Showing papers in "Canadian Electrical Engineering Journal in 1984"
TL;DR: Two simple models for a class of nonlinear elements which can be represented by frequency-dependent AM/AM and AM/PM characteristics are proposed and are appealing for analysis and simulation considerations.
Abstract: In recent years there have been some significant technological advancements in the design of solid power amplifiers (SSPAs). These have made the replacement of travelling wave tube amplifiers (TWTAs) by SSPAs possible and economical, and have stimulated the interest in modelling and analysis of nonlinear elements with memory such as SSPAs. This paper proposes two simple models for a class of nonlinear elements which can be represented by frequency-dependent AM/AM and AM/PM characteristics. The simplicity of these models makes them appealing for analysis and simulation considerations. With these models, the analysis techniques that have been developed to study the behavior of signals through effectively memoryless nonlinear elements such as helix-type TWTAs can directly be applied. Straightforward identification schemes associated with these models are also given.
14 citations
TL;DR: It is shown through exhaustive analysis that the direct data compression technique utilizing adaptive least-squares curve fitting yields a relatively fast and efficient representation of ECG signals at about 1.6 bits/sample, while maintaining visual fidelity and a normalized mean-squared error less than 1%.
Abstract: Many different techniques have recently been proposed for efficient storage of ECG data with data compression as one of the main objectives. Although high compression ratios have been claimed for some of these techniques, the techniques did not always include the word length considerations with regard to the parameters representing the compressed signal. The authors feel that any technique can be meaningfully evaluated only if the resulting compression is expressed in bits/sample rather than the compression ratio that is often used in this field. This paper provides a critical evaluation of two classes of techniques, the direct data compression technique and the transformation technique. It is shown through exhaustive analysis that the direct data compression technique utilizing adaptive least-squares curve fitting yields a relatively fast and efficient representation of ECG signals at about 1.6 bits/sample, while maintaining visual fidelity and a normalized mean-squared error less than 1%.
11 citations
TL;DR: In this paper, the diffraction and blockage efficiencies of the conventional Cassegrain antenna are calculated by using the uniform geometrical theory of diffraction, and physical optics.
Abstract: The diffraction and blockage efficiencies of the conventional Cassegrain antenna are calculated by using the uniform geometrical theory of diffraction and physical optics. The various subefficiency terms corresponding to different diffraction fields are tabulated for a typical antenna and the results are discussed. Design curves that provide the aperture efficiency value as a function of main reflector diameter, subreflector diameter and the feed illumination taper are presented.
6 citations
TL;DR: In this paper, the authors present an overview of how EMT is calculated in power system networks for means of an EMT Program based on travelling wave modelling of transmission lines and use state equations for transmission line modelling.
Abstract: The paper is essentially an overview presenting an outline of how Electro-Magnetic Transients (EMTs) are calculated in power system networks for means of an EMT Program based on travelling wave modelling of transmission lines. This paper presents the following steps: (1) For circuits with lumped parameters, the individual branches are modelled by different equations which are discretized to provide Norton equivalents. These are assembled producing nodal equations, to be solved step-by-step. (2) Transmission lines are modelled by time lags and Norton equivalents, even if their parameters are frequency dependent or multi-phase, in which case model decompositions are used. This paper uses state equations for transmission line modelling. Inclusion of transmission line Norton equivalents in the nodal equations does not complicate the system problem due to the effective time-decoupling of the computations. Some recent developments such as Z-transforms, s-domain analysis and corona modelling are also described.
4 citations
TL;DR: In this paper, a mathematical model to simulate the plugging process is presented and used to predict the transient behaviour of an industrial induction motor under plugging operation, and the effect of the timing of contractor operation on the braking performance is studied.
Abstract: Induction motor transients under `plugging' is investigated. A realistic plugging contractor is considered, which includes disconnecting the supply, `coasting'-a period when no voltage is applied, and applying a negative sequence voltage to cause braking. A mathematical model to simulate the plugging process is presented and used to predict the transient behaviour of an industrial induction motor under plugging operation, Corresponding results obtained experimentally are also presented and discussed. The effect of the timing of contractor operation on the braking performance is studied. Simulated results indicate that the braking time and peak braking torque are affected considerably by the instant when negative sequence voltage is applied.
2 citations
TL;DR: A method for the implementation of the on-line controller and the modulator, using the modified maximum principles (MMP), is presented and illustrated by an example.
Abstract: The problem of finding the optimal control sequences for pulse frequency modulated (PFM) systems with quadratic performance indices and fixed final time is considered. A method for the implementation of the on-line controller and the modulator, using the modified maximum principles (MMP), is presented and illustrated by an example.
2 citations
TL;DR: The present status of multivalued logic is highlighted in a Canadian context and its application to the design of combinational and sequential self-checking systems is demonstrated.
