Power Engineering

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(7,3) Maximum - Length Binary Cycle Code Applied to Single Channel Digital Communication System for Error Correction
(Addis Ababa University, 1996-06) snegash, Yohanne; Alemu, Ketema(phD)
This paper presents the design and hardware implementation of the (7,3) maximum-length binary cyclic code applied to a single channel communication system. In hardware implementation of the system a PC with a data acquisition board with time <- sharing for interfacing the analog signals. A 12-bit digital output of the PC is divided into blocks of 3-bits for processing by the channel encoder The implementation of the system is carried out using shift registers and logic gates. A sinusoidal input waveform is applied to the system input and a circuit designed with a combination of D-type flip-flops and logic gates is used to introduce the effects of a single-random-error and a double-adjacent-burst error to observe the performance of the system. The code resulted in good performance in correcting a single-random-error and a double-adjacent-burst-error.
Active Power Flow Control in Ethiopian High Voltage Transmission Networks Using Phase Shifting Transformer to Enhance Utilization of Transmission Lines
(Addis Ababa University, 2018-06) Yemane, Esayas; Fekadu, Shewarega (PhD)
The electricity supply industry of Ethiopia is undergoing a major transformation that requires a redefined approach to increase the utilization of existing transmission line assets. Overloading of transmission lines in a power system sometimes result stability issues, which may lead to unwanted tripping or failure of equipments. The cause could be uneven loading of interconnectors or parallel transmission lines in meshed networks due to different impedances caused by the tower geometry, conductor sizing, number of sub-conductors and line length. Under these conditions, to ensure economical and reliable operation of the grid, active power flow through the lines should be controlled within their capability limits. In view of above, the power flow needs to be controlled in order to enhance utilization of high voltage transmission lines and secure the power system. Thus Control of power in AC network requires special technology to be implemented on case to case basis. Operating efficiency of electric transmission system can be improved by using appropriate Flexible Alternating Current Transmission System (FACTS) devices. Phase shifting transformer is one of the FACTS families, which can be used for power control in ac network. This thesis presents a study on active power flow control within Ethiopian network for optimum utilization of transmission lines using phase shifting transformer (PST). The study is performed first by reviewing literatures on the use of phase shifting transformers how to redirect active power flow in transmission networks throughout the world. To demonstrate the active power flow control in the network, a 400/400 kV phase shifting transformer having a size of 685 MVA with a phase shifting angle range of -200 to+200 and the high voltage transmission networks was modeled using PSSE software(Power System Simulation for Engineers) for the peak load of 2040 MW in the year 2017. From the power flow studies/solution, various overloaded and under loaded transmission lines are identified. By varying the phase angle of the phase shifting transformer, several simulations are conducted to investigate the impact of PST on the active power flow distribution. In this study, it has been demonstrated that the active power flow patterns which originally flow via the low impedance and lower voltage system is fully controlled and restructured using phase shifting transformer. By varying the phase shifting transformer angle, the active power flow in the transmission lines can be redirected towards the alternate high voltage path. As the Phase shifting transformer angle increased from -20° to +20°, the loading of Wolayta - Gibe II and Sebeta IIGibe II 400kV transmission lines vary from 4% to 35% and 11% to 42% respectively. Similarly, Gelan - Wolayta400kV transmission line load increases from 15% to 43% as the Phase shifting transformer angle decreases from +20° to -20° Conventional ways of solving the network bottlenecks based on reinforcement and building new transmission lines cannot be taken as sufficient and fast due to the problems of acquiring new corridors and environmental limitations. Installation of Phase Shifting Transformer in the transmission network is a better solution for controlling the active power flow and effective utilization of existing high voltage transmission network assets.
