Showing papers on "Electrical network published in 2012"

Network meta‐analysis, electrical networks and graph theory

Abstract: Network meta-analysis is an active field of research in clinical biostatistics. It aims to combine information from all randomized comparisons among a set of treatments for a given medical condition. We show how graph-theoretical methods can be applied to network meta-analysis. A meta-analytic graph consists of vertices (treatments) and edges (randomized comparisons). We illustrate the correspondence between meta-analytic networks and electrical networks, where variance corresponds to resistance, treatment effects to voltage, and weighted treatment effects to current flows. Based thereon, we then show that graph-theoretical methods that have been routinely applied to electrical networks also work well in network meta-analysis. In more detail, the resulting consistent treatment effects induced in the edges can be estimated via the Moore-Penrose pseudoinverse of the Laplacian matrix. Moreover, the variances of the treatment effects are estimated in analogy to electrical effective resistances. It is shown that this method, being computationally simple, leads to the usual fixed effect model estimate when applied to pairwise meta-analysis and is consistent with published results when applied to network meta-analysis examples from the literature. Moreover, problems of heterogeneity and inconsistency, random effects modeling and including multi-armed trials are addressed. Copyright © 2012 John Wiley & Sons, Ltd.

A hybrid battery model capable of capturing dynamic circuit characteristics and nonlinear capacity effects

Abstract: Summary form only given. A high-fidelity battery model capable of accurately predicting battery performance is required for proper design and operation of battery-powered systems. However, the existing battery models have at least one of the following drawbacks: 1) requiring intensive computation due to high complexity, 2) not applicable for electrical circuit design and simulation, and 3) not capable of accurately capturing the state of charge (SOC) and predicting runtime of the battery due to neglecting the nonlinear capacity effects. This paper proposes a novel hybrid battery model, which takes the advantages of an electrical circuit battery model to accurately predicting the dynamic circuit characteristics of the battery and an analytical battery model to capturing the nonlinear capacity effects for accurate SOC tracking and runtime prediction of the battery. The proposed battery model is validated by simulation and experimental studies for single-cell and multicell polymer lithium-ion batteries as well as for a lead-acid battery. The proposed model is applicable to other types and sizes of electrochemical battery cells. The proposed battery model is computational effective for simulation, design, and real-time management of battery-powered systems.

Optimal Electric Network Design for a Large Offshore Wind Farm Based on a Modified Genetic Algorithm Approach

Abstract: The increasing development of large-scale offshore wind farms around the world has caused many new technical and economic challenges to emerge. The capital cost of the electrical network that supports a large offshore wind farm constitutes a significant proportion of the total cost of the wind farm. Thus, finding the optimal design of this electrical network is an important task, a task that is addressed in this paper. A cost model has been developed that includes a more realistic treatment of the cost of transformers, transformer substations, and cables. These improvements make this cost model more detailed than others that are currently in use. A novel solution algorithm is used. This algorithm is based on an improved genetic algorithm and includes a specific algorithm that considers different cable cross sections when designing the radial arrays. The proposed approach is tested with a large offshore wind farm; this testing has shown that the proposed algorithm produces valid optimal electrical network designs.

Time-domain and frequency-domain modeling of nonlinear optical components at the circuit-level using a node-based approach

Abstract: We present a tool that aids in the modeling of optical circuits, both in the frequency and in the time domain. The tool is based on the definition of a node, which can have both an instantaneous input-output relation and different state variables (e.g., temperature and carrier density) and differential equations for these states. Furthermore, each node has access to part of its input history, allowing the creation of delay lines or digital filters. Additionally, a node can contain subnodes, allowing the creation of hierarchical networks. This tool can be used in numerous applications such as frequency-domain analysis of optical ring filters, time-domain analysis of optical amplifiers, microdisks, and microcavities. Although we mainly use this tool to model optical circuits, it can also be used to model other classes of dynamical systems, such as electrical circuits and neural networks.

Modeling and simulation of equivalent circuits in description of biological systems - a fractional calculus approach

Abstract: Using the fractional calculus approach, we present the Laplace analysis of an equivalent electrical circuit for a multilayered system, which includes distributed elements of the Cole model type. The Bode graphs are obtained from the numerical simulation of the corresponding transfer functions using arbitrary electrical parameters in order to illustrate the methodology. A numerical Laplace transform is used with respect to the simulation of the fractional differential equations. From the results shown in the analysis, we obtain the formula for the equivalent electrical circuit of a simple spectrum, such as that generated by a real sample of blood tissue, and the corresponding Nyquist diagrams. In addition to maintaining consistency in adjusted electrical parameters, the advantage of using fractional differential equations in the study of the impedance spectra is made clear in the analysis used to determine a compact formula for the equivalent electrical circuit, which includes the Cole model and a simple RC model as special cases.

