Online ISSN
1751-8679
Print ISSN
1751-8660
IET Electric Power Applications
Volume 1, Issue 1, January 2007
Volumes & issues:
Volume 1, Issue 1
January 2007
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- Author(s): L. Lundström ; R. Gustavsson ; J.-O. Aidanpää ; N. Dahlbäck ; M. Leijon
- Source: IET Electric Power Applications, Volume 1, Issue 1, p. 1 –8
- DOI: 10.1049/iet-epa:20050430
- Type: Article
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Forces due to nonuniform airgaps in rotating electrical machines have been a research topic for over 100 years. However, most research in the area of rotating electrical machines has been performed on motors. Large forces in hydropower generators can lead to expensive damage and failures. Therefore, it is of interest to calculate the forces that arise in a large synchronous generator with an eccentric rotor and study the influence these forces have on the stability of the generator rotor. A 74 MVA synchronous hydropower generator was simulated with an eccentric rotor, using a time-stepping finite-element technique. The forces were calculated using Coulomb's virtual-work method and simulations were performed for no-load and load cases. The resulting force was found to be reduced significantly when a damper winding was taken into account. An interesting effect of the rotor damper winding was that it reduced the eccentricity force and introduced a force component perpendicular to the direction of eccentricity. The results from the finite-element simulations were used to determine how the forces affect the stability of the generator rotor. Damped natural eigenfrequencies and damping ratio for load and no-load conditions are presented. When applying the forces computed in the time-dependent model, the damped natural eigenfrequencies were found to increase and the stability of the generator rotor was found to be reduced compared with when the forces were computed in a stationary model. - Author(s): C. Charalambous and I. Cotton
- Source: IET Electric Power Applications, Volume 1, Issue 1, p. 9 –16
- DOI: 10.1049/iet-epa:20050449
- Type: Article
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The production of stray currents by DC-transit systems leads to the corrosion of nearby buried metallic structures, such as pipelines and cable sheaths. The paper details the corrosion performance of a DC transit system with a floating return rail, for a number of different soil-resistivity structures: uniform, horizontal and vertical-layer models. This builds on previous work carried out in homogenous soils. It is shown that a variation in soil type along the route of a transit system can lead to high local leakage-current densities on buried metallic structures, increasing their vulnerability to corrosion damage. - Author(s): B.-R. Lin ; S.-C. Tsay ; C.-S. Yang
- Source: IET Electric Power Applications, Volume 1, Issue 1, p. 17 –28
- DOI: 10.1049/iet-epa:20050545
- Type: Article
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A soft-switching converter with parallel-connected full-wave rectifiers is presented. In the proposed converter, the primary windings of two transformers are connected in series. Two full-wave rectifiers with ripple current cancellation are connected in parallel at the output side to reduce the current stress of the secondary winding of the transformer. The clamp circuit, based on an auxiliary switch and a clamp capacitor, is connected in parallel with the primary side of the transformer to recycle the energy stored in the leakage inductance. The leakage inductance of transformers, the magnetising inductance and the clamp capacitance are resonant to achieve zero-voltage switching (ZVS) of the auxiliary switch. The resonance between the leakage inductance of the transformer and the output capacitance of the switch will achieve ZVS operation for the main switch in the proposed converter. The pulse-width modulation technique is adopted to regulate the output voltage. The operation principle and system analysis of the proposed converter are provided. Some experimental results for a 200 W (5V/40 A) prototype are given to demonstrate the effectiveness of the proposed converter. - Author(s): M. Popov ; L. van der Sluis ; R.P.P. Smeets ; J. Lopez-Roldan ; V.V. Terzija
- Source: IET Electric Power Applications, Volume 1, Issue 1, p. 29 –35
- DOI: 10.1049/iet-epa:20060124
- Type: Article
