Theses and Dissertations (Electronic Engineering)

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Development of an additive manufacturing re-coater monitoring system for powder bed fusion systems
(Vaal University of Technology, 2018-05) Du Rand, Francois; Pienaar, H. C. v. Z., Prof.; Van Tonder, P. J. M., Dr.
In the world of research and development, the ability to rapidly manufacture a prototype or part has become a significant part of the manufacturing process. This requirement has given rise to some unique manufacturing technologies. One of these technologies is Additive Manufacturing (AM), or also more commonly known as 3D printing. There are several AM technologies available and can be divided into three major AM categories namely: liquid, powder and solid sheet based. For this research study, the primary focus will be on powder-based technologies. Powder-based technologies make use of materials in powder form and use different fusion techniques to fuse the powder particles together. All the powder bed fusion technologies consist of the same basic components, namely a powder chamber, build chamber, re-coater and a powder fusion system. For each layer of the build, the re-coater applies a new layer of powder from the powder chamber to the build chamber, and then the specific type of powder fusion system will fuse the powder particles together. This process will then be repeated until the entire build has completed. Currently, powder bed fusion AM platforms do not have re-coating quality feedback into the printing system. Thus, when errors or defects occur on the powder bed surface during the re-coating process, they can affect the structural integrity of the parts. Parts must then be reprinted, which becomes costly due to wasted raw materials, electricity and time. Raw material and sundry wastage was some of the key factors that reduces the overall efficiency of the identified AM technology. Due to the increased problem with wasted materials, the need arose to develop a re-coater monitoring system, which could be used to increase the overall efficiency of a powder-based system. For the development of a re-coater monitoring system, a review of three different types of monitoring technologies such as computer vision, laser scanning and a time-offlight camera was conducted. Based upon the relatively low cost, low computer resource requirements and high accuracy, computer vision was considered as the best suited technology for development of the monitoring system. To select the correct camera to capture images of the powder bed, the required specifications for the camera, lens and mounting position were determined mathematically. A software program was then developed to autonomously detect re-coating errors on the captured image after each re-coating cycle using image processing techniques. Each of the captured powder bed images were divided into 16 equal sized quadrants, where each quadrant was processed individually. Each of the quadrants was examined using an edge detection algorithm to detect any changes in contrast that would indicate a defect or re-coating error. The probability of a possible re-coating error or defect was calculated for each quadrant and displayed as a percentage value. The active re-coater monitoring system was also integrated into the Voxeljet VX500 to validate the system’s operation. The system was used to monitor a total of seven build jobs on the Voxeljet VX500. However, the first three build jobs could not be successfully monitored as some parameters of the system had to be re-adjusted to ensure proper operation. The last four build jobs were monitored successfully and recorded results that proved that the active re-coater monitoring system could indeed detect defects and re-coating errors when they occurred.
Design and optimisation of a universal battery management system in a photovoltaic application.
(2018-08) Ogunniyi, Emmanuel Oluwafemi; Pienaar, H C vZ
Due to the fickle nature of weather upon which renewable energy sources mostly depend, a shift towards a sustainable renewable energy system should be accompanied with a good intermediate energy storage system, such as a battery bank, set up to store the excess supply from renewable sources during their peak periods. The stored energy can later be utilised to supply a regulated and steady power supply for use during the off-peak periods of these renewable energy sources. Battery banks, however, are often faced with the challenge of charge imbalance due to the disparities that occur in the operating characteristics of the batteries that constitute a bank. When a battery bank with charge imbalance is repeatedly used in applications without an effective battery management system (BMS) through active charge equalisation, there could be an early degradation, loss of efficiency and reduction of service life of the entire batteries in the bank. In this research, a universal battery management system (BMS) in stand-alone photovoltaic application was proposed and designed. The BMS consists majorly of a switched capacitor (SC) active charge equaliser, designed with a unique configuration of high capacitance and relatively low switching frequency, which can be applicable to common battery types used in stand-alone photovoltaic application. The circuit was mathematically optimised to minimise losses attributed to impulsive charging and tested with lead acid, silver calcium, lead calcium and lithium ion batteries being commonly used in stand-alone photovoltaic application. The SC design was verified by comparing its simulation results to the digital oscilloscope results, and with both results showing similar values and graphs, the design configuration was validated. The design introduced a simple control strategy and less complicated circuit configuration process, which can allow an easy setup for local usage. The benefit of its multiple usage with different stand-alone photovoltaic battery types saves the cost of purchasing a different charger and balancer for different battery types. More so, the design is solar energy dependent. This could provide an additional benefit for usage in areas where energy dependence is off-grid.