Analysis and Design of Medium and High Voltage Network of Sendafa Industry Zone for Improved Reliability and Quality
(Addis Ababa University, 2016-07) Hailemariam, Tibebu; Biru, Getachew (PhD)
Since recent years, the Government of Ethiopia has been striding to transform the nation’s economy of currently predominantly agriculture lead to industrial economy. To facilitate and achieve this magnificent ambition, one of the tools at the center piece is the construction of industry zones. It is obvious that building industry zones would help the government to provide all the necessary infrastructures such as road, electricity, water, telecom services, etc. in a reliable and efficient manner. Despite these efforts by the government, as a matter of fact, electric power supply has been a source of despair and dissatisfaction both for the investors and the government due to the frequent power interruptions the industries are suffering. The main reason among others for the lack of quality and reliability of the electric power supply for these industry zones is a deficient network which is not designed and equipped to meet reliability and quality requirements. In this thesis, an assessment on the existing electricity network of Sendafa industry zone is undertaken. The performance of the existing network is quantitatively analyzed with standard reliability indicators like SAIFI (System Average Interruption Frequency Index) and SAIDI (System Average Interruption Duration) and the load flow of the network is also simulated for voltage drops and short circuit level analysis. The existing network is also observed qualitatively in terms of network configuration, contingency, and capacity to handle the increasing demand. With due research on distribution network analysis and design, the industrial network is redesigned considering all the technical and security requirements. Protection coordination calculation, reliability and load flow analysis of the redesigned industrial network is also done including the financial aspects. As discussed in chapter four, the redesigned industrial network with the proposed open loop configuration employing intelligent reclosers, SAIFI is improved by 99.7% and SAIDI improved by 99.4% and the voltage profile in all the nodes is also shown to be within limits for different scenarios. The SAIFI and SAID values of the existing network are 622 interruption/yr.customer and 571 hrs/yr.customer respectively which is too far from the national standard set by Ethiopian Electric Agency as 20 int/yr.cust and 25 hrs/yr.cust respectively. Key words: Network reconfiguration, Industry zone, DIgSILENT, Protection coordination, Distribution reliability
Analysis of Dynamic Voltage Stability on The Penetration of Adama Ii Wind Farm in Ethiopian Grid
(Addis Ababa University, 2017-09) Anchinesh, Mengistu; Fekadu, Shewarega (PhD)
Wind energy is one of the most available and exploitable forms of renewable energy. The importance of wind farm penetration is that it can reduce or replace the existing conventional generators. The integration of wind farm to the existing grid introduces new challenges regarding power system which need to be addressed. Among power system stability concerns, voltage stability due to the integration of wind farms is the one that considerably affect the grid. By now, Ethiopia has wind energy sources with installed capacity of 324 MW that consist of three wind farms. Among them the largest operational wind farm is Adama II, which has been considered in this thesis, uses Doubly Fed Induction Generator Wind Turbine (DFIG WT). In this study, Adama II wind farm is aggregated from 102 wind turbines to single turbine representation. Thus, the dynamic model of DFIG WT has been developed and verified using load flow analysis. And the simplified grid model has been developed also. This model is used to analyze the dynamic voltage stability as regards the penetration of Adama II wind farm in Ethiopian existing national grid. The modeling, simulation studies and analysis has been done using Power System Simulator for Engineering (PSS /E) software. The compliance of the grid code behavior of the wind farm has been investigated based on the detailed analysis of the contingency scenario of that a bolted symmetrical three-phase fault applied at the point of common coupling (PCC) for 150 ms. After fault clearance, the voltage recovers to 1.032 p.u at the PCC and within 0.6 second following the fault clearance other buses restored to the super grid voltage. The active power output and the reactive power restored to 0.9 of the level available immediately before the fault. The results show that Adama II wind farm integrated to the Ethiopian power grid fulfills the wind grid code requirements in response to the short circuit event. The thesis also analyzes the voltage control capability of Adama II wind farm voltage controller on the power system dynamic voltage stability. To study its influence, wind generator equipped with /without voltage controller is considered. The voltage at the PCC gradually recovers to 1.038 p.u and 1.059 p.u with and without voltage controller respectively after the clearance of short circuit fault .It is observed that the voltage with out voltage control strategy exceeds the normal limit of 1.05 p.u. Finally, the analysis of wind farm performance in weak grid has been done . It can be observed that the voltage on the far end substation bus bar is 0.934 p.u and 1.0639 p.u with low and maximum load respectively. In this case, the results show that voltages are violated the standard voltage range. The simulation results depict that, the contribution of voltage controller is visible since it enhances the wind farm capability during the fault as compared with no voltage control is enabled. Therefore, the wind farm is able to fulfill the control characteristic of the controller that can improve power system dynamic behavior such as voltage stability as spelt out in international grid codes. And also it is recommended that EEP has to implement and equipped with voltage controller for all wind farms.
Assessing Transmission Line Loss in Ethiopian Electric Power System Under Contingency Conditions
(Addis Ababa University, 2018-03) Natnael, Muluneh; Getachew, Bekele (PhD)
Ethiopian Electric Power (EEP) is comprised of large interconnected power systems with far apart and geographically remote generators and loads connected by long transmission lines. This results high transmission line loss and transmission line contingencies frequently. Contingency of any one of transmission line increases the losses in the remaining transmission lines and lead to overloading. This overload triggers their corresponding protection system and thereby result in cascaded tripping lines, transformers and generating units. This in turn leads to total or partial blackout. In this thesis work, transmission line loss of EEP high voltage 400 kV and 230 kV grid network have been analyzed, under base case condition and each N-1 transmission line contingency condition, using power world simulator software. From load flow simulation result the base case total transmission loss during peak load is found to be 66.53 MW and the corresponding power loss share obtained for transmission line and transformers are 91.7 % and 8.3% respectively. The annual energy loss due to transmission line power loss is found to be 184.026 Giga Watt hour, amounting to 3.735 million US Dollar financial losses. During N-1 transmission line contingency condition total peak capacity transmission line loss varies with maximum loss of 188.4 MW and minimum loss of 59.37 MW with 10 unsolved simulations. To reduce these; addition of transmission lines and capacitor compensation measures both individually and two methods at a time have been presented. The corresponding transmission line capacity gain obtained form addition of transmission lines, shunt compensation and integrated loss mitigation were 12.86 MW, 4.09 MW and 13.15 MW respectively. N-1 transmission line contingency analysis before loss mitigation techniques and after integrating loss mitigation techniques of the system network recorded a total of 151 and 52 bus voltage limit violations respectively. Accordingly, the result recorded an appreciable loss reduction and the problem of transmission lines overloading, bus bar voltage limit deviation from the normal limits have been partially solved in normal as well as N-1 transmission line contingency conditions.
