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Electric Power Applications, IEE Proceedings -

Issue 2 • Date Mar 2004

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Displaying Results 1 - 14 of 14
  • Analysis of axially magnetised, iron-cored, tubular permanent magnet machines

    Publication Year: 2004 , Page(s): 144 - 150
    Cited by:  Papers (11)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (419 KB)  

    An analysis of tubular permanent magnet machines equipped with axially magnetised magnets and a slotted armature is presented. The magnetic field distribution due to armature reaction is established analytically in the cylindrical co-ordinate system, and the results are verified by finite element calculations. The analytical solution allows the prediction of the machine inductance and reluctance force in closed forms, and facilitates the design optimisation and the evaluation of any possible partial, irreversible demagnetisation of the magnets. View full abstract»

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  • Three-dimensional space vector modulation with DC voltage variation control in a three-leg centre-split power quality compensator

    Publication Year: 2004 , Page(s): 198 - 204
    Cited by:  Papers (8)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (433 KB)  

    Three-dimensional space vector modulation (3DSVM) is proposed for controlling a three-leg centre-split inverter, which is used as a shunt power quality compensator for a three-phase four-wire system. Important issues for 3DSVM, such as 3D space vector allocation, zero-sequence compensation and DC voltage variation, are discussed in detail. In the two-level three-leg centre-split system, all eight vectors contribute to the zero-sequence compensation, which is different from the conventional two-dimensional compensation. Hence, the 3DSVM control strategy is more complicated than conventional 2DSVM. Particularly, in a two-level system there is no vector in 3D case such that the zero state is approximated by two zero vectors, which directly point in positive and negative zero-axis, respectively. Results indicate that the original reference of the 3D vector's allocation is affected by DC voltage variation only along the zero-frame. Conversely, the DC voltage variation can be controlled by adjusting the origin of 3D reference. Simulation results are given to show the validity of the proposed control strategy: 3DSVM with DC voltage variation control. A two-level three-leg centre-split inverter prototype is implemented and controlled by a digital signal processor with 2.5 kHz switching frequency. Experimental results are also presented to show its validity. View full abstract»

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  • Time variable transformers operating at a near-unity transfer ratio and some possible applications

    Publication Year: 2004 , Page(s): 161 - 168
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (402 KB)  

    Time variable transformer network elements are reviewed. Four special topologies are presented which are of benefit, especially in the vicinity of a unity overall transfer ratio. Analytical expressions are derived which indicate the resulting improvements in terms of energy conversion efficiency and systems power density (as well as expected cost). It is shown, that the use of the proposed topologies may, in some cases, improve these figures of merit by a factor of two or more. Additionally, when the time variable transformer realisation is achieved by means of switched mode converters, the dynamic characteristics, and consequently, the dynamic load regulation will improve significantly. Application of the resulting topology in an active ripple cancellation stage of a unity-power-factor rectifier clearly validates the proposed approach. View full abstract»

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  • Carrier-rotation strategy for voltage balancing in flying capacitor multilevel inverter

    Publication Year: 2004 , Page(s): 239 - 248
    Cited by:  Papers (18)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (561 KB)  

    A carrier-rotation PWM technique to solve the voltage unbalancing problem of flying capacitors in the flying capacitor multilevel inverter (FCMI) is proposed. The PWM technique equalises the utilisation of phase leg voltage redundancies corresponding to the charging and the discharging state of individual flying capacitors during one switching period of all the switches. Therefore, the charging and the discharging quantities of the flying capacitors are equal, which causes the average variation of the flying capacitor voltages to become zero and keeps their voltage stable during a minimum specified period. The proposed PWM technique also has the same switch utilisation and the reduced harmonic content of the output voltage since the switching frequency of each switch is identical and all the carrier signals are in phase. Hence, it is more suitable for the FCMI than the phase-shift PWM method. The proposed PWM technique is analysed in a flying capacitor three-level inverter and is then expanded to an N-level FCMI (N>3). Simulation and experimental results on the laboratory prototype flying capacitor three-level inverter confirm the validity of the proposed PWM technique. View full abstract»

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  • Novel battery charging regulation system for photovoltaic applications

    Publication Year: 2004 , Page(s): 191 - 197
    Cited by:  Papers (22)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (959 KB)  