Abstract: The present status of multivalued logic is highlighted in a Canadian context. A particular example is given of the use of ternary circuits in the solution of the problem of testability of binary logic, through the introduction of a new concept called 2-of-3-valued logic. Its application to the design of combinational and sequential self-checking systems is demonstrated. Topics discussed include: multivalued logic, testability, reliability, ternary logic, CMOS logic, and fault tolerance.
2 citations
TL;DR: A sensitivity method is used to select the most suitable model for the equivalent external system among several hypotheses and local system responses, due to an intentional disturbance, are used for the parameter identification of external equivalent model.
Abstract: A dynamic equivalent of an external electric power system is estimated from locally measured information. A sensitivity method is used to select the most suitable model for the equivalent external system among several hypotheses. Local system responses, due to an intentional disturbance, are used for the parameter identification of external equivalent model. The estimated dynamic equivalent is verified by comparing the dynamic interacting effects of the original external system with those of the equivalent external system. It is further verified by short-circuit tests.
2 citations
TL;DR: A novel method based on node tearing analysis for the solution of power system load flow problems based on linearized real and reactive power models obtained in the fast decoupled load flow method is presented.
Abstract: Presents a novel method based on node tearing analysis for the solution of power system load flow problems. The technique is applied to the linearized real and reactive power models obtained in the fast decoupled load flow method. By considering node tearing as the reduction of subnetworks to multiterminal equivalents, sparsity and sparse network reduction techniques are widely used. Heuristic structural decomposition techniques are presented. The results of applying this methodology to standard test systems are illustrated and compared with a one-piece solution.
1 citations
TL;DR: In this paper, the basic principles of spread spectrum systems are discussed to demonstrate their capabilities of suppressing noise and interference, and other significant advantages of using such systems, and the factors which affect the capability for interference and noise suppressions and the performance of the systems.
Abstract: Reviews strategies of suppressing interference and noise under various circumstances in order to justify the applications of spread spectrum systems. The basic principles of spread spectrum systems are discussed to demonstrate their capabilities of suppressing noise and interference, and other significant advantages of using such systems. The paper is also examines the factors which affect the capability for interference and noise suppressions and the performance of the systems. It is obvious that the systems can suppress various forms of interference and noise effectively and still achieve other significant goals. The ability of suppressing noise and interference depends on the process gain and correlation properties of the codes of the systems. The overall system performance depends on the degree of synchronization which can be accomplished by the systems.
1 citations
TL;DR: In this paper, the authors review the concepts behind HVDC systems and the advantages of their integration with AC power systems, and present available modelling and analysis techniques for HVDc-AC systems for load flow, and steady state and transient stability studies.
Abstract: This paper reviews the concepts behind HVDC systems and the advantages of their integration with AC power systems. Available modelling and analysis techniques for HVDC-AC systems are presented for load flow, and steady state and transient stability studies.
TL;DR: In this article, two link voltage control methods for uninterruptible power supply systems are discussed, where a boost chopper is activated to maintain the DC link voltage constant when the battery voltage dips below its rated value.
Abstract: Typical specifications for uninterruptible power supply systems require constant regulated output AC voltage under variable or temporarily defaulted AC utility bus conditions. Such an operating environment results in a variable DC link operation with serious derating of the UPS inverter, the output transformer and the output filter components. Two link voltage control methods that overcome this problem are discussed in this paper. With the first method, a boost chopper is activated to maintain the DC link voltage constant when the battery voltage dips below its rated value. In this mode, the chopper operates only during small time intervals, thus not contributing to system losses. With the second method, the battery voltage is stepped-up under feed-back control through a boost chopper. This allows the use of fixed inverter switching patterns with further improvement in the utilization of system components. Specifically, it is found that power handling capacity is improved by 65% without compromise in the system complexity and/or system performance.
TL;DR: The concept of scatter in firing sequences is introduced and an approach and a lowerbound on the scatter of any firing sequence-leading from an initial marking to a reachable final marking on a given marked graph are presented.
Abstract: Marked directed graphs are a special case of Petri nets introduced by Carl Petri as a model for information flow in systems exhibiting asynchronism and parallelism. Commoner, Holt, Even and Pnueli (1971) have studied several structural and algorithmic aspects of marked graphs using graph theory and network flow algorithms. Subsequently, Murata (1977) has studied these graphs using a circuit-theoretic approach. In this paper, the authors combine the ideas of both these works and present algorithms for certain problems on marked graphs. In particular, they introduce the concept of scatter in firing sequences and present algorithms for determining minimum scatter firing sequences for different classes of graphs. An approach for the general case and a lowerbound on the scatter of any firing sequence-leading from an initial marking to a reachable final marking on a given marked graph are presented.
TL;DR: An approach to transforming an image in order to facilitate threshold selection, where a desirable histogram which would ease threshold selection is specified and the original image is transformed into one whose histogram has that desirable distribution.
Abstract: An approach to transforming an image in order to facilitate threshold selection is presented. A desirable histogram which would ease threshold selection is specified and the original image is transformed into one whose histogram has that desirable distribution. A threshold is then easily selected for the image. Experiments have been performed by specifying bimodel histograms for single-level thresholding, and by specifying multi-model histograms for multi-level thresholding. The results of these are presented.
