Masters Degrees (Electrical Engineering)

Permanent URI for this collectionhttps://hdl.handle.net/10413/6856

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Control of five-level voltage source converters used with a type-4 wind turbine.
(2023) Zungu, Ndumiso Hosana Nduduzo.; Agee, John Terhile.
Wind Energy Conversion Systems (WECSs) have attracted considerable attention and emerged as a highly promising and advancing renewable energy option. A typical WECS setup involves a Permanent Magnet Synchronous Generator (PMSG) connected to the power grid via power electronics converters. Nevertheless, the commonly used two-level Voltage Source Converter (2L VSC) configurations suffer from drawbacks such as increased switching losses, significant harmonic distortion at the output, and the need for additional Electromagnetic Interference (EMI) filters. Overcoming these challenges can be achieved through the adoption of multi-level converter topologies, which offer several advantages over conventional ones. These benefits include reduced switching losses, improved overall efficiency, and a decreased number of filtering elements required. By employing multi-level converters, the limitations of traditional 2L VSC topologies can be mitigated, making them a more efficient and suitable replacement. The main objective of this research was to optimize the control of the proposed WECS by utilizing the Five Level Neutral Point Clamped (5L NPC) Voltage Source Converter (VSC) topology. The ultimate goal was to enhance the stability and power quality of the WECS when integrated into the grid system. The research findings are based on simulations carried out using the Power Systems Computer-Aided Design (PSCAD) software, which incorporates built-in power electronics device models. The study focused on controlling both sides of the converter, namely the Machine Side Converter (MSC) controller and the Grid Side Converter (GSC) controller, with the aim of improving the overall system performance. To achieve this, the control scheme employs the Vector-Oriented Control (VOC) strategy, along with phase lead and lag compensators, to effectively regulate the power flow delivered to the grid and achieve a unity power factor. Ultimately, the simulation results convincingly demonstrated the enhanced efficiency of the overall system performance. Specifically, the study analyzed and compared Total Harmonic Distortion (THD) with a conventional converter topology under varying wind speeds. The THD values for the simulated voltage and current using the 2L VSC were found to be: 56.48% at 8m/s, 58.03% at 16m/s, and 2.35% at 8m/s, 8.95% at 16m/s, respectively. Nevertheless, by substituting the 2L NPC with the suggested 5L NPC topology, substantial improvements were achieved. The THD voltage saw a significant reduction of 26.63% at 8m/s, 30.5% at 16m/s while the current experienced a slight drop of 0.2% at 8m/s, 6.52% at 16m/s respectively.
Design and parametric analysis of prototyped differential amplifier using double-gate mosfet.
(2023) Tekisi, Thabiso.; Srivastava, Viranjay Mohan.
Differential Amplifiers (DA’s) are extensively utilized in a wide variety of electronic circuits, including operational amplifiers, instrumentation amplifiers, and Communication Systems (CS’s). They are typically built with BJTs and MOSFETs. Nevertheless, each type of transistor presents its own set of barriers when designing a DA. Amongst other challenges with BJTs is suffering from input base-emitter junctions with non-ideal input impedance. Decreased gain and loading effects may come from this. Due to the base-to-emitter voltage's dependence on temperature, they are susceptible to temperature changes, and they have a limited input voltage range, beyond which the transistors can be damaged. On the other side, Because of gate-source capacitance and gate leakage current, Single-Gate (SG) MOSFETs are more prone to noise; they suffer from Short Channel Effect (SCE) and have a limited input voltage range. The design process for a DA using a double gate MOSFET is presented in this work. The double gate MOSFET is a potential contender for use in analog circuit design because of its improved EC, low noise characteristics, reduced SCEs, and power consumption. The DA circuit proposed comprises two double-gate MOSFETs, BF998, constructed in a differential pair with a resistive load and a Constant Current Source (CCS). The proposed circuit is designed and simulated using a multism tool and was also constructed on Vero Board (VB). Various parameters are analysed on both simulated and practical circuits, such as differential output voltage gain, Common Mode Voltage Gain (CMVG), Common Mode Rejection Ratio (CMRR), Frequency Response (FR), and losses, to observe the performance of the proposed circuit. Simulated results for a differential voltage gain, common-mode gain, CMRR, and FR were obtained to be 24 dB, -224.22 dB, 246.86 dB, and 65 MHz, respectively. Practical results were obtained to be 24.44 dB, -73.81 dB, and 98.29 dB. A comparison has been made between the proposed circuit and the already existing designs, and the findings demonstrate that, when compared to traditional BJT and MOSFETbased DA’s, the presented DA using a double gate MOSFET offers considerable improvements in terms of differential voltage gain, cut-off frequency, CMRR, reduced SCEs, linearity, and noise performance. Therefore, based on these results, the designed DA is justified for use in operational amplifiers as input stage, RF, and other low-power electrical/electronic devices.
Transient stability analysis of an integrated photovoltaic systems in a power system.
(2023) Mzebetshana, Sibonakaliso.; Sarma, Rudiren.
