Showing papers on "Electrical network published in 2015"

An Optimal and Distributed Method for Voltage Regulation in Power Distribution Systems

Abstract: This paper addresses the problem of voltage regulation in power distribution networks with deep-penetration of distributed energy resources, e.g., renewable-based generation, and storage-capable loads such as plug-in hybrid electric vehicles. We cast the problem as an optimization program, where the objective is to minimize the losses in the network subject to constraints on bus voltage magnitudes, limits on active and reactive power injections, transmission line thermal limits and losses. We provide sufficient conditions under which the optimization problem can be solved via its convex relaxation. Using data from existing networks, we show that these sufficient conditions are expected to be satisfied by most networks. We also provide an efficient distributed algorithm to solve the problem. The algorithm adheres to a communication topology described by a graph that is the same as the graph that describes the electrical network topology. We illustrate the operation of the algorithm, including its robustness against communication link failures, through several case studies involving 5-, 34-, and 123-bus power distribution systems.

Fractional electrical circuits

Abstract: We study three different types of electrical circuit equations using fractional calculus and various definitions of fractional derivative therein. Using plotting tools, we compare different types of solutions of each equation among themselves as well as with its classical solution.

Identification of a Proton-Exchange Membrane Fuel Cell’s Model Parameters by Means of an Evolution Strategy

Abstract: This paper presents the parameter identification of an equivalent circuit-based proton-exchange membrane fuel cell model. This model is represented by two electrical circuits, of which one reproduces the fuel cell’s output voltage characteristic and the other its thermal characteristic. The output voltage model includes activation, concentration, and ohmic losses, which describe the static properties, while the double-layer charging effect, which delays in fuel and oxygen supplies, and other effects provide the model’s dynamic properties. In addition, a novel thermal model of the studied Ballard’s 1.2-kW Nexa fuel cell is proposed. The latter includes the thermal effects of the stack’s fan, which significantly improve the model’s accuracy. The parameters of both, the electrical and the thermal, equivalent circuits were estimated on the basis of experimental data using an evolution strategy. The resulting parameters were validated by the measurement data obtained from the Nexa module. The comparison indicates a good agreement between the simulation and the experiment. In addition to simulations, the identified model is also suitable for usage in real-time fuel cell emulators. The emulator presented in this paper additionally proves the accuracy of the obtained model and the effectiveness of using an evolution strategy for identification of the fuel cell’s parameters.

Electrical characteristics of cold ironing energy supply for berthed ships

Abstract: The reduction of emissions in harbours is of particular importance due to the proximity to human habitation. Vessels normally run onboard generators, typically using diesel fuel, to provide the service loads while berthed. New and upcoming regulations aim to decrease emissions from shipping, and coupled with increased environmental consciousness of ship owners and harbour operators, shore supply is becoming a more popular and feasible option. Cold ironing provides an alternative locally emission-free solution by having berthed ships plug in to the shore electrical network, such that the onboard electrical energy demand is supplied from land. Electrically, a number of different shore network topologies are possible, providing different infrastructural options of supplying power to multiple berths. This paper examines the electrical characteristics of one such installation and the impact on the shoreside electrical network for an existing port using actual visiting ship power profiles. The paper examines how the cold ironing system influences important electrical network characteristics such as bus voltages and power quality, as well as the potential impact on the rest of the utility distribution system.

Multimodal vibration damping of a beam with a periodic array of piezoelectric patches connected to a passive electrical network

Abstract: A multimodal damping strategy is implemented by coupling a beam to its analogue electrical network. This network comes from the direct electromechanical analogy applied to a transverse lattice of point masses that represents the discrete model of a beam. The mechanical and electrical structures are connected together through an array of piezoelectric patches. A discrete and a semi-continuous model are proposed to describe the piezoelectric coupling. Both are based on the transfer matrix formulation and consider a finite number of patches. It is shown that a simple coupling condition gives a network that approximates the modal properties of the beam. A multimodal tuned mass effect is then obtained and a wide-band damping is introduced by choosing a suitable positioning for resistors in the network. The strategy and the models are experimentally validated by coupling a free-free beam to a completely passive network. A multimodal vibration reduction is observed, which proves the efficiency of the control solution and its potential in term of practical implementation.

Realizability of Fractional-Order Impedances by Passive Electrical Networks Composed of a Fractional Capacitor and RLC Components

Abstract: This paper deals with realization of fractional-order impedance functions by passive electrical networks composed of a fractional capacitor and some RLC components. The necessary and sufficient conditions for the existence of such a realization are found in a general case. Also for impedance functions described by a class of fractional-order transfer functions, the realizability conditions are stated as some algebraic conditions on the parameters of the transfer function. Moreover, a procedure is proposed for implementation of such impedance functions by passive electrical networks composed of a fractional capacitor and some RLC components. Numerical examples are presented to show the usefulness of the results of the paper in design of fractional-order electrical circuits.