Assessment and Improvement of Reliability of Electrical Power Distribution System Case Study: - Sheno 15 Kv Distribution Feeder, Debre Berhan
(Addis Ababa University, 2019-10) Meron, Alebachew; Singh, N.P. (Prof.)
Distribution feeders are to deliver energy consistently to customers as electric power distribution systems reliability is a foremost concern to any electric power utility company. Power utility companies are working to provide reliable power through many systems. This thesis assesses the reliability of an electric power distribution feeder named Sheno 15 kV distribution feeder among the feeders that supplies an electric power to Debre Berhan city, an old city in Ethiopia. Power interruption data on daily basis for a period of two years on the feeder was collected and analyzed for the main causes of interruptions along with other two feeders namely Enewary and Aliyu Amba. Based on the data collected, system reliability indices (SAIFI, SAIDI, CAIDI, ASAI, EENS and ECOST) of the feeder were calculated using both mathematical and simulation methods andthe obtained results are 103.1271 f/customer.yr, 289.7872 hr/ customer.yr, 2.81 hr/customer interruption, 0.9669 Pu, 1361.01 MWhr/yr and 5,820,054 $/yr respectively. These values indicate poor reliability of the feeder when the results obtained are compared with averages of some countries. Currently, power utilities are trying to provide reliable electric power to their customers through many possible ways. Studying these methods; the method of adding a distributed wind power seems better option for our case study. Predictive reliability assessment of the feeder under study with the added distributed wind power along with possible locations of connection is performed and the results showed much improvement in system reliability indices of the feeder at bas bar 34(B34). These are 36.9719 f/customer.yr, 107.6154 hr/ customer.yr, 2.911 hr/ customer interruption ,0.9877 Pu , 579.565 MWhr/yr and 2,758,927 $/yr. Afterwards, the cost of realizing this method of reliability improvement for the distribution feeder has been performed. The cost analysis showed that reliability improvement with the help of distributed wind power can be realized economically.
Assessment of Resource Potential And Modeling of Standalone Pv/Wind Hybrid System for Rural Electrfication, Case Study Axum District
(Addis Ababa University, 2014-07) Kiros, Solomon; Bekele, Getachew(PhD)
So far the Ethiopian Electric Power Corporation (EEPCo) has been electrifying the remote rural areas of the country by extending the national grid. Despite the tremendous efforts exhibited during the past few years, there are still exceedingly many people without access to electricity services. Some among them is rural populations living in the historically important district of Axum. However, the district has renewable energy resources, such as Wind and solar, with the capability of providing the needed service without requiring the extension of the national grid. But little studies investigating the value of such alternatives exist. This thesis work focuses on comparing the economic performance of using various scenarios of stand-alone PV-Wind hybrid system,- with battery storage and diesel as a backup,- for electrifying Kutur village of Awlio kebele of the Axum district (which is 30 kms away from the closest national grid) to - the possibility of extending the grid. Axum district which is located at latitude of 14° 07' N and longitude of 38° 43' E is found to have 4.28 m/s wind speed at a height of 10m, and 6.19KWh/m2/day solar radiation. Two electric load scenarios are estimated by considering set of incandescent and efficient lamps for lighting for the existing 120 households. The over mentioned solar radiation and wind speed are then used as an input to simulate the hybrid setup for the high and low load estimation using HOMER. Simulation result shows that the NPC corresponding to high and low load scenarios were $278,856and $194,174, respectively. In addition, a simple load forecasting is done by considering 2013 G.C as a reference year to see the effect of the increase in electric demand of the community on the required investment to install stand alone hybrid setup. The NPC after load forecasting is found to be more than three folds of the NPC required for the reference simulation result. In both cases the results of the simulation indicates that using standalone PV/wind hybrid system with battery storage and diesel generator as a backup for electrifying Kutur village is cost effective and comparable against the cost required for electrifying the village by extending the grid. Key words: national grid, hybrid PV-Wind, battery storage, diesel and HOMER.
Coding and Transmission of Non Uniform Alphabets
(Addis Ababa University, 1998-12) Kassahun, Yohannes; Ayele, Hailu (PhD)
Two algorithms are developed in such a way that the decoding and encoding times for Huffinan encoding scheme are minimized. Algorithm One is tested for compression and decompression of text files, while Algorithm Two is tested for compression and decompression of any form of file, real time text transmission, and compression and decompression of bitmap graphics files. Programs used in the implementation of the developed algorithms in the above mentioned applications are presented. Results of the implementations are also included.
Comparative Studies of FACTS Devices for Power Loss Reduction and Voltage Profile Improvement in Radial Distribution Systems (Case Study: Sebbata-I Substation Outgoing Feeder)
(Addis Ababa University, 2023-07) Tamene Adugna; Singh N.P. (Prof.)
