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Electric Power Applications, IEE Proceedings -

Issue 6 • Date Nov 1994

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Displaying Results 1 - 13 of 13
  • Analysis of GTO-based static VAr compensators

    Page(s): 293 - 302
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (560 KB)  

    The growing availability of high-power gate turn-off thyristors (GTOs) has meant that power electronic convertor circuits can be manufactured with the ability to both absorb and generate reactive power. These circuits constitute the next generation of static VAr compensators (SVCs) which may eventually supersede the conventional thyristor-controlled reactors (TCRs) and thyristor-switched capacitors (TSCs) used in power systems at present. The paper gives an analysis of both 6-pulse and 12-pulse GTO-SVCs based on voltage-source convertor circuits, and equations are derived that describe the performance of each circuit. In addition, the conditions leading to circuit resonances are discussed together with possible methods of avoiding the problems View full abstract»

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  • Feasibility of using unsupervised learning, artificial neural networks for the condition monitoring of electrical machines

    Page(s): 317 - 322
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (452 KB)  

    The feasibility of using an artificial network for identifying faults in induction motors has been demonstrated previously by the authors. In this work, the network was used as a learning and pattern recognition device, and was able to successfully associate input signal patterns with appropriate machine states. The neural network used was the multilayered perceptron (MLP), trained by a backpropagation algorithm. However, MLP lacks flexibility since it requires fully labelled input-output pairs (i.e. training of the network is supervised). This limitation can be removed by the use of an alternative approach, using unsupervised methods, such as the Kohonen feature maps (KFM) technique. The results of applying KFM to condition monitoring of electrical drives are reported in this paper, and they reveal the practical advantages of unsupervised systems, which include the ability to learn and produce classifications without supervision. Because of the natural parallel architecture of neural networks, they are also ideally suited to the use of multiple transducer inputs, which can greatly enhance the reliability of decisions made regarding the state of machine performance or condition View full abstract»

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  • Acoustic noise of electromagnetic origin in an ideal frequency-converter-driven induction motor

    Page(s): 341 - 346
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (432 KB)  

    With the advent of power electronics, there has been increasing demand for variable-speed drives in industrial applications because significant energy savings can be achieved. However, the use of frequency converters in driving induction motors has resulted in significant increase in acoustic-noise radiation. While there have been numerous studies on the acoustic-noise-generation mechanisms in variable-speed drives, the problem remains unsolved. The increase in acoustic-noise radiation in inverter-fed induction motors has been mainly attributed to the time harmonics introduced by the converters. A general algorithm is presented to compute the change in sound-power level of a variable-speed induction motor due to the change in the speed of operation in the absence of time harmonics (i.e. driven by an ideal frequency converter). General qualitative results based on this algorithm indicate that, even if an ideal converter can be designed to eliminate all the time harmonics, the acoustic-noise radiation of electromagnetic origin can still be significantly increased by the change in speed. This algorithm can therefore be used to help establishing the lowest limit of acoustic-noise radiation which can ever be achieved independent of frequency-converter configurations for a variable-speed induction motor View full abstract»

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  • Field-weakening performance of brushless synchronous AC motor drives

    Page(s): 331 - 340
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (716 KB)  

    The paper examines the theoretical and practical limitations to the field-weakening performance of surface permanent magnet, synchronous reluctance and interior permanent magnet motors when driven from an inverter with a limited volt-ampere rating. It is shown that the `optimal' field-weakening performance consists of an infinite constant-power speed range but is limited to an inverter utilisation of about 0.7. The new concept of the interior permanent magnet parameter plane is introduced. This graphically illustrates the effect of varying the drive parameters on the shape of the field-weakening characteristic. The interior permanent magnet parameter plane is used to show that there are three types of optimal field-weakening designs. When practical factors and considerations are taken into account, the optimal high-saliency interior permanent magnet motor design is the most promising for applications requiring a wide field-weakening range. A 7.5 kW design was built and a constant-power speed range exceeding 7.5:1 was demonstrated View full abstract»

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  • Mathematical model of gate-turn-off thyristor for use in circuit simulations

    Page(s): 284 - 292
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (592 KB)  

    Owing to the lack of a detailed mathematical model for the gate-turn-off (GTO) thyristor, accurate simulation of power-electronic circuits involving GTO thyristors has not been feasible. The paper describes the theoretical development of an accurate analytical model of the GTO thyristor and the practical implementation of the model in industry-recognised circuit simulators. The GTO model is based on a network representation of the device structure. The derivation of the equations has been aided by known theoretical work, observations of experimental data and finite-element analyses of internal device behaviour. This development approach has enabled characteristics unique to power devices to be accounted for, including the effects of conductivity modulation and dynamic charge storage in the mid-region. The model has been implemented in SPICE simulators and the Saber simulator. Comparison of simulation results and experimental data verifies that the model has a high degree of accuracy over a wide range of operating conditions. A practical application of the GTO model in the design of the inverter is also given View full abstract»