Integration of PV systems into the grid is growing rapidly around the world, and PV penetration plays a huge role in minimizing the effect of greenhouse gases in the atmosphere and also contributes to minimizing the impact of load shedding. However, PV systems contribute to grid integration issues such as transients, voltage, and frequency instabilities and reductions in the generator’s inertia, respectively; therefore, it is essential to investigate the effect of the PV system on the grid before integrating it. This research utilized a modified IEEE 9 bus system to investigate the impact of large-scale PV on the power system, and PSCAD software has been used for this study. Four scenarios with different PV penetration levels were considered in this dissertation. Moreover, for each scenario, the transient stability was assessed based on five parameters, namely: active power, reactive power, rotor angle, rotor speed, and the terminal voltage. Scenario 1 examines the PV systems integrated into a single bus and finds that the optimal PV penetration is 60% of the total power generation. Scenario 2 investigates the effect of integrating PV systems using the optimal PV penetration of 60% distributed into two buses, which was found to be the best for transient stability improvement after a fault condition. Scenario 3 investigates the impact of the power system stabilizer (PSS), using the optimal PV penetration of 60%, and the results reveal that system stability improves when a fault occurs on the bus where the PV system is also connected. Scenario 4 investigates the effectiveness of the fault clearing time on the response of the system with an integrated PV system, using the optimal PV penetration of 60%. The results revealed that a PV system only improves transient stability if the fault-clearing time is below 0.5 seconds; otherwise, the system loses stability. Overall, the study demonstrates that the system’s stability improves up to 60% of the PV penetration level of total generation power.
Investigation into the effects of traction converters on lineside transformers.
(2023) Muthen, Justine.; Swanson, Andrew Graham.
25kV AC rail infrastructure applications, single-phase lineside transformers are used to supply power to lineside railway equipment. This consists of train condition monitoring and authorisation systems which are extremely sensitive to power supply inconsistencies. If there is a failure in the power supply to this lineside equipment, a resultant inaccuracy in the signals received from this equipment can affect the throughput of trains. Due to the nature of the 25 kV traction power system, power quality issues can affect the lineside transformer. This study followed two key aspects, the first being the investigation of the lineside transformer. Here, the validity of the known parameters of the transformer are investigated and discussed. Since, there is little information available about these 16kVA, 25kV/230V lineside transformers and for the remaining parameters required for the simulation of the transformer model, a similar rated transformer was tested. Its behaviour was then modelled to suit the lineside application. Overvoltage’s are studied in detail to determine the saturation limits for the transformer to be developed. This model, constructed using MATLAB, was then used to model the traction power system, which includes the traction substation, electrical infrastructure and train. The formation of all of these components have been detailed in the investigation. The second aspect was studying the distortion in the voltage waveform experienced by the lineside transformer. This was analysed firstly, under two conditions, loaded, where the train is connected to the system and secondly, during regeneration, which is active via dynamic braking. The behaviour of the model was also observed, whilst increasing the switching frequency of the converter onboard the locomotive, increasing the fault level, as well as taking the over overvoltage situation into consideration. Here, the most prominent harmonic orders are determined and dsicussed. Specifically, noting that whilst analysing the model during over voltage characteristics, the magnetising current in the lineside transformer was found to have increased by approximately 70% due to the harmonics experienced at multiple frequencies. Throughout this investigation it is clear that, the specification of the lineside transformer is ill-equipped to deal with the overvoltage characteristics required for this application and in some cases tends to saturate during operation. This became apparent at lower tap changer positions for core flux density levels of 1.7 T and 1.6 T. Hence, a dedicated lineside transformer specification is suggested, detailing all the necessary design parameters, insulation level and harmonics, that should be adhered to, in order to prevent this.
Reconfigurable intelligent surface assisted modulation for next generation networks.
(2023) Morar, Yashil.; Pillay, Narushan.; Xu, Hongjun.
The demand for increased link reliability, higher data rates, improved error performance (EP) and increased spectral efficiency (SE) in wireless communications systems (WCS) is increasing exponentially year after year. Furthermore, the overall data traffic and number of mobile users is growing, and continues to grow, rapidly each year. In theory, multiple-input multiple-output systems can achieve these goals, but not without their drawbacks and challenges. These drawbacks include low energy efficiency, high computational complexity and increased harmful radiation emission. Hence, it is evident that to meet the current and future wireless demands and standards, the next generation of wireless networks can no longer be an extension of the previous generation. Rather, the next generation of wireless networks requires totally novel concepts, implementations and foundations from which to build upon. As such, reconfigurable intelligent surfaces (RISs) provide a completely new paradigm in this respect. RISs are man-made electromagnetic (EM) surfaces with adjustable parameters capable of modifying the impinging signal to enhance signal strength and quality. In other words, RISs allow control over what was previously assumed to be the uncontrollable wireless propagation environment. The key principle in using the RIS is that its adjustable parameters may be reconfigured to effect a change on the EM wave, thereby improving various aspects of WCS. RISs hold attractive advantages which make them a key competitor of MIMO systems. Firstly, RISs are nearly passive surfaces, meaning they do not require additional energy sources to operate. Secondly, RISs are cost-effective as they operate on low-power electronics and do not require converters or power amplifiers. Thirdly, they are easily deployable on walls, ceilings, buildings, facades, billboards, vehicles and even clothes. Lastly, RISs are environmentally friendly, and meet the requirements of green communications. Motivated by this, this dissertation presents a study on RIS-aided WCS. In particular, this dissertation provides an investigation into how RISs may improve the EP of WCS. This dissertation investigates the effect of both passive and active RIS elements on the EP and SE of WCS by considering hybrid RISs to assist data transmission. This dissertation also provides a study on RIS-aided systems in Rician fading channels to investigate the impact of the line-of-sight component of the RIS on the EP of WCS. The theoretical average bit error probability of each scheme is provided and validated by Monte-Carlo simulations. The findings in this dissertation illustrate that hybrid RIS-aided systems can achieve significant improvements in EP over conventional RIS-aided systems, and that Rician fading channels have a distinct impact on the EP of RIS-aided WCS due to the line-of-sight component associated with Rician fading.
