Optimization of Large-Scale Hydrothermal System Operation

This paper presents the development of a mathematical model to optimize the management and operation of the Brazilian hydrothermal system. The system consists of a large set of individual hydropower plants and a set of aggregated thermal plants. The energy generated in the system is interconnected by a transmission network so it can be transmitted to centers of consumption throughout the country. The optimization model offered is capable of handling different types of constraints, such as interbasin water transfers, water supply for various purposes, and environmental requirements. Its overall objective is to produce energy to meet the country's demand at a minimum cost. Called HIDROTERM, the model integrates a database with basic hydrological and technical information to run the optimization model, and provides an interface to manage the input and output data. The optimization model uses the General Algebraic Modeling System (GAMS) package and can invoke different linear as well as nonlinear programming solvers. The optimization model was applied to the Brazilian hydrothermal system, one of the largest in the world. The system is divided into four subsystems with 127 active hydropower plants. Preliminary results under different scenarios of inflow, demand, and installed capacity demonstrate the efficiency and utility of the model. From this and other case studies in Brazil, the results indicate that the methodology developed is suitable to different applications, such as planning operation, capacity expansion, and operational rule studies, and trade-off analysis among multiple water users. DOI: 10.1061/(ASCE)WR.1943-5452.0000149. (C) 2012 American Society of Civil Engineers.

Worldwide spread of Dengue virus type 1

BACKGROUND: DENV-1 is one of the four viral serotypes that causes Dengue, the most common mosquito-borne viral disease of humans. The prevalence of these viruses has grown in recent decades and is now present in more than 100 countries. Limited studies document the spread of DENV-1 over the world despite its importance for human health. METHODOLOGY/PRINCIPAL FINDINGS: We used representative DENV-1 envelope gene sequences to unravel the dynamics of viral diffusion under a Bayesian phylogeographic approach. Data included strains from 45 distinct geographic locations isolated from 1944 to 2009. The estimated mean rate of nucleotide substitution was 6.56 × 10⁻⁴ substitutions/site/year. The larger genotypes (I, IV and V) had a distinctive phylogenetic structure and since 1990 they experienced effective population size oscillations. Thailand and Indonesia represented the main sources of strains for neighboring countries. Besides, Asia broadcast lineages into the Americas and the Pacific region that diverged in isolation. Also, a transmission network analysis revealed the pivotal role of Indochina in the global diffusion of DENV-1 and of the Caribbean in the diffusion over the Americas. CONCLUSIONS/SIGNIFICANCE: The study summarizes the spatiotemporal DENV-1 worldwide spread that may help disease control.

The Iasi-Ungheni pipeline: a means of achieving energy independence from Russia? Moldova's attempts at gas supply diversification. OSW Commentary No. 118, 2013-10-08

Since taking power in 2009, the Alliance for European Integration (AIE) has been trying to end Moldova’s dependence on Russian gas. Currently, natural gas accounts for about 50% of the country’s energy balance (excluding Transnistria), and Gazprom has a monopoly on the supply of gas to the republic. The key element of Chișinău’s diversification project is the construction of the Iasi-Ungheni pipeline, which is designed to link the Moldovan and Romanian gas transmission networks, and consequently make it possible for Moldova to purchase gas from countries other than Russia. Despite significant delays, construction work on the interconnector began in August 2013. The Moldovan government sees ensuring energy independence from Russia as its top priority. The significance and urgency of the project reflect Chișinău’s frustration at Moscow’s continued attempts to use its monopoly of Moldova’s energy sector to exert political pressure on the republic. Nonetheless, despite numerous declarations by Moldovan and Romanian politicians, the Iasi- -Ungheni pipeline will not end Moldova’s dependence on Russian gas before the end of the current decade. This timeframe is unrealistic for two reasons: first, because an additional gas pipeline from Ungheni to Chisinau and a compression station must be constructed, which will take at least five years and will require significant investment; and second, because of the unrelenting opposition to the project coming from Gazprom, which currently controls Moldova’s pipelines and will likely try to torpedo any energy diversification attempts. Independence from Russian gas will only be possible after the the Gazprom-controlled Moldova-GAZ, the operator of the Moldovan transmission network and the country’s importer of natural gas, is divided. The division of the company has in fact been envisaged in the EU’s Third Energy Package, which is meant to be implemented by Moldova in 2020.

