Dissertations / Theses on the topic 'Energy-generation methods'

High harmonic generation (HHG) is a nonlinear light matter interaction that results in the generation of high order harmonics of a driving optical field. It is routinely used to generate coherent short wavelength radiation in the soft x-ray and extreme ultraviolet (XUV) regimes. HHG-based XUV sources require a highly intense driving pulse to be focused into a target gas typically within a gas cell, gas jet or hollow capillary. They can be used for a variety of applications, one of which is nanoscale imaging. The work presented in this thesis focuses on the development of two high flux HHG sources for use in tabletop nanoscale imaging; a capillary based HHG system using a Ti:Sapphire based laser and a gas cell based HHG system using an Yb-doped fibre laser. The manufacture and use of a 7 cm hollow core capillary in HHG is described. The propagation of the pump pulse is modelled using a new nonlinear propagation model and compared to experimental results. The pulse is found to undergo pulse self-compression using a new regime of high ionisation pulse compression. The pulse is observed to reduce in length from 53 fs to 28 fs, with post compression reducing this further to 15 fs. The XUV spectrum from the 7 cm capillary is measured and its dependence on gas pressure discussed using calculations of the XUV transmission within the capillary. Using the observations made of the 7 cm capillary a new more efficient 4.5 cm capillary is designed and manufactured. Comparison between the two capillaries shows an increase in flux of the new capillary design of more than an order of magnitude, with a calculated value of 5.3x10^12 ph harm^-1 s^-1 cm^-2, one of the highest in the world. A gas cell is used in the Yb-doped fibre laser based HHG source and the XUV signal is measured using an XUV photodiode. The XUV signal is characterised by measuring its dependence on focal position, gas pressure and pump laser power. A novel method of increasing the flux by twisting of a second lens outside the vacuum chamber is discovered and was found to double the measured signal. The maximum flux for this fibre laser based HHG source is calculated and found to be 2.2x10^12 ph s^-1, the highest measured for a fibre based HHG source.

The restructuring of the electric energy market and the proliferation of intermittent renewable-energy based power generation have introduced serious challenges to power system operation emanating from the uncertainties introduced to the system variables (electricity prices, congestion levels etc.). In order to economically operate the system and efficiently run the energy market, a statistical analysis of the system variables under uncertainty is needed. Such statistical analysis can be performed through an estimation of the statistical moments of these variables. In this thesis, the Point Estimate Methods (PEMs) are applied to the optimal power flow (OPF) problem to estimate the statistical moments of the locational marginal prices (LMPs) and total generation cost under system uncertainty. An extensive mathematical examination and risk analysis of existing PEMs are performed and a new PEM scheme is introduced. The applied PEMs consist of two schemes introduced by H.P. Hong, namely, the 2n and 2n+1 schemes, and a proposed combination between Hong's and M. E Harr's schemes. The accuracy of the applied PEMs in estimating the statistical moments of system LMPs is illustrated and the performance of the suggested combination of Harr's and Hong's PEMs is shown. Moreover, the risks of the application of Hong's 2n scheme to the OPF problem are discussed by showing that it can potentially yield inaccurate LMP estimates or run into unfeasibility of the OPF problem. In addition, a new PEM configuration is also introduced. This configuration is derived from a PEM introduced by E. Rosenblueth. It can accommodate asymmetry and correlation of input random variables in a more computationally efficient manner than its Rosenblueth's counterpart.
Master of Science

Kite energy systems are an emerging renewable energy technology. Unlike conventional turbines, kite energy systems extract wind power using tethered kites which can move freely in the wind or underwater in an ocean current. Due to the mobility, kite power systems can harvest power from regions with higher and steadier power density by moving in high-speed cross flow motion. An airborne kite energy system harnesses wind power at an altitude higher than the conventional wind turbines, while an undersea kite energy system extracts power close to the ocean surface. In this dissertation, the physical limitation, mathematical modeling, and control system design of the kite energy systems are studied. First, three major physical effects that are acting on the kite energy systems are investigated, including potential force, steady aero-/hydro-dynamic force and added mass effects. Furthermore, the dissipativity of the steady aero-/hydro-dynamic forces with respect to the apparent velocity is established. Based on this analysis, the power generation limit of the kite energy systems is studied. A power limit formulation is given which generalize the two-dimensional result to three-dimensional case. The different physical phenomenon is modeled in different coordinate systems, the difference of the density, viscosity between air and water are significant, and the kite energy system can operate in two distinct modes. To combine different physical effects into a single simulation framework, the equivalences of the kite model in different coordinate systems are established through kinematic analysis. Using these equivalent relations, a unified simulation model for airborne and undersea kite energy systems are derived. The control system design of kite energy systems is also investigated. The resulting equations of motion of kite energy systems are highly nonlinear. Therefore, Lyapunov methods are used to analyze the system behavior. Three different techniques are reviewed, including Lyapunov analysis for autonomous and non-autonomous systems, the ultimate boundedness and input-to-state stability and passivity methods. For the fixed tether length kite energy systems, the ultimate boundedness of the kite translation is established through the dissipativity of the steady aero-/hydro-dynamic force. For the variable tether length kite energy system, the input-to-state analysis is used to design the tether tension that guaranteed the boundedness of the kite translation. In both cases, the Lyapunov based methods are used to design kite rotational control systems which result in PD type control signals. Although this control scheme generates consecutive power cycles for kite energy systems. It is shown that the kite aero-/hydro-dynamical performance is unstable in the simulation which could result in unsteady power generation. To provide a steadier performance in kite translation and power output, the relative dynamics of the kite translation is first proposed. In this model, the kite apparent speed and attitudes, the angle of attack and side-slip angle, are used to describe the kite translation. A nonlinear control scheme is designed to regulate the angle of attack and side-slip angle using back-stepping methods by using the kite angular velocity and control inputs. However, due to the magnitude limit of the angular velocity, the residual error of the apparent attitude tracking remain large for the large desired angle of attack and side-slip angle. To achieve a better power harvesting and aero-/hydro-dynamics performance, the geometric properties of kite angle of attack and side-slip angle are studied. A geometric attitudes trajectory is constructed to track given apparent attitudes. A rotational control system is designed based on the back-stepping and sliding mode methods for the desired geometric attitude, and the high gain observer is applied to acquire the information needed for the rotational control signal. Through the geometric apparent attitudes tracking control algorithm, the angle of attack and side-slip angle act as direct control inputs to the kite translational motion. The kite translational dynamics under the geometric apparent attitude tracking is studied. These dynamics give the possibility of controlling the kite translational motion only through the rotational control scheme.

