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Electric Power Applications, IEE Proceedings -

Issue 4 • Date 8 July 2005

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Displaying Results 1 - 25 of 31
  • Time and frequency domain analysis of fault-tolerant space vector PWM VSI-fed induction motor drive

    Page(s): 765 - 774
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (530 KB)  

    The use of a new space-vector modulation strategy for a voltage source inverter supplying a fault tolerant induction motor drive is investigated. Such a system uses two distinct space-vector modulation strategies to switch from the healthy to the faulty operation. The proposed modulation strategy for the faulty operation has the same symmetry as in a classical B6 inverter. The purely analytical results both in the time and frequency domain are based on the Laplace transform of the voltage space vectors. There is an excellent agreement between the analytically calculated waveforms and the experimentally determined ones. Therefore, the proposed analytical model becomes a very useful method under unbalanced, as well as balanced, supply conditions. View full abstract»

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  • Practical EMI-filter-design procedure for high-power high-frequency SMPS according to MIL-STD 461

    Page(s): 775 - 782
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (779 KB)  

    The paper presents a very practical EMI-filter design procedure for high-power high-frequency switch-mode power supplies (SMPS), conforming to the military standard MIL-STD 461. The design procedure is based on the knowledge of base-line common-mode (CM), and differential-mode (DM) EMI. Conducted-emission tests are carried out first according to MIL-STD 461. The measuring current probe only is used to separate the total conducted EMI into CM, and DM components, without the need for a special noise separator. The current attenuation of the filter is then simulated by a MATLAB program, using simplified high-frequency equivalent-circuit models for CM- and DM-filter components. Based on the proposed design procedure, a prototype EMI filter has been implemented for a unity-power-factor boost convertor, operating at a switching frequency of 20 kHz and an output power of 4 kW. Practical aspects in the implementation, such as filter-layout considerations and component selection, are discussed. The performance tests were carried out experimentally on the implemented filter according to MIL-STD 461, to verify the validity of the design procedure. View full abstract»

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  • Modulating functions for modelling PWM switching converters

    Page(s): 783 - 792
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (375 KB)  

    The aim of the work is to identify continuous average models of switching converters from input-output data. Among the various identification techniques, modulating functions were chosen due to their capability for revealing converter dynamics, even in the case of fast time constants. Due to its low-pass filtering property, such an identification technique reveals its effectiveness in the case of the evaluation of average models for switch-mode DC-DC converters. Following a brief description of the modulating functions properties, simulation and experimental examples of application are presented, first for the case of the basic boost converter and then for more complex topologies, like the half-bridge current doubler converter. The last example considers the application of such a technique to a resonant converter: a relevant result is that the technique allows an easy modelling particularly in critical cases of resonant converters where traditional averaging techniques fail. View full abstract»

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  • High-efficiency DC/DC converter with high voltage gain

    Page(s): 793 - 802
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (484 KB)  

    A high-efficiency converter with high voltage gain applied to a step-up power conversion is presented. In the proposed strategy, a high magnetising current charges the primary winding of the coupled inductor, and the clamped capacitor is discharged to the auxiliary capacitor when the switch is turned on. In contrast, the magnetising current flows continuously to boost the voltage in the secondary winding of the coupled inductor, and the voltages across the secondary winding of the coupled inductor, the clamped capacitor and the auxiliary capacitor are connected in series to charge the output circuit. Thus, the related voltage gain is higher than in conventional converter circuits. Moreover, this scheme has soft-switching and voltage-clamped properties, i.e. the switch is turned on under zero-current switching and its sustainable voltage is comparatively lower than the output voltage, so that it can select low-voltage low-conduction-loss devices and there are no reverse-recovery currents within the diodes in this circuit. In addition, closed-loop control methodology is utilised in the proposed scheme to overcome the voltage drift problem of the power source under the load variations. As a result, the proposed converter topology can promote the voltage gain for a conventional boost converter with a single inductor, and deal with the problem of the leakage inductor and demagnetisation of the transformer for a coupled-inductor-based converter. Some experimental results via examples of a proton exchange membrane fuel cell power source and a traditional battery are given to demonstrate the effectiveness of the proposed power conversion strategy. View full abstract»

