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Electric Power Applications, IEE Proceedings -

Issue 6 • Date Nov 1995

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Displaying Results 1 - 10 of 10
  • Unified AC/DC power flow for system simulation in DC electrified transit railways

    Page(s): 345 - 354
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (900 KB)  

    The paper presents the improvements of a commercially available train simulator, the Energy Management Model (EMM), to evaluate the power flows in DC electrified transit railways. The sequential Gauss-Seidel power flow program used in EMM has been replaced by a unified Newton-Raphson AC/DC power flow to speed up the calculations. A precise model of the uncontrolled bridge rectifier with commutation impedance has been applied to the power flow formulation. Effects of regenerative braking on rectifier operations are also taken into account. Both the improved and the original train simulators have been tested on the Blue Line of Taipei Rapid Transit System which is under construction. Simulation results show that the proposed power flow program, with excellent convergence characteristics and accuracy, is of great value for train simulation View full abstract»

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  • Relevance of step-lap joints for magnetic characteristics of transformer cores

    Page(s): 371 - 378
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    It has been stated that multistep-lap (MSL) jointed cores show distinct improvements regarding power losses P in comparison to single-step-lap (SSL). On the other hand, model core experiments tend to yield contradictory results. In the paper, special emphasis was put on the underlying physical mechanisms, taking into consideration that model cores usually show `perfect' stacking, while full-size cores exhibit considerably high air gap lengths g as well as shifts s between the overlap regions of adjoining packages. It is shown that an increase of the number N of steps reduces the sensitivity of the core in respect to variations of g and s. This is due to increasing `critical induction' B C as of which the excitation VL of the overlap region steeply increases. Low VL corresponds to lower balancing interlaminar flux in the overlap/gap regions and thus to a generally more homogeneous flux distribution linked with lower P. The quantity BC can be assumed to be of high practical relevance for the design of transformer cores View full abstract»

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  • Robust speed control of brushless direct-drive motor using integral variable structure control

    Page(s): 361 - 370
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (988 KB)  

    A robust speed control technique for a brushless direct-drive motor (BLDDM) using a variable structure control (VSC) approach is presented. The significant problems of conventional VSC are investigated in view of the practical implementation and an integral variable structure control with a load torque observer is proposed as an effective way of overcoming these problems. By employing the proposed control scheme, the robustness against the unknown disturbance can be improved in the transient state and the steady-state error can be minimised by an integral action. Furthermore, the reduction of the chattering is also realised by using a load torque observer. The proposed algorithms are implemented using the software of DSP TMS320C30 and the effectiveness is verified through the comparative simulations and experiments for the BLDDM driven by a three phase voltage-fed PWM inverter View full abstract»

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  • Position control with fuzzy adaptation for induction servomotor drive

    Page(s): 397 - 404
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    The paper presents a two-degree-of-freedom (2DOF) controller with a reference model following fuzzy adaptation for position control of an induction motor drive. First, an indirect field-oriented induction servomotor drive is implemented, and a 2DOF controller is designed at nominal case according to the given tracking and regulating drive specifications. Then the resulting closed-loop tracking transfer function is used as the reference model, and the 2DOF controller is augmented by a model following error-driven fuzzy adaptation mechanism to reduce the effects of parameter variations on the desired performances. The effectiveness of the proposed controller is demonstrated by simulated and experimental results View full abstract»

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  • PWM control method for a four-level inverter

    Page(s): 390 - 396
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (556 KB)  

    Several PWM techniques for three-level inverters have been introduced. However, multilevel inverters with more voltage levels have not been considered yet. The paper proposes a PWM control method for four-level inverters. The four-level inverter uses six power switches per leg, but the blocking voltage of each switch is equal to one third of the DC-link voltage. The control method is based on closed loop regulation of the line to line voltages. It uses independent hysteresis comparator controllers to regulate the direct and quadrature axis components of the three-phase output voltages. The vector selection is adjusted according to the input reference to improve the voltage generation. The DC capacitor voltage balance is considered, and a method to control the variations is introduced. Computer simulations and the result of an experiment are given to confirm the validity of the proposed control scheme View full abstract»

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  • Transformer for multimegahertz power applications

    Page(s): 379 - 389
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1468 KB)  

    It is established that the eddy current losses in transformer windings at frequencies of 1 MHz or more, even when primary and secondary turns are interleaved in alternate layers, are unacceptably high. An improved winding arrangement is proposed in which primary and secondary turns are interleaved on the same winding layer. This almost eliminates leakage flux, to the extent that AC winding losses are due to skin effects only. Measurements on a prototype device confirm this. An improved transformer structure is described which makes interleaved turns practicable. A combination of substrate metallisation and aluminium wire bonding over a toroidal core is used to construct the transformer. Diodes are positioned in the centre of this structure to produce a transformer/rectifier assembly, and measurements on prototype units confirm that they operate efficiently. A hybrid method of computing winding losses is referred to and described briefly. It uses a three-dimensional finite element package to compute filament inductances, and tensor solution of a circuit description to calculate current distributions and winding losses. The effect of variable loadings in multiple secondaries on AC losses is also investigated. It is demonstrated that fractional turns ratios can be achieved with these transformers by suitable series and parallel connection of turns, similarly, a `suboptimal' technique of interleaving turns is also introduced, which can reduce winding complexity at the expense of increased losses. A formal method of undertaking these designs is proposed View full abstract»

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  • Transformerless four-wire PWM rectifier and its application in AC-DC-AC converters

    Page(s): 410 - 416
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (684 KB)  

    The paper introduces a transformerless four-wire power-factor-corrected boost rectifier which does not draw low-order harmonic currents from the supply neutral. The four-wire rectifier topology and control is described. The main application of such a rectifier is a new transformerless, four-wire AC-DC-AC converter for uninterruptible power supplies. Simulation results show the steady-state and dynamic response of the four-wire rectifier and the four-wire AC-DC-AC converter View full abstract»

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  • Contactless measurement of the secondary position in linear reluctance motors

    Page(s): 355 - 360
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (484 KB)  

    A new method of measuring the position of the secondary in a linear reluctance motor (LRM) is described, based on sampled measurements of the primary phase currents and the airgap flux density at the primary surface. Corrections must be applied for primary slot openings, primary end effects, and currents induced in a conducting barrier between the primary and the secondary. A static positional accuracy of ±1°, representing ±0.55% of the pole pitch, has been achieved in an experimental machine with load angles of up to 30°. The method is particularly suited to applications where the LRM is used for materials handling in a sealed containment system, since the secondary position can be determined from measurements made on the primary side of a conducting barrier. It should be capable of accurate position measurement at speeds of up to 1 m/s, which is the nominal upper limit for systems of this kind View full abstract»

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  • Active reactive-power controller

    Page(s): 405 - 409
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (484 KB)  

    A novel technique for building reactive power compensators using the switched-capacitor technique is presented. Normally when switched-capacitor are used for reactive power compensation they are operated at the supply frequency; in the proposed technique the capacitors are switched at higher frequencies, typically 800 Hz. The main advantages of this approach is that it provides a stepless variation in reactive power without the generation of harmonics as is the case with the conventional approach. The paper includes the details of theoretical and experimental investigation carried out at Brunel University to assess the new technique View full abstract»

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  • Index

    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (308 KB)  

    First Page of the Article
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