Overview of current development in electrical energy storage technologies and the application potential in power system operation

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

Power electronics

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

Engineering education in K-12 classrooms is a small but growing phenomenon that may have implications for engineering and also for the other STEM subjects--science, technology, and mathematics. Specifically, engineering education may improve student learning and achievement in science and mathematics, increase awareness of engineering and the work of engineers, boost youth interest in pursuing engineering as a career, and increase the technological literacy of all students. The teaching of STEM subjects in U.S. schools must be improved in order to retain U.S. competitiveness in the global economy and to develop a workforce with the knowledge and skills to address technical and technological issues. Engineering in K-12 Education reviews the scope and impact of engineering education today and makes several recommendations to address curriculum, policy, and funding issues. The book also analyzes a number of K-12 engineering curricula in depth and discusses what is known from the cognitive sciences about how children learn engineering-related concepts and skills. Engineering in K-12 Education will serve as a reference for science, technology, engineering, and math educators, policy makers, employers, and others concerned about the development of the country's technical workforce. The book will also prove useful to educational researchers, cognitive scientists, advocates for greater public understanding of engineering, and those working to boost technological and scientific literacy.

http://www.nmu.edu/seaborg/sites/DrupalSeaborg/files/UserFiles/Files/NGSS/Engineering_in_k-12_education-_Understanding_the_status_and_improving_the_prospects.pdf

Engineering in K-12 Education: Understanding the Status and Improving the Prospects.

The number of semiconductor switches in a modular multilevel converter (MMC) for HVDC transmission is typically two orders of magnitudes larger than that in a two or three level voltage-sourced converter (VSC). The large number of devices creates a computational challenge for electromagnetic transient simulation programs, as it can significantly increase the simulation time. The paper presents a method based on partitioning the system's admittance matrix and deriving an efficient time-varying Thevenin's equivalent for the converter part. The proposed method does not make use of approximate interfaced models, and mathematically, is exactly equivalent to modelling the entire network (converter and external system) as one large network. It is shown to drastically reduce the computational time without sacrificing any accuracy. The paper also presents control algorithms and other modelling aspects. The efficacy of the proposed method is demonstrated by simulating a point-to-point VSC-MMC-based HVDC transmission system.

/pdf/efficient-modeling-of-modular-multilevel-hvdc-converters-mmc-j1tm8tzxo3.pdf

Efficient Modeling of Modular Multilevel HVDC Converters (MMC) on Electromagnetic Transient Simulation Programs

Corporate research centers, universities, power equipment vendors, end users, and other market participants around the world are beginning to explore and consider the use of dc in future transmission and distribution system applications. Recent developments and trends in electric power consumption indicate an increasing use of dc-based power and constant power loads. In addition, growth in renewable energy resources requires dc interfaces for optimal integration. A strong case is being made for intermeshed ac and dc networks, with new concepts emerging at the medium-voltage (MV) level for MV dc infrastructure developments.

Ship to Grid: Medium-Voltage DC Concepts in Theory and Practice

Grid level energy storage systems are a cornerstone of future power networks and smart grid development. Better energy storage systems are one of the last hurdles hindering the integration of renewable generation. There are currently many methods of implementing energy storage, ranging from pumped hydro storage to sodium-sulfur battery storage. All energy storage technologies share a common disadvantage which is high initial installation costs. This survey was undertaken with the intent of identifying the technological state of battery energy storage for power systems, as well as providing a background on the modeling and simulation of those battery technologies.

Survey of battery energy storage systems and modeling techniques

This paper proposes an adaptive control architecture for maximum power point tracking (MPPT) in photovoltaic systems. MPPT technologies have been used in photovoltaic systems to deliver the maximum available power to the load under changes of the solar insolation and ambient temperature. To improve the performance of MPPT, this paper develops a two-level adaptive control architecture that can reduce complexity in system control and effectively handle the uncertainties and perturbations in the photovoltaic systems and the environment. The first level of control is ripple correlation control (RCC), and the second level is model reference adaptive control (MRAC). By decoupling these two control algorithms, the system achieves MPPT with overall system stability. This paper focuses mostly on the design of the MRAC algorithm, which compensates the underdamped characteristics of the power conversion system. The original transfer function of the power conversion system has time-varying parameters, and its step response contains oscillatory transients that vanish slowly. Using the Lyapunov approach, an adaption law of the controller is derived for the MRAC system to eliminate the underdamped modes in power conversion. It is shown that the proposed control algorithm enables the system to converge to the maximum power point in milliseconds.

Maximum Power Point Tracking Using Model Reference Adaptive Control

The installation and of a 5 MVA, 4.16 kV Distribution-level Static Reactive Compensator (D-STATCOM) was completed in July, 1999 at the Seattle Iron & Metals Corporation's new steel recycling facility in Seattle, Washington, USA. The D-STATCOM technology was selected as the preferred option for the voltage flicker compensation of a 4000 hp shredder motor, which will be operated at the new facility. For voltage flicker applications, the D-STATCOM technology provides rapid-response compensation to correct for the voltage fluctuation characteristics imposed on the interconnected system during the shredder motor operation. In this application, the D-STATCOM system will be operating at 4.16 kV and will provide reliable power quality for both the new steel recycling facility and the interconnecting utility, Seattle City Light, which provides power to the plant at 26.4 kV. Final field testing and commissioning of the D-STATCOM System was completed in February, 2000.

Application of a 5 MVA, 4.16 kV D-STATCOM system for voltage flicker compensation at Seattle Iron and Metals

The application of FACTS and HVDC technologies, in the form of voltage sourced converter (VSC) based designs; continue to be implemented throughout North America and other parts of the world for improved transmission system control and operation. FACTS and HVDC-link technologies allow more efficient utilization of existing transmission networks and help to better facilitate needed transmission system expansion. The wide-scale application of these technologies leads to numerous benefits for electrical transmission system infrastructure, including increased capacity at minimum cost; enhanced reliability increased capacity at minimum cost; enhanced reliability through proven performance; higher levels of security by means of sophisticated control & protection; and improved system controllability with state-of-the-art technology concepts. Both conventional and advanced forms of FACTS and HVDC transmission technologies exist and are in operation today. Advanced solutions are in the form of VSC based designs, including configurations for static synchronous compensators (STATCOM), unified power flow controllers (SSSC), and VSC-based back-to-back DC links (VSC-BTB), to name a few. This paper highlights the advantages provided by the VSC design concept for FACTS ad HVDC-link system applications.

Gregory F. Reed

Papers

Ship to Grid: Medium-Voltage DC Concepts in Theory and Practice

Survey of battery energy storage systems and modeling techniques

Maximum Power Point Tracking Using Model Reference Adaptive Control

Application of a 5 MVA, 4.16 kV D-STATCOM system for voltage flicker compensation at Seattle Iron and Metals

Advantages of voltage sourced converter (VSC) based design concepts for FACTS and HVDC-link applications