Otimização de sistemas híbridos para a eletrificação de minirredes com fontes renováveis: aspectos de projeto, operação e gestão

Em sistemas híbridos de geração de eletricidade (SHGEs) é fundamental avaliar corretamente o dimensionamento, a operação e a gestão do sistema, de forma a evitar seu colapso prematuro e garantir a continuidade do fornecimento de energia elétrica com a menor intervenção possível de usuários ou de empresas geradoras e distribuidoras de eletricidade. O presente trabalho apresenta propostas de otimização para as etapas de dimensionamento, operação e gestão de SHGEs atendendo minirredes de distribuição de eletricidade. É proposta uma estratégia de operação que visa otimizar o despacho de energia do sistema, identificando a melhor relação, sob aspectos técnicos e econômicos, entre o atendimento da carga exclusivamente via fontes renováveis e banco de baterias ou exclusivamente via grupo gerador, e o carregamento do banco de baterias somente pelas fontes renováveis ou também pelo grupo gerador. Desenvolve-se, também, um algoritmo de dimensionamento de SHGEs, com auxílio de algoritmos genéticos e simulated annealing, técnicas meta-heurísticas de otimização, visando apresentar a melhor configuração do sistema, em termos de equipamentos que resultem na melhor viabilidade técnica e econômica para uma dada condição de entrada definida pelo usuário. Por fim, é proposto um modelo de gestão do sistema, considerando formas de tarifação e sistemas de controle de carga, cujo objetivo é garantir uma relação adequada entre a disponibilidade energética do sistema de geração e a carga demandada. A estratégia de operação proposta combina as estratégias de operação descontínua do grupo gerador, da potência crítica e do ponto otimizado de contribuição do gerador no carregamento do banco de baterias, e seus resultados indicam que há redução nos custos de operação globais do sistema. Com relação ao dimensionamento ótimo, o algoritmo proposto, em comparação a outras ferramentas de otimização de SHGEs, apresenta bons resultados, sendo adequado à realidade nacional. O modelo de gestão do sistema propõe o estabelecimento de limites de consumo e demanda, adequados à realidade de comunidades isoladas atendidas por sistemas com fontes renováveis e, se corretamente empregados, podem ajudar a garantir a sustentabilidade dos sistemas.

Algoritmo tabu search especializado para o problema de planejamento da expansao de sistemas de transmissão

Pós-graduação em Engenharia Elétrica - FEIS

Field analysis of solar PV-based collective systems for rural electrification.

This article analyses the long-term performance of collective off-grid photovoltaic (PV) systems in rural areas. The use of collective PV systems for the electrification of small medium-size villages in developing countries has increased in the recent years. They are basically set up as stand-alone installations (diesel hybrid or pure PV) with no connection with other electrical grids. Their particular conditions (isolated) and usual installation places (far from commercial/industrial centers) require an autonomous and reliable technology. Different but related factors affect their performance and the energy supply; some of them are strictly technical but others depend on external issues like the solar energy resource and users’ energy and power consumption. The work presented is based on field operation of twelve collective PV installations supplying the electricity to off-grid villages located in the province of Jujuy, Argentina. Five of them have PV generators as unique power source while other seven include the support of diesel groups. Load demand evolution, energy productivity and fuel consumption are analyzed. Besides, energy generation strategies (PV/diesel) are also discussed.

Nationwide impact and vehicle to grid application of electric vehicles mobility using an activity based model

This paper describes the impact of electric mobility on the transmission grid in Flanders region (Belgium), using a micro-simulation activity based models. These models are used to provide temporal and spatial estimation of energy and power demanded by electric vehicles (EVs) in different mobility zones. The increment in the load demand due to electric mobility is added to the background load demand in these mobility areas and the effects over the transmission substations are analyzed. From this information, the total storage capacity per zone is evaluated and some strategies for EV aggregator are proposed, allowing the aggregator to fulfill bids on the electricity markets.

