Renewable Energy Global Innovations features: General Equations of Lumped Parameter Ladder Circuits and a Special Approach to Analyzing Electrical Line Transient States

Significance Statement

The Telegrapher’s equations, two linear partial differential equations, one for voltages and the other for currents, describe the behavior of voltages and currents in each moment and at any point along an electrical line. They can only be integrated in special cases e. g. if the voltage is sinusoidal function of time and the obtained solution is well-known as the General Line Equations. However, these equations are limited in that they are only convenient for analysis of the transmission lines operating in steady state regimes. Also, these equations are not sufficiently accurate in the case of a lumped parameter ladder circuit that is formed in practice by transmission line ground wires and the belonging tower footing electrodes, especially in the cases when the number of the considered spans is small.

Furthermore, the Telegrapher’s equations can be integrated in the transient regime only using operational calculus, i.e. the Laplas Transformation. However, on the basis of such solution   the finally obtained analytical expressions are not convenient for the interpretation and analysis of resonant phenomena, as well as for determination of transient over-voltages in transmission lines.

Conversely, knowledge exists that lumped parameter ladder circuits represent universal physical and mathematical models of systems having distributed parameters and as such can also be used for analyses of electrical lines. However, these circuits were without the adequate general solutions, i.e. without the equations analogous to the General Line Equations.

Dr. Ljubivoje Popovic at J.P. Elekdrodistribucija-Beograd in Serbia has managed to develop an alternative analytical procedure for obtaining the well-known General Line Equations. Also, on the basis of the same procedure he has obtained the, so far unknown equations and named them “General Equations of Lumped Parameter Ladder Circuits”. These equations enable correct determination of ground fault current distribution for a fault at any point along an HV transmission line. Moreover, these equations enable the analysis of electrical quantities along any actual (with distributed parameters) line in steady state by applying relatively simple mathematical operations and with a desired degree of accuracy.

However, the most important research result is the developed analytical procedure itself, because it opens possibilities for a new approach in analyzing resonant phenomena and transient states in electric-power lines.  The author began by representing an electrical line through its lumped parameter model as a base and then applied the principle of superposition and a summation of the especially formed finite and infinite geometric series. The researcher was able to make observations such as: the developed analytical procedure resulted in relatively simple analytical expressions for the relationship between currents and voltages at different points of transmission lines in transient state conditions. Secondly, the developed analytical procedure was performed to follow, one-by-one, all the phases of the actual physical process occurring during transient states in electrical lines. Eventually, the researcher applied his analytical procedure in a numerical example concerning determination of switching over-voltages in transmission lines and show that this problem can be solved without specially developed computer programs. His research work is now published in the peer-reviewed journal, Electrical Power and Energy Systems.

About The Author

Ljubivoje M. Popović was born in Markovac (at Mladenovac), Serbia, in 1944, graduated (1969) and received Master (1983) and Doctor (1991) degrees, all at the School of Electrical Engineering, University of Belgrade.

In 1969 joined the Electric Power Distribution Company of Belgrade, where he stayed until retirement in 2007.  In 1999 he was elected an associated professor at the School of Electrical Engineering, University of Belgrade and in 2010 he was elected an IEEE R8 Industry Lecturer (Industry Continuing Education Program).

At the beginning of his professional carrier he worked on design of different power installations, including the first 110/10 kV substations in the power distribution network of Belgrade. At the end of the seventies, he moved to the Development and Research Department of the same company.

His research work has been mainly focused on the following  topics:

– Grounding systems of HV substations located in urban areas,
– Ground fault current distribution along the overhead and cable feeding lines,
– Fault locator algorithms,
– Resonant phenomena in the transmission lines and transformer windings,
– Influence of metal installations surrounding the feeding line on the ground fault current distribution,
– Influence of electric-power lines on surrounding metal installations,
– Influence of surrounding metal installations on the transfer characteristics of distribution lines.

