Mekelle University Institutional Repository
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The Mekelle University Institutional Repository is a digital collection of scholarly and research outputs created by the university's faculty, students, and researchers. This repository provides open access to a wide range of materials, including articles, theses, dissertations, conference papers, books, and more."
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- Promote knowledge sharing and collaboration within the academic community.
- Preserve and disseminate valuable scholarly works for future generations
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- A central archive for Mekelle University’s institutional abstract books from academic and research conferences.
Recent Submissions
Distributed Power Flow Controller Based Power Quality Improvement for Grid Connected Wind Farm- Case Study Ashegoda Wind Farm
(Mekelle University, 2025-09-23) Ashenafi Selema
Grid penetration level of renewable energy is growing and merging dramatically. However, poor power quality creates a major integration and operation problems. Ashegoda wind farm represents Ethiopian first large scale wind power installation, having a total rated capacity of 120 MW. The substation is equipped with two 230kv buses that interconnect Lachi and Alamata substations. In the analyzed system, both transmission lines experienced high reactive power flow approximately 43MVAr and more than 3% current total harmonic distortion (THD), which leads to additional power loss, voltage drop, equipment overheating, and network congestions. On the other hand, the on-load tap changer (OLTC) transformer used to support voltage sag, swell, under-voltage, and over-voltage has slow response time up to 10 seconds per tap, and creates transformer overheating and mechanical fatigue. To solve such integration challenges, the incorporation of a distributed power flow controller (DPFC) with in the system is necessary for improved power quality and reliability. This study analyzed and modeled the integration, impact, cost benefit analysis, and Genetic Algorithm (GA) based optimal sizing and placement of DPFC for Ashegoda wind farm. The objective was to model, simulate, and asses its impact on voltage stability, reactive power compensation, and steady state and dynamic performance. The result indicated that, without DPFC the 230kv system operated at under-voltage of 0.89 pu with 5% current THD at bus 690v. After integration of 8MVA series and 25MVA shunt DPFC controller, the voltage profile is improved to 0.96 pu and current THD is minimized to 1.8%. Integrating DPFC exhibited excellent performance in maintaining voltage stability and limiting short-circuit current levels under different fault scenarios. The cost benefit analysis was carried out over a 20-year period. The total net present value (NPV) is estimated around $15,310,316.0 US dollars, while the total investment cost amounts $7,883,000.00 US dollars. By implementing the system, Ethiopian electric utility is expected to gain $7.5 million US dollars profit without considering scrap value. Generally, the researcher proved that DPFC is technically and economically feasible. MATLAB/Simulink 2018a and Excel-2013 was employed to model, simulate, and analyze the proposed DPFC system.
Quantitative Analysis of Potentially Toxic Elements (Pb, Cd, Co, Cr, Fe, Mn, and Ni) in Lipstick Brands Available in Mekelle Markets, Tigray, Ethiopia
(Mekelle University, 2025-09-25) Asfaw Mulugeta Gebremedhin
Lipsticks, widely used cosmetic products, can be a significant source of potentially toxic elements exposure through unintentional ingestion. This poses potential long-term health risks due to the bioaccumulative nature of metals like Pb, Cd, and Cr. This study aimed to quantify the concentrations of seven potentially toxic elements (Pb, Cd, Co, Cr, Fe, Mn, and Ni) in three widely available and commonly sold lipstick brands from local markets in Mekelle, Ethiopia. Samples were prepared using a wet acid digestion method with a concentrated 5:1:1 mixture of HNO3, HCl, and H2O2 and analyzed through Flame Atomic Absorption Spectrophotometer (FAAS). Cd was not detected in any sample. The concentration ranges across all samples in ppm were: Pb (0.0400–0.1000), Co (3.740–5.570), Cr (10.62–18.05), Fe (75.00–1838), Mn (0.1500–0.1600), and Ni (12.83–51.41). The levels of Pb were well below the 10 ppm guidance limit set by international bodies like Health Canada, U.S. Food and Drug Administration (FDA), their consistent presence is a concern. However, concentrations of Cr and Ni, known sensitizers, were notable. As an intentionally added pigment, Fe showed the highest and most variable concentrations. Although the detected levels of toxic metals were within international permissible limits, their consistent presence is a public health concern. Given the direct ingestion route and frequency of application, daily use may contribute to the cumulative body burden of these metals over time. This study, though limited by a small sample size, highlights the urgent need for healthy regulatory oversight and routine quality control of cosmetics in Ethiopia. Further research is essential to assess a wider range of products and evaluate the associated health risks for consumers.