Simulation and real-time implementation of shunt active filter i d -i q control strategy for mitigation of harmonics with different fuzzy membership functions

Abstract: In this research study, the shunt active filter (SHAF) is used to improve the power quality of the electrical network by mitigating the harmonics with the help of different fuzzy membership functions (M.Fs) (trapezoidal, triangular and Gaussian). It is quite difficult to optimise the performance of power system networks using conventional methods, because of the complex nature of the systems that are highly non-linear and non-stationary. Three-phase reference current waveforms generated by the proposed scheme are tracked by the three-phase voltage source converter in a hysteresis band control scheme. The performance of the proposed control strategy has been evaluated in terms of harmonic mitigation and dc-link voltage regulation under various source conditions. The proposed SHAF with different fuzzy M.Fs is able to eliminate the uncertainty in the system and SHAF gains outstanding compensation abilities. The detailed simulation results using Matlab/Simulink software are presented to support the feasibility of the proposed control strategy. To validate the proposed approach, the system is also implemented on a real-time digital simulator hardware and adequate results are reported for its verification.

Systems and methods for detecting faults and/or adjusting electrical therapy based on impedance changes

Abstract: System and methods for detecting impedance changes and for adjusting electrical therapy based on impedance changes are disclosed herein. A method in accordance with a particular embodiment includes applying a therapeutic, paresthesialess electrical signal to a patient via a patient modulation system that includes a signal delivery device in electrical communication with a target neural population of the patient. The method can include monitoring on a periodic basis an impedance of an electrical circuit that includes the signal delivery device. The method can further include detecting a change in the impedance that indicates a fault and providing an indication that the fault exists.

An Equivalent Electrical Circuit Model of Proton Exchange Membrane Fuel Cells Based on Mathematical Modelling

Abstract: Many of the Proton Exchange Membrane Fuel Cell (PEMFC) models proposed in the literature consist of mathematical equations. However, they are not adequately practical for simulating power systems. The proposed model takes into account phenomena such as activation polarization, ohmic polarization, double layer capacitance and mass transport effects present in a PEM fuel cell. Using electrical analogies and a mathematical modeling of PEMFC, the circuit model is established. To evaluate the effectiveness of the circuit model, its static and dynamic performances under load step changes are simulated and compared to the numerical results obtained by solving the mathematical model. Finally, the applicability of our model is demonstrated by simulating a practical system.

Constant-Parameter $RL$ -Branch Equivalent Circuit for Interfacing AC Machine Models in State-Variable-Based Simulation Packages

Abstract: Transient simulation programs, either nodal analysis-based electromagnetic transient program (EMTP-like) or state-variable-based, are used very extensively for modeling and simulation of various power and energy systems with electrical machines. It has been shown in the literature that the method of interfacing machine models with the external electrical network plays an important role in numerical accuracy and computational performance of the overall simulation. This paper considers the state-variable-based simulation packages, and provides a constant-parameter decoupled RL-branch equivalent circuit for interfacing the ac induction and synchronous machine models with the external electrical network. The proposed interfacing circuit is based on the voltage-behind-reactance formulation which has been shown to have advantageous properties. For the synchronous machines, this paper describes both implicit and explicit (approximate) interfacing methods. The presented case studies demonstrate the advantages of using the proposed interfacing method over the traditional -models that are conventionally used in many simulation packages.

Port-Hamiltonian Formulation of Systems With Memory

Abstract: In this paper, we consider memristors, meminductors, and memcapacitors and their properties as port-Hamiltonian systems. The port-Hamiltonian formalism naturally arises from network modeling of physical systems in a variety of domains. Exposing the relation between the energy storage, dissipation, and interconnection structure, this framework underscores the physics of the system. One of the strong aspects of the port-Hamiltonian formalism is that a power-preserving interconnection between port-Hamiltonian systems results in another port-Hamiltonian system with composite energy, dissipation, and interconnection structure. This feature can advantageously be used to model, analyze, and simulate networks consisting of complex interconnections of both conventional and memory circuit elements. Furthermore, the port-Hamiltonian formalism naturally extends the fundamental properties of the memory elements beyond the realm of electrical circuits.