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For the specification of winding insulation of transformers, it is important to know the electrical stresses to which the winding can be exposed during fast transient oscillations. These oscillations occur during switching operations performed by circuit breakers, or when gas-insulated substations (GIS) are used. Therefore one of the priorities is to use a high-frequency transformer model capable to simulating fast transient oscillations in the windings. The model presented requires only information about the geometry of the winding and the core, as well the electrical and magnetic parameters for the used materials. In the transformer model, the frequency-dependent core and copper losses are included. Numerical computations are performed with and without the core losses being taken into account. Two types of measurement are taken to verify the validity of the model. First, the voltage transients are measured and computed by the application of a step impulse with a rise time of 50 ns. Then, the transformer is switched by a vacuum circuit breaker, and the multiple reignitions, which contain oscillations with a wide frequency range, are analysed. The results verify that the model is suitable to simulate the voltage distribution in transformer windings over a wide frequency range. - Author(s): B.A. Potter ; S.A. Shirsavar ; M.D. McCulloch
- Source: IET Electric Power Applications, Volume 1, Issue 1, p. 36 –42
- DOI: 10.1049/iet-epa:20050524
- Type: Article
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The results of a study of the variation of three-phase induction machines’ input impedance with frequency are proposed. A range of motors were analysed, both two-pole and four-pole, and the magnitude and phase of the input impedance were obtained over a wide frequency range of 20 Hz–1 MHz. For test results that would be useful in the prediction of the performance of induction machines during typical use, a test procedure was developed to represent closely typical three-phase stator coil connections when the induction machine is driven by a three-phase inverter. In addition, tests were performed with the motor's cases both grounded and not grounded. The results of the study show that all induction machines of the type considered exhibit a multiresonant impedance profile, where the input impedance reaches at least one maximum as the input frequency is increased. Furthermore, the test results show that the grounding of the motor's case has a significant effect on the impedance profile. Methods to exploit the input impedance profile of an induction machine to optimise machine and inverter systems are also discussed. - Author(s): H.C. Chen ; Y.C. Chang ; C.K. Huang
- Source: IET Electric Power Applications, Volume 1, Issue 1, p. 43 –48
- DOI: 10.1049/iet-epa:20060140
- Type: Article
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The effect of the carrier sequences on the voltage spectrum of MCU(microcontroller)-based random-frequency pulse-width modulation (RFPWM) is presented. To optimise the carrier sequence efficiently, first all possible sequences are classified into groups according to the time-shift and time-reverse properties of the Fourier transform. Then, some evaluation indexes are proposed to obtain the optimal sequence quickly with the end of a personal computer (PC). Finally, some optimised carrier sequences with only two carrier frequencies are recommended. The experimental results also indicate that we should pay more attentions to the carrier sequences than to the selection of carrier frequency and on the numbers of carrier frequencies. - Author(s): F.T. Wakabayashi and C.A. Canesin
- Source: IET Electric Power Applications, Volume 1, Issue 1, p. 49 –58
- DOI: 10.1049/iet-epa:20060049
- Type: Article
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An electronic ballast for multiple tubular fluorescent lamp systems is presented. The proposed structure has a high value for the power factor, a dimming capability, and soft switching of the semiconductor devices operated at high frequencies. A zero-current switching pulse width modulated SEPIC converter is used as the rectifying stage and it is controlled using the instantaneous average input current technique. The inverting stage consists of classical resonant half-bridge converter with series-resonant parallel-loaded filters. The dimming control technique is based on varying the switching frequency and monitoring the phase shift of the current drained by the filters and lamps in order to establish a closed loop control. Experimental results are presented that validate the theoretical analysis. - Author(s): P. Kurronen and J. Pyrhönen
- Source: IET Electric Power Applications, Volume 1, Issue 1, p. 59 –63
- DOI: 10.1049/iet-epa:20060093
- Type: Article
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It is proved that fast semi-analytic methods can be applied to perform the three-dimensional design calculation of axial-flux permanent magnet machines successfully. The analytic calculation can be summarised in the following three steps: first, each axial-flux permanent-magnet machine pole pair – or several pole pairs in the case of fractional slot windings – is divided on the airgap surface radially into sectors-of-rings, which then form the airgap surfaces of elementary machines. Secondly, the behaviour of each elementary machine is calculated individually assuming a two-dimensional flux problem. Thirdly, the machine properties are found by summing the results given by all the elementary machines and all pole pairs of the machine. - Author(s): S.-C. Tan ; Y.M. Lai ; C.K. Tse ; L. Martinez-Salamero
