Optimal Coordination of Directional Overcurrent Relays in a Microgrid System Using a Hybrid Particle Swarm Optimization

Abstract

Recently, microgrid operation increased significantly with increasing distributed renewable energy resources in the<br><br>power system. Microgrids can operate with and without utility. Fault currents are significantly different in island and utility<br><br>connected operation modes. Therefore, microgrid protection is one of the important subjects in microgrid operation. In this<br><br>paper, a hybrid particle swarm optimization (HPSO) approach has been developed for coordination of directional overcurrent<br><br>relays (DOCRs) in a microgrid system. The coordination constraints include the utility connected and an autonomous condition<br><br>of the microgrid operation. In the optimization procedure, the current setting (Iset) of relays is considered as discrete parameters<br><br>and time multiplier settings (TMS) is assumed as continues parameter. The proposed algorithm has two parts, in the first part,<br><br>PSO is used to calculate the Iset and in the second part, linear programming is applied to calculate the TMS of each relay. In the<br><br>case study, loads connected to the network are divided into critical and noncritical ones. In normal operation of the system,<br><br>distributed generators (DGs) operate in parallel with the utility. When a fault occurs on the utility side, noncritical loads are<br><br>disconnected from the network and DGs are operated in microgrid as islanded mode. Regarding to simulation results, DOCRs<br><br>have a suitable and reliable operation in both conditions of microgrid operations. In addition, overall operating time of the primary<br><br>relays is properly minimized.