Impact of electric vehicles on GB electricity demand and associated benefits for system control

This paper investigates the impact that electric vehicle uptake will have on the national electricity demand of Great Britain. Data from the National Travel Survey, and the Coventry and Birmingham Low Emissions Demonstration (CABLED) are used to model an electrical demand profile in a future scenario of significant electric vehicle market penetration. These two methods allow comparison of how conventional cars are currently used, and the resulting electrical demand with simple substitution of energy source, with data showing how electric vehicles are actually being used at present. The report finds that electric vehicles are unlikely to significantly impact electricity demand in GB. The paper also aims to determine whether electric vehicles have the potential to provide ancillary services to the grid operator, and if so, the capacity for such services that would be available. Demand side management, frequency response and Short term Operating Reserve (STOR) are the services considered. The report finds that electric cars are unlikely to provide enough moveable demand peak shedding to be worthwhile. However, it is found that controlling vehicle charging would provide sufficient power control to viably act as frequency response for dispatch by the transmission system operator. This paper concludes that electric vehicles have technical potential to aid management of the transmission network without adding a significant demand burden. © 2013 IEEE.

Les interconnexions électriques entre la France et ses voisins européens depuis 1970 : un vecteur méconnu de l'intégration européenne

Les ouvrages de transport d’électricité ont d’abord été pensés un par un, reliant un excédent de production à un besoin de consommation. Ils ont ainsi parfois très naturellement et dès l’origine traversé les frontières des États pour répondre à leur raison d’être. Les secteurs électriques se structurant fortement lorsque le virage électrique fut pris, les interconnexions entre pays furent conçues par les techniciens comme une mesure élémentaire de sûreté et d’équilibre de ce produit atypique qu’est l’électricité. En France plus particulièrement, lorsque la production électronucléaire se développa à partir des années 1970, ces interconnexions devinrent petit à petit sources de revenus pour l’entreprise nationale, et d’équilibre pour la balance commerciale nationale. L’intérêt grandissant porté au secteur électrique par les institutions européennes à la fin des années 1990 vient ébranler les acteurs économiques géographiques verticaux, et rebat les cartes des enjeux à adresser à une maille plus large que l’État nation. Dans ces transformations successives, les interconnexions aux frontières, et particulièrement aux frontières françaises, jouent ainsi un rôle tout à fait spécifique et de plus en plus structurant pour les économies ouvertes des pays européens. Les réseaux de transport électriques continuent ainsi une mutation entamée dans les années 1970 qui les a conduits de la condition de mal nécessaire à celle de vecteurs indispensables de transformation des économies européennes. L’objet de ce mémoire est d’illustrer la très grande capacité d’adaptation de ces organes industriels, économiques, sociétaux et politiques, dont on pourrait faussement penser qu’ils sont immobilisés par leur nature capitalistique, à travers les enjeux portés par les interconnexions aux frontières françaises. Les sources sont à la fois issues de données des opérateurs techniques, de la documentation – encore peu fréquente – sur ces sujets, ainsi que des statistiques officielles du ministère français. Cette capacité d’innovation et de développement de « couches de services » permet aujourd’hui aux grands réseaux de transport de traverser les époques et la variabilité des orientations de leurs environnements, durablement.

Les interconnexions électriques entre la France et ses voisins européens depuis 1970 : un vecteur méconnu de l'intégration européenne

