This thesis presents methods for voltage management in distribution systems with high photovoltaic (PV) power production. The high PV penetration leads to both new challenges such as voltage profile violation and reverse power flow, and also new opportunities. Traditionally, the voltage control in the distribution network is achieved by common devices in the networks such as capacitor banks, static synchronous compensators (STATCOMs) and on-load tap changers (OLTCs). This thesis has considered existing reactive power capable solar PV inverters together with STATCOMs to provide voltage support for the distribution network. In this thesis, two effective coordination methods using the STATCOM and PV inverters are developed in order to study their interaction and how they together can stabilize the voltage level. Data from existing low-voltage (LV) and medium-voltage (MV) networks are used for a case study. The first control method is developed for LV network’s voltage control by means of PV inverter and STATCOM. The second control method is developed for both LV and MV networks’ voltage control, where reactive power control in PV inverters and STATCOMs are used in the LV network and only STATCOMs in the MV network. The control methods follow a hierarchical structure where reactive power compensation using PV inverters are prioritized. The STATCOMs, first in the LV and thereafter in the MV network in the second control method, are used only when the PV inverters are not able to provide or consume enough reactive power. This is beneficial due to the significant reduction in numbers of STATCOMs and their operation. The simulation results indicate that the proposed method is able to control both the over- and undervoltage situations for the test distribution networks. It is also shown that reactive power supply at night by the PV inverters can be an important resource for effective voltage regulation by using the proposed coordinated voltage control method.

This dissertation contains a strategy to minimize the non-technical electrical energy losses in an electrical distribution network. In order to develop the strategy, a model was constructed that simulates an electrical distribution network and includes different parameters that calculate the estimated technical losses in the electricity distribution network. The model was then used as the base to develop the strategy to minimize the electrical energy losses in an electrical distribution network. Increasing energy costs and environmentalists actions to protect the natural resources, force energy supply companies to conserve and reduce energy usage. Therefore the research focused on the reduction of electrical energy losses in distribution networks. The loss occurrences are divided into two categories: technical and non-technical losses. Reducing these losses ensure that the cost of electricity to customers will be reduced and in turn improve the efficiency of the distribution network. The model developed to calculate the non-technical losses in an electrical distribution network was tested at two different networks. Firstly at the University of Pretoria, where the network segment consisted of different network busses delivering electrical energy. Secondly results were obtained in a residential network of the Tshwane Metropolitan Council. In this network there was only one bus but various different time intervals were used to determine the time interval most suitable for determining the electrical energy losses in the electrical distribution network. The model was used primarily to quantify the technical losses as a base point towards determining the non-technical losses. Using the model one is able to forecast the technical energy losses of a section in the electricity distribution network and this enabled one to develop a strategy to minimize the energy losses in the distribution network. The model will enable municipalities or electricity distribution companies to estimate electrical energy losses in their electrical supply networks and facilitate the development of strategies to reduce electrical energy losses. / Dissertation (MEng (Electrical Engineering))--University of Pretoria, 2006. / Electrical, Electronic and Computer Engineering / unrestricted

Orientador: André Nunes de Souza / Resumo: A crescente demanda por energia elétrica, combinada com questões ambientais e financeiras, vem promovendo a integração de unidades geradoras distribuídas nas redes de distribuição. Essa configuração topológica, construída próxima aos consumidores, consiste em um conceito chamado de microgrid, desenvolvido nos últimos anos. Esse modelo é caracterizado por um conjunto de pequenas unidades geradoras, cargas e dispositivos de armazenamento de energia, capazes de operar em modo paralelo ou isolado, em relação à rede existente. Vários estudos apontam que as microrredes influenciam o planejamento, operação e manutenção da rede de distribuição elétrica, principalmente porque as microrredes funcionam em um fluxo de energia bidirecional em vez do modo unidirecional convencional. Essa topologia de rede pode influenciar significativamente o perfil de tensão, estabilidade, qualidade de energia e comportamento de proteção do sistema elétrico. Em relação ao esquema de proteção, esses sistemas podem interferir na coordenação e seletividade dos equipamentos que constituem a rede. Nesse sentido, o objetivo desta dissertação é analisar o impacto da contribuição da corrente de curto-circuito das conexões de microrrede no sistema de proteção de sobrecorrente nas redes de distribuição convencionais. A análise é desenvolvida modelando uma rede de distribuição IEEE de 34 barras. O software OpenDss é usado em conjunto com um aplicativo Python desenvolvido para avaliar os impactos na coordenação e sel... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The growing demand for electricity, combined with environmental and financial issues, fostered the integration of distributed generating units into distribution networks. This topological configuration, build up nearby the consumers, consist of a concept called microgrid, which has been developed in recent years. This model is characterized by a set of small generating units, loads and energy store devices, capable of operating in a parallel or isolated mode, concerning the existing network. Several studies point out that the microgrids influence the planning, operation, and maintenance of the electrical distribution network, mainly because of microgrids woks with a bidirectional power flow rather than the conventional unidirectional mode. This network topology can significantly influence the voltage profile, stability, power quality, and electrical system protection behavior. Regarding the protection scheme, these systems can interfere with the coordination and selectivity of the equipment that constitutes the network. In this sense, the purpose of this dissertation is to analyze the impact of the short circuit current contribution from the micro-network connections in the overcurrent protection system in the conventional distribution networks. The analysis is developed by modeling an IEEE 34-bar distribution network. The OpenDss software is used in conjunction with a developed Python application to assess the impacts on coordination and selectivity of the overcurrent protec... (Complete abstract click electronic access below) / Mestre