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  • Dynamic simulation of cage induction machine with air gap eccentricity

    Page(s): 803 - 811
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (622 KB)  

    This paper describes a method for the dynamic simulation of a cage induction machine with static and dynamic air gap eccentricity. The method is based on the winding function theory and extension of this theory to the nonuniform air gap case. A method of calculating all inductances in a machine with both static and dynamic air gap eccentricity is presented and a numerical analysis of a machine with specified parameters is presented. Stator line current spectra collected experimentally for both the static and dynamic eccentricity conditions confirm the results obtained by the proposed numerical model. View full abstract»

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  • Equivalent circuit modelling of new brushless synchronous alternator

    Page(s): 812 - 820
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (356 KB)  

    A new type of brushless synchronous machine has been described in the companion paper 'New brushless synchronous alternator' (Brown, N.L. and Haydock, L.: IEE Proc., Electr. Power Appl. 2003, 150, (6), pp. 629-635.) The machine combines permanent magnet and wound coil excitation to provide a single-stage brushless alternator. The simple construction conceals a difficult magnetic circuit that displays complex interactions between excitation sources in the presence of saturation and leakage fields. A design procedure for such a machine using equivalent circuit models is described and the theoretical results are compared with measured values. View full abstract»

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  • Analysis and design of power gyrators in sliding-mode operation

    Page(s): 821 - 826
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (282 KB)  

    The use of sliding-mode techniques and the insertion of damping networks in fourth-order convertors with both input and output filters lead in certain cases to a stable equilibrium point with gyrator characteristics. The buck convertor with input filter and the Cˇuk convertor are shown to have stable dynamics and an equilibrium point with gyrator characteristics for certain parameter values. The analytical predictions are verified by means of simulation and experimental results. View full abstract»

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  • Cascade controller for DC/DC buck convertor

    Page(s): 827 - 831
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (208 KB)  

    In order to deal with the increasing demand for good load and supply-voltage regulation of DC/DC convertors, a new cascade controller is proposed. The control of DC/DC buck convertor is first decomposed into a primary voltage-control loop and a secondary current-control loop. The cascade controller is then implemented based on the buck-converter settings with the dynamics of the secondary loop much faster than these of the primary loop. A robustness analysis of the cascade controller against load changes and supply changes is presented. Experimental results are included to demonstrate the effectiveness of the proposed control scheme over a conventional single-loop PI controller. The proposed controller can be implemented as a low-cost addon to a conventional single-loop controller. Detail design equations are presented. View full abstract»

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  • Thermal analysis of high-frequency transformers using finite elements coupled with temperature rise method

    Page(s): 832 - 836
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (311 KB)  

    In this paper, a three-dimensional (3D) thermal model of a high-frequency transformer is presented. The finite element method (FEM) is used to solve the 3D steady state and/or transient heat flow equation which describes the thermal model. The local losses are initially estimated from electromagnetic field analysis based on the FEM, then, a method for recalculating the loss distribution based on the principle that the initial rate of rise of temperature at any point is proportional to the loss generated at that point. More accurate temperature distributions within the transformer are then computed from the resulting loss density distribution. The validity and accuracy of the proposed method are checked by comparing the results with those obtained from test. View full abstract»

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  • Formulation of the energy-storage factor for isolated power convertors using integrated magnetics

    Page(s): 837 - 844
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (247 KB)  

    The energy storage in energy-storage components is examined for isolated power convertors. In addition to the basic convertors such as the flyback and forward, the paper also develops the analysis for the various isolated versions of power convertors as well as convertors with integrated magnetics. It is interesting to study the variation of energy-storage factor so that their capability for energy storage can be examined. The factor can therefore give an equivalence of the AC power factor for the DC circuit. View full abstract»

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  • Dead-time compensation strategy for permanent magnet synchronous motor drive taking zero-current clamp and parasitic capacitance effects into account

