Emerald | COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering | Table of Contents

Full wave numerical modelling of terahertz systems for nondestructive evaluation of dielectric structures

Fri, 03 May 2013 00:00:00 +0100

Abstract

Purpose – The purpose of this paper is to describe the full-wave modelling of pulsed terahertz systems utilized in non-destructive testing. Design/methodology/approach – At the outset, some basic information on the terahertz NDT are outlined and then, general remarks on its numerical modelling are presented. Frequency domain FEM and time domain FDTD analysis is carried out. Finally comparison of computed and measured signals is shown in order to prove numerical analysis correctness. Findings – It is possible to model in a relatively simple way a terahertz system for nondestructive evaluation of dielectric materials. In contrast to other published work, the entire measuring setup is modelled, including photoconductive antenna with hemispherical lens, focusing lens and evaluated material with exemplary defect. Originality/value – This paper gives a description of the terahertz non-destructive testing system with comparison of simulated and measured results.

The application of chaotic PWM control for EMI suppression

Fri, 03 May 2013 00:00:00 +0100

Abstract

Purpose – Four-quadrant AC-DC converters are one kind of the most common and popular AC-DC converters, which are serious EMI sources. The purpose of this paper is to propose a novel control for four-quadrant AC-DC converters to suppress the generated electromagnetic interference (EMI). Design/methodology/approach – A chaotic carrier plays an important role to implement the chaotic PWM control. The relationship between the EMI distribution and carrier frequency is given by deducing and analyzing the harmonic components of the AC-DC converter. The comparison of chaotic PWM control and random PWM control in suppressing EMI are provided. Findings – The simulation results prove the effectiveness of the proposed chaotic PWM control on EMI reduction. Research limitations/implications – The effects of EMI suppression under different chaotic carriers will be theoretically analyzed in the future work. Practical implications – The proposed chaotic PWM control can suppress EMI for converters without adding additional devices or components, therefore, without increasing the volume, weight and cost of converters. Originality/value – In this paper, a novel chaotic pulse width modulation (PWM) control is proposed and implemented into a four-quadrant AC-DC converter for electromagnetic interference (EMI) suppression, moreover, the total harmonic distortion (THD) of the input AC current is also improved under chaotic PWM control.

Controller design for an electric power steering system based on LQR techniques

Fri, 03 May 2013 00:00:00 +0100

Abstract

Purpose – This paper aims to present a linear quadratic regulator (LQR) employed to improve performance of an electrical power steering (EPS) system. Design/methodology/approach – Generally, EPS is a full electric system having an electrical motor which provides the assist torque on the steering mechanism in order to reduce the workload and to enhance the steering feel of the driver during the steering process. Since the torque sensors are considerably expensive, the authors present a control strategy that eliminates the driver torque sensor by introducing a torque estimator. Three main technical areas are described in this paper. First, the principle and structure of EPS are presented including the dynamic model. Second, LQR and Kalman filter techniques are employed to derive an optimal controller for the EPS system. Finally, the simulations and hardware results are depicted. Findings – The combined tools of Matlab/Simulink and dSPACE provide the environment for modelling the controller in software and applying it to the actual hardware via a digital signal processing board based on the DS1401 MicroAutoBox. The controller is evaluated via simulation results, dSPACE hardware results, and verified on vehicle testing data. Originality/value – This paper presents a controller design for an EPS system based on the LQR techniques. Within the controller concept shown, elimination of the driver torque sensor offers advantages in terms of both cost and mechanical performance. Simulations and measured data prove the good functionality of the controller proposed.

M×N-ary chaotic pulse-width-position modulation: An effective combination method for improving bit rate

Fri, 03 May 2013 00:00:00 +0100

Abstract

Purpose – This paper presents and investigates a method named M×N-ary chaotic pulse-width-position modulation (CPWPM) which is based on the combination of M-ary chaotic pulse-position modulation (CPPM) and N-ary chaotic pulse-width modulation (CPWM) in order to provide a better performance in noise-affected environments as well as improve significantly bit rate. Design/methodology/approach – Analysis of schemes for modulator and demodulator are presented in detail through describing the schemes of the individual methods and their combination. Theoretical evaluation of bit-error rate (BER) performance in presence of additive white Gaussian noise (AWGN) is provided. Chaotic behavior with tent map in variation of modulation parameters is also investigated. In order to verify the theoretical analyses, numerical simulations are carried out and their results are reported. Findings – Both evaluation and simulation results show that when the number of symbols increases, the bit rate is improved significantly but the BER performance is just slightly worse. This makes M×N-ary CPWPM become an effective method for chaos-based digital communication. Originality/value – Although CPPM, CPWM and M-ary modulation methods have been described in the literature separately, their combination is presented and investigated for the first time in this paper.