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For manufacturing firms to succeed in the global marketplace it is important that they have an efficient supply chain that is well adapted to the characteristics of the products. This thesis explore the companies' challenge to adapt its supply chain to the characteristics of  heir products. A case study has been conducted on a global manufacturing company's distribution network. The company, which is in focus of the study, has conducted extensive effort with standardization and centralization of the distribution network to improve the performance indicators. Consequently, the study focuses on examining how the factors, standardization and centralization, impact the performance indicators in the distribution network. The empirical results show that the company's distribution network is designed to operate efficiently for Make-To-Stock (MTS)  products.  Nonetheless,  the  network  does  not  work as efficiently for Make-To-Order (MTO) products. These products are forced through a  series of non-value activities. The lack of flexibility in the network leads to manually bypasses, which increases both the workload and risk. Therefore, the performance  indicators are improved  by  a  more  flexible  design  adapted  to  the  product  characteristics and customer needs. The study identifies four barriers preventing the company to adapt its distribution network to a more flexible design An excessive focus on economies of scale Imbalance between central and regional capabilities in the organization Rigid processes and lack of software support Complexity in transfer pricing and revenue sharing between entities Finally, the study contributes with suggested actions aimed to increase the flexibility of the company's distribution network.

Power line communications (PLC) has been considered by utility companies for over a half century and for home networking in recent years. However, PLC at the IC level, or even at the PCB level, has not been investigated outside Dr. Ha's research group. This thesis investigates the feasibility of PLC over power distribution networks (PDNs) of advanced microprocessors. A PDN in an integrated circuit (IC) is ubiquitous as seen by the internal logic, i.e., a power line is accessible to any internal node. This suggests the possibility of monitoring or controlling the logic value of any internal node through a power line by attaching a simple sensing/control circuit to the node. Routing the data through a power line avoids the necessity of preplanning the routing of a data path between the node and an external data pin. PLC over microprocessor PDNs also provide a viable means for "run-time testing" as well as for monitoring the so called "large time-constant errors" resulting from aging and temperature variations. In this thesis, we considered impulse-based ultra wideband (I-UWB) communication technology for PLC over PDNs of microprocessors. I-UWB has several advantages for PLC over PDNs due to its robustness to multipath effects, simple hardware for transmission and reception of pulses and, more importantly, reduced interference to the normal operation of microprocessors. A microprocessor PDN is heavily decoupled to damp the resonances in the power supply impedance as well as to reduce the slew rate of current variations by locally supplying (sinking) currents to (from) the switching nodes. Consequently, a PDN behaves like a bulky lowpass filter for high frequency signals. However, the inductance component of decoupling capacitors becomes more significant beyond the self resonant frequency (SRF) of the capacitors. So, a PDN becomes essentially a distributed circuit beyond the SRF and is no longer a lowpass filter. Indeed, high frequency PDN models developed earlier at Dr. Ha's group show that there exist multiple frequency bands where high frequency signals can propagate through the PDN with relatively low attenuation [3] [4]. The major contributions of our research lie in three areas. First, we verified existence of passbands on PDN's transfer characteristics through measurements. We carried out high frequency measurements on the PDN of Intel's 65 nm Pentium processor and 45 nm Core 2 Duo processor. We measured PDN transfer characteristics up to several GHz from a core power pin on a tester board to an on-chip power node for both active and cold microprocessor dies. The measurements show the existence of narrow, sporadic and migratory passbands i.e. location of passbands change from one generation of processor to the next. The migratory nature of passbands requires the I-UWB receiver and a transmitter to cover a wide range of frequencies rather than a specific passband. Second, we have developed a PDN communication channel model for system level study. To develop the channel model, we also performed noise measurements on Intel microprocessors. The link budget was calculated based on the channel model and appropriate modulation schemes were suggested through the system level study. Third, we investigated design of an I-UWB receiver and a transmitter, which cover a wide bandwidth. The proposed receiver and transmitter designs were evaluated through simulations in TSMC 0.18 μm CMOS process. Our simulation indicates that the PLC over a PDN is feasible with a relatively simple digital-process friendly I-UWB receiver and a transmitter. / Ph. D.

