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Electric Power Applications, IET

Issue 9 • Date Nov. 2010

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Displaying Results 1 - 9 of 9
  • Current transients in the small salient-pole alternator during sudden short-circuit and synchronisation events

    Page(s): 687 - 700
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1136 KB)  

    Small salient-pole machines, in the range 30 kVA to 2 MVA, are often used in distributed generators, which in turn are likely to form the major constituent of power generation in power system islanding schemes or microgrids. In addition to power system faults, such as short-circuits, islanding contains an inherent risk of out-of-synchronism re-closure onto the main power system. To understand more fully the effect of these phenomena on a small salient-pole alternator, the armature and field currents from tests conducted on a 31.5 kVA machine are analysed. This study demonstrates that by resolving the voltage difference between the machine terminals and bus into direct and quadrature axis components, interesting properties of the transient currents are revealed. The presence of saliency and short time-constants cause intriguing differences between machine events such as out-of-phase synchronisations and sudden three-phase short-circuits. View full abstract»

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  • Tracking control of thrust active magnetic bearing system via hermite polynomial-based recurrent neural network

    Page(s): 701 - 714
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1350 KB)  

    A Hermite polynomial-based recurrent neural network (HPBRNN) is proposed to control the rotor position on the axial direction of a thrust active magnetic bearing (TAMB) system for the tracking of various reference trajectories in this study. First, the operating principles and dynamic model of the TAMB system using the non-linear electromagnetic force model is derived. Then, the HPBRNN is developed for the TAMB system with enhanced control performance and robustness. In the proposed HPBRNN, each hidden neuron employs a different orthonormal Hermite polynomial basis function (OHPBF) as an activation function. Therefore the learning ability of the HPBRNN is effective with high convergence precision and fast convergence time. Moreover, the connective weights of the HPBRNN using the supervised gradient descent method are updated online and the convergence analysis of the tracking error using the discrete-type Lyapunov function is provided. Finally, some experimental results of various reference trajectories tracking show that the control performance of the HPBRNN is significantly improved compared to the conventional proportional-integral-derivative and recurrent neural network controllers and demonstrate the validity of the proposed HPBRNN for practical applications. View full abstract»

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  • Classification of dynamic insulation failures in transformer winding during impulse test using cross-wavelet transform aided foraging algorithm

    Page(s): 715 - 726
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (924 KB)  

    Bacterial foraging-based approach for identification of fault characteristics of dynamic insulation failure in transformer during impulse test has been proposed. The winding currents acquired by tank current method during impulse test are analysed for identification of fault characteristics. The time-frequency domain-based features extracted from cross-wavelet spectra of winding currents of insulation failed and no-fault (healthy) insulation of transformer are given as input to the foraging algorithm for identification of dynamic insulation failure characteristics. The required winding currents to extract the significant features are acquired by emulating different dynamic insulation failures in the developed analogue model of 33 kV winding of 3 MVA transformer. To emulate various fault characteristics in analogue model, suitable fault emulator modules have been developed. Results show that the proposed foraging algorithm with cross-wavelet transform features could successfully identify the fault characteristics of dynamic insulation failure with acceptable accuracy. The classification accuracy of proposed foraging algorithm is also compared with fuzzy c-means classification algorithm. The concepts of dynamic arc model simulation, cross-wavelet transform feature extraction, emulation of dynamic insulation failure in analogue model of transformer and fault characteristics identification are explained. View full abstract»

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  • Practical approach to model electric motors for electromagnetic interference and shaft voltage analysis

    Page(s): 727 - 738
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1137 KB)  

    This study presents a practical method to find a high-frequency model of AC machine in order to predict leakage current and shaft voltage. A voltage-source inverter with hard switches generates pulse width modulated voltage with high dv/dt and common-mode voltage, which causes leakage current and shaft voltage due to stray capacitances in an electric motor. At fundamental frequency (a few hundred hertz), an equivalent circuit of an electric motor consists of inductances and resistances without considering stray capacitances. This study presents a practical approach in extracting high-frequency parameters of an electric motor for leakage current and shaft voltage analysis. Input impedance (magnitude and phase values) of several configurations of an AC motor is measured using a network analyser. All capacitive couplings between windings, stator and rotor are extracted based on theoretical analysis and measurement results. Simulations are compared with test results to verify the proposed method and model. View full abstract»

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  • Design and analysis of high-speed coreless axial flux permanent magnet generator with circular magnets and coils

    Page(s): 739 - 747
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (685 KB)  