    Page(s): 845 - 853
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (409 KB)  

    A dead-time compensation strategy is presented for a permanent-magnet synchronous motor drive taking zero-current clamp and parasitic capacitance effects into account. To improve the performance of dead-time compensation around the zero-crossing point of phase current, two strategies are proposed. One is to correct failure in polarity reversal of the dead-time compensation voltage (DTCV) caused by the zero-current clamp phenomenon. The other is to adjust the amplitude of DTCV to deal with variation in transition time due to the parasitic capacitance of switching devices. Experimental results demonstrate that current ripple for the proposed dead-time compensation strategy decreases by half compared with that of the conventional method. View full abstract»

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  • Comparison of two techniques for two-dimensional finite-element inductance computation of electrical machines

    Page(s): 855 - 861
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (219 KB)  

    The modelling of electrical machines by equivalent circuits requires an appropriate calculation of inductance values. The energy-perturbation and flux-linkage methods have been devised (and extensively used) to determine inductance values of electrical machines from two-dimensional finite-element solutions. That both methods are numerically equivalent and give approximately the same values of inductance is shown. However, the flux-linkage method requires less computation resources and is numerically more robust than the energy perturbation method when two-dimensional calculated fields are used. Hence, it is concluded that the flux-linkage approach should be chosen as the preferred method for two-dimensional inductance calculation of electrical machines. The numerical characteristics and equivalence of the energy-perturbation and flux-linkage methods are demonstrated by calculating the time-varying 'apparent' inductances of the stator and rotor field windings of a turbine generator running under transient conditions. View full abstract»

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  • Modelling and prediction of iron loss with complex flux waveforms

    Page(s): 862 - 870
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (319 KB)  

    The paper describes the first phase of a project to improve the prediction and modelling of iron loss for use in the design of switched-reluctance (SR) machines. Earlier models are reviewed and the development of a comprehensive model is described. Its parameters are obtained from commonly available manufacturers' data and this allows the prediction of not only average loss but also instantaneous power flow for a given flux waveform. Its validation against experimental measurements for sinusoidal and triangular fluxes up to 2 kHz, including superimposed DC bias, is demonstrated. The measurement work using toroidal specimens reveals some unexpected behaviour and a challenge to the measurement technique. View full abstract»

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  • Small-signal model-based design of digital current-mode control

    Page(s): 871 - 877
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (334 KB)  

    Based on a small-signal model of the power converters, a digital current-mode controller for power converter applications is designed. The model-based derivation of the control law results in the designed controller being applicable to three basic types of converters; (i) boost; (ii) buck; and (iii) buck-boost converters. The designed digital current-mode controller exhibits a fast current response to changes in a reference signal without the instability problem normally observed in converter applications that use a conventional analog-type current-mode controller. Simulations and experiments are presented to show the usefulness of the designed controller. View full abstract»

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  • Analysis of a capacitive-filter, half-wave rectifier fed by a parallel-load resonant tank

    Page(s): 878 - 884
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (217 KB)  

    The capacitive-filter, half-wave type of rectifiers, connected to a parallel-load resonant tank, is a simple and useful rectifier topology. It finds application in high-voltage supplies, various inductive power/information links and radio frequency identification systems. Yet, the characteristics of this rectifier topology have not been studied up to the present. The various uses of the rectifier are reviewed and a way of analysing the rectifier circuit using a semi-analytical method is proposed. Accurate analytical solutions are also provided by means of curve-fitting techniques. Results from an experiment conducted on a prototype rectifier show a very close match with the analysis predictions. View full abstract»

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  • Safety assessment of AC earthing systems in a DC traction-supply substation

    Page(s): 885 - 893
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (272 KB)  

