The increasing interest in integrating intermittent renewable energy sources into microgrids presents major challenges from the viewpoints of reliable operation and control. In this paper, the major issues and challenges in microgrid control are discussed, and a review of state-of-the-art control strategies and trends is presented; a general overview of the main control principles (e.g., droop control, model predictive control, multi-agent systems) is also included. The paper classifies microgrid control strategies into three levels: primary, secondary, and tertiary, where primary and secondary levels are associated with the operation of the microgrid itself, and tertiary level pertains to the coordinated operation of the microgrid and the host grid. Each control level is discussed in detail in view of the relevant existing technical literature.

Trends in Microgrid Control

Distributed generation: definition, benefits and issues

▪ Abstract After a brief survey of fuel cell types, attention is focused on material requirements for SOFC and PEMFC stacks, with an introductory section on materials technology for reformers. Materials cost and processing, together with durability issues, are emphasized as these now dominate materials selection processes for prototype stack units. In addition to optimizing the cell components, increasing attention is being given to the composition and processing of the bipolar plate component as the weight and volume of the relevant material has a major influence on the overall power density and cost of the fuel cell stack. It is concluded that the introduction of alternative materials/processes that would enable PEMFC stacks to operate at 150–200°C, and IT-SOFC stacks to operate at 500–700°C, would have a major impact on the successful commercialization of fuel cell technology.

Recent Advances in Materials for Fuel Cells

This paper attempts to present the state of art of research work carried out on the optimal planning of distributed generation (DG) systems under different aspects. There are number of important issues to be considered while carrying out studies related to the planning and operational aspects of DG. The planning of the electric system with the presence of DG requires the definition of several factors, such as: the best technology to be used, the number and the capacity of the units, the best location, the type of network connection, etc. The impact of DG in system operating characteristics, such as electric losses, voltage profile, stability and reliability needs to be appropriately evaluated. For that reason, the use of an optimization method capable of indicating the best solution for a given distribution network can be very useful for the system planning engineer, when dealing with the increase of DG penetration that is happening nowadays. The selection of the best places for installation and the preferable size of the DG units in large distribution systems is a complex combinatorial optimization problem. This paper aims at providing a review of the relevant aspects related to DG and its impact that DG might have on the operation of distributed networks. This paper covers the review of basics of DG, DG definition, current status of DG technologies, potential advantages and disadvantages, review for optimal placement of DG systems, optimizations techniques/methodologies used in optimal planning of DG in distribution systems. An attempt has been made to judge that which methodologies/techniques are suitable for optimal placement of DG systems based on the available literature and detail comparison(s) of each one.

Optimal planning of distributed generation systems in distribution system: A review

Access to electric power supply has always had a significant role in promoting improvements in all the society sectors, nevertheless nowadays 1.3 billion of people still do not have electricity access. Moreover, most of them live in rural areas of developing countries which are often isolated, scattered populated and characterized by poor infrastructure and services. In this situation, the growing consideration towards the target of universal access to energy has emphasized the role of rural electrification, and off-grid small-scale generation represents one of the most appropriate options. As a consequence, the scientific literature has devoted attention to this topic with a large number of papers. In this frame, the present analysis focuses on off-grid systems for rural electrification and provides a general framework to this topic and an analytical review of the literature. The work is based on the review of more than 350 papers mainly published from 2000 to 2014 within selected journals, and it is organized in two sections. In the first one we describe the role of small-scale generation systems throughout the process of electrification, the main features of rural areas and their typical energy uses, and we propose a new comprehensive taxonomy for off-grid systems for rural electrification. In the second one we develop an extensive review of the selected literature according to the proposed classification and to five main research areas: Technology: layout and components; Models and methods for simulation and sizing; Techno-economic feasibility analyses and sustainability analyses; Case studies analyses; Policy analyses. The work results in a comprehensive review which organizes and capitalizes the main fundamentals of the addressed topic and provides elements to get acquainted with the literature.

Peter Dondi

Papers

Network integration of distributed power generation