- Source: IET Electric Power Applications, Volume 1, Issue 1, p. 64 –74
- DOI: 10.1049/iet-epa:20060067
- Type: Article
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A family of fixed-frequency pulsewidth-modulation-based sliding-mode voltage controllers for DC–DC converters operating in the discontinuous conduction mode is proposed. The proposed topology is developed for buck, boost and buck–boost converters. Preliminary verification and evaluation of these controllers are performed through computer simulations using precise models of the systems. - Author(s): G. Díaz ; P. Arboleya ; C. González-Morán ; J. Gómez-Aleixandre
- Source: IET Electric Power Applications, Volume 1, Issue 1, p. 75 –81
- DOI: 10.1049/iet-epa:20060169
- Type: Article
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The paper evaluates the impact that the relationship between purely rotational and alternating losses has on the computation of core losses in induction motors. At frequencies other than 50 Hz, the analysis is simplified if statistical loss theory is considered, as discussed in the paper. The paper outlines a practical method of computation of hysteresis and excess losses when the rotation of flux is considered and loss data for these terms at 50 Hz are available. An imposed constraint is that the quantity of experimental loss data available for the motor designer is, in general, reduced. To deal with the problem, Kochmann general relationships for 36 NO grades, covering the main spectrum of electrical steel grades at 50 Hz, have been found to be helpful. An approach is proposed to convert these relationships, so that they can be fitted into the statistical loss theory. The results are validated using FEA and bench tests. As a conclusion, the loss estimate is improved in all cases, not incurring an overestimation with respect to bench results. - Author(s): B.-R. Lin ; H.-K. Chiang ; C.-C. Chen ; C.-S. Lin ; A. Chiang
- Source: IET Electric Power Applications, Volume 1, Issue 1, p. 82 –92
- DOI: 10.1049/iet-epa:20050534
- Type: Article
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The system analysis and design consideration of a zero voltage switching (ZVS) converter with series-connected transformers are presested. Based on the operational behaviour, each transformer in the adopted converter can be operated as an inductor or a transformer. Therefore no output filter inductor is needed in the adopted converter. To reduce the voltage stress of the switching device in the conventional forward converter, an active snubber based on a clamp switch and a clamp capacitor is used to recycle the energy stored in the transformer leakage. During the transition interval, the resonance based on the junction capacitance of switches and transformer leakage inductance can achieve ZVS operation of switches. The centre-tapped rectifier is used at the secondary side to achieve full-wave rectification. The operating principles, steady-state analysis and design equations of the proposed converter are provided. Finally, experimental results for a 100 W (5 V/20 A) prototype circuit are provided to verify the converter performance. - Author(s): J. Shukla and B.G. Fernandes
- Source: IET Electric Power Applications, Volume 1, Issue 1, p. 93 –104
- DOI: 10.1049/iet-epa:20050539
- Type: Article
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A novel soft-switched inverter topology in which three mutually coupled inductors at a time are involved in the resonance process is proposed. By the introduction of magnetic coupling between three resonant inductors, the zero-voltage instants for the inverter can be generated by one auxiliary switch. Also, the resonant energy can be recycled, and the maximum voltage stress on the auxiliary circuit diode components is confined to the DC-link clamp voltage level. The DC link can be clamped to 1.1–1.3 times the DC-source value. This is unlike the soft-switched inverter in which two mutually coupled inductors are at a time are involved in a resonance process , wherein the clamping diode experiences voltage stress of the order of 11 per unit when clamping the DC-link voltage at 1.1 per unit. The proposed inverter also provides pulse-width modulated operation. An analysis of this novel quasi-resonant DC-link inverter topology is presented to reveal its soft-switching characteristics. Simulation and laboratory experiments are performed to validate the analysis. - Author(s): M. Jabloński and E. Napieralska-Juszczak
- Source: IET Electric Power Applications, Volume 1, Issue 1, p. 105 –111
- DOI: 10.1049/iet-epa:20060018
- Type: Article
