Conventional power system stabilisers (PSS) are designed to eliminate poorly damped, low frequency power oscillations that occur between remote generating pools or power stations, due to different types and settings of the automatic voltage regulators at different power stations. The supplementary control of the PSS is exerted on the power system through a generator's excitation system to which the PSS is attached. In order to design these conventional power system stabilisers , requires accurate system data and an in-depth knowledge of classical control theory. This thesis investigates the use of an intelligent, non-linear PSS that utilises fuzzy logic techniques. Others have proposed the concept of such a PSS, since it does not require accurate system data. This thesis describes the basic aspects of power system stability . Thereafter the methods of modelling synchronous machines in a multi-machine power system are presented. The sample power system being studied and the simulation packages used in the investigations are introduced and the methods involved to design and tune a conventional power system stabiliser using classical control theory and design methods proposed by others, are discussed. The general concept of fuzzy logic is introduced and the application of fuzzy logic techniques to controller design is explained. Using the principles of fuzzy logic controller design, a fuzzy logic power system stabiliser utilising 9 rules is designed and tuned for the multi-machine power system under investigation. The fuzzy logic stabiliser is then applied to a synchronous motor in a pump storage scheme. Previous work has applied fuzzy logic stabilisers only to synchronous generators . To further compare the performance of the 9 rule fuzzy stabiliser, a 49 rule stabiliser developed by other researchers, and adapted to operate on the synchronous motor, is evaluated. Computer simulated results of each of the stabiliser's performances are presented. The results of the 9 rule fuzzy stabiliser are compared with the performance of a conventional linear stabiliser as well as with a 49 rule fuzzy stabiliser. The robustness properties of the fuzzy stabilisers are evaluated. The results further prove that with proper membership function selection, a simple fuzzy stabiliser that demands very little computational overheads can be achieved to provide adequate system damping. / Thesis (M.Sc. Eng.)-University of Natal, Durban, 2003.

This thesis investigates the design of damping controllers to alleviate the problem of low frequency electro-mechanical oscillations in power systems. The operating point and network parameters of power systems are continually changing, resulting in changes in system dynamics. The conventional controller design methodology has therefore come under increasing scrutiny for its lack of considerations for robustness. The thesis first outlines the conventional design of a power system stabilizer (PSS) and then applies two robust techniques (Hoo and Quantitative Feedback Theory, QFT) to the design problem. The single machine infinite bus (SMIB) model is used to illustrate the procedure for all three design techniques. The final design is undertaken to illustrate the more important problem of robust multi-machine PSS design using QFT. The design requires linearised models of the multi-machine system. A brief discussion is given on how these can be obtained. An introduction to decentralized control design in QFT is included to support the multi-machine design. Chapter three proceeds through the design steps required to generate a conventional PSS. The technique is shown to be simple for a given set of operating conditions. The controller is shown to be adequately robust over the given set of operating conditions albeit not by design. Chapter four introduces a design technique that directly addresses robustness issues during the controller design. For a restricted range of operating conditions the designed controller demonstrates the desired robustness and performance characteristics. The inherent difficulties with Hoo in PSS design become more apparent as the operating range is extended. Chapter five introduces the second robust controller design technique. QFT is shown to be more adept at dealing with increased operating ranges and changing specifications in the single-machine infinite-bus case. The controller is easy to generate and performs well over the entire range of operating conditions. QFT is also applied to the controller design for a four-machine study system. The design is a marginally more complex than in the single machine case but is still easily accomplished. This thesis confirms previous attempts at solving the design problem using the methods outlined above. The performance of all controllers is assessed for small and large disturbances using non-linear time domain simulations with models developed using PSCAD/EMTDC and MATLAB. / Thesis (M.Sc.)-University of Natal,Durban, 2002.

The control of electrical drives, or motion control, is important in modern industry. In order to satisfy the requirements of industry, it is important for tertiary institutions to produce graduates skilled in this field. The theoretical content of a typical electrical engineering course will prepare students to tackle design and offline simulation of a digital motion controller. However, to gain an in-depth understanding of the field, students need to be able to implement and test their designs in practice. The complete design process of a digital motion controller is an inherently lengthy process requiring a number of diverse skills, for example microprocessor based hardware and software design. While hardware design issues can be minimised by a choice of a commercially available controller board, the coding of real-time software for a complex controller can pose a steep learning curve. At the undergraduate level, students seldom will possess sufficient practical expertise to fully implement a challenging motion control design in the limited time frames allocated for such projects. This thesis presents a complete rapid prototyping environment for the design of motion control, the Control System Development Environment (CSDE). The CSDE allows a seamless progression of a motion control project through all stages, from initial design and simulation, through real-time implementation to final online tuning and validation. Users are freed from all low-level software and hardware design issues. In the context of undergraduate design projects, the CSDE allows students to design, simulate and prototype challenging solutions in the limited time available. Thus, students can gain in-depth, system level expertise in the design of motion control without being hampered by low-level design issues. The CSDE has been successfully tested by a number of undergraduate students at the Department of Electrical Engineering at the University of Natal. In particular, the CSDE's effectiveness has been demonstrated by its application during two prize winning final year design projects.

