Robust Coordination of Overcurrent and Undervoltage Protection Devices for Microgrids

The development of a proper protection system is essential for the secure and reliable operation of microgrids. In a microgrid, operating conditions that produce limited magnitudes of fault currents will be insufficient to activate the overcurrent protective devices. Therefore, it will be necessary to propose new protection systems for its safe and reliable operation. In this work, a new methodology for optimal coordination of protection devices based in a robust optimization is proposed. This proposal uses a protective device based on the combined action of overcurrent and undervoltage elements, which are operating in an interleaved manner. Internal time coordination of both protection elements is required. Once the overcurrent element is established as the primary protection, and the undervoltage element as the backup protection, the operating times of the protective devices are optimized. The methodology was evaluated in the ESUSCON microgrid, which is a low-voltage isolated microgrid located in northern Chile. The simulation results show a better performance of the proposed device than the existing protection system of the microgrid. The proposed methodology proved its effectiveness by clearing all evaluated faults in a timely and coordinated manner.