Micro electrical network energy management system

Abstract: The utility model provides a micro electrical network energy management system which is suitable for micro electrical network energy management and provides monitoring and control functions for a micro electrical network system which comprises distributed power supply and energy storage units such as wind power generation, photovoltaic generation, minimized gas turbines etc. The energy management system can monitor running states of a whole micro electrical network, makes corresponding optimal control strategies according to current electrical network running conditions and external application requests, employs reasonable energy management optimization technique to utilize the distributed power supply as fully as possible according to power output characteristics of the distributed power supply and fully exploits low carbon and economic advantages of the micro electrical network.

Combination of power flow controller and short-circuit limiter in distribution electrical network using a cascaded H-bridge distribution-static synchronous series compensator

Abstract: A novel method to limit the short-circuit current in the distribution network is introduced in this study. The short-circuit limiter is a part of cascade H-bridge distribution-static synchronous series compensator (D-SSSC), which is placed in series with the line to manage the power flow in the loop distribution network. Hence, the short-circuit limitation and power flow management is achieved using only one power converter. During the fault, the D-SSSC inverter is changed to a rectifier by turning off the converter switches and using the anti parallel diodes. The transient thermal analysis of the converter verifies that the components operate within the safe operation area during the fault. The appropriate selection of the DC bus capacitors are discussed both, to limit the fault current below the diode surge current, and to prepare adequate reactive power for normal power flow control. Simulation studies are based on a model inspired by a part of the Tehran electrical distribution network. Moreover, a seven level cascade H-bridge is implemented to control the power flow and to limit the short-circuit in the simple line model.

Wind power integration

Abstract: This chapter presents an overview of the opportunities and problems associated with the integration of wind energy into electrical networks currently in operation or under development. A description is given of the requirements for wind energy integration and the consequences that the particular characteristics of this energy source, namely, its unpredictability and the fluctuations of the generated power, can give rise to in the electrical network to which it is connected. A presentation is made of distributed systems, and the benefits of wind energy integration into normal interconnected microgrids and stand-alone microgrids are described. This is followed by a discussion of wind forecasting and economic questions. Finally, future trends of these systems are described.

Communication-based secondary control in microgrids with voltage-based droop control

Abstract: Smart microgrids are becoming an important concept to cope with the increasing demand of electricity and to integrate the large amounts of intermittent power sources in the electrical network. Microgrids are able to operate in grid-connected and islanded mode and present themselves to the utility network as controllable entities. For the primary control of the inverter-interfaced DG units, voltage-based droop controllers have been developed. With this fully distributed controller, an optimized integration of renewable energy is obtained, by possibly increasing the penetration depth of renewable DG units and mitigating over-voltage conditions. The main reason is the usage of a constant-power band with a width dependent on the nature of the energy source. This paper investigates the usage of secondary control in a microgrid with primary voltage droops. The secondary control operates at a slower rate than the voltage-based primary control and is communication-based, opposed to the primary controller. The secondary controller regulates the voltage at pilot points in the microgrid, the voltage at the point of common coupling or the power exchange between microgrid and utility network. The set-points for secondary control can be determined based on an optimisation scheme such as for losses, power quality and economic revenue. Dependent on these set-points, the microgrid secondary controller changes the power set-points of the DG units.

Evaluation of induced AC voltages in underground metallic pipeline

Abstract: Purpose – The purpose of this paper is to make a study of electromagnetic interference between electrical power lines and nearby underground metallic pipelines.Design/methodology/approach – The equivalent electrical circuit of the studied electromagnetic interference problem between electrical power lines and nearby metallic pipelines is created and solved using a loop currents technique based on a hybrid method. The used circuit solving technique was implemented in a software application developed by the authors.Findings – The authors have identified the influence of phase sequence on induced voltage level in an underground pipeline for a double circuit electrical power line. Also the effect of different normal operation and phase to earth fault currents have been revealed.Practical implications – The study has been made through a research project with the Romanian gas transportation company, in order to find the proper protection techniques for underground metallic pipelines.Originality/value – The pape...

