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Power systems optimal load flow studies are performed for standard test cases using several methods of minimization. Comparisons of the solutions are made based on digital computer results. A general discussion is made of optimization and the necessary conditions for solution. Cost functions are written for the minimum costs and losses problem and then augmented to satisfy variable constraints. Through the use of common routines and format, sufficient basis for comparison of the several methods was established. Among the methods, steepest descent was chosen as most attractive and a further study was performed. Results of this are presented and conclusions drawn to improve the economical operation of our power system utilities. / Master of Science

This thesis contains contributions in three areas: the theory of generalized calculus, numerical algorithms for operations research, and applications of optimization to problems in modern electric power systems. A geometric approach is used to advance the theory and tools used for studying generalized notions of derivatives for nonsmooth functions. These advances specifically pertain to methods for calculating subdifferentials and to expanding our understanding of a certain notion of derivative of set-valued maps, called the coderivative, in infinite dimensions. A strong understanding of the subdifferential is essential for numerical optimization algorithms, which are developed and applied to nonsmooth problems in operations research, including non-convex problems. Finally, an optimization framework is applied to solve a problem in electric power systems involving a smart solar inverter and battery storage system providing energy and ancillary services to the grid.

Thesis (M.Eng.)--Memorial University of Newfoundland, 2002. / Bibliography: leaves 116-119.

Thesis (Ph.D)--Electrical and Computer Engineering, Georgia Institute of Technology, 2010. / Committee Chair: Meliopoulos, A. P. Sakis; Committee Member: Deng, Shijie; Committee Member: Divan, Deepakraj; Committee Member: Harley, Ronald; Committee Member: Taylor, David. Part of the SMARTech Electronic Thesis and Dissertation Collection.

published_or_final_version / Electrical Engineering / Master / Master of Philosophy

Large boilers have typically been designed for continuous operation from 60-100% load. With restructuring of electrical supply and in some cases because of local fuel supply constraints, some of these boilers are run for only two shifts per day and this entails warm start ups. A reasonable objective is to bring the plant online as quickly as possible within the equipments constraint and without risk of tripping major plant equipment such as feed pumps and circulation pumps. The project required the development of a model accurate enough to represent the boiler thermal dynamics. The thesis compares the simulated model results with the measured results from a Benson boiler from Majuba power station. The developed model is then used to investigate gain scheduled and robust control approaches to the design of the control system for collector vessel level and evaporator flow rate. Once the control problems are clearly understood, an investigation into fast start up is undertaken. The subject of the start up of Benson boilers has limited open literature. This is because flexibility in plant operation has only recently become an important issues with electricity utilities. The limited research in the field of robust control of start up of Benson boiler has made the extensive work done by both Eitelberg and Boje [2001,2002,2004] state of the art. Most of the research done in this thesis follows from the work done by Eitelberg and Boje. / Thesis (M.Sc.)-University of KwaZulu-Natal, Durban, 2005.

This thesis aims to verify the use of quantitative feedback theory (QFT) as a viable tool for designing power system stabilisers (PSS) for a single machine infinite bus system. The result of the QFT design is verified by simulation of the linear and nonlinear models representing the power system, and also by experimental procedures carried out in a laboratory. QFT falls into the classical control category, and is a frequency domain design method. It is an alternative to other design methods such as root locus and Hoo . The QFT design procedure can be extended to a multimachine system and QFT designs of MIMO systems has gained impetus. From theory, through simulation, and to the final laboratory testing on a single machine, infinite bus system, it will be shown that the application of QFT to robust PSS design does indeed work. QFT is a design method that allows the designer to choose a set of realistic operating points and to produce a design that include those points. Other methods allow the designer to produce a design for single operating point, and one has no idea how the design performs at the other operating points. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2003.

Voltage unbalance performance of a power line depends on a few parameters that are not necessarily constant at any given instance. The random nature of a power system raises questions around the ability of a system planner to allocate equitable share of the power quality parameters, like voltage unbalance, at design stage. Even a more interesting question is whether applying current methods will guarantee that emissions will be under the set limits. The presence of single or dual phase feeders on such a line will result in a more dynamic voltage unbalance. The first part of this research is a study on deterministic method of voltage unbalance allocation presented by the IEC. The IEC 61000-13-3 report is a comprehensive guideline and the best place to start when looking to develop an emissions standard for voltage unbalance. This dissertation presents a method that can be used to set planning levels for unbalance emission at various voltage levels in order to avoid high voltage unbalance at the end user. The method depends on the agreed power of the customer, the power of the unbalanced load, and the system characteristics. The method works well for short feeders with roughly the same negative sequence impedance and equal short circuit levels. In South Africa, however, there are radial feeders that span over 100km. Hence on such a feeder, there can be ratios of 1:10 between sending end and the last customer on the line. Preliminary research revealed that IEC 61000-6-3, a report on allocation of harmonics, has a method applicable to long feeders. This method was investigated extensively and applied to voltage unbalance allocation. At the core of the method is the assumption that feeders have an even distribution of load. To illustrate the application of this method an example is given. The second part of the study explores a stochastic method of voltage unbalance allocation. In this study the possibility of random connection is considered. A Monte Carlo study is presented. The impact of various parameters are analysed and the findings reveal that phase allocation has the most influence on emission. The results show that the method of random connection of loads can be applied in special conditions only i.e. were sizes of loads do not differ greatly and the number of required connections are low. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2011.

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