Utilization of Supercapacitors in Microgrids for Improving the Resiliency of RoCoF and Under-Frequency Protection Schemes

Microgrids provide an environmentally friendly, stable, reliable, and cost-effective energy supply for remote and off-grid areas. However, the stable and reliable operation of Microgrids is more complex than power grids, due to the lack of grid support during islanded mode. During faults and disturbances in the Microgrid, the rate of change of frequency (RoCoF) is higher than in conventional power systems, due to the lower inertia and highly resistive lines. This makes the control of frequency, and reliable operation of Microgrid more challenging. The main and mandatory solution for protecting the Microgrid against these disturbances is under-frequency and RoCoF protection relays, which de-energize the main loads to keep the Microgrid in operation. Despite making sure of not exceeding the frequency from the limitation area, this solution causes a loss of load in the Microgrid. In this regard, the integration of supercapacitors in an attractive and feasible way could control the dynamics of Microgrids, as well as frequency. Supercapacitors are expected to play a key role in Microgrids in terms of fast and controllability in transient phenomena. In this paper, supercapacitors are implemented in an islanded Microgrid to provide an alternative solution for maintaining the frequency in the approved grid code range before the operation of under-frequency relays. The effectiveness of the proposed solution is investigated in the CIGRE testbed in the PowerFactory - DIg SILENT simulation environment.