During the operation in a modern power distribution system, some abnormal events may happen, such as over-voltage, faults, under-frequency and overloading, and so on. These abnormal events may cause a power outage in a distribution system or damages on the equipment in a distribution system. Hence these abnormal events should be identified and isolated by protection systems as quickly as possible to make sure we can maintain a stable and reliable distribution system to supply adequate electric power to the largest number of consumers as we can. To sum up, we need stable and reliable protection systems to satisfy this requirement. Chapter 1 of the dissertation is a brief introduction to my research contents. Firstly, the background of a distribution system and the protection systems in a power system will be introduced in the first subchapter. Then there will be a review of existing methods of optimum coordination of overcurrent relays using different optimal techniques. The dissertation outline will be illustrated in the end. Chapter 2 of the dissertation describes a novel method of optimum online adaptive coordination of overcurrent relays using the genetic algorithm. In this chapter, the basic idea of the proposed methods will be explained in the first subchapter. It includes the genetic algorithm concepts and details about how it works as an optimal technique. Then three different types of simulation systems will be used in this part. The first one is a basic distribution system without distributed generations (DGs); the second one is similar to the first one but with load variations; the last simulation system is similar to the first one but with a distributed generation in it. Using three different simulation systems will demonstrate that the coordination of overcurrent relays is influenced by different operating conditions of the distribution system. In Chapter 3, a larger sized distribution system with more distributed generations and loads will be simulated and used for verifying the proposed method in a more realistic environment. In addition, the effects of fault location on the optimum coordination of overcurrent relays will be discussed here. In Chapter 4, the optimal differential evolution (DE) technique will be introduced. Because of the requirement of the online adaptive function, the optimal process needs to be accomplished as soon as possible. Through the comparison between genetic algorithm and differential evolution on the optimum coordination of overcurrent relays, we found that differential evolution is much faster than the genetic algorithm, especially when the size of the distribution system grows. Therefore, the differential evolution optimal technique is more suited than the genetic algorithm to realize online adaptive function. Chapter 5 presents the conclusion of the research work that has been done in this dissertation.

The smart grid offers a new infrastructure for the management of energy demand and generation towards a sustainable future. Accordingly, there is the objective to provide consumers with a response capacity to stimuli of the electricity market, and at the same time, to efficiently manage the generation system which tends to a diversification of the generators and the energy sources. For that purpose, this thesis is first focused on providing to consumers methods for managing their energy consumption and then reducing costs according to their production activities. Next, this thesis focuses on electricity generation, tackling the problem of how to share out energy production among a set of distributed generators using self-organisation. Finally, it tackles the problem of planning the placement of new generators suing meta-heuristics.
La xarxa elèctrica intel·ligent ofereix una nova infraestructura per a la gestió de la demanda i generació d'electricitat cap a un futur més sostenible. En aquest sentit, hi ha l'objectiu de proveir els consumidors de capacitat de reacció davant d'estímuls del mercat elèctric i, al mateix temps, gestionar de forma eficient un sistema de generació que tendeix cap a una diversificació. Amb aquest objectiu, aquesta tesi primer es centra a desenvolupar mètodes perquè els consumidors puguin gestionar els seus consums i així també reduir-ne els costos d'acord amb les seves activitats de producció. Posteriorment, la tesi es centra en la generació elèctrica abordant el problema de com repartir la producció d'energia d'entre un conjunt de generadors distribuïts utilitzant mètodes auto-organitzatius. Finalment, s'aborda la planificació de nous generadors utilitzant mètodes metaheurístics.

Due to the increased demand for reliable and resilient controls in advanced power generation systems, new control methods are required to tackle traditional problems within these systems. This work discusses a control method and an estimation method for advanced control systems. The control method is sliding mode controls of a higher order, which is used to control the nonlinear wind energy conversion system while lessening the chattering phenomena that causes mechanical wear when using first order sliding mode controls. The super-twisting algorithm is used to create a second order sliding mode control. The estimation method is the derivation of a Resilient Extended Kalman filter, which can estimate and control the system through sensor undergoing failures with a binomial distribution rate and known mean value. Simulations on these dynamical systems are presented to show the effectiveness of the proposed control methods; the former is applied to a wind energy conversion system and the latter is applied to an single machine infinite bus. Both methods are also compared with more traditional methods in their respective applications, those being first order sliding mode controls and the Extended Kalman filter.

In this thesis design, optimization, fabrication and performance characterization of MEMS thermoelectric (TE) energy harvesters for harnessing waste heat in mobile systems are presented. As a proof of concept, chromium and nickel are used as the thermoelectric material in the proposed design. The feasibility of the state of the art thermoelectric materials is also discussed. MEMS TE energy harvesters proposed in this study are designed to generate power at relatively lower &Delta
T values. The performance of the MEMS TE energy harvesters was optimized using analytical and 3-D finite element models. An analytical code was used for profiling the electrical power output with varying geometry. The design points with maximum generated power were selected, and the microfabricated thermoelectric energy harvesters were designed accordingly. The fabricated devices are formed on a silicon wafer and composed of Nickel and Chromium thermocouples on SiO2/Si3N4 diaphragms, and Titanium heater and monitor resistors for testing purposes. Microfabrication was followed by the performance characterization of MEMS TE energy harvesters with the conducted tests. For 10 °
C temperature difference between the hot and cold junctions (a heat source at 35 °
C), the proposed TE energy harvesters are capable of providing 1.1 µ
W/cm2 power density and 1.71 V voltage. The performance of the thermoelectric generators in general is limited by Carnot cycle efficiency. Nevertheless, the validated practical performance of MEMS TE energy harvesters proposed in this thesis is comparable to other examples in literature. It is anticipated by the calculations that this design will be able to provide the highest thermoelectric efficiency factor (4.04 µ
W/K2cm2) among the lateral TE energy harvesters if thermoelectric materials having high Seebeck coefficient values (such as p-Si, n-Si, polysilicon, Bi2Te3 etc.) are used. According to the performance results, the MEMS TE energy harvesters can be implemented in mobile systems to convert waste heat into electricity. The fabrication process can be adapted to CMOS with some modifications if needed. The lateral MEMS thermoelectric energy harvesters can also be combined with vibration energy harvesters to realize multi-mode energy scavenging. For prospective study, vertical thermoelectric generator configurations are also discussed in order to further increase the power density generated. The finite element simulations for proposed vertical configurations with air and water convection were completed. The vertical TE generators proposed can supply up to 4.2 mW/cm2 with a heat source at a temperature of 310 K.