Generalized differential modulation with signal space diversity for m-ary quadrature amplitude modulation (m-qam) constellations.
(2023) Masango, Goitsemang Eulanda.; Xu, Hongjun.
Due to an increase in wireless communication usage on several devices, the demand for high transmission rate and reliable connection has increased. In this dissertation, a generalized differential modulation with signal space diversity (GDM-SSD) for a multi-dimensional M-ary quadrature amplitude modulation (M-QAM) scheme is presented to improve the error performance of non-coherent systems in wireless communications. Signal space diversity (SSD) comprises two fundamental stages: constellation rotation and component interleaving. The angle at which the constellation is rotated is determined based on a design criterion which maximizes the diversity order by minimizing the Euclidean square product or, alternatively, minimizes a symbol error probability (SEP) expression. In this dissertation, an angle of 31.7 degrees is used as an angle of rotation in order to achieve SSD in two dimensions. This dissertation aims to improve the error performance of a non-coherent generalized differential modulation (GDM) wireless communication system. The proposed generalized differential scheme (GDM-SSD) is based on optimal power allocation, signal rotation and component interleaving/de-interleaving. GDM-SSD divides a frame into a reference part and normal part. The reference part is transmitted at a higher power than the normal part, and is used to encode and decode the information in the normal part. Optimal power allocation is applied to the system, and the results demonstrate that the SEP performance of the proposed GDM-SSD scheme losses about 5dB performance gap over coherent SSD scheme. It is observed that the performance of GDM-SSD detection gets better as the number of transmitted symbols in a frame increase.
The effect of graphene as a hydrophobic additive on the pollution performance and accelerated ageing of coatings when applied to ac high voltage ceramic insulator materials.
(2023) du Plessis, Barend Jacobus Gert Wessel.; Jarvis, Alan Lawrence Leigh.; Stephen, Robert.; Bekker, Nelius.; Vosloo, Wallace.
This study focuses on the development and pre-testing of a modified insulator coating. The study aims to investigate and evaluate the performance of Pristine Graphene (PG) and Nanoplatelet Graphene (NPG) doped Room-Temperature Vulcanising Silicone Rubber (RTV SR) coatings at different weight percentages (wt%). Key properties such as surface resistivity, hydrophobicity, hydrophobicity transfer/recovery, tracking resistance, and erosion resistance were analysed to assess the effectiveness of the modified coating. From an electrical insulation resistance perspective, NPG doped RTV SR coatings with over 3 wt% demonstrated more than twice the reduction in surface resistivity compared to the reference RTV SR coating. Furthermore, the Inclined Plane Tests (IPT) confirmed that the addition of NPG particles to the RTV SR mixture lowers the combustion temperature of the ATH (Aluminium-Trihydrate) filler, resulting in faster ignition during electrical discharging or DBA (Dry Band Arcing) events. However, the project presented promising performance in terms of hydrophobicity, recovery, and transfer properties. A 10 wt% NPG weight fraction led to an approximate 10% increase in static contact angle measurements compared to the unfilled RTV SR coating. The presence of NPG did not hinder the hydrophobicity recovery and transfer mechanisms within the RTV SR matrix. After pollution application, similar large static contact angles were measured as those observed on a clean 10 wt% NPG doped RTV SR coating surface. This observation led to a hypothesis that physical entanglement and/or interfacial interaction between Low-Molecular-Weight (LMW) silicones and the free-floating NPG sheets within the bulk layer of the modified coating material could result in the transfer of NPG sheets to the surface during polluted surface conditions. Consequently, this encapsulation of pollution particles would develop a pollution layer with a hydrophobicity level comparable to that of a clean NPG doped RTV SR coating surface over time. Several recommendations are proposed for future research, including the setup of an inclined plane tester to evaluate hydrophobicity resistance and transfer principles, exploration of alternative fillers which do not decrease combustion temperature when adding to virgin RTV SR material, implementation of thermogravimetric analysis to study the modified coating’s chemical and physical phenomena, and conducting outdoor pollution performance and ageing tests in severe marine environments. Additionally, further investigation of the LMW silicones and NPG hydrophobicity transfer "package" hypothesis, accurate measurement of pollution layer thickness and homogeneity, Scanning Electron Microscopy (SEM) studies to determine morphological characteristics, and improvement of NPG mixing and dispersion quality are recommended. Furthermore, evaluation and comparison of PG doped RTV SR samples as well as corona activity analysis between different PG/NPG doped RTV SR weight percentages is also recommended. The study concludes by emphasising the need for standardised tests and procedures to evaluate the long-term durability of superhydrophobic coatings and highlights the potential of semiconductive coatings, enhanced by graphene, to prevent flashovers, by governing small leakage currents. The reason for the study is to see if RTV SR coating can be modified to be superhydrophobic.
Damping subsynchronous resonance using HVDC supplementary controls.
(2021) Tambwe, Christophe Basila.; Pillay, Rudiren Carpanen.
