Browsing by Author "Gieras, Jacek F"

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    Analysis of a permanent magnet hybrid linear stepping motor
    (1998) Wang, Rong-Jie; Gieras, Jacek F
    Hybrid linear stepping motors (HLSMs) are regarded as an excellent solution to positioning systems that require a high accuracy and rapid acceleration. The advantages such as high efficiency, high throughput, mechanical simplicity, high reliability, precise open-loop operation, low inertia of the system, etc. have made this kind of motor more and more attractive in such applications as factory automation, high speed positioning, computer peripherals, numerically controlled machine tools and welding apparatus. This motor drive is especially suitable for machine tools in which the positioning accuracy and repeatability are the key problems. Using the microprocessor controlled microstepping mode, a smooth operation with standard resolution of a few hundred steps/mm can be obtained. Although rotating hybrid stepping motors are well covered· by literature, there are only a few papers on HLSMs published so far. The objective of this thesis is to apply the reluctance network approach (RNA) and the finite element method (FEM) to performance calculations of HLSMs. A comparison with the experimental measurements is done to evaluate advantages and disadvantages of these two methods. The static characteristics show that the FEM demonstrates a better correlation with the experimental results than the RNA. The reason is that some assumptions have been made in order to obtain a simplified model in the RNA. The RNA, in general, tends to overestimate the forces. In the case of instantaneous characteristics simulation, both the FEM and RNA compare favourably with the experimental data though the FEM gives more accurate (albeit underestimated) results. However, the RNA is a very efficient approach considering the computation time. The optimisation of the finite element model is very important for obtaining the best possible results. The density of the finite element meshes, the aspect ratio of the elements and reducing the problem in size by using symmetry are vital considerations. The studied HLSM possesses a very small airgap, which made a judicious mesh scheme extremely important. Different methods of force calculations were analysed and it was found that both the Coulomb's approach and the Maxwell stress tensor are efficient and accurate methods to implement. The classical virtual work CVW method is very time-consuming since it requires two solutions. The determination of small incremental displacement is also difficult in the CVW. The experimental investigations of the small HLSM need a very high accuracy, Considerable efforts are needed to minimize all sources of noise and interference. It has been found that amplitude of instantaneous force ripple increases when the phase current amplitude increases. The superimposition of the 3rd harmonic on phase current can effectively reduce the force ripple. The transient tests focused on the start-up and braking characteristics. The start-up tests show that the higher the load is applied the longer the start-up time is required. On the contrary, the braking time can be significantly reduced with an increase in load. It can also be concluded that the higher the step resolution, the less settling time is needed for both start-up and braking processes. The recommendations from this thesis for further research on the subject of the HLSM analysis are that the reluctance network model should be improved to take into account the magnetic saturation and edge effects and the FEM enhanced classical approach should be attempted to take advantages of the high accuracy of the FEM without significant increase in the solution time.
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    Open Access
    Analysis of an energy efficient permanent magnet brushless universal motor
    (1996) Wing, Mitchell, 1968-; Gieras, Jacek F
    The vast improvements made in the development of rare earth magnets, power electronics and micro-electronics over the last two decades can claim to be the major driving forces behind the rapid growth of permanent magnet (PM) brushless motor drives. The state of the art in PM motor technology is the PM universal motor, i.e. a combination of a PM synchronous and a PM brushless direct current (DC) motor. The PM universal motor has the capability to operate as a variable speed DC shunt motor with high torque at low speeds, and also as a synchronous motor at constant speed with high efficiency. The literature on synchronous and PM brushless motors is very extensive, although no studies have dealt with the concept of a PM brushless universal motor in any detail. The objective of this thesis is to develop an energy efficient, high performance, reliable and inexpensive electrical motor to replace induction motors, in the 21st century. Initial research of different AC motors highlighted the importance of correctly designing electrical motors. The different PM synchronous motors used in this study revealed that a sound knowledge of the motor's performance characteristics, at the design stage, is crucial to the successful and optimal design of any PM motor.
