scispace - formally typeset
Search or ask a question

Showing papers on "Electrical network published in 1990"


Journal ArticleDOI
TL;DR: In this article, the effects of dynamic coupling between a structure and an electrical network through the piezoelectric effect are derived. But the authors focus on the case of a cantilevered beam with surface mounted piezoceramics and indirect voltage and current drive.
Abstract: The paper models the effects of dynamic coupling between a structure and an electrical network through the piezoelectric effect. The coupled equations of motion of an arbitrary elastic structure with piezoelectric elements and passive electronics are derived. State space models are developed for three important cases: direct voltage driven electrodes, direct charge driven electrodes, and an indirect drive case where the piezoelec tric electrodes are connected to an arbitrary electrical circuit with embedded voltage and current sources. The equations are applied to the case of a cantilevered beam with surface mounted piezoceramics and indirect voltage and current drive. The theoretical derivations are validated experimentally on an actively controlled cantilevered beam test article with indirect voltage drive.

715 citations


Journal ArticleDOI
TL;DR: In this paper, a mathematical framework is presented for the solution of the economic dispatch problem, and the application of the Dantzig-Wolfe decomposition method is emphasized to solve the problem.
Abstract: A mathematical framework is presented for the solution of the economic dispatch problem The application of the Dantzig-Wolfe decomposition method for the solution of this problem is emphasized The system's optimization problem is decomposed into several subproblems corresponding to specific areas in the power system The upper bound technique along with the decomposition method are applied to a 16-bus system and a modified IEEE 30-bus system, and numerical results are presented for larger systems The results indicate that the presented formulation of the reactive power optimization and the application of the decomposition procedure will facilitate the solution of the problem The algorithm can be applied to a large-scale power network, where its solution represents a significant reduction in the number of iterations and the required computation time >

342 citations


Journal ArticleDOI
TL;DR: In this paper, a new method is presented for the solution of load flow in radially operated distribution networks, based on an electric equivalent and on the elimination of the voltage phase angle in the equations to be solved, which makes it possible to obtain the exact solution working only with voltage magnitudes.
Abstract: A new method is presented for the solution of load flow in radially operated distribution networks. The method is based on an electric equivalent and on the elimination of the voltage phase angle in the equations to be solved, which makes it possible to obtain the exact solution working only with voltage magnitudes. In this way, a simple and efficient method for the exact load flow solution for this type of network is obtained, allowing the modeling of voltage-dependent loads and the formulation of related problems like the radial load flow with voltage constraints. The method can easily be programmed and has good convergence characteristics, as shown by examples. >

308 citations


Journal ArticleDOI
G.A. Maria1, C. K. Tang1, J. Kim1
TL;DR: In this article, a hybrid method of power system transient stability analysis, which combines the desirable features of both the time-domain simulation technique and the direct method of transient analysis, is presented.
Abstract: The hybrid method of power system transient stability analysis, which combines the desirable features of both the time-domain simulation technique and the direct method of transient stability analysis, is presented. The hybrid method first computes the actual system trajectory using time-domain simulation, then evaluates the transient energy function in order to derive a stability index for fast derivation of transient stability limits. Proper criteria are proposed to stop the time-domain simulation of the system trajectory to reduce CPU time, once the status of the system has been identified. The method was successfully applied to three test systems varying in size from four generators to 50 generators. The method is shown to be a potential tool for online calculation of transient stability limits. >

178 citations


Journal ArticleDOI
TL;DR: In this paper, it is shown that a load flow solution with feasible voltage magnitude for radial distribution networks always exists and is unique and demonstrated that different patterns of load demand require different power supply from the substation.
Abstract: On the basis of voltage level, an electric power system can be viewed as consisting of a generation system, a transmission system, and a distribution system. The steady-state operation of a power system requires that the power supply, transmission losses, and load demand be balanced, as described by the load flow equations. The configuration of a transmission network is that of a loop while the configuration of a distributed network is radial. It is well recognized that the number of load flow solutions for transmission networks, if they exist, are multiple. In contrast, it is shown here that a load flow solution with feasible voltage magnitude for radial distribution networks always exists and is unique. These results demonstrate the weak ability of radial distribution networks to meet load demands in the sense that different patterns of load demand require different power supply from the substation. >

174 citations


Journal ArticleDOI
TL;DR: It is shown that, for an infinite graph of linear growth, Kirchhoff's laws combined with the finite power condition ensures the existence and uniqueness of an electric current when a current generator is added.