    The paper assesses safety of AC earthing systems in a DC traction-supply substation (TSS) by comparing the designed mesh and step voltages to the maximum tolerable voltages. Generally, IEEE 80 criteria are based on the maximum tolerable body current to prevent fibrillation of the human heart, and this current is then translated into tolerable touch and step voltages. As a result, safety assessment of AC earthing systems in a DC TSS is referred to a procedure by which the designed mesh and step voltages are computed and compared with the tolerable touch and step voltages. Computation results of AC earthing systems for the orange line at O19 TSS in Taipei rapid-transit systems are presented as an example. View full abstract»

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  • Dynamic field modelling of torque and radial forces in vector-controlled induction machines with bearing relief

    Page(s): 894 - 904
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (594 KB)  

    The paper addresses the bearingless induction motor based on the concept of dual-pole windings, one controlling the motor torque and the other the generated radial forces. Such machines have been investigated experimentally in the past. The paper presents a simulation model capable of investigating the effect of induction-machine design on the generation and control of the radial force. The simulation is based on the dynamic reluctance-mesh field model embedded in vector control systems for the decoupled control of torque, flux and radial force. In the paper, the rotor is constrained by a mechanical bearing so that the radial force is used to cancel the rotor weight to effect 'bearing relief'. The paper summarises the modelling method, investigates the radial force production in both cage and wound rotor machines, and introduces a mixed field orientation method for the decoupled control of the torque and radial forces. Simulations are undertaken showing good generation of radial force under zero speed, acceleration and transient load conditions. View full abstract»

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  • Front-end low-frequency switched-mode rectifier and its control for permanent-magnet synchronous-motor drive

    Page(s): 905 - 914
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (710 KB)  

    The low-frequency switching-mode rectifier (LF-SMR) possesses the advantages of lower switching frequency, higher conversion efficiency and simpler control, and thus it is extensively utilised in domestic appliances. However, most of the existing LF-SMRs still lack robust operating performance owing to their open-loop control configuration. The development of an AC-switch based LF-SMR and its closed-loop control for PMSM drives are presented. First, the analysis, design and implementation of the power circuit are carried out. The power-circuit components are properly designed considering the compromise between some key performance parameters. Voltage-control aspects of the uncertain effects of double-frequency voltage ripple on the stable closed-loop control behaviour are first studied. On this basis, the voltage-feedback controller type is determined, and its parameters are designed according to the estimated plant model, the properly specified tracking-response requirements and the limitations of LF-SMR. Independently, to improve further the voltage-regulation conrol, an equivalent load-power disturbance is observed and used to perform the disturbance-feedforward-cancellation control. After the effectiveness of the designed LF-SMR has been confirmed, it is applied to serve as a front-end convertor for two types of permanent-magnet synchronous motor (PMSM) drives further to test its validity experimentally. View full abstract»

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  • High-performance flux-based two-degrees-of-freedom uninterruptible power supply

    Page(s): 915 - 921
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (318 KB)  

    A three-phase flux-based two-degrees-of-freedom uninterruptible power supply with improved voltage regulation performance is presented. The proposed AC supply is controlled using an outer P+resonant voltage regulation loop to ify voltage tracking errors and compensate for unbalanced voltages. Within this outer voltage loop is a flux-based two-degrees-of-freedom inner current regulation loop for the fast compensation of dynamic load changes and other external disturbances. This inner current regulator originates from the combined use of classical two-degrees-of-freedom control theory and a hysteretic flux modulation technique. By integrating the individual advantages of P+resonant compensators, two-degrees-of-freedom control and flux modulation, the proposed AC supply can achieve both precise steady-state tracking and a fast transient response. Theory and experimental results are presented to validate the performance of the proposed AC supply. View full abstract»

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  • Development and analysis of novel soft-starter/energy-saver topology for delta-connected induction motors

    Page(s): 922 - 932
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1241 KB)  

    A thyristorised star/delta switch is proposed as a soft starter and energy saver for delta-connected induction motor drives. A low-cost microprocessor-based hardware is developed and used for the control of the star/delta switch. The use of the star/delta switch for starting is first explained followed by its application as an energy saver. Three schemes of switching transitions are proposed and implemented for the star (delta) to delta (star) changeover process. Extensive simulation and experimental results are presented to show that the proposed circuit is a promising candidate as a starter/energy saver for delta-connected induction motor drives. View full abstract»

