Broadband surface impedance boundary conditions for higher order time domain discontinuous Galerkin methodIrene Woyna; Erion Gjonaj; Thomas Weiland
2014 COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering
doi: 10.1108/COMPEL-08-2013-0260
Purpose – The purpose of this paper is to present a time domain discontinuous Galerkin (DG) approach for modeling wideband frequency dependent surface impedance boundary conditions. Design/methodology/approach – The paper solves the Maxwellian initial value problem in a computational domain, which is spatially discretized by the higher order DG method. On the boundary of the computational domain the paper applies a suitable impedance boundary condition (IBC). The frequency dependency of the impedance function is modeled by auxiliary differential equations (ADE). Findings – The authors will study the resonance frequency and the Q factor of different types of cavity resonators including lossy materials. The lossy materials are modeled by means of IBCs. The authors will compare the results with analytical results, as well as numerical results obtained by direct calculations where lossy materials are included explicitly into the numerical model. Several convergence studies are performed which demonstrate the accuracy of the approach. Originality/value – Modeling of frequency dependent boundary conditions in time domain with finite difference time domain method (FDTD) method is considered in numerous papers, as well as in frequency domain finite element method (FEM), and in a few papers also time domain FEM. However, FDTD method is only first order accurate and fails in modeling of complicated surfaces. FEM allows for high order accuracy, but time domain modeling is numerically extremely expensive. In frequency domain, broadband modeling of frequency dependent boundary conditions requires several simulations as opposed to the time domain, where a single simulation is needed. The time domain DG method proposed in this paper allows to overcome the difficulties. The authors introduce a broadband surface impedance formulation based on the ADE approach for the higher order DG method.
Polynomial fitting of nonlinear sources with correlating inputsJanne P. Aikio; Timo Rahkonen; Ville Karanko
2014 COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering
doi: 10.1108/COMPEL-11-2012-0353
Purpose – The purpose of this paper is to propose methods to improve the least square error polynomial fitting of multi‐input nonlinear sources that suffer from strong correlating inputs. Design/methodology/approach – The polynomial fitting is improved by amplitude normalization, reducing the order of the model, utilizing Chebychev polynomials and finally perturbing the correlating controlling voltage spectra. The fitting process is estimated by the reliability figure and the condition number. Findings – It is shown in the paper that perturbing one of the controlling voltages reduces the correlation to a large extend especially in the cross‐terms of the multi‐input polynomials. Chebychev polynomials reduce the correlation between the higher‐order spectra derived from the same input signal, but cannot break the correlation between correlating input and output voltages. Research limitations/implications – Optimal perturbations are sought in a separate optimization loop, which slows down the fitting process. This is due to the fact that each nonlinear source that suffers from the correlation needs a different perturbation. Originality/value – The perturbation, harmonic balance run and refitting of an individual nonlinear source inside a device model is new and original way to characterize and fit polynomial models.
Multiscale simulation of organic heterojunction light harvesting devicesMatteo Porro; Carlo de Falco; Maurizio Verri; Guglielmo Lanzani; Riccardo Sacco
2014 COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering
doi: 10.1108/COMPEL-12-2012-0365
Purpose – The purpose of this paper is to develop a computational model for the simulation of heterojunction organic photovoltaic devices with a specific application to a light harvesting capacitor (LHC) consisting of a double layer of organic materials connected in series with two insulating layers and an external resistive load. Design/methodology/approach – The model is based on a coupled system of nonlinear partial and ordinary differential equations describing current flow throughout the external resistive load as the result of exciton generation in the bulk, exciton dissociation into bonded pairs at the acceptor‐donor material interface, and electron/hole charge generation and drift‐diffusion transport in the two device materials. Findings – Numerical simulation results are shown to be in good agreement with measured on‐off transient currents and allow for novel insight on the microscopical phenomena which affect the external LHC performance, in particular, the widely different time scales at which such phenomena occur and their relation to the overall device dynamics. Originality/value – The LHC demonstrates the viability of a novel approach for converting light energy into an electric current without a steady state flow of free charge carriers through the semiconducting layers. The new insight about the microscopic working principles that determine the macroscopically observed behavior of the LHC obtained via the model proposed in this paper are expected to serve as a basis for studying techniques for exploiting the full potential of the LHC.