Cálculo de pilas con aparatos de apoyo tipo POT y tablero con punto fijo

In recent years a great number of high speed railway bridges have been constructed within the Spanish borders. Due to the demanding high speed trains route's geometrical requirements, bridges frequently show remarkable lengths. This fact is the main reason why railway bridges are overall longer than roadway bridges. In the same line, it is also worth highlighting the importance of high speed trains braking forces compared to vehicles. While vehicles braking forces can be tackled easily, the railway braking forces demand the existence of a fixed-point. It is generally located at abutments where the no-displacements requirement can be more easily achieved. In some other cases the fixed-point is placed in one of the interior columns. As a consequence of these bridges' length and the need of a fixed-point, temperature, creep and shrinkage strains lead to fairly significant deck displacements, which become greater with the distance to the fixed-point. These displacements need to be accommodated by the piers and bearings deformation. Regular elastomeric bearings are not able to allow such displacements and therefore are not suitable for this task. For this reason, the use of sliding PTFE POT bearings has been an extensive practice mainly because they permit sliding with low friction. This is not the only reason of the extensive use of these bearings to high-speed railways bridges. The value of the vertical loads at each bent is significantly higher than in roadway bridges. This is so mainly because the live loads due to trains traffic are much greater than vehicles. Thus, gravel rails foundation represents a non-negligible permanent load at all. All this together increases the value of vertical loads to be withstood. This high vertical load demand discards the use of conventional bearings for excessive compressions. The PTFE POT bearings' higher technology allows to accommodate this level of compression thanks to their design. The previously explained high-speed railway bridge configuration leads to a key fact regarding longitudinal horizontal loads (such as breaking forces) which is the transmission of these loads entirely to the fixed-point alone. Piers do not receive these longitudinal horizontal loads since PTFE POT bearings displayed are longitudinally free-sliding. This means that longitudinal horizontal actions on top of piers will not be forces but imposed displacements. This feature leads to the need to approach these piers design in a different manner that when piers are elastically linked to superstructure, which is the case of elastomeric bearings. In response to the previous, the main goal of this Thesis is to present a Design Method for columns displaying either longitudinally fixed POT bearings or longitudinally free PTFE POT bearings within bridges with fixed-point deck configuration, applicable to railway and road vehicles bridges. The method was developed with the intention to account for all major parameters that play a role in these columns behavior. The long process that has finally led to the method's formulation is rooted in the understanding of these column's behavior. All the assumptions made to elaborate the formulations contained in this method have been made in benefit of conservatives results. The singularity of the analysis of columns with this configuration is due to a combination of different aspects. One of the first steps of this work was to study they of these design aspects and understand the role each plays in the column's response. Among these aspects, special attention was dedicated to the column's own creep due to permanent actions such us rheological deck displacements, and also to the longitudinally guided PTFE POT bearings implications in the design of the column. The result of this study is the Design Method presented in this Thesis, that allows to work out a compliant vertical reinforcement distribution along the column. The design of horizontal reinforcement due to shear forces is not addressed in this Thesis. The method's formulations are meant to be applicable to the greatest number of cases, leaving to the engineer judgement many of the different parameters values. In this regard, this method is a helpful tool for a wide range of cases. The widespread use of European standards in the more recent years, in particular the so-called Eurocodes, has been one of the reasons why this Thesis has been developed in accordance with Eurocodes. Same trend has been followed for the bearings design implications, which are covered by the rather recent European code EN-1337. One of the most relevant aspects that this work has taken from the Eurocodes is the non-linear calculations security format. The biaxial bending simplified approach that shows the Design Method presented in this work also lies on Eurocodes recommendations. The columns under analysis are governed by a set of dimensionless parameters that are presented in this work. The identification of these parameters is a helpful for design purposes for two columns with identical dimensionless parameters may be designed together. The first group of these parameters have to do with the cross-sectional behavior, represented in the bending-curvature diagrams. A second group of parameters define the columns response. Thanks to this identification of the governing dimensionless parameters, it has been possible what has been named as Dimensionless Design Curves, which basically allows to obtain in a reduced time a preliminary vertical reinforcement column distribution. These curves are of little use nowadays, firstly because each family of curves refer to specific values of many different parameters and secondly because the use of computers allows for extremely quick and accurate calculations.

