Electrical Computer Engineering

Permanent URI for this collectionhttps://etd.hu.edu.et/handle/123456789/74

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Start date: 2020End date: 2025

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    VOLTAGE CONTROL OF A DC-DC BUCK CONVERTER FOR ELECTROLYSIS USING FRACTIONAL ORDER SLIDING MODE CONTROL
    (Hawassa University, 2020-10-22) DEMOZ LISANEWORK WELDETSADIK
    Switching DC-DC converters are non-linear and the most widely used circuits in power electronics. Generally, they are used in all conditions where there is need of stabilizing a given DC voltage to a desired value. DC-DC buck converters are used in voltage step down applications. A DC solar energy is converted to the desired voltage level using the a buck converter, for hydrogen generation with electrolysis process have been investigated. The electrolysis load for hydrogen production especially needs low voltage and high currents. To have these conditions the converter must be designed and controlled sensitively. For this aim, the fractional order sliding mode (FOSM) controller is used as a solution in this paper. Simulation results showed that, FOSM controller improved the rise time and settling time by 2% and 15.3% respectively compared the values using PID controller. Similarly, FOSM controller shows comparatively best performance improvement over SOSM in terms of high reduction of unwanted oscillation in addition to the rise time, settling time improvements. The overshoot is reduced from 46.3% to 5.208% using PID controller while it is totally removed when SOSM and FOSM controllers are applied. Both SOSM and FOSM controllers overcome the effect of electrolysis load variations. The actual output voltage is not deviated from desired value even for large input voltage variation using FOSM controller. Furthermore, the performance of controller was tested by increasing and decreasing 58.52% electrolysis load from operating point while desired output voltage is decreased by 50% and increased up to 20% from operating point. Generally, from the above analysis results it is evident enough that FOSM is better and preferable controller than the SOSM and PID controller
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    DESIGN AND SIMULATION OF DC MICROGRID FOR ELECTRIC VEHICLE CHARGING STATION (A CASE STUDY HAWASSA CITY)
    (Hawassa University, 2020-08-17) MATHEWOS HADERO GUTENA
    Development of electric vehicle has been established as an effective way to ensure energy security and realize emission reduction. However, the public electric vehicles charging station which is important element of using electric vehicles is not installed in Ethiopia. Therefore design of DC microgrid for charging station is proposed in this paper. In Ethiopia the electric energy infrastructure is not modernized enough and it is really difficult to fully depend on the energy obtained from grids. Thus, it is important to integrate the renewable energy (solar), grids and energy storage. However, the reliability of integration of renewable energy is dependent on the ability of the system to accommodate expected and unexpected changes (in production and consumption) and disturbances, while maintaining quality and continuity of service to the customers. Thus to improve real-time control performance and reduce possible seasonal variation forecasting is proposed for the solar energy used in the system. Thus in this study the author used the metrological data from Hawassa station and used machine learning algorithm for train the model with collected data and python used as programming language to develop forecasting model score system. Python is one of a well known high level programming language in data science.In this thesis, Jupiter notebook is used to write Python codes to develop a solar energy forecasting system.The designed forecasting system can predict the next day irradiance with accuracy of 97.56%. Next MATLAB simulation tool is used to integrate system. The proposed maximum operating voltage of this DC microgrid charging station is 500 Vdc. Power flow management using fuzzy logic controller keeps voltage within expected range with standard voltage deviation 2.2 and improved the response time 1.645 ms. More over the author also investigated the operating costs per year for this design. The operating costs for energy is $43,651per year if you use grid only for charging of EVs. On the other hand if 400 kW of PV and 680 kWh of battery capacity is integrated to the grid it reduce the operating costs to$6,344 /yearwith annualized saving of $37,306.This implies as the hybrid system has investment payback of 3.06 years and an IRR of 32.7%.Thus, clearly the result obtain in this thesis have great potential in future charging station design