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CNPQ
The Distributed Generation (DG) can improve the power quality indices associated with Short Duration Voltage Variations (SDVV) due to the reduction in the electric network loading, which in turn causes an improvement in the pre-fault voltage profile. On the other hand, the DG can also deteriorates the power quality indices related to SDVV due to the increasing in the fault currents, which in turns reduce the post-fault voltages. Furthermore, the assessment of the DG impact on SDVV is more difficult with the presence of renewable energy resources. This complexity is due to fluctuations in output power caused by stochastic variations in the primary energy source (sun, wind, tide levels, etc.). Additionally, the bibliographical review on Predictive Assessment of Short Duration Voltage Variations (PAVV) revealed that none of the existing methodology considered the impact of fluctuations in the output power of a wind DG on power quality indices related to SDVV. It was also noticed that the load variations during the study period are ignored in the papers on SDVV. The existence of these deficiencies and the governmental incentives for the use of wind generation motivated this research. The main aim of this dissertation is the development of a methodology for the PAVV capable of recognizing uncertainties associated with wind DG and load fluctuations. The modeling of these uncertainties was carried out using NonSequential Monte Carlo Simulation (MCS). The nodal voltages in the fault scenarios generated by MCS were evaluated using the Admittance Summation Method (ASM) in phase coordinates. The combination of the MCS with the ASM allowed estimating the following indices related to SDVV: the expected value of the SARFI (“System Average RMS – Variation – Frequency Index”) and expected nodal frequency of SDVV. Furthermore, the probability distributions and box plots of the SARFI index have been obtained. The proposed method for the PAVV was tested and validated in a test system with 32 buses. The tests results demonstrated that the DG insertion causes an improvement in the power quality indices associated with SDVV. Additionally, the substitution of conventional DG by wind DG cause a small deterioration in the power quality indices related to SDVV due to fluctuations in the output power of the wind DG. Finally, it was observed that the load fluctuations during the study period cause significant variations in the SARFI index.
A Geração Distribuída (GD) pode melhorar os índices de qualidade de energia associados com as Variações de Tensão de Curta Duração (VTCD) devido a redução no carregamento da rede elétrica, que por sua vez causa uma melhoria no perfil de tensão pré- falta. Por outro lado, a GD também pode degradar os índices de qualidade de energia associados com VTCD devido ao aumento nas correntes de falta, que por sua vez reduzem as tensões pós-falta. Além disso, a avaliação do impacto da DG sobre VTCD é mais difícil com a presença de fontes de energia renováveis. Esta complexidade se deve as flutuações na potência de saída causadas pelas variações estocásticas na fonte de energia primária (sol, vento, níveis de maré, etc.). Adicionalmente, a revisão bibliográfica realizada sobre Avaliação Preditiva de VTCD (APVT) revelou que nenhuma metodologia existente considerou o impacto de flutuações na potência de saída de geradores eólicos nos índices de qualidade referentes às VTCD. Também foi observado que flutuações de carga ao longo do período de estudo são desconsideradas nos artigos sobre APVT. A existência destas deficiências nos métodos de APVT e os incentivos governamentais para o uso de geração eólica motivaram esta pesquisa. O principal objetivo desta dissertação é o desenvolvimento de uma metodologia para a APVT capaz de reconhecer as incertezas associadas com a GD eólica e flutuações de carga. A modelagem destas incertezas na APVT foi realizada através do uso da Simulação Monte Carlo (SMC) não-sequencial. As tensões nodais nos cenários de falta gerados pela Simulação Monte Carlo (SMC) foram calculadas usando-se o Método de Soma de Admitância (MSA) em coordenadas de fase. A combinação da SMC com o MSA permitiu estimar os seguintes índices probabilísticos relacionados com as VTCD: valor esperado do SARFI (“System Average RMS – Variation – Frequency Index”) e frequência nodal esperada de VTCD. Além disso, foram obtidas distribuições de probabilidade e diagramas de caixa associados com o SARFI. O método proposto nesta dissertação para a APVT foi testado em uma rede de distribuição de 32 barras. Os resultados dos testes mostram que a inserção de GD causa uma melhoria nos índices de qualidade associados com as VTCD. Adicionalmente, a substituição de GD convencional por GD eólica causa uma pequena deterioração nos índices de qualidade referentes às VTCD devido as flutuações na potência de saída da GD eólica. Finalmente, também foi observado que as flutuações na carga ao longo do período de estudo causam variações significativas no índice SARFI.

Recently, a lot of research work has been dedicated toward enhancing performance, reliability and integrity of distributed energy resources that are integrated into distribution networks. The problem of islanding detection and islanding prevention (i.e. anti-islanding) has stimulated a lot of research due to its role in severely compromising the safety of working personnel and resulting in equipment damages. Various Islanding Detection Methods (IDMs) have been developed within the last ten years in anticipation of the tremendous increase in the penetration of Distributed Generation (DG) in distribution system. This work proposes new IDMs that rely on transient and distributed behaviors to improve integrity and performance of DGs while maintaining multi-DG islanding detection capability. In this thesis, the following questions have been addressed: How to utilize the transient behavior arising from an islanding condition to improve detectability and robust performance of IDMs in a distributive manner? How to reduce the negative stability impact of the well-known Sandia Frequency Shift (SFS) IDM while maintaining its islanding detection capability? How to incorporate the perturbations provided by each of DGs in such a way that the negative interference of different IDMs is minimized without the need of any type of communication among the different DGs? It is shown that the proposed techniques are local, scalable and robust against different loading conditions and topology changes. Also, the proposed techniques can successfully distinguish an islanding condition from other disturbances that may occur in power system networks. This work improves the efficiency, reliability and safety of integrated DGs, which presents a necessary advance toward making electric power grids a smart grid.
Ph.D.
Doctorate
Electrical Engineering and Computer Science
Engineering and Computer Science
Electrical Engineering

Tato práce o energetickém využití čistírenských kalů obsahuje popis vlastností kalu (hustota, měrná tepelná kapacita a dynamická viskozita). Stěžejní kapitoly jsou věnovány desintegraci kalu pro zvýšení obsahu sušiny po odvodnění a experimentálnímu zkoumání tvorby emisí při spalování kalu, kde byl posuzován vliv přídavku alkálie. Spalování vysušeného kalu proběhlo ve fluidní vrstvě, byla zkoumána produkce škodlivin a distribuce těžkých kovů. Druhá ucelená část práce je věnována termochemické desintegraci stabilizovaného kalu, přičemž byl experimentálně vyhodnocován vliv na obsah vody v odvodněném kalu. Provedené experimenty sloužily k detekci vhodné teploty a dávky chemikálie. Výsledky experimentů byly rovněž podkladem pro ekonomickou bilanci, která je založena na úsporách za likvidaci menšího množství kalu.

Thesis (MScIng)--University of Stellenbosch, 2004.
ENGLISH ABSTRACT: This thesis investigates methods to extract the maximum amount of electrical energy from a py panel. The thesis is divided into four parts, focussing on different aspects relating to this topic. The first part will investigate the role that py energy is likely to play in South Africa's future energy scenario, by looking at topics like the greenhouse effect and the economics of energy production. Secondly the thesis will look at how to position py panels optimally for maximum energy generation through the year. A software model of a py panel is developed which can calculate available py energy and energy generation costs for a given location, based on parameters like the positioning of the py panel and historic weather data. Thirdly the optimal design of a maximum power point tracker is investigated. The optimal design, based on a k-sweep voltage ratio maximum power point tracking algorithm, is implemented using a DSP controlled boost converter circuit. Finally, the best methods to store energy generated using py panels are explored. Energy storage technologies are compared for rural, off-grid applications in South Africa, and the design and implementation of a pulse-charging lead-acid battery charging strategy is explained.
AFRIKAANSE OPSOMMING: Hierdie tesis ondersoek maniere waarop die maksimum hoeveelheid elektriese energie vanuit 'n py paneelonttrek kan word. Die tesis word in vier dele verdeel, wat elkeen fokus op 'n ander aspek van die onderwerp. Die eerste kyk na die rol wat PV energie potensieël kan speel in die toekomstige energie produksie binne Suid Afrika, deur te kyk na onderwerpe soos die kweekhuis effek, en die ekonomiese sy van energie produksie. Tweedens kyk die tesis na metodes om 'n py paneeloptimaal te posisioneer vir maksimum energie deur die jaar. 'n Sagteware model van 'n PV paneel word ontwikkel wat die hoeveelheid beskikbare energie, en die kostes daarvan, kan bereken vir 'n spesifieke plek, gebaseer op PV paneel data en vorige jare se atmosferiese data. Derdens word agtergrond oor maksimum drywingspunt volgers gegee, en die ontwerp en bou van 'n k-variërende, spannings verhouding maksimum kragpunt volger verduidelik, geimplimenteer deur van 'n DSP en 'n opkapper baan gebruik te maak. Laastens word die beste maniere om PV energie te stoor, vir landelike toepassings weg vanaf die Eskom netwerk, ondersoek. Alle beskikbare tegnologieë word eers vergelyk met mekaar, waarna die ontwerp en bou van 'n puls-laai loodsuur batterylaaier verduidelik word.