The power quality of any radial distribution system is determined in terms of voltage profile and power loss level of the system. The FACTS controllers can improve the performance of power transfer capability through controlling of the parameters of the distribution system. This thesis carries out comparative studies and performance analysis of DSTATCOM, SVC and UPQC devices in improving the performance of a radial distribution system. Sabbata-I substation 15 kV outgoing feeder-12 radial distribution network is considered to be a test system to evaluate the effectiveness of these devices. The location for placement of DSTATCOM, SVC and UPQC devices is determined by selecting the buses with higher values of loss sensitivity index which is calculated using MATLAB software. The size of these FACTS devices for each of the candidate buses are decided by using Particle Swarm Optimization (PSO) method. The effectiveness of each of these devices in improving the voltage profile and reducing the power loss under 75%, 100% and 125% of full load condition is evaluated through simulation studies. From the load flow analysis under normal operating conditions bus numbers 83, 36, 33, 81 and 54 are identified as weak buses for the integration of FACTS controllers. The simulation output reveal with installation of DSTATCOM device, the distribution system voltage profile enhanced by 1.86%, 2.97% and 4.18% under the respective loading conditions as compared to those of the system without installation of these devices. It is further observed that installation of SVC device improves the voltage profile by 1.65%, 1.75% and 1.86% while installation of UPQC device results in voltage profile improvement by 2.86%, 4.15% and 5.54% under the same loading conditions. It is also found that with installation of DSTATCOM device, reduction of the real power loss is 48.06%, 49.49% & 50.92% while installation of SVC device results in active power loss reduction by 34.45%, 33.51% and 31.02% under respective loading conditions. It is further observed that with installation of UPQC device, the real line loss is reduced by 64.85%, 65.72% and 66.61% under the same loading conditions. It is also found that with installation of DSTACOM device, the reactive power loss is reduced by 46.22%, 47.70% and 49.19% respective loading conditions. The simulation results further reveal that installation of SVC device results in reduction of reactive power loss by 35.91%, 34.45% and 31.70% while by using UPQC device the corresponding reactive power loss reduction is 64.13%, 65.02% and 65.93% under the respective loading conditions. The cost-benefit analysis reveals that installation of DSTATCOM, SVC and UPQC devices result in saving of 4,349,766.76 ETB, 2,945,561.84 ETB and 5,776,106.31 ETB respectively per annum under full load condition on account of power loss reduction. It is also found that the investment cost on account of installation of DSTATCOM, SVC and UPQC devices requires 8,780,813.64 ETB, 15,074,587.21 ETB and 11,728,658.22 ETB respectively under full load condition. It is concluded that effectiveness of UPQC device is better than those of DSTATCOM and SVC devices in regard to reducing the loss and enhancing the voltage profile of outgoing feeders under reduced, normal as well as overloaded operating conditions. Moreover, UPQC device is cost effective as compared to DSTATCOM and SVC devices. Therefore, use of UPQC device is recommended for power loss reduction and voltage profile improvement of distribution systems rather than using DSTATCOM and SVC devices.
Design and Modeling of Superconducting Fault Current Limiter for a High Voltage Substation A Case study: AkAki substation II (400KV to 230KV)
(Addis Ababa University, 2017-10) Dereje, Nigussie; Getachew, Bekele (PhD)
Modern electric power systems are becoming more complex in order to meet high load demand with good quality. So, the increasing amount of on-site generation should be integrated into the power grid. This translates to more sophisticated electric network with intrinsically high short circuit current capacity. A superconducting fault current limiter (SFCL) is proposed as a solution in order to increase safety margin of circuit breakers (CBs) by reducing the maximum short-circuit current below the breaking capacity of the substation. SFCL is a device with negligible impedance under normal operating conditions that immediately switches to a high impedance state in case of over-current. This advantage makes SFCL a key component in this regard. At AkAki II substation, 230 kV bus-bar, a hybrid-resistive SFCL is designed. The design procedure encompasses collection of the substation data, short-circuit analysis of the substation and designing of all parts of the SFCL. The short-circuit analysis is done using ETAP simulation software. Then, a hybrid-resistive SFCL is designed to have a current-limitingresistor with 143.2 MW rating at 4.111 kA and 8.476 Ω, 5.832 cm width and 721.76 m length of selected (Yttrium, bismuth, strontium, copper and oxygen)YBCO coated-conductor, fastswitch interrupting 9.35 kA within 48 ms, and a cooling requiring 80 liters of liquid nitrogen and 256 kW condenser. This designed SFCL is modeled using Matlab/Simulink and the result showed that the SFCL can minimize the maximum short-circuit current from 44 kA to 35 kA and enables the substation to clear the fault without problem. This means that the substation can be integrated to additional power coming from a generation having short-circuit rating of 3585 MVA with the previous safety margin still. To implement the SFCL system, the whole system components cost $320,000/phase and require 10m × 20m area by 1.8m height space of the substation.