In addition to realization of the numerous studies and projects, in the area of power delivery he published: over 50 research papers in international journals and proceedings of international conferences, 2 chapters in two international scientific books and one scientific book, Actual Parameters of Power Lines Passing through Urban Areas.

Some of his papers and research results have had an impact on the following IEC publications: Technical Report IEC 60909-2, Ed 1(1992-09) and IEC standard 60909-3, Ed 2 (2003-09)), and was specially highlighted by: ”Vertical News”, ”High-beam Research”, ”High-beam Business”, ”Goliath Business News” and ”News-edge”. Two of his papers published in 2014 have been selected by ”Renewably Energy Global Innovations” as the key scientific articles.

He was elected a member of the IEC Technical Committee – IEC/TC73- Short Circuit Currents from 2004. A member of IEEE since 1987, he became Senior Member in 1991 and was the Chair of IEEE PES Serbia and Montenegro Chapter from 2002 until 2009.

He received: national ”Nikola Tesla” Award in 2006, IEEE PES Chapter Outstanding Engineer Award, and Certificate of Appreciation for Notable Services and Contributions towards advancement if IEEE and Engineering Professions.

Reference

Ljubivoje M. Popovic. General equations of lumped parameter ladder circuits and a special approach to analyzing electrical line transient states. Electrical Power and Energy Systems, volume 95 (2018) pages 568–576.

 

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Renewable Energy Global Innovations features: Ultralong cycling stability of carbon-nanotube/LiFePO4 nanocomposites as electrode materials for lithium-ion batteries

Significance Statement

The long cycle stability of electrode materials is required for lithium-ion batteries used in electric vehicles.  The effective conductivity and the stable structure of these electrode materials are critical to the cycle stability. The olivine-type lithium iron phosphate is one such electrode material, that is able maintain its crystal structure stability, which in turn minimizes volumetric changes in the charge-discharge process. Advances geared towards improving the effective conductivity have been made by increasing the electrical conductivity of lithium iron phosphate electrode materials through applying carbon nanotubes in these materials. However, the preparation of uniformly distributed carbon nanotubes in the lithium iron phosphate faces many obstacles that some synthetic techniques have tried to address.

In a recent paper published in Electrochimica Acta and led by Professor Tong De Shen and Professor Yu Qing Qiao at Yanshan University developed an innovative technique of coating carbon nanotubes with polyvinylpyrrolidone, which effectively combines the carbon nanotubes and lithium iron phosphate to produce a nanocomposite that exhibits an excellent ultralong cycling stability and high-rate capacity.

The research team made polyvinylpyrrolidone-carbon nanotube-water dispersions which were subjected to repeated freezing and thawing to produce modified carbon nanotubes. They then prepared lithium iron phosphate particles which were then combined with the modified carbon nanotubes to produce lithium iron phosphate-carbon nanotube electrode material. The polyvinylpyrrolidone acts as a dispersant, surfactant and binder. The nanocomposite was heated at 600 ^OC in the presence of nitrogen to eliminate the polyvinylpyrrolidone, after which the carbon nanotubes were manipulated to form uniform three-dimensional conductive networks in lithium iron phosphate electrode.

The authors deduced that the polyvinylpyrrolidone coating process reduces the amount of disordered and defected carbon atoms. It was observed that the synthesized lithium iron phosphate exhibits a single phase of orthorhombic olivine-type structure. The observed average crystallite size of the lithium iron phosphate was about 30 nm.

The research team observed that the discharge capacity of the lithium iron phosphate electrode material with 3% carbon nanotubes, is about 9.4% greater than the lithium iron phosphate without any carbon nanotubes.

From the impedance spectra, it was deduced that there was a lower charge-transfer resistance in the electrode with 3% carbon nanotubes, which was about a third of the charge transfer resistance of the electrode without any carbon nanotubes. This shows that about 3% carbon nanotubes can develop a conductive network that is highly efficient, and therefore the lithium iron phosphate electron conduction is significantly improved.