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    Computer simulation of steady state and transient performance for permanent magnet DC motors
    (1992) Wing, Mitchell; Gieras, Jacek F
    Permanent magnet motors have outstanding performance for applications such as industrial robots, computer peripherals and automobiles. Since these motors are being used in a growing number of applications, the techniques used to model them are becoming more important in an attempt to obtain the best possible performance from any new design. The objective if this thesis is to develop an understanding of the classical and the finite element theory in an attempt to obtain the full characteristics of small commutator permanent magnet direct current motors. A comparison of the two methods is done in an attempt to obtain the most effective method of designing new motors. The comparison is done by calculating the performance of two segmental magnet de motors using the two methods. The methods are investigated separately to ensure that the best possible results are obtained from the simulations. The comparison of the steady state and transient characteristics of the motors are done separately.
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    Open Access
    Influence of higher time harmonics on the electrical and mechanical performance of an inverter-fed squirrel cage induction motor
    (1991) Roeber, Jochen Erich; Gieras, Jacek F
    Due to the ruggedness, reliability and low maintenance required, small inverter-fed induction motors (1.5 kW to 25 kW) have earned a reputation and are utilized more and more frequently in industry for variable speed applications. The applied voltage and current waveforms are generally quite non-sinusoidal and polluted with higher time harmonic components. The higher time harmonics affect the electrical and mechanical performance significantly, and adverse effects are investigated. Literature on the effect of higher time harmonics is reviewed. Recommendations referring to various aspects under non-sinusoidal excitation are made when installing inverter-fed induction motors. Different inverter supplies (6-Pulse Square Wave voltage source inverter (VSI), PWM VSI and sinusoidal excitation) are used with a small 3-Phase, 3-kW squirrel cage induction motor, configured under synchronous characteristic Vᵣ/50 and subsynchronous characteristic Vᵣ/87. The respective voltage and current frequency spectrums of the excitation source are analyzed and the harmonic content determined. Performance executed under identical operating respectively and results are compared with pure sinusoidal (fundamental) excitation. tests are conditions respect to To determine the electrical performance the efficiency, power factor, temperature rise of the stator and induced shaft voltages were analyzed. The mechanical performance under inverter operation was analyzed by measuring the torque, torque pulsations, critical speeds and resonance frequencies of frame vibrations and torque oscillations as well as vibrations in x-, y-, and z-direction of the inverter-fed induction machine. Consequences of time harmonics on the induction motor and system are discussed. Conclusions on the effect of time harmonics and performance of different inverter types compared to sinusoidal excitation are drawn and are theoretically summarized and justified. Summary in English and German. Bibliography: pages 148-154.
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    Performance analysis for a shaded-pole linear induction motor
    (1998) Davidson, Innocent Ewean Agbongiague; Gieras, Jacek F
    The induction motor remains the prime mover of present day industry with it's associated components in drive applications. In many such applications, fractional horse-power motors find ready use in small mechanisms where three-phase power supply is not available. In Southern Africa, these motors can be used is rural areas with simple reticulation systems, hence the renewed interest in the development of these low-power electrical motors, especially specialised models such as linear versions of such motors for special applications. This research is in the area of single-phase LIMs. The objective has been to model the shaded-pole LIM, in an attempt to enhance it's performance through improved design methods. This was carried out using an integrated analysis approach, involving circuital and field theory in the analysis of the practical motor, and computer simulation of it's equivalent model using the finite element method. Linear counterparts are possible for all the various forms of rotating electrical machines. All cylindrical machines can be 'cut' along a radial plane and 'unrolled' [32]. LIMs convert electrical energy directly into mechanical energy of translatory motion. Some advantages of linear version of induction motors are: they are gearless and often require minimal material thus minimising cost. While their scope of application are somewhat limited when compared to rotary versions, they do however give excellent performance in special situations where translator motion is required. However, the output power-to-mass and output power-to-volume of active materials ratio is reduced compared to rotary induction motors[45]. These disadvantages are caused by the large air-gap and the open magnetic circuit, which produces parasitical effects.