Showing papers on "Electrical network published in 2004"

Harmonic interaction between a large number of distributed power inverters and the distribution network

Abstract: Power quality problems associated with distributed power (DP) inverters, implemented in large numbers onto the same distribution network, are investigated. Currently, these power quality problems are mainly found in projects with large penetration of photovoltaics (PV) on rooftops of houses and commercial buildings. The main object of this paper is to analyze the observed phenomena of harmonic interference of large populations of these inverters and to compare the network interaction of different inverter topologies and control options. These power quality phenomenons are investigated by using extensive laboratory experiments, as well as computer modeling of different inverter topologies. A complete network simulation study on an existing residential network with large penetration of PVs, is included.

Piezoelectric passive distributed controllers for beam flexural vibrations

Abstract: Recent technological developments have made available efficient bender transducers based on the piezoelectric effect. In this paper an electrical circuit analog to the Timoshenko beam is synthesized using a Lagrangian method and by paralleling capacitive flux linkages to rotation and transverse displacement. A Piezo-ElectroMechanical (PEM) beam is conceived by uniformly distributing piezoelectric transducers on a beam and interconnecting their electric terminals via the found analog circuit, completed with suitable resistors. The high performance features of the synthesized novel circuit include the following. (i) The circuit topology is extremely reduced, the used components are all but one two-terminal elements, and the only two-port network needed is an ideal transformer. (ii) One and the same dissipative circuit ensures a multiresonance coupling with the vibrating beam and the optimal electrical dissipation of mechanical vibrations energy. (iii) For a prototype of a PEM beam, the design of the analog ...

Fuel cell power system and high power DC-DC converter

Abstract: This paper discusses the principle and electrical characteristics of the fuel cell, designs an innovative hybrid power system, and proposes a new DC/DC converter scheme to combine the fuel cell with the storage system. An effective converter scheme for the fuel cell is obtained by analyzing the high efficient topology as well as the phase shifted pulse-width modulation. Through comparing several different control modes of converters, a 75-kW prototype system is constructed, moreover, which steady-state operating characteristics are illustrated and discussed in detail. At last, experimental results are also shown to verify the proposed scheme.

Real time digital simulation for control and protection system testing

Abstract: Today's power system environment is becoming more and more complex. Electrical power networks are being pushed closer to their limits, while at the same time higher reliability and efficiency are demanded. As a result, electrical equipment manufacturers are developing advanced equipment and installations to meet these requirements. Part of the challenge in designing such apparatus is the need to accurately simulate (prove) and test these devices before they are installed in an actual power system. The real time digital simulator (RTDS) allows developers to accurately and efficiently simulate electrical power systems and their ideas to improve them. The RTDS simulator operates in real time, therefore not only allowing the simulation of the power system, but also making it possible to test physical protection and control equipment. This gives developers the means to prove their ideas, prototypes and final products in a realistic environment. This paper will summarize the fundamental design of the RTDS simulator, with particular emphasis on recent developments and enhancements. It will also describe practical applications of the simulator in the various stages of power system design, testing and implementation. A brief description of ongoing development for the real time simulation of voltage source converter (VSC) converters is included.

Numerical modeling of magnetic devices

Abstract: We present a general approach to directly couple finite-element models with arbitrary electric circuits for application to electromagnetic devices. We describe both two-dimensional (2-D) and three-dimensional (3-D) transient finite-element models, with emphasis on 3-D using a T-/spl Omega/ formulation. For 3-D transient and circuit coupling, the derivation of the induced voltage is an integral part of the coupling approach, and the induced voltage links the magnetic field and the electrical circuit together. The system of electric circuits is created automatically. Then graph theory is used to deduce the circuit by tree/cotree and loop analysis. The resulting field equations and circuit equations are coupled together and solved simultaneously at each time step in the time domain. We give three examples of applications: a brushless dc motor drive, a permanent-magnet synchronous motor drive, and a three-phase power transformer with rectifier and load circuit.

Maximising energy capture from distributed generators in weak networks

Abstract: The paper discusses the implications of the increasing capacity of synchronous generators at the remote ends of rural distribution networks where the line resistances are high and the X/R ratios are low. Local voltage variation is specifically examined and two methods of compensation are proposed. The first of them is a deterministic system that uses a set of rules to switch intelligently between voltage and power factor control modes, while the second is based on a fuzzy inference system that adjusts the reference setting of the automatic power factor controller in response to the terminal voltage. Extensive simulations have verified that the proposed approaches may increase the export of real power while maintaining voltage within the statutory limits.