A New Solution for Low-Voltage Distributed Generation Interface Protection System

Abstract: In this paper, a new solution is proposed for the remote monitoring and control of distributed generators (DGs) and energy storage systems (ESSs) connected to low-voltage distribution networks. The proposed system fulfills the in-force standard requirements for the connection of DGs to the utility grid. Moreover, it allows implementing some enhanced functions for the remote control of inverters of DGs and ESSs, not only in terms of disconnection but also in terms of voltage regulation and power shuttering. The proposed solution is based on a new interface protection system and a dedicated secondary substation concentrator, which allows the communication between the distributed system operator and the inverters of DGs or ESSs. The proposed system was tested on field in the electrical network of the island of Ustica. An experimental characterization was carried out to find the best communication conditions, i.e., the frequency band with the lowest noise and attenuation, considering the signal amplitude and signal-to-noise ratio constraints, as well as the desired transmission data rate and transfer time.

High-Frequency Planar Transformer Parameter Estimation

Abstract: This paper presents different methods to determine the parameters for the equivalent electrical circuit model of a high-frequency planar transformer. The first method is implemented in the circuit simulation software utilizing a 1-D electromagnetic analysis. The second method uses a 3-D electromagnetic analysis and is implemented in a finite-element analysis software. The third method is a differential evolution (DE)-based algorithm using the experimental transformer data. The first two methods are useful in the design stage to predict the performance of a planar transformer, while the third one can be applied to validate the design. The performance and accuracy of the three methods are assessed by comparing each method’s parameter estimate of an actual planar transformer. The comparison showed that the predictions of magnetizing inductance by the two numerical analyses are accurate and comparable with that of the DE-based estimation method. However, the series resistance and leakage inductance determined by the DE algorithm tend to be higher, as predicted by the two numerical methods, due to the nonconsideration of the measuring leads impedance in the numerical models.

Oscillatory phenomena between wind farms and HVDC systems: The impact of control

Abstract: Field experience has shown that sub-synchronous oscillation (SSO) and harmonic resonance can happen due to the interaction of wind energy conversion system's (WECS) converter controller, HVDC converter controller and impact of system impedance. This paper investigates the operation and control of WECS employing full-scale converter connected to the electrical network through voltage source converter (VSC)-based high voltage dc (HVDC) transmission system. SSO and harmonic resonance are observed depending on the control implementation of the ac collection bus side HVDC converter. The origin of these oscillations can be attributed to the propagation of the WECS 15 Hz resonance through the WECS full converter DC link and the interaction between the WECS and the dc link dynamics of the HVDC system. An active damping scheme is proposed to improve the system performance. The active damping is implemented to an offshore HVDC system installed with the purpose of integrating two wind farms. An analysis and time domain simulation results and its spectral analysis are presented to show how effective the application of the proposed active damping is.

Current Controllers of Active Power Filter for Power Quality Improvement: A Technical Analysis

Abstract: Non-linear load deteriorates the quality of current waveforms at the point of common coupling of various consumers. Active power filter (APFs) is used to mitigate the most concern harmonic pollution in an electrical network. The controller part is the nucleus of an active power filter configuration. Active power filter performance is affected significantly by the selection of current control techniques. The active filter and its current control must have the capability to track sudden slope variations in the current reference to compensate the distorted current drawn by the voltage source inverter. Therefore, the choice and implementation of the current regulator is more important for the achievement of a satisfactory performance level. In this survey, technical reviews of various types of controllers covering a wide range have been presented. This work also reveals the advantages and disadvantages of the practiced control strategies. The effectiveness of the study will help the researchers to choose the proper control methods for various applications of active power filter.

How Affine Arithmetic Helps Beat Uncertainties in Electrical Systems

Abstract: The ever-increasing impact of uncertainties in electronic circuits and systems is requiring the development of robust design tools capable of taking this inherent variability into account. Due to the computational inefficiency of repeated design trials, there has been a growing demand for smart simulation tools that can inherently and effectively capture the results of parameter variations on the system responses. To improve product performance, improve yield and reduce design cost, it is particularly relevant for the designer to be able to estimate worst-case responses. Within this framework, the article addresses the worst-case simulation of lumped and distributed electrical circuits. The application of interval-based methods, like interval analysis, Taylor models and affine arithmetic, is discussed and compared. The article reviews in particular the application of the affine arithmetic to complex algebra and fundamental matrix operations for the numerical frequency-domain simulation. A comprehensive and unambiguous discussion appears in fact to be missing in the available literature. The affine arithmetic turns out to be accurate and more efficient than traditional solutions based on Monte Carlo analysis. A selection of relevant examples, ranging from linear lumped circuits to distributed transmission-line structures, is used to illustrate this technique.