Index‐aware model order reduction: LTI DAEs in electric networksN. Banagaaya; W.H.A. Schilders; G. Alì; C. Tischendorf
2014 COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering
doi: 10.1108/COMPEL-12-2012-0362
Purpose – Model order reduction (MOR) has been widely used in the electric networks but little has been done to reduce higher index differential algebraic equations (DAEs). The paper aims to discuss these issues. Design/methodology/approach – Most methods first do an index reduction before reducing a higher DAE but this can lead to a loss of physical properties of the system. Findings – The paper presents a MOR method for DAEs called the index‐aware MOR (IMOR) which can reduce a DAE while preserving its physical properties such as the index. The feasibility of this method is tested on real‐life electric networks. Originality/value – MOR has been widely used to reduce large systems from electric networks but little has been done to reduce higher index DAEs. Most methods first do an index reduction before reducing a large system of DAEs but this can lead to a loss of physical properties of the system. The paper presents a MOR method for DAEs called the IMOR which can reduce a DAE while preserving its physical properties such as the index. The feasibility of this method is tested on real‐life electric networks.
Dielectric breakdown simulations of an OLTC in a transformerMaximilian Wiesmüller; Beate Glaser; Franz Fuchs; Oliver Sterz
2014 COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering
doi: 10.1108/COMPEL-12-2012-0363
Purpose – The purpose of this paper is to report on the simulation of an on‐load tap‐changer (OLTC) in a power transformer. During design and test of the electrical insulation the influence of the environment on the OLTC is normally neglected. The authors investigate how large these influences are. Design/methodology/approach – The environment of the OLTC is taken into account by modeling tap leads in detail as well as transformer windings. The electric fields are computed and resulting breakdown voltages are estimated by using the streamer criterion. The results are compared to the ones of an OLTC without transformer and leads. Findings – For the investigated typical example the influence of the transformer and the tap leads on the internal OLTC insulation is small enough to neglect them during design optimization and test procedures. Originality/value – New is the execution of a finite element simulation and breakdown evaluation of such a complex geometric structure as the complete system consisting of OLTC combined with tap leads and windings. Furthermore, standard design and test procedures used by OLTC manufacturers are justified.
Robust DC and efficient time‐domain fast fault simulationBratislav Tasic; Jos J. Dohmen; E. Jan W. ter Maten; Theo G.J. Beelen; Wil H.A. Schilders; Alex de Vries; Maikel van Beurden
2014 COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering
doi: 10.1108/COMPEL-12-2012-0364
Purpose – Imperfections in manufacturing processes may cause unwanted connections (faults) that are added to the nominal, “golden”, design of an electronic circuit. By fault simulation one simulates all situations. Normally this leads to a large list of simulations in which for each defect a steady‐state (direct current (DC)) solution is determined followed by a transient simulation. The purpose of this paper is to improve the robustness and the efficiency of these simulations. Design/methodology/approach – Determining the DC solution can be very hard. For this the authors present an adaptive time‐domain source stepping procedure that can deal with controlled sources. The method can easily be combined with existing pseudo‐transient procedures. The method is robust and efficient. In the subsequent transient simulation the solution of a fault is compared to a golden, fault‐free, solution. A strategy is developed to efficiently simulate the faulty solutions until their moment of detection. Findings – The paper fully exploits the hierarchical structure of the circuit in the simulation process to bypass parts of the circuit that appear to be unaffected by the fault. Accurate prediction and efficient solution procedures lead to fast fault simulation. Originality/value – The fast fault simulation helps to store a database with detectable deviations for each fault. If such a detectable output “matches” a result of a product that has been returned because of malfunctioning it helps to identify the subcircuit that may contain the real fault. One aims to detect as much as possible candidate faults. Because of the many options the simulations must be very efficient.
