Showing papers on "Electrical network published in 2005"

Dynamic models and model validation for PEM fuel cells using electrical circuits

Abstract: This paper presents the development of dynamic models for proton exchange membrane (PEM) fuel cells using electrical circuits. The models have been implemented in MATLAB/SIMULINK and PSPICE environments. Both the double-layer charging effect and the thermodynamic characteristic inside the fuel cell are included in the models. The model responses obtained at steady-state and transient conditions are validated by experimental data measured from an Avista Labs SR-12 500-W PEM fuel-cell stack. The models could be used in PEM fuel-cell control related studies.

Transmission network expansion planning with security constraints

Abstract: A mathematical model and a methodology to solve the transmission network expansion planning problem with security constraints are presented. The methodology allows one to find an optimal and reliable transmission network expansion plan using a DC model to represent the electrical network. The security (n-1) criterion is used. The model presented is solved using a genetic algorithm designed to solve the reliable expansion planning in an efficient way. The results obtained for several known systems from literature show the excellent performance of the proposed methodology. A comparative analysis of the results obtained with the proposed methodology is also presented.

Measurement location for state estimation of distribution networks with generation

Abstract: State estimation is important for the automatic management and control of complex distribution networks with significant distributed generation. State estimation has been used extensively on transmission systems where, generally, measurements of busbar voltages and line power flows exist. However, distribution systems normally have only a limited number of measurements. In such systems additional measurements are expensive and careful selection of location becomes important. The paper presents a heuristic approach to identify potential points for location of voltage measurements for state estimation as part of a proposed distribution management system controller. The developed technique identifies measurement locations to reduce the voltage standard deviation of the busbars which do not have a measurement. It addresses the problems of classical transmission meter placement methods, which are not directly applicable to distribution systems due to limited measurements, and unobservability of the network.

A 3-D model for concentrator solar cells based on distributed circuit units

Abstract: A three-dimensional (3-D) distributed model for high-concentrator solar cells based on elementary units made up of electrical circuits is presented. The recombination mechanisms are dealt with in detail, paying special attention to the perimeter properties. No ohmic effect is omitted making this a powerful simulation tool for concentrator solar cells. A shunt resistance is also included. The model allows the simulation of the external connections and nonuniform illumination profiles making this model very useful for optimizing future structures and technological processes. The proposed 3-D model is compared with a lumped, two-diode model in the simulation of a GaAs solar cell operating from 1 to 2000 suns. It is found that the 3-D distributed model agrees satisfactorily with the experimental data for all concentrations. The agreement cannot be made simultaneously for both low and high concentrations for the lumped model.

Voltage stability in weak connection wind farms

Abstract: The total operating wind power capacity in the world increases fast, and these types of generating units also bring new opportunities and problems to the utilities and customers. It becomes necessary and important to evaluate their impact on the electrical network voltage stability, especially for weak connected systems. This paper uses the detailed wind energy conversion system and the full order induction generator model to analyze the voltage stability in a weak connection wind farm. The possibility of network voltage drop and instability are investigated by the detailed electromagnetic transient simulation program. Some techniques to improve the transient response of voltage are also discussed.

LMI approach for H linear parameter-varying state feedback control

Abstract: Linear matrix inequality conditions are given for the existence of a stabilising linear parameter dependent state feedback gain for continuous time-varying systems in convex polytopic domains. Although there exist several results dealing with this problem in the literature, up to now all approaches assume that some matrices describing the system must be constant and/or must satisfy structural constraints. Here, all the system matrices are assumed to be affected by time-varying uncertainties and there are no structural constraints. The strategy proposed is much simpler than standard gain scheduling techniques, being specially adequate for systems with parameters that have unbounded or a priori unknown rates of variation, for instance, switched systems. Moreover, the conditions can also assure a guaranteed H/sub /spl infin// attenuation level for the closed-loop system under arbitrarily fast parameter variations significantly improving the results based on a fixed gain obtained through quadratic stabilisability conditions. Numerical examples illustrate the use of the proposed control design with applications to two physical systems: a linear model of a helicopter subject to actuator failures and an electrical circuit used as a lowpass filter in the output stage of power converters.