Les ouvrages de transport d’électricité ont d’abord été pensés un par un, reliant un excédent de production à un besoin de consommation. Ils ont ainsi parfois très naturellement et dès l’origine traversé les frontières des États pour répondre à leur raison d’être. Les secteurs électriques se structurant fortement lorsque le virage électrique fut pris, les interconnexions entre pays furent conçues par les techniciens comme une mesure élémentaire de sûreté et d’équilibre de ce produit atypique qu’est l’électricité. En France plus particulièrement, lorsque la production électronucléaire se développa à partir des années 1970, ces interconnexions devinrent petit à petit sources de revenus pour l’entreprise nationale, et d’équilibre pour la balance commerciale nationale. L’intérêt grandissant porté au secteur électrique par les institutions européennes à la fin des années 1990 vient ébranler les acteurs économiques géographiques verticaux, et rebat les cartes des enjeux à adresser à une maille plus large que l’État nation. Dans ces transformations successives, les interconnexions aux frontières, et particulièrement aux frontières françaises, jouent ainsi un rôle tout à fait spécifique et de plus en plus structurant pour les économies ouvertes des pays européens. Les réseaux de transport électriques continuent ainsi une mutation entamée dans les années 1970 qui les a conduits de la condition de mal nécessaire à celle de vecteurs indispensables de transformation des économies européennes. L’objet de ce mémoire est d’illustrer la très grande capacité d’adaptation de ces organes industriels, économiques, sociétaux et politiques, dont on pourrait faussement penser qu’ils sont immobilisés par leur nature capitalistique, à travers les enjeux portés par les interconnexions aux frontières françaises. Les sources sont à la fois issues de données des opérateurs techniques, de la documentation – encore peu fréquente – sur ces sujets, ainsi que des statistiques officielles du ministère français. Cette capacité d’innovation et de développement de « couches de services » permet aujourd’hui aux grands réseaux de transport de traverser les époques et la variabilité des orientations de leurs environnements, durablement.

Probabilistic Security Constrained Fuzzy Power Flow Models

In restructured power systems, generation and commercialization activities became market activities, while transmission and distribution activities continue as regulated monopolies. As a result, the adequacy of transmission network should be evaluated independent of generation system. After introducing the constrained fuzzy power flow (CFPF) as a suitable tool to quantify the adequacy of transmission network to satisfy 'reasonable demands for the transmission of electricity' (as stated, for instance, at European Directive 2009/72/EC), the aim is now showing how this approach can be used in conjunction with probabilistic criteria in security analysis. In classical security analysis models of power systems are considered the composite system (generation plus transmission). The state of system components is usually modeled with probabilities and loads (and generation) are modeled by crisp numbers, probability distributions or fuzzy numbers. In the case of CFPF the component’s failure of the transmission network have been investigated. In this framework, probabilistic methods are used for failures modeling of the transmission system components and possibility models are used to deal with 'reasonable demands'. The enhanced version of the CFPF model is applied to an illustrative case.

Multistage and coordinated planning of the expansion of transmission systems

In this paper, an efficient genetic algorithm (GA) is presented to solve the problem of multistage and coordinated transmission expansion planning. This is a mixed integer nonlinear programming problem, difficult for systems of medium and large size and high complexity. The GA presented has a set of specialized genetic operators and an efficient form of generation of the initial population that finds high quality suboptimal topologies for large size and high complexity systems. In these systems, multistage and coordinated planning present a lower investment than static planning. Tests results are shown in one medium complexity system and one large size high complexity system.

Analysis of heuristic algorithms for the transportation model in static and multistage planning in network expansion systems

The usefulness of the application of heuristic algorithms in the transportation model, first proposed by Garver, is analysed in relation to planning for the expansion of transmission systems. The formulation of the mathematical model and the solution techniques proposed in the specialised literature are analysed in detail. Starting with the constructive heuristic algorithm proposed by Garver, an extension is made to the problem of multistage planning for transmission systems. The quality of the solutions found by heuristic algorithms for the transportation model is analysed, as are applications in problems of planning transmission systems.

Applied sub-transmission & distribution reliability assessment of SEQEB network in Queensland

In this paper a combined subtransmission and distribution reliability analysis of SEQEB’s outer suburban network is presented. The reliability analysis was carried out with a commercial software package which evaluates both energy and customer indices. Various reinforcement options were investigated to ascertain the impact they have on the reliability of supply seen by the customers. The customer and energy indices produced by the combined subtransmission and distribution reliability studies contributed to optimise capital expenditure to the most effective areas of the network.

Power control and transmission scheduling for network utility maximization in wireless networks

We consider a joint power control and transmission scheduling problem in wireless networks with average power constraints. While the capacity region of a wireless network is convex, a characterization of this region is a hard problem. We formulate a network utility optimization problem involving time-sharing across different "transmission modes," where each mode corresponds to the set of power levels used in the network. The structure of the optimal solution is a time-sharing across a small set of such modes. We use this structure to develop an efficient heuristic approach to finding a suboptimal solution through column generation iterations. This heuristic approach converges quite fast in simulations, and provides a tool for wireless network planning.