Classification of Data to Extract Knowledge from Neural Networks

A major drawback of artificial neural networks is their black-box character. Therefore, the rule extraction algorithm is becoming more and more important in explaining the extracted rules from the neural networks. In this paper, we use a method that can be used for symbolic knowledge extraction from neural networks, once they have been trained with desired function. The basis of this method is the weights of the neural network trained. This method allows knowledge extraction from neural networks with continuous inputs and output as well as rule extraction. An example of the application is showed. This example is based on the extraction of average load demand of a power plant.

NUMERICAL SIMULATION STUDY OF VIBRATION MITIGATION EFFECTIVENESS OF TUNED MASS DAMPERS FOR TRAFFIC SIGNAL MAST ARM STRUCTURES

Fatigue damage in the connections of single mast arm signal support structures is one of the primary safety concerns because collapse could result from fatigue induced cracking. This type of cantilever signal support structures typically has very light damping and excessively large wind-induced vibration have been observed. Major changes related to fatigue design were made in the 2001 AASHTO LRFD Specification for Structural Supports for Highway Signs, Luminaries, and Traffic Signals and supplemental damping devices have been shown to be promising in reducing the vibration response and thus fatigue load demand on mast arm signal support structures. The primary objective of this study is to investigate the effectiveness and optimal use of one type of damping devices termed tuned mass damper (TMD) in vibration response mitigation. Three prototype single mast arm signal support structures with 50-ft, 60-ft, and 70-ft respectively are selected for this numerical simulation study. In order to validate the finite element models for subsequent simulation study, analytical modeling of static deflection response of mast arm of the signal support structures was performed and found to be close to the numerical simulation results from beam element based finite element model. A 3-DOF dynamic model was then built using analytically derived stiffness matrix for modal analysis and time history analysis. The free vibration response and forced (harmonic) vibration response of the mast arm structures from the finite element model are observed to be in good agreement with the finite element analysis results. Furthermore, experimental test result from recent free vibration test of a full-scale 50-ft mast arm specimen in the lab is used to verify the prototype structure’s fundamental frequency and viscous damping ratio. After validating the finite element models, a series of parametric study were conducted to examine the trend and determine optimal use of tuned mass damper on the prototype single mast arm signal support structures by varying the following parameters: mass, frequency, viscous damping ratio, and location of TMD. The numerical simulation study results reveal that two parameters that influence most the vibration mitigation effectiveness of TMD on the single mast arm signal pole structures are the TMD frequency and its viscous damping ratio.

Energy Management of a Battery-Ultracapacitor Hybrid Energy Storage System in Electric Vehicles

Electric vehicle (EV) batteries tend to have accelerated degradation due to high peak power and harsh charging/discharging cycles during acceleration and deceleration periods, particularly in urban driving conditions. An oversized energy storage system (ESS) can meet the high power demands; however, it suffers from increased size, volume and cost. In order to reduce the overall ESS size and extend battery cycle life, a battery-ultracapacitor (UC) hybrid energy storage system (HESS) has been considered as an alternative solution. In this work, we investigate the optimized configuration, design, and energy management of a battery-UC HESS. One of the major challenges in a HESS is to design an energy management controller for real-time implementation that can yield good power split performance. We present the methodologies and solutions to this problem in a battery-UC HESS with a DC-DC converter interfacing with the UC and the battery. In particular, a multi-objective optimization problem is formulated to optimize the power split in order to prolong the battery lifetime and to reduce the HESS power losses. This optimization problem is numerically solved for standard drive cycle datasets using Dynamic Programming (DP). Trained using the DP optimal results, an effective real-time implementation of the optimal power split is realized based on Neural Network (NN). This proposed online energy management controller is applied to a midsize EV model with a 360V/34kWh battery pack and a 270V/203Wh UC pack. The proposed online energy management controller effectively splits the load demand with high power efficiency and also effectively reduces the battery peak current. More importantly, a 38V-385Wh battery and a 16V-2.06Wh UC HESS hardware prototype and a real-time experiment platform has been developed. The real-time experiment results have successfully validated the real-time implementation feasibility and effectiveness of the real-time controller design for the battery-UC HESS. A battery State-of-Health (SoH) estimation model is developed as a performance metric to evaluate the battery cycle life extension effect. It is estimated that the proposed online energy management controller can extend the battery cycle life by over 60%.

