Browsing by Author "McLaren, S G"

Now showing 1 - 10 of 10
  • Thumbnail Image
    Item
    Open Access
    Automatic digital scaling of analog computers
    (1972) Glaum, Frederick Charles; McLaren, S G
    The purpose of this work is to develop an algorithm for use on a small digital computer in the conversational mode. This algorithm to scale and determine the patching configuration for the simulation of any system on an analog computer. Further, this should be in a form suitable for the implementation of automatic patching in a hybrid computer which contains the necessary switching matrix and hardware. The method of solution chosen here relies heavily on modern control theory, and in this lies both its strength and its weakness. The advantage of the method is that it forms a direct link between the State Space representation of a system and the analog computer simulation of that system. The chief disadvantage is that it is cumbersome in the handling of non-linear systems. The method can be divided broadly into two sections: 1) Digital simulation of system in order to determine the maximum values of all variables. 2) Scaling and analog set-up.
  • Thumbnail Image
    Item
    Open Access
    The design and evaluation of "short-sighted" stochastic optimal controllers
    (1986) Kleynhans, Bernardus Gerhard; McLaren, S G
    The quality of control provided by what is termed "short-sighted" stochastic optimal controllers controlling a linear heating system subjected to a random disturbance is evaluated by computer simulation and by experimentation.
  • Thumbnail Image
    Item
    Open Access
    Direct digital control of a D.C. machine
    (1972) Weehuizen, Hermanis Frans; McLaren, S G
    The object of this thesis is to build an interface between a computor and a three phase thyristor bridge rectifier, enabling the computor to control its D.C. output voltage. By writing a suitable computor program, this system was extended to provide closed loop computor control of the speed of a D.C. machine. The first interface and computor program were so designed that the computer provided the required analogue triggering delay for voltage control of the D.C. output. This setup did not allow for infinite variation of the voltage and occupied a large portion of the computor time. Thus it was decided to modify the interface, letting it provide its own delay, thus freeing the computor of the delay routine and giving it more time to do other tasks. Control of the bridge rectifier was also improved. When closed loop control was implemented, the system was found to be unstable. It was thus simulated and stabilized on the analogue computor. A new digital computor program was written incorporating those characteristics which were found necessary in the simulation to make the system stable. The modified form of compensation was found to give a satisfactory performance for both step and ramp inputs to the system as well as load transients on the D.C. motor. Various types of tachogenerator were tested to find which was the most suitable for operation with the computer. All the types tested gave satisfactory performances. The major factor affecting performance was the quality of the tachogenerator.
  • Thumbnail Image
    Item
    Open Access
    Direct digital control of a synchronous machine
    (1977) Tatlow, Gavin Mark; McLaren, S G
    With the advancement of thyristor technology, variable speed alternating current drives are providing improved performance over conventional systems. The aim of this thesis is to investigate the possibilities of direct digital control of a thyristor converter and to determine the major parameters affecting the operation of a variable speed synchronous machine drive.
  • Thumbnail Image
    Item
    Open Access
    Direct digital control of D.C. machines
    (1972) Von Zwiklitz, Aubrey Paul; McLaren, S G
    This thesis set out to improve on previous methods of digital control of a three phase fully controlled thyristor bridge, using phase control of the thyristors, and to use this bridge for the purpose of controlling the speed of a separately excited D. C. machine, under the supervision of a small digital computer. Interfacing equipment for this purpose was designed and built. Various methods of speed detection were considered, and a simple digital tachometer designed and built. This tachometer was able to feed a digital number, related to the speed of the machine, to the computer, and was accurate to better than 1%. A direct digital control system was then implemented. The behaviour of the system was first studied under open loop conditions in order to determine the parameters of the system, and to discover any shortcomings in it. The behaviour of the closed loop system was then studied, using z-transform analysis, at sampling rates of from twice to eight times the natural frequency of the machine. Initially, the computer was used as an integral controller. The behaviour of the mathematical model was compared to that of the actual system, and the correlation found to be very good. The control system was then compensated, using compensation routines based on the z-transform analysis, and the behaviour of various compensated systems studied at sampling rates varying from 0,4 to 1 second. Again, the actual system response was found to correspond closely to the designed behaviour. Finally, a dual-machine control system, on a time sharing basis, was implemented, and a degree of interrelation between the speeds of the two machines introduced. The control algorithms developed were able to provide speed control to better than l% accuracy, with a 5% or less overshoot in the step response, a delay of one sampling period but no overshoot in the ramp response, and satisfactory behaviour under load transient conditions. The time, and memory, utilization was such that such algorithms could be extended to the control of several machines, using the single computer, if sufficient input and output facilities were available.
