This paper presents a review of control strategies, stability analysis, and stabilization techniques for dc microgrids (MGs). Overall control is systematically classified into local and coordinated control levels according to respective functionalities in each level. As opposed to local control, which relies only on local measurements, some line of communication between units needs to be made available in order to achieve the coordinated control. Depending on the communication method, three basic coordinated control strategies can be distinguished, i.e., decentralized, centralized, and distributed control. Decentralized control can be regarded as an extension of the local control since it is also based exclusively on local measurements. In contrast, centralized and distributed control strategies rely on digital communication technologies. A number of approaches using these three coordinated control strategies to achieve various control objectives are reviewed in this paper. Moreover, properties of dc MG dynamics and stability are discussed. This paper illustrates that tightly regulated point-of-load converters tend to reduce the stability margins of the system since they introduce negative impedances, which can potentially oscillate with lightly damped power supply input filters. It is also demonstrated that how the stability of the whole system is defined by the relationship of the source and load impedances, referred to as the minor loop gain. Several prominent specifications for the minor loop gain are reviewed. Finally, a number of active stabilization techniques are presented.

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DC Microgrids—Part I: A Review of Control Strategies and Stabilization Techniques

DC microgrids (MGs) have been gaining a continually increasing interest over the past couple of years both in academia and industry. The advantages of dc distribution when compared to its ac counterpart are well known. The most important ones include higher reliability and efficiency, simpler control and natural interface with renewable energy sources, and electronic loads and energy storage systems. With rapid emergence of these components in modern power systems, the importance of dc in today's society is gradually being brought to a whole new level. A broad class of traditional dc distribution applications, such as traction, telecom, vehicular, and distributed power systems can be classified under dc MG framework and ongoing development, and expansion of the field is largely influenced by concepts used over there. This paper aims first to shed light on the practical design aspects of dc MG technology concerning typical power hardware topologies and their suitability for different emerging smart grid applications. Then, an overview of the state of the art in dc MG protection and grounding is provided. Owing to the fact that there is no zero-current crossing, an arc that appears upon breaking dc current cannot be extinguished naturally, making the protection of dc MGs a challenging problem. In relation with this, a comprehensive overview of protection schemes, which discusses both design of practical protective devices and their integration into overall protection systems, is provided. Closely coupled with protection, conflicting grounding objectives, e.g., minimization of stray current and common-mode voltage, are explained and several practical solutions are presented. Also, standardization efforts for dc systems are addressed. Finally, concluding remarks and important future research directions are pointed out.

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DC Microgrids—Part II: A Review of Power Architectures, Applications, and Standardization Issues

Microgrids energy management systems: A critical review on methods, solutions, and prospects

This paper performs an extensive review on control schemes and architectures applied to dc microgrids (MGs). It covers multilayer hierarchical control schemes, coordinated control strategies, plug-and-play operations, stability and active damping aspects, as well as nonlinear control algorithms. Islanding detection, protection, and MG clusters control are also briefly summarized. All the mentioned issues are discussed with the goal of providing control design guidelines for dc MGs. The future research challenges, from the authors’ point of view, are also provided in the final concluding part.

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Review on Control of DC Microgrids and Multiple Microgrid Clusters

There is huge expectation from smart power grid to provide sustainable energy services using bi-directional flow of data and power enabled by advanced information, communication and control infrastructure. An important element of such a smart grid is prosumers i.e. the consumers who also produce and share surplus energy with grid and other users. Prosumers are not only an important stakeholder of the future smart grids but also have a vital role in peak demand management. Therefore, it is needed to investigate and review the Prosumers based Energy Management and Sharing (PEMS) along with associated challenges. It will help in understanding and analyzing the impact of prosumers in future smart grids. In order to achieve these objectives, this paper presents a comprehensive review of PEMS in smart grid environment and associated impact on power system reliability and energy sustainability. The process of energy sharing among prosumers involves two key elements: information and communication technologies and optimization techniques. These two elements have been discussed in detail to cover the PEMS implementation requirements. The relevant communications technologies presented in the paper include wired, wireless, short and long range options while linear and nonlinear optimization techniques, in context of PEMS, are described. Various technologies, methodologies and mechanisms adopted for PEMS are comprehensively discussed in order to enhance readers’ intuition. Challenges and issues faced by prosumer communities and energy sharing have also been elaborated in detail.

Prosumer based energy management and sharing in smart grid

Fuzzy-based cooperative interaction between stand-alone microgrids interconnected through VSC-based multiterminal converter

One essential distributed energy resource (DER) in smart microgrids (MGs) is the Energy Storage System (ESS) based on batteries, which enables many power and energy functionalities. However, when a microgrid includes more than one ESS, or when multiple ESSs interact within a multi-prosumer environment, their charging and discharging processes should be managed to avoid uneven degradation. This paper presents the modeling and implementation of two different strategies for scheduling the DERs using mixed-integer linear programming (MILP) and quadratic programming (QP) in a multi-prosumer grid-connected microgrid. Each prosumer has its own battery-based ESS with various capacities. The proposed strategies were implemented as a real-time energy management system (EMS) in an experimental laboratory Microgrid based on a rolling horizon scheme. The equalization of the ESSs' state of charge (SoC) is achieved in both cases but there is a compromise between cost and execution time. Meanwhile, the IoT-based smart meter allows the EMS to react in real-time to mismatches between predicted and real load.

Nelson L. Diaz

Papers

Fuzzy-based cooperative interaction between stand-alone microgrids interconnected through VSC-based multiterminal converter

State-of-Charge Equalizations Comparison in a Multi-prosumer Environment Based on Real-Time Energy Management Systems with IoT-Support