TL;DR: In this paper, the authors investigated the performance of rigid steel, thin-walled steel and aluminium conduits for minimizing the potential difference between internal and external current return paths under fault conditions.
Abstract: Rigid steel, thin-walled steel and aluminium conduits are investigated for their effectiveness in minimizing shock hazard under fault conditions. This analysis considers two extreme cases of internal and external current return paths which exhibit markedly different characteristics. Current distribution in, and potential difference along, the conduit wall also depend on its thickness and permeability. The longitudinal potential difference in rigid steel conduit is considerably larger for external current return paths than for aluminium or thin walled steel conduit. The use of rigid steel conduit grounded before entry to the area may reduce the hazard in installations where even a low potential difference can be hazardous, such as in patient care areas and operating theatres of hospitals. A multiple-bonded conduit may increase the hazard through an increased surface potential gradient.
TL;DR: In this paper, a multiphase transmission line is modelled by sinusoidally distributed charges on a cylindrical surface, and the field is uniform and outside the cylinder it can be obtained by a rotating equivalent dipole.
Abstract: A multiphase transmission line is modelled by sinusoidally distributed charges on a cylindrical surface. In its inside, the field is uniform and outside the cylinder it can be obtained by a rotating equivalent dipole. Total charge, capacitance, required number of conductors and natural power are calculated for this idealized multiphase line model, with or without ground wires and shielding. The practical advantages of this model are presented in its application to actual multiphase transmission line geometries for the calculation of the ground level potential gradient and of maximum conductor surface gradients.
TL;DR: In this paper, the design and fabrication procedure for an aberration-free, rounded-edge waveguide geodesic lens is described, and the precise position of the focal plane is determined after the lens fabrication.
Abstract: The design and fabrication procedure for an aberration-free, rounded-edge waveguide geodesic lens is described. This paper concludes that in any system using a geodesic lens, the precise position of the focal plane will have to be determined after the lens fabrication.
TL;DR: A general modelling of d.c. c. motor fed by static converter using matrix transformation and specific functions and to check the results, a program of simulation is made directly from the differential equations describing the systems in different modes of operation and the digital controller equations whose parameters are calculated from the proposed model.
Abstract: A general modelling of d.c. motor fed by static converter is proposed using matrix transformation and specific functions. The application proposed concerns a single phase converter which imposes discontinuous current flow through a d.c. motor. The digital controller consists of proportional-integral controller for the speed and a special integral one for the current. The recurrence matrix for small perturbations may be explicitly written by the use of the general modelling method so that the controller parameters can be calculated for any required behaviour. To check the results, a program of simulation, based on Runge-Kutta numerical method, is made directly from the differential equations describing the systems in different modes of operation and the digital controller equations whose parameters are calculated from the proposed model.
TL;DR: In this paper, the effects of the primary feed supporting struts on the radiation patterns of a symmetric paraboloid reflector are investigated, and the effect of the strut dimensional parameters on the reflector gain, sidelobe levels and the cross-polarization is determined and presented graphically.
Abstract: The effects of the primary feed supporting struts on the radiation patterns of a symmetric paraboloid reflector are investigated. Both linear and circular polarization of the feed are considered, and the reflector secondary fields are generated using the physical optics approximation for the surface current on the reflector. The strut fields, on the other hand, are computed by assuming the strut currents as those generated on an infinite cylinder illuminated by a plane incident wave. For struts of circular cross-section, the overall-radiation patterns of the reflector are computed and compared with those of an unblocked reflector. Based on this comparison, the effects of the strut dimensional parameters on the reflector gain, sidelobe levels and the cross-polarization are determined and presented graphically.
TL;DR: In this paper, the authors describe a digital simulator for the analysis of any thyristor converter, based upon a topological method of formulation of state equations, and modelled power thyristors and diodes as inductances.
Abstract: Describes a digital simulator for the analysis of any thyristor converter. The analysis is based upon a topological method of formulation of state equations. Power thyristors and diodes are modelled as inductances. The value of each thyristor inductance changes from a finite value equal to the di/dt limiting series inductance, while conducting, to an infinite value when blocked. The simulator takes into consideration the presence of the snubber circuits associated with each thyristor element. The simulator library which has been named ATOSEC I has been developed with computer aided design power electronic converters in mind. It has been implemented on a CDC CYBER and will be available from the authors.
TL;DR: In this paper, a practical scheme for solving the resetting term problem in PFM control systems is presented, where the modulator can be described mathematically without resetting terms.
Abstract: When analysing type-II pulse-frequency modulated (PFM) control systems, particularly when attempting to optimize these systems, the `resetting term' in the equation describing the modulator makes the analysis very awkward. An equivalent set of equations is given which show that this modulator can be mathematically described without the resetting term. A novel practical scheme for accomplishing this is presented.