Transient electromagnetic field, losses and forces in a synchronous turbogenerator rotor

Fri, 03 May 2013 00:00:00 +0100

Abstract

Purpose – The paper seeks to present a methodology of computer simulation of 3D transient electromagnetic fields, losses and forces due to negative sequence currents in fragments of large synchronous turbogenerator rotors. The methodology allows for the preparation of initial data for further computations of thermal and mechanical behaviour of rotors. Design/methodology/approach – The governing equations for 3D negative sequence transient electromagnetic fields with the Coulomb gauge using magnetic vector potential and scalar electric potential A, V – A are solved by the nodal finite element method in a Cartesian coordinate system moving synchronously with the rotor. Findings – The presented methodology of 3D transient electromagnetic phenomena computation seems to be effective because the electromagnetic field in the rotor of a synchronous generator is generally three dimensional, and therefore 2D field-computation approaches and software are not able to simulate intrinsically 3D electromagnetic processes in turbogenerator rotors. Research limitations/implications – Currently it is difficult to carry out accurate numerical simulation of 3D transient electromagnetic fields and therefore losses and forces within the whole structure of the rotor because of the resulting huge computational expenses. This paper is devoted to the finite element analysis of electromagnetic fields, losses and forces in separate structural parts of the rotor. As an example of practical utilization of the developed technique, the computer simulation of electromagnetic phenomena in junctions of nonmagnetic rotor slot wedges of a 300?MVA class synchronous turbogenerator is carried out. Practical implications – The methodology can successfully be used during the design process of modern large synchronous turbogenerators. Originality/value – This paper presents numerical analysis of intrinsically 3D transient electromagnetic phenomena in large turbogenerator rotors.

Determining the active and reactive power range in AC circuits

literatinetwork@emeraldinsight.com (Lubomir Kolev) — Fri, 03 May 2013 00:00:00 +0100

Abstract

Purpose – The purpose of this paper is to suggest a polynomial complexity method for determining the range of the active and reactive power consumed in AC uncertain parameter circuits whose uncertain parameters are given as intervals. Design/methodology/approach – First, the original problem is formulated as a corresponding interval quadratic range determination (IQRD) problem. Next, it is shown that the IQRD problem can be transformed equivalently into an interval linear range determination (ILRD) problem. Findings – An efficient numerical method for solving the associated ILRD problem has been developed, capable of tackling the present active (or reactive) power range problem. It is based on the use of the outer solution y of an associated interval linear system defining the constraints in the ILRD problem. Research limitations/implications – The method yields the exact active and reactive power range if the number of the components yi of y containing zero is relatively small (which is most often the case); otherwise, it provides tight outer bounds on the ranges sought. Practical implications – The present method can be an alternative to the widely used Monte-Carlo method since the former method provides exact (within rounding errors) results or tight outer approximations for lesser computation times. Originality/value – To the best of the author's knowledge, the present paper suggests, for the first time, a simple interval analysis method of polynomial complexity for solving the problem considered which is inherently a NP-hard problem (of exponential complexity).

A knowledge-supported improvement of the PSO method

literatinetwork@emeraldinsight.com (Deniz Sevis, Kamil Senel, Yagmur Denizhan) — Fri, 03 May 2013 00:00:00 +0100

Abstract

Purpose – The Particle Swarm Optimization (PSO) method makes few or no assumptions about the optimization problem at hand and is applicable without much information about the problem. Although this fact constitutes one of the most important advantages of the PSO method, it can also be considered as a waste of available knowledge about the specific problem, which could have drastically improved the search performance. This paper aims to introduce an improvement to the PSO method such that the exploitation of any available knowledge about the specific optimization problem can be combined with the powerful blind-search ability of the original method. Design/methodology/approach – The improvement is achieved by the so-called Knowledge Supported PSO (KS-PSO), which consists of a combination of two modes: a mode that operates according to the original PSO approach and a knowledge-based mode which the user has to design for the specific problem. Findings – The application of the proposed KS-PSO method is presented for two rather different optimization problems chosen from the domain of control and computer engineering: the model-free tuning of a Fractional-Order PID controller and the training of a single-layer perceptron. The simulation results demonstrate the performance improvement in KS-PSO as compared to the original PSO. Originality/value – This paper presents a novel version of the well-known PSO method, which achieves performance improvement by combining the original blind-search capability with the exploitation of available knowledge about the specific problem.