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    ARTIFICIAL NEURAL NETWORK BASED FAULT CURRENT MINIMIZATION IN DISTRIBUTION SYSTEM USING SUPERCONDUCTING FAULT CURRENT LIMITER. (CASE STUDY: HOSANNA SUBSTATION-DISTRIBUTION SYSTEM)
    (Hawassa University, 2021-08-17) ZENABU DUGUNO WAKERO
    High magnitude of short circuit fault current takes place in electric power distribution system. This unexpected high magnitude of short circuit fault current can cause the failure of Hossana substation switchgear equipment’s and even if due to this problem most of industries sharing power from Hossana substation and end users of Hossana substation cannot get power properly. So, fault current minimization in distribution system is a critical issue and to minimize the maximum short circuit fault current in distribution system, superconducting fault current limiter (SFCL) device is applicable in this thesis work. By installing superconducting fault current limiter (SFCL) device to the Hossana substation distribution feeder especially for Gimbichu feeder maximum short circuit fault current to be minimized for different types of short circuit faults like, Line to Ground (L-G) fault, Line to Line (L-L) fault, Double line to Ground (LL-G) fault and balanced three phase faults in distribution feeder. Under this thesis work the case study area focus on Hossana Substation - Distribution system feeders especially from the nine of feeders Gimbichu 15KV feeder. The reason why this feeder is selected is because of this feeder covers long distance approximately 150KM and high system interruption take place frequently. In this thesis work ANN controller is used to control the SFCL device and both ANN controller and SFCL device are modeled in MATLAB/Simulink. After developing SFCL in MATLAB and connect this device to the distribution feeder it is possible check the fault current magnitudes before and after installing SFCL device to the system. Before installing SFCL device to the system the magnitude of short circuit fault current is 20KA to 40KA for L-G fault, L-L fault, LL-G fault and balanced three phase faults in Gimbichu 15 KV feeder. But, after installing SFCL device to the case study area maximum short circuit fault current magnitude become minimized 140A up to 150A for all types of short circuit faults. Finally, the payback period is calculated after installing SFCL device to the 15KV Gimbichu feeder. Therefore, the calculated payback period is 1.14 years i.e., the year of back payment of this thesis work is 1 year,1 month and 21 days
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    Design of Wavelength Division Multiplexing based Passive Optical Network Transmission System using Heterodyne Receiver for 5G Transport
    (Hawassa University, 2022-12-11) Wondmagegn Wana
    Fifth Generation network standard has put higher peak data rate (10x) and very low latency requirements (1/10) as compared to its predecessor 4G network. In any mobile network implementation, the transport network is critical component for delivering the intended services. The demand for high data rate in 5G requires massive capacity upgrade in the transport network. On the other hand, latency in 4G and older technologies is too much as compared to 5G requirements. Hence Building low-latency and high-capacity transport networks is vital for new high-speed cellular technologies. Optical fiber-based technologies are essential to meet the high bandwidth demands of 5G transport Network. The two contending optical technologies for 5G transport are point-to-point (P2P) fiber access and point-to-multipoint (P2MP). P2P fiber access has low fiber efficiency and requires infrastructure installation for new deployment. Point-to multipoint fiber has high fiber efficiency as compared to P2P. Among the P2MP fiber options, TDM-PON uses dynamic bandwidth allocation (DBA) to multiplex services which introduces 1ms delay. On the other hand, WDM-PON doesn't require DBA, thus is a good candidate for low latency services. Studies on WDM-PON are using homodyne receiver. The proposed network was simulated in Opti Wave Optisystem simulation software. In this thesis, a new 2.4 Tbps WDM-PON based network using heterodyne receivers was built as solution for 5G transport network requirements. The performance of the new system was compared with back to-back model using BER and OSNR. An OSNR of 15.4 is required to obtain a BER of 10−3 dB for Heterodyne System while an OSNR of 14.8 dB is required for Back-to-Back System which is 0.6 dB higher. The results obtained from the Heterodyne system simulation are very close to the result found in case of back-to-back system. Hence, the WDM Dual Polarization 8-PSK PON system with heterodyne receiver can be used in 5G transmission
