Browsing by Author "Shiferaw, Dereje (PhD)"

Now showing 1 - 5 of 5
  • No Thumbnail Available
    Item
    Design and Simulation of a Neuro-Fuzzy Based Temperature Controller for Neonatal Incubator
    (2016-12) Demerwe, Dagmawi; Shiferaw, Dereje (PhD)
    Premature infant’s birth is a worldwide problem. Their organs are not mature enough to allow normal postnatal survival relative to normal babies, consequently they will became hypothermic, which leads them to death. Premature neonates survive in a very narrow core temperature range (36.5-37.5ºC) and suitable relative humidity. As a result, some parameters have to be monitored and their accuracy remains an important matter. Infant incubators are complex medical devices, which are often used immediately after delivery and for the coming few months of their life depending on the infant’s health condition. They use the convection of warm and humidified air to control the temperature of the infant. They have two modes of operation, either the incubator’s air temperature is sensed and used to control the heat flow or infant’s skin temperature is sensed and used in the feedback control system. Infant’s skin temperature control only often leads to large fluctuations in the incubator’s air temperature, similarly incubator’s air temperature control only also leads to infant’s skin temperature fluctuations. This thesis presents the application of adaptive neuro fuzzy inference controller for ATOM V-850 model infant incubator system, in order to control the incubator’s air temperature and the infant’s skin temperature simultaneously. The corresponding fuzzy logic controller is designed for the same system, in order to work with structured knowledge in the form of rules in the FIS. However, there exists no formal framework for the choice of various design parameters and optimization of these parameters generally is done by trial and error technique. The combination of artificial neural networks and fuzzy logic systems offers the possibility of solving tuning problems and design difficulties of fuzzy logic system. The performance comparison between the proposed ANFIS controller and FLC is analyzed through various conditions using MATLAB/Simulink® software. Simulation results show that the performance of the proposed ANFIS Controller, in tracking the desired incubator’s air temperature and desired infant’s skin temperature, improved to 0.39% and 0.2% error from 16.6% and 1.47% error in the FLC respectively. Results also show that, the ANFIS model on the closed loop infant incubator system provides best control performance over a wide range of operating conditions relative to FLC. Key Words: Neonatal incubator, Preterm infant, ANFIS controller, ANN, FLC, MATLAB/Simulink®
  • No Thumbnail Available
    Item
    Design of SlidingMode Controller Based Antilock Braking System of a Vehicle
    (Addis Ababa University, 2017-04) Asmare, Mekete; Shiferaw, Dereje (PhD)
    Anti-lock braking system (ABS) is the most common safety system in the vehicles, which works to increase the generated braking force between the tire and the road surface for enhancing passenger safety specifically related to accident avoidance. However, designing an ABS is a challenging task considering the fact that it is highly nonlinear and a time varying system. The interaction between the tires and the road surface, the dynamics of the whole vehicle and the characteristics of key components in ABS are all nonlinear and time varying. Due to the nonlinearities of the brake actuation system, robust braking control system with a faster response is required to handle even sudden, extreme variations in driving conditions with little loss of traction and steering ability. In this thesis, out of the robust controlling mechanisms, a sliding mode controller based antilock braking systemof a vehicle is introduced. The objective of this SMC based ABS is to keep the wheel slip at an ideal value so that the tire can still generate lateral and steering forces as well as shorter stopping distances in order to prevent the controlledwheel frombecoming fully locked. In order to control the system based on wheel slip, a Quarter car in terms of wheel slip is modelled and the model is validated by using open loop response analysis by usingMATLAB. Then a controller is designed and implemented using MATLAB. During our controller design, in order to resolve the drawback of SMC i.e. chattering, a nonlinear integral surface is defined. The designed SMC based ABS and the conventional ABS are then evaluated under dry nominal, dry concrete and dry slippery road types. And also the performance of the two systems are evaluated under three different initial vehicle velocities and the system responses are then compared in terms of wheel speed and stopping distance. As the numerical simulation shows, on a dry nominal road, for an initial vehicle speed of 40 km/hr, the stopping distance that is obtained from the SMC based ABS and the conventional ABS are 14.5000mand 15.7080mrespectively. In the same road type, for an initial velocity of 90 km/hr, the stopping distance that is obtained from the SMC based ABS and the conventional ABS are 73.5122mand 79.6029m respectively. And also for an initial vehicle speeds of 40km/hr and 90km/hr, the braking time of the SMC based ABS is 0.11 Second and 0.39 Second faster than the conventional ABS respectively. At last, the proposed SMC based ABS achieves a robust system, minimum braking time and minimum stopping distance than the conventional ABS for all road types. Keywords: SlidingMode Control, Antilock Braking System, Sliding surface, wheel slip
  • No Thumbnail Available
    Item
    Fuzzy PID Based Temperature Control of Electric Furnace for Glass Tempering Process
    (Addis Ababa University, 2017-03) Achenef, Sisay; Shiferaw, Dereje (PhD)
    Tempered glass is a safety glass processed by a controlled thermal or chemical treatment to increase its strength compared with the ordinary (or annealed) glass. In thermal tempering process, the glass is heated to a temperature just below the softening point and is then quenched rapidly in air. Thus, in thermal tempering manufacturing process temperature control of tempering furnace is the main task. Our country Ethiopia has some glass manufacturers hence we can use thermal tempering process to manufacture tempered glass. This thesis deals with the temperature control of electric furnace. The temperature of electric furnace is controlled to a desired value. In tempered glass furnace industry, the widely used controller for temperature control is conventional PI and PID controllers. Since electric furnaces are nonlinear and time varying processes, using PID controllers is difficult to meet the control requirement. Because they are not robust, haven’t good dynamic response and have large overshoot. Hence in this thesis, fuzzy logic controller which is fault tolerant and nonlinear controller is used to improve the PID and achieve steady state and transient requirements. Therefore, in this thesis a model of glass tempering furnace is prepared using MATLAB/SIMULINK and then fuzzy PID controller has been designed and simulated and its performance has been compared with conventional PID controllers. The performance of the controllers is compared in terms of disturbance rejection, transient and steady sate performance. It is observed from the simulation results that the average overshoot is 2.129%, rising time is 44 seconds and the settling time is 170s seconds with the proposed fuzzy PID controller while overshoot is 16.129%, rise time is 45 second and settling time is 290 seconds with PID controller. Moreover, the robustness and disturbance rejection of the controllers is checked by parameter variation like time constant, delay time & DC gain and giving disturbance signal after settling time respectively. It is further observed that the proposed controller has better disturbance rejection and more robust. Key words: Glass tempering furnace temperature control, Fuzzy PID controller, PID controller.