Advanced adaptive algorithms in 2D finite element method of higher order of accuracy

literatinetwork@emeraldinsight.com (Pavel Karban, František Mach, Ivo Doležel) — Fri, 03 May 2013 00:00:00 +0100

Abstract

Purpose – The paper presents the principal elements of automatic adaptivity built in our 2D software for monolithic solution of multiphysics problems based on a fully adaptive finite element method of higher order of accuracy. The adaptive techniques are illustrated by appropriate examples. Design/methodology/approach – Presented are algorithms for realization of the h-adaptivity, p-adaptivity, hp-adaptivity, creation of curvilinear elements for modelling general boundaries and interfaces. Indicated also is the possibility of combining triangular and quadrilateral elements (both classical and curved). Findings – The presented higher-order adaptive processes are reliable, robust and lead to a substantial reduction of the degrees of freedom in comparison with the techniques used in low-order finite element methods. They allow solving examples that are by classical approaches either unsolvable or solvable at a cost of high memory and time of computation. Research limitations/implications – The adaptive processes described in the paper are still limited to 2D computations. Their computer implementation is highly nontrivial (every physical field in a multiphysics task is generally solved on a different mesh satisfying its specific features) and in 3D the number of possible adaptive steps is many times higher. Practical implications – The described adaptive techniques may represent a powerful tool for the monolithic solution of complex multiphysics problems. Originality/value – The presented higher-order adaptive approach of solution is shown to provide better results than the schemes implemented in professional codes based on low-order finite element methods. Obtaining the results, moreover, requires less time and computer memory.

Characteristics study of an electronic systems design strategy

Fri, 03 May 2013 00:00:00 +0100

Abstract

Purpose – This work seeks to present the theoretical study considerations and the characteristics of a general design methodology in optimal time for electronic systems using numerical methods and optimal control theory. Through this, the design problem of a system is formulated in terms of optimal control in minimal time. Design/methodology/approach – This general design methodology includes the traditional design strategy (TDS), and the modified traditional design strategy (MTDS), where the model of the system is part of the optimization procedure but an objective function of the optimization process is constructed such as includes the traditional objective function and some penalty functions that feign the model of the system. Many special control functions are introduced artificially to generalize the methodology and produce several design trajectories for the same optimization process – the first and final trajectories correspond to TDS and MTDS, respectively. The combination of these trajectories produce an infinite number of design strategies, some of these are quasi-optimal in time and only one is optimal in time. Findings – Qualitative and numeric results of this iterative process are generated in a personal computer in a C++ language elaborated with a visual C++ graphic user interface. An algorithm is constructed to form an optimal in time design strategy switching from a MTDS subset to a TDS subset. Results of measured times are analyzed, showing that there is a control input U, such that the objective function is minimized in a minimum time. Originality/value – These ideas are proposed using method of gradient optimization and special acceleration effect.

Exact and Physical-Optics analysis of the electromagnetic scattering by an elliptic cone

literatinetwork@emeraldinsight.com (Michael Kijowski, Ludger Klinkenbusch) — Fri, 03 May 2013 00:00:00 +0100

Abstract

Purpose – The purpose of this paper is to compare exact and Physical-Optics-approximated results of the electromagnetic field scattered by a perfectly conducting semi-infinite elliptic cone illuminated by a plane wave. The results are important for judging the reliability of Physical-Optics based field estimations of electrically large environments which include tip-like structures (e.g. airport scenarios). Design/methodology/approach – The spherical-multipole analysis is applied to determine the exact total field outside a perfectly conducting semi-infinite elliptic cone. The underlying boundary-value problem is solved by a separation of variables of the Helmholtz equation in sphero-conal coordinates leading to a two-parametric eigenvalue problem with two coupled Lamé differential equations. The exact scattered far field is determined from the exact surface current on the cone using a bilinear expansion of the dyadic Green's function. The Physical-Optics (PO) field is evaluated similarly starting from a surface current which is directly found from the incident magnetic field. Findings – The diffraction coefficients of the exact scattered field and the PO scattered field are compared for different parameters (polarization and angle of incidence) of the plane wave. Reasonably well corresponding results are obtained for those angles of incidence of the plane wave where the entire cone is illuminated, otherwise the error of the PO approximation is increasing not just in the shadow region. Originality/value – If carefully applied, the Physical-Optics method can be useful and sufficient to obtain fields scattered by cone-like structures.