Traction system unbalance problem-analysis methodologies

Abstract: This paper presents a novel methodology using a utility's existing software for the accurate prediction of total unbalance (UB) impact due to ac traction loads with emphasis on the estimation of negative sequence (N-Seq) current injection into utility generators. Traditionally, due to the requirement of complex 3/spl Phi/ power-flow simulation, UB analysis has been limited to the evaluation of UB voltage at the point of common coupling (PCC) without addressing whether supply of this N-Seq current would exceed the remaining margin of each utility generator. By using the salient feature that a utility's N-Seq network is basically "sourceless" as such for any N-Seq current injection at a specific node, the "contribution ratio" of each utility generator for that N-Seq current injection is fixed irrespective of the magnitude of that injection, this paper provides a solution to this important problem by using a utility's existing fault analysis software.

Control of power electronic interfaces in distributed generation microgrids

Abstract: Technological advances and environmental pressures are driving the interconnection of renewable energy sources to the distribution network. The interconnection of large amounts of non-traditional generation however causes problems in a network designed for ‘conventional’ operation. The use of power electronics interfaces and the ‘bundling’ of micro-generation and loads into so-called Microgrids, offers a potential solution. Each Microgrid is designed to operate as a ‘good citizen’ or near ideal conventional load. This paper discusses the various elements of the new Microgrid concept and presents suggestions for some typical control strategies for the various system elements.

Artificial neural network-based dynamic equivalents for distribution systems containing active sources

Abstract: An approach to identify generic dynamic equivalents to distribution systems using recurrent artificial neural networks (ANN)s is presented. It is expected that in the near future a large number of active sources will be utilised within distribution systems and thus, neither detailed modelling nor lumped-load representation for distribution areas will be acceptable. Therefore, the paper suggested training a recurrent ANN to represent the dynamic behaviour of the distribution network is. To involve the dynamic characteristics in the ANN, values of the features that are involved are also introduced at the input layer, thereby defining the order of the dynamic equivalent. The approach depends on variables at the boundary buses, hence no knowledge of the parameters and the topology of the distribution system is needed. At the same time, the computational requirements and the accuracy of the proposed technique are independent of the size and complexity of the network. A 16-machine test network with 112 active distributed sources in the low-voltage area is used to verify the suggested method. Comparisons between the response of the original system and the ANN-based dynamic equivalent show the accuracy of the equivalent model and the validity of the proposed method.

Model-order reduction of finite-element approximations of passive electromagnetic devices including lumped electrical-circuit models

Abstract: A methodology is presented for the development of reduced-order macromodels for multiport passive electromagnetic devices that include embedded lumped elements. The proposed methodology utilizes a discrete state-space model for the electromagnetic device, generated through the application of the finite-element method for the spatial discretization of Maxwell's curl equations. The incorporation of lumped resistors, inductors, and capacitors is effected through the direct stamping of the state-space voltage-current relationship for these elements in the matrices of the generated state-space form of the discrete model. The conditions necessary for the discrete model to be passive are discussed. The subsequent reduction of the discrete state-space model is effected through the application of a Krylov-subspace-based model-order reduction scheme that guarantees the passivity of the generated multiport macromodel, provided that the original state-space model is passive. The proposed methodology is demonstrated and validated through its application for the generation of reduced-order macromodels for a coaxial cable circuit and a microstrip directional coupler circuit.

A comparison of fundamental gate-driver topologies for high frequency applications

Abstract: The gate-driver in most power electronic converters is seldom given sufficient attention during the design stage even though it is the circuit exposed to much of the same voltage stresses as the switching devices and yet despite this, is a crucial component to a sound functioning system. At higher switching frequencies, and either low power or high voltage applications, the effect of the gate-driver on the overall converter performance becomes even more pronounced. When considering a gate-driver for a power electronic system, the converter topology, operating conditions and requirements, voltage and current ratings, and switching frequency determines the suitability and applicability of a chosen gate-driver to the application. This paper discusses different gate-drivers, represented by three fundamental gate-driver topologies that are evaluated in terms of suitable operating conditions, construction and losses. These gate-drivers, constructed using two different methods, a hybrid and SMD, also forms part of the evaluation. In addition, some of the issues as switching frequencies keep increasing is also addressed.

