Masters Degrees (Electrical and Electronic Engineering)
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Browsing Masters Degrees (Electrical and Electronic Engineering) by browse.metadata.advisor "Beukes, H. J."
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- ItemAnalysis and design of a voltage regulator based on an AC-to-AC converter(Stellenbosch : Stellenbosch University, 2003-04) Van Schalkwyk, Christine; Mouton, H. du T.; Beukes, H. J.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.ENGLISH ABSTRACT: This thesis discusses the analysis and design of a voltage regulator based on an AC-to-AC converter. A background study was performed on the best topology for the purpose. The chosen topology was analysed and the converter was designed in detail. A voltage sign-detector and an over-current detector were designed and built. They were used for control and protection. Three methods of control were investigated. The first was a slow but reliable method of computing the RMS value of the input voltage and then using that value and the RMS value of the desired output voltage to compute the duty ratio of the converter. The second method was fast and is an open-loop control method, where the measured input voltage and a reference value of the desired output voltage are used to compute the duty ratio. The third method is a closed-loop control method in which the input voltage, output voltage and the same reference values used in the second method are used to compute the duty ratio. All of these methods were implemented and tested.
- ItemAnalysis of voltage regulation and network support technologies(Stellenbosch : Stellenbosch University, 2000-12) Rossouw, Frans Jacobus; Beukes, H. J.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.ENGLISH ABSTRACT: Recent advances in semiconductor device development pushed a large number of network devices onto the market. These devices can solve network problems more effectively and economically than ever before. Network planners need tools to analyse and implement such devices to help solve the largest network problem in South Africa: voltage regulation. Rural networks experience the majority of voltage-regulation problems in South Africa. The networks are long sub-transmission and reticulation networks and are modelled by two generic networks, namely a radial network and a two-source ring network. The equations describing voltage regulation for the generic networks are developed and implemented in PSAT, a software analysis tool. The voltage regulation for two case studies that represent the two generic networks are analysed. Four generic network devices are defined and various control methods for these devices are developed to solve the network problem. The aim of PSAT is to help the network planner to quickly evaluate a number of possible solutions and to choose the best solution for further studies. This is demonstrated with the aid of the case studies. PSAT provides a sturdy platform on which future developments, such as stability analyses, can be built. However, PSAT can already function as a stand-alone analysis tool to solve voltage regulation as a network problem.
- ItemBidirectional converter for a stirling energy system(Stellenbosch : University of Stellenbosch, 2004-12) Redecker, H. H. (Hans Henning); Beukes, H. J.; University of Stellenbosch. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.ENGLISH ABSTRACT: This thesis discusses a 23 kW three-phase AC bus system that is utilized together with the “Stirling Energy System (SES) Integrated Solar Dish-Stirling Module” to function as a mini-grid for off-grid locations. The system is designed to supply power to 27 rural households. This three-phase AC bus system includes a bidirectional 4-wire PWM converter and a battery bank for energy storage. The simulations and results presented show that the system can function as a rectifier and as an inverter. The system operates as an inverter when the SES starts up and when different AC loads are connected to the AC bus. The unit functions as a rectifier when the battery bank is charged. The design was implemented successfully in a practical system and measurements revealed that the system functioned as a standalone unit.
- ItemThe comparison of AC and DC alternatives for sub-transmission networks(Stellenbosch : Stellenbosch University, 2001-12) Engelbrecht, Frank; Beukes, H. J.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.ENGLISH ABSTRACT: Recent advances in semiconductor technology extended the economic power range for DC transmission to just a few MW. Network planners need tools to compare AC and DC alternatives in order to find the best technical and economic solution for a specific network. TESAT, a software analysis tool, is developed to determine the optimum conductor and line technology for a network. Voltage regulation problems are identified and can be solved with network devices which have the potential to solve network problems more effectively and economically than ever before. PSAT, another software analysis tool developed in previous research, is used to model networks and support technologies. Hence, with the aid of TESAT and PSAT, line and support technologies are combined in an attempt to find the most effective solution in terms of cost and technical performance. This is demonstrated with the aid of a case study. Furthermore, interfaces between PSAT and the real world are developed. This includes an extension to the input interface of PSAT that calculates the equivalent impedances of a transmission line automatically, as well as an interface to share data between ReticMaster and PSAT. A dispersed generation and support technology database is also developed as an extension to the output interface ofPSAT.