Design and development of an off-grid e-learning centre for rural communities
(2015-01) Selaule, Vusimuze Edgar; Schoeman, R. M.; Pienaar, H. C. v Z.
The lack of electricity in off-grid rural communities in South Africa (SA) and Africa as well as the budget constraints on these communities restrict these communities from connecting to any online resources (internet and e-books) for educational purposes, thus creating a major contributor to the global digital divide. Renewable energy sources such as solar energy, wind energy and biomass were presented as potential alternatives to grid-connected electricity for remote rural locations. Solar energy was identified as the amply available alternative energy resource in SA. Solar radiation was converted by photovoltaic technology to electricity. National power grid isolation (off-grid) was achieved by using a stand-alone photovoltaic system. Photovoltaic technology classification, material categorisation and system sizing for an e-learning centre was presented. Practical set-ups were utilised to determine the most cost-effective equipment mix of power utilization, power management/storage and ICT equipment to build a pilot e-learning centre. It was established that one photovoltaic panel can be employed to fully recharge a battery of a pilot e-learning centre with an operational period of 7 hours using the available sunlight hours. Owing to the susceptibility of the Vaal Triangle region to thunderstorms causing overcast conditions for days, a ratio of back-up battery capacity (Ah) to number of days (seven hours per day) without sunlight was determined. An algorithm was also derived for sizing the pilot e-learning centre for full scale implementation. Future research recommendations based on this study for a reduced system costs of an off-grid e-learning for rural communities powered by a renewable energy resource were presented. This will increase access to basic education in SA and reduce the global digital divide.
Technology development of a maximum power point tracker for regenerative fuel cells
(2015-06) Jansen van Rensburg, Neil
Global warming is of increasing concern due to several greenhouse gases. The combustion of fossil fuels is the major contributor to the greenhouse effect. To minimalise this effect, alternative energy sources have to be considered. Alternative energy sources should not only be environmentally friendly, but also renewable and/or sustainable. Two such alternative energy sources are hydrogen and solar energy. The regenerative fuel cell, commonly known as a hydrogen generator, is used to produce hydrogen. The current solar/hydrogen system at the Vaal University of Technology’s Telkom Centre of Excellence makes use of PV array to supply power to an inverter and the inverter is connected to the hydrogen generator. The inverter provides the hydrogen generator with 220VAC. The hydrogen generator has its own power supply unit to convert the AC power back to DC power. This reduces the efficiency of the system because there will be power loss when converting DC power to AC power and back to DC power. The hydrogen generator, however, could be powered directly from a PV array. However, the hydrogen generator needs specific input parameters in order to operate. Three different input voltages with their own current rating are required by the hydrogen generator to operate properly. Thus, a DC-DC power supply unit needs to be designed to be able to output these parameters to the hydrogen generator. It is also important to note that current PV panel efficiency is very low; therefore, the DC-DC power supply unit also needs to extract the maximum available power from the PV array. In order for the DC-DC power supply unit to be able to extract this maximum power, a maximum power point tracking algorithm needs to be implemented into the design. The DC-DC power supply is designed as a switch mode power supply unit. The reason for this is that the efficiency of a switch mode power supply is higher than that of a linear power supply. To reach the objective the following methodology was followed. The first part of the research provided an introduction to PV energy, charge controllers and hydrogen generators. The problem statement is included as well as the purpose of this research and how this research was to be carried out. The second part is the literature review. This includes the background study of algorithms implemented in MPPT’s; it also explains in detail how to design the MPPT DC-DC SMPS. The third part was divided into two sections. The first section is the design, programming and manufacturing of the MPPT DC-DC SMPS. The second section is the simulation of the system as a whole which is the simulation of the PV array connected to the MPPT DC-DC SMPS and the hydrogen generator. The fourth part in the research compared the results obtained in the simulation and practical setup. The last part of the research provided a conclusion along with recommendation made for further research. The simulation results showed that the system works with an efficiency of 40,84%. This is lower than expected but the design can be optimised to increase efficiency. The practical results showed the efficiency to be 38%. The reason for the lower efficiency is the simulation used ideal components and parameters, whereas the practical design has power losses due to the components not being ideal. The design of the DC-DC switch mode power supply, however, indicated that the hydrogen generator could be powered from a PV array without using an inverter, with great success.
