Browsing by Author "Khan, Mohamed Azeem"

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    Assessing the potential for urban wind energy in Cape Town
    (2018) Gough, Matthew Brian; Madhlopa, Amos; Khan, Mohamed Azeem
    As the demand for alternative and renewable sources of energy grows worldwide, it has been argued that small-scale Urban Wind Energy (UWE) could have the potential to provide a significant portion of the electricity demand for urban areas. However there is currently a lack of knowledge surrounding the realisable potential for UWE, especially in the South African context. In order to gain a better understanding of the potential for UWE and the barriers acting against its widespread uptake, it is essential to first quantify the resource potential. This study appraise and evaluate the UWE resource potential at six locations in Cape Town, South Africa in order to gain a solid understanding of the UWE resource potential and thus begin to build the knowledge base around UWE. In order to meet the research objectives, wind data was obtained from the South African Weather Service for six locations in Cape Town at five minute recording intervals for a period of two years. These locations were: The Royal Cape Yacht Club located in the Table Bay harbour, the Astronomical Observatory located in Observatory, and the Kirstenbosch Botanical Gardens located in Kirstenbosch, the Molteno reservoir located in Oranjezicht, the Automatic Weather station located near the Cape Town International Airport as well as the Cape Town Weather Office (WO) station which is also located at the Cape Town International Airport. The data sets are then analysed using a script written in the programming language R in order to quantify the wind energy resource potential of the chosen locations. The wind energy resource potential of each site was combined with four commercially available wind turbines power curves in order to calculate the expected annual energy production values of the various turbines at the each of the locations. Results from this study highlight the significant variability resource potential of the wind regime that occurs between the six locations. The lowest yearly average wind speed was 2.044m/s which was recorded at the Kirstenbosch recording station, while the highest average wind speed was 5.06m/s which was recorded at the WO station. The average of all six stations for the two year period was 3.24m/s. Therefore the WO station had the highest energy potential with a value of 1474 kWh/m²/year and the station with the lowest energy potential was the Kirstenbosch station with a value of 80 kWh/m²/year. Combining these resource potential values with power cures from four commercially available wind turbines yields the Annual Energy Production (AEP) values for the chosen site and wind turbine. These AEP values also varied drastically with the high of 4304 kWh/year being calculated for the SkyStream turbine at the WO station and a low of just 0.66 kWh/year being calculated at the Kirstenbosch station with the Turby turbine. This variability hampers the wide spread uptake of small scale wind power as the results from one area cannot be reliably used to infer the wind resource potential at another nearby site. Out of the six chosen locations in the Cape Town area, three of the locations (Royal Cape Yacht Club, the Automatic Weather Station (AWS), and the Cape Town Weather Office (WO)) showed potential for the installation of a small scale wind turbine, with the Horizontal Axis Wind Turbines (HAWTs) performing better than the Vertical Axis Wind Turbines (VAWTs). This is possibly due to the lower cut in wind speeds of the HAWTs compared to the cut in wind speeds for the VAWTs. The conclusions of this study show that the UWE resource potential in Cape Town is characterised by high resource variability between the various locations. Three of the six locations that were evaluated showed potential for UWE installations. This study has identified the major challenges associated with UWE to be the turbulence, lower hub heights of the wind turbines (this study used 20m as the standard hub height), and variability of the wind regime between locations.
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    Contributions to permanent magnet wind generator design including the application of soft magnetic composites
    (2006) Khan, Mohamed Azeem; Pillay, Pragasen
    The main objective of this dissertation is to contribute knowledge toward the design of small PM wind generators, which includes the application of soft magnetic composite (SMC) materials to the desing of these machines. A problem is first addressed of adapting a PM wind generator, intended for high-speed operation with a small 3-bladed wind turbine, for low speed operation with a new multi-blade, high solidity turbine. An analytical model is formulated and then used to examine the effect of several changes to the design of the wind generator. A new specification of the redesigned machine is then set. The overall performance of the redesigned machine coupled to the new turbine is shown to be satisfactory.
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    Design and implementation of a grid-connected variable-speed PM WECS
    (2010) Sager, Stefan Thomas; Khan, Mohamed Azeem
    As renewable energy (RE) sources are increasingly becoming an integral part of the world's power generation capacity, they are becoming more sophisticated and provide a solid platform for power generation today. Wind Energy is the fastest growing RE source. The correct understanding of issues associated with this technology and how to address them is integral in furthering this RE source... The main objective of the work presented in this thesis is the full understanding and implementation of a PM Wind Turbine System.