Because DGs are introduced into distribution systems, the coordination of fuses and reclosers doesn’t work well. It means the original protection schemes are not available for the distribution systems with DGs. This thesis paper presents the study on the impacts of DGs on the fault current and voltage in the distribution system by the simulation of a model distribution system. After we study the impacts of DG on distribution systems, there is an introduction of current several current protection schemes and fault locations methods. At last, an adaptive protection scheme with a more efficient fault location method for the distribution systems is discussed in this thesis paper.

Astrophysical models that address stellar energy generation and nucleosynthesis require a considerable amount of input from nuclear physics and are very sensitive to the detailed structure of nuclei, both stable and unstable. Radioactive nuclei play a dominant role in several stellar environments such as supernovae, X-ray bursts, novae etc. and nuclear data are important in the interpretation of these phenomena. When carbon, nitrogen and oxygen isotopes are present in substantial quantities in a star of sufficient mass, the fusion of four hydrogen nuclei to form a helium nucleus proceeds via the CNO cycles. Energy release in the CNO cycles is limited by the long lifetimes of 14O and 15O. In explosive stellar scenarios such as X-ray bursts, the energy output is very large, suggesting a breakout from the CNO cycles. 15O(α,γ)19Ne is the first reaction that breaks out of the CNO cycle. Nuclear structure information on high lying states in 19Ne is required to calculate the rate of the 15O(α,γ)19Ne reaction. This work focuses on the study of states in 19Ne above 3.53 MeV. The lifetimes of five states in 19Ne above 3.53 MeV were measured in this work. The states in 19Ne were populated via the 3He(20Ne,α)19Ne reaction at a beam energy of 34 MeV. The lifetimes were measured using the Doppler Shift Attenuation Method. The lifetimes of five states were measured and an upper limit was set on the lifetime of a sixth state. Three of the measurements are the most precise thus far. The lifetimes of the other three states agree with the values of the only other measurement of the lifetimes of these states. An upper limit on the rate of the 15O(α,γ)19Ne reaction was calculated at the 90% confidence level using the measured lifetimes. The contributions to the 15O(α,γ)19Ne reaction rate from several states in 19Ne at different stellar temperatures are discussed.

Firstly, this dissertation proposes a new characterization and classification method for daily sky conditions by using the daily sky clearness index (KD) and the daily probability of persistence (POP-KD) that can be derived from ground-based irradiance measurement data. Quality of daily solar irradiance is characterized by a newly proposed parameter, POP-KD. This characterized daily quality is varying and uncertain at the middle level of the quantity, but high and more certain at very high and low quantity levels. In addition, the proposed characterization method shows interesting results for KD and POP-KD: a statistical consistency for multiple years and similarity for their seasonal trends. The classification results also indicate an existence of dominant classes, and transitions between the dominant classes are significant for all locations. This dissertation also generates annual synthetic sequences of KD and POP-KD using a Markov approach. The generated sequences show statistical similarities with observed sequences. Secondly, this dissertation proposes methodologies to estimate day-ahead solar irradiance using the National Weather Service (NWS) sky cover forecast. For model development, this paper splits up a direct estimation process from the sky cover forecast to solar irradiance into two stages: forecast verification and cloud-to-irradiance conversion. Uncertainty for each stage and for the overall estimation process is quantified. NWS forecast uncertainty (about 20%) is identified as the main source of uncertainty for the overall process. In addition, verification of the sky cover forecast shows approximately 20% overestimated bias at days with a high irradiance level. Thus, the NWS sky cover forecast needs to be adjusted based on the type of day. This dissertation also proposes a conversion equation relating daily quantity of cloud information and daily quantity of solar irradiance. The proposed conversion equation achieves accuracy with simplicity. Five day-ahead solar irradiance quantity estimation methods are proposed in this dissertation. The proposed methods incorporate different schemes for dealing with the bias discovered in the cloud forecast. The observed data are regularly found within the 95% confidence intervals of the estimated values. Estimation results demonstrate the effectiveness of the conditional adjustment schemes at different irradiance levels. Lastly, this dissertation proposes a methodology to estimate day-ahead solar irradiance using fluctuation information of the NWS sky cover forecast. POP-KD was used as a parameter for the quality of daily solar irradiance. POP-KD efficiently represents the quality of daily solar irradiance. In addition, POP-KD indicates the probability that solar irradiance variability is within the ramp rates of common generators in power systems at a certain photovoltaic penetration level. This dissertation also proposes a new equation for the conversion from cloud fluctuation information to daily quality of surface solar irradiance. The proposed equation achieves accuracy. The proposed day-ahead solar irradiance quality estimation method is based on fluctuation information provided by the NWS sky cover forecast. This method uses a normalization approach to relate fluctuation of cloud forecast and fluctuation of cloud observation. The observed data are regularly found within the 95% CIs of the estimated values.
Ph. D.

A novel probabilistic method has been developed for modelling the operation of energy storage in electricity systems with significant amounts of wind and solar powered generation. This method is based on a spectral analysis of the variations of wind speed and solar irradiance together with profiles of electrical demand. The method has been embodied in two Matlab computer programs: Wind power only: This program models wind power on any time scale from seconds to years, with limited modelling of demand profiles. This program is only capable of modelling stand-alone systems, or systems in which the electrical demand is replaced by a weak grid connection with limited export capacity. 24-hours: This program models wind power, solar PV power and electrical demand, including seasonal and diurnal effects of each. However, this program only models store cycle times (variations within a time scale) of 24 hours. This program is capable of modelling local electrical demand at the same time as a grid connection with import or export capacity and a backup generator. Each of these programs has been validated by comparing its results with those from a time step program, making four Matlab programs in total. All four programs calculate the power flows to and from the store, satisfied demand, unsatisfied demand and curtailed power. The programs also predict the fractions of time that the store spends full, empty, filling or emptying. The results obtained are promising. Probabilistic program results agree well with time step results over a wide range of input data and time scales. The probabilistic method needs further refinement, but can be used to perform initial modelling and feasibility studies for renewable energy systems. The probabilistic method has the advantage that the required input data is less, and the computer run time is reduced, compared to the time step method.

Nowadays islanding has become a big issue with the increasing use of distributed generators in power system. In order to effectively detect islanding after DG disconnects from main source, author first studied two passive islanding methods in this thesis: THD&VU method and wavelet-transform method. Compared with other passive methods, each of them has small non-detection zone, but both of them are based on the threshold limit, which is very hard to set. What’s more, when these two methods were applied to practical signals distorted with noise, they performed worse than anticipated. Thus, a new composite intelligent based method is presented in this thesis to solve the drawbacks above. The proposed method first uses wavelet-transform to detect the occurrence of events (including islanding and non-islanding) due to its sensitivity of sudden change. Then this approach utilizes artificial neural network (ANN) to classify islanding and non-islanding events. In this process, three features based on THD&VU are extracted as the input of ANN classifier. The performance of proposed method was tested on two typical distribution networks. The obtained results of two cases indicated the developed method can effectively detect islanding with low misclassification.

Thèse de doctorat : Sciences de l'Ingénieur : Strasbourg 1 : 2007. Thèse de doctorat : Sciences de l'Ingénieur : Wroclaw - Pologne : 2007.
Thèse soutenue en co-tutelle. Titre provenant de l'écran-titre. Bibliogr. p. 147-150.

