Theses and dissertations (Engineering and Built Environment)
Permanent URI for this collectionhttp://ir-dev.dut.ac.za/handle/10321/10
Browse
7 results
Search Results
Item Design and application of passive filters for improved power quality in standalone PV system(2024-05) Dlamini, Sandile; Adebiyi, Abayomi Aduragba; Kabeya, MusasaHarmonic components have developed in power systems due to the non-linear properties of the circuit components utilized in power electronics-based products and their rapid application. Power systems rely on fundamental quantities like sinusoidally varying voltage and current, which oscillate at a frequency of 50 Hz. The standard restrictions of IEEE-519-1992 were utilized as a benchmark in this study. To generate the best output, the total harmonic distortion (THD) should be decreased below the limit, even for certain individual harmonic numbers, and reflect the power factor output. Using the results of the simulation and projections for each mitigation strategy, the THDI can be reduced below the IEEE-519 standard whilst also providing cost and electrical advantages. Analysed and modelled is the PV system, which comprises solar panels, a DC-DC converter, a DC-AC inverter, and a non-linear load. Passive filters are an effective solution for improving power quality in standalone photovoltaic (PV) systems. This dissertation provides an overview of the design and application of passive filters for this purpose. Firstly, an introduction to PV systems and the power quality issues associated with them was preferred. Next, different types of passive filters, namely LC filters, LCL filters and LLCL filters, are discussed along with their advantages and disadvantages, and the design considerations for these filters, including the selection of filter components and the calculation of filter parameters. The application of passive filters in standalone PV systems was then discussed, including their implementation in DC-DC converters and Z-Source inverters and, the design of PWM controllers such as the constant boost control method and simple boost control method. The analysis of the outcome of the engineered systems was conducted according to the IEEE standard and SANS 10142 Standard to protect the connected equipment within the off-grid network. The outcomes pertain to the single-phase stand-alone/off-grid photovoltaic system and the single-phase Z-Source inverter. The Z-Source inverter is equipped with two distinct methods for PWM control, namely the constant boost control method and the simple boost control method. All three designs incorporate three passive filters, namely the LC filter, the LCL filter and the LLCL filter. The results were obtained from the network consisting of three distinct designs. LLCL demonstrates superior performance as a passive filter, substantiating its position as the optimal choice. The optimal outcomes of a single-phase off-photovoltaic (PV) network can be achieved using LC, LCL and LLCL filters, with corresponding percentages of 2.99%, 2.45% and 1.71% respectively. Unfiltered was 89.05%, which is not good for the equipment connected to the network. The Z-Source showcases the capability of voltage amplification to an infinite level, rendering it highly effective in minimizing total harmonic distortion. This research investigation further demonstrated the efficacy of the Z-Source Inverter with Constant Control Boost Method and Simple Boost Control Method, achieving unfiltered total harmonic distortion levels of 38.85% and 44.96% respectively. The Z-Source inverter, when combined with the Constant Boost Control method and Simple Boost Control method, exhibits various filter configurations such as LC, LCL, and LLCL filters. In the context of the constant boost control and simple boost control methods, it is imperative to assess the total harmonic distortion percentage of voltage and current for LC, LCL, and LLCL configurations. The constant boost control voltage (LC, LCL, LLCL) and current total harmonic distortion (LC, LCL, LLCL) are measured at 4.177%, 2.655%, 1.951%, and 2.958%, 2.09%,1.465% correspondingly. The voltage-based boost control methods, namely LC, LCL and LLCL, exhibit total harmonic distortion levels of 2.345%, 1.920% and 0.211%, respectively. Similarly, the current-based boost control methods, LC, LCL and LLCL, demonstrate total harmonic distortion levels of 2.346%, 1.921%, 0.211%, and 2.346%, 1.921%, 0.211%, respectively. Finally, the dissertation wrapped up by exploring the potential of passive filters for enhancing power quality in standalone PV systems. The thesis offers a comprehensive investigation of the design and implementation of passive filters in standalone PV systems, providing valuable insights for engineers and researchers in the field. It enhances understanding and utilization of these imperative devices.Item Development of an Intelligent Standalone Solar Photovoltaic 48V DC microgrid system(2024-05) Makhanya, Thandeka; Pillay, N; Sewsunker, RWith load shedding negatively affecting South Africans there are many concerns regarding stable power delivery to residential households. Amid all the power delivery concerns some rural communities are still not connected to the existing power infrastructure. Implementation of newer efficient clean energy sources is in demand. A standalone Photovoltaic (PV) Solar distributed renewable energy Direct Current (DC) microgrid can be the best possible approach to