Multi-moment statistical characterization and nonlinear filtering of chaos

literatinetwork@emeraldinsight.com (Valeri Kontorovich, Zinaida Lovtchikova) — Fri, 03 May 2013 00:00:00 +0100

Abstract

Purpose – The purpose of this paper is to provide the results of investigation of multi-moment statistical characteristics of chaos and apply them to improve the accuracy of nonlinear algorithms for chaos filtering for real-time applications. Design/methodology/approach – The approach to find multi-moment statistical properties of chaos-multi-moment cumulant (covariance) functions of higher order is a generalization of the previously proposed (by the authors) “degenerated cumulant equations” method. Those multi-moment cumulants functions are applied in the generalization of the Stratonovich-Kushner equations (SKE) for the optimum algorithm of nonlinear filtering of chaos as well as for synthesis of the quasi-optimum algorithms. Findings – Results are presented to investigate the multi-moment statistical properties of chaos and formulate the theoretical background for synthesis of multi-moment optimum and quasi-optimum algorithms for nonlinear filtering of chaos with the improved accuracy in the presence of additive white noise. Originality/value – The paper presents new theoretical results of the statistical description of chaos, previously partially reported only from experimental studies. A novel approach for chaos filtering is also presented. The proposed approach is dedicated to further improvement of the filtering accuracy for the case of low (less than one) SNR scenarios and is important for implementation in real-time processing. As an important practical example, the new modified EKF algorithm is proposed with the rather opportunistic characteristics of the filtering fidelity together with algorithm complexity – practically the same as the “classic” one-moment EKF algorithm.

On the improved computational speed and convergence of the Newton Raphson iteration method for selective harmonics elimination PWM applied to cascaded multilevel inverter with equal and non-equal DC sources

literatinetwork@emeraldinsight.com (Zainal Salam, Seh Soon Yee, Yasir Saleem) — Fri, 03 May 2013 00:00:00 +0100

Abstract

Purpose – This paper proposes an improved algorithm to compute selective harmonics elimination pulse width modulation (SHEPWM) angles, based on the Newton-Raphson (NR) iteration for cascaded multilevel inverter (CMI). Design/methodology/approach – Newton Raphson (NR) is a very popular numerical method for transcendental equations that lack analytical solutions. It has been successfully used to compute the angles for selective harmonics elimination pulse width modulation (SHEPWM) schemes. Despite its effectiveness, NR has not been used for SHEPWM with cascaded multilevel inverter (CMI) structure with equal and non-equal DC voltage sources. It is known that for CMI, inappropriate selection of initial angles causes long-iteration time and possibly non-convergence takes place. The computational difficulty is compounded by the fact that the SHEPWM switching angles need to be correctly sequenced, i.e. each angle must be assigned to the correct output voltage level of the CMI. In this work, an attempt is made to reduce the iteration time and to resolve the non-convergence problem. The main idea is to relax the switching angle constraint by placing the switching angle sequencing outside the main loop of NR iteration. This allows for the program to run more freely and able to generate more possible solutions for the switching angles. Then these angles are selected to fulfill the requirements of multilevel sequencing. The performance of the proposed technique will be compared with the standard NR for CMI with equal and non-equal DC sources. The latter case is quite common for CMI with renewable energy applications because the sources normally have different voltage levels. Findings – Using MATLAB simulation, it will be shown that using this scheme, accurate SHEPWM angles can be achieved for a wide range of fundamental components. Furthermore, significant reduction in iteration time to compute the SHEPWM switching angles is achieved. Originality/value – This paper proposes an improved algorithm to compute SHEPWM angles based on NR iteration.

MATLAB implementation of the complex power flow

literatinetwork@emeraldinsight.com (Gianpietro Granelli, Mario Montagna) — Fri, 03 May 2013 00:00:00 +0100

Abstract

Purpose – The purpose of this work is that of providing the guidelines of an efficient implementation of power flow computations using the MATLAB computation environment. Design/methodology/approach – The goal of obtaining high efficiency from MATLAB programs often proves elusive unless special care is taken in exploiting the vectorising capability of MATLAB programming. In the present paper the implementation of Newton-Raphson power flow in MATLAB is examined with particular emphasis on the way of obtaining a vectorisable code capable of achieving effective numerical performance by exploiting its formulation in terms of complex variables. Findings – Tests on actual networks with up to 1,300 buses are presented. They show that the complex power flow is as efficient as the best implementations of the Newton Raphson power flow using real variables, as long as the operations involved are reordered with the aim of exploiting the vectorisation capabilities of the MATLAB environment. Originality/value – It is shown that improved numerical efficiency in the MATLAB can be obtained through its formulation in terms of complex variables. The complex Newton-Raphson load flow, not very common in practical uses, is shown to have many desirable qualities from the point of view of MATLAB programming and is presented in detail.