Performance study of two different compensating devices in a custom power park

Abstract: Simulation study of a custom power park (CPP) is presented. It is assumed that the park contains unbalanced and nonlinear loads in addition to a sensitive load. Two different types of compensators are used separately to protect the sensitive load against unbalance and distortion caused by the other loads. It has been shown that a shunt compensator can regulate the voltage of the CPP bus, whereas the series compensator can only regulate the sensitive load terminal voltage. Additional issues such as the load transfer through a static transfer switch, detection of sag/fault etc. are also discussed. The concepts are validated through PSCAD/EMTDC simulation studies on a sample distribution system.

Capacitor placement in large-sized radial distribution networks

Abstract: The capacitor-placement problem consists of finding specific locations to install capacitor banks in an electrical distribution network. Consequently, the losses are reduced due to the compensation of the reactive component of power flow. This problem can be formulated as a nonlinear mixed-integer optimisation model and its solution has represented a challenge for many optimisation methods in the past decades. This work proposes a new method, based on evolutionary algorithms, capable of solving large network instances that appear in real-world settings. Our evolutionary approach makes use of a memetic algorithm that employs a hierarchical organisation of the population in overlapping clusters. This structure leads to special selection and reproduction schemes, which improve the algorithm's overall performance. Computational tests were executed with two small-sized instances, usually utilised as a test set in previous works, and with two real large-sized distribution networks. Tests include a sensitivity analysis of the algorithm to the optimisation's critical parameters such as the energy cost, the maximum budget available to acquire and install the capacitors, and the amortization term of the investment.

An efficient method to compute transfer function of a transformer from its equivalent circuit

Abstract: The dynamics of an electrical network can completely be described from the knowledge of its poles and zeros. Computation of poles and zeros of the transfer function (TF) of a transformer winding, represented as a coupled ladder network, involves solution of a large-sized equivalent circuit. This paper presents a novel solution based on state space analysis approach. It is shown, how the linearly transformed state space formulation, together with algebraic manipulations, can become useful. In the proposed formulation, symbolic variables (i.e., Laplace variable, s) are suitably manipulated, so as to render computations purely numerical. With this feature, there is practically no limit on the size of networks and topologies (including resistances to model losses) that can be represented. So, virtually any number of windings of a transformer can be considered, permitting a comprehensive analysis of winding behavior and its interactions, that was until now severely limited, by the simplifying assumptions imposed by existing methods.

Circuit protector monitoring assembly kit and method

Abstract: Monitoring assemblies, kits and methods for determining an operational state of a circuit protector in an electrical circuit.

Structural control with regenerative force actuation networks

Abstract: A Regenerative Force Actuation (RFA) Network consists of multiple electromechanical forcing devices distributed throughout a structural system and actuated in such a way as to reduce the response of the structure when subject to an excitation. The associated electronics of the devices are connected together such that they are capable of sharing electrical power with each other. This makes it possible for some devices to extract mechanical energy from the structure, while others re-inject a portion of that energy back into the structure at other locations. The forcing capability of an RFA network is constrained only by the requirement that in the aggregate the total network must always dissipate energy. The electromechanical currents generated by RFA networks must be controlled to create the desired structural forces. This control is facilitated by the alternation of a multitude of power-electronic transistor switches in the electrical network. In this study, a sliding-mode switching controller is proposed for realizing zero-error force command tracking. It is shown that parameter uncertainty is a critical issue for force commands which require the network to operate near its optimum transmissive efficiency. RFA networks can be used to create velocity-proportional damping forces in structures. However, unlike traditional structural damping, RFA networks have the ability to create non-local and asymmetric damping forces. It is shown that this more generalized damping capability can lead to significant improvements in the forced response of a structure, as compared with traditional linear damping. RFA networks may also be used for feedback control. In this context, the forcing capability of the RFA network is constrained by its physical limitations. In this study, a systematic method of nonlinear control design called "Damping-Reference" control is proposed, which guarantees a certain level of quadratic performance for the structural response. Variants of the control law synthesis are proposed for quadratic regulation, stochastic control, and H[infinity] control contexts. These ideas are illustrated in the context of earthquake engineering through a simulation example, involving a three-story structure with a two-actuator RFA network installed. In this example, it is shown that the "power sharing" nature of the RFA network has a significant influence on the response.