As South Africa's electricity consumption increases, Eskom is promoting Demand Side Management (DSM) to aid control of both the electricity consumption and its more effective usage, thereby delaying the need to construct new power stations, which pose large economic and environmental problems. Eskom has investigated various DSM strategies, such as load shifting, co-generation, alternative fuels and energy efficient processes, and has targeted the areas of load shifting and energy efficiency as prime areas for energy savings as they are relatively inexpensive and easy to implement. Pumps and fans form a large part of the industrial load. By improving the power usage of these devices with the use of variable speed drives, large energy savings may be achieved. To enable the energy usage of industrial loads to be evaluated, a test bed system which enables a variable speed drive to be loaded with a configurable load, was constructed. The test bed system forms a tool for evaluating and demonstrating the energy savings that are possible, by replacing fixed speed drives with variable speed drives when controlling the flow rate of pumps and fans. Results from the test bed system show that by using variable speed operation of pumps and fans, some energy savings are achievable when compared to existing methods of flow control. The achievable energy savings are dependent on the system properties and the duty cycle of the pump or fan system. / Thesis (M.Sc.)-University of Natal, Durban, 2001.

During the past two decades, Quality of Supply has become a serious problem for Variable Speed Drives in the industrial and commercial sectors. Quality of Supply problems can trip Variable Speed Drives, which results in loss of production, which is a significant problem in the paper and pulp industry. Researchers have proposed that Quality of Supply problems can be minimised in-house, using controlled front end rectifiers (boost rectifier), to maintain a regulated DC link voltage in the Variable Speed Drive configuration, as most faults are created by a varying supply voltage. This thesis extends the work performed on boost rectifiers by investigating the feasibility of replacing the classical controllers with a Continual Online Trained Artificial Neural Network current controller. The approach adopted in this thesis was to evaluate and extend the work previously performed on conventional boost rectifier current controllers and Continual Online Trained Artificial Neural Network current controlled inverter, at the University of Natal. During this evaluation, the respective controller shortcomings were identified and addressed. Thereafter the Continual Online Trained Artificial Neural Network current controller was modified, according to the control requirements of the boost rectifier, and used as a replacement for the conventional current controller in the boost rectifier system. Finally, the Continual Online Trained Artificial Neural Network current controller was evaluated to assess its viability as a current controller for a boost rectifier. The concept of implementing the real-time Continual Online Trained Artificial Neural Network current controller using a DSP (Digital Signal Processor) was described, along with the main features and practical limitations of existing commercial DSP's. It is shown that at the time of writing of this thesis, the commercially available DSP' s are not powerful enough to implement the Continual Online Trained Artificial Neural Network current controller. However this thesis also shows that it is feasible to implement the real-time controller on the newly released TMS320C67 DSP card. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2000.

Poorly damped oscillations that occur between the generators in large interconnected power systems often limit the amount of power that can be transmitted through a transmission corridor and are a threat to secure system operation. Coordinated insertion and removal of capacitors in series with a transmission line is one of the approaches that has been known for many years to be capable of enhancing the damping of power system oscillations. Unfortunately however, this approach historically relied on the operation of mechanical circuit breakers which were too slow and unreliable for the high-speed and repetitive operation that such an application demands. Recently-emerged, high-speed power-electronic-based switching devices are finding increasing use in modem power systems in the so-called Flexible AC Transmission Systems (F ACTS) concept. One particular FACTS impedance controller, namely the inverter-based series compensator, can rapidly alter the magnitude of capacitive compensating reactance in series with the line to make it practically feasible to enhance the damping of power system oscillations via dynamically-controlled series compensation. This thesis identifies, in the literature, an insightful approach to the design of an idealised controllable series compensator (CSC) damping scheme; such an approach has been considered in the analyses of the thesis. Three mathematical models of a single-machine infinite bus (SMIB) system are developed and are subsequently used in the initial design and analysis of a CSC damping controller carried out in the thesis. The simple SMIB system case study is used to identify and investigate the factors that have a significant impact on the performance of a CSC damping controller before studying the more complex issue of inter-area mode damping using a CSC. This thesis successfully confirms the results of a previous analytical study in which an idealised representation of the CSC was used, and extends the scope of that previous study by also considering a detailed representation of one particular type of CSC: the inverter-based series compensator. The two key findings of this extended investigation are that the inverter-based form of controllable series compensator can successfully be used to damp power oscillations and that, where the damping of oscillations is the particular focus of study, an idealised representation of the inverterbased CSC is suitable for the analyses. In the case of the inter-area mode damping problem, the selection of an appropriate input signal to the CSC damping controller is a key issue, since the oscillations that are to be damped involve a number of participating generators. This thesis examines the suitability of a few candidate input signals that have been proposed in the literature using the conceptually simpler SMIB system analytical models that have been developed. Finally, the thesis applies the understanding of CSC damping controller design gained from the SMIB study to the problem of inter-area mode damping on a four-generator study system. Time-domain simulation results are presented to demonstrate the impact of the controlled inverter-based series compensator on the damping of the inter-area mode of this system. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2000.