ABSTRACT: In power transmission lines, series capacitors are used to increase power transfer capability. However, series capacitors are the primary source of subsynchronous torsional oscillations of nearby turbogenerator shafts. These electronic components in transmission lines expose the turbogenerator system's torsional dynamics to a resonance phenomenon. Typically, this phenomenon appears in the form of supersynchronous and subsynchronous resonance. Subsynchronous resonance is often the most dangerous for its harmful effects, leading to shaft failure and power system instability. It differs from supersynchronous resonance, which does not adversely affect system stability. A turbogenerator set commonly consists of natural modes with frequencies smaller than the power system rated frequency. When the torsional frequencies resulting from the transmission line's series capacitors affect the turbine-generator shaft's operation by coinciding with one of its natural frequencies, they induce the phenomenon known as subsynchronous resonance. Supersynchronous resonance refers to torsional oscillations whose frequencies exceed the nominal frequency of the electrical network. Researchers have used many approaches to solve the subsynchronous resonance phenomenon in power systems. This research focuses on exploiting supplementary controls of a parallel HVDC system to address the subsynchronous resonance problem. However, owing mainly to the converter's current regulators and many other parameters, the HVDC system can also potentially induce subsynchronous oscillation on nearby turbine-generator shafts. This work focuses on a power system comprising a modified IEEE First Benchmark Model to incorporate a parallel HVDC link. This power system is subjected to torsional instability from either the resonant line AC line, HVDC controls, or both. Thus, this study contrasts the effectiveness of single-mode and multimodal damping controllers when the turbogenerator shaft's torsional dynamics undergo instability from the parallel AC-DC system. Furthermore, this thesis utilizes the time domain-based test signal and phase correction methods to design the supplementary subsynchronous damping controllers. These two approaches allow obtaining the optimal parameters of the damping controllers. The controller consists of a Power System Stabilizer to control the inertial mode and Synchronous Damping Controller to control other unstable torsional modes to achieve positive damping. This research uses the FFT analysis to assess the performance of supplementary HVDC damping controllers on the torsional dynamics of the turbogenerator shaft in the parallel AC-DC system.
Solution of combined heat and power economic dispatch problem using genetic algorithm.
(2022) Ohaegbuchi, Dedacus Nnadozie.; Saha, Akshay Kumar.
The combination of heat and power constitutes a system that provides electricity and thermal energy concurrently. Its high efficiency and significant emission reduction makes it an outstanding prospect in the future of energy production and transmission. The broad application of combined heat and power units requires the joint dispatch of power and heating systems, in which the modelling of combined heat and power units plays a vital role. This research paper employed genetic algorithm, artificial bee colony, differential evolution, particle swarm optimization and direct solution algorithms to evaluate the cost function as well as output decision variables of heat and power in a system that has simple cycle cogeneration unit with quadratic cost function. The system was first modeled to determine the various parameters of combined heat and power units in order to solve the economic dispatch problem with direct solution algorithm. In order for modelling to be done, a general structure of combined heat and power must be defined. The system considered in this research consists of four test units, i.e. two conventional power units, one combined heat and power unit and one heat-only unit. These algorithms were applied to on the research data set to determine the required decision variables while taking into account the power and heat units, operation bound of power and heat-only units as well as feasible operation region of the cogeneration unit. Power and heat output decision variables plus cost functions from Genetic Algorithm, differential evolution, Particle Swarm Optimization and artificial bee colony were determined using codes. Also, the decision variables and cost function value were obtained by calculations using direct solution algorithm. The findings of the research paper show that there are different ways in which combined heat and power economic dispatch variables can be determined, which include genetic algorithm, differential evolution, artificial bee colony, particle swarm optimization and direct solution algorithms. However, each solution method allows for different combined heat and power output decision variables to be found, with some of the methods (particle swarm optimization and artificial bee colony) having setbacks such as: large objective function values, slower convergence and large number solution. The analysis revealed that the differential evolution algorithm is a viable alternative to solving combined heat and power problems. This is due in most part to its faster convergence, minimum cost function value, and high quality solution which are diverse and widespread, more as a result of its effective search capability than genetic algorithm, particle swarm optimization, direct solution and artificial bee colony algorithms. The methods investigated in this research paper can be used and expanded on to create useful and accurate technique of solving combined heat and power problems.
Sub transmission insulator and conductor ageing in coastal environments.
(2022) Ramsoomar, Ashwin.; Swanson, Andrew Graham.
Globally, power grids are gradually unbundling to encourage multiple sources of small to medium scale renewable generation, aiding in relieving demanding power constraints [1]. The additional generation product requires an effective and efficient power evacuation system; however, the constrained transmission and sub transmission systems are burdened with the higher power transfer limits coupled with aged infrastructure. Operations and maintenance strategies assist in alleviating the temporary system load increases; however, an asset management strategy is required to ensure that the power system operates at a peak without encouraging a redesign or replacement of the entire power system [2]. The guiding principles of an asset management strategy is understanding the effective utilization of sub systems and components. Effective utilization of components can only be achieved, once a useful lifespan is determined, replacing, refurbishing, or instituting life extension measures once the component end of life is neared. To avert underutilizing or overutilizing the asset, the asset age base needs to be determined incorporating in-situ conditions to provide a reliable and generic prediction model. In sub transmission and transmission systems, maintenance funding, is allocated to critical components such as insulators, ACSR phase conductor and galvanized steel shield wire. These high failure-impact components are susceptible to a higher rate of corrosion related failure, attributed to environmental conditions such as high humidity and high air contamination found in coastal environments. The corrosion models guided by ISO 9223 [3], makes use of empirical degeneration rates for Aluminium, Steel and Zinc. These models understate the initiation of the corrosion reaction for the first year only, requiring the derivation of an acceleration model to represent the degeneration of the composite conductor over its lifespan. The resulting model predicts the useful life of the conductor by measuring the loss in tensile strength attributed to corrosion. Age prediction modelling of the silicone composite insulator is achieved by predicting the loss of creepage or resistive layer on the insulator surface. The coastal environmental conditions, contribute significantly to degenerating the resistive layer leading to a flashover at line voltage. The validation of the insulator and conductor ageing models are achieved by comparing the calculated lifespans to measured field-samples tests. The results showed a standard deviation of 4 years between the measured and calculated values.