  • Thumbnail Image
    Item
    Open Access
    Investigation of an optimalising controller
    (1969) Luxat, J C; McLaren, S G
    This dissertation presents a comprehensive investigation of an optimalising controller and its behaviour when controlling a simulated plant. In addition certain theoretical aspects of optimalising control are presented. Design criteria and details of the circuitry of the experimental controller, built as part of this research project, are given. The necessity to deactivate the controller, for a certain period during each cycle of operation, is shown to be a result of measurement delay in the optimalising loop, and an expression for evaluating the deactive time is derived. Utilising describing function techniques, the steady-state response of the control system is predicted and the results are shown to be in good agreement with the experimental results. The adaptive response of the system is investigated and it is shown that the bandwidth of the adaptive response maybe predicted from steady-state response characteristics. The limitations imposed upon both the steady-state and adaptive response, by measurement delay, are shown . With respect to the theory of optimalising control, a framework for stability analysis is developed and stability criteria for the basic optimalising control loop are derived.
  • Thumbnail Image
    Item
    Open Access
    Predictive and adaptive extremal control
    (1976) Kimmel, Ivriani; McLaren, S G
    The time-optimal predictive control strategy for second order relay or bang-bang control systems is investigated along with modifications of this strategy for third order systems. One basis of this strategy is the utilization of a model, a replica of the plant, run in a fast-time mode so as to obtain the future output of the plant under the present input. Based upon these measurements, corrections to the plant may be implemented to achieve the desired response. The concept of the fast model is a useful one in that it falls into the synthesis of the more general time-optimal trajectory and switching functions for various second, third and higher order plants. However the difficulties in providing the exact time-optimal control for these plants result in the generation of acceptable sub-optimal and near time-optimal strategies. The nature of plant sensitivity, parameter variation and identification are investigated as well as a novel self-adoptive controller which dispenses with the identification phase but identifies a certain surface in the state space and establishes a stable sub-optimal control strategy. These control techniques are applied to a small DC motor with responses close to time-optimal.
  • Thumbnail Image
    Item
    Open Access
    Simulation of distributed computer networks
    (1987) Weehuizen, Hermanis Frans; McLaren, S G
    This is a study of the simulated performance of two local area networks, Ethernet and the MAP network, respectively based on the IEEE standards 802.3 and 802.4. The simulation language chosen is of the discrete event type rather than the more usual analytical model. This is done in order to observe the interaction between the various entities of a network in order to gain a better understanding of the method of operation of such a system. The performance demanded of a node entity by the networks is determined. The performance of some commercially available hardware is derived from manufacturer's specifications and compared with that required by the network. It is found that there is a significant disparity, with the network requirements far exceeding that of the hardware capabilities. The simulation models developed are used to determine the performance of the networks both with and without the limitations imposed by currently available hardware. While the inclusion of the hardware performance causes little ·loss in performance for the Ethernet network, it has a highly detrimental effect on that of the MAP network. A possible solution is found to this limitation which requires minimal change to the existing protocol. The conclusions reached are that with currently available hardware a group of nodes are able to fully utilise the performance of the Ethernet LAN although a single pair of nodes is unable to do so. With regard to the MAP network, the network performance is limited by that of the node performance although this can be offset to a certain extent by careful choice of one of the protocol parameters, or modification of the hardware design.
  • Thumbnail Image
    Item
    Open Access
    Uranium plant identification using correlation methods
    (1974) Braae, Martin; McLaren, S G
    Theory relating to identification of an uranium plant using on-line correlation techniques is described. Generation and properties of pseudorandom ternary m-sequences are discussed, particular attention being given to selection of a suitable sequence for testing a system. The geometry and control policy of the uranium plant is outlined and existing and experimental equipment required for realizing perturbation of the plant is considered. A theoretical model of the plant is studied to detect effects that might adversely affect the experimental results. Programs written to evaluate correlation functions and for general data handling are briefly outlined. The pseudo-random ternary m-sequence noise is selected with reference to the plant characteristics as deduced from plant records. Results of pilot tests enabled the pseudo-noise to be correctly selected for the main test. All tests and their results are briefly described. Finally, the analytic and empiric models of the plant are derived and the validity of the model obtained from the correlation method is tested by comparing theoretical predictions with experimental observations.
  • Thumbnail Image
    Item
    Open Access
    Vector acoustic miss distance indication
    (1985) Thomson, R G W; McLaren, S G
    In 1981 the author decided to investigate means of accurately measuring the passage of anti-aircraft shells past a towed airborne target. This decision was based on the observation that available literature showed a need for low cost miss distance indication equipment. A feasibility study showed that the task would be multi-disciplinary entailing aerodynamics telemetry, weapons performance studies and investigation of the techniques of measurement of shell location currently in use. The decision was made by the author to concentrate on a study of the technique measurements of shell location and the analysis of such measurements in view of the fact that, at least in isolation, knowledge of the other factors mentioned was fairly complete although unevenly spread in South Africa. Initial work concerned a study of the General Requirements for such target systems and the classification of these. A literature survey was conducted by the author which indicated that systems already in service made use of several measurement techniques, including photographic, radar and acoustic phenomena. Of these, acoustic means appeared to offer a cheap and simple solution to the measurement problem. The author then explored the principles and potential of Acoustic Miss Distance indication and arrived at the conclusion that such a system, based on measurements of the period of the shockwave accompanying a supers6nic shell, would be feasible. This conclusion led to the Thesis presented in this document, that firstly measurement of the shock-wave period could enable deduction of the distance between the sensor and the flight path of a supersonic shell and secondly, that several such measurements would enable the miss vector to be calculated.