tackle the power grid shortcomings and to electrify communities that are not yet covered by the power grid or communities that want to transition to clean energy. The research focuses on the design of an optimal 48 VDC Multiple-PV Standalone microgrid in remote areas not covered by the main grid. The proposed microgrid can be typically used for lighting, charging phones, and other low-power applications. The microgrid will consist of 4 microgrid subgrids, each consisting of a dedicated Solar PV array, battery storage systems, loads, and other components that connect to the DC Bus and need to be monitored and controlled for efficient operation. Furthermore, the subgrids were designed based on the meteorological data of the selected location and the load demand for each subgrid. The microgrid design enables the subgrids to share power through a bidirectional DC-DC converter based on certain conditions. A power-sharing management system was implemented to manage power-sharing ensuring that the sharing subgrid does not drive its users to load shedding. Moreover, the microgrid design was simulated on Matlab/Simulink to observe the operation of the designed system and to determine if the proposed design would be able to achieve the desired goal. The results obtained from simulations indicate that the proposed microgrid design can provide an optimal service to its users by allowing the subgrid with surplus energy to share its power with the subgrid when needed.Item An investigation into harvesting solar energy using thermoelectric generator coupled IBR sheeting(2024-05) Malik, Momina; Gilpin, Mark; Graham, Bruce RobertThere is a current global impending need for clean and renewable energy sources. Fossil fuels are non-renewable finite resources, which are dwindling because of high cost, and environmentally damaging retrieval techniques. South Africa’s coal resources may soon reach their end, which further stresses the need for green energy. An efficient and more feasible alternative is solar energy. Thermoelectric generators (TEGs) may use the energy from the sun to generate power and are an innovative means to harvest electricity. The proposed study intends to validate whether TEGs are a potential method to harvesting solar power. The study herein is a preliminary experimental investigation into a development in a TEG modular prototype. Relevant tests are run, and the performance characteristics obtained from experiments are discussed. The TEG system developed and tested in this study consists of 2 equally sized pieces of Inverted Box Rib (IBR) sheeting with one side exposed to a light source, while the other side remains shaded. An Arduino, connected and coded to read and display resulting temperatures, Peltier tiles, magnets, simple heatsinks and Multimeters are connected to measure open circuit voltage and closed-circuit current generated from the temperature difference between the two sides of the IBR sheeting. The system aims to harvest energy whilst keeping the assembly and construction simple, practical, and minimalistic. Outdoor experiments were conducted to determine the temperatures and the resultant temperature gradients the configuration may experience in operation. The data collected established parameters for the laboratory experimental setup. The laboratory experiments characterized the power output of the units. For comparative purposes, some variables were removed, such that the testing variable was isolated. Some environmental variables were removed by testing in a laboratory. The TEG was tested in the vertical position to allow for maximum natural convection, and hence may not reflect results that would be obtained in all applications. The TEG system is exposed to the light source at different distances, perpendicular to the sheets. The study intends to investigate the effect that the 2 variables have on the amount of solar power generated i.e., the colour of metal IBR sheeting, and the ideal electrical arrangement for scalability of Peltier tiles for maximum power output (𝑃𝑚𝑎𝑥). The IV curve generation method (later explained in chapter 2.4.1) is used to read the parameters required to calculate 𝑃𝑚𝑎𝑥. The results show a strong influence of the black coated sheets on the power output of the TEGs. It is deduced from solar experiments, that the aluminium rods used as the heatsink fulfilled its purpose of regulating a ∆T of 1-2°𝐶. Furthermore, the TEG in series configuration, generated the highest 𝑃𝑚𝑎𝑥 when located 300mm from the heat source, followed by 600mm and lastly, 900mm. The same pattern is found for the unit and parallel configurations. It may be concluded from the proposed TEG system that TEGs are a potential method of harvesting solar energy on IBR sheeting, specifically in a vertical position. However, applications of different orientations and geographical locations require further investigation. The results merit further investigation and refinement into the use of TEGs on IBR sheeting where the herein designed TEG system is set-up in a user friendly, simple, cost effective and practical manner for solar energy harvesting. While the power output per TEG tile is small in magnitude, the proposed configuration has potential in the coupling of multiple units to increase power output. The current work shows potential for the use of TEGs in this application. Through further investigation, refinement and cost analysis, the system may prove to be a practical