Renewables and energy storage to optimise the amount of electrical energy consumed in a building.
(2022) Naidoo, Ulika Devina.; Swanson, Andrew Graham.
The rising cost of electricity and fuel, along with the looming threat of load shedding has frustrated not only the business owner but the homeowner as well. The need to reduce costs, and the growing pressure for companies and individuals to become more environmentally friendly, is becoming more apparent. To reduce costs and the effects of load shedding, and to become more sustainable, the integration of renewable energy is a clear solution. The solution has led to the investigation of a hybrid system that uses grid-supplied power and renewable energy supplied power which will achieve an effective and efficient optimization of cost. This dissertation is centred on minimising the total cost of ownership over twenty years. This is done by comparing different optimisation algorithms and identifying a cost-effective way of integrating a source of renewable energy, specifically solar energy, with an existing grid-supplied building. The zoning of buildings was found to have an impact on the total cost of ownership as the tariffs were different. By developing a function, the efficiency of a system was quantified based on the load, and what type of building it was. The load has a direct impact on the total cost of ownership. The electrical energy used in a building, and the property type, whether industrial, commercial or residential zone, affects the optimisation algorithm that is used. To minimise the total cost of ownership over twenty years, consideration was given to trade-offs between the available solar, oversizing the PV installation, the cost of electricity at different hours and the use of a storage system. To ensure that the total cost of ownership was correct, financial equations for growing annuity and the prescribed rates for assets, maintenance, and electricity were used. Further to this, South African energy tariffs, actual prices of inverters, solar panels, batteries and solar data of South Africa was used. MATLAB was the application of choice of software due to its optimisation capabilities. Examples of each type of building were analysed to find the optimisation that returned the lowest TCO. Particle Swarm Optimisation, when used for industrial buildings produced the lowest TCO, while smaller loads from commercial buildings and a residential housing, showed that the lowest TCO came from Teaching-Learning Based Optimisation. In each case, the fastest and slowest optimisation technique was Pattern Search and Firefly Optimisation respectively.
Optimizing the protection of an auto-recloser in a DG integrated distribution network.
(2022) Gumede, Siyabonga Brian.; Saha, Akshay Kumar.
The integration of distributed generation into distribution networks is growing as most of the distributed generators have a sustainable power supply and can be used to improve the voltage profile. However, the type of a distributed generator and location in the distribution network can determine how a voltage profile behaves in a distribution feeder. They also contribute fault current in a new or same direction as the fault current from the utility. With this change in the fault current, the existing protection scheme may maloperate since the protection scheme was designed for fault current from the utility generator. One of the protection devices that can mal-operate is the auto-recloser. This is a device used for the self-remediation of the distribution network when there is a temporary fault. The IEEE and IEC standard for the international use of auto-reclosers in voltages between 1000 V and 38 kV states that the minimum tripping current shall be stated by the manufacturer with a tolerance not exceeding +/- 10% or 3 A, and the preferred operating sequence for auto-reclosers shall be; open – time delay of 0.5 seconds - close and open-second time delay 2 seconds - close and open - third-time delay of 5 seconds - close and open then lock out. However, these parameters can be violated when distributed generators are introduced into the distribution network. The change in the fault current may vary the operating time of the auto-recloser and it may not operate in this manner. The inverse time-current characteristics of the auto-recloser relay cause this. However, the operating time problem can be optimized. The inverse time-current characteristic of the auto-recloser relay can be used to formulate the auto-recloser operating time problem. The settings can be optimized to reduce the time and mitigate mal-operations such as protection blinding, fuse and auto-recloser losing coordination, and sympathetic tripping. To optimize the settings, optimization algorithms can be applied. In this research, the development of a single-shot auto-recloser is conducted. The IEEE 13-node and 34- node radial distribution feeders are used as a passive distribution network. The Wind Turbine and Solar Photovoltaic systems are distributed generators. MATLAB/Simulink is used for simulations, and the results obtained show that the integration of the distributed generators into a passive distribution network causes mal-operations in the auto-recloser when there is a fault. The factors that contribute to these mal-operations is the fault location, fault type, distributed generator type, distributed generator penetration and location. However, the auto-recloser shows improvement when the settings are optimized in these conditions.
Investigation of traction motor control systems for electric vehicle applications.
(2022) De Klerk, Matthew Liam.; Saha, Akshay Kumar.