A simulation-optimization methodology was used to assess monitoring strategies for a drinking water distribution network. Multiple simulation trials of contamination events were used to create input data for an integer optimization problem. A network model, based on the Blacksburg, VA water distribution system, was used as the basis for a case study of contaminant transport under conditions of uncertainty. The model was not calibrated due to the lack of reliable field data. Optimization of monitoring plans was performed within the context event based simulation trials. This precluded the design of monitoring plans that were directly compatible with requirements of water quality regulations. However, the results of the optimization did provide information that may be of use to the broader problem of compliance monitoring. Optimal plans were assessed in comparison with several alternative plans using a separate set of simulation trials. Optimization of monitoring plans derived from simulated source node contamination events was generally effective at choosing points that provided better detection of source node contamination than alternative plans based on random sampling or judgement sampling. Optimal monitoring plans derived from simulated random node contamination events were ineffective at detecting random node contamination. The results of optimization and the separate analysis of monitoring plan performance indicated that the number of simulation trials may have been inadequate to completely describe the stochastic behavior of the system. Additionally, comparison of these results with those obtained from a previous simulation study indicate that the results of any simulation of distribution system contamination may be very sensitive to the level of contaminant loading and the size and layout of the system. / Master of Science

Power line communications (PLC) as applied to electrical power grid is known since long; however, PLC in microprocessors was recently introduced by VTVT Lab. Since power distribution network (PDN) inside a microprocessor is ubiquitous, therefore, any node inside a microprocessor can be accessed by attaching a simple communication circuit to it. The scheme is extremely attractive as it avoids the routing overhead of the data-path between an internal node and an I/O pin. A number of applications are possible for PLC in microprocessors such as on-line testing, monitoring/control of internal nodes, fault diagnosis etc. Feasibility of the PLC approach has been extensively studied by earlier researchers at VTVT. The feasibility studies investigated the frequency response of a microprocessor's PDN and looked for existence of passbands — frequency bands where signal attenuation through the PDN is small. Two different approaches were followed—the first approach employed analytical modeling of the high frequency characteristics of the PDN, while the second approach conducted measurements on Intel® microprocessors' PDN. Although, differences were observed in the results of the two approaches; both the approaches demonstrated existence of passbands, thus affirming the feasibility of the PLC scheme. This thesis presents a system level study conducted to estimate performance of the PLC scheme. Measurement results were used to model the PDN channel. The study provides useful insights for the design of microprocessor level PLC system. Specifically, the study estimates optimal pulse width required to maximize the system performance and the range of achievable data-rates. The study demonstrates that it is feasible to communicate data through a microprocessor's PDN without inducing large disturbances on the power line. The other work presented in this thesis is the design of low power receiver for microprocessor level PLC, also called data recovery block. The proposed design of data recovery block employs Correlation Detection (CD) receiver architecture. The design has been implemented in IBM 0.13 µm CMOS process and has been verified to operate reliably across Process, Voltage and Temperature variations. The design has a small foot-print of 300 µm x 160 µm and consumes 3.58 mW while operating from 1.2 V power supply. / Master of Science

