrent relays (DOCRs) is a vital issue when dealing with microgrids with SDGs. In addition to the connection of DGs, frequent line outages affect the DOCR settings and cause device maloperation leading to miscoordination issues. This paper deals with optimal coordination of DOCRs for microgrids considering DG and line outages. A coordination model is proposed which involves the constraints corresponding to all N-1 contingencies, which can be a result of line / DG outage. In addition, cases of multiple fault locations are also included in the model to provide effective settings under all circumstances. The problem is modeled as a linear interval programming (ILP) problem and solved using invasive weed optimization (IWO) method. The ILP problem is stated as a sub-problem to IWO which would make it a hybrid optimizer. The proposed method is tested on 9 bus microgrid test system and results are presented.