http://ieeexplore.ieee.org/iel5/5610941/5624686/05624745.pdf

Power electronics

This paper provides an overview of grid code technical requirements regarding the connection of large wind farms to the electric power systems. The grid codes examined are generally compiled by transmission system operators (TSOs) of countries or regions with high wind penetration and therefore incorporate the accumulated experience after several years of system operation at significant wind penetration levels. The paper focuses on the most important technical requirements for wind farms, included in most grid codes, such as active and reactive power regulation, voltage and frequency operating limits and wind farm behaviour during grid disturbances. The paper also includes a review of modern wind turbine technologies, regarding their capability of satisfying the requirements set by the codes, demonstrating that recent developments in wind turbine technology provide wind farms with stability and regulation capabilities directly comparable to those of conventional generating plants.

A review of grid code technical requirements for wind farms

The authors discuss high-voltage power conversion. Conventional series connection and three-level voltage source inverter techniques are reviewed and compared. A novel versatile multilevel commutation cell is introduced: it is shown that this topology is safer and more simple to control, and delivers purer output waveforms. The authors show how this technique can be applied to either choppers or voltage-source inverters and generalized to any number of switches.<<ETX>>

Multi-level conversion : high voltage choppers and voltage-source inverters

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.

/pdf/dc-microgrids-part-ii-a-review-of-power-architectures-69j8nn2rpd.pdf

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

https://web.stanford.edu/group/efmh/jacobson/Articles/I/DJEnPolicyPt2.pdf

Providing all global energy with wind, water, and solar power, Part II: Reliability, system and transmission costs, and policies

The wave energy is having more and more interest and support as a promising renewable resource to replace part of the energy supply, although it is still immature compared to other renewable technologies. This work presents a complete analysis of the wave energy technology, starting with the characterisation of this global resource in which the most suitable places to be exploited are showed, and the classification of the different types of wave energy converters in according to several features. It is also described in detail each of the stages that are part in the energy conversion, that is, from the capture of the energy from the waves to the extraction of a proper electrical signal to be injected to the grid. Likewise, existing offshore energy transmission alternatives and possible layouts are described.

Review of wave energy technologies and the necessary power-equipment

Microgrids are a suitable, reliable and clean solution to integrate distributed generation into the mains grid. Microgrids can present both AC and DC distribution lines. The type of distribution conditions the performance of distribution line and implies different features, advantages and disadvantages in each case. This paper analyses, in detail, all this parameters for AC and DC microgrids in order to identify and describe the available alternatives for building and configuring a microgrid. Elements and issues involved in the implementation and development, such as protections, power converters, economic analysis, and availability are discussed and described. This analysis constitutes a tool for selecting a suitable configuration of a microgrid adapted to the needs in each situation. In addition, the paper provides a picture of the current situation of microgrids, and identifies and proposes future research lines.

AC and DC technology in microgrids: A review

Distributed generation is emerging as a new technology for supplying the increasing demand for electricity. Microgrids are attracting a great deal of attention since they integrate distributed generation in the main grid reliably and cleanly. When designing the control system of a microgrid, several functions must be considered, such as the management of electrical and thermal energy, load management, synchronisation with the main grid, etc. Both companies and institutions have carried out research into the control of microgrids over recent years and many proposals can be found in the literature. Thus, the design of the control system of a microgrid is a complex task due to its multiple functions and the large number of proposed solutions. This paper presents a complete description of the main features of a microgrid and describes the characteristics of the control systems used. Details are provided of the control tasks involved and of the main types of controls proposed in the literature. In addition, this paper describes the controls used in existing microgrids all over the world and proposes future areas for research.

General aspects, hierarchical controls and droop methods in microgrids: A review

The increase of the wind power penetration in the electrical grids of Denmark, Germany, Spain and other countries and regions is challenging the stability of the system. The subject of this paper is to review the main problems of the connection of wind farms to the grid and how the grid codes must be adapted in order to integrate wind power generation capacity without affecting the quality and stability of the grid. This paper also summarizes the grid codes that have already been modified to incorporate high levels of wind power.

Connection requirements for wind farms : A survey on technical requierements and regulation

The oceans represent a huge energy reservoir. Although today all of the marine power projects are very near from the shore and they are rated at low power, the huge potential of the seas may in a not very distant future bring marine power further into the sea. Also offshore oil and gas exploration is moving into deeper waters and at longer distances from land. New carbon sequestration projects under the seabed are on the way which require a vast amount of electric power consumption. The substitution of offshore power generators by power provided from the grid may have environmental benefits, but the deployment of offshore transmission of bulk electrical power to or from offshore platforms to the electrical grid onshore is a mayor challenge. The main objective of this paper is to focus on trends that can lead to a feasible transmission system in offshore energy systems far from land, and to introduce the technological alternatives which could help to reach that goal. The paper describes the main alternatives and the technical and economical aspects of the transmission of electrical power offshore.

Jon Andreu

Papers

Review of wave energy technologies and the necessary power-equipment

AC and DC technology in microgrids: A review

General aspects, hierarchical controls and droop methods in microgrids: A review

Connection requirements for wind farms : A survey on technical requierements and regulation

Transmission alternatives for offshore electrical power