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Electric Power Applications, IEE Proceedings -

Issue 5 • Date Sep 1998

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Displaying Results 1 - 12 of 12
  • Dynamic modelling and control of a normal-force actuator

    Page(s): 449 - 454
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (624 KB)  

    The authors describe the dynamic modelling and control of a simple form of electromagnetic actuator comprising a laminated core with a coil and a `mover' section of the magnetic circuit separated by a small airgap. The modelling of the ideal case, in which a constant voltage is applied to the coil, is considered first. The important idea of control using freewheeling is then introduced. The model is developed to incorporate saturation, eddy currents and realistic circuit components and measured performance is compared with model results. The comparison demonstrates that this relatively simple model is capable of describing the behaviour of an actual device with good accuracy. The behaviour of the actuator when lifting a range of masses is then presented and it is shown to have a high force density and be capable of lifting loads up to 500 N. Finally, several control strategies are discussed which link the load to the length of freewheeling time with the aim of achieving an optimum balance between speed of action and efficient operation. One technique is recommended for further work View full abstract»

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  • Design considerations for permanent magnet synchronous motors for flux weakening applications

    Page(s): 435 - 440
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (564 KB)  

    The required parameter values of a permanent magnet synchronous motor designed for very large power-speed range are determined based on a linear dq model. It is shown that unconventional motor constructions with the d-axis inductance equal to, or bigger than, the q-axis inductance can provide superior torque, power factor and control characteristics. The initial sizing state of a design procedure is described. Analytical equations are developed and used to illustrate the influence of the rotor configuration, electromagnetic loading and air-gap length on the performance of a relatively large range of medium-sized motors. Suggestions regarding the improvement of efficiency, power factor, overload performance and PM protection against permanent demagnetisation are also given. The results of the analytical design procedure have been checked against finite element computations and experimental data View full abstract»

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  • Influence of rotor skew on cage motor losses

    Page(s): 414 - 422
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (916 KB)  

    A technique for calculating the total losses in a skewed induction motor, based upon a multi-slice finite-element model, is presented. The ability of this model to predict the axial variation in flux-density in the motor is initially verified. The model is then used to investigate how skew affects the losses in one induction motor. It is shown that skew alters the balance between the rotor iron loss and high-frequency rotor joule loss in the machine View full abstract»

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  • Corona screen effectiveness in large machines under high voltage, high frequency transient conditions

    Page(s): 469 - 474
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (572 KB)  

    The slot sections of pre-formed coils used in the manufacture of stator windings for high voltage rotating machines are conventionally finished with a layer of graphite loaded tape, known as a corona screen, for the purpose of suppressing electrical discharge between the coil side and slot wall. The screen resistivity is a compromise between the requirement to limit voltage rise on the screen between points of contact to the slot wall and the need to prevent significant current flow between adjacent stator core laminations. The authors present theoretical analyses and experimental results to show that, at frequencies associated with starting transients and some supply voltage disturbances, the voltage distribution along the corona screen surface may be quite different from that developed in normal operational conditions. Sufficient voltage may be developed at some points to permit discharge to the slot wall even when most of the screen is still intact and effectively earthed. Measurements of discharge current under simulated high frequency transient conditions have shown that the discharge may persist as an arc with much higher potential than normal slot discharge for accelerating surface degradation of coil sides View full abstract»

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  • Impact of surface coating insulation on small motor performance

    Page(s): 409 - 413
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (520 KB)  

    A range of tests exist for the characterisation of the surface insulation of motor steels. Attempts to correlate readings from these tests with expected motor performance suggests that, at low interlaminar EMFs, formalised insulation may be of secondary importance. However, coatings continue to play a key role in machine fabrication View full abstract»

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  • Design optimisation of electric motors by genetic algorithms

    Page(s): 475 - 483
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (832 KB)  

    A new approach to the design optimisation of three-phase electric motors is presented. The novelty lies in combining a motor analysis procedure with a genetic algorithm to optimise an objective function such as the motor torque, the efficiency, the material cost or some other motor figures or a combination of these. Two approaches to the motor analysis are presented: the first is based on a fully analytical procedure; while the second utilises the finite element method. Some optimised design examples, with reference to surface-mounted permanent-magnet three-phase motors, are included, and a comparison between the genetic algorithm optimisation technique and the classical hill-climbing direct-search method is made. A discussion on the limitations and benefits of the proposed design approach concludes the paper View full abstract»

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  • Heat transfer in a through-ventilated induction motor

    Page(s): 429 - 433
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (460 KB)  