- ItemDesign of a Self Regulated and Protected Electrification Transformer(Stellenbosch : University of Stellenbosch, 2007-03) Beckers, Peter C.; Beukes, H. J.; University of Stellenbosch. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.Electrification of rural areas is one of the biggest challenges faced by ESKOM and methods are required to extend medium voltage distribution lines to these often remote areas. As loads increase due to line-extension, in-fills and energy theft, maintenance cost and life expectancy of distribution and power transformers becomes more critical. The thesis addresses these two aspects with the development of a self regulated and protected electrification transformer that makes use of current, voltage and ambient temperature measurements to regulate voltage and protect hardware from overloading. The design of the hardware that allows the system to run at 200% load without decreasing the lifetime of the transformer is examined. Temperature estimation techniques are used to estimate the temperatures in the 16 kVA, 22 kV to 230 V, distribution transformer to run above nameplate ratings without causing damage. The control of the system is implemented on TMS320F2812 digital signal processor from TI that is DSP/BIOS compatible. The control software is implemented using DSP/BIOS, which allows real-time scheduling and monitoring of procedures. Furthermore a distribution transformer was fitted with temperature sensors and heat run tests were performed. The results of the temperature tests were used to verify the estimation techniques and to determine constants used for temperature estimation.
- ItemDigital control of line-interactive UPS(Stellenbosch : University of Stellenbosch, 2011-03) Van Papendorp, J. F.; Beukes, H. J.; University of Stellenbosch. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.ENGLISH ABSTRACT: The digital control of UPS systems has been difficult in the past due to a lack of DSP technology. It was for this reason not possible to establishing the necessary control to regulate the voltages and currents of the UPS systems. Recent advances in DSP technology have however provided the means of establishing central control of the UPS system as well as incorporating more complex closed-loop control algorithms by utilising a single floating-point DSP. Closed-loop control strategies are investigated and the central control of a line-interactive UPS is established in this study. Both the status of the physical system as well as various system parameters are controlled. The system both regulates and charges the storage batteries when the main utility supply is maintained. In the event that the utility fails, the converter instantaneously changes power flow towards the load with the aim of maintaining an uninterrupted voltage supply. Several closed-loop deadbeat based control strategies are investigated for the regulation of the inductor current. A solution for the regulation of the DC-link is also developed and implemented. Furthermore, an intensive study is done on the regulation of the voltage supplied to the load in the event that the utility supply fails. The investigation is initially approached by considering classical control theory. Although these control strategies provided sufficient results, a predictive strategy that is based on the physical conditions of the switching converter is finally investigated to establish closed loop control of the output voltage. This resulted in a high-bandwidth voltage controller capable of maintaining control under a wide-array of load conditions.
- ItemDynamic digital control schemes for three-phase UPS inverters(Stellenbosch : Stellenbosch University, 2002-12) Uys, Jacobus Johannes; Beukes, H. J.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.ENGLISH ABSTRACT: This thesis presents the design and implementation of a voltage controller for an Uninterruptible Power Supply (UPS) Inverter. The inverter is capable of producing a nearly sinusoidal output voltage waveform, thereby keeping the Total Harmonic Distortion (THD) to a minimum. Digital controllers introduce a time delay in the control law that causes system instability. Various control techniques, which includes Pade approximations and system augmentation, are investigated to eliminate the effect of the time delay. These controllers employ classical control as well as modem control techniques. The selection of the various control parameters is verified by mathematical equations. A load-disturbance compensation scheme, implementing feed-forward and gain scheduling, is also developed to improve voltage distortion when varying loads, such as non-linear loads, are connected to the system. It is shown that the constructed pulse-width modulated (PWM) control scheme can achieve fast dynamic response as well as a low THD.
- ItemElectronic voltage regulator technology for rural electrification(Stellenbosch : Stellenbosch University, 2008-03) Serdyn, J. J.; Beukes, H. J.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.ENGLISH ABSTRACT: This thesis discusses the development of a 5 kVA single phase AC voltage regulator, specifically designed to assist in the reduction of electrification costs in sparsely populated rural areas. The voltage regulator is based on a solid state auto-transformer tap changer, designed to be robust and maintenance free. Electrification cost savings can be realized if the length of the LV network can be extended to reach more households. To accomplish this, a voltage regulator can be installed onto the extended LV feeder at the point where the LV voltage will drop below the minimum valid voltage, thereby boosting the voltage downstream and enabling more customers to be connected. A variety of voltage regulator topologies were investigated to obtain the best topology for the application. The voltage regulator design is discussed in detail with careful attention given to the power loss incurred, surge voltage protection requirements, protection coordination with the existing LV network and the thermal design requirements. An electronic controller based on a digital signal processor together with an appropriate power supply is designed and built. The software to control the voltage regulator is developed, integrated with the hardware and debugged. The complete voltage regulator is evaluated through extensive laboratory testing and field trials are performed to verify the performance of the device.
