Browsing by Subject "Electrical engineering"

Now showing 1 - 5 of 5
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    9-Phase inverter driven motor
    (1983) Hoffman, Keith Paul
    The behaviour of a 9-phase squirrel cage induction motor is studied when it is excited with unmodulated and chopper modulated quasi-square phase voltages. A 9-phase bridge inverter, which produces the quasi-square waveforms, and its digital controller have been constructed and tested. A theoretical analysis is included, which shows the influence of phase current harmonics upon output torque.
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    Open Access
    Analysis and feedback control of magnetic bearings with reference to flywheel energy storage.
    (1984) Bredenkamp, Gordon Leslie; Enslin, NC de V
    In high speed applications magnetic bearings offer many potential advantages over mechanical bearings. The type of magnetic bearing most suitable for energy storage flywheels is selected and analysed for the purpose of designing feedback control loops. A nonlinear as well as a small signal linear model of the "current driven" magnetic bearing with unlaminated magnetic components is derived. Subsequently describing functions characterising the small- as well as large signal behaviour of the same bearing in the "voltage driven" mode, are obtained. It is shown that workable results are obtained for most practical situations by using linear systems theory, although the magnetic bearing is a nonlinear device. The describing function model enables the designer to identify the mechanisms leading to limit cycles under adverse operating conditions. Feedback control loops designed around the small signal characteristics produce practical results in the case of the "voltage driven" mode which are superior to that of the "current driven" case. An essential refinement, where energy losses and vibrations arising from rotor imbalance are eliminated, is described. A discrete time filtering technique is used. Two experimental models were built and fully tested in order to verify the above theoretical approaches.
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    Open Access
    Energy efficient path planning: the effectiveness of Q-learning algorithm in saving energy
    (2014) Ogunniyi, Samuel; Tsoeu, Mohohlo Samuel
    In this thesis the author investigated the use of a Q-learning based path planning algorithm to investigate how effective it is in saving energy. It is important to pursue any means to save energy in this day and age, due to the excessive exploitation of natural resources and in order to prevent drops in production in industrial environments where less downtime is necessary or other applications where a mobile robot running out of energy can be costly or even disastrous, such as search and rescue operations or dangerous environment navigation. The study was undertaken by implementing a Q-learning based path planning algorithm in several unstructured and unknown environments. A cell decomposition method was used to generate the search space representation of the environments, within which the algorithm operated. The results show that the Q-learning path planner paths on average consumed 3.04% less energy than the A* path planning algorithm, in a square 20% obstacle density environment. The Q-learning path planner consumed on average 5.79% more energy than the least energy paths for the same environment. In the case of rectangular environments, the Q-learning path planning algorithm uses 1.68% less energy, than the A* path algorithm and 3.26 % more energy than the least energy paths. The implication of this study is to highlight the need for the use of learning algorithm in attempting to solve problems whose existing solutions are not learning based, in order to obtain better solutions.
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    Open Access
    Hot-thermistor spirometry for the artificial ventilation of infants
    (1982) Hughes, Timothy John
    This thesis describes equipment and techniques which were developed for use in monitoring mechanical aspects of artificial ventilation and optimising ventilation procedures. A strong emphasis is placed on the clinical applicability of the techniques and clinical applications are discussed. A new temperature-compensated hot-thermistor anemometer/spirometer was developed because the wide variety of spirometers described previously for-measuring respiratory volumes •and volume flow rates were unsatisfactory for routine use in monitoring infant ventilation. The principles of hot-thermistor spirometry were investigated both theoretically and experimental.ly to develop new temperature-compensation techniques and to predict the effect of gas composition changes on spirometer celebration. New electronic circuits were developed which greatly simplify the construction of temperature-compensated hot- thermistor anemometers and extend the dynamic range off low rates that can be measured.
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    Microprocessor controlled mildew detector
    (1981) Bensch, Dagobert; Case, M
    Downy Mildew is a vineyard disease which has cost the Economy tens of millions of rand in terms of both harvest loss and pest control measures. However, the weather conditions conducive to an outbreak of the disease have been well researched, thus it should be possible to monitor these in the vineyard and subsequently raise an alarm, whereupon systematic application of fungicide agents should prevent an outbreak of the disease. The work presented describes a Microprocessor based Monitor/Alarm system whose purpose it is to alert the farmer to an imminent outbreak of Downy Mildew.