Woven fabric-based electrical circuits. Part I: Evaluating interconnect methods

Abstract: In recent years, a new area of research has emerged on textile-based electronics, called "electrotextiles." Most of the ongoing research in electrotextiles is driven by the motiva tion of creating multifunctional fiber assemblies that can sense, actuate, communicate, compute, etc. This paper discusses the development of fabric-based electrical circuits by interlacing conducting and nonconducting threads2 into woven textile structures. Wired interconnections of different devices attached to the conducting elements of these circuits are made by arranging and weaving conductive threads so that they follow desired electrical circuit designs. In a woven electrically conductive network, routing of electrical signals is achieved by the formation of effective electrical interconnects and disconnects. Resistance welding is identified as one of the most effective means of producing crossover point interconnects and disconnects. Interconnects are evaluated by measuring the DC resistance associated with the crossover...

Precision measurements of a simple chaotic circuit

Abstract: We describe a simple nonlinear electrical circuit that can be used to study chaotic phenomena. The circuit employs simple electronic elements such as diodes, resistors, and operational amplifiers, and is easy to construct. A novel feature of the circuit is its use of an almost ideal nonlinear element, which is straightforward to model theoretically and leads to excellent agreement between experiment and theory. For example, comparisons of bifurcation points and power spectra give agreement to within 1%. The circuit yields a broad range of behavior and is well suited for qualitative demonstrations and as a serious research tool.

A PC-Based Real-Time Parallel Simulator of Electric Systems and Drives

Abstract: This paper presents the RT-LAB Electrical Drive Simulator technology along with practical applications. The RT-LAB[Opal-RT Technologies inc.] simulation software enables the parallel simulation of electrical circuit on clusters of PC running QNX or RT-Linux operating systems at sample time below 10 µs. Using standard Simulink models including SimPowerSystems models, RT-LAB build computation and communication tasks necessary to effectively make parallel simulation of electrical systems on low cost off-the-shelf PC technology. To accommodate the high bandwidth of electrical systems, the RT-LAB Electrical Drive Simulator comes with special Simulink-based modelisation tools, namely ARTEMIS[Opal-RT Technologies Inc.] and RT-Events[Opal-RT Technologies Inc.], that permits real-time simulation of electrical systems at practical time step of 10 µs but with sub-µs equivalent precision through the use of interpolation techniques.

Advanced Control Methods for Optimization of Arc Welding

Abstract: In this thesis the objective is to optimize the control algorithms for the manual pulsed Gas Metal Arc Welding (GMAW) process, with the aim of enhancing the quality of welded joints. To be able to develop controllers for the GMAW process, and also for enabling process simulation, a mathematical model describing the GMAW process is developed. The mathematical model includes a description of the electrical circuit, the drop dynamics, and the melting rate, and also, the model includes criteria for drop detachments. Basically, the electrical circuit consists of the welding machine, the wires, the electrode, and the electrical arc. The drop is modelled as a mass-spring-damper system influenced by a number of external forces. Of these external forces the electromagnetic force is the most significant. Due to the importance of the electromagnetic force, a thorough derivation of the electromagnetic force is included in the thesis. The melting rate of the consumable electrode is modelled both from a statically (steady-state) point of view, and from a dynamically point of view. The static model is a simple equation describing the melting rate, while the dynamic model is more complex. The structure of GMAW control is discussed, and based on this discussion a general control structure is presented. This structure includes an arc length controller and a metal transfer controller, and also, an inner loop controlling the welding current. The current is assumed to be controlled by a traditional PI-controller, and therefore, this inner control loop is not considered in the thesis. For arc length control, a nonlinear controller based on feedback linearization is proposed, and robustness and performance are considered. For metal transfer control an approach based on obtaining a uniform drop size prior to pulse initiation is proposed. This is carried out by calculating the amount of melted electrode between the current pulses during the welding process. The purpose of the uniform drop size approach is to enhance the robustness of the drop detachment process. In addition to the arc length controller and the metal transfer controller, an arc length minimization algorithm is proposed for enhancing the ability to focus the arc, and also, to minimize the heat input into the workpiece. Simulation programs for testing the controllers and algorithms have been developed, and successful tests have been carried out.