70 citations


Journal ArticleDOI
TL;DR: In this paper, an efficient pole-placement method is developed with straightforward formulation and a reduced computation requirement for an unstable nine-machine system, which not only ensures the exact pole-position of the unstable mechanical modes, but also improves the dampings of the poorly damped mechanical modes.
Abstract: Power system stabilizers (PSS) are designed for an unstable nine-machine system. Participation factors are used to select the sites and number of stabilizers. An efficient pole-placement method is developed with straightforward formulation and a reduced computation requirement. The design not only ensures the exact pole-placement of the unstable mechanical modes, but also improves the dampings of the poorly damped mechanical modes, resulting in a well-coordinated damping for the entire system. >

69 citations


Proceedings ArticleDOI
01 Jan 1990
TL;DR: In this paper, the effects of dynamic coupling between a structure and an electrical network through the piezoelectric effect were derived. And the theoretical derivations were validated experimentally on an actively controlled cantilevered beam test article with indirect voltage drive.
Abstract: The paper models the effects of dynamic coupling between a structure and an electrical network through the piezoelectric effect. The coupled equations of motion of an arbitrary elastic structure with piezoelectric elements and passive electronics are derived. State space models are developed for three important cases: direct voltage driven electrodes, direct charge driven electrodes, and an indirect drive case where the piezoelectric electrodes are connected to an arbitrary electrical circuit with embedded voltage and current sources. The equations are applied to the case of a cantilevered beam with surface mounted piezoceramics and indirect voltage and current drive. The theoretical derivations are validated experimentally on an actively controlled cantilevered beam test article with indirect voltage drive.

55 citations


Journal ArticleDOI
TL;DR: In this article, the authors present a comprehensive large-signal stability analysis of a solar-array power system with a typical nonlinear load characteristic, and employ stateplane analysis techniques to characterize the dynamic behavior of the system from an arbitrary initial condition.
Abstract: The authors present a comprehensive large-signal stability analysis of a solar-array power system. The stability of the equilibrium points of a system with a typical nonlinear load characteristic is analyzed. Employing state-plane analysis techniques, the dynamic behavior of the system from an arbitrary initial condition is characterized, and the region of the desired stable operation is identified. The stability and transient response of the system operation near the solar array's maximum power point are evaluated. The dynamic response of the spacecraft power system operating in the shunt mode and battery-discharge mode is analyzed. >

54 citations


Journal ArticleDOI
TL;DR: In this article, an approach that combines the load flow and state estimation techniques is proposed to improve the numerical stability and provide an external network model for online security analysis, where an initial load flow study is followed by a state estimation using pseudomeasurements and proper weighting factors.
Abstract: An approach that combines the load flow and state estimation techniques is proposed to improve the numerical stability and provide an external network model for online security analysis. An initial load flow study that provides a preliminary solution for the external network is followed by a state estimation using pseudomeasurements and proper weighting factors. Methods for handling multiple observable islands in the external network modeling process are described, and simulation tests are carried out on a practical system with realistic complexity. >

35 citations


Journal ArticleDOI
TL;DR: In this paper, a utility-type, 20-G kHz, AC power distribution system for the space station employing resonant power-conversion techniques is presented, where the system converts raw DC voltage from photovoltaic cells or three-phase, low-frequency AC voltage from a solar dynamic generator into a regulated, 20G kHz AC voltage for distribution among various loads.
Abstract: A utility-type, 20-kHz, AC power distribution system for the space station employing resonant power-conversion techniques is presented. The system converts raw DC voltage from photovoltaic cells or three-phase, low-frequency AC voltage from a solar dynamic generator into a regulated, 20-G kHz AC voltage for distribution among various loads. Operations of the components of the system such as driver inverter, DC receiver, bidirectional receiver, and three-phase AC receiver are discussed. EASY5 computer modeling and simulations were performed to study the local and global performance of the system. Simulation results show that the system has fast response and good transient behavior. The AC bus voltage is effectively regulated using the phase-control scheme, which is demonstrated with both line and load variations. The feasibility of paralleling the outputs of driver modules is illustrated with the driver modules synchronized and sharing a common feedback loop. A high-frequency, sinusoidal AC voltage is generated in the three-phase, AC input case, when the driver modules are phased 120 degrees away from one another and their outputs are connected in series. >

Patent
02 Feb 1990
TL;DR: In this article, a light input energizes an optical transmitter providing a light output to a waveguide indicating a process variable, and an electrical circuit receives the sensor output and generates an electrical transmitter output indicating the process variable adjusted by a changeable parameter stored in the electrical circuit.
Abstract: A light input energizes an optical transmitter providing a light output to a waveguide indicating a process variable. The transmitter has a process variable sensor generating a sensor output. An electrical circuit receives the sensor output and generates an electrical transmitter output indicating the process variable adjusted by a changeable parameter stored in the electrical circuit. The electrical circuit has an input energizing the circuit. An LED converts the electrical transmitter output to the light output. A gallium arsenide photodiode converts a first portion of received light into electrical energy provided to the energization input and converts a second portion of the received light into an electrical output controlling the stored parameter.