- ItemEvaluation and implementation of anti-islanding methods for converter-fed distributed generation(Stellenbosch : University of Stellenbosch, 2009-12) Hobbs, Ivan Kevin; Beukes, H. J.; University of Stellenbosch. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.ENGLISH ABSTRACT: As the number of distributed generation units connected to a distribution network increase, the possibility of island formation increases. An island is formed when distributed generation units continue to energize local loads within a section of the grid, which has been disconnected from the main distribution network. These islands pose significant danger to maintenance personnel as well as to members of the public. In this study, an investigation is done into various anti-islanding methods. The modes of operation of these methods are discussed, as well as their strengths and weaknesses. The slip-mode frequency shift method and the Sandia voltage shift method, in combination with over/under voltage and frequency protection, are simulated and tested to confirm their functionality. The results obtained show that it is possible to prevent distributed generation units from energizing local loads when the grid is disconnected.
- ItemGeneric energy storage controller for a power conditioner(Stellenbosch : Stellenbosch University, 2004-03) Mostert, J. P. F.; Beukes, H. J.; Du Toit, J. A.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.ENGLISH ABSTRACT: This thesis presents the design of a DSP based controller system for an auxiliary converter for generic energy storage connection to a line-interactive power compensator. The aim is to utilize a wide range of energy storage systems and incorporate them into the existing power compensator. This was done by adding a second converter to the system. The new controller was developed to control this converter and thereby the energy storage. A study was done on lead acid batteries, flow batteries and flywheels in order to gain a basic understanding of these systems and identify the requirements for their control. Based on these findings, a new DSP based controller and measuring system was developed. To test the new system a dc to dc converter was implemented for the control of lead acid and flow batteries. A dc to ac converter was also tested for the control of flywheel energy storage.
- ItemIncreasing distributed generation penetration when limited by voltage regulation(Stellenbosch : Stellenbosch University, 2014-04) Nye, Jonathan Mark; Beukes, H. J.; Bello, M.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.ENGLISH ABSTRACT: This work investigated the influence of photo-voltaic generators on the voltage control of distribution feeders and the methods that can be used to increase the maximum penetration levels of these feeders. Initially, a brief overview of the reasons why it is necessary to increase the generation penetration levels on distribution feeders was provided. A review of various issues associated with connecting generation to the distribution network; methods and technologies that can be used to increase penetration levels; and ways to improve voltage regulation on MV feeders was given. The grid code for renewable power plants and the voltage apportionment standard were reviewed to determine what limits penetration levels and what can be done to increase them. The operation and control of a typical distribution network, without any connected generation, was initially investigated. A control strategy was implemented that provided suitable voltage regulation on the feeder during both high and low load. The influence of connecting generation to this typical distribution network, without making any modifications to the control of the feeder, was investigated. Base penetration levels, for various generation connection cases, were found. It was shown that the penetration is limited by the rapid voltage change or voltage rise. The base penetration levels were compared to the optimal amount of generation that provides the lowest losses. It was shown that the penetration needs to be increased by between 100% and 200% for the feeder’s losses to be minimised. Voltage regulator and capacitor control was influenced by the generation and they could not function as expected. It was shown that flicker will not be an issue, even with penetration limits well above the current allowable limits. Various methods that can be used to increase the amount of generation that is connected to the typical network were investigated. On-load tap changer setpoint reduction, reactive power control and electronic voltage regulators are some of the methods or technologies that can be used to increase penetration levels. It was shown that each of the technologies can assist, depending on the circumstance, in increasing penetration. The individual modifications can increase penetration up to 100% at the cost of increased tap changes and in some cases losses. Two proposed control strategies were assessed, that combine the investigated technologies. The results showed that it is possible to increase penetration levels by 50-80%, while improving power quality and reducing losses when compared to the base generation connection case.
- ItemMethods to extract maximum electrical energy from PV panels on the earth's surface(Stellenbosch : Stellenbosch University, 2004-12) Bekker, Bernard; Beukes, H. J.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.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.