Optimal frequency sweep method in multi‐rate circuit simulationKai Bittner; Hans Georg Brachtendorf
2014 COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering
doi: 10.1108/COMPEL-11-2012-0346
Purpose – Radio‐frequency circuits often possess a multi‐rate behavior. Slow changing baseband signals and fast oscillating carrier signals often occur in the same circuit. Frequency modulated signals pose a particular challenge. The paper aims to discuss these issues. Design/methodology/approach – The ordinary circuit differential equations are first rewritten by a system of (multi‐rate) partial differential equations in order to decouple the different time scales. For an efficient simulation the paper needs an optimal choice of a frequency‐dependent parameter. This is achieved by an additional smoothness condition. Findings – By incorporating the smoothness condition into the discretization, the paper obtains a non‐linear system of equations complemented by a minimization constraint. This problem is solved by a modified Newton method, which needs only little extra computational effort. The method is tested on a phase locked loop with a frequency modulated input signal. Originality/value – A new optimal frequency sweep method was introduced, which will permit a very efficient simulation of multi‐rate circuits.
Quasi 3D modelling and simulation of axial flux machinesOssi Niemimäki; Stefan Kurz
2014 COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering
doi: 10.1108/COMPEL-11-2012-0352
Purpose – The purpose of this paper is to investigate the theoretical foundation of the so‐called quasi 3D modelling method of axial flux machines, and the means for the simulation of the resulting models. Design/methodology/approach – Starting from the first principles, a 3D magnetostatic problem is geometrically decomposed into a coupled system of 2D problems. Genuine 2D problems are derived by decoupling the system. The construction of the 2D simulation models is discussed, and their applicability is evaluated by comparing a finite element implementation to an existing industry‐used model. Findings – The quasi 3D method relies on the assumption of vanishing radial magnetic flux. The validity of this assumption is reflected in a residual gained from the 3D coupled system. Moreover, under a modification of the metric of the 2D models, an axial flux machine can be presented as a family of radial flux machines. Research limitations/implications – The evaluation and interpretation of the residual has not been carried out. Furthermore, the inclusion of eddy currents has not been detailed in the present study. Originality/value – A summary of existing modelling and simulation methods of axial flux machines is provided. As a novel result, proper mathematical context for the quasi 3D method is given and the underlying assumptions are laid out. The implementation of the 2D models is approached from a general angle, strengthening the foundation for future research.
Convergence behaviour of coupled pressure and thermal networksAndreas Blaszczyk; Reto Flückiger; Thomas Müller; Carl‐Olof Olsson
2014 COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering
doi: 10.1108/COMPEL-12-2012-0378
Purpose – The purpose of this paper is to present a method for thermal computations of power devices based on a coupling between thermal and pressure networks. The concept of the coupling as well as the solution procedure is explained. The included examples demonstrate that the new method can be efficiently used for design of transformers and other power devices. Design/methodology/approach – The bidirectional propagation of temperature signal is introduced to the pressure network, which enables control of the power flow and a close coupling to the thermal network. The solution method is based on automatic splitting of the network definition (netlist) into two separate networks and iteratively solving the model using the Newton‐Raphson approach as well as the adaptive relaxation enhanced by the direction change control. Findings – The proposed approach offers reliable convergence behaviour even for models with unknown direction of the fluid flow (bidirectional flows). The accuracy is sufficient for engineering applications and comparable with the computational fluid dynamics method. The computation times in the range of milliseconds and seconds are attractive for using the method in engineering design tools. Originality/value – The new method can be considered as a foundation for a consistent network modelling system of arbitrary thermodynamic problems including fluid flow. Such a modelling system can be used directly by device designers since the complexity of thermodynamic formulations is encapsulated in predefined network elements while the numerical solution is based on a standard network description and solvers (Spice).