Le problème pratique support de la thèse concerne l’optimisation de la stratégie de production journalière d’énergie électrique et thermique urbaine de la société GENCO. Le support informatique au processus d’optimisation en place à savoir le logiciel BoFiT TEP (Daily Operation Optimization and Portfolio Management) permet de construire un modèle simulant le fonctionnement du réseau de centrales. Le résultat du processus de décision est un scénario de production obtenu par un processus itératif. Pour initier le processus, un expert propose un scénario à partir de données liées au marché. Les caractéristiques des scénarios de production sont fournies au logiciel BoFiT TEP qui dans un premier temps les transforme en un problème d’optimisation de type mixed integer problem (MIP) dont le but est de trouver la combinaison de ressources du réseau à faire fonctionner au moindre coût et dans les contraintes du scénario. L’optimisation est ensuite réalisée par un outil standard CPLEX. L’expert analyse ensuite le résultat pour le valider ou proposer un nouveau scénario. Le processus se poursuit dans un temps limité (1h) et une décision est prise par l’expert. Les temps de calcul sont considérés comme trop long car ils ne permettent pas à l’expert de réaliser suffisamment d’itérations. Les temps de calcul augmentent avec le nombre d’éléments de détails mis dans le modèle. Le problème initial peut être exprimé sous la forme d’une contradiction : nous voulons avoir beaucoup d'éléments dans le modèle afin d'améliorer la stratégie de production (maximisation du bénéfice pour GENCO), et en même temps nous ne voulons pas avoir pas beaucoup d'éléments dans le modèle parce que la consommation de temps du processus de calcul augmente avec le volume de données à traiter. [Figure 1. Processus de production de scénario] La compréhension approfondie du système de production de scénarios en vue de son optimisation n’est pas immédiate pour plusieurs raisons :Le nombre de variables à traiter est important et évolue dans le temps, Le processus de préparation des scénarios relève de connaissances de plusieurs domaines, le marché et les statistiques, les divers modèles de production d’énergie, des processus de calcul. Certaines activités du processus, notamment la production de scénarios et leur validation, relèvent de connaissances implicites. En fait, l’interface entre les modèles cités précédemment n’est pas formalisée. Pour les raisons évoquées précédemment, une perception de l’influence des différents systèmes composant le processus de production de scénarios sur son optimisation s’avère nécessaire. L’un des objectifs de cette thèse est de proposer une démarche et des outils permettant d’identifier les problèmes clés liés à l’évolution du processus de production des scénarios et de donner une vision de leurs liens, d’aider à la prise de décision quant aux tactiques de résolution et, enfin, de mettre en forme cet ensemble de problèmes dans un formalisme permettant l’utilisation itérative d’outils et de méthodes de résolution de problèmes inventifs. Ce dernier point est nécessaires dans notre cas, car l’optimisation individuelle des éléments du système de production de scénario ne permettra pas de satisfaire les performances attendues à terme du système ; il faudra donc modifier le modèle du système, en inventer un nouveau qui résoudra des contradictions inhérentes au système existant. En principe, différents outils et méthodes générales sont disponibles pour atteindre les résultats escomptés cités dans le paragraphe précédent. Deux approches s’opposent pour l’exploitation de ces outils. La première consiste à choisir un outil générique d’analyse de notre système et de l’adapter au problème traité. La seconde approche, que nous avons choisie, est de combiner des méthodes existantes pour tirer profit des valeurs ajoutées de leurs différences. La difficulté lors de l’emploi de cette tactique est de combiner à bon escient et de contrôler l’extraction de l’information utile au traitement de notre problème spécifique. En effet, d’une part les informations issues de ces méthodes se recouvrent partiellement et, d’autre part, les informations de différentes natures issues de ces méthodes sont à mettre en cohérence. Le second objectif de cette thèse est d’apporter une contribution méthodologique aux démarches générales d’analyse de systèmes complexes en vue de la résolution des contradictions associées à leur évolution (i. E : les résultats de l’analyse doivent permettre l’utilisation des méthodes de résolution de problème issues des théories de résolution des problèmes inventifs). En terme de conception de méthode, le conflit à résoudre est résumé sur la figure 2 ci-dessous. [Figure 2: Contradiction associée à la construction de la méthode d’analyse] La méthode proposée en résultat de nos travaux repose sur la maîtrise et le contrôle des différents outils utilisés à partir d’une classification en trois familles: Les outils d’exploration qui permettent de décrire et d’explorer le système étudié, Les outils permettant d’orienter et de guider vers les étapes suivantes, Les outils de gestion de l’information et d’évaluation. Le mémoire se compose de 6 chapitres. Le chapitre 1 décrit les approches connues d'analyse des systèmes complexes et formule le problème méthodologique abordé dans cette étude. Le chapitre 2 présente le système préparation et de validation de scénarios de production d’énergie. Le chapitre 3 présente la catégorisation des outils d’analyse utilisés pour le traitement du cas d’étude. Le chapitre 4 aborde l’utilisation d’outils d’analyse proposés sur le cas de la génération d’une stratégie de production. Le chapitre 5 présente la méthode proposée. La conclusion et les perspectives du travail sont présentées dans le chapitre 6. Portée et buts L'introduction présente en détail les propriétés de quelques approches de résolution de problème et d’analyse de système complexe (théorie des agents, théorie des systèmes dynamiques, etc. . ). Les caractéristiques principales d’un système complexe sont présentées sur l'exemple des systèmes traités en ingénierie de l’environnement. La comparaison des approches existantes et des caractéristiques des systèmes complexes est employée pour formuler le but et la portée de notre recherche. Le système de préparation de la stratégie journalière de production Le système de préparation des stratégies de production journalière est introduit dans ce chapitre. Le système est décrit de plusieurs points de vue : sa position dans l’environnement, le processus de prise de décision. L’utilisation du modèle technologique et des scénarios par le logiciel BoFiT TEP sont également présentés. Outils d'analyse - introduction Les outils d'analyse utilisés sont classés dans les catégories suivantes : des théories, des méthodes, des techniques, des procédures, des règles, des modèles et des concepts. Des outils d'analyse appliqués dans le chapitre suivant sont classés selon la description de l'objectif et du domaine d'application. Analyse du problème de préparation de scénarios L'analyse du problème de la préparation de la génération d'énergie débute par l'application d’outils simples permettant de collecter l’information de base sur le système. Ce type d’outils est appelé par la suite « outils d’exploration ». Ces outils sont complétés par des outils d’organisation des résultats de l’analyse. Synthèse et généralisation : l’approche proposée La construction de cette approche a été effectuée pendant lors de l’analyse du système de préparation des scénarios. La méthode d’analyse peut elle aussi être considérée comme un système d’activités. L’analyse de ce système montre qu’il lui manque un système de contrôle. Ce système de contrôle de l’analyse est porte sur trois points : l’exploration du système, une aide à l’orientation des activités suivantes, et enfin la gestion des informations. Le rôle du système de contrôle est de combiner judicieusement et d’aligner les méthodes existantes au cas particulier traité. Ainsi les outils existants utilisés lors d’une étude ne sont pas connus au départ de l’application de la méthode. Conclusion et perspectives La méthode proposée permet de tirer parti de l’utilisation de plusieurs méthodes sans en avoir les inconvénients pratiques grâce au système de contrôle de l’information. Cette approche permet de construire en temps réel la démarche adaptée à un système donné. Cette approche a permis dans le cas de la préparation des stratégies journalières de production d’énergie d’améliorer la communication avec les experts de divers domaines, d’avoir une compréhension globale et partagée entre experts des problèmes clés, et enfin d’avoir une meilleure compréhension des sous problèmes.