- ItemOpportunities for in-line, transistorbased technologies on MV and LV power distribution networks(Stellenbosch : Stellenbosch University, 2000-12) Meyer, Bernard; Beukes, H. J.; Stephen, R. G.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.ENGLISH ABSTRACT: Once more opportunities exist for innovative technologies to be applied on MV and LV power distribution networks to meet the new challenges set by government through its National Electrification Programme (NEP) to electrify a further 2,5 million households of which a large majority are in low-density rural areas. Electronic means of voltage compensation of long MV and LV networks supplying these low-density rural areas are now possible in the form of electronic voltage regulators mounted on the secondary side of distribution transformers and service connection boxes along the LV feeders. Furthermore, it is now possible to provide remote rural agricultural customers with singlephase supplies supported by end-use technologies in the form of electronic phase converters that eliminate the need for three-phase supplies. This hybrid of supply- and end-use technologies together with Eskom's "self-build" policy has made the dream of Eskom grid power a reality.
- ItemOptimisation methods applied to compensator placement(Stellenbosch : University of Stellenbosch, 2004-12) Burger, I.; Beukes, H. J.; University of Stellenbosch. Faculty of Engineering. Dept. of Electrical Engineering.ENGLISH ABSTRACT: The optimal placement of different types of compensators on electrical networks is a complex task faced by network planners and operations engineers. The successful placement of these devices normally involves a large number of power flow studies and relies heavily on the experience of the engineer. Firstly the operation and application of the different types of compensators must be clearly understood. Secondly the application of combinations of different compensators on a specific network must be investigated. Then the dynamics of the network and interaction between the network and the compensator/s must be studied under a wide variety of network conditions and load levels. This task is further complicated by the non-linear nature of the mathematical equations that govern the power flow and voltage distribution on an electrical network. Yet another complication is the fact that some of the variables that describe an electrical network can be non smooth or discrete. For instance, the discrete value of a tap position of a power transformer can only assume an integer value. To simplify the problem of compensator placement, advanced software tools are available that are capable of solving power flows of networks containing compensators. To a large degree, however, these tools still rely on the user to make intelligent decisions as to the configuration of networks and the placement of compensators. In many cases trial and error is the only way to find a good solution. The purpose of this thesis is to show the different techniques available to implement intelligent algorithms capable of finding optimal solutions specific to the placement of voltage regulators. State of the art algorithms are implemented in Matlab that can place voltage regulators on sub transmission, reticulation and low voltage networks. The sub transmission and reticulation placement algorithm is a combination of an SQP technique and a simple combinatorial algorithm. The low voltage placement program is based on a simple genetic algorithm with a few customized features that has been developed to ensure fast convergence. The programs developed were used to do optimal voltage regulator placement on a number of networks. As far as possible real world networks were used. Where real world networks were not available test networks were used that closely resemble real networks, as they exist on typical networks owned by Eskom Distribution. It was found that SQP is a very efficient algorithm for optimising large non-linear problems such as the placement of a Step Voltage Regulator on a large electrical network. This algorithm however does not handle discrete variables very well and is also limited in handlingany reconfiguration of the network due to the placement of series devices such as voltage regulators. To cater for reconfiguration, it is necessary to combine the SQP algorithm with a combinatorial algorithm. The genetic algorithm used to do optimal placement of multiple Electronic Voltage Regulators on low voltage networks was found to be very efficient and robust. This can be attributed to the simplicity of the algorithm as well as the fact that it does not rely on the availability of derivative and second derivative information to move towards an optimal solution. Instead, it only uses fitness values obtained from function evaluations to optimise the placement problem. Another useful feature of using a genetic algorithm is that the algorithm does not get stuck in sub optimal areas in the solution space. Both the placement programs developed are relatively simple and do not consider all the factors involved in the placement of voltage regulators. However, the addition of any number of factors is however possible with further development of the programs as presented in this thesis.