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    Design of a permanent magnet generator for a sustainable wind energy capture and storage system
    (2011) Jagau, Hartmut; Khan, Mohamed Azeem; Barendse, Paul Stanley
    The main objective of this dissertation is the detailed design, sizing, analysis and experimental validation of the sustainable wind generator. The proposed machine topology for the generator uses permanent magnets (PMs) from discarded hard disk drives (HDDs). The PM configuration inherently produces a non-uniform air gap flux-density distribution and the pole pitches of the PMs are relatively small. This would result to an unbalanced generator output and a number of stator inter-connecting leads, if conventional tooth-concentrated non-overlapping winding configurations are used. Hence, a concentrated full-pitch overlapping wave winding configuration is developed, which overcomes the aforementioned challenges. The proposed sustainable coreless axial flux generator is then analyzed with classical machine theory and verified by finite element analysis (FEA) software. It is shown that the traditional sizing approach for axial flux machines needs modification to accommodate the design of the proposed machine topology. For the numerical analysis, 3D-FEA is used to verify the 2Dmodel which is subsequently employed in the numerical analyses.
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    Design of an axial-flux generator for a small-scale wind electrolysis plant
    (2010) Wanjiku, John Gitonga; Khan, Mohamed Azeem
    The main objective of this study is the selection and design of a wind generator to meet electrolyser requirements. These are the hydrogen production rate, the power requirements and the operating temperature. This requires the analysis of the load, sizing and characterizing of an electrolyser and finally, the design of a wind generator that meets electrolyser requirements. A hybrid system that combines the use of hydrogen as an efficient form of energy storage, and the growing renewable energy (RE) industry is discussed in detail.
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    Design, analysis and prototyping of a high speed surface mounted permanent magnet machine
    (2018) Ng'onga, Maxas; Khan, Mohamed Azeem
    Over the recent years, there has been a rise in the demand for high speed and high power density machines for various applications in industry ranging from basic household power tools to the flight controls for aircrafts in the aerospace sector. This has also seen advancements in the power electronics and controls for these machines to deal with the large operating frequencies. The increase in demand for high speed machines has been driven by the industry’s requirement for cost reductions, higher robustness & higher efficiencies. This thesis aims to contribute knowledge to the design and development of a high-speed surface mounted permanent magnet machine. A numerical procedure for the detailed sizing of a high-speed surface mounted permanent magnet (SPM) machine is outlined in this dissertation. An analytical per phase model is formulated to examine the performance parameters of the machine. The analytical model is validated against results obtained from Ansys Electromagnetics Finite Element Analysis (FEA) software. The estimation of core losses in high-speed machines is also of critical importance during electromagnetic design. An immense amount of research has been conducted on the estimation of core losses in machines, however, not much has been done to cover the estimation of highspeed core losses as compared to the traditional low-speed machines. As part of the development of the high-speed machine, the numerical estimation of the highspeed core losses was examined and validation performed using FEA software. On average, there was a difference of about 3-11% between the analytical results and FEA results of the eddy current loss and hysteresis loss. These results demonstrate that the analytical method used to estimate core losses is reasonably accurate when compared to FEA results obtained from ANSYS Maxwell. The prototyping of a high-speed surface mounted permanent magnet machine is investigated. Focus is placed on the major components of the machine whilst highlighting the use of precision machining and the need to maintain high accuracy during manufacturing and assembly of the machine prototype.
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    Development of a grid emulator for network integration studies
    (2014) Khan, Akrama; Khan, Mohamed Azeem; Barendse, Paul Stanley
    The economic and environmental side effects of fossil fuels have forced governments and authorities to investigate sustainable solutions. Main interest is focused on environment friendly benefits, provided by renewable energy sources. The growth rate of these energy sources has increased remarkably in the past few years. Correspondingly the research and development in the field of power electronics has also increased, especially in medium voltage and high power grid connected systems. The grid behaviour of the renewable energy systems is heavily influenced by the control techniques of these systems. For further development of these control methods the most basic and conventional way is to simulate, test and prove the system performance on a down-scaled lab test bench. The objective of this thesis is to develop a laboratory test bench grid emulator for network integration studies. Design and performance are investigated by introducing several kinds of unbalanced voltage conditions to test the behavior of connected systems. Voltage dips and swells are implemented to test the system’s performance.