    A battery-charging system for stand-alone photovoltaic (PV) applications is presented. Advantages of the proposed method are: better exploitation of the available PV energy by means of a maximum power point tracking (MPPT) technique employed in the control algorithm, increased battery lifetime due to higher level state of charge operation, and the charging control process does not depend on accurate battery current measurements, reducing the effect of the current sensor sensitivity on the battery final state of charge. Also, since it is based on the battery current regulation principle, it can be effectively used with large battery strings. The experimental results verify that, using the proposed method, a better exploitation of the available PV energy, compared to a commercial battery charger based on the on/off principle, is achieved, and simultaneously a 100% battery state of charge is reached in shorter time. View full abstract»

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  • Analytical estimation of torque enhancement of the SR machine with saw-shaped (shark) pole surfaces

    Publication Year: 2004 , Page(s): 223 - 229
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (423 KB)  

    The paper presents an electromagnetic analysis of the switched-reluctance (SR) machine with saw-shaped (shark) pole surfaces. This design aspect facilitates an increase of the 'maximum/minimum' inductance ratio, relative to the flat-pole structure, and, as such, it has drawn attention as a concept for the enhancement of the 'torque/volume' ratio. The analysis is based on the analytical model for estimation of the minimum and maximum inductances, which determine the extreme flux-linkage against current characteristics. These characteristics are used to predict the average phase torque at a constant current, from a given set of geometric parameters and the B-H curve describing the machine. The optimisation of the axial airgap profile is carried out by varying the tooth angle and the axial airgap pitch of the shark structure, while the other geometric parameters were kept the same as in the conventional (flat-pole) machine, which was optimised to produce the maximum torque/volume ratio. The maximum torque achievable with the shark machine is compared with the torque of the conventional SR machine at their rated currents. View full abstract»

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  • Design, analysis and realisation of a high-performance magnetic gear

    Publication Year: 2004 , Page(s): 135 - 143
    Cited by:  Papers (98)  |  Patents (25)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (437 KB)  

    Magnetic gears offer significant potential advantages compared with mechanical gears, such as reduced maintenance and improved reliability, inherent overload protection, and physical isolation between the input and output shafts. However, to date they have received relatively little attention, probably due to the relatively poor torque transmission capability of the magnetic circuit topologies which have been proposed. A new magnetic gear topology which combines a highly competitive torque transmission capability and a very high efficiency is described. View full abstract»

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  • Comparison of single-phase three-level pulse width modulation strategies

    Publication Year: 2004 , Page(s): 205 - 214
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (716 KB)  

    Five methods for producing three-level pulse width modulation for single-phase inverters are compared. The basic strategies are described and the advantages and disadvantages of each method are expressed in terms of complexity and implementation. Experimental and simulation results are presented to highlight the differences between the resulting pulse width modulated waveforms and to demonstrate the relative harmonic content resulting from each strategy. Key characteristics that define a harmonic minimised waveform are highlighted and it is shown that sampling-based methods for the generation of pulse width modulated waveforms show considerable advantages when compared to exact switching angle methods. View full abstract»

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  • Dual two-level inverter scheme for an open-end winding induction motor drive with a single DC power supply and improved DC bus utilisation

    Publication Year: 2004 , Page(s): 230 - 238
    Cited by:  Papers (11)  |  Patents (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (704 KB)  

    A dual two-level inverter fed open-end winding induction motor drive with a single DC-power supply is proposed. The proposed scheme produces voltage space vector locations identical to those of a conventional three-level inverter. In the conventional neutral-clamped three-level inverter, the series-connected DC link capacitors carry the load current, resulting in a fluctuating neutral point. Also, a three-level inverter requires bulky DC link capacitors. In the proposed scheme, the DC link capacitors carry currents of higher frequency and hence the neutral point fluctuations are reduced. A PWM switching strategy to suppress the zero sequence currents for all the voltage space phasor combinations is also proposed. This strategy is an improvisation of the one that uses a switched neutral to eliminate the triplen harmonic currents and results in an improved DC bus utilisation. View full abstract»

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  • Electromagnetic design of axial-flux permanent magnet machines

