Browsing by Author "Jayatissa, N. W. K."

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Analysis for maximum energy transfer from existing DC-to-DC converter topologies.
(International Research Symposium on Pure and Applied Sciences, 2017 Faculty of Science, University of Kelaniya, Sri Lanka., 2017) Nagahapitiya, N. W. H. G. B.; Jayatissa, N. W. K.
A voltage regulator is an electronic device, which maintains a constant output voltage for varying input voltages. There are different types of voltage regulators with various types of control schemes to achieve great accuracy and fast regulation but it requires more complex circuitry and cutting edge technology. The direct current-to-direct current (DC-to-DC) power converters are designed to provide unregulated dc voltage inputs and to regulate constant voltage output. DC-to-DC converters are applicable to a variety of applications including power supplies of personal computers, office equipment, spacecraft power systems, laptop computers and telecommunication equipment as well as DC motor drives. Thus, high efficiency is invariably required in DC-to-DC converters for maximum energy transfer in these kinds of applications. In this study, theoretical and practical analysis were done on existing DC-to-DC converter topologies. Moreover, behavior of Buck and Boost converters with variable Inductor, variable Capacitor and different duty cycles were investigated in detail. Also, change of output voltage waveform with the above three factors was analyzed. Three basic DC-to-DC converter topologies were analyzed by using theoretical calculations and transfer functions of the converters were derived. Further, Buck and Boost converter was analyzed significantly in practical method. Then results of both the sections were compared to understand the behavior of converters. Introducing a input filter to the switching converter significantly reduced the switching harmonics in the input stage. Another important factor of introducing an input filter is that the control of electromagnetic interference (EMI) appeared in the input signal. So in this study, this phenomenon was analyzed with different types of input filter combinations. The switching converters are the controller unit of the converters. The clarity of the pulse with modulated (PWM) signal is important for stable controller output. This study reveals a technology to provide stable output voltage from distorted PWM signal.
Design and performance investigation of a canonical circuit model for power converters
(Research Symposium on Pure and Applied Sciences, 2018 Faculty of Science, University of Kelaniya, Sri Lanka, 2018) Sandanayake, P. S. D.; Jayatissa, N. W. K.
A “Switched Mode Power Supply (SMPS)” is an electronic device that involves switching regulation for efficient power conversion. They take power from an AC or a DC input, and produce a processed current/voltage output of DC power. The major advantage of a SMPS over linear supplies is the higher efficiency. Since the control elements of them are continuously swung between their low dissipation, full-ON/full-OFF states, only allowing them to be in high dissipation modes and consume power during only a small amount of time, thereby reducing the energy wastage. This ideally converts power with 100% efficiency. In this study, an attempt was made to design a “Canonical Circuit Topology” that automatically switches between Buck (output voltage is less than the input), Boost (output voltage is greater than the input) or Buck-Boost (in the margin of both buck & boost modes, alternating between both) mode by continuously monitoring the input and output voltages, and operating in the user-set parameters. Fundamentals SMPS’s such as Buck, Boost & Buck-Boost were studied theoretically using MATLAB Simulink modelling and they were compared with physical implementation. It was seen that real behavior of them is very much deviating from ideal behavior due to inherent issues of common MOSFETs and inductor coils. The Conventional Buck converter performs well in terms of conversion ratio and efficiency (71% maximum) for very small loads of few ohms, with inherent input noise issues. The Conventional Boost converter performs well in terms of conversion ratio for large loads of few kilo ohms, but efficiency was inappreciable, with inherent output noise issues. Different candidates for a Canonical Circuit Topology were identified, and the 4-switch buck-boost converter was selected as the most plausible, due to its power range of operation, efficiency (up to 96% maximum), simplicity & cost effectiveness. MATLAB Simulink model simulations revealed the input noise problems in both modes, yet the output was smooth. The physically implemented model showed that the circuit behavior is slightly deviating from ideal behavior, with an average efficiency of 70% in buck mode. It provided a linear correlation among conversion ratios with respect to the duty cycle of the control signal. Further, in order to improve the behavior in terms of conversion ratio and noise, super capacitors were introduced and it brought about significant results, raising the conversion ratio from 0.82 to 0.947 for 100% duty cycle in buck mode.
Improving the response time of an ultrasonic wind speed measuring system using a temperature measurement
(Research Symposium on Pure and Applied Sciences, 2018 Faculty of Science, University of Kelaniya, Sri Lanka, 2018) Pieris, T. P. D.; Jayatissa, N. W. K.
Natural wind in the open air is a three-dimensional vector but vertical component of the wind is ignored in the most meteorological operations. Therefore, the surface wind is considered as a two-dimensional vector in this study. Wind speed changes rapidly. So, the anemometers must have better response. Ultrasonic waves with frequency more than 20 kHz that are inaudible to humans propagate at a speed of 340 m/s in wind free conditions. Ultrasonic wind speed measuring systems are used to measure the wind speed due to few advantages such as its sensitivity for low wind speeds and lack of moving parts. This anemometer has two pairs of ultrasonic transmitting/receiving devices fixed facing each other across a specified span. Ultrasonic wave pulse signals are repeatedly emitted alternately by each pair of transmitters at certain time intervals. Emitted signals are received by the ultrasonic receivers. The time taken for the sound wave to travel is measured by a system for both directions. The wind direction and speed are derived through vector analysis. Two simultaneous equations were obtained using speeds of sound wave, time taken for the travel and distance between transducers. The speed of sound wave obtained from the two equations above is the summation of the wind speed and the speed of sound through still air for one direction and vice versa. From the two simultaneous equations, the speed of sound through still air was rejected and wind speed was obtained. A sensor that has a filtering system was used to reject the ultrasonic noises from the environment. Usually, the systems use average values to avoid gusting. Gusting is a random fluctuation of wind speed and direction. Due to the averaging, the response time of the system was decreased to around 20 seconds. The speed of sound through still air can be calculated using the ambient temperature. This temperature measurement is directly related to the wind speed. Hence, the wind speed can be calculated with a single time measurement and single equation instead of rejecting the speed of sound through the still air. Then, the response of the system is improved.