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    Development of a scaled doubly-fed induction generator for assessment of wind power integration issues
    (2016) Dehnavifard, Hossein; Khan, Mohamed Azeem; Barendse, Paul Stanley
    Years of experience have been dedicated to the advancement of thermal power plant technology, and in the last decade the investigation has focused on the wind energy conversion system (WECS). Wind energy will play an important role in the future of the energy market, due to the changing climate and the fossil fuel crisis. Initially, wind energy was intended to cover a small portion of the energy market, but in the long term it should compete with conventional fossil fuel power generation. The movement of the power system towards this new phenomena has to be investigated before the wind energy share increases in the network. Therefore, the wind energy integration issues serve as an interesting topic for authors to improve the perception of integration, distribution, variability and power flow issues. Several simulation models have been introduced in order to resolve this issue, however, the variety in types of wind turbines and the network policies result in these models having limited accuracy or being developed for specific issues. The micro-machine is introduced in order to overcome the challenges of simulation models and the costs involved in field tests. In the past, the grid integration issue of large turbo-alternators was solved by the micro-machines. A variety of tests are possible with the micro-machines and they also increase the flexibility of the system. The increased accuracy as well as the ability to carry out real-time analysis and compare actual field test data are strengths worth utilizing. This project involves the designing and the prototyping of a scaled doubly-fed induction generator (micro-DFIG). The machine is also analysed and tested. The scaling of the micro-machine is achieved by means of a dimensional analysis, which is a mathematical method that allows machines and systems to be downscaled by establishing laws of similitude between the reference model and its scaled model. MATLAB/SIMULINK, Maxwell and Solid Work are employed to achieve the objectives of this project.
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    Development of a system for testing grid-connected permanent magnet wind generators
    (2011) De la Bat, Jaques Gerard; Khan, Mohamed Azeem; Barendse, Paul Stanley
    Renewable energy will be included in the South African Energy Mix over the next two decades. The introduction of renewable energy will reduce South Africa's carbon emissions and also stimulate the economy through job creation as well as creating a local manufacturing sector. South Africa has a large coastal region which is ideal for wind energy deployment. The integration of wind power into the grid needs to be understood as well as the possible problems associated with it. The objective this thesis is to develop a laboratory-based system which can serve as a tool for studying non-ideal conditions associated with the integration of grid-connected Permanent Magnet (PM) wind generators.
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    Dynamic modelling and emulation of a high temperature proton exchange membrane fuel cell (HT PEMFC)
    (2011) De Beer, Chris; Barendse, Paul Stanley; Khan, Mohamed Azeem
    Fuel cells (FC) are power sources that convert chemical energy into electrical and thermal energy in a clean and efficient manner. In the 21st century, fuel cells appear poised to meet the power demands of a variety of applications, ranging from portable electronics to utility power plants. Compared to systems utilizing fossil fuels, fuel cells offer greater efficiency and superior reliability. In particular, proton exchange membrane FCs (PEMFCs) presents a good alternative energy source for distributed generation (DG) systems. FCs however, have had limited commercial success despite their performance, durability and low environmental impact in comparison to other energy conversion and power generation devices. This lack of success has led to low commercial production levels resulting in high costs. Therefore, an increase in research and development is being conducted with the aim of producing cost effective, more efficient and reliable fuel cells for portable transportation and stationary applications. This dissertation aims to produce an emulator design for a HT PEM FC system. A model is developed that takes into account the steady state and the dynamic characteristics of the fuel cell. The emulator hardware is developed from first principles and tested to evaluate performance under dynamic operating conditions. Phenomena such as polarization curve hysteresis and fuel starvation is investigated, simulated and reproduced with the emulator system. The experimental results are compared with that of an actual HT PEM FC stack and evaluated. It was shown that the final system is able to deliver accurate steady state and transient state outputs when compared with the fuel cell stack. The final design can be used for hardware in the loop applications, specifically for fuel cell power conditioning system development.
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    Effects of voltage unbalanced supplies on energy-efficient motors
    (2010) Van Wyk, Ashwill Louis; Khan, Mohamed Azeem; Barendse, Paul Stanley
    Eskom DSM has recently introduced an Energy Efficiency (EE) Motor program, which provides incentives to industrial customers to retrofit standard motors with EE motors. The main objective of the program is to realize energy savings through the replacement of standard (STD) induction motors with higher efficiency EE motors. Although the principle of the program is correct, there are several significant power quality and performance issues with EE motors.These issues need to be thoroughly investigated in order to achieve the overall energy saving objectives of program.