An automotive 16 phases DC-DC converter

Abstract: Next future vehicles will change battery voltage front 14 to 42 V. As a consequence, new converters are being developed to cover the needs of the electrical circuits. In the meantime, vehicles will have dual battery system (14 and 42 V). A 1 kW bidirectional 14-42V DC-DC converter has been built and tested for these vehicles. The goodness of the digital control allows the use of a high number of interleaved converters, yielding to a low profile (10 mm height) circuit without current sensing.

Envelope Following Method to Compute Steady State Solutions of Electrical Circuits

Abstract: The paper deals with the determination of the steady-state solution of both autonomous and nonautonomous circuits. Only time-domain methods are considered, and, in particular, the shooting (SH) and multishooting (MSH) ones. It is well known that one of their main drawbacks is the lack of convergence if they are not started from an initial guess "close enough" to the steady-state solution. To overcome this problem, we present an envelope-following method that efficiently brings the operating point of the circuit into the convergence region of the shooting (SH) and multishooting (MSH) algorithms.

Electrical Signal Application Strategies for Monitoring a Condition of an Elevator Load Bearing Member

Abstract: An elevator load bearing member (30) monitoring device includes a controller (42) that applies a selected electrical signal to tension members (32) of the load bearing member (30). In one example, connectors (40) are associated with ends of the load bearing member (30) to establish an electrical interface between the controller (42) and the tension members (32). The connectors (40) facilitate establishing electrical circuit loops along the tension members (32) such that only non-adjacent tension members are energized at a selected time. A variety of circuit configurations are disclosed. The applied electrical signal in one example has a potential that is negative compared to a ground potential of a hoistway in which the elevator belt is used. In another example, the electrical signal comprises a plurality of pulses and has a duty cycle that is on the order of about one percent.

Algorithm for Extracting Corrosion Parameters from the Response of the Steel-Concrete System to a Current Pulse

Abstract: The transient response to a current pulse applied to steel reinforcement bars in concrete has been analyzed by means of a new computational algorithm based on discretised approximation of the fractional difference operator. An optimization strategy has been designed to obtain a set of optimal values for the characteristic corrosion parameters from the information contained in the potential-time transient (specially, in the decaying part of the trace). The method compares the experimental response with the simulated response in the time domain obtained from an electrical circuit model which includes the effects of a constant-phase element and diffusion coupled with charge transfer. The practical possibilities of this method for extracting corrosion parameters (in particular, the charge-transfer resistance) have been demonstrated with steel reinforcements embedded in concrete in the presence and absence of chloride additions.

Probabilistic power flow with nonconforming electric loads

Abstract: A comprehensive model for probabilistic power flow is proposed for the purpose of estimating the statistics of bus voltage magnitudes and circuit currents, given the statistics of the loads. The proposed method is based on the quadratized power flow model and a nonconforming electric load model. The statistics of the electric load are accurately represented with the statistics of a few independent random variables and the statistics of bus voltage magnitudes and circuit current flows are computed from the linearized model of bus voltage and circuit current flow with respect to these independent load random variables. The method is validated via Monte Carlo simulations in which the problem is fully solved for each random sample, thus incorporating nonlinearities resulting from the AC power flow equations. Both the linearization solution and the Monte Carlo approach are based on the single phase quadratic power flow (SPQPF) model of the power system. The proposed method has been implemented and applied to the IEEE reliability test system (RTS). The results are presented in the paper.

Modified Newton-Raphson load flow analysis for integrated AC/DC power systems

Abstract: The significant increase in planned offshore wind parks and the tendency towards large parks in considerable distances offshore, make the well established HVDC technology a favorable solution for the connection of these large & distant offshore wind parks to the main power grid onshore. It is therefore necessary to adequately model the HVDC transmission links and integrate them in the load flow analysis of the complete AC-DC system. In this paper, the well known Newton-Raphson method for the load flow analysis is modified to achieve compatibility for AC-DC systems with integrated DC links in the AC network. The elements of the residual vector and the Jacobian matrix for the AC network are kept unchanged and are merely complemented by a new vector and a new matrix, which represent the modifications due to the DC link. The modified Jacobian equation includes the DC real and reactive power at the AC-DC buses, and their dependency on the AC system variables. The modified Newton-Raphson method is evaluated on an AC-DC test system with a load flow computation in Matlab and the results are presented.