A utilização da energia eólica é ainda recente no setor elétrico e, por isso, apresenta inúmeros desafios na operação e integração dessa nova tecnologia com o sistema elétrico. Desta forma, este trabalho aborda o impacto da injeção de correntes harmônicas que as Centrais de Geração Eólica geram no Sistema Interligado Nacional. Inicialmente, aborda-se a fundamentação teórica e o conceito básico da energia eólica, principalmente em relação ao panorama desta fonte renovável no Brasil e no mundo e, de uma forma sucinta, aborda-se também sobre o aspecto tecnológico dos aerogeradores. Outro aspecto relevante deste trabalho, é o levantamento do estado da arte sobre os conceitos e cálculos das distorções harmônicas, bem como sobre o processo de integração das novas Centrais de Geração Eólica à rede básica. O principal resultado obtido neste trabalho, é o estudo de sensibilidade da distorção harmônica de tensão, no ponto de acoplamento da Central à rede básica de transmissão, frente à variação topológica da rede coletora da Central de Geração Eólica. Para tal estudo, foi modelada uma Central de Geração Eólica e aplicadas as metodologias estudadas no estado da arte. Os resultados obtidos do estudo de sensibilidade, é de grande interesse para os operadores da rede e transmissão de energia elétrica, bem como às geradoras de energia eólica.
The use of wind energy is still recent in the electric sector and, therefore, presents numerous challenges in the operation and integration of this new technology with the electric system. In this way, this work approaches the impact of the injection of harmonic currents generated by the Wind Generation Plants in the National Interconnected System. Initially, it addresses the theoretical basis and the basic concept of wind energy, mainly in relation to the panorama of this renewable source in Brazil and in the world and, briefly, it also addresses the technological aspect of wind turbines. Another relevant aspect of this work is the state of the art survey on the concepts and calculations of harmonic distortions, as well as on the integration process of the new Wind Generation Plants into the basic grid. The main result obtained in this work is the sensitivity study of the harmonic distortion of voltage at the coupling point of the Central to the basic transmission network, in front of the topological variation of the collecting network of the Wind Generation Plant. For such study, a Wind Generation Plant was modeled and the methodologies studied in the state of the art were applied. The results obtained from the sensitivity study, is of great interest to the network operators and transmission of electricity, as well as to wind power generators.

Attempts to reduce greenhouse gas emissions are promising with the recent dramatic increase of installed renewable energy sources (RES) capacity. Integration of large intermittent renewable resources affects smart grid systems in several significant ways, such as transient and voltage stability, existing protection scheme, and power leveling and energy balancing. To protect the grid from threats related to these issues, utilities impose rigorous technical requirements, more importantly, focusing on fault ride through requirements and active/reactive power responses following disturbances. This dissertation is aimed at developing and verifying the advanced and algorithmic methods for specification of protection schemes, reactive power capability and power control requirements for interconnection of the RESs to the smart grid systems. The first findings of this dissertation verified that the integration of large RESs become more promising from the energy-saving, and downsizing perspective by introducing a resistive superconducting fault current limiter (SFCL) as a self-healing equipment. The proposed SFCL decreased the activation of the conventional control scheme for the wind power plant (WPP), such as dc braking chopper and fast pitch angle control systems, thereby increased the reliability of the system. A static synchronous compensator (STATCOM) has been proposed to assist with the uninterrupted operation of the doubly-fed induction generators (DFIGs)-based WTs during grid disturbances. The key motivation of this study was to design a new computational intelligence technique based on a multi-objective optimization problem (MOP), for the online coordinated reactive power control between the DFIG and the STATCOM in order to improve the low voltage ride-through (LVRT) capability of the WT during the fault, and to smooth low-frequency oscillations of the active power during the recovery. Furthermore, the application of a three-phase single-stage module-integrated converter (MIC) incorporated into a grid-tied photovoltaic (PV) system was investigated in this dissertation. A new current control scheme based on multivariable PI controller, with a faster dynamic and superior axis decoupling capability compared with the conventional PI control method, was developed and experimentally evaluated for three-phase PV MIC system. Finally, a study was conducted based on the framework of stochastic game theory to enable a power system to dynamically survive concurrent severe multi-failure events, before such failures turn into a full blown cascading failure. This effort provides reliable strategies in the form of insightful guidelines on how to deploy limited budgets for protecting critical components of the smart grid systems.

As fontes renováveis de energia, em especial a energia solar fotovoltaica vem ganhando espaço nos últimos anos devido ao avanço da tecnologia, redução dos custos e redução das fontes não-renováveis. Os painéis fotovoltaicos isoladamente ou para pequenas aplicações geram uma baixa tensão de saída e a adequação dos níveis de tensão fornecidos em sua saída aos requeridos pela concessionária de energia elétrica é um desafio. Neste trabalho é apresentada uma nova estrutura modificada da topologia do conversor SEPIC que usa as técnicas de acoplamento magnético série e células multiplicadoras de tensão em conjunto, afim de obter um elevado ganho de tensão, visando a aplicação em fontes renováveis de energia. Optou-se pela solução não isolada, pois esta apresenta diversas vantagens em relação a solução isolada, como: menor peso, volume, custo e maior eficiência energética devido a menores perdas de potência nos indutores acoplados. Também, a utilização da indutância de dispersão, que é um parâmetro intrínseco de um acoplamento magnético, permite a operação com comutação suave ZCS (ZCS, do inglês Zero Current-Switching) no interruptor, aumentando a eficiência da estrutura com a redução das perdas por comutação. No decorrer do trabalho são realizadas as análises das etapas de operação de diversos conversores a partir do conversor SEPIC modificado, evolui-se pela adição de técnicas elevadoras de tensão até a estrutura proposta neste trabalho. Por fim, é realizado o controle em malha fechada utilizando um controlador PID analógico que fornece uma resposta rápida e consequente correção a possíveis mudanças na variável controlada. Os resultados teóricos e experimentais do conversor proposto são descritos neste trabalho para validar as análises desenvolvidas e demonstrar a eficiência da estrutura. O protótipo é desenvolvido para uma aplicação com potência nominal de 200 W, tensão nominal de saída igual a 450 V e uma tensão de entrada variando entre 20 V e 40 V. O rendimento obtido para o conversor proposto operando na frequência de 35 kHz na potência nominal é de 91,28% e eficiência igual a 89,04% para a potência nominal de 200 W na frequência de 90 kHz.
The renewable energy resources, in special the photovoltaic energy has been achieve more space in last years due to technology advances, cost reduction and decrease of the non-renewable energy sources. The photovoltaic panels in isolation or to small applications generate a low output voltage and to comply with of voltage levels provided in panel’s output to those required by electric power concessionaire is a challenge. In this work is presented a new structure modified of the SEPIC converter topology who uses the coupling magnetic series and voltage multiplier cell techniques together, in order to obtain a high voltage gain aiming at application in renewable energy resources. It was has been choosen non-isolated solution, because this present several advantages in relation to the isolated solution, such as: lower weight, volume, cost and high energy efficiency due to smaller power losses in the coupled inductors. The use leakage inductance, who is an intrinsic parameter of the a magnetic coupling, allows soft-switching operation ZCS in switch, increasing the structure’s efficiency with reduction of switching losses. During the work are perform the analysis of the operation steps of several converters as of the modified SEPIC converter and evolves by addition high voltage techniques until the structure proposed in this work. Finally, is performed the closed loop control using the analog PID controller who provides a fast response and consequent correction to possible changes in the controlled variable. The theoretical and experimental results of the proposed converter are described in this work to validate the developed analysis and demonstrate the structure’s efficiency. The prototype is developed to a application with nominal power of 200 W, nominal output voltage equal 450 V and an input voltage varying between 20 V and 40 V. The efficiency obtained to proposed converter operating in frequency of the 35 kHz in nominal power is 91,28% and efficiency equal 89,04% to nominal power in frequency of the 90 kHz.