Development of 3D inkjet printing heads for high viscosity fluids
(2015-07) Van Tonder, Petrus Jacobus Malan; Pienaar, H. C. v Z.; De Beer, D. J.
Opening up local markets for worldwide competition has led to the fundamental change in the development of new products. In order for the manufacturers to stay globally competitive, they should be able to attain and sustain themselves as ‘World Class Manufacturers’. These ‘World Class Manufacturers’ should be able to:  Deliver products in fulfilling the total satisfaction of customers.  Provide high quality products.  Offer short delivery time.  Charge reasonable cost.  Comply with all environmental concern and safety requirements. When a design is created for a new product there is great uncertainty as to whether the new design will actually do what it is desired for. New designs often have unexpected problems, hence prototypes are part of the designing process. The prototype enables the engineers and designers to explore design alternatives, test theories and confirm performance prior to standing production of new products. Additive Manufacturing (AM) technologies enable the manufacturers to produce prototypes and products which meet the requirements mentioned above. However the disadvantage of AM technologies, is that the printing material which is required is limited to that of the supplier. When uncommon printing materials must be used to manufacture a prototype or product, the 3D printing process stood out above the rest owing to its printing method. However the printing heads used in current commercially available 3D printers are limited to specific fluid properties, which limits new and unique powder binder combinations. Owing to the problem mentioned, the need arose to develop a more ‘rugged’ printing head (RPH) which will be able to print with different fluid properties. The RPH could then be used to print using unique and new powderbinder combinations. The RPH was designed and constructed using the solenoid inkjet technology as reference. In order to determine the effect which the fluid properties have on the droplet formation, fourteen different glycerol-water test solutions were prepared. The fluid properties were different for each of the glycerol-water solutions. The fluid properties included the viscosity, density and surface tension of the solution. The control parameters of the RPH were theoretically calculated for each of the glycerol-water solutions and nozzle orifice diameter sizes. The control parameters of the RPH included the critical pressure and time. Using an experimental setup, droplets ejected from the RPH could be photographed in order to be analysed. It was determined that the theoretically calculated critical times could not be used in the RPH, as the pulse widths were much lower than the recommended minimum valve pulse width of the solenoid valve used. The control parameters were then determined practically for each of the different glycerol-water solutions as well as for each nozzle orifice diameter size. The practically determined control parameters were also compared to that of the theoretically determined parameters. A mathematical model was formulated for each of the practically determined critical pressure and time parameters. Non-glycerol-water solutions were also prepared in order to determine whether the control parameters could be calculated using the practically determined mathematical models. It was found that the practically determined mathematical models, used to calculate the control parameters, could not be used with non-glycerol-water solutions. Using the practically determined mathematical models, the drop formation process of the non-glycerol-water solutions was not optimized and satellite droplets occurred. Although the practically determined models did not work for non-glycerol-water solutions, the methods used to determine the control parameters for the glycerol-water solutions could still be used to determine the practical critical pressure and time for Newtonian solutions.
Controlling a photovoltaic module's surface temperature to ensure high conversion efficiency
(2015-06) Ozemoya, Augustine; Swart, James; Pienaar, Christo
In order to facilitate sustainable development, it is necessary to further improve and increase the energy efficiency and use of renewable energy and its related technologies. The main limiting factors to the extensive use of photovoltaic (PV) modules include the high initial investment cost and the relatively low conversion efficiency. However, other factors, such as an increase in ambient temperature, exert a considerable negative influence on PV modules, with cell efficiencies decreasing as the cell’s operating temperature increases. Higher PV module surface temperatures mean lower output voltages and subsequent lower output power. Therefore, this dissertation focuses on optimizing the available output power from a PV module by investigating and controlling the effect that the PV module’s surface temperature exerts on the amount of electrical energy produced. A pilot study was conducted by using a PV module set to three different tilt angles with an orientation angle and temperature sensors placed at different points. This was done to determine temperature distribution on the PV module surfaces as well as identify which tilt angle produces the highest PV module surface temperature. The main study was designed to investigate the electrical performance of a PV module with different cooling systems (water and forced air) as against a referenced measurement (no cooling). The cooling systems will be switched on and off at specific time intervals with the help of an electronic timer circuit incorporating a PIC microcontroller. The pilot study was conducted for a 50 week period where the results indicated a direct correlation between temperature rise and voltage decrease. The PV module’s temperature is highest at a tilt angle of 16° during the day and lowest at night time. It further reveals that the PV module’s front and back surface temperature can be distinctly different, with the highest recorded values occurring at the back of the PV module. The main study was conducted for a period of 15 weeks with results indicating that the water cooling system resulted in an average higher output power of 49.6% when compared to the reference system (no cooling system). Recommendations are made that sufficient space should be included between the module frames and mounting structure to reduce high operating temperatures owing to poor air circulation.