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    DISTRIBUTION SYSTEM RELIABILITY IMPROVEMENT USING DISTRIBUTED GENERATION AND NETWORK RECONFIGURATION
    (Hawassa University, 2021-10-28) MEKLIT GIRMA
    Power supply reliability is the basic issue for economic and technology development of the country. The sufficient or adequate and secure supply of power will assure the reliability of the system. Unreliability of the system occur due to high outage frequency and duration, system overload and unsecure system or protection system. When the distribution system is reliable, it has capacity to meet the demand of customer and operate under adverse condition. Arbaminch distribution system has encountered frequent power interruption and power quality problem. The interruptions are mainly caused by system overload and short circuit fault. The reliability of the distribution system is assessed based on the data from Ethiopian Electric Power Corporation. Arbaminich substation of feeder -05 is selected as case study, which has high rate of interruption. Feeder -05 has SAIDI value of 236.8386 Hr./cust. /yr. and SAIFI of 221.6338 f/cust. /yr. The reliability indexes values of feeder -05 are not within the ranges of bench marks of reliability requirement. This thesis focused on reliability improvement of distribution system with better placement of distributed generation and network reconfiguration. Particle swarm optimization algorithm is used for placement of DG, size and network reconfiguration. The algorithm is done using MATLAB 2016 software. Based on the availability in the area, efficiency, cost and emission level, Solar and Microturbine sources are used as distributed generation. The suitable site and size of DG are found at bus 10 with suitable size 4.5 MW. For network reconfiguration sectionalizing switch is used. Before reconfiguration the switch was placed at bus 20, 21, 22,23 and 24. During network reconfiguration switch changed to bus 3, 4,12,24 and 31. The reliability indices SAFI, SAIDI and EENS value improved by 82.81%,78.89% and 78.10% respectively after DG with reconfiguration used. Expected interruption cost before applying the proposed method is 9,758,852$ /year. After the proposed method used expected interruption cost reduced to 2,995,270$ /year. This indicates that, 6,763,582 $/year is saved after using the proposed techniques
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    Reliability Enhancement and Power Loss Reduction in Distribution System by Optimal Reconfiguration (A case study of Kombolcha Distribution Network)
    (Hawassa University, 2020-10-26) DEGAREGE ANTENEH YALEW
    The purpose of power system is to provide an adequate and secured electrical supply to its customers as economical as possible with reasonable level of reliability. In distribution system, reliability and power loss are the major issues for the consumers and utility. This thesis presents a research work on the reliability assessment and optimal reconfiguration of Kombolcha radial distribution network to minimize the overall distribution losses, to enhance reliability and improve the voltage profile by using a proposed MSSO algorithm and ETAP. In the power flow analysis, the effectiveness of the proposed MSSO algorithm is conducted and compared in two cases (before reconfiguration and after reconfiguration) of Kombolcha distribution at line-3, which is severe. A modeling of electrical system elements were first developed to have a complete single line diagram of the existing network using ETAP. The reliability enhancement is measured and analysis by different reliability indices that include SAIFI, SAIDI and EENS. Reliability index values have been compared with standard benchmark values and comparison clearly indicates that Kombolcha feeder-3 distribution system is extremely unreliable. Generally, after optimal reconfiguration of the network, power loss of the system is minimized by 60%, SAIFI has been reduced by 85% as compared with the average reliability index value of the system in the base years. Similarly, SAIDI and EENS have been reduced by 86% and 70% respectively.