    The effects of varying the cooling air flow and its distribution on the heat transfer in a high-voltage, strip-wound, four-pole induction motor are reported. The flow variations were achieved by altering the motor speed, by removing the wafters, by increasing the flow resistance of the motor air inlets, or by insertion of heat transfer augmentation devices in the stator-frame ducts. Heat transfer coefficients were deduced from the measurement of input power, and from miniature heat flux gauges attached to the surfaces. The overall heat transfer coefficient on the end-winding at the air outlet end (the fan end) was roughly double that at the air inlet end, the converse of the situation for lap and concentric wound motors. Large spatial variations in the end-winding local heat transfer coefficients occurred. This is attributed to the open nature of the winding which results in the individual loops behaving as separate bodies, each with a flow pattern dependent upon the angle of the approaching flow. There was a large increase in the overall heat transfer coefficient on the winding at the fan end when the wafters were removed. The use of transverse ribs in the stator-frame ducts was found to enhance heat transfer View full abstract»

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  • Operation of a fault tolerant PM drive for an aerospace fuel pump application

    Page(s): 441 - 448
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (884 KB)  

    The paper discusses the design of a fault tolerant permanent magnet drive based on a 16 kW, 13000 rev/min aircraft fuel pump specification. A `proof of concept' demonstrator has been built to this design and key parameters measured on the demonstrator drive are given. A novel current controller with near optimal transient performance is developed to enable precise shaping of the phase currents at high shaft speeds. A list of the most likely electrical faults is considered. Fault detection and identification schemes are developed for rapid detection of turn to turn faults and power device short circuit faults. Post fault control strategies are described which enable the drive to continue to operate indefinitely in the presence of each fault. Finally, results show the initially healthy drive operating up to, through and beyond the introduction of two of the more serious faults View full abstract»

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  • Effects of end winding porosity upon the flow field and ventilation losses in the end region of TEFC induction machines

    Page(s): 423 - 428
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (536 KB)  

    The authors describe the fundamental nature of the flow field and the influence of the end winding's porosity within the end region of a TEFC induction machine. A simulated end winding of simplified geometry was used for the investigation. Effects upon the flow field and ventilation losses are reported. Owing to the physical size and positioning of the end winding, changes in porosity produce large changes in flow rate and circulation affecting the flow rates by varying the flow resistance at the fan outlet and affecting the amount of flow through the end winding itself. This affects all aspects of the flow field by altering the angular momentum in the flow circulation. The changes in flow rate and circulation are also reflected by large changes in the ventilation losses View full abstract»

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  • Experimental investigations on the stators of electrical machines in relation to vibration and noise problems

    Page(s): 455 - 461
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (760 KB)  

    Accurate assessment of excitation forces and vibration behaviour is essential to arrive at a suitable design for the quiet operation of an electrical machine. From the vibration point of view, the stator of an electrical machine can be modelled as a system consisting of a number of masses interconnected by springs and damping elements to facilitate the analytical solution of the dynamic behaviour of the structure. The distribution of the mass and stiffness, which are essential to the determination of the resonances, are well documented in the literature. However, not much information is available on the nature and amount of damping present in electrical machine stators. Since vibration damping is not amenable to mathematical formulation, often one has to resort to experimental information for its determination. The authors present a fundamental study on the vibration behaviour of electrical machine stators using an experimental modal analysis. Modal testing is a process of forcing a structure to vibrate predominantly at a selected resonance. To achieve this, distributed electromagnetic forces were used. Detailed investigations were conducted on the stator models of a 120 hp induction motor to study their vibration behaviour, and to critically examine the damping present in them. Physical interpretations of the results are given to enable a better understanding of the vibration behaviour of electrical machine structures View full abstract»

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  • Influence of stator geometry upon vibratory behaviour and electromagnetic performances of switched reluctance motors

    Page(s): 462 - 468
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (548 KB)  

    The vibrations and the acoustic noise produced by switched reluctance motors (SRMs) are linked to current waveforms and to their structural properties. The authors carried out a parametric study to quantify the influence of the stator geometry upon vibratory behaviour of a 6/4 SRM. Their study shows the important influence of stator yoke thickness on vibration reduction compared to the other stator shape parameters. Moreover, a less noisy structure is proposed, based on the simultaneous analysis of electromagnetic performances and elastic characteristics View full abstract»

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  • Design of an in-wheel motor for a solar-powered electric vehicle

    Page(s): 402 - 408
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1108 KB)  

    The design of an in-wheel electric motor for the solar-powered vehicle `Aurora', entered in the 1996, 3010 km Darwin-Adelaide World Solar Challenge solar car race is described. Compared to other entrants in the race, the brushless DC motor is more efficient (97.5% compared to 92-95%) and lighter (8.3 kg compared to 12-16 kg) than all other direct-drive motors, and more efficient than all motor/gear combinations. This is achieved by the use of high flux-density rare-earth magnets, and computer aided optimisation of an axial-flux configuration consisting of a Halbach magnet array and an ironless air-gap winding View full abstract»

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