Extended Brauer model for ferromagnetic materials: analysis and computationTimo Hülsmann; Andreas Bartel; Sebastian Schöps; Herbert De Gersem
2014 COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering
doi: 10.1108/COMPEL-11-2012-0359
Purpose – The purpose of this paper is to develop a fast and accurate analytic model function for the single‐valued H‐B curve of ferromagnetic materials, where hysteresis can be disregarded (normal magnetization curve). Nonlinear magnetoquasistatic simulations demand smooth monotone material models to ensure physical correctness and good convergence in Newton's method. Design/methodology/approach – The Brauer model has these beneficial properties, but is not sufficiently accurate for low and high fields in the normal magnetization curve. The paper extends the Brauer model to better fit material behavior in the Rayleigh region (low fields) and in full saturation. Procedures for obtaining optimal parameters from given measurement points are proposed and tested for two technical materials. The approach is compared with cubic spline and monotonicity preserving spline interpolation with respect to error and computational effort. Findings – The extended Brauer model is more accurate and even maintains the computational advantages of the classical Brauer model. The methods for obtaining optimal parameters yield good results if the measurement points have a distinctive Rayleigh region. Originality/value – The model function for ferromagnetic materials enhances the precision of the classical Brauer model without notable additional simulation cost.
Analyzing distortion contributions in a complex device modelTimo Rahkonen; Janne P. Aikio
2014 COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering
doi: 10.1108/COMPEL-11-2012-0354
Purpose – The purpose of this paper is to propose a method to reduce the non‐linear distortion of a transistor to its input and output ports to aid distortion contribution analysis (DCA). This is especially needed when the internal structure of a device model is complex. Design/methodology/approach – The non‐linear distortion generated by all non‐linear sources inside a device model are reduced to transistor i/o ports by LMSE fitting techniques. Simulations of an LDMOS power transistor are used to compare the reduced distortion results with the actual non‐linear sources. Findings – It is shown, that device models where the current sources are split by intermediate nodes cause superficial results, when distortion contributions are calculated as a superposition of contributions from individual non‐linear sources. The proposed iterative fitting technique works. Research limitations/implications – Some non‐quasistatic effects and the transfer functions from external terminals to internal controlling nodes are not covered. Practical implications – The analysis is a step toward a generic non‐linear distortion contribution simulation tool that would aid the designers to develop more linear analog circuits. Originality/value – The concept of DCA itself is fairly new. This paper makes a step to represent the distortion sources in a canonical way.
Modeling of streamers in transformer oil using OpenFOAMNils Lavesson; Jonathan Jogenfors; Ola Widlund
2014 COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering
doi: 10.1108/COMPEL-12-2012-0361
Purpose – A model for streamers based on charge transport has been developed by MIT and ABB. The purpose of this paper is to investigate the consequences of changing numerical method from the finite element method (FEM) to the finite volume method (FVM) for simulations using the streamer model. The new solver is also used to extend the simulations to 3D. Design/methodology/approach – The equations from the MIT‐ABB streamer model are implemented in OpenFOAM which uses the FVM. Checks of the results are performed including verification of convergence. The solver is then applied to some of the key simulations from the FEM model and results presented. Findings – The results for second mode streamers are confirmed, whereas the results for third mode streamers differ significantly leading to questioning of one hypothesis proposed based on the FEM results. The 3D simulations give consistent results and show a way forward for future simulations. Originality/value – The FVM has not been applied to the model before and led to more confidence in second mode result and revising of third mode results. In addition the new simulation method makes it possible to extend the results to 3D.