Design and development of a remote monitoring system for fuel cells
(2006-07) Komweru, Laetitia; Pienaar, H. C. v Z.
This dissertation presents the design and development of a remote monitoring system (RMS) for polymer electrolyte membrane fuel cells (PEMFC) to facilitate their efficient operation. The RMS consists of a data acquisition system built around the PIC 16F874 microcontroller that communicates with a personal computer (PC) by use of the RS232 serial communication standard, using a simple wired connection between the two. The design also consists of a human machine interface (HMI) developed in Visual Basic 6.0 to provide a platform for display of the monitored parameters in real time. The first objective was to establish performance variables and past studies on PEM fuel cells revealed that variables that affect the system's performance include: fuel and oxidant input pressure and mass flow rates as well as operation temperature and stack hydration. The next objective was to design and develop a data acquisition system (DAS) that could accurately measure the performance variables and convey the data to a PC. This consisted of sensors whose outputs were input into two microcontrollers that were programmed to process the data received and transfer it to the PC. A HMI was developed that provided graphical display of the data as well as options for storage and reviewing the data. The developed system was then tested on a 150Watt PEM fuel cell stack and the data acquisition system was found to reliably capture the fuel cell variables. The HMI provided a real-time display of the data, with alarms indicating when set minimums were exceeded and all data acquired was saved as a Microsoft Excel file. Some recommendations for improved system performance are suggested.
Design and development of a high performance zinc air fuel cell
(2006-06) Lourens, Dewald; Pienaar, H. C. v Z.
The demand for efficient and environmentally friendly power sources has become a major topic around the world. This research explores the capability of the zinc-air fuel cell to replace conventional power sources for various applications, more specifically telecommunication systems. The research consisted of a theoretical study of the zinc-air fuel cell and its components, as well as their performance characteristics. A zinc-air fuel ce.ll and test rig were built, and the system was tested under various conditions. It was found that the zinc-air fuel cell has an advantage over other fuel cells in that it does not require any expensive materials or noble metals, reducing the overall cost of such a system. The fuel cell showed the potential to power various applications, but problems persisted in the fueling process as well as constant leaking of the aqueous electrolyte.
Design and development of a 100 W Proton exchange membrane fuel cell uninterruptible power supply
(2006-01) Du Toit, Johannes Paulus; Pienaar, H. C. v Z.
This study presents the design of a proton exchange membrane fuel cell stack that can be used to replace conventional sources of electrical energy in an uninterruptible power supply system, specifically for use in the telecommunications industry. One of the major concerns regarding the widespread commercialization of fuel cells is the high cost associated with fuel cell components and their manufacturing. A fuel cell design is presented in which existing, low-cost, technologies are used in the manufacture of cell components. For example, printed circuit boards are used in the manufacturing of bipolar flow plates to significantly reduce the cost of fuel cells. The first objective was to design, construct and test a single fuel cell and small fuel cell stack in order to evaluate the use of printed circuit boards in bipolar plate manufacturing. Since the use of copper in a fuel cell environment was found to reduce the lifetime of the cells, the bipolar plates were coated with a protective layer of nickel and chrome. These coatings proved to increase the lifetime of the cells significantly. Power outputs of more than 4 W per cell were achieved. The second objective was to analyze a small fuel cell stack in order to obtain a model for predicting the performance of larger stacks. A mathematical model was developed which was then used to design an electronic circuit equivalent of a fuel cell stack. Both models were adapted to predict the performance of a fuel cell stack containing any number of cells. The models were proven to be able to accurately predict the performance of a fuel cell stack by comparing simulated results with practical performance data. Finally, the circuit equivalent of a fuel cell stack was used to evaluate the capability of a switch mode boost converter to maintain a constant voltage when driven by a fuel cell stack, even under varying load conditions. Simulation results showed the ability of the boost converter to maintain a constant output voltage. The use of supercapacitors as a replacement for batteries as a secondary energy source was also evaluated.
