Utilizing supercapacitors for resiliency enhancements and adaptive microgrid protection against communication failures

Islanded microgrids do not have sufficient resources to contribute enough fault current to legacy protection devices to continue operation. Therefore, when a fault happens in an islanded microgrid, relays with high fault current setting will fail to detect and clear the fault. Contemporary adaptive protection schemes rely on communication technologies to adjust the relay settings to adapt to the microgrids' modes of operation; grid-connected or islanded. However, the risk of communication link failures and cyber security threats such as denial-of-service represent major challenges in implementing a reliable adaptive protection scheme. In order to address this issue, this paper proposes an adaptive protection scheme which utilize super capacitive energy storage to enhance resiliency against communication outages. This paper also introduces an autonomous control algorithm developed for the super-capacitor's AC/DC converter. The proposed control is capable of deciding upon charging, discharging of the super-capacitor, and whether or not to feed fault currents in the AC side, based on direct voltage and frequency measurements from its connection point with the microgrid. This eliminates the need for a control command to be sent from the point of common coupling of the microgrid with main grid to adjust the controller's mode of operation and thus reducing the risk of controller failure due to cyber-attacks or other communication issues. Additionally, the paper proposes a Solution to avoid installing a larger super-capacitor by temporarily disconnecting the uncritical pulsed load during the fault instant. The proposed protection scheme was investigated through simulation for various fault types and showed successful results using the proposed scheme in eliminating the aforementioned faults when the communication were available or attacked. (C) 2017 Elsevier B.V. All rights reserved.