Optimal Power Flow Solution of the Algerian Electrical Network using Differential Evolution Algorithm

Abstract: This paper presents solution of optimal power flow (OPF) problem of a power system via Differential Evolution (DE) algorithm. The purpose of an electric power system is to deliver real power to the greatest number of users at the lowest possible cost all the time. So the objective is to minimize the total fuel cost of the generating units and also maintaining an acceptable system performance in terms of limits on generator reactive power outputs, bus voltages, Static VAR Compensator (SVC) parameters and overload in transmission lines. CPU times can be reduced by decomposing the problem in two subproblems, the first subproblem minimize the fuel cost of generation and the second subproblem is a reactive power dispatch so optimum bus voltages can be determined and reduce the losses by controlling tap changes of the transformers and the static Var Compensators (SVC). To verify the proposed approach and for comparison purposes, we perform simulations on the Algerian network with 114 buses, 175 branches (lines and transformers) and 15 generators. The obtained results indicate that DE is an easy to use, fast, robust and powerful optimization technique compared to the other global optimization methods such as PSO and GA.

Decoupled Double Synchronous Reference Frame current controller for unbalanced grid voltage conditions

Abstract: Due to the growing changes in the electrical network related to the new distributed generation scheme and the integration of renewable energy sources, new requirements for grid-connected power converters are being defined in the new grid codes. The injection of positive- and negative-sequence current components is becoming necessary for achieving new capabilities like the reactive power injection during a grid fault. This paper deals with a fundamental issue in this topic, i.e., the performance of the current controller. Classical dq controllers, which are extensively used in industrial applications, degrade its performance when both sequences are involved, as unavoidable oscillations in the dq axes appear. In this paper, a new scheme for controlling positive- and negative-sequence currents using dq controllers is proposed, based on an enhanced Double Synchronous Reference Frame (DSRF) controller. In this paper the DSRF controller is improved by adding a decoupling network which counteracts the oscillations caused by the presence of both sequences. Experimental results will demonstrate the validity of the proposed Decoupled DSRF (DDSRF) controller.

Optimization of the current flowing technique aimed at semi-passive multi-modal vibration reduction:

Abstract: The paper deals with the analysis and optimization of a semi-passive multi-modal vibration attenuation technique exploiting piezo-benders actuators. Although there are different methods available in the literature, attention has been focused on the current flowing technique as it has a number of advantages with respect to the other approaches. In this context the control bender is linked to an electrical impedance, designed to maximize the mechanical energy dissipation. Though the method has already been presented in the literature, many points have still to be investigated. The paper gives a deeper analysis of this control technique and then presents an algorithm aimed at optimizing the electrical network linked to the bender.

Method for Making an Electrical Circuit

Abstract: A method for making an electrical circuit comprises the steps of: forming a rigid printed circuit board having a plurality of electrical contacts on at least one surface; forming a multilayer flexible circuit board having a plurality of electrical components on at least one surface, and further having a bifurcated area along one edge; forming electrode pads on the inner surfaces of the bifurcated area of the flexible circuit board that are alignable respectively with the electrical contacts on the rigid circuit board when the bifurcated area is spread apart by about 180°; spreading the bifurcated area apart and aligning the electrode pads respectively with the electrical contacts; and forming an electrical connection between the electrode pads and the electrical contacts.

AC and DC power quality of photovoltaic systems

Abstract: Since the penetration of photovoltaic (PV) systems in the electrical network is increasing, the need to register and model the contribution of these systems, in terms of disturbances and power availability, is becoming a crucial issue for optimal management of grid. On the other hand, electrical signature of sources and loads is the unique generation/consumption pattern intrinsic to each individual electrical appliance/piece of equipment. So, this paper, starting from the analysis of the disturbance impact of a 20 kW grid connected PV system, performs a preliminary study on building a method to better understand and explore the nature of electricity generation patterns of PV plants. Through this knowledge, it is possible to explore and develop innovative applications to achieve better utilization of resources and develop more intelligent ways of operation in new smart grids.