Electrical arc phenomena and its interaction on contact material at 42 volts DC for automotive applications

Abstract: In order to fulfill the increasing needs of electrical power in automobiles, the electrical network, currently at 14 VDC, must be changed to 42 VDC This involves that switching DC devices have to be improved to insure reliability and electrical safety Therewith, for improve comprehension of arc phenomena and its interactions with contact materials under 42 VDC, the authors undertook a study on this subject This work summarizes the whole of work and tackles the arc phenomena at break and make, the contact material transfer and the problems of welding at make Thus, we studied break arc duration, arc length (gap) and material transfer versus the effect of material, opening speed and loads We have established that the arc duration and its length are extremely extended by a few millimeters compared to the arc in 14 VDC At 42 VDC and low current, erosion and transfer direction is similar to the previous one obtained at low arcing length in 14 VDC However at large gap, with 42 VDC inductive loads or high current, new mechanism erosion mode takes place which induce the cathode and the anode loss Erosion and arc length of AgSnO/sub 2/ contacts is higher than other material: for this particular behavior, some complementary investigations, using X chemical analysis, have been undertaken It seems that electrical arc enriches in tin element the contacts surfaces leading to this behavior In other way, we have investigated make arc erosion, welding tendency and welding forces for all materials It was found that contrary to the 14 VDC case, the make arc takes place during the total bounce period The rating material performances at make seem to be reversed than at break This study enables to understand the material effect at this higher voltage and thus should allow the improvement of the material itself Anyway, the commutation devices of 42 VDC should employ improved materials and also additional systems of arc reduction

Circuitized connector for land grid array

Abstract: A connector for electrically connecting to pads of a land grid array formed on an electronic component includes a dielectric layer including opposing first and second surfaces, and a multiple number of contact elements extending above the first surface of the dielectric layer. Each contact element includes a conductive portion disposed to engage a respective pad of the land grid array for providing electrical connection to the land grid array. The connector further includes an electrical circuit formed on or within the dielectric layer. The electrical circuit is electrically connected to at least one of the multiple number of contact elements. In one embodiment, the electrical circuit includes an electrical component, such as a decoupling capacitor. In another embodiment, the electrical circuit operates to connect two contact elements together. For instance, the contact elements connecting to the ground potential can be connected together through the electrical circuit.

Combination hand tool and electrical testing device

Abstract: The invention is directed to a device combining a handled tool, such as wire strippers, with one or more testing components useful for testing electrical circuits, such as continuity testers and voltage detectors, with the testing components integrated into a like number of handle grips.

HVDC Dynamic modelling for small signal analysis

Abstract: The conventional quasi-steady model of HVDC is not able to describe the dynamic switching behaviour of HVDC converters. By means of the sampled-data modelling approach, a linear time-invariant (LTI) small-signal dynamic model is developed for the HVDC main circuit in the synchronous rotating d-q reference frame. The linearised model is validated by time-domain simulation, and it can be seen that the model represents the dynamic response of the static switching circuits to perturbations in operating points. The model is valid for analysing oscillations including high frequency modes such as subsynchronous oscillation (SSO) and high frequency instability. The model is applied in two cases: (i) SSO analysis where the results are compared with the quasi-steady approach that has shown its validation for normal SSO analysis; (ii) high frequency eigenvalue analysis for HVDC benchmark system in which the results of root locus analysis and simulation shows that increased gain of rectifier DC PI controller may result in high-frequency oscillatory instability.

Global linearization of non-linear state equations

Abstract: The global linearization method is used to solve multivariable non-linear state equations. This method makes use of a simple and invertible change of coordinates based on global diffeomorphism. A full agreement of the solutions of the linear and non-linear models was obtained. Two examples of practical application of this method have been presented: the first - a non-linear model of a DC drive system, and the second - an electrical circuit with a non-linear diode.

Power flow in distribution networks with earth return

Abstract: The problems of wave propagation and power flow in the distribution network composed of an overhead wire parallel to the surface of the ground have not been satisfactorily solved. While a complete solution of the actual problem is impossible, as it is explained in the famous Carson's paper (1926), the solution of the problem, where the actual earth is replaced by a plane homogenous semi-infinite solid, is of considerable interest. In this paper, a power flow algorithm in distribution networks with earth return, based on backward–forward technique, is discussed. In this novel use of the technique, the ground is explicitly represented. In addition, an iterative method for determining impedance for modelling ground effect in the extended power flow algorithm is suggested. Results obtained from single-wire and three-wire studies using IEEE test networks are presented and discussed.