Development of a simulator-to-simulator interface for geographically distributed simulation of power systems in real time

Abstract: The geographically distributed simulation concept enables connecting laboratories over long distances with the goal of sharing simulation resources and integrating multiple (Power) Hardware-in-the-Loop setups. The main obstacle in applying this concept is the impact of the communication medium on fidelity and stability of the simulation. This paper presents advantages and challenges of developing a simulator-to-simulator interface based on the time-frequency representation of interface quantities. The proposed approach is first analyzed using a simple electrical circuit as case study, and then conclusions are verified on a larger system including voltage-source converters that realize a high-voltage dc point-to-point link which connects two ac systems. To assess the approach in a realistic framework, an Internet-distributed simulation platform that integrates two remote real-time digital simulators, OPAL-RT (located at University of South Carolina, USA) and OPAL-RT (located at RWTH Aachen University, Germany) is developed and both linear and nonlinear system models are simulated.

Quantities Affecting the Behavior of Vibrational Magnetostrictive Transducers

Abstract: Through the conversion from mechanical to electrical energy it is possible to monitor a vibrating machine of any kind by exploiting the mechanical energy produced by the vibration. To this end, one can use direct force devices inserted in the supports or in the kinematic chain of the vibrating contrivance or cantilever devices with seismic masses. Regarding the devices of the first type, the maximization of the electrical output depends on various parameters. This paper, through a combined experimental and modeling approach, analyzes the behavior of a transducer based on a rod of Terfenol-D. Many parameters are analyzed, such as the frequency of the vibration, amplitude of the force transmitted by the vibration, characteristics of the coupled electrical circuit, magnetic, and mechanical bias. It is shown how the output power and electrical current are strongly influenced by the mechanical and magnetic bias. In addition, avoiding tensile stresses, this paper shows how the maximum output power is obtained when the mechanical bias is close to the amplitude of the dynamic force imposed by the vibration.

Smart grid: Algorithms for control of active-adaptive network components

Abstract: The construction of automated systems intended for the control of electric power systems requires high-speed mathematical tools. The research is aimed at developing algorithms for the construction of automated systems to control active components of the electrical network. The method applied by the authors to describe the object of control is based on the universal approach to the mathematical modeling of nonlinear dynamic system of a black-box type represented by the Volterra polynomial of the N-th degree. The paper presents a new algorithm for the identification of Volterra polynomial of the second degree for non-stationary dynamic systems which allow an active experiment using test sets of input signals. This makes it possible for the input and output characteristics of the object to obtain an adequate and fast mathematical description. The results enable us to assess the applicability of this mathematical apparatus to the control of active components of electric power system in which power quality parameters are taken into account as an objective vector.

Modeling Percolation in Polymer Nanocomposites by Stochastic Microstructuring

Abstract: A methodology was developed for the prediction of the electrical properties of carbon nanotube-polymer nanocomposites via Monte Carlo computational simulations. A two-dimensional microstructure that takes into account waviness, fiber length and diameter distributions is used as a representative volume element. Fiber interactions in the microstructure are identified and then modeled as an equivalent electrical circuit, assuming one-third metallic and two-thirds semiconductor nanotubes. Tunneling paths in the microstructure are also modeled as electrical resistors, and crossing fibers are accounted for by assuming a contact resistance associated with them. The equivalent resistor network is then converted into a set of linear equations using nodal voltage analysis, which is then solved by means of the Gauss-Jordan elimination method. Nodal voltages are obtained for the microstructure, from which the percolation probability, equivalent resistance and conductivity are calculated. Percolation probability curves and electrical conductivity values are compared to those found in the literature.

Normal positive electrical circuits

Abstract: A new notion of normal positive electrical circuits is proposed. It is shown that any positive second-order electrical circuit with 2-inputs and 2-outputs is normal and a positive electrical circuit with m-inputs and p-outputs (m, p ≥ 2) is normal if its system matrix A has distinct eigenvalues or its system matrix is symmetric.