Novel lumped-parameter thermal model for electrical systems

Abstract: The lumped parameter thermal model has been used for a long time for calculating the temperature rises in electrical systems (e.g electrical machines or power electronic systems). As is known, this method is used to solve thermal problems by applying thermal networks, in analogy to electrical circuits. In spite of being popular, generally this method is not applied correctly for elements with distributed heat generation. It is shown that loading the thermal model with the total power losses leads to wrong results. In this paper, a correct lumped-parameter method is developed and explained

Energy transfer in electrical circuits: A qualitative account

Abstract: We demonstrate that the use of the Poynting vector for a model of the surface charge of a current carrying conductor can help qualitatively explain the transfer of energy in a dc closed circuit. The application of the surface charge model to a simple circuit shows that electromagnetic energy flows from both terminals of the battery, mainly in the vicinity of the wires (and not inside them) to the load where it enters and is converted into heat at a rate obtained from Ohm’s law.

Numerical tools and models for Monte Carlo studies of the influence on embedded generation on voltage limits in LV grids

Abstract: If significant amounts of distributed electricity generation (DG) units are embedded in the low-voltage (LV) distribution networks, a major issue is to keep the voltage between the EN 50160 limits. This technical constraint is often considered to be a major limitation to the admissible level of embedded generation in an LV network. This paper deals with a study of the influence of embedded generation. The starting idea is that considering the worst-case load and generation combinations is too pessimistic. Therefore, a stochastic approach has been chosen. Loads and embedded generation production are modeled as stochastic processes whose characteristics depend on season and peak/low demand periods. Monte Carlo simulations yield the amount of time where the voltages are out of limits at one point in the network. The simulation results can be efficiently interpreted using the concept of critical network length and show how it is affected by the embedded generation. A reference LV radial distribution configuration is taken and different values of specific area load densities (kW/km/sup 2/), cable-loading densities (kilowatts/kilometers), and LV network lengths are considered. For the evaluation of the networks currents and node voltages, a simple current injection method was chosen for its efficiency for studying the radial distribution network operating in the voltage limits (limited voltage regulation). The method was adapted for distributed loads. To conclude, a specific case with a substantial amount of additional DG is considered.

Spectrometer system for optical reflectance measurements

Abstract: A spectrometer system includes a thermal light source for illuminating a sample, where the thermal light source includes a filament that emits light when heated. The system additionally includes a spectrograph for measuring a light spectrum from the sample and an electrical circuit for supplying electrical current to the filament to heat the filament and for controlling a resistance of the filament. The electrical circuit includes a power supply that supplies current to the filament, first electrical components that sense a current through the filament, second electrical components that sense a voltage drop across the filament, third electrical components that compare a ratio of the sensed voltage drop and the sensed current with a predetermined value, and fourth electrical components that control the current through the filament or the voltage drop across the filament to cause the ratio to equal substantially the predetermined value.

An effective SSC control scheme for voltage sag compensation

Abstract: Voltage sags are very frequent events associated with faults in the network, with energization of transformers or starting of large motors. Although their duration is very short, they can represent a big problem for industrial plants, especially for those characterized by the presence of sensitive loads, like power electronics devices. In this paper, the problem of the design of a device able to compensate voltage sags, namely a Static Series Compensator (SSC), is thoroughly analyzed, both from the point of view of the choice of the components and their rating and from the stand-point of the control system. The model has been implemented with the aid of the electromagnetic code PSCAD-EMTDC and has been tested in a radial distribution network for the protection of a nonlinear load consisting of a diode rectifier.

Optimal Power Flow of the Algerian Electrical Network using an Ant Colony Optimization Method

Abstract: This paper presents solution of optimal power flow (OPF) problem of a power system via an Ant Colony Optimization Meta-heuristic method. The objective is to minimize the total fuel cost of thermal generating units and also conserve an acceptable system performance in terms of limits on generator real and reactive power outputs, bus voltages, shunt capacitors/reactors, transformers tap-setting and power flow of transmission lines. Simulation results on the Algerian Electrical Network show that the Ant Colony Optimization method converges quickly to the global optimum.