Evaluating the effects of radio-frequency treatment of rocks: textural changes and implications for rock comminution
(2010-12) Swart, Arthur James; Pienaar, H. C. v Z.; Mendonidis, P.
Ore, from a mining operation, goes through a process that separates the valuable minerals from the gangue (waste material). This process usually involves crushing, milling, separation and extraction where the gangue is usually discarded in tailings piles. Current physical methods used for crushing of rocks in the mineral processing industry result in erratic breakages that do not efficiently liberate the economically valuable minerals. Research studies have found that the rock comminution and mineral liberation can be enhanced through various electrical treatment techniques, including pulsed power, ultrasound and microwave. These electrical treatment techniques each have their own advantages and disadvantages which are discussed in this dissertation. However, this research proposes a new technique in an attempt to improve the rock comminution process. The main purpose of this research is to evaluate the effect that RF power exerts on rock samples, with particular focus on textural changes. Four valuable scientific contributions to the fields of metallurgical and electrical engineering were made in this regard. Firstly, a new technique for the treatment of rock samples using RF heating is substantiated. The effect of RF power on textural changes of the rocks is evident in their surface temperature rise, where the RF heating of dole-rite (JSA) and marble (JSB, JS 1 and JS2) resulted in surface temperatures of approximately 100 °C within two minutes of treatment. A particle screening analysis of particles obtained form a swing-pot mill of both the untreated (not exposed to RF power) and treated (exposed to RF power) rock samples were performed to ascertain if the treated samples' size had changed. Two samples (JSA and JSD) revealed a notable change in their particle size distribution. The fact that the percentage of larger sized particles increased (from 38 J..Lm to 90 J..Lffi as seen in Chapter 6) suggests that the rock was strengthened rather than weakened. Secondly, an innovative coupling technique (using a parallel-plate capacitor with dimensions of 28 x 47 mm) to connect rock samples to high powered RF electronic equipment is described. The feasibility of this technique is confirmed by repeated correlated measurements taken on a vector voltmeter and network analyser. Low SWR readings obtained from an inline RF Wattmeter in a practical setup also proves the viability of the matching network used in the coupling technique. Thirdly, anoriginal coupling coefficient (81.58 x 10-3) for the parallel-plate capacitor is presented. This value may be used in similar sized capacitors to determine the specific heat capacity of dielectric materials. However, the value of the coupling coefficient was only verified for seven (relatively dark in surface colour) out of the ten rock samples. Therefore, this coupling coefficient may hold true for all dark coloured rock samples, as it represents the coupling of energy between the parallel-plate capacitor and the rock sample. Finally,this research defines the mathematical models for 10 rock samples for the VHF range of frequencies (30 - 300 MHz), providing unique phase angle to resonance equations for each sample. These equations can be used with each specific rock to determine the resonating frequency where the maximum current flows and the minimum resistance is present. Evaluating the effects of RF power treatment on rocks has brought to light that mineral grain boundaries within specified rock samples are not significantly weakened by RF treatment. This was firstly confirmed by the similar electrical properties of the untreated and treated samples, where consistent values for the resonating frequency were obtained from the network analyser. Secondly, the SEM analysis of the untreated and treated rock samples revealed no significant changes in the form of fractures or breakages along the mineral grain boundaries. Photomicrographs of the thin sections of all ten rock samples were used in this analysis. The particle size distribution of both samples further revealed no weakening or softening of the rock, as the percentage of smaller sized particles did not increase in the treated samples. It may therefore be stated that treating rock samples with RF power within the VHF range will not significantly improve rock comminution and mineral liberation.