Design and Simulation of Hybrid Photovoltaic, Wind and Fuel Cell Distributed Generation System for Yekatit 12 Referral Hospital (Fuzzy Based)
(Addis Ababa University, 2018-10) Haileselassie, Gebrehiwot; Getachew, Bekele (PhD)
This thesis deals with the detailed design and simulation of hybrid distributed generation system model of solar/wind and fuel cell in Matlab Simulink, and the power generated from these combined three renewable energy sources serves as a small scale alternative source of electrical energy for four power sensitive departments (Emergency department, Maternity department, surgery department, and Neonatology department) of Yekatit 12 referral hospital with a load demand of around 40KW, and this load to be supplied using the three hybrid components, when the commercial main power is not available. Due to the production cost and other associated advantages of solar power production over wind and fuel cell power production, 50% of the power demand which is around 20KW is produced from the solar panels, and 20% of the load demand which is around 8KW is produced from wind, and the remaining 30% of the load demand which is around 12KW is produced from the backup Fuel cell Technology which serves during solar power energy shortage seasons. To use the produced power using the above mentioned three energy resources efficiently, fuzzy logic controller is used to make an intelligent decision by sensing the type and amount of resources available, then it selects the appropriate alternative source, and to perform this Fuzzy rule have been written in fuzzy rule editor and each components of the proposed hybrid system has been modeled using Matlab/Simulink.
Design of Electrical Networks Through Computer-Aidedoptimization Techniques
(Addis Ababa University, 1993-06) Zewde, Solomon; Mullisa, Girma(PhD)
The objective of the study reported in this thesis has been to develop a unified algorithm for the computer-aided design of a wide range of electrical network configurations. While the design has been based on well-known techniques established earlier by other researchers, the present work has made significant contributions in simplifying the uses of nodal equation formulation method, graph theoretic concepts and topological formulas, as well as applications of a modified least p-th Taylor method, component damping techniques, sensitivity analyses and related design concepts. The basic computer-aided design approachfor a selected network was realized byfirst generating a voltage gain transfer function from the network connectivity details. Information concerning the gradient vector necessary in the course of an optimization process was then derived through a direct method of sensitivity analysis, without performing the normally needed first orderpartial differentiations. Comparison of a transfer function against desired response was preceded by sampling of the latter at selected frequency points and the whole adjustment was eventually automated via the least p-th Taylor method of optimization. It has been established that this approach avoided the time consuming calculation of a Hessian matrix that is usually required for performing network optimization. Convergence properties of the least p-th Taylor method were improved through a use of Fletcher's modification of the classicalLevenberg-Marquardt method together with component damping techniques. The concept of dynamic memory allocation has also been exploited. The resulting computer-aided network design technique was therefore efficient in terms of both processing time and memory requirements and the entire package has been termed as a Pascal program for optimal network design or P-POND. The algorithm has beenfully tested in its usefor designing both passive and active network types by specifying initial network parameters and input-output relations.
Design of Fuzzy Sliding Mode Controller for the Ball and Plate System
(Addis Ababa University, 2011-07) Negash, Andinet; Singh, N.P (Professor)
The Ball and Plate system is a non-linear, multivariable and under-actuated system which provides a suitable experimental platform for control algorithm development and investigation of both stabilization and trajectory tracking control of unstable systems. Sliding mode control, as one of the tools available to design robust controllers, is introduced in the outer loop of a double-loop feedback configuration. Since the robustness of sliding mode control is obtained at the cost of infinite switching of the control input, undesirable phenomenon known as chattering will be a concern in practical implementations. To this end, Fuzzy Logic is used to tune the gain of the switching control component based on the distance of the system trajectory from the sliding surface. Genetic algorithm is implemented to determine the parameters of the fuzzy system in an optimal manner. Linear algebraic method is used to design an inner loop angle controller from a set of Diophantine equations. An implementable zero-position error transfer function is selected from tabulated results of analog computer simulations of Integral of Time Multiplied Absolute Error (ITAE) optimal systems. Specifications for the desired settling time and limitation in the actuator voltage are used as constraints to obtain the coefficients of the overall transfer function. The mathematical model of the Ball and Plate system, solved from Euler-Lagrange Equations of Motion, is investigated by realizing the designed controllers using Simulink ® and Real-Time Windows Target™ rapid prototyping software. The 3-D model of the system designed using V•Realm™ Builder based on the standards of Virtual Reality Modeling Language (VRML) is interfaced with the Simulink ® model via Simulink® 3D Animation™ product. Simulation results show that the ball could be stabilized anywhere on the plate in 3.5 seconds and it could also track a circular trajectory of 0.4m radius at 0.8 rad/s in 10 seconds without significant chattering. Key Words: Fuzzy Sliding Mode Control, Variable Structure Control, Linear Algebraic Method, Ball and Plate control, VRML, Simulink® 3D Animation™/MATLAB®