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The paper deals with internal faults in large power transformers. The explanation of such faults is followed by the description of an analytical method proposed for the calculation of the power flow during an interturn fault, including the current supplied by the power grid, the current in a group of short-circuited turns and the current in the spot of short-circuiting. The currents are calculated for cylindrical windings as a function of the fault area and its location with respect to the winding height for different structural configurations. An appropriate modification of Rogowski's coefficient is introduced. Computational results based on theoretical considerations are shown to be in good agreement with measurements carried out on a realistic model. - Author(s): Y. Ye ; B. Zhang ; K. Zhou ; D. Wang ; Y. Wang
- Source: IET Electric Power Applications, Volume 1, Issue 1, p. 112 –118
- DOI: 10.1049/iet-epa:20050518
- Type: Article
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A novel cascade-type repetitive controller with phase-cancellation filter is proposed for a constant-voltage constant-frequency pulse-width-modulated DC–AC converter to achieve very low total harmonic distortion and fast transient response. The paper reveals the principle of phase cancellation for the performance improvement of RC. In the form of real-time window filtering, a phase-cancellation filter is developed for the repetitive controller. Experimental results show that a high-quality AC source can be achieved by the proposed scheme even under nonlinear rectifier load and parameter uncertainties. - Author(s): J.-L. Shi ; T.-H. Liu ; S.-H. Yang
- Source: IET Electric Power Applications, Volume 1, Issue 1, p. 119 –126
- DOI: 10.1049/iet-epa:20060151
- Type: Article
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The paper proposes a nonlinear adaptive backstepping speed controller which can be used in both the constant-torque region and the field-weakening region for an interior-permanent-magnet synchronous motor. By using the proposed method, the adjustable speed range can be extended to 1.6 times that of the base speed. In addition, the d-axis current is suitably adjusted to increase the output torque of the interior-permanent-magnet synchronous motor. A DSP-based fully digital speed-control system is implemented. The DSP is used to execute the current and the nonlinear speed-loop control algorithms. The implemented system has satisfactory performance, including good transient responses, good load-disturbance-rejection responses, and good tracking ability. Several experimental results validate the theoretical analysis. - Author(s): H.C. Chen ; Y.C. Chang ; C.K. Huang
- Source: IET Electric Power Applications, Volume 1, Issue 1, p. 127 –132
- DOI: 10.1049/iet-epa:20060162
- Type: Article
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Brushless DC motors (BDCMs) possess higher efficiencies than the conventional induction motors and BDCMs have therefore been used widely in inverter-fed compressors. Since the Hall position sensors cannot work well in the high-temperature environment of refrigerants, sensorless control schemes play an important role in the application of inverter-fed BDCM compressors. Sensorless control for actual BDCM compressor is proposed and implemented. First, the sensorless circuits used have been analysed in detail to find the design rules of the circuit parameters for various compressor motors. Then, the limitations of sensorless control are discussed to develop a practical speed controller for BDCM compressors. The developed starting strategy and sensorless algorithms are presented and digitally implemented. Finally, some experimental results are displayed to demonstrate the proposed sensorless speed control for BDCM compressors.
Influence on the stability of generator rotors due to radial and tangential magnetic pull force
Influence of soil structures on corrosion performance of floating-DC transit systems
Soft-switching DC–DC converter with parallel-connected full-wave rectifiers
Modelling, simulation and measurement of fast transients in transformer windings with consideration of frequency-dependent losses
Study of the variation of the input impedance of induction machines with frequency
Development of optimised carrier sequence in MCU-based random-frequency PWM
Electronic ballast for multiple fluorescent lamp systems
Analytic calculation of axial-flux permanent-magnet motor torque
Special family of PWM-based sliding-mode voltage controllers for basic DC–DC converters in discontinuous conduction mode
Revision of the hysteresis and excess loss computation method as a means of improving the rotational loss estimate in induction motors
Analysis and implementation of soft switching converter with series-connected transformers
Three-phase soft-switched PWM inverter for motor drive application
Internal faults in power transformers
High-performance cascade-type repetitive controller for CVCF PWM inverter: analysis and design
Nonlinear-controller design for an interior-permanent-magnet synchronous motor including field-weakening operation
Practical sensorless control for inverter-fed BDCM compressors
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