Design and development of a high frequency Mosfet driver
(2004-11) Swart, Arthur James; Pienaar, H. C. van Z
A high-power Mosfet was incorporated as a switching device into the efficient Class E configuration, where the switching device switches current through itself either completely on or completely off at high frequencies. The first objective of this project was to demonstrate the effectiveness of a phase-lock loop circuit in generating stable high frequencies when connected in an indirect frequency synthesizer configuration. The indirect frequency synthesizer has established itself as a versatile frequency generator capable of generating high frequencies based on a lower stable reference frequency. The frequency generation stage incorporates a phaselock loop circuit, a frequency divider and a stable reference frequency section. The phase-lock loop section incorporates the TTL based 74HC 4046 that is based upon the common CMOS 4046 integrated circuit. The frequency divider section is built around the CMOS-based 4526 whilst the reference frequency section incorporates the CMOS-based 4060. The frequency synthesizer produced a range of frequencies from 50 kHz to 8 MHz in 50 kHz steps. The output voltage was constant at 5,5 V. The second objective was to show that the complementary emitter follower is indeed a worthy Mosfet gate drive circuit at high frequencies. The Mosfet driver stage produced a voltage signal of at least 11 V, being able to source and sink relatively high peaks of current, especially at high frequencies. Voltage amplification occurred through the use of multiple CMOS-based 40106 inverters. The complementary emitter follower, known for its low output impedance and its ability to source and sink large amounts of current, was an important component in the final Mosfet gate section.
A flight data recorder for radio-controlled model aircraft
(2013-02) Du Plooy, Andre Fred; Swart, James; Pienaar, Christo
In the ever growing sport of model aircraft, pilots are challenged with many obstacles. In the division of gliders, one of the biggest problems is the loss of model aircraft. Pilots launch their aircraft off mountain tops and if the aircraft crashes below, the pilot must make use of his best estimates in order to locate the aircraft. This either takes several hours, or the aircraft is never recovered. Pilots are also at a loss with regard to real time data, such as, but not limited to, battery levels, fuel levels, altitude and speed. Model aircraft competitions are also limited to the best estimate of officials. In this work an attempt has been made to design and develop a remote tracking device for model aircraft. This device will retrieve Global Positioning System (GPS) co-ordinates from the aircraft and relay them to the pilot on the ground. In the event of a crash, the pilot will retrieve the last GPS co-ordinates and then proceed to the location to collect the aircraft. An attempt will also be made to design add-on telemetry components that will allow for measurement and transmission of battery levels, fuel levels, altitude, G-Force, orientation, acceleration, wind and ground speed. Some of the data retrieved from the Flight Data Recorder (FDR) in trial 1 are: maximum altitude above sea level of 2139.20 m, maximum speed over ground which was 57.34 m/s and the average battery voltage for transceiver and servos was 15.2 v.
Optimising the output power available from a photovoltaic panel through empirical testing
(2013-09) Osamede, Asowata; Swart, James; Pienaar, H. C. v Z.
Einstein said, ‘‘the release of energy has not created a new problem, but has made more urgent the necessity of solving an existing one’’. This dissertation presents a method of optimising the available output power from a photovoltaic (PV) panel through empirical testing as this will enable a higher yield of solar energy thereby reducing dependence on traditional energy sources such as fossil fuels. The proposed study intends using existing equations of latitude, mathematical models and simulation packages in combination with the experimental data to analyse the optimum tilt and orientation angles for PV panels. This will assist in identifying ways to improve the installation of PV panels for optimum output power in the Vaal Triangle. Photovoltaic panels are semiconductor devices that convert incident direct beam radiation to electrical energy and the panel is composed of several unitary cells connected in series and/or in parallel. The optimisation process involves the empirical testing of the entire system with the use of existing equations of latitude as suggested by literature for PV installation in the southern hemisphere, power conditioning devices (such as an DC-DC converter, solar charger with MPPT) in order to validate results as well as the correlation of empirical results with a simulation package. The first objective was to have an overview of the types of PV panels that exist; this was done in order to be able to make a right choice of PV panel to be used in this research. A concise literature review was carried to enable this research to have a background of existing information in the areas of optimisation of power from PV panels. The next objective was to carry out a pilot study, this was done to form the foundation for the main study. A data-logging interface circuit (DLIC) was incorporated in the system for some reasons presented in subsequent chapters of this dissertation. At the end of this study data were taken over a two year period, the data were analysed and conclusions were drawn and some recommendation in optimising available output power from a PV panel are suggested.
Design and development of a 200 W converter for phosphoric acid fuel cells
(2013-03) Kuyula, Christian Kinsala; Janse van Rensburg, J. F.
