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Electric Power Applications, IEE Proceedings -

Issue 2 • Date March 2002

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Displaying Results 1 - 12 of 12
  • Equivalent heat circuit based power transformer thermal model

    Page(s): 87 - 92
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (604 KB)  

    An equivalent heat circuit based thermal model of oil-immersed power transformers and a methodology for model construction using intelligent learning based on real-world data are presented. The proposed thermal model is established to calculate the real-time temperatures of the main parts of a natural oil, natural air (ONAN) and forced oil, forced air (OFAF) cooled power transformer, which is based on the principles of heat exchange and electric circuit laws. A genetic algorithm is used as a search method, based on a few onsite measurements, to determine the thermal model parameters. View full abstract»

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  • Zero-current switching switched-capacitor quasiresonant step-down converter

    Page(s): 111 - 121
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (863 KB)  

    Current stress is usually high for conventional switched-capacitor converter circuits, because of short-circuiting when charging up the capacitors. In this paper, two zero-current switching switched-capacitor resonant step-down converter families are presented which can improve the current stress problem. They are able to provide 1/2 to 1/n, and -1 to -1/n conversion ratios respectively by using only two switches. Principles of operation, computer simulation and experimental results of the proposed converters are presented. The measured efficiency is high and all parts of the circuits are under zero-current switching conditions View full abstract»

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  • Influence of power converter on induction motor acoustic noise: interaction between control strategy and mechanical structure

    Page(s): 93 - 100
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (821 KB)  

    A general method for reducing noise due to the coupling of an electric machine and a power converter is presented. This problem is generally broken down into three parts: machine design, switch control and mechanical structure response. This may involve the use of numerical methods, which require much computation, and is not well suited to the analysis of the complete drive. The method presented is semianalytical and based on rotating field theory, while the fast Fourier transform permits a global approach to the problem. This method may be used at the design stage of the electric machine (slot number, slot aperture, stator yoke thickness) or for the choice of PWM strategy and parameters for the power converter. The theory is illustrated by experimental results based on a 700 W induction motor associated with a natural sampling power converter. Acoustic measurements, made in a semianechoic room, show that minor modifications of the PWM control strategy greatly improve acoustic performance View full abstract»

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  • Power factor improvement and closed loop control of an AC-to-DC resonant converter

    Page(s): 101 - 110
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (851 KB)  

    This paper presents the characteristics and dynamic performance of a modified series-parallel resonant converter (MSPRC) with a capacitive output filter and operating on the utility line. The power factor of this converter is very high, even with no active control of the input line current. Fixed frequency control is used to regulate the magnitude of the output voltage and power. The sampled-data modelling technique of the MSPRC is used along with a small signal model to achieve excellent voltage regulation. The HF transformer nonidealities (i.e. leakage inductance and winding capacitance) are used as part of a resonant tank circuit. Thus, this converter is most suitable for high-voltage DC applications. Based on complex AC circuit analysis, the AC-to-DC MSPRC is designed for a 500 W, 1 kV output rating. Finally, simulation results are compared with experimental results View full abstract»

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  • Generator operations of saturated induction machines

    Page(s): 122 - 128
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (705 KB)  

    This paper shows that, due to the saturation of the main magnetic circuits, the generator behaviour of induction machines may not be evaluated theoretically with accuracy by means of traditional mathematical models, especially when operations at variable frequencies are dealt with. For this reason the paper presents a mathematical model of saturated machines. Voltage and current space vectors are used. The model has been carried out on the basis of two air-gap machine inductances (one differential and the other rational) previously introduced by another author (Kovacs, 1984). It has been validated at steady state by comparing the theoretically evaluated and experimentally measured armature currents of a mass-produced machine. The influence of saturation on armature current amplitudes is evidenced by comparing numerical results obtained by the suggested model with those of a traditional model. The model is also used for the performance analysis of dynamic and steady-state generator behaviour of cylindrical induction machines and for carrying out conditions that obtain self-excitation and stable operations of machines supplying passive electrical networks View full abstract»

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  • PWM inverter switching strategy for a dual two-level inverter fed open-end winding induction motor drive with a switched neutral

    Page(s): 152 - 160
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (797 KB)  

    A dual two-level inverter fed open-end winding induction motor drive is proposed in this paper. A total of 64 voltage space phasor combinations are possible in this scheme since each inverter produces eight voltage space phasors. The scheme produces voltage space phasor locations similar to that of a three-level inverter except that in a three-level inverter the series-connected DC link capacitors carry the load current, which results in undesirable fluctuating voltage space phasors. Also, a three-level inverter requires a bulky DC link capacitor. In the proposed scheme the DC link capacitor carries only the ripple current and hence the voltage space phasor fluctuations are absent. A PWM switching strategy aimed at suppressing the zero sequence currents is proposed, using auxiliary switch-assisted neutral generation View full abstract»

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  • Position detection and start-up algorithm of a rotor in a sensorless BLDC motor utilising inductance variation

    Page(s): 137 - 142
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (604 KB)  