Potential and field of a homogeneous magnetic spheroid of arbitrary direction in a homogeneous magnetic field in Cartesian coordinates

literatinetwork@emeraldinsight.com (Markus Kraiger, Bernhard Schnizer) — Fri, 03 May 2013 00:00:00 +0100

Abstract

Purpose – The purpose of this paper is to present new expressions in Cartesian coordinates for the potential and magnetic field of prolate and oblate spheroids with arbitrary direction of the symmetry axis in a homogeneous field. Design/methodology/approach – The potentials found in prolate or oblate spheroidal coordinates are transformed to Cartesian coordinates. These results are represented in such a form that they depend only on expressions, which are invariant under rotations around the symmetry axis. Thus, it is easy to change to arbitrary directions of both the symmetry axis and of that of the primary field. The gradients of the potentials are calculated and transformed exactly to the simplest form possible. Findings – The paper presents simple expressions for the magnetic perturbations due to homogeneous prolate or oblate spheroids in a homogeneous magnetic field. Research limitations/implications – Results are exact for single non-ferromagnetic spheroids in a homogeneous field. Practical implications – Superposition of these perturbations presupposes small values of the magnetic susceptibilities of both the spheroids and their environment as in biological tissues. Originality/value – The paper presents novel formulas for fields of homogeneous spheroids in a homogeneous magnetic field which are very useful for modelling biological tissues in studies of magnetic resonance imaging and magnetic resonance spectroscopy.

Determination of correction coefficients of the slot leakage inductance for multi-phase machines

literatinetwork@emeraldinsight.com (István Király) — Fri, 03 May 2013 00:00:00 +0100

Abstract

Purpose – The part of the stator leakage inductance whose quantity changes with the coil pitch is the slot leakage inductance. The purpose of this paper is to determine an analytical expression which accounts for various slot shapes and the coil pitch change. This approach contrasts with the standard one, in which the same characteristics are inaccurately assumed for each slot shape. A further advantage of the proposed analytical expression is that it can also be used to model the slot leakage inductance for different phase numbers. Design/methodology/approach – From the calculated coefficients of a slot by the Finite Element Method (FEM), the characteristics of the slot leakage coefficients are determined by an analytical expression. This helps one to study the connection between the slot shape types and the characteristics of slot leakage coefficients for different phase numbers. Findings – The coefficients, which describe the change of slot leakage, are not the same for every slot type. These inaccuracies can result in deviation from the presented values in the classical literature. Originality/value – By use of parameters, gained from the FEM calculation of a slot, the characteristics of the slot leakage coefficient can be determined as the function of winding pitch for different phase numbers by an analytical expression. Good accuracy of the analytical method is verified by the determination of the characteristics from the measurement of the two-, three- and six-phase windings and by the finite element calculations. Beside the speed of the process, it gives an overview about the connection between the slot shape and the coefficients.

Optimal design of electrical machines: mathematical programming formulations

Fri, 03 May 2013 00:00:00 +0100

Abstract

Purpose – The purpose of this paper is to investigate the impact of different mathematical formulations of the problem of optimal design of electrical machines on the results obtained using a local optimization solver. The aim is to investigate the efficiency and reliability of standard local solvers when handling different mathematical formulations. This could provide guidelines for designers in practical engineering applications. Design/methodology/approach – The paper proposes six equivalent mathematical formulations of the optimal design problem of a slotless permanent-magnet electric rotating machine. The authors investigate the impact of these different mathematical formulations on the results obtained using a local optimization solver which is well-known in the engineering community: MatLab's fmincon function. The paper first computationally compares the six proposed formulations with a fixed value for the number of pole pairs p, that gives continuous optimization problems, then discusses some results when p is free on three mixed-integer formulations. Findings – The paper shows that, even though the considered formulations are mathematically equivalent, their numerical performances are different when an optimization solver, such as the one proposed by MatLab in fmincon, is used. Thus, the designer must take care about the formulation of the design problem in order to make more efficient the use of these kind of algorithms. Originality/value – In the context of engineering applications, one usually resorts to well known and easy to use optimization solvers. The same optimization problem can be often formulated in different ways. Furthermore, the formal description of optimization problems has an impact on the applicability and efficiency of the corresponding solution methods. This is usually not taken into account when optimization solvers are exploited. The originality of this paper is in building on the theory of reformulations in mathematical optimization to investigate and highlight the impact of formulation differences.