Design of Pulse Width Modulation (Pwm) and It’s Implementation In Xilinx Field Programmable Gate Array (Fpga
(Addis Ababa University, 2007-02) Ababu, Teshome; Higelin, Gerald (Professer)
The following thesis describes the design, the synthesis, and the implementation of pulse width modulation (PWM) in Xilinx Field Programmable Gate Array (FPGA). The contribution of this thesis is the development of PWM in Xilinx Integrated System Environment (ISE) CAD tools and The VHDL modeling is used in the design process of PWM. Pulse width modulation has been widely used in many applications especially in communication and control systems. The paper develops high frequency PWM generator architecture for using FPGA. The resulting FPGA frequency depends on the target FPGA speed grade and the duty cycle resolution requirements. In most industrial application due to the need of design integration in control systems FPGA based PWM controller is advantageous over the other controller systems like microprocessor, microcontroller and so on. As geometries shrink and device counts multiply, opportunities abound to do incredible things with in the confines of a single chip (FPGA). Greater focus on design reuse, where earlier design is utilized and reused in later design. The power, compactness and flexibility of the FPGA based controller could be useful in motor control, particularly in robotics where those qualities are important. The FPGA provides advantages over traditional methods such as microcontroller based designs and PLD/ASIC designs by combining the strengths of both. The FPGA allows for implementation of parallel processing for generating the required waveforms. In addition to this the paper describes the architectural features of Xilinx FPGA to the other programmable logic device and explores the design using Very high speed integrated circuit hardware description language (VHDL). The VHDL model was implemented on the Spartan 3e FPGA and optimized for space. The optimized implementation was found to consume 34 numbers of slices, 18 numbers of slice flip flops, 65 numbers of 4 input LUTs and 11 numbers of bonded IOBs.
Design of Self-Tuning Fuzzy Controller for Micro Hydropower Plansts on Irrigation Dams
(Addis Ababa University, 2011-07) Hayato, Jemal; Singh, N.P(PhD)
Micro hydro power plants are stand alone renewable energy sources and free from emission of green house gases. It is an appropriate choice for rural electrification where supplying grid electricity is not economical. In Ethiopia, we have several irrigation dams, streams and running rivers which have considerable hydropower potential. Micro hydropower plants can be installed on the existing irrigation dam with less investment and time. Nowadays, electronic load controller is used to control the frequency of micro hydropower plants. However, electronic load controller wastes big amount of water during low power demand which can be diverted at high head for irrigation purposes. In addition, micro hydropower plants are characterized by parameter variations like damping constants where fixed control does not provide the desired performance under different operating conditions. Thus, development of an appropriate control scheme for micro hydropower seems inevitable to obtain the desired performance under different operating conditions. This thesis proposes fuzzy logic controller to tune the parameters of PI controller for frequency control of a micro hydropower plant and to supervise the energy dissipated on the ballast load. A detail dynamic model of micro hydropower plant is developed to design the proposed controller. Genetic algorithm is used to optimize the membership functions of the fuzzy logic controller. To meet a sudden consumer demand of power, 0.25p.u. power is dissipated on the ballast loads under steady state condition. It is observed from the simulation results that the average overshoot for 30% load change is 4.6% and the settling time is 7.5 seconds with the proposed fuzzy logic controller while overshoot is 8.9% and 13.5% and settling time is 11 seconds and 29 seconds with PI load control and PI flow control, respectively. Moreover, even for 70% load rejection, overshoot is only 11.6% and the settling time is 11 seconds. It is further observed that the change in energy wasted on ballast load from the desired value is always around zero at steady state conditions. Key Words: Micro Hydropower, Irrigation Dams, PI Controller, Fuzzy Logic Controller, Genetic Algorithm Chapter One
Design of Standalone (PV/Micro-Hydro/DG) Hybrid Power Supply for off Grid Rural Community – A Case Study of Maji District (Tum) in South Nation Nationality People Region (SNNPR).