Journal ArticleDOI
P.M. van Oirsouw1
TL;DR: In this paper, a general method has been developed to determine a dynamic equivalent of a large external power system, where the combination of modal coherency and frequency response is a new approach.
Abstract: A general method has been developed to determine a dynamic equivalent of a large external power system. The combination of modal coherency and frequency response is a new approach. The frequency response formula, used to determine the coherency, is obtained by linearizing the total system and diagonalizing the linearized system. The method is tested for classical generator models as well as for fifth-order generator models plus second-order exciter models. The Dutch power system, which is coupled with the West-European UCPTE power system, has been used to illustrate the method. A comparison of the time responses of the original model and the reduced model provides a reliable picture. >

Patent
27 Mar 1990
TL;DR: In this paper, the authors proposed a method for suppressing radiated electromagnetic radiation in high current AC/DC power supplies. This radiation is the result of rectifier diode transient noise which is propagated through the electrical network of the power supply.
Abstract: This invention provides a means for suppressing radiated electromagnetic radiation in high current AC/DC power supplies. This radiation is the result of rectifier diode transient noise which is propagated through the electrical network of the power supply. The transient noise is propagated through the electrical and mechanical connections of the diodes to the transformer secondary. These connections have stray impedance which allows high frequency noise to be propagated through them. The stray impedances can be modulated to suppress the high frequency noise propagation without adding discrete inductor or capacitor elements to the electrical network. The modulation of the stray impedances is accomplished by adjusting the current sharing between rectifier diodes. This is accomplished by splitting the parallel connection between rectifier diodes, and making the connection of the diodes to the transformer secondary at various points along the secondary. The separate impedance of both the transformer and the individual connections will modulate the existing stray impedance to suppress the radiated electromagnetic noise.


Journal ArticleDOI
TL;DR: A review of the existing techniques for the reactive power allocation in large power systems is presented in this article, where the authors describe the problem with its significance to the operation and planning of power systems.
Abstract: This paper reviews of the existing techniques for the reactive power allocation in large power systems. The description of the problem with its significance to the operation and planning of power systems is presented. Merits of the corresponding techniques are reviewed according to their types of formulation.

Journal ArticleDOI
TL;DR: In this paper, minor modifications in the HVDC (highvoltage DC) controls are proposed to improve the damping of AC voltage and tieline power oscillations under heavy loading conditions.
Abstract: Enhancement of the overall system dynamic performance of an AC/DC scheme is possible by minor modifications in the HVDC (high-voltage DC) controls. The Chateauguay HVDC scheme comprises two back-to-back converter blocks, each with a rated capacity of 400 MW. It is designed to export power from Quebec to the NYPA (New York Power Authority) system. Some control modifications currently under consideration for the Chateauguay HVDC scheme (which has interconnections to the Beauharnois generators and to the 765 kV intertie to NYPA) are presented. The salient features of such control modifications are discussed using the results of an investigation by digital and analog simulations that demonstrate the achieved improvements. The modifications lead to a remarkable improvement in the damping of AC voltage and tieline power oscillations under heavy loading conditions. Voltage instability following disturbances under very weak AC-system conditions can also be avoided. >

Patent
16 Apr 1990
TL;DR: A method of manufacturing an electrical circuit system comprising electrical conductors on a flexible film and an article of manufacture made thereby, which may be used in place of printed circuit boards and which conductors form connector means for readily connecting to the leads of one or more sides of an electronic package as discussed by the authors.
Abstract: A method of manufacturing an electrical circuit system comprising electrical conductors on a flexible film and an article of manufacture made thereby, which may be used in place of printed circuit boards and which conductors form connector means for readily connecting to the leads of one or more sides of an electronic package. The electrical conductors also form a means for selectably connecting each electrical conductor from each pin to a selected input or output conductor, comprising a first and second plurality of conductors, such as a matrix having a column of conductors and a row of conductors. The electrical circuit system may be manufactured by numerous methods such as applying a conductive ink or paint by screening, photolithography or drawn by a digital plotter on a plastic film, such as Mylar. The film may include electrical edge connection means to provide input or output to or from said conductors. All or most of the system is integral, thus forming the conductors and the in-line connector portion of the conductors in continuum, using the same conductive material, such as ink, or paint and the same dielectric material, such as ink, or paint. A dielectric covers the appropriate portion of the system.