  • No Thumbnail Available
    Item
    Maximum Power Extraction of PMSG Based Variable Speed Wind Turbine Using Self-Tuning Fuzzy Controller
    (2017-02) Belay, Addisie; Shiferaw, Dereje (PhD)
    The interest in wind energy system is growing worldwide to reduce dependency on fossil fuel and to minimize the adverse impact of climate change. However, because of its unpredictable and random availability, wind power management concepts are essential to extract as much power as possible from the wind when it becomes available. The purpose of this thesis is to develop fuzzy logic controller to tune the parameters of PI controller for a maximum power tracking strategy of variable speed wind turbine. The system consists of 8.5kW direct drive permanent magnet synchronous generator (PMSG), uncontrolled rectifier which is used to convert the ac output voltage from the wind generation unit into dc voltage, a dc/dc switch-mode step up boost converter which is used to catch the maximum power from the wind, and a power control system. The output of the controller was given to the dc-dc converter to adjust the duty cycle and when adjusting the duty cycle the rotor speed of PMSG was controlled to get the maximum power. The proposed control algorithm allows the generator to track the optimal operation points of the wind turbine system under fluctuating wind conditions. This algorithm does not require the knowledge of intangible turbine mechanical characteristics such as its power coefficient curve, power characteristic or torque characteristic instead it uses rotor speed measurement as control variable inputs. MATLAB simulation study results confirm that the proposed controller algorithm is effective in tracking maximum power with good dynamic and steady state performance. From the power extracted plots it is observed that the overshoot given by the self tuning fuzzy PI controller is reduced to 0.09% from 0.2% while the regulation time is reduced to 0.6 s from 1.4s from the PI controller, when the wind speed is 12 m/s (steady state). The overshoot given by the self tuning Fuzzy PI controller is reduced to 0.07% from 0.1% and 0.01% from 0.09% in comparison with the PI controller while the regulation time is reduced to 5.4s from 6.1s and 10.5s from 11.2s from the PI controller, when the wind speed changes suddenly from 12 m/s to 10 m/s and 10m/s to 8m/s respectively. Keywords- Variable Speed Wind Turbine, Permanent Magnet Synchronous Generator, Uncontrolled Rectifier, DC/DC Switch-Mode Boost Converter, PI Controller, and FLC.
  • No Thumbnail Available
    Item
    Voltage Control of A Dc-Dc Buck Converter Using Second Order Sliding Mode Control
    (Addis Ababa University, 2017-02) Tolossa, Zawde; Shiferaw, Dereje (PhD)
    DC-DC converters are non-linear and the most widely used circuits in power electronics. Generally they are used in all situations where there is need of stabilizing a given DC voltage to a desired value. DC-DC buck converter is used in applications for voltage step-down. The output voltage of this converter alone is usually unstable, oscillates, it has large overshoot, and long settling time. Also it is unable to give the desired output voltage under input voltage and load variations. To overcome this problem and obtain constant stable output voltage and fast response various controllers are required. PID controllers have been usually applied to the converters to obtain the desired output voltage because of their simplicity. But application of PID controller is not reliable and satisfactory in the case of non-linear systems. Therefore, non-liner controllers are required to improve system performance. In this thesis second order sliding mode controller based on the prescribed convergence algorithm has been designed to achieve fast and stable performance of buck converter. The proposed controller performance is compared with PID controller based on dynamic response of the system in terms of overshoot, settling time, rise time, and voltage deviation from desired value using MATLAB/Simulink. In order to test the performance of proposed controllers the load resistance increased and decreased by 62.5% from operating point while input voltage decreased by 20.83% and increased up to 41.67% from operating point. Also to test effectiveness of SOSM control the input voltage is varied from operating point (i.e. 24V) up to 200V. Simulation results show that, using SOSM controller the rise and settling time is improved by 5.228% and 46.39% respectively as compared to that obtained using PID controller. The overshoot is reduced from 51.3% to 9.455% using PID controller while SOSM controller totally removes it. Both controllers overcame the effect of load resistance variations. The overshoot is increased from 9.455% to 17.5% for input voltage increased by 41.67% using PID controller is eliminated using SOSM controller. The actual output voltage is not deviated from desired value even for large input voltage variation using SOSM controller. Generally from the result it is possible to conclude that the performance of SOSM controller is better than PID controller. Key words: DC-DC Converter, Buck Converter, PID Control, SOSM Control.