(AAU, 2016-12) Emebet, Tolcha; Fekadu, Shewarega (PhD)
Off-grid electrification from available renewable energy resources with hybrid power supply is the best solution for rural town (village) where grid extension is found costly and infeasible. This thesis studied the feasibility of the main renewable energy resources available for the electrical production in the administrative city of Maji district (Tum) under Bench-Maji Zone in south Nation Nationality People Region (SNNPR) of Ethiopia. Even though Tum is the capital city of Maji district, the task of electrification via grid system has been found very difficult till to date for the main reason that its location is far from the nearest substation which is about 174KM. Kerosene has been used for lighting for most of the communities in the town; diesel power generation for milling and rarely for lighting and TV’s; leaving biomass for cooking and dry cells for radio. In 2008, a local private company initiated to provide electricity to the whole district which unfortunately could not be realized. In this thesis, feasibility of renewable energy resources for electric supply system to Tum has been studied using HOMER software as optimization and sensitivity analysis tool. Meteorological data from National Meteorological Agency of Ethiopia and other sources, such as NASA and PVgis, have been used for comparison of the result obtained by analytical method to estimate the solar energy potential of the area. Electric load for the basic needs of the community, such as lighting, radio, television, electric baker, water pumps and flour mills, have been estimated. Schools, churches, mosques and health centers are also considered as energy users of the community services. The result from Homer simulation showed that micro hydro is the first best optimized system and DG/ Micro hydro the second categorized hybrid system. PV/Micro hydro is found the third and PV/Micro hydro/DG hybrid the fourth categorized result from homer optimization result based on the NPC. The cost of energy for the first, second, third and fourth optimization results of categorized display are $0.058/kWh, $0.058/kWh, $0.060/kWh and $0.061/kWh respectively, which is of course extremely incomparable with what the communities are paying now for diesel generator owner that is estimated at 1.46/KWh for the usage of one lighting bulb only but higher than a grid selling price of Ethiopian Electric Utility (EEU) for domestic load which is about $0.027/KWh. Moreover, load flow analysis is studied using ETAP software to know power flow of the designed power system. A one line diagram is presented as the outcome of the design and after the simulation; the power flow is indicated on it. It includes mainly 33KV and 400V voltage levels. The result shows generation supplies the load plus losses on the system, bus voltages are maintained to near nominal value, the system is not over loaded
Development and Feasibility Study of Medium and Low Voltage Dc Distribution System
(Addis Ababa University, 2017-03) Birhan, Shumye; Biru, Getachew(PhD)
Power distribution system development initially was conceived in the form of DC distribution system. But, due to different drawback of this system and the invention of transformer, it was shifted to AC distribution system. As a result, the manufacturer created AC powered loads to the customers to meet AC generation systems. AC system dominated the market for a long time. Lately, the developments achieved in power electronics area led to further studies in direct current power systems.This research work presents the development and comparative study of DC distribution systems by taking 132/15kV, 20MVA, 50Hz distribution substation system to be extended to MVDC as study of the research. The specific objective of the study is to develop alternative DC distribution system and make a comparative analysis of MVAC and MVDC in terms of power loss, material cost, system efficiency and energy loss cost. carrying capacity of AC and DC distribution system, the total power loss, equipment cost and the system effiecncy was computed and compared each other. Finally, three DC distribution scenarios were developed and evaluated in terms of power loss, efficiency and cost. Each scenarios were compared not only with the traditional AC system but also with each other. The existing AC distribution evaluation system results in 1989.7 KW power loss, 348,595 USD energy loss cost, 3,094,622 USD materials cost and 90 % overall efficiency. In DC distribution, Scenario A evaluation results in 1610 KW power loss, 282,072 USD of energy loss cost, 2,433,290 USD of materials cost and 91.9 % of overall efficiency. Scenario B evaluation results in 2011.5 KW of power loss, 352,418 USD of energy loss cost, 2,989,308 USD of materials cost and 89.9 % of overall efficiency. Scenario C, The DC structure which consists of DC/AC inverter with its system efficeincy 92.6 %, power loss 1486.5 kw, the energy loss cost of 260,438 USD and equipment cost of 2,989,308 USD were achieved in which it was much significantly less than AC distribution system. As the quantitative results showed, around 500 KW power saving and more than 0.2 million USD momentarily saving have been possibly achieved by using scenario C of DC distribution system as compared to the existing AC distribution system. Key word: Distribution, Direct Current, Alternative Current, Power loss, Transformer, Converter, Rectifier, Inverter and Feasibility study.
Development of Voltage Security Assessment and Reactive Power Management Schemes for Online Application
(Addis Ababa University, 2024-09) Ahadu Hilawie; Fekadu Shewarega (Asso. Professor)
Voltage security issues continue to be the concerns of power systems as the stress on power systems increases due to increasing energy demand. To manage this stress and prevent voltage security problems, online voltage security assessment (VSA) and reactive power management (RPM) strategies are coming to play crucial role. However, selecting suitable approach and developing one’s own method requires rigorous assessment of the gaps in existing approaches and devising a strategy to fill the gaps. In this regard, this dissertation work aims at developing VSA and RPM schemes for online application to help the efforts made to mitigate the increasing voltage security problems.The dissertation has two major components, voltage security assessment (VSA) scheme development and reactive power management (RPM) scheme development, as separate entities and as complementary entities. The work focuses on designing the components of the schemes by devising new and improved contents of each scheme. The developed VSA scheme performs three major tasks; estimating the network Thevenin equivalent impedances, determining the voltage stability indices and interpreting the results of voltage stability indices. Computational efficiency improving strategies, which are necessary for online application, are adopted at different levels of the VSA scheme. This begins from selecting the method of voltage security assessment, i.e. Thevenin equivalent based approach. Then, to address the limitation of previous Thevenin equivalent determination techniques