    A method of identifying the rotor position of a brushless DC (BLDC) motor and driving a motor smoothly from standstill without any position sensors is presented. This is done by monitoring the current responses to the inductance variation on the rotor position. The rotor position at standstill is detected by comparing the first and second differences of six current pulses injected into every two phases of the motor. Once the motor starts up, a pulse train, composed of long and short pulses, is injected into the commutation phases corresponding to the maximum torque production and the next commutation phases in alternating fashion. It provides not only the torque, but also information about the next commutation timing when the current responses of the long and short pulses cross each other in the same time delay. A controller for a BLDC motor is developed using a PC, digital signal processor (DSP), inverter and communication circuits in order to verify the proposed algorithm experimentally. It shows that the proposed algorithm can drive a BLDC motor smoothly without any vibration or time delay up to medium speed compared with the conventional back-EMF algorithm. Beyond this medium speed, a sensorless algorithm for rotor-position detection is switched to the back-EMF method to drive a BLDC motor at high speed View full abstract»

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  • Reducing the high frequency transformer losses in an FB ZVT PWM converter

    Page(s): 161 - 164
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (452 KB)  

    This paper proposes a full bridge zero voltage transition (FB ZVT) PWM DC-DC converter, which uses a saturable reactor, instead of two additional switches to achieve zero voltage switching. A conventional, high frequency, phase shifted, FB ZVT PWM DC-DC converter has a disadvantage, in that a circulating current flows through the high frequency transformer and switching devices during the free-wheeling interval. Due to this circulating current, the conduction loss increases. To reduce this loss, the proposed circuit reduces the circulating current. The operation principles are explained in detail and several interesting simulation and experimental results verify the validity of the proposed circuit View full abstract»

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  • Adaptive backstepping speed controller design for a permanent magnet synchronous motor

    Page(s): 165 - 172
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (701 KB)  

    In the paper, a nonlinear adaptive speed controller for a permanent magnet synchronous motor based on a newly developed adaptive backstepping approach (PMSM) is presented. The exact input-output feedback linearisation control law is first introduced without any uncertainties in the system. However, in real applications, the parameter uncertainties such as the stator resistance and viscous constant and load torque disturbance have to be considered. In this case, the exact input-output feedback linearisation approach is not very effective, because it is based on the exact cancellation of the nonlinearity. To compensate the uncertainties and the load torque disturbance, the input-output feedback linearisation approach is first used to compensate the nonlinearities in the nominal system. Then, a nonlinear adaptive backstepping control law and parameter uncertainty, and load torque disturbance adaptation laws, are derived systematically by using adaptive backstepping technique. Simulation and experimental results clearly show that the proposed adaptive scheme can track the speed reference signal generated by a reference model, successfully, and that the scheme is robust to the parameter uncertainties and load torque disturbance View full abstract»

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  • Pulsed voltage-fed sustain circuit for AC plasma display drive

    Page(s): 129 - 136
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (680 KB)  

    A new sustain circuit for an AC plasma display drive is proposed. The proposed circuit uses the instantaneous peak current flowing through the inductor during the charging and discharging of a plasma display panel, to recover most of the energy lost by the capacitive displacement current. This circuit can be realised with a small part-count, and gives the zero-voltage switching characteristics to all the switches even in the presence of a parasitic resistance, essential for the design of a sustain circuit for an AC plasma display. The capacitive displacement current and the required reactive power are greatly reduced in the proposed circuit. A comparative analysis and experimental results are presented to show the validity of the proposed energy recovery circuit View full abstract»

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  • Transient behaviour of salient-pole synchronous machines with internal stator winding faults

    Page(s): 143 - 151
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (769 KB)  

    Internal stator winding faults in salient-pole synchronous machines can cause serious damage to a machine and the system to which it is connected. Thus, it is highly desirable to be able to accurately model their transient behaviour and to predict the resulting currents and voltages in order to develop appropriate protection schemes, particularly for high power machines. Based on the multi-loop circuit method, a general mathematical model for a salient-pole synchronous machine with internal faults is established, and subsequently employed to simulate both the steady-state and transient behaviour for three different types of internal fault. Predicted results are validated by experimental measurements View full abstract»

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  • Study of the mutually coupled switched reluctance machine using the finite element-circuit coupled method

    Page(s): 81 - 86
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (666 KB)  

    This paper studies the electromagnetic characteristics of the mutually coupled switched reluctance machine (MCSRM). The relationship between the MCSRM and the conventional switched reluctance machine (SRM) is emphasised with the MCSRM viewed from the perspective of the conventional SRM. Nonlinear analysis of the MCSRM using the finite element (FE) method is presented, with the peculiarities of the MCSRM highlighted. Control principles for different excitation patterns and operation modes are derived. The modelling difficulties associated with the MCSRM are discussed and the FE-circuit coupled simulation method is used to study the interactions between the MCSRM and the power electronics and to check the control principles derived from the nonlinear analysis. Both simulation and experimental results are provided View full abstract»

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