Höganäs AB's current distribution network for iron powder in the Asia Pacific (APAC) region is subject to high costs incurred by large inventories and high cost of capital. As a result of increasing demand and service level requirements from customers, inventories have steadily increased. Keeping a high inventory level has enabled high service levels irrespective of supply disruptions or changes in demand. It is important that the distribution network incorporates a balance between robustness and cost efficiency and not only focuses on one of these aspects. The purpose of this project is to provide Höganäs AB with scientific data on how the distribution network can be improved in terms of lowering the total cost of warehousing and distribution while maintaining or improving customer service. There are several goals for this project. The first goal is to optimize the flow of material in the distribution network given empirical data of customer demand. The intended model is a linear program. The linear program will solve a multi echelon, period, product, location and transportation mode instance of the distribution network design problem. The second goal is to test the robustness of the optimal solutions resulting from the linear program by stochastic simulation. The simulations utilize the optimal network designs generated by the linear program and is done for a set of possible scenarios where key parameters are changed. By adjusting key parameters and measuring the effect on cost and service level, the goal is to evaluate the robustness of each configuration. By keeping the existing nodes of the distribution network and changing the flow of material and distribution strategy, lower inventories can be maintained and service level kept high regardless of demand growth and supply disruption. The optimal distribution network design is one from the linear program, configured with a 14 day inventory level and 10 day reorder point for warehouses. The optimal design shows that distribution is made more robust and efficient by allowing for distribution between warehouses or supplying customers normally affiliated with other warehouses. It also suggests that a central redistribution warehouse is a possible improvement to the current network design. / Höganäs AB's nuvarande distributionsnätverket for järnpulver i Asien-Stillahavsregionen (APAC) är kostsamt till följd av höga lagernivåer och kapitalkostnader. Ökande efterfrågan och krav på hög servicenivå har inneburit en stadig ökning av lagernivåerna, vilket möjliggjort för företaget att upprätthålla servicenivån oberoende av störningar i leveranskedjan eller förändringar i efterfrågan. Det är viktigt att distributionsnätverket är balanserat avseende stabilitet och kostnadseffektivitet och inte endast optimeras avseende en av faktorerna. Syftet med projektet är förse Höganäs AB vetenskapligt understödd information om hur den totala kostnaden för distributionsnätverket kan sänkas samtidigt som kundservicen upprätthålls eller förbättras. Det finns flera mål för projektet. Det första målet är att optimera materialflödet i distributionsnätverket givet empiriska data över efterfrågan. Den avsedda modellen är ett linjärprogram som löser en instans av distributionsnätverkverksdesign-problemet med multipla lager, perioder, produkter, lokaliseringar och transportsätt. Det andra målet är att utvärdera stabiliteten hos de optimala lösningar som härrör från linjärprogrammet genom stokastisk simulering. Simuleringarna använder de optimala nätverksdesigner som genereras av det linjärprogrammet och genomförs för en uppsättning möjliga scenarier där nyckelparametrar ändras. Genom att justera nyckelparametrar och mäta effekten på kostnad och servicenivå är målet att utvärdera stabiliteten för varje konfiguration. Genom att behålla de befintliga noderna i distributionsnätverket och ändra materialflödet samt distributionsstrategin kan lägre lagernivåer uppnås och servicenivån hålls hög oavsett förändrad efterfrågan och störningar i leveranskedjan. Den optimala distributionsnätverkverksdesignen är en lösning från linjärprogrammet konfigurerat med 14 dagars lagernivå och 10 dagars beställningspunkt. Den optimala designen visar att distributionen görs mer stabil och effektiv genom att tillåta leveranser mellan lagerpunkterna eller att försörja kunder från andra lagerpunkter än de normalt försörjs från. Resultatet påvisar också att en strategiskt placerad omlastningscentral kan förbättra det nuvarande distributionsnätverket.

Asset management and automation are acknowledged by distribution utilities as a useful strategy to improve service quality and reliability. However, the major challenge faced by decision makers in distribution utilities is how to achieve long-term return on the projects while minimising investment and operation costs. Distribution automation (DA) in terms of transformer economic operation (TEO), distribution network reconfiguration (DNR), and sectionalising switch placement (SSP) is recognised as the most effective way for distribution network operators (DNOs) to increase operation efficiency and reliability. Automated tie-switches and sectionalising switches play a fundamental role in distribution networks. A method based on the Monte Carlo simulation is discussed for transformer loss reduction, which comprises of profile generators of residential demand and a distribution network model. The ant colony optimisation (ACO) algorithm is then developed for optimal DNR and TEO to minimise network loss. An ACO algorithm based on a fuzzy multi-objective approach is proposed to solve SSP problem, which considers reliability indices and switch costs. Finally, a multi-objective ant colony optimisation (MOACO) and an artificial immune systems-ant colony optimisation (AIS-ACO) algorithm are developed to solve the reconfiguration problem, which is formulated within a multi-objective framework using the concept of Pareto optimality. The performance of the optimisation techniques has been assessed and illustrated by various case studies on three distribution networks. The obtained optimum network configurations indicate the effectiveness of the proposed methods for optimal DA.