Multiple harmonic source detection and equipment identification with cascade correlation network

Abstract: This paper presents the design of a harmonic source detection system with a cascade correlation network (CCN). Current-injection-based harmonic power flow was used to calculate bus voltages and total harmonic distortion (THD). THD of voltages is used as indices for meter placement in the power network. At metering buses, it shows that the harmonic components of voltages under various loads would form particular patterns in the frequency domain, and can be used to create training examples for CCN. Good meter planning is helpful to reduce the number of meters and training examples. With an IEEE 14-bus power system, computer simulations were conducted to show the effectiveness of the proposed system.

Fault analysis in four-wire distribution networks

Abstract: The neutral wire in most existing power flow and fault analysis software is usually merged into phase wires using Kron's reduction method. In some applications, such as fault analysis, fault location, power quality studies, safety analysis, loss analysis etc., knowledge of the neutral wire and ground currents and voltages could be of particular interest. A general short-circuit analysis algorithm for three-phase four-wire distribution networks, based on the hybrid compensation method, is presented. In this novel use of the technique, the neutral wire and assumed ground conductor are explicitly represented. A generalised fault analysis method is applied to the distribution network for conditions with and without embedded generation. Results obtained from several case studies on medium- and low-voltage test networks with unbalanced loads, for isolated and multi-grounded neutral scenarios, are presented and discussed. Simulation results show the effects of neutrals and system grounding on the operation of the distribution feeders.

Signal propagation modeling in power-line communication networks

Abstract: In this paper, we present a propagation model for the power-line communication (PLC) networks, based on the frequency-domain analysis. First, we set a simple two-port model of the network. Then, we calculate a complex attenuation factor from z-parameters, expressed in terms of impedances, easily calculable/measurable from the network ports. We explain simultaneously calculation and measurement methods based on the same principle, and then compare the results with direct measurements performed in the network designed for this purpose. We provide all of the elements for a simple end efficient propagation model. They include propagation by crosstalk between different circuits in, for example, three-phase networks, as well as the influence of the loads connected to the ports of different circuits in such networks. We have concluded that the model is suitable for PLC channels simulations that give very accurate results and enable modeling of wide-band channel characteristics.

Inclusion of robustness into design using optimization-enabled transient simulation

Abstract: This paper presents an approach to the design of robust power-electronic systems (i.e., those which have optimal operation over a range of operating configurations). Designing nonlinear systems, such as power-electronic converters, to be robust is a challenging task as settings that may be optimal for a given operating configuration may be inadequate for another. This paper extends the method of combining nonlinear optimization with electromagnetic transient simulation, which has previously been successfully applied to the design of optimal systems at only one operating point; to an approach which simultaneously considers a range of operating points. The method is exemplified using two examples. In the first example, a dc power supply is designed to operate optimally over a range of current order settings. The second is the case of an HVdc system, which is optimized to work well with a range of possible ac system configurations.

Parabolic Differential-Algebraic Models in Electrical Network Design

Abstract: In refined network analysis, a compact network model is combined with distributed models for semiconductor devices in a multidimensional approach. For linear RLC networks containing diodes as distributed devices, we construct a mathematical model that joins the differential-algebraic initial value problem for the electric circuit with parabolic-elliptic boundary value problems modeling the diodes. For this mixed initial boundary value problem of partial differential-algebraic equations a first existence and uniqueness result is given, and its asymptotic behavior is discussed.

Aircraft applicable circuit imbalance detection and circuit interrupter and packaging thereof

Abstract: The aircraft applicable current imbalance detection and circuit interrupter interrupts an electrical circuit when a current imbalance is sensed. The current imbalance detection and circuit interrupter includes a housing, power supplies, a sensor system for sensing a current imbalance at the line side of the electrical circuit, a logic controller and a power controller including a power relay having contacts capable of surviving carry-break and make-carry-break types of ground fault conditions at anticipated current levels. At power up, the device performs a test to confirm that none of the relay contacts have failed in a closed position, and to check whether a switching FET which controls the relay coil has shorted.

Design of a miniature permanent-magnet generator and energy storage system

Abstract: The paper describes a methodology for optimizing the design and performance of a miniature permanent-magnet generator and its associated energy storage system. It combines an analytical field model, a lumped reluctance equivalent magnetic circuit, and an equivalent electrical circuit. Its utility is demonstrated by means of a case study on a 15-mW, 6000-r/min generator, and the analysis techniques are validated by measurements on a prototype system.