this work comes up with a new Thevenin impedance determination technique. The developed Thevenin impedance determination technique requires two power flow computations in offline analysis case and only one power flow analysis in the case of online estimation. For the voltage stability assessment task of the VSA scheme two types of voltage stability indices are formulated, which measure proximity to voltage instability, one directly using the power margin and the other indirectly as a simple closeness indicator. The third capability of the VSA scheme is PV and QV curve plotting capability for interpreting the process of development of voltage security problems. The Thevenin equivalent determination capability, greatly, simplifies the maximum power transfer capacity estimation and PV or QV curve determination, which was previously a computationally intensive task.The capabilities of the VSA scheme are tested using simple four bus test system, IEEE 14 bus and IEEE 30 bus test systems. The tests produced results meeting the objectives of producing high accuracy Thevenin parameters, tracking system loading changes, identifying weakest buses, showing the impact of reactive power compensation and showing impact of load increments. Then the scheme is applied to existing Ethiopian Electric Power (EEP) system to examine the performance on large power systems. The application of VSA scheme to EEP system revealed a number of important features of the EEP system pertinent to voltage security, including weakest areas, weakest buses and voltage instability contributing lines. The other scheme, the reactive power management scheme, depends on the results of VSA process. In this case, two approaches are devised for reactive power management purpose. The first is fast reactive power management (FRPM) approach and the second is continuous reactive power management (CRPM) approach. FRPM is proposed considering contingent operating conditions. In this approach the voltage stability indices are used as an indicator of voltage security improvement, while reactive power provisions are made. Reactive power provisions cease when the weakest load buses get far enough from voltage instability. On the CRPM side the objective is to adress the optimization needs of reactive power provisions. In this approach, an improved multi objective particle swarm optimization (IMOPSO) algorithm is proposed. Together with voltage deviation objective function, the algorithm uses the indices developed on the VSA scheme for the multi objective function formulation. In this algorithm, the common multi objective particle swarm optimization (MOPSO) is improved by introducing an adapted binary crossover (ABX) to the new positions obtained by the basic PSO algorithm. Additionally, diversity maintenance strategy is added to the algorithm by employing crowding distance (CD) computation. The developed algorithm is, then, tested and compared with standard MOPSO and NSGA II algorithms. The comparison is made based on the degree of closeness to the true pareto front, as measured by the inverted generational distance (IGD), and based on diversity, as measured by the CDs. The test is made using ZDT1, ZDT2, and ZDT3 common test functions. The IMOPSO showed improved performance over MOPSO and NSGA II algorithms in terms of convergence to the true pareto front and in terms of the speed of convergence as well as in maintaining diversity. The algorithm is then implemented to reactive power optimization of IEEE 14 bus test system and the EEP system. This implementation has resulted diverse options of optimal settings of reactive power controlling parameters. The optimal settings proved to produce an improved voltage security as measured in terms of voltage deviation and voltage stability
Digital Control for Switched Mode Converters Input Power Factor Correction
(Addis Ababa University, 2011-07) Anthony Alemayehu; Mengesha Mamo (PhD)
Input power factor of static power converters is generally low due to angular displacement between input voltage and current plus due to current distortion. On the other hand, static power converters usage is increasing continuously with the increase in use of power supply units to commercial, industrial and residential complex automation and communication systems. This increase in application of power converters has increased the reactive power demand from the utility grid resulting in inefficiency and overloading of the transmission and distribution network. In this thesis, a digitally controlled switched mode PFC (power factor correction) converter has been designed, modeled and simulated. The three major control modes which are used for switched mode converter control are the voltage mode control, current mode control and the PFC mode control. These three control modes have been simulated using the MATLAB Simulink for 100%, 75%, 50%, 25% and 10% power loading. For the 100% load (full load) it has been found that the PFC mode controller achieves a near unity input power factor with power factor of 0.99975. At full load, the voltage mode and current mode controller have a lower power factor of 0.943 and 0.945 respectively. For the other loadings, the PFC mode controller has a near unity power factor which is greater than 0.99, whereas the voltage mode and current mode controller have a lower power factor. The PFC mode controller performs well even if there is variation in input voltage and load. In addition, the lowest total harmonic distortion (THD) and reactive power, and the highest power factor (PF) are obtained using the PFC mode control. From the results obtained, it can be concluded that the PFC mode controller is the best control scheme to be used for such control applications. Digital control for power factor correction is an important field of study since it can be used to reduce the harmonics in the line current, increase the efficiency of power systems, and reduce customers’ utility bills. The results of this study are useful for many applications such as an uninterrupted power supply (UPS), telecom power supply, motor drive inverter, personal computers, battery charging, DC motor drive, welding machine and other power supplies for electronic equipment.
Dsp Based Vector Control of Induction Motor
(Addis Ababa University, 2007-09) Belay, Abraham; Mamo, Mengesha(PhD)
In this thesis Vector control of Induction Motor using DSP board, type TMS320LF2407 from Wintech digital instruments has been studied and implemented. This new family of DSP controllers enables cost-effective design of intelligent controllers for Induction motors, which can yield enhanced operation, fewer system components, lower system cost and increased efficiency. The vector control Algorithm maintains efficiency in a wide speed range and processes the dynamic model of the Induction Motor. The DSP board is successfully programmed by using C and assembly language in a code composer studio working environment, interfaced with an inverter of type DL2646 from DELORENZO and the Induction motor has been driven by V/f control using SVPWM technique. Experimental and simulation results has been presented and discussed.

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