Back‐reflector design in thin‐film silicon solar cells by rigorous 3D light propagation modelingMark Blome; Kevin McPeak; Sven Burger; Frank Schmidt; David Norris
2014 COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering
doi: 10.1108/COMPEL-12-2012-0367
Purpose – The purpose of this paper is to find an optimized thin‐film amorphous silicon solar cell design by numerically optimizing the light trapping efficiency of a pyramid‐structured back‐reflector using a frequency‐domain finite element Maxwell solver. For this purpose short circuit current densities and absorption spectra within the investigated solar cell model are systematically analyzed. Furthermore, the authors employ a topology simulation method to accurately predict the material layer interfaces within the investigated solar cell model. The method simulates the chemical vapor deposition (CVD) process that is typically used to fabricate thin‐film solar cells by combining a ballistic transport and reaction model (BTRM) with a level‐set method in an iterative approach. Predicted solar cell models are far more realistic compared to solar cell models created assuming conformal material growth. The purpose of the topology simulation method is to increase the accuracy of thin‐film solar cell models in order to facilitate highly accurate simulation results in solar cell design optimizations. Design/methodology/approach – The authors perform numeric optimizations using a frequency domain finite element Maxwell solver. Topology simulations are carried out using a BTRM combined with a level‐set method in an iterative fashion. Findings – The simulation results reveal that the employed pyramid structured back‐reflectors effectively increase the light path in the absorber mainly by exciting photonic waveguide modes. In using the optimization approach, the authors have identified solar cell models with cell periodicities around 480 nm and pyramid base widths around 450 nm to yield the highest short circuit current densities. Compared to equivalent solar cell models with flat back‐reflectors, computed short circuit current densities are significantly increased. Furthermore, the paper finds that the solar cell models computed using the topology simulation approach represent a far more realistic approximation to a real solar cell stack compared to solar cell models computed by a conformal material growth assumption. Research limitations/implications – So far in the topology simulation approach the authors assume CVD as the material deposition process for all material layers. However, during the fabrication process sputtering (i.e. physical vapor deposition) will be employed for the Al:ZnO and ITO layers. In the framework of this ongoing research project the authors will extend the topology simulation approach to take the different material deposition processes into account. The differences in predicted material interfaces will presumably be only minor compared to the results shown here and certainly be insignificant relative to the differences the authors observe for solar cell models computed assuming conformal material growth. Originality/value – The authors systematically investigate and optimize the light trapping efficiency of a pyramid nano‐structured back‐reflector using rigorous electromagnetic field computations with a 3D finite element Maxwell solver. To the authors’ knowledge such an investigation has not been carried out yet in the solar cell research literature. The topology simulation approach (to the best of the authors’ knowledge) has previously not been applied to the modelling of solar cells. Typically a conformal layer growth assumption is used instead.
A novel and fast voltage estimation scheme for assessment of power system component outagesSeyed Masoud Fatemi; Mehrdad Abedi; Behrooz Vahidi; Sajjad Abedi; Hassan Rastegar
2014 COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering
doi: 10.1108/COMPEL-06-2013-0206
Purpose – The purpose of this paper is to pursue two following main goals: first, theorizing a new concept named as equivalent bus load in order to make a promising simplification over power system analysis. Second, proposing an outstanding fast and simple approach based on introduced concept for voltage estimation after multiple component outages while satisfying required accuracy. Design/methodology/approach – Equivalent load bus theory introduces three transfer matrices that describe power system topology. Mentioned matrices could be calculated simply after system reconfiguration without matrix inversion. Using transfer matrices a large‐scale power system can be modeled by a simple two‐bus power system from the viewpoint of any desired bus so that load flow calculation leads to same value. The analysis of simplified power system yields to extract a new incremental model based on equivalent bus load theory that will be distinguished as an outstanding fast method for voltage estimation aim. Findings – A deep study for fast voltage estimation aim is dedicated to evaluate proposed method from the accuracy and quickness point of view and the outcomes are compared to a well‐known method as Distribution Factors (DF). Results and computational times unveil that presented approach is more accurate and much faster. Originality/value – A novel and new fast voltage estimation method for assessment of power system component outages is introduced.