Engineering educators the world over are being faced with the dilemma of combining traditional mathematically intensive courses, like Control Systems and Robotics with advances in computational hardware and software. This is because it is impractical to include both software engineering issues as well as conventional course content. A solution to the problem lies in Rapid Prototyping technology to develop and design software, for application on PC's and embedded systems. Rapid Prototyping, based on automatic code generation, allows users to develop advanced software on high level graphical platforms like Simulink® and LabView®, while " hiding" the underlying layers of complex code. This approach allows the advanced hardware, traditionally reserved for software engineers, to be accessed by a much wider audience and is an ideal educational tool. This thesis presents the complete development of the Rapid Application Development Environment (RADE). The RADE system customises the Mathworks Real Time Workshop (RTW) revision 11 for application on both standalone and networked DS? cards. The functionality of the RTW is incorporated into the RADE system. This affords the user seamless code generation, downloading, on-line parameter tuning and on-line data visualisation with storage capability. An added advantage of the RADE system is its easy portability to multiple target platforms, which is demonstrated by its implementation on two different DSP cards. Finally the functionality of the RADE system is demonstrated as an educational tool, with the demonstration of a DC motor speed and position controller. / Thesis (M.Sc.Eng.-University of Natal, Durban, 2001.

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.

South African medium voltage underground electrical networks consist mainly of cables of paper insulated lead covered construction. This construction is still the standard used for most utilities in South Africa. While the in-service performance history of these cables has been excellent, global manufacture of this cable type is decreasing. Internationally, the use of polymeric cables is increasing, resulting in the security of the supply chain for paper cable becoming an increasingly important issue. The most widely used polymeric construction is cross-linked polyethylene. Modern distribution switchgear, which is increasingly used in South Africa, is designed for the newer polymeric technology as this enables more compact construction and reduced equipment footprint. The reduced clearances present installation and operational issues when using modern switchgear with paper insulated cables. Although a comprehensive literature review was conducted, not much academic work has been done on the process of migrating from one cable platform to another. Manufacturer data, academic reference sources, industry experts and software modelling tools are used to demonstrate that the use of polymeric technology is viable for South African utilities. This dissertation focuses on the difference between paper and polymeric technologies, and explores the advantages and disadvantages of each. Integration issues are examined along with the methods used to overcome the challenges of hybrid or mixed dielectric networks. Economic comparisons between paper and polymeric cables with respect to purchase and operating costs (including the cost of losses) as well as steady state, cyclic, distribution and emergency current ratings are made. The dissertation concludes that it makes economic and engineering sense for users of paper cable in South Africa to change to polymeric technology, taking the recommendations given into consideration in order to choose an optimised cable design and gain maximum benefit from the change. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2011.

Studies undertaken by Eskom in 2001 identified three sites near the Northern Cape town of Upington which are suitable for a 100 MW Concentrating Solar Power (CSP) generating plant. Of the CSP technologies investigated, the central receiver option was identified as best for the Northern Cape, however almost none of Eskom’s analysis was made public. The basis of the central receiver’s suitability versus other CSP options is not publicly known. Given recent advances in concentrating systems, an argument exists for reassessing the suitability of various solar thermal technologies for bulk power generation. This study first characterises the incident solar radiation (insolation) levels at Upington from six data sources and assesses their quality. The data are then used to model performance of the parabolic trough, compact linear Fresnel reflector, central receiver, and dish-engine technologies. A software modelling tool of the United States National Renewable Energy Laboratory (System Advisor Model) is used to facilitate the comparison. Simulation results are compared with data from similar studies to ensure consistency of the CSP model inputs and performance outputs. Constraining the results to the environmental conditions of Upington, it is found that while central receiver technology produces less electricity per square kilometre of collector area, it uses less water than parabolic trough technology to obtain a higher annual electric output. Dish-engine technology has the most favourable annual electricity production to water-usage ratio, however, its modest annual electricity output and lack of energy storage capability weaken the case for it to match South Africa’s national load profile substantively. Examining the modelled month-to-month electricity output characteristic, the central receiver technology delivers significantly more electricity during the lower insolation winter period of the year than the competing technologies. This results in the central receiver technology achieving the highest annual electric output of the four technologies compared under the same insolation levels, strengthening the case for its implementation. As a whole, this work characterises the insolation levels at Upington, provides an analysis of the technical performance of competing CSP technologies for the proposed Northern Cape site, and argues quantitatively in favour of the central receiver option. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2012.