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  • Effect of end core flux on the performance of the switched reluctance motor

    Page(s): 308 - 316
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (620 KB)  

    The aim of the paper is to bridge the gap between two-dimensional and three-dimensional finite-element modelling of the switched reluctance motor. The flux linkage/current diagram and static torque profile of a four phase 8/6 machine are computed with the aid of two-dimensional and three-dimensional models. Comparison of the predicted values with measurements on the motor demonstrates the superiority of three-dimensional modelling. Three-dimensional effects in the switched reluctance motor are examined and a suitable procedure for estimating the end-core flux at a range of rotor positions and excitations is proposed. The sensitivity of the end-core flux value to magnetic circuit parameters such as applied MMF, magnetic saturation and path reluctance is presented View full abstract»

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  • Torque harmonics minimisation in permanent magnet synchronous motor with back EMF estimation

    Page(s): 323 - 330
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (460 KB)  

    A predictive current control in the synchronous reference frame with the back EMF estimation using the previous voltages and currents is presented. To reduce the torque harmonics produced by the air gap flux harmonics, the compensated d-axis and q-axis currents from the estimated back EMFs are employed. The effectiveness of the proposed control scheme is compared to the conventional one through simulation and experiment View full abstract»

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  • Improvement of induction machine stability by modulation techniques

    Page(s): 347 - 352
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (428 KB)  

    Instability can occur when an induction machine is supplied by a voltage source inverter-based PWM drive operating in an `open loop' mode, particularly if the machine is lightly loaded. A form of space vector modulation is described in this paper that can be used to improve machine stability substantially. The modulation range of this technique is limited, however different methods of overcoming this limitation are discussed View full abstract»

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  • Parameter identification of inverter drive system

    Page(s): 303 - 307
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (296 KB)  

    The problem of an offline identification of the inverter drive system is presented. The least-squares method and the numerical optimisation method are analysed. Using experimental investigations, the effects of the conditions of supply and load on the inverter motor system are analysed. Changes in the values of identified parameters are approximated by polynomial functions View full abstract»

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  • Empirical thermal model for inverter-driven cage induction machines

    Page(s): 360 - 372
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (848 KB)  

    The paper describes an empirical thermal model which provides an estimate of stator- and rotor-conductor temperatures in an inverter-driven cage induction machine under both transient and steady-state conditions (of heating and cooling), and under constant and variable flux control. The model is based on a widely used thermal-torque derating for inverter-driven induction machines, and features a single frequency-dependent thermal resistance and time constant for each winding. It is easily implemented in real time for online thermal protection and compensation for winding-resistance variation. The technique is demonstrated on two 7.5 kW inverter drives to give temperature estimates to within 10 deg C for both transient and steady-state operation. This accuracy is shown to be sufficient to maintain torque output to within 0.01 p.u. in both voltage-forced and current-forced inverter drives. The model can be generalised for a wide range of machine sizes, without the need for specific physical details, by assuming that induction machines are constructed of similar materials, and have similar insulation thermal limits View full abstract»

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  • Design of an energy efficient motor for irrigation pumps operating under realistic conditions

    Page(s): 269 - 274
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (396 KB)  

    The issues involved in the design of energy-efficient high-performance irrigation pump induction motors operating under typical field conditions are highlighted. Various factors deserving consideration, from the predesign survey to the final design stage, are discussed in detail. By resorting to optimisation techniques, suitable objective functions were evolved to arrive at an improved design, which is constrained by industrial practices and performance requirements. The new design is compared with the standard design, and its salient features are discussed to suggest useful guidelines View full abstract»

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  • Parameter sensitivity of procedures for on-line adaptation of the rotor time constant of induction machines with field oriented control

    Page(s): 353 - 359
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (396 KB)  

    Procedures for on-line adaptation of the rotor time constant are often based on error models involving two or more machine parameters. A mismatch between the parameters in the model and in the machine has strong influence on the adaptation result and therefore on the quality of the field orientation. The parameter sensitivity of four simple adaptation methods is analysed theoretically and investigated by means of simulation studies. A new way to improve the parameter robustness by constructing a vector error signal is shown View full abstract»

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  • New approach to current control of AC-to-DC voltage-type convertors

    Page(s): 275 - 283
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (564 KB)  

    A new phase- and amplitude-based current control strategy for a PWM AC-to-DC voltage-type convertor is presented which introduces state feedback control of an LC filter. The feedback of the state variables of the LC filter connected to the AC side of the convertor not only compensates a DC component of the AC input current but also eliminates the oscillations of the DC output current and voltage waveforms during transients. A mathematical model of the convertor system with proposed control strategy is developed to carry out computer simulation of the system under transient operating conditions. The simulation and the experimental results of the proposed system show that the transient waveforms of AC input and DC output currents are improved greatly, even for low damping effect. The simulated results also show that the dynamic response can be significantly improved even when the DC side capacitance is substantially reduced View full abstract»

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