Orientadores: Ieda Geriberto Hidalgo, Paulo de Barros Correia
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica
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Resumo: A geração de energia elétrica a partir de fontes renováveis constitui uma alternativa interessante para a diversificação da matriz energética de um país. No Brasil, o programa de incentivo às fontes alternativas de energia elétrica (Proinfa), instituído em 2004, teve como objetivo promover a diversificação da matriz energética, buscar alternativas para aumentar a segurança no abastecimento de energia elétrica e permitir a valorização das características e potencialidades regionais e locais. Dentre as fontes renováveis de geração de energia, o destaque deste trabalho é para a biomassa, utilizando o bagaço da cana-de-açúcar. O bagaço da cana é produzido em grandes quantidades no Brasil e possui 1/3 do conteúdo energético da cana. Este recurso permite a geração de energia descentralizada. No setor elétrico brasileiro, a contratação de energia proveniente de empreendimentos de geração a partir do bagaço da cana-de-açúcar pode ser formalizada por meio dos leilões de energia de reserva. A análise de projetos para empreendimentos deste tipo envolve duas variáveis estocásticas: a geração de energia (que depende da disponibilidade do recurso ¿ período sazonal) e o valor da energia no mercado de curto prazo (que depende das condições hidrológicas). Portanto, este trabalho apresenta um modelo de valoração probabilística, para empreendimentos de geração a partir do bagaço da cana-de-açúcar, em leilão de energia de reserva. Esta valoração é feita sob a ótica do empreendedor que deve saber qual é o limite do seu lance no leilão. Deste modo, o destaque da valoração probabilística é para o valor presente líquido (VPL), que determina a medida da probabilidade de ganho ou perda para o empreendedor que participa no leilão de energia de reserva. O método de simulação de Monte Carlo e o fluxo de caixa livre descontado são utilizados para a valoração probabilística. Três estudos de casos são apresentados para uma usina de geração de energia de São Paulo. Para cada cenário simulado, a distribuição de probabilidade do VPL, o VPL médio e a taxa interna de retorno (TIR), que faz com que o VPL médio seja nulo, são calculados. Avalia-se a sensibilidade do retorno do empreendimento para diferentes valores de investimento, taxa mínima de atratividade (TMA) e lance. Os resultados deste trabalho indicam que o benefício, representado pelo VPL do empreendimento, é muito sensível ao valor do lance. Conclui-se também, que a metodologia apresentada pode ser empregada como um instrumento para que os empreendedores, que participam de leilões de contratação de energia possam avaliar o riscos de ter uma perda, decorrente do seu lance dado no leilão
Abstract: Electricity generation from renewable sources is an interesting alternative to diversify the energy matrix of a country. In Brazil, the incentive program for alternative electricity sources (Proinfa), established in 2004, had as goals, promoting the diversification of energy matrix, looking for alternatives to increase energy supply security and allowing the enhancement of the regional and local characteristics and potentials. Among the renewable sources of energy generation, the highlight of this work is to biomass, using bagasse from sugarcane. The bagasse is produced in large quantities in Brazil and it has one third of the sugarcane energy content. This source allows a decentralized power generation. In the Brazilian electricity sector, energy contracting from generation projects that use sugarcane bagasse, as a source, can be formalized through reserve energy auctions. The analysis of this type of projects involves two stochastic variables. Power generation (which depends on the resource availability - seasonal period) and energy price in the spot market (which depends on the hydrological conditions). Therefore, this work presents a probabilistic valuation model for generation projects that use sugarcane bagasse and commercialize energy in reserve energy auctions. This valuation is made from the entrepreneur perspective, who must know which is his auction bidding limit. Thus, the highlight of probabilistic valuation is for the net present value (VPL), which determines the probability measure of gain or loss, for the entrepreneur participating in the reserve energy auction. The Monte Carlo simulation method and the discounted free cash flow are used for the probabilistic valuation. Three case studies are presented for a power generation plant located in São Paulo state. For each simulated scenario, the probability distribution of VPL, the average VPL and the internal return rate (TIR), that make average VPL to be zero, are calculated. Sensitivity of the project¿s return is evaluated to different investment values, minimum acceptable rates of return (TMAs) and auction biddings. The results in this study indicate that the earns, represented by venture VPL, are highly sensitive to auction bidding value. It is also concluded that the methodology presented can be used as an instrument to assist investors, participating in reserve power auctions, in assessing the risk of loss, resulting from its auction bidding
Mestrado
Planejamento de Sistemas Energeticos
Mestra em Planejamento de Sistemas Energéticos

This thesis presents work on a holistic approach for improving the overall design of solar cooling systems driven by solar thermal collectors. Newly developed methods for thermodynamic optimization of hydraulics and control were used to redesign an existing pilot plant. Measurements taken from the newly developed system show an 81% increase of the Solar Cooling Efficiency (SCEth) factor compared to the original pilot system. In addition to the improvements in system design, new efficiency factors for benchmarking solar cooling systems are presented. The Solar Supply Efficiency (SSEth) factor provides a means of quantifying the quality of solar thermal charging systems relative to the usable heat to drive the sorption process. The product of the SSEth with the already established COPth of the chiller, leads to the SCEth factor which, for the first time, provides a clear and concise benchmarking method for the overall design of solar cooling systems. Furthermore, the definition of a coefficient of performance, including irreversibilities from energy conversion (COPcon), enables a direct comparison of compression and sorption chiller technology. This new performance metric is applicable to all low-temperature heat-supply machines for direct comparison of different types or technologies. The achieved findings of this work led to an optimized generic design for solar cooling systems, which was successfully transferred to the market.