    A high-speed coreless surface mounted axial flux permanent magnet generator with circular magnets and coils is proposed and studied. The performances of the machine are estimated and optimised by approximate theoretical analysis and comprehensive three-dimensional (3D) electromagnetic finite element analysis (FEA). Mechanical stresses in the rotor disc developed at high rotational speed are analysed and evaluated by 3D mechanical FEA to ensure the rotor's integrity. Finally, a prototype machine is constructed and tested. Both the experimental and predicted results have shown that the proposed generator possesses distinct advantages such as simple structure and high efficiency. The prototype also demonstrates its utility as a very low-cost generator. View full abstract»

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  • Parameter estimation of an induction machine using advanced particle swarm optimisation algorithms

    Page(s): 748 - 760
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (659 KB)  

    This study proposes a new application of two advanced particle swarm optimisation (PSO) algorithms for parameter estimation of an induction machine (IM). The inertia weight, cognitive and social parameters and two independent random sequences are the main parameters of the standard PSO algorithm which affect the search characteristics, convergence capability and solution quality in a particular application. Two advanced PSO algorithms, known as the dynamic particle swarm optimisation (dynamic PSO) and chaos PSO algorithms modify those parameters to improve the performance of the standard PSO algorithm. The algorithms use the measurements of the three-phase stator currents, voltages and the speed of the IM as the inputs to the parameter estimator. The experimental results obtained compare the estimated parameters with the IM parameters achieved using traditional tests such as the dc, no-load and locked-rotor tests. There is also a comparison of the solution quality between a genetic algorithm (GA), standard PSO, dynamic PSO and chaos PSO algorithms. The results show that the dynamic PSO and chaos PSO algorithms are better than the standard PSO algorithm and GA for parameter estimation of the IM. View full abstract»

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  • Modelling transformer core joints using gaussian models for the magnetic flux density and permeability

    Page(s): 761 - 771
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1426 KB)  

    Simple equivalent permeability and reluctance models are obtained for the transformer core joints from the analysis of the magnetic flux. It is shown that the flux variations in the joint zone can be fitted with simple Gaussian expressions suitable for transformer design purposes. These models are derived from 2D and 3D finite element simulations. The magnetic flux distribution in the transformer core joints is studied for wound cores and stacked-lamination cores with step-lap configurations. The models of the study properly account for the effects of core design parameters such as length of air gaps, number of laminations per step and overlap length. The proposed models, which include saturation and anisotropy, are applied to grain-oriented silicon steel (GOSS) and super GOSS. The new models are intended to estimate, right from the design phase, the magnetic flux density, permeability and the reluctance in the joints. The maximum differences between the Gaussian models of this study and finite element simulations are under 6%. The models of this study can be used to improve core designs with the aim of reducing core losses and magnetising current. A comparison of the total losses computed with the model of the study and measurements on a wound core distribution transformer showed differences of about 2.5%. View full abstract»

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  • Establishment and control of a three-phase switched reluctance motor drive using intelligent power modules

    Page(s): 772 - 782
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1222 KB)  

    This study presents the establishment and control of a digital signal processor-based 5 kW/6000 rpm three-phase switched reluctance motor (SRM) drive. Two three-phase intelligent power modules are employed to construct its converter for achieving a compact power circuit. The motor winding inductance profile is first estimated, and it is used for performing the proper winding current switching control. In the developed ramp-comparison current control PWM scheme, in addition to the adequate feedback control, the current tracking error-adapted commutation instant tuning is made to yield improved current response and torque generating capability. As to the speed control, a feedback controller is augmented with a simple linear model following controller for yielding satisfactory speed tracking and regulation dynamic responses within a wide operation range. The driving performance of an established SRM drive is evaluated experimentally. View full abstract»

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  • Calculation of inductances and torque of an axially laminated synchronous reluctance motor

    Page(s): 783 - 792
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (812 KB)  

    This study focuses on the calculation of inductances and torque of a synchronous reluctance machine having an axially laminated anisotropic rotor. Two techniques based on the winding function (WF) theory are used for the computations. One technique, of the conventional type, uses analytical expressions representing the airgap and the winding whereas the other uses the developed model of rotor and stator geometry shapes with winding placement positions. The second procedure does not make the assumption that the windings are sinusoidally distributed and includes all harmonics while avoiding the cumbersome integrations associated with the conventional WF procedure. The effects of stator slots and rotor axial lamination insulations introduce noticeable distortions in the inductances and torque plots. The results, transformed to rotor reference frame, yielded cross-coupling inductance components. Saturation is modelled by considering the airgap length as a variable, depending on the airgap flux. The results obtained with both WF procedures are compared with results of finite-element calculations and an acceptable correlation is observed. View full abstract»

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IET Electric Power Applications publishes papers of a high technical standard with a suitable balance of practice and theory.

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