Uniformity analysis of magnetic field in an electromagnetic cold crucible used for directional solidification

Fri, 03 May 2013 00:00:00 +0100

Abstract

Purpose – The purpose of this paper is to introduce a numerical calculation method to study the uniformity of the magnetic field in a cold crucible used for directional solidification (DS) and provide information for designing a cold crucible that can induce a uniform magnetic field. Design/methodology/approach – To obtain the characteristics of the magnetic field in a cold crucible and its influence on the directional solidification processing, based on experimental verification, 3-D finite element (FE) models with different crucible configuration-elements and power parameters were established to study the uniformity of the magnetic field in a cold crucible. In addition, different TiAl ingots were directionally solidified with different cold crucibles, and the solid/liquid (S/L) interfaced were examined to investigate the effect of the magnetic field on the macrostructure of those ingots. Findings – The uniformity of the magnetic field in a given domain can be quantitatively analyzed by statistical methods. Numerical calculation results showed that the uniformity of the magnetic field can be improved by optimizing the crucible configuration and adopting lower frequency. Better uniformity of the magnetic field in a cold crucible is beneficial to directional solidification. Originality/value – The calculation of the uniformity of the magnetic field is proposed as a method for quantitative study of the distribution characteristics of the magnetic field in a cold crucible. The relationship between the S/L interfaces of TiAl ingots and the uniformity of the magnetic field is initially characterised; additionally, techniques for improving the uniformity of the magnetic field in a cold crucible are suggested.

Weak limits and their calculation in analog signal theory

literatinetwork@emeraldinsight.com (Željko Juric, Harun Šiljak) — Fri, 03 May 2013 00:00:00 +0100

Abstract

Purpose – This paper aims to improve the mathematical justification of certain analog signal theory concepts and offer a rigorous framework for it. Design/methodology/approach – The framework relies on functional analysis, namely theory of distributions and the concept of weak limit. Its notation is adjusted to resemble the notation usually used in engineering signal theory. It can be used to prove in a rigorous manner already established results in signal theory, but also to establish new ones. Findings – Examples have shown the lack of rigour caused by using ordinary calculus in proving fundamental signal theoretic results. On that basis, concepts of limit, Fourier transform and derivative are revisited in the spirit of functional analysis. A new useful formula for weak limit computation is proved. Originality/value – Functional analysis is efficiently used in signal theory in a manner approachable by engineers. An original and efficient formula for weak limit computation is presented and proved.

Fast evaluation of the lightning electromagnetic field in the time domain with an adaptive piecewise approximation of channel base current

literatinetwork@emeraldinsight.com (Jae-bok Lee, Jun Zou, Mo Li, Sughun Chang) — Fri, 03 May 2013 00:00:00 +0100

Abstract

Purpose – A fast algorithm is proposed to calculate the lightning electromagnetic field over a perfectly conducting earth surface. Design/methodology/approach – The channel base current is approximated by a number of sub-domain quadratic functions using the proposed adaptive sampling technique, and the derivative and integral of the channel base current with respect to time can be analytically expressed. With the help of these approximations, the ideal electromagnetic field of the lightning channel can be evaluated along the lightning channel with respect to the height. Findings – The computational time can be greatly reduced using the proposed approach to evaluate the electromagnetic field of a lightning channel in the time domain. Originality/value – The adaptive sampling technique is a general-purposed approach, which can be potentially used in other applications to fit a function with the minimal number of intervals.

The fuzzy correlation approach in operation of electrical distribution systems

literatinetwork@emeraldinsight.com (Gheorghe Grigoras, Gheorghe Cartina) — Fri, 03 May 2013 00:00:00 +0100

Abstract

Purpose – The purpose of this paper is to introduce a method based on the fuzzy correlation for modelling of active and reactive powers from the substations of the electrical distribution systems, at the peak load. Design/methodology/approach – Based on the correlation theory, the fuzzy models of the loads can be obtained using a new algorithm. If in the case of the principal/connection station there is sufficient database information for a good forecasting of the load, then for those substations where data are missing (there is no continuous monitoring or the measuring system can be broken for a while) the forecasting of the load can be performed using the correlation studies. The starting point of the algorithm is statistical analysis of the active and reactive curves of the substations and utilization of a fuzzy linear regression model. This can be made for different time windows (window 24?h, window 7?h, etc). The window 24?h can be used successfully to estimate the hourly load on any substation. The other time window (7?h) can be used in the peak load estimation of the substations, using the maximum value of the active power recorded in a reference substation. Findings – The numerical data show that the fuzzy correlation models can be used with very good results for determination of the peak load corresponding distribution substations, and further with the state estimation of the system. In this study, the influence of the time window size is presented in detail, and the fuzzy correlation models for the peak loads from the distribution substations are obtained. Originality/value – Starting from the correlation theory, a method of fuzzy modelling of active and reactive powers from the substations of an electrical distribution system is proposed.

