Utilization of Supercapacitors in Protection Schemes for Resiliency Against Communication Outages: A Case Study on Size and Cost Optimization

Adaptive protection techniques used for a microgrid rely on a stable communication link to and from protective devices at the point of common coupling to adjust the settings within these corresponding devices for either a grid-connected or islanded mode of operation. However, during communication outages or in the event of a cyberattack, relays' settings are not changed. Thus, adaptive protection schemes are rendered unsuccessful. Due to their fast response, supercapacitors, which are present in the microgrid to feed pulsed loads, could also be utilized to enhance the resiliency of adaptive protection schemes against communication outages. Proper sizing of the supercapacitors is therefore important in order to maintain a stable system operation and the cost of the protection scheme. This paper presents a two-level optimization scheme for minimizing the supercapacitor size along with optimizing its controllers' parameters. The latter will lead to a reduction of the supercapacitor fault current contribution and an increase in that of other ac resources in the microgrid in the extreme case of having a fault occurring simultaneously with a pulsed load. It was also shown that the size of the supercapacitor can be reduced if the pulsed load is temporarily disconnected during the transient fault period. Simulation results showed that the resulting supercapacitor size and the optimized controller parameters were feeding enough fault currents for several types of faults in different locations and minimizing the cost of the protection scheme. Experimental results on a hardware microgrid setup validated the simulation results.