Quantitative Power Quality and Characteristic Analysis of Multilevel Pulsewidth-Modulation Methods for Three-Level Neutral-Point-Clamped Medium-Voltage Industrial Drives

Abstract: The inherent low switching frequency in medium-voltage alternating-current industrial drives presents power-quality and filter-design challenges. In this paper, four multilevel pulsewidth-modulation methods; phase disposition (PD), switching-loss minimization (SLM), and selective harmonic elimination (SHE) up to the 17th and 29th harmonics, respectively, are considered. The characteristics of long-cable effects on common-mode voltage (CMV) and differential-mode voltage (DMV), inverter losses and efficiency, induction machine voltage, and current harmonics are analyzed. Very little has been published in these quantitative comparisons. It is shown that the SHE method has reduced CMV as compared with the PD and SLM algorithms. Elimination of up to the 29th harmonic achieves the best harmonic performance without needing an output filter, at the expense that the losses are higher with a lower efficiency. Analytical and simulation results using the Piecewise Linear Electrical Circuit Simulation for the power-electronic circuits and MATLAB/Simulink for control systems are experimentally verified with a 1000-hp 4160-V neutral-point-clamped adjustable-speed-drive system that includes a 24-pulse front-end voltage source converter.

Investigation of Nigerian 330 kV Electrical Network with Distributed Generation Penetration – Part I: Basic Analyses

Abstract: The objective of this paper is to present the tools implemented in PowerFactory for the optimization of the proposed network. It involves the calculate optimal power flow analysis (OPF); optimal placement, type and size of capacitors in the net- work; the optimal type of reinforcement cables and overhead lines and lastly, optimization of a certain objective function in a network, whilst fulfilling equality constraints (the load flow equations) and inequality constraints (that is, generator reactive pow- er limits). The applications of the OPF include transmission line overload removal, transmission system control, available transfer capability calculation (ATC), real and reactive power pricing, transmission component valuation, and transmission system mar- ginal pricing. Power capacitors are very useful for power factor correction, loss reduction, voltage profile improvement and dis- tribution system-capacity release/increase. The conductor, which is determined by this optimization method, maintains acceptable voltage levels of the radial distribution system. Besides, it gives maximum saving in the capital cost of conducting material and cost of energy losses. The method also shows that only proper selection of optimum branch conductors reduces losses.

Models for Impact Assessment of Wind-Based Power Generation on Frequency Control

Abstract: This chapter develops a modeling framework for studying the impact of variability and uncertainty in wind-based electricity generation on power system frequency. The focus is on timescales involving governor response (primary frequency control) and automatic generation control (AGC) (secondary frequency control). The framework includes models of synchronous generators, wind-based electricity sources, the electrical network, and the AGC system. The framework can be used to study the impact of different renewable penetration scenarios on system frequency performance metrics. In order to illustrate the framework, a simplified model of the Western Electricity Coordinating Council (WECC) system is developed.

Optimal Power Flow Solution of the Algerian Electrical Network using Differential Evolution Algorithm

Abstract: This paper presents solution of optimal power flow (OPF) problem of a power system via differential evolution (DE) algorithm. The purpose of an electric power system is to deliver real power to the greatest number of users at the lowest possible cost all the time. So the objective is to minimize the total fuel cost of the generating units and also maintaining an acceptable system performance in terms of limits on generator reactive power outputs, bus voltages, static VAR compensator (SVC) parameters and overload in transmission lines. CPU times can be reduced by decomposing the problem in two subproblems, the first subproblem minimize the fuel cost of generation and the second subproblem is a reactive power dispatch so optimum bus voltages can be determined and reduce the losses by controlling tap changes of the transformers and the static VAR compensators (SVC). To verify the proposed approach and for comparison purposes, we perform simulations on the Algerian network with 114 buses, 175 branches (lines and transformers) and 15 generators. The obtained results indicate that DE is an easy to use, fast, robust and powerful optimization technique compared to the other global optimization methods such as PSO and GA.

A Novel Method for Connecting Multiple Piezoelectric Transformer Converters and its Circuit Application

Abstract: The electrical circuit and model of piezoelectric transformers (PTs) ELS-60 is developed. Rosen-type PT and many other nonisolated conversion circuits have the inherit problem of the common neutral between the input and output that make it difficult to connect the output in series like the magnetic transformer. A new method based on the bootstrap method is proposed to solve the aforementioned problem. A new circuit for output summation of voltage level in the output side of each PT is developed. The impact of load and output filter capacitor on the conversion ratio and resonant frequency is discussed. Experimental results based on one printed circuit board prototype of double-level PT and boost convertor validate the previous theoretical analysis and simulation results. The paper finally proposes a multilevel concept for many PT connected together for voltage summation. The method proposed can be applied to other multiple conversion circuits, which are based on common neutral between the input and output.