Modelling electricity demand with representative load curves

Models for electricity planning require inclusion of demand. Depending on the type of planning, the demand is usually represented as an annual demand for electricity (GWh), a peak demand (MW) or in the form of annual load-duration curves. The demand for electricity varies with the seasons, economic activities, etc. Existing schemes do not capture the dynamics of demand variations that are important for planning. For this purpose, we introduce the concept of representative load curves (RLCs). Advantages of RLCs are demonstrated in a case study for the state of Karnataka in India. Multiple discriminant analysis is used to cluster the 365 daily load curves for 1993-94 into nine RLCs. Further analyses of these RLCs help to identify important factors, namely, seasonal, industrial, agricultural, and residential (water heating and air-cooling) demand variations besides rationing by the utility. (C) 1999 Elsevier Science Ltd. All rights reserved.

Dynamic load management in a smart home to participate in demand response events

In future power systems, in the smart grid and microgrids operation paradigms, consumers can be seen as an energy resource with decentralized and autonomous decisions in the energy management. It is expected that each consumer will manage not only the loads, but also small generation units, heating systems, storage systems, and electric vehicles. Each consumer can participate in different demand response events promoted by system operators or aggregation entities. This paper proposes an innovative method to manage the appliances on a house during a demand response event. The main contribution of this work is to include time constraints in resources management, and the context evaluation in order to ensure the required comfort levels. The dynamic resources management methodology allows a better resources’ management in a demand response event, mainly the ones of long duration, by changing the priorities of loads during the event. A case study with two scenarios is presented considering a demand response with 30 min duration, and another with 240 min (4 h). In both simulations, the demand response event proposes the power consumption reduction during the event. A total of 18 loads are used, including real and virtual ones, controlled by the presented house management system.

Spatial load forecasting using a demand propagation approach

A method for spatial electric load forecasting using multi-agent systems, especially suited to simulate the local effect of special loads in distribution systems is presented. The method based on multi-agent systems uses two kinds of agents: reactive and proactive. The reactive agents represent each sub-zone in the service zone, characterizing each one with their corresponding load level, represented in a real number, and their relationships with other sub-zones represented in development probabilities. The proactive agent carry the new load expected to be allocated because of the new special load, this agent distribute the new load in a propagation pattern. The results are presented with maps of future expected load levels in the service zone. The method is tested with data from a mid-size city real distribution system, simulating the effect of a load with attraction and repulsion attributes. The method presents good results and performance. © 2011 IEEE.

Demand side response to mitigate electrical peak demand in Eastern and Southern Australia

The aim of this work is to develop a Demand-Side-Response (DSR) model, which assists electricity end-users to be engaged in mitigating peak demands on the electricity network in Eastern and Southern Australia. The proposed innovative model will comprise a technical set-up of a programmable internet relay, a router, solid state switches in addition to the suitable software to control electricity demand at user's premises. The software on appropriate multimedia tool (CD Rom) will be curtailing/shifting electric loads to the most appropriate time of the day following the implemented economic model, which is designed to be maximizing financial benefits to electricity consumers. Additionally the model is targeting a national electrical load be spread-out evenly throughout the year in order to satisfy best economic performance for electricity generation, transmission and distribution. The model is applicable in region managed by the Australian Energy Management Operator (AEMO) covering states of Eastern-, Southern-Australia and Tasmania.