Electric vehicles are a promising solution to the current pollution and greenhouse gas issues faced by the transport sector. As such, the traction motor control system of an electric vehicle is worthy of investigation. Direct torque and indirect field-oriented control are commonly applied control techniques, enabling advanced control of the induction and permanent magnet synchronous motors currently used in most electric vehicles being produced. Various improvements have been made to current traction motor control schemes to reduce ripple, improve parameter insensitivity, and increase powertrain efficiency. Consequently, the objective of the research conducted is to contribute to the field of electric vehicle powertrains through comprehensive investigations into the suitability and performance of direct torque and indirect field-oriented control in the traction motor control system of an electric vehicle. A four-stage simulation-based investigation was undertaken, with five motor control techniques initially assessed, which were conventional direct torque and field-oriented control, two space vector modulation-based direct torque control systems and fuzzy logic-based direct torque control. Results from the first stage of the simulation-based study highlighted expected issues with conventional direct torque control and showed that fuzzy logic-based direct torque control and space vector modulational-based direct torque control with closed-loop torque and flux control present promising solutions for use in the traction motor control system of an electric vehicle. Extensions of the simulation-based investigation in stages two and three included the integration and assessment of field-weakening control and sensorless speed estimation. Furthermore, stage four concluded the investigation with an essential analysis of a complete control mechanism in realistic urban and highway driving conditions. The fourth stage utilised sections of the New York City Cycle and Highway Fuel Economy Test cycle, with a simulated vehicle load. The complete study indicated that space vector modulation-based direct torque control with closed-loop torque and flux control performs suitably for electric vehicle applications, providing favourable speed, torque, current and stator flux results with a faster computation time than some comparable control options. The comprehensive investigation extends current literature and forms a basis for further investigation in the field of traction motor control systems for electric vehicle applications.
Implementation of Iterative Learning Control on a Pneumatic Actuator.
(2022) Rwafa, James.; Ghayoor, Najafabadi Farzad.
Pneumatic systems play a pivotal role in many industrial applications, such as in petrochemical industries, steel manufacturing, car manufacturing and food industries. Besides industrial applications, pneumatic systems have also been used in many robotic systems. Nevertheless, a pneumatic system contains different nonlinear and uncertain behaviour due to gas compression, gas leakage, attenuation of the air in pipes and frictional forces in mechanical parts, which increase the system’s dynamic orders. Therefore, modelling a pneumatic system tends to be complicated and challenges the design of the controller for such a system. As a result, employing an effective control mechanism to precisely control a pneumatic system for achieving the required performance is essential. A desirable controller for a pneumatic system should be capable of learning the dynamics of the system and adjusting the control signal accordingly. In this study, a learning control scheme to overcome the highlighted nonlinearity problems is suggested. Many industrial processes are repetitive, and it is reasonable to make use of previously acquired data to improve a controller’s convergence and robustness. An Iterative Learning Control (ILC) algorithm uses information from previous repetitions to learn about the system’s dynamics. The ILC algorithm characteristics are beneficial in real-time control given its short time requirements for responding to input changes. Cylinder-piston actuators are the most common pneumatic systems, which translate the air pressure force into a linear mechanical motion. In industrial automation and robotics, linear pneumatic actuators have a wide range of applications, from load positioning to pneumatic muscles in robots. Therefore, the aim of this research is to study the performance of ILC techniques in position control of the rod in a pneumatic position-cylinder system. Based on theoretical analysis, the design of an ILC is discussed, showing that the controller can satisfactorily overcome nonlinearities and uncertainties in the system without needing any prior knowledge of the system’s model. The controller has been designed in such a way to even work on non-iterative processes. The performance of the ILC-controlled system is compared with a well-tuned PID controller, showing a faster and more accurate response.
Frequency response analysis of a current limiting reactor.
(2022) Kuppan, Levashen.; Swanson, Andrew Graham.; Jarvis, Alan Lawrence Leigh.
With the demand for electricity continuously increasing, power systems are required to increase capacity to meet such demands which can entail integrating renewable energy resources to the grid. This increase in capacity would mean a likewise increase in fault levels in the network which can result in costly damage to components such as circuit breakers, transformers and cables. Air-core reactors are commonly employed to prevent such damages from occurring, however, the increase in fault levels must also be accounted for in the design of reactors as they are also subject to transients. This dissertation documents the development of models to accurately represent an Air-core reactor in order to gain a better understanding of the design considerations required. Two models are developed for two desktop reactors using different methods as a form of cross-validation. The first model is developed in MATLAB r2020a and utilises an analytical approach through an equivalent circuit method (ECM). Equations are used to compute the inductive, capacitive and resistive components which are then used to guide the development of the FEM models. The second model is developed using COMSOL Multiphysics software which is based on the Finite Element Method (FEM) approach. A 2D-axisymmetrical model is constructed and simulated using COMSOL’s Magnetic and Electric field physics in the frequency domain from which a frequency response is obtained as well as values for the inductive, resistive and capacitive components. Final validation of the FEM models is done through comparisons to measured results of the two desktop reactors. FEM simulated RLC components showed fairly good agreement to the measured values, particularly the inductance having a difference of 3.4 μH and a capacitance difference of 1 pF for Reactor 1. The FEM simulated frequency response of 1.5 MHz differed by 0.4 MHz when compared to the measured frequency response for Reactor 2 of 1.9 MHz. A sensitivity analysis is conducted for the FEM model in order to obtain an understanding of the design considerations required for the air-core reactor. Simulations are performed on the FEM model with changes to geometry, permittivity of the insulation medium and resistivity of the copper coil. The effects of these changes on the RLC parameters and resonance frequencies are documented. The FEM model is then scaled to a full-scaled reactor which showed good agreement between the expected inductance of 2.24 mH and the simulated inductance of 2.28 MH. The resultant resonant frequency was observed to occur at 380 kHz. The aim of this is to develop an understanding of parameters and equations that should be considered in the design process of reactors which will then be employed in the development of a superconducting fault current limiter (SFCL).