“If we think oil is a problem now, just wait 20 years. It’ll be a nightmare.” — Jeremy Rifkin, Foundation of Economic Trends, Washington, D.C., August 2003. This statement harmonises with the reality that human civilisation faces today. As a result, humankind has been forced to look for alternatives to fossil fuels. Among possible solutions, fuel cell (FC) technology has received a lot of attention because of its potential to generate clean energy. Fuel cells have the advantage that they can be used in remote telecommunication sites with no grid connectivity as the majority of telecommunication equipment operates from a DC voltage supply. Power plants based on phosphoric acid fuel cell (PAFC) have been installed worldwide supplying urban areas, shopping centres and medical facilities with electricity, heat and hot water. Although these are facts regarding large scale power plants for on-site use, portable units have been explored as well. Like any other fuel cell, the PAFC output power is highly unregulated leading to a drastic drop in the output voltage with changing load value. Therefore, various DC–DC converter topologies with a wide range of input voltages can be used to regulate the fuel cell voltage to a required DC load. An interleaved synchronous buck converter intended for efficiently stepping down the energy generated by a PAFC was designed and developed. The design is based on the National Semiconductor LM5119 IC. A LM5119 evaluation board was redesigned to meet the requirements for the application. The measurements were performed and it was found that the converter achieved the expectations. The results showed that the converter efficiently stepped down a wide range of input voltages (22 to 46 V) to a regulated 13.8 V while achieving a 93 percent efficiency. The conclusions reached and recommendations for future research are presented.
Development of a universal bidirectional galvanic isolated switch module for power converter applications
(2013-06) Mokhalodi, Kopano; Janse van Rensburg, J. F.
The global trends towards energy efficiency have facilitated the need for technological advancements in the design and control of power electronic converters for energy processing. The proposed design is intended to make the practical implementation of converters easier. The development of a universal bidirectional galvanic isolated switch module will be used to drive any MOSFET or IGBT in any position in any topology whether the load is AC or DC. Semiconductor switches are required and are also integrated for fast switching times in power converter applications The structure of the power switch module consists of an opto-coupler which will provide an isolation barrier for maximum galvanic isolation between the control circuitry and power stage. It also consists of a high performance gate drive circuit for high speed switching applications with a floating supply.
Design and development of a direct methanol fuel cell for telecommunications
(2013-08-28) Joubert, Hardus; Pienaar, H. C. v Z;
The demand for higher efficiency and cleaner power sources increases daily. The Direct Methanol Fuel Cells (DMFC) is one of those power sources that produces reliable electrical energy at high efficiencies and very low pollution levels. Remote telecommunication sites need power sources that can deliver reliable power. This dissertation informs the reader about the working principles of the DMFC and the materials it consists of. A good amount of theoretical background is also given on the DMFC, especially on the Membrane Electrode Assembly (MEA). Different membranes as well as their properties are discussed. Results from other researchers on DMFCs are also captured. A DMFC stack including a test rig, was built. The DMFC stack consisted of five single DMFC cells. Each cell contained an MEA, Gas Diffusion Layers (GDLS), highly corrosive resistant metal support grids, bipolar flow field plates and end plates. The DMFC stack was operated and tested in a test rig. The test rig held the air blower which supplied the cathode with the required oxidant (air), and the methanol solution tank plus its liquid pump. The liquid pump circulated the methanol solution through the anode side of the stack. It was observed that the DMFC is very susceptible to corrosion, especially if the methanol solution becomes conductive owing to solubility of C02 in it. Methanol itself is a corrosive substance. However the results obtained from the experiments clearly indicate that the DMFC can be implemented as an electrical power source for telecommunications.
The design of a system for evaluating glare from small lighting sources
(2013-08-22) Joubert, Theresa; Dicks, D. A.; Case, M. J.