A two‐step model to optimise transcutaneous electrical stimulation of the human upper armMichela Goffredo; Maurizio Schmid; Silvia Conforto; Filiberto Bilotti; Claudio Palma; Lucio Vegni; Tommaso D’Alessio
2014 COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering
doi: 10.1108/COMPEL-04-2013-0118
Purpose – A novel model of the upper arm under transcutaneous electrical stimulation with multi‐pad electrodes is presented and experimentally validated. The model aims at simulating and analysing the effects of surface electrical stimulation on biceps brachii. The paper aims to discuss these issues. Design/methodology/approach – Both the passive properties of tissues surrounding nerve bundles and the active characteristics of the nervous system are included. The output of the proposed model is nerve recruitment and muscle contraction. Findings – Simulations and experimental tests on six healthy young adults have been conducted and results show that the proposed model gives information on electrically elicited muscle contraction in accordance with in‐vivo tests and literature on motor unit recruitment order. Tests with different electrodes configurations show that the spatial distribution of active electrodes is a critical factor in electrically elicited muscle contractions, and that multi‐pad electrodes can optimise the stimulation effectiveness and patient comfort with sequences of biphasic pulses of 350 μ s at 30 pulses/s and threshold values of 2 mA. Originality/value – Results encourage the use of the proposed model of the upper arm as a valid and viable solution for predicting the behaviour of the neuromuscular system when surface electrical stimulation is applied, thus optimising the design of neuroprosthetics.
A multi‐valve controlled saturable reactor and its harmonic optimizationYifan Wang; Guozhu Chen
2014 COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering
doi: 10.1108/COMPEL-04-2013-0136
Purpose – As arc suppression coils (ASCs), magnetically controlled reactors (MCRs) are usually operated in the single‐phase mode. Due to the lack of a third order harmonic compensation circuit, the current harmonics are high. The purpose of this paper is to propose a novel structure of MCR and a genetic algorithm (GA) to determine the parameters which will result in minimum total harmonics. Design/methodology/approach – This paper proposes the structure and the working principle of the multi‐valve controlled saturable reactor (MCSR). There are several sorts of magnetic valves in the iron cores of the MCSR. The saturation degree of each magnetic valve is different when the same direct component of the magnetic flux is generated in the iron core, therefore current harmonics of different phases emerging, i.e. the total harmonics can be reduced. The magnetization characteristics and the mathematical model of the current harmonics of the MCSR are presented by introducing three parameters. The optimal values of the parameters that result in the smallest total harmonic distortion in the output current are calculated by a GA. Findings – The simulation and experimental results are coincident with the theoretical analyses, which prove the effectiveness of the proposed method on harmonic suppression. Practical implications – The method proposed in this paper can successfully reduce the current harmonics of the conventional MCR, including but not limited to the ASC. A prototype MCSR (540 kVA/10 kV) has been designed and constructed. Originality/value – In this paper, a MCSR is proposed. The mathematical model of the MCSR for harmonic analysis is developed. The optimal parameters that result in the smallest THD in the output current are calculated. The mathematical model can be also used for the harmonic analysis of conventional MCRs.
Distorted constriction contact resistance between clamped slabsGrigore A. Cividjian
2014 COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering
doi: 10.1108/COMPEL-07-2013-0250
Purpose – The purpose of this paper is the more exact evaluation of distorted constriction contact resistance between two clamped slabs or thin films, having a bi‐dimensional current lines structure. Design/methodology/approach – Mathematical modeling using conformal mappings. Findings – The influence of the tarnish film on the distorted constriction resistance is clarified and three new exact formulas are proposed for the distorted constriction resistance between clamped slabs with rectangular contact spot. Comparisons with early proposed formula for constriction resistance of slab narrowing and with finite element analysis results are presented. Research limitations/implications – The research is limited to direct current and homogeneous and isotropic media and the results can be extended at alternate current when the skin effect is negligible. Practical implications – Exact evaluation of 2D constriction contact resistance which appears in macro‐scale contacts electrical equipment and in MEMS devices, particularly in crimp contacts. Originality/value – The proposed formulas are new, original, simple and exact.