method of solar energy harvesting.Item Solar energy-battery storage optimization for satellite-to-ground communication(2023-09) Ntlela, Simphiwe A.; Davidson, Innocent Ewaen; Moloi, KThe creation of ubiquitous broadband systems has piqued the interest of both academics and industry to fulfil the exponential growth in demand for multimedia services on mobile devices and to support access anywhere on the earth. The implementation of such systems is anticipated to heavily rely on satellite networks in general and Low Earth Orbit (LEO) satellite constellations. Therefore, increasing their service life has become a significant engineering and scientific challenge. The main finding of this thesis is that by sharing the power of a satellite's batteries with another spacecraft that is still in the sun, one may considerably extend the service life of a satellite. Over 30% of the time that LEO constellation satellites are in the earth's shadow, they are powered by batteries. Although the batteries are replenished by sunlight, the depth of discharge they experience during an eclipse has a major impact on their lifetime and, consequently, the service life of the satellites. A 15% increase in the DoD can almost halve the service life of the batteries. The major section of this thesis includes a variety of strategies we think may help LEO constellations' batteries last longer. The market's demand for satellite communication networks has changed recently. Low-EarthOrbit (LEO) satellite constellations have therefore received increased attention because they are expected to address these needs. In the current LEO satellite constellation-based communication system, the satellite close to the satellite terminal that submits the communication request answers to it regardless of the state of its battery. However, in cases of significant battery deterioration, this communication technique reduces the lifetime of the satellite. This means that in big satellite constellations when operating costs are a concern, this communication mechanism is unsuccessful. To extend the battery's lifespan, we design a communication mechanism in this work that regulates the transmission power and transmission gain of a satellite antenna based on the battery's state of deterioration. Large-scale LEO satellite constellations can be created and used thanks to the decrease in operating expenses that results from extending battery life. Future demands for satellite communication should be met by the system that has been put in place. Through simulation, the usefulness of the suggested approach is confirmed. The use of solar energy for satellite power is an attractive option due to its sustainability and cost-effectiveness. However, satellite communication requires a constant and reliable power supply, which is challenging to achieve with solar energy alone, particularly in periods of low solar activity or during eclipses. This is where battery storage optimization comes into play. In this study, we propose an optimization model for the use of solar energy and battery storage in satellite-to-ground communication systems. The model takes into account various factors such as solar irradiance, battery capacity, and communication power requirements. The optimization objective is to maximize the utilization of solar energy while ensuring uninterrupted communication. We apply the proposed model of Q-theory to a case study of a Low Earth Orbit (LEO) satellite. The simulation results show that the proposed optimization model can significantly improve the performance of the satellite power system. Specifically, it can reduce the reliance on battery power during periods of low solar activity, leading to longer battery life and more reliable communication.Item Performance evaluation of control strategies for grid connected wind power generator(2023-05) Ntuli, Welcome Khulekani; Kabeya, Musasa; Sharma, GulshanSouth Africa is currently experiencing a significant load-shedding situation because of rising electricity demand. The renewable energy power producer (RPP) sector is growing rapidly to become an important source of power in South Africa and nations across the globe. Companies within this sector provide a variety of clean energy sources, including wind, solar, hydroelectric, biomass and geothermal. Despite its ability to support the power system and conserve the environment that sustains life, the rising usage of renewable distributed generators (RDGs) poses power quality problems in the overall distribution network, such as the voltage instability at buses, the increase in voltage/current harmonics distortions, etc. The technical requirements for connecting RDGs to the power system have been defined in standard grid code to ensure the safe, secure and proper functioning of the overall power system. The specifications defined in the grid code include the limit of voltage variations (i.e., +/-1 pu), the limit of frequency variations (i.e., +/-5%), and the limit of current/voltage harmonic distortions (i.e., total harmonic distortion voltage (THDv) of 0.1% and total harmonic distortion current (THDi) of 5%), and a power factor limit of Pf = (0.9-0.95). Additionally, RDGs must remain connected throughout a fault condition and assist in voltage recovery. In this dissertation, control strategies for grid connected wind energy conversion system (WECS) are investigated for dynamic performance evaluation. This work focuses on