The authors noted that the lithium iron phosphate electrode material with 3% carbon nanotubes had a lithium ion diffusion coefficient that was 25 times faster as compared with that without any carbon nanotubes, which shows that the carbon nanotubes effectively improve the diffusion of lithium ions. Also, the conductivity of the former is about 7.5 times higher as compared with the latter.

Further analysis showed excellent cycle stability of the lithium iron phosphate electrode containing about 3% carbon nanotubes, such that after about 1000 charge/discharge cycles at a discharge rate of 10C, there was only 1.6% loss in capacity, and a discharge capacity that was as high as about 123.0 mAhg^-1. Additionally, the nanocomposite was observed to have a cycling lifetime of 3400 cycles as compared with 750 cycles for the commercially available lithium iron phosphate electrode materials.

Loss in capacity of various LiFePO4/carbon nanocomposites with 1D to 3D carbon as conducive agents after 1,000 cycles at a discharge rate of 10C. PVP: polyvinylpyrrolidone; CNSs: carbon nanosheets; CFs: carbon fibers; RGO: reduced graphene oxide; GN: graphene; N-GN: nitrogen-doped graphene; GNO: graphene oxide.

About The Author

Prof. Qiao is a professor with the College of Environmental and Chemical Engineering at Yanshan University. She received her Ph.D. degree in 2006 from Yanshan University. Her current research interests are on the processing and performance of nanostructured electrode materials for energy storage and conversion. She has authored/coauthored more than 50 papers.

About The Author

T.D. Shen is a professor with the Coellege of Materails Science and Engineering at Yanshan University. He obtained the National 1000 Talents award in 2010. He received his B. S. degree in Materials Science from the Zhejiang University in 1986 and his Ph.D. degree in Material Sciences from the Institute of Metal Research, Chinese Academy of Sciences in 1995. He was a postdoctoral associate from 1995 to 1998 and a Staff Member from 1998 to 2008, both with the U.S. Department of Energy’s (DOE) Los Alamos National Laboratory (LANL) in Los Alamos, New Mexico.

His current research interests are on the processing, characterization, and physical/mechanical/electrochemical properties of nanocrystalline, nanostructured, and amorphous materials. He has authored/coauthored more than 100 papers.

Reference

Yu Qing Qiao, Wei Liang Feng, Jing Li, Tong De Shen. Ultralong cycling stability of carbon-nanotube/LiFePO₄ nanocomposites as electrode materials for lithium-ion batteries. Electrochimica Acta 232 (2017) 323-331.

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Renewable Energy Global Innovations features: Decision Framework for Feasibility Analysis of Introducing the Steam Turbine Unit to Recover Industrial Waste Heat Based on Economic and Environmental Assessment

Significance Statement

Various technologies involved in reduction of carbon emissions have been implemented in order to provide an equal source of energy supply and in essence, produce gases which are non-toxic to the environment. In view of advancing energy efficiency, recovery of heat energy from industrial waste which can be classified as a source of renewable energy can certainly satisfy both economic and environmental benefits.

A steam turbine unit can efficiently serve as one of the techniques used for waste heat recovery. However, little or no assessment has been made in essence, of providing a decision framework to test its economic and environmental impacts.

Wujie Zhang and colleagues from Zhejiang University in China provided a decision framework for initiating a feasible criterion by simply undergoing an economic and environmental assessment of an industrial waste heat recovery from a steam turbine unit. The research is now published in Journal of Cleaner Production.

Two working modes of the steam turbine unit were considered as a result of their energy output; electrical and mechanical driving force. After certain assumptions, the authors established economic and environmental models which were based on cost-benefit analysis and life-cycle assessment in order to ascertain the benefits of waste heat recovery from the steam turbine unit according to their respective working modes.