Efficient evaluation of the earth return mutual impedance of overhead conductors over a horizontally multilayered soilJae‐bok Lee; Jun Zou; Benliang Li; Munno Ju
2014 COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering
doi: 10.1108/COMPEL-08-2013-0265
Purpose – The per‐unit‐length earth return mutual impedance of the overhead conductors plays an important role for analyzing electromagnetic transients or couplings of multi‐conductor systems. It is impossible to have a closed‐form expression to evaluate this kind of impedance. The purpose of this paper is to propose an efficient numerical approach to evaluate the earth return mutual impedance of the overhead conductors above horizontally multi‐layered soils. Design/methodology/approach – The expression of the earth return mutual impedance, which contains a complex highly oscillatory semi‐infinite integral, is divided into two parts intentionally, i.e. the definite and the tail integral, respectively. The definite integral is calculated using the proposed moment functions after fitting the integrand into the piecewise cubic spline functions, and the tail integral is replaced by exponential integrals with newly developed asymptotic integrands. Findings – The numerical examples show the proposed approach has a satisfactory accuracy for different parameter combinations. Compared to the direct quadrature approach, the computational time of the proposed approach is very competitive, especially, for the large horizontal distance and the low height of the conductors. Originality/value – The advantage of the proposed approach is that the calculation of the highly oscillatory integral is completely avoided due to the fact that the moment function can be evaluated analytically. The contribution of the tail integral is well included by means of the exponential integral, though in an asymptotic way. The proposed approach is completely general, and can be applied to calculate the earth return mutual impedance of overhead conductors above a soil structure with an arbitrary number of horizontal layers.
Simulation of charge packet formation in layered polymer filmMeng H. Lean; Wei‐Ping L. Chu
2014 COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering
doi: 10.1108/COMPEL-09-2013-0291
Purpose – The purpose of this paper is to describe a rapid and robust axisymmetric hybrid algorithm to create dynamic temporal and spatial charge distributions, or charge map, in the simulation of bipolar charge injection using Schottky emission and Fowler‐Nordheim tunneling, field‐dependent transport, recombination, and bulk and interfacial trapping/de‐trapping for layered polymer films spanning the range from initial injection to near breakdown. Design/methodology/approach – This hybrid algorithm uses a source distribution technique based on an axisymmetric boundary integral equation method (BIEM) to solve the Poisson equation and a fourth‐order Runge‐Kutta (RK4) method with an upwind scheme for time integration. Iterative stability is assured by satisfying the Courant‐Friedrichs‐Levy (CFL) stability criterion. Dynamic charge mapping is achieved by allowing conducting and insulating boundaries and material interfaces to be intuitively represented by equivalent free and bound charge distributions that collectively satisfy all local and far‐field conditions. Findings – Charge packets cause substantial increase of electric stress and could accelerate the breakdown of polymeric capacitors. Conditions for the creation of charge packets are identified and numerically demonstrated for a combination of impulsive step excitation, high charge injection, and discontinuous interface. Originality/value – Metallized bi‐axially oriented polypropylene (BOPP) dielectric thin film capacitor with self‐clearing and enhanced current carrying capability offer an inexpensive and lightweight alternative for efficient power conditioning, energy storage, energy conversion, and pulsed power. The originality is the comprehensive physics and multi‐dimensional modeling which span the dynamic range from initial injection to near breakdown. This model has been validated against some empirical data and may be used to identify failure mechanisms such as charge packets, gaseous voids, and electroluminescence. The value lies in the use of this model to develop mitigation strategies, including re‐designs and materials matching, to avoid these failure mechanisms.
Iso‐geometric shape optimization of magnetic density separatorsNguyen Dang Manh; Anton Evgrafov; Jens Gravesen; Domenico Lahaye
2014 COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering
doi: 10.1108/COMPEL-07-2013-0234
Purpose – The waste recycling industry increasingly relies on magnetic density separators. These devices generate an upward magnetic force in ferro‐fluids allowing to separate the immersed particles according to their mass density. Recently, a new separator design has been proposed that significantly reduces the required amount of permanent magnet material. The purpose of this paper is to alleviate the undesired end‐effects in this design by altering the shape of the ferromagnetic covers of the individual poles. Design/methodology/approach – The paper represents the shape of the ferromagnetic pole covers with B‐splines and defines a cost functional that measures the non‐uniformity of the magnetic field in an area above the poles. The authors apply an iso‐geometric shape optimization procedure, which allows us to accurately represent, analyze and optimize the geometry using only a few design variables. The design problem is regularized by imposing constraints that enforce the convexity of the pole cover shapes and is solved by a non‐linear optimization procedure. The paper validates the implementation of the algorithm using a simplified variant of the design problem with a known analytical solution. The algorithm is subsequently applied to the problem posed. Findings – The shape optimization attains its target and yields pole cover shapes that give rise to a magnetic field that is uniform over a larger domain. Research limitations/implications – This increased magnetic field uniformity is obtained at the cost of a pole cover shape that differs per pole. This limitation has negligible impact on the manufacturing of the separator. The new pole cover shapes therefore lead to improved performance of the density separation. Practical implications – Due to the larger uniformity the generated field, these shapes should enable larger amounts of waste to be processed than the previous design. Originality/value – This paper treats the shapes optimization of magnetic density separators systematically and presents new shapes for the ferromagnetic poles covers.