Parallel computing applied to inductance calculation for flexible inductors

Fri, 03 May 2013 00:00:00 +0100

Abstract

Purpose – The motivation for this research work is the need for an efficient software tool for inductance calculation of components in flexible electronics. A software package PROVOD has been developed and it has produced very accurate results but the applied numerical method can lead to a huge amount of calculations. The aim of this research is to apply the parallel computing to this specific computational technique and to investigate the impact of increasing the number of parallel executing threads. Design/methodology/approach – The largest possible amount of operations is put in parallel using the fact that the inductance between two segments is a sum of independent elements. OpenMP and Microsoft's Concurrency Runtime have been tested as parallel programming techniques. Findings – Parallel computing with a different number of threads (up to 24) has been tested with OpenMP. A significant increase in computational speed (up to 21 times) has been obtained. Research limitations/implications – The research is limited by the available number of parallel processors. Practical implications – Accurate and fast inductance calculation for flexible electronic components is possible to achieve. The impact of parallel processing is proven. Social implications – The proposed method of calculation acceleration of inductances can be helpful in the design and optimization of new flexible devices in electronics. Originality/value – Parallel computing is applied to the design of flexible electronic components. It is shown that a large number of parallel processors can be efficiently used in this type of calculation. The obtained results are interesting for people involved in the design of flexible components, and generally, for researchers/engineers dealing with similar electromagnetic problems.

Estimation of parameters in the state space model of stochastic RL electrical circuit

literatinetwork@emeraldinsight.com (Rahman Farnoosh, Arezoo Hajrajabi) — Fri, 03 May 2013 00:00:00 +0100

Abstract

Purpose – The purpose of this paper is to consider the stochastic differential equation of the RL electrical circuit as the dynamic model of a state space system when the current in the circuit is hidden and corrupted by the measurement noise. Estimation of the corrupted current and the values of missing or unknown parameters (resistance, the observed current variance in the measurement model, the mean and variance of the current prior distribution) which are the main concern in electrical engineering is considered. Design/methodology/approach – Optimal filtering is proposed for estimation of the hidden current from the noisy observations. Also, the problem of analyzing this model based on estimation of the unknown parameters is addressed from the likelihood-based and Bayesian perspective. Findings – Computational techniques for parameter estimation are carried out by the Maximum likelihood (ML) approach using Expectation-Maximization type optimization and Bayesian Monte Carlo perspective using Metropolis-Hastings scheme. The explicit formulas for the ML estimator are obtained and it is shown that the smoothers, the filters and the predictions for the current have the best confidence intervals, respectively. Some numerical simulation examples which are performed by R programming software are considered to show the efficiency and applicability of the proposed approaches. Results show an excellent estimation of the parameters based on these approaches. Practical implications – Due to the fact that in an empirical situation of electrical engineering, observing the current in the circuit regardless of the measurement noise and knowing the exact value of the parameters are unrealistic assumptions, this paper can be used in various types of real time projects. Originality/value – To the best of the authors' information, the problem of analyzing the state space model of RL electrical circuit has not been studied before. Furthermore, the estimation of the hidden current as the state of the system and estimation of the unknown parameters of the model via both ML and Bayesian approaches have been investigated for the first time in the present study.

Analysis and calculation of slot leakage reactance in the stator bar strands of deficient transposition

literatinetwork@emeraldinsight.com (Liang Yan-ping, Yu Hong-hao, Bian Xu) — Fri, 03 May 2013 00:00:00 +0100

Abstract

Purpose – The purpose of this paper is to introduce an analytic method to calculate the slot leakage reactance of stator bar strands in alternative current machines whose stator windings have multiple bars per layer and using deficient transposition. Design/methodology/approach – Based on the analysis of deficient transposition, the calculation model of mutual slot leakage reactance between any two strands in one bar is established. The subsection integral method is presented to calculate the slot leakage reactance and analytic function is listed. A pump motor used in nuclear power is taken as an example, and the slot self leakage reactance of any strand in its top layer winding and the slot mutual leakage reactance between one strand and other strands in the same bar are calculated depending on the method described above. The slot leakage reactance of all strands in the top layer winding is calculated when different transposition angles are applied in stator bars. Findings – The results show that subsection integral method is effective in calculating the slot leakage reactance of stator bar strands of deficient transposition. The slot leakage reactance distribution of all strands is obtained. The transposition angle has a great impact on the slot leakage reactance distribution of stator bar strands. Originality/value – This paper presents an available method to calculate the slot leakage reactance of any strands in alternative current machine whose stator windings have multiple bars per layer and using deficient transposition, and discusses the impact of transposition angle on the slot leakage reactance. The conclusion can lay the foundation of the effective calculation of circulating current losses in stator bars with deficient transposition.