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    PERFORMANCE ANALYSIS OF HYBRID OPTICAL FIBER/FSO COMMUNICATION SYSTEM USING ADVANCED MODULATIONS
    (Hawassa University, 2021-04-21) FISEHA ZELALEM
    Due to its lower attenuation and high bandwidth, current telecommunication infrastructure uses optical fibers for high data long haul transmission. Free space optics (FSO) technology is a good option for short-distance multi-gigabits per second or beyond data transmission. Nowadays, it has different application areas such as indoor, outdoor, underwater, and deep-space communications. A key area within this new generation is the combination of optical fiber and FSO network to provide high bandwidth for both long and short-distance services. The hybrid link uses coherent optical advanced modulation and dispersion compensation techniques to achieve the best performance with the existence of atmospheric turbulence effect and fiber limitations. Orthogonal frequency division multiplexing (OFDM) and dual-polarization quadrature phase-shift keying (DP-QPSK) are considered promising technologies to satisfy the demand for bandwidth expansion in broadband services. OFDM can overwhelm optical fiber limitations such as polarization mode dispersion (PMD) and chromatic dispersion (CD), whereas DP-QPSK provides good noise immunity. This thesis concentrates on designing, simulation, and performance analysis of 100Gbits/s data rate hybrid optical fiber/FSO systems using coherent optical OFDM and DP-QPSK modulation techniques. MATLAB software and OptiSystem simulation tool are used to design and simulate the hybrid system. To study the performance of the systems and the quality of the signals the bit error rate and the Q-factor are considered. As a result, for 100Gbits/s per channel with DP-QPSK based system, the link coverage is up to 468m in FSO and 202km by fiber cable; and up to 510m FSO link and 220km by fiber optics for CO-OFDM system. It is observed that the CO-OFDM system has high tolerance against linear signal distortion effects and sensitive to nonlinear effects which affects the system performance
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    Performance Analysis of High Speed Fiber Optic Communication Systems with Optical OFDM and Dispersion Compensation Technique
    (Hawassa University, 2022-04-20) GIRMA HASENA HINSENE
    Several designers are employing fiber optics instead of copper wire to transport information between data ports to fulfill the high-speed requirements of today's communication systems since it offers several advantages such as high transmission capacity and low losses. Limitations and flaws such as chromatic dispersion hamper the performance of optical fiber communication systems. Tolerating the effects of chromatic dispersion in optical communication systems, various classic dispersion compensation techniques such as Dispersion Compensation Fiber (DCF) and Fiber Bragg Grating (FBG) have been used. Advanced modulation schemes, such as orthogonal frequency division multiplexing (OFDM), are excellent candidates for improving spectrum efficiency in communication systems by reducing chromatic dispersion effects. That is FBG uses the principle of recompression of light signals with different wavelengths to reduce the effect of chromatic dispersion. And OFDM uses the orthogonality principle between subcarriers with the insertion of cyclic prefix and guard bands to reduce the effect of chromatic dispersion. The performance of a high-speed optical fiber communication system was investigated using coherent optical OFDM (Co-O-OFDM) and Fiber Bragg grating (FBG) as dispersion compensation techniques in this thesis study. The system models were simulated using Optisystem simulation software, and the output was plotted using MATLAB. Performance measuring metrics such as optical signal to noise ratio (OSNR), bit error rate (BER) and Quality-factor were used to thoroughly examine the results. RF spectrum, optical spectrum, and constellation diagram of the signal were examined at different distances to see the effect of chromatic dispersion. The performance of both DP-16QAM Co-O-OFDM and FBG integrated DP-16QAM Co-O-OFDM systems declined as the signal propagated long distances of fiber optic for four different rates due effect of chromatic dispersion, and FBG integrated DP-16QAM Co-O-OFDM system performed better for the same rate and distance due to integration of FBG.