the doubly fed induction generator (DFIG) – based WECS incorporating a proportional integral (PI) controller; the permanent magnet synchronous generator (PMSG) – based WECS incorporating a PI controller; DFIGb-based WECS incorporating a voltage source converter (VSC) with a fuzzy-logic controller, the proportional integral derivative (PID), and fuzzy-PID controller. A comparative analysis of the different WECS topologies was further conducted in terms of the steady-state error, the percentage overshoot, and the settling time of the voltage/current or power output signals and dc-link voltage signals.The VSC was selected as compared to the line-commutated converters (LCCs) because of the commutation that is not dependent on voltage and current AC signals. The grid-side converter was applied to regulate DC-link voltage and reactive power to their reference values. The rotor side converter provided rotor speed regulation on the DFIG to control the power output signal. The vector control method was used for the dynamic performance analysis. The simulations were done using MATLAB/SIMULINK. From the simulation results, it was found that the DFIG-based WECS incorporating a fuzzyPID controller performed efficiently compared to the other topologies of WECS.Item Design of control strategies for frequency stability of PV-thermal interconnected power system(2021-02) Estrice, Milton Solomon; Sharma, Gulshan; Akindeji, Timothy KayodeRenewable energy in particular solar energy is a viable option to meet the increasing energy demand for the modern world. The Solar resource in South Africa is among the highest in the world. With the progression of modern society, both energy demands and energy prices are increasing, which has welcomed the introduction of renewable energy resources as an alternative. However, solar radiation varies over the complete day sometimes over the season, and sometimes over the complete year. Further, the power demand is highly variable in nature. Hence, the generated power should match the customer demands over the period of twenty-four hours, and further, it should be economical for customers and electrical utilities. Hence, this study will focus on integrating PV plants with thermal plants to meet the rising customer power demand. The integration of PV with thermal power plants will bring some new challenges in the domain of power system operation & control which is the frequency of the power system should be restricted to well-defined values. Hence, suitable control strategies are to be developed for the successful and smooth operation of the power system. In this research work, an attempt is made to investigate an interlinked system comprising of a thermal and a PV generation system. The control strategies based on PID controllers and their gains tuned through effective tuning techniques are presented. In addition, the concept of fuzzy logic is used to address the problem of frequency managing of PV-Thermal via effectively designing fuzzy proportional, fuzzy integral, and fuzzy PI built control strategies to ensure the frequency regulation of the energy system. The obtained results are shown via a graphical approach, and the best control design is explore and suggested for the considered system. In addition, the scope for further improvement and possible direction areas are also explored and listed in this report.Item Application of optimal control for power systems considering renewable energy technologies(2021-03) Chetty, Dhanpal; Sharma, Gulshan; Davidson, Innocent EwaenOver the last decade, power generation from renewable energy sources such as wind, hydro and solar energies have substantially increased globally and in South Africa. Of all the renewable energy sources, wind energy appears to be the most promising, considering design and costs. However, due to the intermittent nature of wind, the increased integration of wind energy into existing power systems raises several control challenges related to load frequency control (LFC) and tie-line power system stability. The stability of modern power systems, incorporating wind energy generations, will be significantly enhanced with the development of LFC strategies based on modern control theory, which is the focus of this research. This thesis presents the design, modelling and analysis, of two LFC control strategies for interconnected power systems, having wind power integrations. The first design is an optimal control strategy, based on error minimization through full state vector feedback, for a two-area interconnected power system consisting of hydro-thermal generations. The second design is a model predictive control (MPC) strategy, based output vector feedback of system state parameters, for a two-area interconnected power system consisting of thermal generations in each area. Both designs include the active power support from doubly fed induction generator based wind turbines (DFIG) in conjunction with the combined effort of a thyristor control phase shifter (TCPS) and super conducting magnetic energy storage unit (SMES). Both control strategies were simulated in MATLAB Simulink and positive results were obtained. The results show that the optimal control strategy is enhanced with power integrations using DFIG based wind turbines combined with the TCPS-SMES units and the MPC strategy is very robust and provides better dynamic performances even with parameter variations and generation rate restrictions.