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    High Speed flywheel and test rig design for rural energy storage
    (2010) Okou, Richard; Pillay, Pragesen; Khan, Mohamed Azeem; Barendse, Paul Stanley
    There is considerable growth in the renewable energy sector to contribute to sustainable development, environmental conservation and most importantly to provide affordable energy to isolated rural communities of sub-Saharan Africa. Renewable energy sources such as solar and wind require energy storage since the source of energy is intermittent. Electrochemical batteries especially from lead acid are commonly used to store energy in Solar Home Systems (SHS) for rural electrification in sub-Saharan Africa. Disadvantages such as low efficiencies, low life cycle costs, high maintenance, comparatively short life and serious environmental and human toxicity effects exist. Since recycling is not widespread, replacement costs are high, as are the resultant environmental damage and health hazards from lead and sulphuric acid. In this thesis, an electromechanical flywheel energy storage device is proposed as an alternative to a lead acid battery in order to increase efficiency, life expectancy, increased high depth of discharge, low life cycle cost and elimination of adverse environmental effects. Due to income and service skill constraints in rural areas, the proposed, high speed flywheel systems (for long time energy storage) will require the use of low cost configurations and topologies, special considerations on the flywheel rotor profile design, robust electrical machines, simple power electronics and a low cost bearing set. Low loss magnetic bearings are also possible but were limited by time while also making their maintenance complex especially in rural areas. Conventional high strength composite materials used in flywheel rotor manufacture for high speed operation are expensive. Therefore there is a need to develop techniques to profile the rotor shape so as to improve on material usage and exhibit lower mechanical stresses. A robust electrical machine topology for high speed operation and a simple drive system are investigated to ensure simple assembly, low cost and low maintenance. vii The various flywheel components were designed using analytical and numerical methods. Two techniques were used to develop two optimal profiles for the flywheel rotor structure. Partial differential equations and analytical solutions were employed to develop the profiles. Analytical equations were used to design the electrical machine, drive, bearing system and other accessories. The final electromechanical battery prototype consisted of a composite flywheel rotor made from E-glass fibre materials, double rotor Axial Flux Permanent Magnet (AFPM) machine and a drive system using Brushless DC (BLDC) mode of operation. The system was designed for 300Wh of energy storage for the delivery of 100W and 500W of power and an operating speed range of 8,000 rpm-25,000 rpm. The design and development of the flywheel energy storage system and test rig using locally available materials was investigated. Experiments were conducted for speeds up to 6,000 rpm. The electromechanical battery was able to store a maximum of 77Wh of energy. The shortfall of the system to meet its design specifications was investigated and found to have been caused by vibrations resulting from prototyping issues. A thermal model was developed to predict the temperature rise in the system which showed a good correlation with the experimental results.
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    Impact assessment of large-scale penetration of permanent magnet synchronous generators on power quality
    (2017) Ntsadu, Ntlahla; Folly, Komla A; Khan, Mohamed Azeem
    Wind power generation has gained a large share in the renewable energy market over the past few years. This study investigates the impact of large scale penetration of permanent magnet synchronous generator (PMSG) based wind turbines on power quality of the grid. PMSGs are attractive due to the absence of a gearbox in the drive-train, which results in lower maintenance costs and higher reliability. Moreover, the advancements in power electronics have facilitated PMSGs to generate optimal power at varying wind speed conditions. This is achieved through the use of maximum power point tracking algorithms. The drawbacks of PMSG-based wind energy systems are that they inject harmonics into the network and cause flicker as well as other power quality issues. Despite these disadvantages, the grid code requires that PMSGs stay connected to the grid even under grid disturbances. This is because the reactive power control capability of PMSG-based wind energy systems can actually assist with voltage support. It will be shown in this study that disconnecting large scale PMSGs based wind turbines during grid disturbances has a detrimental effect on transient stability of the grid. This study will show that PMSG-based wind energy systems improve transient stability and assist in voltage support through reactive power control. Moreover, the impacts of large scale PMSG based wind turbines on power quality of the grid can be reduced by various means, which are also addressed in the study.
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    The impact of variable speed drives on energy efficient induction motors
    (2011) Anyang, Ernest Ohene; Khan, Mohamed Azeem
    In an era when the world is faced with diminishing resources and energy security concerns, the slightest energy savings can prove essential in energy conservation. Induction motors and motorised loads consume an estimated 60% of the total energy required in the South African industry. This figure stands at 40% worldwide. Energy Efficient induction motors have proven to be an effective solution in the quest to reduce energy consumption. In South Africa, there have been efforts to replace the standard motors already in operation with energy efficient motors. The South African Utility, ESKOM, through its energy efficiency motor programme, has been providing incentives to its industrial customers to speed up this process.