This dissertation examines the application of various classical root finding methods to digital maximum power point tracking (DMPPT). An overview of root finding methods such as the Newton Raphson Method (NRM), Secant Method (SM), Bisection Method (BSM), Regula Falsi Method (RFM) and a proposed Modified Regula Falsi Method (MRFM) applied to photovoltaic (PV) applications is presented. These methods are compared among themselves. Some of their features are also compared with other commonly used maximum power point (MPP) tracking methods. Issues found when implementing these root finding methods based on continuous variables in a digital domain are explored. Some of these discussed issues include numerical stability, digital implementation of differential operators, and quantization error. Convergence speed is also explored. The analysis is used to provide practical insights into the design of a DMPPT based on classical root finding algorithms. A new DMPPT based on a MRFM is proposed and used as the basis for the discussion. It is shown that this proposed method is faster than the other discussed methods that ensure convergence to the MPP. The discussion is approached from a practical perspective and also includes theoretical analysis to support the observations. Extensive simulation and experimental results with hardware prototypes verify the analysis.
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碩士
國立彰化師範大學
機電工程學系
106
Taiwan is densely populated and the redevelopment of the wind farm in the onshore area is limited. Compared to the onshore wind farm, the offshore wind farm is richer in resources and has not yet been developed. It has obtained a more reliable assessment of the wind energy in the western Taiwan sea area. Follow-up on the development of wind farms in the western coast of Taiwan is even more important. The geographical position of the Taiwan Strait is unique. According to a survey conducted by an international research institute, the average wind energy density in the coastal areas of Taiwan exceeds 750 W/m^2, especially wind speeds of over 7 meters per second, which are rare in the world. With an area of 2,300 square kilometers, Changhua Offshore Wind Farm has 4GW of huge wind capacity. Accounting for 56% of the total wind power generation in Taiwan. The investment and development of an offshore wind farm is in the tens of billions to 100 billion. The assessment of wind energy at the site is particularly important, and it will be a key to investment profitability. Offshore wind power generation in Taiwan is still in its infancy. At present, there is not much research on wind power in Changhua wind farm. This paper is different from satellite observation or numerical simulation of wind energy, using the Taipower company has just completed the construction of wind energy data collected by the Meteorological Observation Tower, using a variety of MCP (Measure correlate Predict) method, to regress to Changfeng offshoe wind farm ten years of wind The data can be used to analyze the wind energy of Changhua site more accurately and objectively and estimate the wind farm power generation.

Cheap and reliable electricity is an essential stimulus for economic and social development. Currently fossil fuels are used for the majority of global electricity generation, but energy shortages and pressure on all industries to reduce CO2 emissions provide incentives for growing emphasis on the development of alternative energy-generation methods. Presently hydropower contributes about 17% of global energy generation, which is only a fraction of its total potential. In Africa only 5% of its estimated hydropower potential has been exploited, making it the most underdeveloped continent in terms of hydropower. An often overlooked source of hydropower energy is found in conduits, where pressure-reducing stations (PRSs) are installed to dissipate excess energy. The energy dissipated by these devices can instead be captured as hydroelectricity if turbines are installed in the conduits, either by replacing pressure-reducing valves (PRVs) with a turbine, or by installing the turbine in parallel with the PRV. An initial scoping investigation indicated that significant potential exists for small-scale hydropower installations in water-distribution systems in South Africa. Almost all of the country’s municipalities and water-supply utilities have pressure-dissipating stations in their water-distribution systems, where hydropower potential may exist. This dissertation reflects the development of a Conduit Hydropower Decision Support System (CHDSS), summarised in a series of flow diagrams that illustrate the developmental process (Figure i(a) provides an example). A Conduit Hydropower Development (CHD) Tool was developed to facilitate the calculation of necessary factors (the Phase 1 Economic Analysis is shown in Figure i(b)). The objective of this CHDSS was to assist municipalities and engineers in identifying conduit hydropower potential in South Africa and to provide proper guidance for the development of potential sites.
Dissertation (MEng)--University of Pretoria, 2013.
gm2014
Civil Engineering
Unrestricted

No
This paper proposes a hybrid optimization method for optimal allocation of wind turbines (WTs) that combines a fast and elitist multiobjective genetic algorithm (MO-GA) and the market-based optimal power flow (OPF) to jointly minimize the total energy losses and maximize the net present value associated with the WT investment over a planning horizon. The method is conceived for distributed-generator-owning distribution network operators to find the optimal numbers and sizes of WTs among different potential combinations. MO-GA is used to select, among all the candidate buses, the optimal sites and sizes of WTs. A nondominated sorting GA II procedure is used for finding multiple Pareto-optimal solutions in a multiobjective optimization problem, while market-based OPF is used to simulate an electricity market session. The effectiveness of the method is demonstrated with an 84-bus 11.4-kV radial distribution system.

The United State’s renewable portfolio standards call for a large increase of renewable energy and improved conservation efforts over today’s current system. Wind will play a ma jor role in meeting the renewable portfolio standards. As a result, the amount of wind capacity and generation has been growing exponentially over the past 10 to 15 years. The proposed unit commitment method integrates wind energy into a scheduable resource while keeping the formulation simple using mixed integer programming. A reserve constraint is developed and added to unit commitment giving the forecasted wind energy an effective cost. The reserve constraint can be scaled based on the needs of the system: cost, reliability, or the penetration of wind energy. The results show that approximately 24% of the load can be met in the given test system, while keeping a constant reliability before and after wind is introduced. This amount of wind will alone meet many of the renewable portfolio standards in the United States.

The capacity value (CV) of a power generation unit indicates the extent to which it contributes to the generation system adequacy of a region’s bulk power system. Given the capricious nature of the wind resource, determining wind generation’s CV is nontrivial, but can be understood simply as how well its power output temporally correlates with a region’s electricity load during times of system need. Both wind generation and load are governed by weather phenomena that exhibit variability across all timescales, including low frequency weather cycles that span decades. Thus, a data-driven determination of wind’s CV should involve the use of long-term (i.e., multiple decades) coincident load and wind data. In addition to the challenge of finding high-quality, long-term wind data, existing load data more than several years old is of limited utility due to shifting end usage patterns that alter a region’s electricity load profile. Due to a lack of long-term data, current industry practice does not adequately account for the effects of weather variability in CV calculations. To that end, the objective of this thesis is to develop a model to “hindcast” what the historic regional load in New England would have been if governed by the conjoined influence of historic weather and a more current load profile. Modeling focuses exclusively on summer weekdays since this period is typically the most influential on CV. The summer weekday model is developed using multiple linear regression (MLR), and features a separate hour-based model for eight sub-regions within New England. A total of eighty-four candidate weather predictors are made available to the model, including lagged temperature, humidity, and solar insolation variables. A reanalysis weather dataset produced by the National Aeronautics and Space Administration (NASA) – the Modern Era Retrospective-Analysis for Research and Applications (MERRA) dataset – is used since it offers data homogeneity throughout New England over multiple decades, and includes atmospheric fields that may be used for long-term wind resource characterization. Weather regressors are selected using both stepwise regression and a genetic algorithm(GA) based method, and the resulting models and their performance are compared. To avoid a tendency for overfitting, the GA-based method employs triple cross-validation as a fitness function. Results indicate a regional mean absolute percent error (MAPE) of less than 3% over all hours of the summer weekday period, suggesting that the modeling approach developed as part of this research has merit and that further development of the hindcasting model is warranted.

This thesis presents a method for reliability assessment of a power grid with distributed generation providing support to the system. The distributed generation units considered for this assessment are Combined Heat and Power (CHP) units operated by individual customers at their site. CHP refers to the simultaneous generation of useful electric and thermal energy. CHP systems have received more attention recently due to their high overall efficiency combined with decrease in costs and increase in reliability. A composite system adequacy assessment, which includes the two main components of the power grid viz., Generation and Distribution, is done using Monte Carlo simulation. The State Duration Sampling approach is used to obtain the operating history of the generation and the distribution system components from which the reliability indices are calculated. The basic data and the topology used in the analysis are based on the Institution of Electrical and Electronics Engineers - Reliability Test System (IEEE-RTS) and distribution system for bus 2 of the IEEE-Reliability Busbar Test System (IEEE-RBTS). The reliability index Loss of Energy Expectation (LOEE) is used to assess the overall system reliability and the index Average Energy Not Supplied (AENS) is used to assess the individual customer reliability. CHP reliability information was obtained from actual data for systems operating in New England and New York. The significance of the results obtained is discussed.