A main challenge in the practical implementation of a microgrid is the design of an adequate protection scheme in both grid-connected and islanded modes of operation. Microgrid protection requires a fast, reliable, and robust communication system to adjust relay settings to the appropriate current level according to the operation mode. Various approaches have been implemented to deal with this problem, yet the most promising ones are the use of adaptive protection techniques abiding by the International Electrotechnical Commission (IEC) 61850 communication standard. This paper presents a review of the technical challenges for the use of classical protection techniques and the need for an enhanced, adaptive, smart protection system. However, the risk of communication link failures and cyber security threats still remain a challenge in implementing a reliable adaptive protection scheme. A contingency is essential in the event that a communication failure prevents a relay from adjusting between grid-connected and islanded mode. An adaptive protection scheme is proposed, which utilizes energy storage devices to enhance resiliency against communication outages. The proposed solution does not incur additional costs to the network, as the energy storage devices are already utilized for other purposes. A case study experimentally verifies this contingency under a worst-case scenario, where a fault occurs simultaneously with a pulsed load while operating in islanded mode with a communication failure.

The operation of the smart grid is anticipated to rely profoundly on distributed microprocessor-based control. Therefore, interoperability standards are needed to address the heterogeneous nature of the smart grid data. Since the IEC 61850 emerged as a wide-spread interoperability standard widely accepted by the industry, the Sampled Measured Values method has been used to communicate digitized voltage and current measurements. Realizing that current and voltage measurements (i.e., feedback measurements) are necessary for reliable and secure noperation of the power grid, firstly, this manuscript provides a detailed analysis of the Sampled Measured Values protocol emphasizing its advantages, then, it identifies vulnerabilities in this protocol and explains the cyber threats associated to these vulnerabilities. Secondly, current efforts to mitigate these vulnerabilities are outlined and the feasibility of using neural network forecasters to detect spoofed sampled values is investigated. It was shown that although such forecasters have high spoofed data detection accuracy, they are prone to the accumulation of forecasting error. Accordingly, this paper also proposes an algorithm to detect the accumulation of the forecasting error based on lightweight statistical indicators. The effectiveness of the proposed methods is experimentally verified in a laboratory-scale smart grid testbed.

The main challenge of the microgrid is to design a suitable protection scheme due to the complexity of the architecture of the microgrid. The importance of the proposed protection technique is threefold. First, it presents a co-simulation platform to integrate between a simulated model on power system computer aided design (PSCAD)/real time digital simulator computer aided design (RSCAD) software's and physical devices schweitzer engineering laboratories (SEL) 421-7 relays to protect the microgrid that includes different resources connected based on inverter interface. Second, it presents a comprehensive hardware/software setup to test the protective relays in a closed loop system and shows how to configure the protective relay's International Electrotechnical Commission 61850 communications. Third, IEEE 1588 standard is used to provide sub nanoseconds latency between the simulated model that emulated on real time digital simulator (RTDS) and the external devices. Also, the measurement signals are synchronized between RTDS and the external devices using giga-transceiver synchronization card (GTSYNC) interface card and SEL-2488 satellite-synchronized network clock. The results showed that the co-simulation infrastructure introduces a highly dependable design, analysis, and testing environment for cyber and physical data flow in the system. Besides that, the voltages at ac/dc sides and frequency at fault condition were maintained due to the energy storage device contributions at different modes of operation.

Microgrids' adaptive protection techniques rely on communication signals from the point of common coupling to adjust the corresponding relays' settings for either grid-connected or islanded modes of operation. However, during communication outages or in the event of a cyberattack, the 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 pulse 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 pulse load. It was also shown that the size of the supercapacitor can be reduced if the pulse load is temporarily disconnected during the transient fault period. Simulations, which were also experimentally verified, showed that the resulting supercapacitor size and the optimized controller parameters from the proposed two-level optimization scheme were feeding enough fault currents for different types of faults and minimizing the cost of the protection scheme.