    Publication Year: 2004 , Page(s): 151 - 160
    Cited by:  Papers (36)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (475 KB)  

    A general, analytic approach to the calculation of magnet fields in a slottless, axial-flux, permanent magnet generator is presented. The basic 'building block' is the vector potential produced by a current sheet situated between two, infinitely permeable, iron surfaces. By modelling the magnet by currents at its periphery, and integrating over the magnet thickness, the vector potential and magnetic field due to the permanent magnets can be found. In contrast the armature winding is represented by a current sheet close to the stator iron surface. Magnetic field results produced by the analytic equations have been compared with two-, and three-, dimensional finite element studies and found to produce results comparable to within 5%. In addition emf, flux and inductance measurements have been made on two generators and compared with both finite element and analytic results. The analytic model predicts the emf to within 5%. The 'end winding' inductance of a toroidal, air-gap, armature winding, is shown to contribute significantly to the overall inductance with the analytical model predicting the inductance to within 10% of the measured values. View full abstract»

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  • Novel high-efficiency step-up converter

    Publication Year: 2004 , Page(s): 182 - 190
    Cited by:  Papers (133)  |  Patents (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (378 KB)  

    As a result of the equivalent series resistor of the boost inductor, conventional boost converters are not able to provide high voltage gain. A high-efficiency high step-up converter is proposed, with low voltage stress on power switch, power diodes and output capacitors. The circuit topology of the proposed converter consists of an energy clamp circuit and a voltage boost cell. The boost converter functions as an active clamp circuit to suppress the voltage spike on power switch during the turn-off transient period. The boost converter output terminal and flyback converter output terminal are serially connected to increase the output voltage gain with the coupled inductor. By serially connecting the secondary windings of the boost inductor, a high voltage gain is achieved with less voltage stress on the power devices, such as power MOSFET and power diodes. The operational principle and steady-state analysis are described. A 35 W converter with simulation and experimental results is presented to demonstrate the performance. It shows that the efficiency of the proposed converter is very high (nearly 93%) with four times the voltage output. View full abstract»

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  • Analysis of 4th-order LCLC resonant power converters

    Publication Year: 2004 , Page(s): 169 - 181
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (496 KB)  

    A methodology is presented for the high-speed, steady state analysis of 4th-order LCLC resonant power converters. Both current-output and voltage-output variants are considered. State-variable dynamic descriptions of the circuits are derived and subsequently employed to rapidly determine the steady-state cyclic behaviour and the voltage and current characteristics of the resonant-tank and output-filter, and to estimate the voltage and current stresses on resonant components. Simulated and experimental results for two prototype 4th-order converters (inductive and capacitive output variants) confirm that the accuracy of the model is comparable with SPICE simulations, while requiring less than 10-4 of the computational time. View full abstract»

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  • Unidirectional three-phase rectifier with high power factor

    Publication Year: 2004 , Page(s): 215 - 222
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (576 KB)  

    A three-phase three-level rectifier with less power switches is proposed. Four power switches with voltage stress of half DC bus voltage are used in the circuit. A carrier-based current control strategy is proposed to draw the sinusoidal line currents with nearly unity power factor. The switching signals for power switches are derived from the DC bus voltage controller and neutral point voltage compensator. The mathematical model of the rectifier is derived and the control scheme is provided. To verify the proposed operation scheme, performance characteristics are given by experimental results. View full abstract»

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  • Design of voltage model flux observer

    Publication Year: 2004 , Page(s): 129 - 134
    Cited by:  Papers (5)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (408 KB)  

    The voltage model flux observer can accurately estimate the stator flux when operating at high speed. However, at low speed this estimation is highly sensitive to the stator resistance variation. Also the observer needs voltage sensors for actual voltage measurements and becomes less accurate if command voltages are used, especially beyond the linear modulation region, where the command voltages are no longer equal to the actual ones. These problems are addressed through the design of a closed-loop voltage model flux observer that is completely insensitive to stator resistance variation, and thus it can work at high as well as low speed. The proposed observer also does not require any voltage signal information, either command or measured one, thus making it more accurate even beyond the linear modulation region without adding any voltage sensors. The observer stability has been verified. Simulation and experimental results are presented to validate the proposed algorithm. View full abstract»

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