The decision framework incorporates three possible outcomes each for both economic benefit and environmental impact of the steam turbine unit. Nine possible combinations were also provided by the cost-benefit analysis and life-cycle assessment results in order to maximize the economic and environmental benefits of the steam turbine unit. Further analysis, however, indicated that the working mode based on the mechanical driving force showed more environmental benefits, but the economic profits remained the same for the two working modes.

The derived decision framework when utilized in a case study of a petrochemical plant, producing terephthalic acid in China, observed a payback period of 2.28 years with energy conservation as high as 2 x 10⁵ GJ for an approximate payback period of 0.12 years. This result shows that the decision framework provided by the way of the authors, can efficiently assess the environmental and economic benefits of an industrial waste heat recovery system.

With the aid of decision framework, in view of providing feasibility analysis on a waste heat recovery technique, the authors were able to show that the steam turbine unit not only conforms to a renewable energy source, but also provides both economic and environmental benefits to consumers.

Journal Reference

W. Zhang^1,2, F. Gu³, F. Dai^1,2, X. Gu^1,2, F. Yue^1,2, B. Bao^1,2, Decision Framework for Feasibility Analysis of Introducing the Steam Turbine Unit to Recover Industrial Waste Heat Based on Economic and Environmental Assessment, Journal of Cleaner Production 137 (2016) 1491-1502.

Show Affiliations

1. Key Laboratory of Advanced Manufacturing Technology of Zhejiang Province, College of Mechanical Engineering, Zhejiang University, Hangzhou, 310027, China.
2. The State Key Laboratory of Fluid Power Transmission and Control, College of Mechanical Engineering, Zhejiang University, Hangzhou, 310027, China.
3. Faculty of Science and Engineering, University of Nottingham, Ningbo, 315100, China.

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Renewable Energy Global Innovations features: Central versus localized optimization-based approaches to power management in distribution networks with residential battery storage

Significance Statement

Different approaches have been proposed previously for scheduling demand-side battery storage, usually with one of two objectives; alleviating the need for distribution grid reinforcement by managing bi-directional power flows or reducing electricity bills for customers. However, without careful coordination, the potentials of demand-side approaches might not be fulfilled.

Dr. Elizabeth Ratnam from the University of California Berkeley (formerly of the University of Newcastle, Australia) and Professors Steven Weller and Christopher Kellett from the University of Newcastle in Australia investigated two optimization-based algorithms to balance an increase in the operational savings that accrue to residential customers with combined photovoltaic (PV) battery storage systems against management of distribution grid power flows to alleviate voltage rise and other local conditions that necessitate grid reinforcement. The article was published in the International Journal of Electrical Power and Energy Systems.

The two optimization-based approaches used are a centralized quadratic program energy-shifting, where selected customers implement a distributor-specified day-ahead battery schedule and a second approach, referred to as local quadratic program energy-shifting, where distributor-specified weights are incorporated into a quadratic program-based algorithm implemented directly by customers to obtain an individual day-ahead battery charge and discharge schedule. The algorithms were applied to load and generation data from 145 Australian residential customers to investigate the customer-distributor benefits of coordinated residential battery scheduling.

The researchers introduced a modeling framework consisting of a dynamical model of a residential energy system and a distribution region described by a directed graph. Residential customers were identified in a specified region and considered ways to coordinate their day-ahead battery schedules under the assumption of a financial policy of net metering.

The two different optimization-based approaches require load and generation forecasts at different locations in the network.  Forecasting is performed by the distributor in the centralized QP case, while in the local QP case the forecasting is done at each residence.  The authors described an approach to emulate imperfect forecasts using historical data.

As a particular application of the techniques presented, the authors investigated the case where the distributor identifies its “weakest link” (via a power flow analysis), which then provides the distribution region of interest and places constraints on the optimization problems.