Performance load testing and structural adequacy evaluation of road bridge decks

Many ageing road bridges, particularly timber bridges, require urgent improvement due to the demand imposed by the recent version of the Australian bridge loading code, AS 5100. As traffic volume plays a key role in the decision of budget allocations for bridge refurbishment/ replacement, many bridges in low volume traffic network remain in poor condition with axle load and/ or speed restrictions, thus disadvantaging many rural communities. This thesis examines an economical and environmentally sensible option of incorporating disused flat rail wagons (FRW) in the construction of bridges in low volume, high axle load road network. The constructability, economy and structural adequacy of the FRW road bridge is reported in the thesis with particular focus of a demonstration bridge commissioned in regional Queensland. The demonstration bridge comprises of a reinforced concrete slab (RCS) pavement resting on two FRWs with custom designed connection brackets at regular intervals along the span of the bridge. The FRW-RC bridge deck assembly is supported on elastomeric rubber pads resting on the abutment. As this type of bridge replacement technology is new and its structural design is not covered in the design standards, the in-service structural performance of the FRW bridge subjected to the high axle loadings prescribed in AS 5100 is examined through performance load testing. Both the static and the moving load tests are carried out using a fully laden commonly available three-axle tandem truck. The bridge deck is extensively strain gauged and displacement at several key locations is measured using linear variable displacement transducers (LVDTs). A high speed camera is used in the performance test and the digital image data are analysed using proprietary software to capture the locations of the wheel positions on the bridge span accurately. The wheel location is thus synchronised with the displacement and strain time series to infer the structural response of the FRW bridge. Field test data are used to calibrate a grillage model, developed for further analysis of the FRW bridge to various sets of high axle loads stipulated in the bridge design standard. Bridge behaviour predicted by the grillage model has exemplified that the live load stresses of the FRW bridge is significantly lower than the yield strength of steel and the deflections are well below the serviceability limit state set out in AS 5100. Based on the results reported in this thesis, it is concluded that the disused FRWs are competent to resist high axle loading prescribed in AS 5100 and are a viable alternative structural solution of bridge deck in the context of the low volume road networks.

Transit line passenger transmission and productiveness under high load conditions

Deterministic transit capacity analysis applies to planning, design and operational management of urban transit systems. The Transit Capacity and Quality of Service Manual (1) and Vuchic (2, 3) enable transit performance to be quantified and assessed using transit capacity and productive capacity. This paper further defines important productive performance measures of an individual transit service and transit line. Transit work (p-km) captures the transit task performed over distance. Passenger transmission (p-km/h) captures the passenger task delivered by service at speed. Transit productiveness (p-km/h) captures transit work performed over time. These measures are useful to operators in understanding their services’ or systems’ capabilities and passenger quality of service. This paper accounts for variability in utilized demand by passengers along a line and high passenger load conditions where passenger pass-up delay occurs. A hypothetical case study of an individual bus service’s operation demonstrates the usefulness of passenger transmission in comparing existing and growth scenarios. A hypothetical case study of a bus line’s operation during a peak hour window demonstrates the theory’s usefulness in examining the contribution of individual services to line productive performance. Scenarios may be assessed using this theory to benchmark or compare lines and segments, conditions, or consider improvements.

Smart grid-demand side response model for optimization air conditioning

The growing demand of air-conditioning is one of the largest contributors to Australia’s overall electricity consumption. This has started to create peak load supply problems for some electricity utilities particularly in Queensland. This research aimed to develop consumer demand side response model to assist electricity consumers to mitigate peak demand on the electrical network. The model developed demand side response model to allow consumers to manage and control air conditioning for every period, it is called intelligent control. This research investigates optimal response of end-user toward electricity price for several cases in the near future, such as: no spike, spike and probability spike price cases. The results indicate the potential of the scheme to achieve energy savings, reducing electricity bills (costs) to the consumer and targeting best economic performance for electrical generation distribution and transmission.