Optimization of Hybrid Renewable Electrical Energy Systems for a Port.
(2022) Nkosi, Mbonisi Shephaerd.; Swanson, Andrew Graham.; Carpanen, Rudiren Pillay.; Ghayoor, Najafabadi Farzadna.
The port terminals in South Africa currently face significant challenges linked to electricity constraints and security. South Africa is predominantly reliant on coal-generated electricity from the local utility for the provision of base-load electricity to power operations, and municipal distribution systems in many areas. A reduction in power in the latter part of 2015 has resulted in the curtailment of load shedding that is continuing to date, 2019. This risk is not mitigated, it is ongoing. Port terminals in South Africa rely on the throughput of the vessels to ensure that freight is moved speedily. The aspects of port operations that are generally considered in measuring port performance and efficiency are berth productivity measured in moves or volumes per ship working hour also known as across the shipping rate, cargo dwell times, crane moves per hour, ship turnaround time with less focus or no energy management. The port operations are dependent on the throughput of the operation. The energy consumed for port operations is thus independent and is difficult to control in any sort of energy management plan. Coupling this with the time of use tariffs and demand penalties, the need for an adaptable hybrid system can alleviate some stresses and contribute positively to an energy management plan. This study aims to determine that the distributed generation and storage performed by a variety of small, grid-connected referred to as distributed energy resources mitigate the energy cost issues in the port environment and reduction of Green House Gases (GHG) emissions. Distributed resources can help reduce the capacity problems to which an aging or overstressed grid is liable. The study is contributing to reducing dependence on major power plants supply and redirecting the source of supply to renewable technologies. This results in eliminating the need to erect new big power generation and deferral of new capacity. It also demonstrates that PV Solar and Wind Turbine Generation can reduce environmental impacts and gas greenhouse gas emissions. Compared to the coal power plants, distributed generators units are renewable or low emission generator-based sources. The Homer Grid simulation tool suggest distributed generation to be the solution for the port i.e., the hybrid supply that includes the integration of photovoltaic generation, wind power generation, battery energy storage system (BESS) into the electricity Municipal Grid. Both Matlab and HOMER Grid optimizations tools are used to outline different options for reducing electricity costs. These tools compare the costs and savings and uses a powerful optimization to find the system that maximizes savings. We used these tools to analyze the distributed generation grid potential, peak renewables penetration, ratio of renewable sources to total energy, and grid stability. The tools present different study cases with optimal results. The outcome shows a decrease in the cost of energy in the long term and can contribute towards the better energy management of the port.
Study the effect of topology on the performance of an advanced metering infrastructure network.
(2021) Ngcobo, Thobekile Joyce.; Ghayoor, Najafabadi Farzadna.
A smart grid operates based on the integration of various renewable energy sources, distributed generators and storage units in order to deliver an uninterrupted energy supply to consumers. Such a complex grid requires a network of intelligent sensors and an effective communication infrastructure to provide bi-directional flows of information between different grid entities for monitoring and control purposes. A crucial part of the smart grid communication network is the advanced metering infrastructure connecting a utility company to end-users to support telemetry and remote-control applications. Although different technologies and standards for smart metering systems exist, the G3-PLC standard, which uses the power-line communication (PLC) technology, is the accepted standard in South Africa for connecting smart meters to data concentrators. Studying the topology of an AMI network can help improve the network’s Quality-of-Service to support more advanced applications. The analytical analysis is usually considered a viable method for studying the topological effect on the performance of PLC-based AMI networks, as physically altering such networks can become very costly. Therefore, in this research, such methods have been used to investigate the effect of topology on the performance of the G3-PLC AMI network. To better understand the system, an overview of the G3-PLC standard for smart metering application has been covered. This includes covering the DLMS/COSEM protocol at the application layer and its relation to the G3-PLC. This follows by providing the mathematical model for the G3-PLC AMI network to study the effect of topology on its performance. Based on the provided method, first, the distances between data concentrators and smart meters are identified. Then the graph theory has been used to calculate the transfer function between every node in the system for obtaining the system’s total capacity. It was shown that the performance of the system decreases as longer branches are added to the network.
Design of a novel axial-flux induction machine for traction applications.
(2021) Mushid, Cinyama.; Dorrell, David Goerge.
Induction motors are an important element in the industrial world; they are used in many applications, such as electric fans, elevators, pumps, conveyor belts, compressors and now even traction motors. Electric motors consume about 70 % of all industrial power consumption. Induction machines are also the source of the power generation such as in wind turbines. In recent years, the increase in price and supply-chain issues of rare earth magnets, which are currently an important material in brushless permanent machines, which are the most popular vehicular drive motor, has led to a focus on non-permanent magnet machine replacements, such as the induction machine. The induction machine is still undergoing design development and being used in an increasing number of applications. They can be used in fixed speed (grid-connected) or variable speed (variable-frequency inverter-connected) depending on the application. Loss reduction, weight, size, as well as minimizing the cost of raw materials for manufacturing, are some of the issues in design improvement. In view of this, it is important to develop innovative methods for producing electrical machines that will reduce losses and minimizing cost of production. The aim of this research work is to develop an appropriate analytical design procedure for designing an axial-flux induction machine and to evaluate the performance of the designed machine under various conditions. The machine must be robust and cheaper. ANSYS Maxwell software is used for 3D finite element modelling and simulation of the proposed axial-flux induction machine AFIM). For fast calculation, a simple sizing exercise is done using a pre-defined stator core. Then a radial-flux machine representation is developed in Siemens SPEED motor design software for fast assessment. The electromagnetic motor model is further tested to take into account the variations in rotor design. A proof-of-concept prototype was constructed for initial validation that the machine works and this design was modelled. The result of the simulation and the measurements from the laboratory design prove the possibility of the proposed AFIM for use in automotive application. Further design was carried out to improve the prototype using more substantial windings and a longer rotor. This design was tested with ANSYS Maxwell and SPEED. The designed machine offers a cost effective solution for future drive systems in automotive applications.