When assessing the benefits of residential battery scheduling with reference to a 52-week period, the baseline profile exceeded the upper limit for the edge of interest at subgraph forecast constraints of 300KW on 9 days in a year and falls below the lower limit of -150KW on 5 days in the year. It can be said that on most days, subgraph members received a reliable supply of electricity when they do not use or have a battery.

When assessing operational savings accrued to a single subgraph member (i.e., each residence) over a period of 52 weeks denoted by annual savings in $/year, it was seen that local quadratic program energy-shifting may disproportionately penalize some customers when implementing a local quadratic program-based battery schedule.  In fact, using such a localized approach resulted in a few customers seeing additional annual costs.

By contrast, the authors demonstrated that, in terms of customer benefit, the centralized quadratic program-based approach was preferable in that all customers received the same annual savings, so that no customers were penalized for utilizing battery storage.

About The Author

Elizabeth L. Ratnam received the B.E. (Hons I) degree in Electrical Engineering in 2006, and the Ph.D. degree in Electrical Engineering in 2016, both from the University of Newcastle, Australia. She subsequently held a research position with the Center for Energy Research at the University of California, San Diego. During 2001?2012 she gained engineering experience at Ausgrid, one of the largest electricity distribution networks in Australia.

Since 2016, Elizabeth has held a research position with the Berkeley Energy and Climate Institute at the University of California, Berkeley. Her research interests lie in areas that facilitate the integration of renewable energy into power systems. 

About The Author

Steven R. Weller received the B.E. (Hons.I.) degree in Computer Engineering in 1988, the M.E. degree in Electrical Engineering in 1992, and the Ph.D. degree in electrical engineering in 1994, all from the University of Newcastle, Australia. During 1994?1997, he was a Lecturer in the Department of Electrical and Electronic Engineering, University of Melbourne, Australia. In 1997, he joined the University of Newcastle, where he is currently an Associate Professor.

He served as Head of School of Electrical Engineering and Computer Science (2007-2009), and since 2013 has served as Deputy Head of the Faculty of Engineering and Built Environment. He is the recipient of an IET Control Theory and Applications Premium Award. His research interests lie in the areas of control theory and its application to energy systems and climate. 

About The Author

Christopher M. Kellett received the B.Sc. in Electrical Engineering and Mathematics from the University of California, Riverside in 1997 and the M.Sc. and Ph.D. in Electrical and Computer Engineering from the University of California, Santa Barbara in 2000 and 2002, respectively.  He subsequently held research positions with the Centre Automatique et Systemes at Ecole des Mines de Paris (France), the Department of Electrical and Electronic Engineering at the University of Melbourne (Australia), and the Hamilton Institute at the National University of Ireland, Maynooth.

Since 2006, Chris has been with the School of Electrical Engineering and Computer Science at the University of Newcastle, Australia, where he is currently an Associate Professor.

A/Prof. Kellett is an Associate Editor for IEEE Transactions on Automatic Control, the European Journal on Control, and Mathematics of Control, Signals and Systems, as well as a member of the IEEE Control Systems Society Conference Editorial Board.  He has been the recipient of an Australian Research Council Future Fellowship (2011-2015), an Alexander von Humboldt Research Fellowship (2012-2013), and the 2012 IET Control Theory and its Applications Premium Award.

His research interests are broadly in the area of systems and control, with specific emphases on stability and robustness properties for nonlinear systems, high speed model predictive control, applications in electricity distribution networks, and applications in social systems such as carbon pricing and opinion dynamics.

 

 

Journal Reference

Elizabeth L. Ratnam¹, Steven R. Weller², Christopher M. Kellett ². Central versus localized optimization-based approaches to power management in distribution networks with residential battery storage, International Journal of Electrical Power and Energy Systems 80 (2016) 396-406.

Show Affiliations

1. Center for Energy Research, Department of Mechanical and Aerospace Engineering, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0411, USA.
2. School of Electrical Engineering and Computer Science, University of Newcastle, University Drive, Callaghan, NSW 2308, Australia.

 

 

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