Smart White Cane.
(In: Proceedings of the International Postgraduate Research Conference 2017 (IPRC – 2017), Faculty of Graduate Studies, University of Kelaniya, Sri Lanka., 2017) Kaushalya, K. W. A.; Fernando, A. P. N.; Ekanayake, H. M. P. K.; Jayatissa, N. W. K.
Blindness or visual impairment affects many people around the world. There are nearly 14 % visual disables in Sri Lanka. Blind people use white canes to identify obstacles by moving the cane. Over the years, blind people have had different reasons for using canes. The modern white cane, as we know it, did not come in to existence until World War I. There is much debate surrounding which country developed the white cane first. Along with the development of useful canes and proper techniques came laws to allow blind people equal access to public streets and buildings. The research focused to improve the facilities in existing white cane with minimal changes of the original white cane. Ultrasonic sensors measure the distance of target objects or materials through the air using ‗non-contact‘ pulse echo technology. In the pulse echo method, a burst of pulses is sent through the transmission medium and is reflected by an object kept at a specified distance. The time taken for the pulse to propagate from the transmitter to receiver is proportional to the distance of object. The amplitude of the received signal gets significantly attenuated and is a function of nature of the medium and the distance between the transmitter and target. By recording the elapsed time between the sound wave being generated and the sound wave bouncing back, it is possible to calculate the distance between the sonar sensor and the object. A development board placed in the cane is powered by a 9V battery with three ultrasonic sensors for the front, right and left sides. The front sensor sensitivity is adjusted as 30 cm so that when the obstacle is within less than 30 cm distance, a unique vibration is given to the user‘s handle through the cloth covering the cloth. Left and right side sensitivities are adjusted to 25 cm. Therefore, when the obstacle is in the tracking range, the Cane provides different, unique vibrations to the user. Different vibration frequencies are used in this device to identify the direction of the obstacle. If the obstacles are in the front side, the vibration frequency is high while other two sides give different vibration than the front side. User required to short time training before using the cane. We have to give instructions to the user before they start to use the smart white cane as they do not know how to identify vibration differences and guide them to keep it with correct angle.
Thermal desalination process - Design perspectives.
(International Research Symposium on Pure and Applied Sciences, 2017 Faculty of Science, University of Kelaniya, Sri Lanka., 2017) Jayatissa, N. W. K.
Urban areas, although better served than rural areas, are struggling to keep up with the population growth. Population increase on Earth, is directly related to the global food and energy demand. Expansion of the agricultural sector and the energy sector considerably increase the competition for water. Population growth is directly proportional to the demand of fresh water. Decision for using new water resources is always challenged by the factor of cost. Thermal water desalination process is so far less efficient but very close to the natural water cycle. This study is based on designing a thermal desalination plant, which is suitable for desalinating sea water. The paper discusses the important factors that are required to be considered, while designing a thermal desalination plant. The plant is designed to run with a small scale experimental solar pond which is located in the University of Kelaniya, Sri Lanka (Latitude 6o 58’ 23.17524 N, Longitude 79o 54’ 54.91315 E). The plant has two major tanks known as the evaporator and the condenser and each tank has a volume of 0.085 m3. Boiler and pressure vessel international codes published by the American Society of Mechanical Engineers (ASME) and equations published in the Coulson & Richardson’s Chemical Engineering Design book were used to estimate the necessary thickness of tank walls and pipes. Steam flash nozzles were installed inside the evaporator for efficient flash evaporation and fresh water spray nozzles were installed inside the condenser for direct steam condensation. Due to the low thermal storage in the small scale solar pond, the plant is designed to deliver 1 liter of fresh water per hour. However, this design is constructed with two steam pipes instead of one to obtain maximum desalination rate of the plant. Size of the steam pipes between condenser and evaporator depends on steam generation rate and condenser temperature of the plant. Inappropriate designs may cause explosions in the tubes. The evaporator and condenser liquid temperatures of this design are 60oC and 55oC respectively. The pressure required to evaporate 60oC water can be found from the standard steam tables and it was found to be 20 kpa. Specific volume of steam at this pressure and temperature is nearly 7.667 m3/kg and this value changes to 9.600 m3/kg when the steam transfers to the condenser side of the plant. A steam velocity of 2.06 m/s between evaporator and the condenser is required to provide one litre per hour fresh water output. Considering the specific volume and the mass flow rate of the steam, the diameter of the steam pipe should be at least 4 cm. The ASME guidelines provide the required thickness for steam pipes. However, it is important to separate small water droplets in the steam before entering to the condenser. To achieve this goal, a locally made plate demister is installed between the evaporator and condenser. Water droplets separated by the demister are again fed back to the evaporator of the plant. Water level inside the condenser and evaporator must be maintained at a certain level to conserve the efficiency of the system. Increasing water level inside the condenser and evaporator tanks cause to increase the pressure inside the plant will hence decrease the efficiency of the system. Therefore, a water circulation pump system is established to maintain both water levels in the condenser and in the evaporator. The plant is already designed and constructed at the premises of the University of Kelaniya. The system can be vacuumed to the required pressure without difficulty and ready to desalinate the water when the hot reservoir is set to provide 60oC hot water.