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    Modelling and detection of faults in axial-flux permanent magnet machines
    (2016) Ogidi, Oladapo Omotade; Barendse, Paul Stanley; Khan, Mohamed Azeem
    The development of various topologies and configurations of axial-flux permanent magnet machine has spurred its use for electromechanical energy conversion in several applications. As it becomes increasingly deployed, effective condition monitoring built on reliable and accurate fault detection techniques is needed to ensure its engineering integrity. Unlike induction machine which has been rigorously investigated for faults, axial-flux permanent magnet machine has not. Thus in this thesis, axial-flux permanent magnet machine is investigated under faulty conditions. Common faults associated with it namely; static eccentricity and interturn short circuit are modelled, and detection techniques are established. The modelling forms a basis for; developing a platform for precise fault replication on a developed experimental test-rig, predicting and analysing fault signatures using both finite element analysis and experimental analysis. In the detection, the motor current signature analysis, vibration analysis and electrical impedance spectroscopy are applied. Attention is paid to fault-feature extraction and fault discrimination. Using both frequency and time-frequency techniques, features are tracked in the line current under steady-state and transient conditions respectively. Results obtained provide rich information on the pattern of fault harmonics. Parametric spectral estimation is also explored as an alternative to the Fourier transform in the steady-state analysis of faulty conditions. It is found to be as effective as the Fourier transform and more amenable to short signal-measurement duration. Vibration analysis is applied in the detection of eccentricities; its efficacy in fault detection is hinged on proper determination of vibratory frequencies and quantification of corresponding tones. This is achieved using analytical formulations and signal processing techniques. Furthermore, the developed fault model is used to assess the influence of cogging torque minimization techniques and rotor topologies in axial-flux permanent magnet machine on current signal in the presence of static eccentricity. The double-sided topology is found to be tolerant to the presence of static eccentricity unlike the single-sided topology due to the opposing effect of the resulting asymmetrical properties of the airgap. The cogging torque minimization techniques do not impair on the established fault detection technique in the single-sided topology. By applying electrical broadband impedance spectroscopy, interturn faults are diagnosed; a high frequency winding model is developed to analyse the impedance-frequency response obtained.
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    Non-intrusive efficiency estimation of induction machines
    (2010) Herndler, Barbara Linda; Barendse, Paul Stanley; Khan, Mohamed Azeem
    Determining the efficiency of an in-service motor requires the motor to be decoupled from its load or the use of highly specialised equipment which is often unavailable on site. In order to assess the efficiency of an induction machine, it is subjected to numerous testing procedures established by recognised international testing standards. These procedures are considered to be time consuming, manually intensive and disruptive to the machine’s operation. Also, the efficiency of the machine quoted after these laboratory tests often does not reflect the motor’s efficiency under operating conditions. This thesis aims to address the aforementioned concerns by implementing a non-intrusive efficiency estimation technique that is applicable to induction motors in industry.
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    Single stage boost inverter for standalone fuel cell applications
    (2015) Moraka, Otshepeng Johny; Barendse, Paul Stanley; Khan, Mohamed Azeem
    The proton exchange membrane fuel cell (PEMFC) is a promising technology that can be manufactured in South Africa because of the platinum catalyst required. South Africa is rich in platinum and, therefore, the PEMFC system can be cost-effectively produced. In residential stationary applications of the PEMFC a power conditioning system is required to convert the de voltage output of the PEMFC to ac voltage. Therefore, the focus of this thesis is to analyse, simulate and design a power electronic dc-ac converter. The power electronic dc-ac converter is based on a transformerless single stage power conversion scheme, which has better weight, volume and efficiency than the commonly used two stage power conversion schemes. The selected topology is the boost inverter that consists of two identical boost converters for boosting and inversion of the PEMFC de voltage. Moreover, it achieves reliable operation under nonlinear loads, sudden load changes and inrush current, using a double loop control strategy. Initially, the double loop control strategy was introduced with proportional integral (Pl) controllers. Recently, with the widespread use of proportional resonant PR controllers, the PI controllers were replaced with PR controllers to achieve zero steady state error for the ac components of the reference. However, during the implementation of the PR controllers on the boost inverter, a significant de offset in the output voltage of the boost inverter was observed, which was due to the mismatch of the boost converters' parameters. The de voltage affects pulsating torque AC machines, accuracy in domestic watt-meter and safety of residual current protection. Furthermore, the output voltages of the boost converters showed a clipping effect, which was caused by the dead time of the switching devices used in the boost converters. An integral term was added to the PR controller to form the controller here called the proportional integral resonant (PIR) controller. This controller achieved satisfactory results of de and ac voltage reference following capability and maintains the same advantages of the PI controllers. However, the efficiency was not high due to the high resistance of the inductor used in the boost inverter system.