Climate Change-Induced Hydroclimatic Extremes in the Drylands of Northern Ethiopia: Implications for Water Resources Management
(Mekelle University, 2025-10-16)
Climate change is increasingly impacting society and the environment around the world, with water-scarce regions such as dry lands being particularly vulnerable due to their limited resource availability. In East Africa, recent intensification of climate variability and change has worsened existing environmental challenges, including extreme rainfall events, floods, and frequent droughts. Ethiopia, is among the most susceptible areas to these changes, having endured some of the most severe droughts in recent decades. This shifting climate poses a significant threat to water resources, especially in northern Ethiopia, where persistent land degradation and frequent droughts—largely driven by fluctuating rainfall patterns have intensified the vulnerability of the region. The climate and hydrological systems of northern Ethiopia, especially in the Tigray region, are highly complex, influenced by diverse topography, and pronounced seasonal and spatial variability in rainfall, varied soil types, and dynamic land use changes. These factors, combined with variability in physiography, lithology, vegetation cover, and land management, lead to substantial differences in hydrological processes across basin or sub-basins such as in the Geba sub-basin, which is part of the headwaters of the Tekeze River. The sub-basin, exhibits pronounced inter annual rainfall variability, sparse vegetation, steep slopes, flood and recurring drought events. Addressing these issues demands a comprehensive understanding of climate variability and change, its impacts across multiple spatial and temporal scales to support resilient water resource development and management in this vulnerable region. Despite the recent development in climate and hydrology, a comprehensive understanding of hydro climatic variability—particularly its link to global sea surface temperature anomalies— remains limited. Moreover, the dynamics of extreme events such as intense rainfall, floods, and droughts under future climate conditions and uncertainties propagated to hydrological simulations are quite unexplored. Given this gap, this study aims to explore and better understand hydro climatic variability and extreme events under climate change within the Geba Sub-basin, situated in the northern highlands of Ethiopia. To achieve this, an integrated approach was employed—combining statistical analysis of daily long-term hydro climatic data (1981-2017), remote sensing, field surveys, laboratory investigations, and climate–hydrological modeling at the sub-basin scale.
Artificial Neuro-Fuzzy Inference System (ANFIS) Based Speed Control of Separately Excited DC Motor for Load Torque Variations
(Mekelle University, 2025-09-09) Kibrom Zerau
Separately excited direct Motor (SEDCM) is an electromechanical actuator used to power different loads across several industrial and domestic applications. One fundamental characteristic for controlling when driving is the motor's speed. The external load linked to the drive negatively impacts speed if the controller is weak and the load varies. Objective of this thesis work is to design an Artificial Neuro-Fuzzy Inference System (ANFIS)-based speed control mechanism for a separately excited DC motor under varying load torque conditions. The ANFIS controller integrates neural networks and fuzzy logic to improve motor speed regulation, ensuring robust performance despite disturbances in load torque. Additionally, this this work explores the effectiveness of armature voltage control (source voltage adjustment) for dynamically regulating motor speed, comparing its performance with conventional control strategies. ANFIS, fuzzy logic controllers, PID controllers, and open loop (without controller) have all been used to measure the speed of an independently stimulated SEDC motor. At first, the motor speed can be regulated and modified by changing the armature voltage (the input supply voltage).When the torque of the load grows and the transient and steady state faults rise, the motor's speed falls in the absence of a controller. The motor performs poorly as a result, and its speed will not maintain its rated level. A PID controller improves the motor's speed over an open loop, but the overall performance is still poor and there are still some transient and steady state issues. Although fuzzy logic controllers perform better than PID controllers in terms of system performance, the speed still fluctuates as the torque of the load changes. However, ANFIS better than fuzzy, PID, and open loop control systems, operates at its rated speed, has low steady state and transient errors, and keeps the motor's speed constant as the load increases.
In conclusion, NFIS is superior to fuzzy and PID controllers due to its zero overshoot and reduced 38.31% settling time compared to fuzzy and 50.93 % compared to PID, reduced 37.12% rise time compared to fuzzy and 44.87 % compared to PID, and reduced 85% steady-state error compared to fuzzy and 98.5 % compared to PID. Additionally, by resolving the motor's nonlinear properties, the system's overall performance will improve.
Voltage Control of DC-DC Boost Converter Using Lyapunov Rule Based Model Reference Adaptive Controller
(Mekelle University, 2024-10-24) : Mebrahtu Ngusse
The switched mode DC-DC converters are the simplest power electronic circuits that facilitate the conversion of electrical voltage from one level to another through a switching process efficiently.
DC-DC boost converters are utilized for step-up voltage in various applications. The output voltage of boost converter has, oscillation, overshoot, undershoot, and steady-state error. PID controllers have been usually applied to the converters because of their simplicity to obtain the desired voltage. But, PID controller could work well in one operating condition and cannot continuously adapt the changes in the process dynamic. To overcome this problem an advanced controller is required. The proposed Lyapunov Rule Based MRAC is adaptive and non-linear controller designed to overcome the uncertainties and nonlinearities for DC-DC boost Converter under Continuous Conduction Mode (CCM) operating condition. Using MATLAB/Simulink the performance of the proposed Lyapunov rule based MRAC is compared with that of the PID controller based on the dynamic response of the system. Using PID controller, overshoot and settling time have been improved by reducing from 67.5229% to 7.7717% and 0.6985 Sec to 0.277 Sec respectively. In the case of the proposed controller (Lyapunov rule based MRAC), overshoot, settling time, and undershoot have been improved by reducing from 67.5229% to 4.5993%, from 0.6985 Sec to 0.1458 Sec, and from 0.0036% to 0.0% respectively. To test the performance of the DC-DC boost converter, it is assumed that, the input voltage has been decreased and increased from its operating point by 25% and 41.67% respectively. Also the load resistance is assumed to be decreased and increased from its operating load resistance by 25% and 20% respectively. An external disturbance is applied to the system to check how the controller handles to uncertainties and PID controller has shown deviation from the desired value but, the controller MRAC maintained the desired value.