- ItemOptimization of wind energy transfer using wind turbines(Stellenbosch : Stellenbosch University, 2003-12) Moor, Gary Duncan; Beukes, H. J.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.ENGLISH ABSTRACT: The effect of topography and terrain on wind is examined in order to ensure that the wind turbine positioning will encourage a greater availability of wind energy to it. Maximum power point tracking methods are presented whereby the loading on the wind turbine is controlled to ensure that the maximum available energy from the wind is captured. The wind turbine system is modelled and used in simulations to evaluate the three proposed maximum power point trackers, named anemometer control, calculation control and constant step control for the purpose of this thesis. An additional analog system is also created whereby the complete wind turbine system is able to be simulated. An inverter is used to replicate the generator and the loading is controlled using an active rectifier since this will be used on the practical system. The results from the simulations and analog system are presented whereby one of the trackers is shown to be inadequate and the other two trackers are shown to be close to ideal. The appeal of the calculation method is in the redundancy of an anemometer making it attractive to less expensive, small-scale systems.
- ItemPower system stabilizer and controlled series capacitor small-signal stability performance analysis(Stellenbosch : Stellenbosch University, 2002-12) Fourie, Gert; Beukes, H. J.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.ENGLISH ABSTRACT: This thesis presents results of a study on the small-signal stability of a single-machine infinite-bus power system. Conditions of generator loading and network impedance are identified that require additional stability support. Two methods of stability enhancement are investigated, namely the power system stabilizer and the controlled series capacitor. Both stabilizers employ the conventional (classic) control structure, and parameters are evaluated for optimum performance using an integral-of-the-squared-error-based method. Results for damping capability versus generator loading and system impedance were generated. The ability of the power system stabilizer and controlled series capacitor to provide stability support is compared. This comparison is based on (a) the ability to provide more damping torque when needed, and (b) the amount of damping torque contributed by the stabilizer.
- ItemA practical comparison between the three-phase series-stacked and neutral point clamped multilevel converter topologies(Stellenbosch : Stellenbosch University, 2003-12) Lee, G. B.; Beukes, H. J.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.ENGLISH ABSTRACT: The versatility of power electronic converters has made them a dominant force in the current electrical and electronic engineering industry. So too industry presents a wider range of applications, forever demanding operation at higher power levels. To meet this need a variety of multilevel converters have evolved. The challenge often lies in the selection of the appropriate topology for a specific application. This thesis presents a practical comparison between the Series-Stacked and Neutral Point Clamped multilevel converter topologies as candidates for Medium Voltage Direct Current and Traction applications. Their configurations, characteristics, switching techniques and practical performances are compared, in order to aid the topology selection process.
- ItemShunt active power filtering algorithms for unbalanced, non-linear loads(Stellenbosch : Stellenbosch University, 2003-12) Gous, Marthinus Gerhardus Faculin; Beukes, H. J.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic EngineeringENGLISH ABSTRACT: This thesis presents the design and implementation of shunt active power filtering algorithms for unbalanced, non-linear loads. A three-phase four-wire topology is developed in the dqO space. Based on this development an accurate dynamic system model, taking into account the effect of the neutral inductor is developed. The synchronous reference frame technique is expanded to enable the isolation of the zero sequence current component into its instantaneous active and reactive current components. Additionally a prediction method is proposed that will enable the proper prediction of the reference currents in a threephase four-wire system. Two categories of reference current signal tracking algorithms are investigated; namely the predictive current controller and the sliding mode current controller. A compensating technique is proposed to compensate for the effects that sampling and computational time delay have on the performance of the system. Additionally, an investigation is done into the effect that dead-time has on the performance of the system, and based on this investigation a dead-time compensating strategy is proposed. Finally simulation and practical results are provided to validate the discussed theories.
- ItemShunt reactive compensation of voltage dips and unbalance(Stellenbosch : University of Stellenbosch, 2010-12) Welgemoed, Frans Marx; Beukes, H. J.; University of Stellenbosch. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.ENGLISH ABSTRACT: The use of power electronic converters provides a more efficient, accurate and dynamic solution to reactive compensation. In this thesis the application of power electronic converters to shunt reactive compensation will be discussed. In particular voltage dips and voltage unbalance are considered as both can be mitigated by means of shunt reactive compensation. A pre-existing uninterruptible power supply is adapted to operate as a shunt reactive compensator. The uninterruptible power supply consists of a 250 kVA three phase voltage source inverter. The modifications are limited to software and control algorithms that do not alter the normal operation of the uninterruptible power supply. Control algorithms are designed and discussed in detail. A typical double loop control strategy is implemented on the power electronic converter. The inner loop consists of a dead-beat current controller. The outer loop consists of three proportional and integral controllers controlling the DC-bus voltage, AC voltage and voltage unbalance respectively. Voltage dips and unbalance are compensated for using only reactive power. Focus is placed on producing a result can be used easily in practice.