Discomfort glare is a topic that has been investigated for many years without any reasonable explanation regarding its effect on the human visual system. Results of previous research concluded that established methods have a lot of similarities in implementation; but a number of differences when comparing the results of observer's evaluations with the mathematically calculated glare ratings. Therefore, an alternative method of evaluating the influence of exposure to an unshielded light source was investigated to establish a more reliable and realistic response from observers. In order to address the discrepancies of previous evaluation systems concerning observer's varying opinions regarding the level of discomfort experienced, it was decided to investigate the feasibility of evaluating the brain activity of the observers exposed to an unshielded incandescent lamp. This was done in order to facilitate the differences in each individual observer's sensitivity to bright light sources and the influence of personal taste therefore, eliminating the effect of personal interpretation. The main purpose of this study was to determine whether it would be possible to get any response regarding brain functions when an observer is exposed to a bare light source. In order to determine the pathway of visual stimuli it was necessary to investigate the operating principles of the human eye in detail. Because the eye is only an instrument that makes seeing possible; it was also important to investigate the brain and all its different functions. The part of the brain where visual interpretation takes place was indicated as the occipital lobe. This is the part of the brain monitored for any change of functional status by taking measurements with an electroencephalogram (EEG). Measurements were indeed possible; it was presented as a suppression of the alpha brain activity. During the testing procedure it was observed that the observers were not equally photosensitive. There was also a difference in the amount of alpha suppression with the observer's eyes open and closed respectively. Because the alpha rhythm has a tendency to increase with closed eyes it was much easier to notice the suppression.
Current source converters for extraction of power from HVAC lines
(2013-08-22) Janse van Rensburg, Johannes Frederik; Case, M. J.
Two methods to convert an AC current source to an AC voltage source are presented. Both methods make use of a current transformer to provide energy extraction from the main system while maintaining galvanic isolation between the main system and the output system. Control is via a pulse width modulation scheme in both instances. The ftrst method uses a storage element to provide a DC voltage, which feeds an inverter that supplies the AC load with a voltage source. The second method does not use a storage element but is a direct AC current source to AC voltage source converter employing a current transformer. This has not been done before. A possible application of this study is in the extraction of power from high voltage transmission lines without the conventional substation and rural grid to supply small users such as the telecommunication industry.
Non-conventional methods for energy extraction from high voltage transmission lines
(2013-08-22) Nicolae, Dan Valentin; Case, M. J.
A comprehensive study upon "Non-conventional methods for energy extraction from the high voltage transmission lines" was addressed in this thesis. As defined in this study, a non-conventional method to extract energy is one that does not touch the conductors of the line. The theoretical framework which originated in the Maxwell's equations was presented as a base for discussion of all the methods and the conditions for the extraction to be possible. This study presents various methods such as capacitive and inductive to extract energy from high voltage alternating current transmission lines (HVAC). Although in theory, for high voltage direct current transmission lines (HVDC), the conditions for extraction are not matched, there remain some methods that could still attract interest. The centre point of this thesis is the new power application of the Rogowski coil. This method is analysed in full extent starting from theoretical modelling, computer simulations, design of the actual Rogowski coil and power electronics associated with it, and experimental results on a reduced scale model. In doing this, strong mathematical tools and computer software such as Matlab 6, Quick Field and MathCAD were used. At the end of this thesis, some conclusions are presented together with new ideas for further research in the field.
Analysis of the environmental impact on the design of fuel cells
(2013-08-22) Sibiya, Petros Mandla; Pienaar, H. C. v Z
The air-breathing Direct Methanol Fuel Cell (DMFC) and Zinc Air Fuel Cell (ZAFC)were experimentally studied in a climate chamber in order to investigate the impact of climatic environmental parameters such as varying temperature and relative humidity conditions on their performance. The experimental results presented in the form of polarization curves and discharge characteristic curves indicated that these parameters have a significant effect on the performance of these fuel cells. The results showed that temperature levels below 0ºc are not suitable for the operation of these fuel cells. Instead, it was found that air-breathing DMFC is favored by high temperature conditions while both positive and negative effects were noticed for the air-breathing ZAFC. The results of the varying humidity conditions showed a negative impact on the air-breathing DMFC at a lower temperature level but a performance increase was noticed at a higher temperature level. For air-breathing ZAFC, the effect of humidity on the performance was also found to be influence by the operating temperature. Furthermore, common atmospheric air pollutants such as N20, S02, CO and N02 were experimentally investigated on the air-breathing DMFC and ZAFC. At the concentration of 20 ppm, these air contaminants showed to have a negative effect on the performance of both air-breathing DMFC and ZAFC. For both air-breathing DMFC and ZAFC, performance degradations were found to be irreversible. It is therefore evident from this research that the performance of the air-breathing fuel cell will be affected in an application situated in a highly air-polluted area such as Vaal Triangle or Southern Durban. It is recommended the air-breathing fuel cell design include air filters to counter the day-to-day variations in concentration of air pollutants.

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