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  • Equivalent circuit for the brushless doubly fed machine (BDFM) including parameter estimation and experimental verification

    Page(s): 933 - 942
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (589 KB)  

    Experimental results from a frame size 180 brushless doubly fed (induction) machine (BDFM) fitted with four rotor designs are presented. The machine is intended for use as a variable speed generator, or drive. A per phase equivalent circuit for the machine has been developed and a method of obtaining parameters for the circuit is described. Expressions for the torque as a function of speed have been derived and predictions of machine performance in both self-cascaded and synchronous (doubly fed) modes have been verified experimentally. The work illustrates the link between rotor equivalent circuit parameters and machine performance and a comparison between rotor designs has been made. View full abstract»

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  • Analysis of a high-power-factor AC-DC converter with reduced current and voltage stresses

    Page(s): 943 - 952
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (371 KB)  

    Single-stage power-factor-corrected AC-DC converters (S2PFCCs) usually suffer from high current and voltage stresses due to the repeated process of input power through the power switch and power imbalance between the input and output, respectively. The paper presents a detailed analysis of an improved single-switch S2PFCC with an auxiliary transformer, which provides a direct linkage between the input and output stages of the converter. The auxiliary transformer is the key to reducing the voltage stress across the storage capacitor on decreasing load, to reduce the current stress on the power switch and to obtain a high power factor through elimination of input-current dead angle. Detailed analyses of the component stresses and the input current relating to the circuit parameters are presented. The theoretical analysis and effectiveness of the proposed approach are confirmed experimentally with a 15 V 60 W hardware prototype. View full abstract»

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  • Variable-structure observer for solar-array current estimation in a photovoltaic power-generation system

    Page(s): 953 - 959
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (462 KB)  

    A variable-structure observer for solar-array current estimation in a photovoltaic power-generation system is presented. The solar-array-current information is obtained from the variable-structure observer and fed into the maximum-power-point tracker to update the reference voltage. The parameter values such as inverter DC-link capacitances can be changed by up to 50% from their nominal values and the linear observer cannot estimate the correct state values under parameter variations and noisy environments. The configuration of the variable-structure observer is simple, but it shows robust tracking performance against parameter variations and modelling uncertainties. The method for constructing the variable-structure observer is presented and the convergence of the proposed observer is verified using the Lyapunov method. The mathematical modelling and the experimental results verify the validity of the proposed method. View full abstract»

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  • Harmonic adjusted power factor correction in nonsinusoidal environment

    Page(s): 960 - 966
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (184 KB)  

    An optimisation criterion is presented which allows proper calculation of optimum fixed LC combination in a power factor installation. Optimisation maximises the harmonic-adjusted power factor. In the paper, it is assumed that the load harmonics are not sufficiently serious to suggest tuned filters, but, when combined with source harmonics, the use of a pure capacitive compensator would degrade power factor and overload equipment. Consequently, an LC compensator is selected. It appears that this approach is practical, justifiable, compatible with existing rate structures and relatively easy to implement. The contribution of the developed method is demonstrated in examples taken from previous publications. View full abstract»

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  • Line-start performance of single-phase synchronous reluctance motor with controlled capacitor

    Page(s): 967 - 976
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (425 KB)  

    This paper reports the effect of values of starting and synchronisation (running) capacitors on the line-start performance of a single-phase cage-rotor synchronous reluctance motor. The d-q rotor reference frame dynamic equations were used to select the values of capacitors best suited for starting and running and it is shown that for a near-instantaneous starting, the capacitances should be varied (within the selected peaks) in line with the machine speed error. One single three-terminal capacitor device controlled by speed error signal is found to be very useful in realising a faster acceleration than obtainable with conventional and other known methods. Peak torque pulsations and current drawn by the main winding were found to be reduced, suggesting a more efficient motor drive performance. Simulated and experimental results bear a resemblance. View full abstract»

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