Patent
19 Jun 1990
TL;DR: In this article, a test probe for testing electronic circuits is provided with a flexible conductive pad disposed at the end of the test probe, which compresses and does not damage either the electrical circuit or the probe itself.
Abstract: A test probe for testing electronic circuits is provided with a flexible conductive pad disposed at the end of the test probe. The flexible conductive pad is resilient so that when it makes physical and electrical contact with an electronic circuit, it compresses and does not damage either the electrical circuit or the probe itself.

Patent
26 Oct 1990
TL;DR: In this article, a window pane from a direct current network of a motor vehicle is used to energize a heating element of a window panes from the direct-current network of the vehicle.
Abstract: The device for energizing a heating element of a window pane from a direct current network of a motor vehicle includes a converting device for converting the d.c. voltage of the direct current network into an alternating current voltage of a predetermined frequency and a resonant circuit connected to the output of the converting device having a Q-factor high enough to produce a low number of harmonics in operation. The resonant circuit has a resonant frequency corresponding to that of the alternating current voltage. The heating element is a part of a resistance of the resonant circuit. The converting device can include a control circuit for producing alternating control signals, a base driving circuit controlled by the control signals and having two outputs connected respectively to a base of a switching transistor. The device can also include a protecting circuit for picking up energy during opening of the respective switching transistors and returning the picked-up energy to the d.c. network.

Proceedings ArticleDOI
01 Jan 1990
TL;DR: A method is described for broadband damping augmentation of a structural system in which the active members were developed such that their mechanical input impedance can be electrically adjusted to maximize the energy dissipation rate in the structural system.
Abstract: A method is described for broadband damping augmentation of a structural system in which the active members (with feedback control) were developed such that their mechanical input impedance can be electrically adjusted to maximize the energy dissipation rate in the structural system. The active member consists of sensors, an actuator, and a control scheme. A mechanical/electrical analogy is described to model the passive structures and the active members in terms of their impedance representation. As a result, the problem of maximizing dissipative power is analogous to the problem of impedance matching in the electrical network. Closed-loop performance was demonstrated for single- and multiple-active-member controlled truss structure.

Journal ArticleDOI
01 Nov 1990
TL;DR: In this article, a method of modelling involving the step by step solution of differential equations based on a simple d-q equivalent circuit, with damping represented by a single element in each axis, is described.
Abstract: Modelling of generators for power systems studies is a difficult task. Uncertainties surrounding the choice of equivalent circuit and parameter measurement are compounded by the effects of saturation, whereby machine reactances vary with changes in voltage and current. The paper addresses these problems. A method of modelling is described involving the step by step solution of differential equations based on a simple d-q equivalent circuit, with damping represented by a single element in each axis. Saturation is included and is shown to have a significant influence on dynamic behaviour. The equivalent circuit parameters and their saturation characteristics are derived using semi-empirical curve fitting techniques from the results of standard works tests. Changes caused by saturation are introduced at each step in the solution to modify parameters in accordance with prevailing voltages and currents. The effectiveness of the model and the methods it employs were tested successfully, using results from a micromachine model and from practical generators.

Journal ArticleDOI
TL;DR: In this article, a numerical model for the equivalent electrical circuit of a capacitive discharge that includes the effects of finite closure time of switches and finite transit time in the transmission line is presented, and an approximate analytical method to predict the oscillations that can be excited in the circuit is developed.
Abstract: A numerical model for the equivalent electrical circuit of a capacitive discharge that includes the effects of finite closure time of switches and finite transit time in the transmission line is presented. An approximate analytical method to predict the oscillations that can be excited in the circuit is developed. The model yields complex behavior over time of the magnitudes of currents and voltages in pulsed circuits in the simple circuit configurations studies. Some of the oscillations predicted by the calculations admit simple physical interpretations in limiting cases (and are then predictable without the need of complex calculations); however, the rest of the observed features are not amenable to easy interpretation. The numerical solutions of the model are compared with experimental signals measured in a plasma focus device. Good agreement with many of the observed features is noted. The model can be extended easily to other types of circuits (Marx generators, Blumlein lines, etc.). >