Numerical investigation of a high order hybridizable discontinuous Galerkin method for 2d time-harmonic Maxwell's equations

literatinetwork@emeraldinsight.com (Liang Li, Stéphane Lanteri, Ronan Perrussel) — Fri, 03 May 2013 00:00:00 +0100

Abstract

Purpose – This work is concerned with the development and the numerical investigation of a hybridizable discontinuous Galerkin (HDG) method for the simulation of two-dimensional time-harmonic electromagnetic wave propagation problems. Design/methodology/approach – The proposed HDG method for the discretization of the two-dimensional transverse magnetic Maxwell equations relies on an arbitrary high order nodal interpolation of the electromagnetic field components and is formulated on triangular meshes. In the HDG method, an additional hybrid variable is introduced on the faces of the elements, with which the element-wise (local) solutions can be defined. A so-called conservativity condition is imposed on the numerical flux, which can be defined in terms of the hybrid variable, at the interface between neighbouring elements. The linear system of equations for the unknowns associated with the hybrid variable is solved here using a multifrontal sparse LU method. The formulation is given, and the relationship between the considered HDG method and a standard upwind flux-based DG method is also examined. Findings – The approximate solutions for both electric and magnetic fields converge with the optimal order of p+1 in L2 norm, when the interpolation order on every element and every interface is p and the sought solution is sufficiently regular. The presented numerical results show the effectiveness of the proposed HDG method, especially when compared with a classical upwind flux-based DG method. Originality/value – The work described here is a demonstration of the viability of a HDG formulation for solving the time-harmonic Maxwell equations through a detailed numerical assessment of accuracy properties and computational performances.

A reversible flux linkage model of the switched reluctance motor with rotor position computable

Fri, 03 May 2013 00:00:00 +0100

Abstract

Purpose – The purpose of this paper is to present a reversible flux linkage model of the switched reluctance motor so that the rotor position can be computed analytically. Design/methodology/approach – The presented flux linkage model uses a Fermi function like equation with four coefficients to fit flux linkage characteristics. In this work, the coefficients are calculated from flux-current-angle data using numerical curve fitting with the least squares method. A rotor position model is then derived by inverting the flux linkage model. With a simple estimation scheme based on the rotor position model, the rotor position is estimated continuously. Simulation and experiments are then performed to verify the proposed method. Findings – The presented flux linkage model agrees well with flux linkage characteristics. The average absolute relative error (AARE) of the model varies between 0.3 per cent and 5.3 per cent. With the derived rotor position model, rotor position can be estimated conveniently for either steady or dynamic operations. Practical implications – The simulation and experimental results indicate that the presented model is an eligible candidate for applications such as rotor position estimation, performance simulation and other model based controls. Originality/value – Unlike previously reported methods, the presented flux linkage model is reversible so that a rotor position model can be derived and the rotor position can be computed analytically.

Modeling of jitter in bang-bang clock and data recovery circuits

literatinetwork@emeraldinsight.com (Habib Adrang, Seyed Saleh Ghoreishi) — Fri, 03 May 2013 00:00:00 +0100

Abstract

Purpose – Bang-bang clock and data recovery (BBCDR) circuits are hard nonlinear systems due to the nonlinearity introduced by the binary phase detector (BPD). The specification of the CDR frequency response is determined by jitter tolerance and jitter transfer. In this paper, jitter transfer and jitter tolerance of the BBCDR are characterized. Design/methodology/approach – The presented method is enough to be used for designing the BBCDR loop parameters. Findings – In this paper, jitter characteristics of the BBCDR are characterized. As a result, a new equation is presented to obtain angular frequency. Also, the jitter tolerance is expressed in closed form as a function of loop parameters. The analysis is verified using behavioral simulations in MATLAB. Simulation results show that good conformance between analytical equations and simulation results. Originality/value – The proposed approach offers two advantages compared to conventional designing methods. First, this approach does not consider any value restriction to the capacitor. Second, a new condition has been presented to guarantee that the value of jitter peaking is approximately zero.

Recent advances in nonlinear dynamics with selected applications in electrical engineering

literatinetwork@emeraldinsight.com (Kyandoghere Kyamakya) — Fri, 03 May 2013 00:00:00 +0100