Modelling of streamer breakdown under positive polarity HVDC in subtropical conditions.
(2021) Moodley, Keshlan.; Swanson, Andrew Graham.
Atmospheric air is an essential component in high voltage power systems as it is used to provide electrical insulation. Therefore, it is required that research is extensively performed on the gaseous insulator to ensure reliability of the system. This dissertation presents the research that has been performed on the streamer breakdown of needle-plane air gaps that were less than 15 cm in length. An experiment was conducted to investigate the streamer breakdown in air gaps. The investigation also included determining the influence of humidity and pressure on the breakdown voltage when HVDC is applied to the high voltage electrode in subtropical conditions. The results indicated that humidity did not influence the breakdown voltage for small gap lengths but both humidity and pressure have a directly proportional relationship with the breakdown voltage of air gaps longer in length. It was observed in the results that the breakdown voltage reduced in magnitude when the humidity increased, and this could have been a result of the breakdown developing out of the glow discharge without impulses when the HVDC was applied. It was observed that the atmospheric pressure did not influence the breakdown voltage for the smaller gap lengths, but the breakdown voltage was directly proportional to the pressure for larger gap lengths. High-speed photography was implemented in the experiment to capture the streamer breakdown mechanism that occurred in these air gaps. An analysis of the results obtained from the experiment showed that the needle-plane electrode combination created single, straight streamers whose stem increased in length when the gap length increased. Branches would also occur from the streamer when the gap length was greater than or equal to 12 cm and the streamer would occasionally take a bent path for gap lengths greater than 10 cm when propagating towards the cathode. Streamers would take this bent path because of space charge being present along the normal path when propagating towards the cathode. This caused the streamer to propagate around the space charge as it is unable to propagate through regions of high concentration. The dissertation also consisted of a numerical simulation on COMSOL Multiphysics which modelled the initiation of a cathode directed streamer and the propagation of it in an air gap. The necessary steps that were taken for the implementation and simulation of the electrical streamer in a 0.1 cm needle-plane gap is also included. The results of the numerical simulation were presented and analysed. The model was used to investigate the influence of both humidity and pressure on the breakdown voltage. The results indicated that the breakdown voltage of an air gap increased when humidity increased in the system as the atmospheric pressure was controlled. The breakdown voltage is also directly proportional to the atmospheric pressure when the humidity in the system was controlled. The experimental results and the numerical results obtained indicate that the breakdown voltage of an air gap is dependent on the humidity and pressure of the system and that space charge influences the path a streamer takes when propagating to the cathode.
Voltage control and stability analysis in a multi-machine power system with increasing penetration of intermittent renewable energy generation.
(2020) Loji, Kabulo.; Tiako, Rémy.
Among multiple distributed generation (DG) supply means, photovoltaic (PV) and wind technologies are the most important and widely used renewable energy sources (RES) throughout the world. However, solar intermittency and the stochastic nature of radiation on one hand and grid integration-related issues on the other are fundamental concerns in the development and smooth deployment of solar energy contribution to conventional power systems networks. In addition, given that they modify both the structure and the operation of the distribution networks, RES increase uncertainty in power system operations, thus affecting power systems variables such as the voltage profiles and direction of network power flows. It is also largely established that a high penetration of DGs at the distribution end is associated amongst others, with voltage rises at PV buses that may lead to the violation of grid codes, if not adequately mitigated. There is a need to investigate both the effect and the impact of increasing penetration of these intermittent RES on, particularly, voltage and frequency stability power systems and the utilization thereof of such sources to improve voltage stability margins and predict voltage stability conditions. This research work investigated voltage control and stability conditions at Solar PV buses through various case studies and scenarios simulated using the Power Factory® tool, both in static and dynamic analysis modes. A modified standard IEEE 9-Bus Sub-transmission system was used to assess the voltage profile, system loadability and system stability. The comparison and discussion of the results obtained from the integration of the Solar PV and FACTS devices under various scenarios revealed that their respective impacts and abilities to improve voltage stability differ. The results confirmed that under any operating conditions, reactive power control remains the most effective method to control voltage stability and power transfer capability, especially in the context where an increasing penetration of renewable and inertia-less generating sources is planned. The results further revealed that there is a specific location and a specific siting architecture for a given size of PV that produces the best results for voltage stability, as well as improved system stability and loadability conditions for a given load distribution profile in a particular network. Lastly, the results demonstrated the effectiveness of the use of a Battery Energy Storage System (BESS) in achieving voltage control and regulation in distribution networks highly penetrated by PV generation, subsequently enabling greater RE penetration.

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