Journal ArticleDOI
TL;DR: In this article, a severe form of the low-order harmonic resonance problem was identified in a HVDC/AC system and a proper design of the voltage-dependent current order limiter (VDCOL), the current regulator, and the timing pulse generator was proposed.
Abstract: A severe form of the low-order harmonic resonance problem was identified in a HVDC/AC system. Solutions to the problem were sought by HVDC control means and were achieved by a proper design of the voltage-dependent current order limiter (VDCOL), the current regulator, and the timing pulse generator. Supplementary control loops were also introduced, resulting in a satisfactory performance as compared to that obtained with the use of an uncharacteristic harmonic filter on the AC side. Robustness of all the options has been demonstrated through recovery performance of the DC link in response to three-phase five-cycle faults on both rectifier and inverter commutating buses. >

Journal ArticleDOI
TL;DR: In this article, the Laplace transforms of the nonstationary mean and the stationary autocorrelation function are derived for a class of stochastic processes called alternating renewal processes that appear particularly suitable for modeling air-conditioning loads on electrical power systems.
Abstract: Results are derived for a class of stochastic processes called alternating renewal processes that appear particularly suitable for modeling air-conditioning loads on electrical power systems. Expressions for the Laplace transforms of the nonstationary mean and the stationary autocorrelation function are obtained. If the on-duration and off-duration random variables have gamma distributions of the particular type known as Erlang-n, then the transforms will turn out to be rational functions. Therefore, this class of air-conditioning loads can be characterized by the poles and zeros of these functions. Moreover, pole and zero locations determined empirically under quasi-equilibrium conditions can be used to predict the payback transient. How these results permit the prediction of transient behavior after an outage based on measurements taken under nominal conditions is explained. >

Patent
31 Jan 1990
TL;DR: In this paper, a normally closed electrical switch having a plurality of electrically conductive contacts normally arranged in overlapping electrical communication is described. But the switch does not have a pressure-directing mechanism.
Abstract: A normally-closed electrical switch having a plurality of electrically conductive contacts normally arranged in overlapping electrical communication. A preferred embodiment of the present invention also comprises a pressure directing mechanism for directing and actuating pressure to specific portions of the electrically conductive elements. The normally-closed electrical switch of the present invention interrupts an electrical circuit in response to an applied pressure.

Journal ArticleDOI
TL;DR: In this paper, the problem of transmission networks expansion has been solved by considering the cost of losses as well as the investment in the objective function using an exact quadratic programming technique.
Abstract: In this paper, the problem of transmission networks expansion has been solved by considering the cost of losses as well as the cost of investment in the objective function. The problem is solved using an exact quadratic programming technique. This new formulation has been applied to a 6- bus system. The final configurations, which are characterized by minimum cost of losses show that as the cost of the Kwh increases, the total system cost decreases.

Patent
28 Feb 1990
TL;DR: In this paper, a compact, reliable, and handy electrical connector for connecting two flat cables to a circuit board, by connecting the electrical circuit on the front side of the circuit board to one flat cable and the electrical circuits on the rear side of a circuitboard to another flat cable, is presented.
Abstract: The invention comprises a compact, reliable, and handy electrical connector for connecting two flat cables to a circuit board, by connecting the electrical circuits on the front side of the circuit board to one flat cable and the electrical circuits on the rear side of the circuit board to another flat cable.

Journal ArticleDOI
TL;DR: The problem of image restoration using the maximum entropy (ME) method is considered, and an iterative scheme which can be used to solve the ME image restoration problem can be defined.

Journal ArticleDOI
TL;DR: It is shown that a digital real-time control system can be interfaced with a digital simulator of a power system through time-transposition, and the control is synchronized with the system time-domain solution while operating in packets of real time.
Abstract: The concept of incorporating real-time controls into established computer programs simulating AC/DC systems is introduced. It is shown that a digital real-time control system can be interfaced with a digital simulator of a power system. Through time-transposition, the control is synchronized with the system time-domain solution while operating in packets of real time. The requirements and options for implementing this approach to simulation and recommendations for its application are presented. The specific problems of operating in the different time frames and the computational aspects of scheduling the control and its interface with the system computer simulation are discussed. Implementation with reference to DC converter control is described. Synchronizing and software interface aspects are discussed. >