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Electrical and Computer Engineering, Canadian Journal of

Issue 3 • Date July 1993

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Displaying Results 1 - 13 of 13
  • Canadian Journal of Electrical and Computer Engineering - Front cover

    Page(s): c1
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  • Inside front cover

    Page(s): c2
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  • Table of contents

    Page(s): 1
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  • News from the editors

    Page(s): 94
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  • The 1992 R.A. Ross medal

    Page(s): 95
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  • Computer-aided design of direct static converters

    Page(s): 97 - 103
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    The notion of the commutation cell has been introduced and used to study the local and systemic aspects of the commutation process, such as the functioning modes of a switch and the commutation mechanism. The authors show that this notion can also be a tool in a computer-aided design software, for the study and synthesis of the topologies of static converters. In this light, general laws and rules for electronic commutation are defined. Their application in an elementary commutation cell allows a graphical analysis of input and output waveforms (current and voltage at the switches). View full abstract»

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  • Transmission capacity assessment

    Page(s): 105 - 110
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    The problem of electric power transmission limitations due to finite reactive resources is studied. Maximum system load, i.e., loadability, is determined using a nonlinear optimization technique (Modified Augmented Lagrangian) which accommodates limits on reactive generation as well as other practical constraints. The sensitivities of the system loadability with regard to transmission-element primitive admittances are by-products of the proposed optimization method. These parameters indicate the relative strength of the transmission elements at the voltage stability limit. The weakest element is considered to be the one exhibiting the greatest sensitivity. Electrical strengthening of this element would enhance the system loadability. Sample results are presented for a 30-bus system. View full abstract»

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  • A critical assessment of the implementation of PWM techniques in switchmode magnet power supplies

    Page(s): 111 - 115
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    The characteristics of a carrier-based pulse-width modulator under different modulation techniques are evaluated. Modulation with the most commonly used carrier waveforms (triangular and sawtooth waveforms) and sampling methods (uniform, double and natural sampling) is studied. In each case, the switching harmonics at the modulator output are calculated and the frequency response of the modulator is determined. Different modulation techniques are then compared, and the one that best suits switchmode magnet power supply applications is identified. View full abstract»

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  • A microprocessor-based measuring unit for high-speed distance protection

    Page(s): 117 - 125
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    This paper describes a microprocessor-based measuring unit which is suitable for use in high-speed digital distance relays. The unit uses an algorithm that provides accurate estimates of apparent resistance and inductance of the line in relatively short times. The algorithm deals effectively with the presence of nonfundamental frequency components in signals without making assumptions about their compositions. The hardware and software of the unit are described. Test results indicate that the estimates converge to their true values within about 10 ms after fault inception. Also, the ability of the unit to provide accurate estimates is not adversely affected by the system frequencies drifting from its nominal value and by the distortion of the input signals. View full abstract»

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  • Modelling of an autonomous power system at variable speed for transient simulation using Lagrange's laws

    Page(s): 127 - 131
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    The dynamical equations of a power system are usually obtained by applying the laws of electrotechnics and Newton's second law. The authors extend the use of Lagrange's laws, classically used to model mechanical systems, to the derivation of the dynamical model of an autonomous power system. One of the major advantages of the proposed approach is its simplicity, which directly derives from the unified aspect of the modelling procedure. The obtained dynamical model is transformed into a generalized state-space model, and is used to simulate the transient behaviour of the autonomous power system to the presence of variable speed. View full abstract»

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  • Input-output-buffered broad-band packet-switch architectures with correlated input traffic

    Page(s): 133 - 139
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    The paper investigates the robustness of the nonblocking asynchronous transfer mode (ATM) switch architecture with input-output buffering and backpressure control under correlated input traffic conditions. The traffic correlation is modelled by two parameters; namely, the mean active duration of the ON-OFF source feeding each input port, and the spacing between the cells generated within an active period. This spacing can be fixed or random. The effect of these parameters on the switch performance in terms of the cell-loss behaviour and the mean switching delay is investigated. The performance of different selection mechanisms needed to resolve output-port contention is evaluated, taking into consideration the performance enhancements obtained by incorporating different arbitration criteria within the selection mechanisms. The study indicates that the burst-length factor significantly affects the buffering requirements of the switch to achieve a certain cell-loss probability, even if the switch is operated at fairly low utilization. The spacing between cells within a burst has a considerable effect on the cell-loss performance of the switch. Using the longer-input-queue criterion as the arbitration criterion between cells contending for the same output port results in smaller buffer sizes for given cell-loss probability and value of applied load, than is the case when the arbitration criterion is implemented according to the earlier arrival time at the head-of-line (HOL) position of the input queues. Since the longer-queue criterion does not involve time-stamping, as is the case with the HOL-time criterion, it is also the more attractive solution from an implementation point of view. This result confirms previously reported conclusions under the uniform random traffic case. View full abstract»

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  • [Back inside cover]

    Page(s): c3
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  • [Back cover - [advertisement]]

    Page(s): c4
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Aims & Scope

The role of the Canadian Journal of Electrical and Computer Engineering is to provide scientific and professional activity for its members in Canada, the CJECE complements international journals and will be of particular interest to anyone involved in research and development activities in the field of electrical and computer engineering.

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Meet Our Editors

Editor-in-Chief
Dr. Shahram Yousefi
Dept. of Electrical and Computer
     Engineering
Queen's University