Design and performance analysis of live model of Bessel beamformer for adaptive array systemM. Yasin; Pervez Akhtar
2014 COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering
doi: 10.1108/COMPEL-04-2013-0117
Purpose – The purpose of this paper is to design and analyze the performance of live model of Bessel beamformer for thorough comprehension of beamforming in adaptive environment and compared with live model of least mean square (LMS) in terms of gain and mean square error (MSE). It presents the principal elements of communication system. The performance of designed live model is tested for its efficiency in terms of signal recovery, directive gain by minimizing MSE using the “wavrecord” function to bring live audio data in WAV format into the MATLAB workspace. These adaptive techniques are illustrated by appropriate examples. Design/methodology/approach – The proposed algorithm framework relies on MATLAB software with the goal to obtain high efficiency in terms of signal recovery, directive gain by minimizing MSE using the “wavrecord” function to bring live audio data in WAV format. It is assumed that this audio signal is only the message or the baseband signal received by the computer. Here the authors consider computer (laptop) as a base station containing adaptive signal processing algorithm and source (mobile phone) as a desired user, so the experiment setup is designed for uplink application (user to base station) to differentiate between desired signal, multipath and interfering signals as well as to calculate their directions of arrival. Findings – The presented adaptive live model is reliable, robust and lead to a substantial reduction of MSE, signal recovery in comparison with the LMS technique. The paper contains experimental data. Obtained results are presented clearly and the conclusion comes directly from the presented experimental data. The paper shows that the presented method leads to superior results in comparison with the popular LMS method and can be used as a better alternative in many practical applications. Research limitations/implications – The adaptive processes described in the paper are still limited to simulation. It is because of the non‐availability of real system for testing, therefore chosen research approach that is platform of MATLAB is opted for simulation. Therefore, researchers are encouraged to test the proposed algorithms on real system if possible. Practical implications – The paper contains experimental data. The paper's impact on the society is acceptable. These implications are consistent with the findings and the conclusions of the paper. However, there is a need to extend this paper to a next level by implementing the proposed algorithms in the real time environment using FPGA technology. Social implications – This research will improve the signal quality of wireless cellular system by increasing capacity and will reduce the total cost of the system so that cost toward subscribers be decreased. Originality/value – The live model presented in this paper is shown to provide better results. It is the original work and can provide scientific contribution to signal processing community.
Control of limit cycles in buck convertersMarissa Condon; Brendan Hayes
2014 COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering
doi: 10.1108/COMPEL-09-2013-0293
Purpose – The purpose of this paper is to investigate limit cycles in digitally Proportional, Integral and Derivative (PID) controlled buck regulators. Filtering is examined as a means of removing the limit cycles in digitally controlled buck regulators. Design/methodology/approach – The paper explains why limit cycles occur in a digitally PID controlled buck converter. It then proceeds to propose two filters for their elimination. Results indicate the effectiveness of each of the filters. Findings – The paper gives a mathematical analysis of the occurrence of limit cycles in digitally controlled PID buck regulators. It finds that notch and comb filters are effective for the purpose of eliminating limit cycles in buck regulators. Originality/value – The paper employs a model of the buck regulator inclusive of the inductor loss – this was not done to date for this type of work. The paper analyses PID control. This was not done in the manner given. The paper addresses filtering as a means of removing limit cycles. It examines the effect of changing the digital controller parameters on the requirements of the filters.