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    PERFORMANCE ANALYSIS OF DECISION THRESHOLDS ON DUAL-HOP CRNs BASED ON ENERGY DETECTIONS
    (Hawassa University, 2022-12-17) TSEGAYE AYELE ABERA
    Cognitive radio is a robust technology that helps to overcome spectrum underutilization. In recent generations, there has been an exponential growth in bandwidth usage and arising underutilization of radio spectrum resources, due to increasing the extent of radio spectrum demands. However, the spectrum detection and decision threshold techniques are a promised wireless communication technology dedicated to the efficient use of the free spectrum bands. The main challenges in cognitive radio network (CRN) are an inefficient use of licensed spectrum bands due to noise uncertainty, the selection of the most appropriate decision threshold technique based on fading environments. Therefore, investigations on minimizing interferences to obtain accurate information from the desired sensing region of licensed bands at the fusion center during the energy detection process. In this thesis work, performance analysis of decision thresholds on dual-hop CRN’s based on energy detection (ED) to conquer the reviewed problems on kinds of literature. Thus, the comparatives of fixed and adaptive threshold techniques receiver operating characteristic (ROC) curve plots based on the effect of noise uncertainty (NU) parameters and different SNR Environments to obtain outperformed decision thresholds. In addition, evaluating the effect of the number of signal samples size on detection probability during the ED process, the performance analysis of adaptive ED at different SNR environments based on ROC and complementary ROC curve plots. Moreover, in the evaluation of hard decision rules performance for adaptive thresholds of ED at fusion center (FC), the obtained ROC curve plots for ‘’Logic-OR’’ fusion rule performs high false alarming probability with high detection probability than ‘’Logic-AND’’ Rules. Based on discussion results, adaptive decision thresholds performed better than fixed thresholds at low SNR conditions, while the fixed decision thresholds relatively had better performance in high SNR environments. Furthermore, when the sample size increases the detection performance also increases proportionally at perceived SNR ranges. Lastly, the performance evaluations are executed using MATLAB R2018a software and an OFDM signal with Quadrature Phase Shift Keying (QPSK) scheme is advanced based on desired values of false alarming probability (PFA ≤ 0.1) and detection probability (PD ≥ 0.9) at different SNR and number of sample size (N) values.
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    IDENTIFICATION, CLASSIFICATION AND MITIGATION OF POWER QUALITY ISSUES IN DISTRIBUTION NETWORK USING STOCKWELL TRANSFORM AND DISTRIBUTION STATIC COMPENSATOR (A CASE STUDY OF YIRGALEM SUBSTATION)
    (Hawassa University, 2022-10-27) EPAPHROS MENGISTU
    Power quality has become a crucial concern recently due to the increase of the consumption of electrical load and the increment in the use of sensitive devices connected to power systems. In spite of that, complexity in modern daily life and the increased usage of semiconductors make non linear load a real threat to power quality level. In order that maintain power quality and to ensure its reliability, power quality disturbances must be identified and classified correctly and precisely. Thus, identification algorithms support decision makers to identified and mitigate the disturbance, and protect the power network from a high level of financial loss. In this thesis study identification, classification and mitigation of power quality issues in Awada industry zone. The measured voltage and current harmonic distortion levels are compared with the IEEE 519-2014 and IEC 61000-2-2 / -3-4 standards. The harmonic voltage distortion level in the factory has found to be well under the limits set by these standards while the current harmonic distortion levels on one of the transformer among four transform exceeds the limits with a maximum percentage total harmonic distortion current value of up to 23.09%. First, an identification process covering the most important and common power quality issues for further analyzed and discussed. Then after, most of the powerful processing algorithms in addition to support vector machine technique was investigated and their results are discussed. SVM then classify complex data and enhancing the evaluation process. This method achieved a sufficient detection algorithm, which overcame the Wavelet, Fourier and Hilbert limitations and resulted in an overall accuracy of 91.08%, 88.91% and 86.8% respectively. This resulted in a substantial improvement in terms of overall accuracy, with more than 97.1% when using Stockwell transform. In addition to the average classification accuracy, other common performance measures computed from the confusion matrix also presented and highest average accuracy of SVM is 98.3%. For mitigating, the current harmonic distortion level in the industry a D-STATCOM in current control mode is designed. The performance of the D-STATCOM is evaluated by simulating the distribution network with and without D-STATCOM. The simulation results show that the source current becomes pure sinusoidal and in-phase with the source voltage within 0.02 second and THDI reduced to 4.36% after the enabled of the D-STATCOM in the system.