The operation of multiple microgrids (MGs) in coordination with distribution system enables high penetration of locally available distributed energy resources (DERs). This approach enhances the reliability and resiliency of the power supply significantly. Also, the overall cost of energy gets reduced because of the integration of cost-free power from photovoltaic panels and wind turbines. The most effective utilization of DERs can be achieved through networked MGs. However, the implementation of the concepts of networked MGs requires extensive research. This paper presents a comprehensive literature review of the most important research works on networked MGs. Major benefits and challenges related to this new and highly exploring area have been analyzed. Also, some of the most important research areas related to networked MGs have been highlighted and discussed as the future perspectives.

Networked Microgrids: State-of-the-Art and Future Perspectives

AC microgrid protection – A review: Current and future prospective

The electrical power system has experienced several changes during the last decade, raised by continuously increasing load demand, rapid depletion in fossil fuels, and newly electrical deregulation policy. In the past, numerous review literatures has been published in the field of Load Frequency Control (LFC), which deals with different and recent control strategies for the successful operation of the power system. Moreover, due to changes in lifestyle, increasing load demand, expansion of industrialization, and environmental issues, Renewable Energy Sources (RES) integration becomes the obvious adaptive choice. Since generation from RES is stochastic in nature and depends upon the weather condition and other aspects at every instant of time. Therefore, high penetration may reflect specific issues regarding voltage instability, frequency stabilization, and reliability obstruction. Hence this issue has been covered effectively in this review work. Furthermore, the work precisely summarized and briefly explained the different scenarios of Energy Storage (ES), micro-grid and Flexible AC Transmission System (FACTS) to explore the possible solutions and future aspects. The merit and demerit of different controllers are also investigated with the help of a comparison's tables and also some other analytical comparisons. The overall study examines an in-depth review of recent technical core aspects for LFC based on classical and modern power system which involves the non-linear model, controller design parameters, soft-computing application, attributes of Load forecasting, as well as integration of RES in a deregulated environment. This effective, comprehensive literature survey is very helpful for researchers to bridge the gap between recent development, implementation, challenges and future trends of RES in LFC. 

A literature survey on load frequency control considering renewable energy integration in power system: Recent trends and future prospects

Protection of AC microgrid integrated with renewable energy sources – A research review and future trends

https://pure.tue.nl/ws/files/107082613/Review_Version.pdf

Power system protection with digital overcurrent relays: a review of non-standard characteristics

Nowadays, distributed generations (DGs) and microgrids play a significant role in development of power systems, but DGs produce several protection problems especially in optimal coordination of directional overcurrent relays (DORs). Optimal coordination of DORs is a highly constrained nonlinear programming problem, which has attracted attention of many research studies in recent years. Cuckoo optimization algorithm (COA) is introduced as an optimization tool based on behavior patterns of Cuckoos. In this paper, COA and linear programming (LP) are combined as a new hybrid COA-LP optimization algorithm in order to optimize the coordination protection of DORs in microgrids and find the optimum value of fault current limiter at the point of common coupling. The optimum settings of DORs are obtained for both modes of operation: 1) grid-connected and 2) island mode. The proposed algorithm is applied to Canadian distribution benchmark and a modified IEEE 14 bus networks and compared with particle swarm optimization (PSO) and genetic algorithm (GA). The obtained results show that the computational efficiency of the proposed COA-LP is better than PSO and GA in terms of speed and total operating time of DORs.

Optimal Coordination of Directional Overcurrent Relays in Microgrids by Using Cuckoo-Linear Optimization Algorithm and Fault Current Limiter

In this article, a new Under Frequency Load Shedding (UFLS) method for Inverter-Based Microgrids (IBMs) is presented. The proposed strategy uses frequency variations to estimate the power deficit in IBMs without using wide communication platform and calculating system inertia time constant. Variations of power generation are considered during the load shedding process. The shortage of power is also compensated by the load shedding during several stages. Estimated droop coefficient is updated in each load shedding stage, enabling the proposed method to have a reliable performance in the case of the microgrid's parameters changes which could happen during the load shedding process. The proposed method is simulated and implemented in an IBM by using MATLAB\Simulink software package; the obtained results show the effectiveness and the correctness of the proposed scheme to recognize power deficit and to compensate power shortage.

Under Frequency Load Shedding in Inverter Based Microgrids by Using Droop Characteristic

A new fault location topology implemented in DC microgrid systems is presented in this paper. Due to existing high level fault current in DC microgrids, the detection, isolation, and location of faults are in great degrees of importance. The main structure of proposing fault location unit is an H-bridge controlled by control electronic platform. Based on the selective switching frequency of the semiconductor switches and the amplitude of input DC voltage, the proposed scheme can be used in structurally different microgrids. Low cost design, portability, simple structure, high performance and the acceptable accuracy of the output voltage are the main advantages of the proposed method. The error estimation of the presenting topology in terms of fault position and fault resistance is compared with lastly reported methods. The correctness of the proposed fault location topology is verified through computer simulation.

Developing a new fault location topology for DC microgrid systems

This paper presents a novel DSP-FPGA based real-time implementation of Level-Shifted Pulse Width Modulation (LS-PWM) method for a 5-level NPC inverter. In this brief, by proposing a new communication architecture between a DSP and a FPGA, data transfer bus between the two devices is completely removed. The presented method benefits from simple conceptual strategy, compact design, reduced cost, and high pulse resolution. Simulation and experimental results prove the correctness and practical feasibility of the proposed approach.

A New Real-Time Implementation of Level Shifted-PWM Method for a Three Phase 5-Level NPC Inverter

Recently, the protection of Inverter-Based Microgrids (IBMs) has attracted a lot of attention. It is partly because the penetration level of Inverter-Based Recourses (IBRs) is increasing continually and partly because of different and sometimes unusual behavior of these resources under fault conditions. The distinctive fault characteristic of IBRs makes the protection of the inverter-based microgrids rather uniquely challenging. This paper tries to shed light on the current challenges in the protection of the IBMs by providing time-domain simulations. Two possible solutions to address some of the main challenges are also discussed by providing simulation-based results using MATLAB Simulink software.

Ehsan Dehghanpour

Papers

Optimal Coordination of Directional Overcurrent Relays in Microgrids by Using Cuckoo-Linear Optimization Algorithm and Fault Current Limiter

Under Frequency Load Shedding in Inverter Based Microgrids by Using Droop Characteristic

Developing a new fault location topology for DC microgrid systems

A New Real-Time Implementation of Level Shifted-PWM Method for a Three Phase 5-Level NPC Inverter

Protection of Inverter Interfaced Microgrids: Challenges and Solutions