Enhancement of microgrid dynamic responses under fault conditions using artificial neural network for fast changes of photovoltaic radiation and FLC for wind turbine

Abstract: Microgrid is a low voltage electrical network with distributed generations, energy storage devices and controllable loads. This paper utilizes artificial neural network (ANN) to predict the optimum voltages in order to extract the maximum power and increment the efficiency of photovoltaic system. In this regard, the optimum voltages are achieved by the genetic algorithm (GA). Then these optimum values are used in ANN method. The results of ANN-GA is compared with the other methods that verified the proposed method with high accuracy which can track the maximum power point (MPP) under different insolation and temperature circumstances and also, meet the load demand with less fluctuation around the MPP.; also it can increase the convergence speed to achieve the MPP. As well as, the evaluation of fuzzy logic controller (FLC) in comparison with the PI controller in pitch angle of wind turbine (WT) is carried out. In order to control the output power of wind turbine, by implementing the wind speed and active power as inputs of FLC, it has faster responses, smoother power curves, less oscillation than aforementioned methods which lead to improve the dynamic responses of WT. The models are developed and applied in the Matlab/Simulink program.

Design and Numerical Analysis of the 15 kV Class Coreless Inductive Type SFCL

Abstract: Superconducting fault current limiters (SFCLs) are the most attractive devices for the power network, because limiters can be used to limit the short current in electrical network. This paper presents the design, the numerical model, and the calculated electrical parameters of the new 15-kV class SFCL prototype. The coreless superconducting fault current limiter consists of three windings: a primary and secondary windings made of SF12050 tape and a parallel connected primary copper winding. All windings are inductively coupled and intended to work in liquid nitrogen. The transient magnetic FEM-circuit numerical models of SFCL were used to analyze the current, resistance, and temperature of SFCL in the limitation state.

Scalable model of PV cell in variable environment condition based on the manufacturer datasheet for circuit simulation

Abstract: The paper, starting from the well-known five-parameters model, proposed a new mathematical model of a Photo-Voltaic (PV) cell which can be used also for modeling a PV module or a PV string in any environment condition. The proposed approach allows to write a new descriptive equation, whose terms are function of the information always available in the modern datasheet of the PV module's manufacturers. This implies that no pre-processing of the datasheet's parameters is needed to use the proposed model, whichever are the solar irradiance and the cell/module temperature. Moreover, this model is interpreted from a circuital point of view, providing an electrical circuit constituted by basic electrical components. Particularly, in order to take into account the variability of the environment parameters, a variable resistor and several voltage-controlled sources are used.

Disturbance rejection via control by interconnection of port-Hamiltonian systems

Abstract: In this paper we present a new result on rejection of unmatched external disturbances on port-Hamiltonian systems using Control by Interconnection (CbI). The PHS structure is used to design a controller that rejects unmatched constant disturbances from non-passive outputs. In the PHS framework, the disturbance rejection problem has been addressed adding integral action and using a change of coordinates. In our approach, we avoid a change of coordinates keeping the original state vector, which contains variables with physical interpretation. The methodology proposed in this paper is illustrated on an electrical circuit and on a permanent magnet synchronous motor. Simulation of the later example shows the performance of the control design.

Capacitor and Method of Production Thereof

Abstract: The present invention relates generally to the fields of electrical engineering and electronics. More specifically, the present invention relates to passive components of electrical circuit and more particularly to a capacitor intended for energy storage and method of production thereof.

Two-layer predictive control of a micro-grid including stochastic energy sources

Abstract: A two-layer control scheme based on Model Predictive Control (MPC) operating at two different timescales is proposed for the energy management of a micro-grid (MG), including a battery, a gas-turbine generator, a photovoltaic (PV) generator and the input from the electrical network. The high-level optimizer, which acts at a slow timescale and relies on a simplified model of the system, is in charge of computing the nominal operating conditions for each MG component so as to optimize an economic performance index on the basis of available predictions for the PV generation and load request. The low-level controller acts at higher frequency, adjusts the MG operation, and relies on a stochastic MPC algorithm that ensures probabilistic constraints satisfaction. Detailed models and simulations of the overall control system are presented.

On equivalent resistance of electrical circuits

Abstract: While the standard (introductory physics) way of computing the equivalent resistance of nontrivial electrical circuits is based on Kirchhoff's rules, there is a mathematically and conceptually simpler approach, called the method of nodal potentials, whose basic variables are the values of the electric potential at the circuit's nodes. In this paper, we review the method of nodal potentials and illustrate it using the Wheatstone bridge as an example. We then derive a closed-form expression for the equivalent resistance of a generic circuit, which we apply to a few sample circuits. The result unveils a curious interplay between electrical circuits, matrix algebra, and graph theory and its applications to computer science. The paper is written at a level accessible by undergraduate students who are familiar with matrix arithmetic. Additional proofs and technical details are provided in appendices.