COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering

Accurate minor loops calculation with a modified Jiles-Atherton hysteresis model : Table of Contents

Jean V. Leite, Abdelkader Benabou, Nelson Sadowski — Sun May 17 14:15:04 BST 2009

Abstract:
Purpose – Although the original Jiles-Atherton (J-A) hysteresis model is able to represent a wide range of major hysteresis loops, in particular those of soft magnetic materials, it can produces non-physical minor loops with its classical equations. The purpose of this paper is to show a modification in the J-A hysteresis model in order to improve the minor and inner loops representation. The proposed technique allows the J-A model representing non-centred minor loops with accuracy as well as improving the symmetric inner loops representation. Design/methodology/approach – Only the irreversible magnetization component is slightly modified keeping unchanged the other model equations and the model simplicity. The high-variation rate of the irreversible magnetization, which causes the non-physical behaviour of minor loops, is limited by introducing a new physical parameter linked to the losses. Contrarily to other modifications of the original model found in the literature, the previously knowledge of the magnetic field waveform is not needed in this case. Findings – The modified hysteresis model is validated by comparison with experimental results. A good agreement is observed between calculations and measurements. The modified model retains the low-computational effort and numerical simplicity of the original one. Originality/value – This paper shows that a classical scalar hysteresis model can be suitably used to take into account the minor loops behaviour and be included in a finite element code. The methodology is useful for the design and analysis of electromagnetic devices under distorted flux patterns.

Electromagnetic modelling of short circuited coreplates : Table of Contents

Sun May 17 14:15:04 BST 2009

Abstract:
Purpose – Coreplates in large generators may suffer from local short circuits. An accurate analysis is required to avoid these failures and detect them when occurring. The purpose of this paper is to develop a lamination stack model compliant with interlamination default analysis. Design/methodology/approach – An electromagnetic model should account for the eddy-current in the lamination stack. To avoid the modelling of the insulation between the steel sheets, the authors propose to introduce a condition on the fields applied between each sheet. In the case of electric fault between several sheets, the conducting domain, i.e. the sheets, is not simply connected. Then, T-O formulation must be adapted to solve such problem. Findings – The model allows to account for thin plates, insulating layers and electrical faults in electromagnetic modeling of core plates. This study leads to a first evaluation of eddy current losses in steel laminations with defaults. Research limitations/implications – The present study does not take into account thermal effects. The next step will consist in a magneto-thermal computation. Thus, an electromagnetic finite element software must be coupled with a thermal one. An other improvement will rely on the study of actual situation in order to evaluate the accuracy of industrial sensors and to compare with measurements. Originality/value – The paper develops a lamination stack model compliant with interlamination default analysis. As far as the authors know, this is the first study on 3D electromagnetic modeling.

Comparison of a simple and a detailed model of magnetic hysteresis with measurements on electrical steel : Table of Contents

Hanif Tavakoli, Dierk Bormann, David Ribbenfjärd, Göran Engdahl — Sun May 17 14:15:04 BST 2009

Abstract:
Purpose – For efficient magnetic field calculations in electrical machines, the hysteresis and losses in laminated electrical steel must be modeled in a simple and reliable way. The purpose of this paper is to investigate and discuss the potential of a simple complex-permeability model. Design/methodology/approach – A frequency dependent complex-permeability model as well as a more detailed model (describing hysteresis, classical eddy current effects, and excess losses separately) are compared to single-sheet measurements on laminated electrical steel. It is discussed under which circumstances the simple complex-µ model is an adequate substitute for the more detailed model. Findings – A satisfactory agreement of the simple complex-µ model was found with both detailed model and measurements, improving with increasing frequencies. This is true not only for the effective permeability function, but holds also for the detailed H-B characteristics (hysteresis). Originality/value – It is demonstrated that the complex-µ model is a reliable and convenient starting point for the estimation of flux distribution and losses in complicated magnetic core geometries.

Modelling dynamic hysteresis loops in steel sheets : Table of Contents

Krzysztof Chwastek, Jan Szczyglowski, Wieslaw Wilczynski — Sun May 17 14:15:04 BST 2009

Abstract:
Purpose – The aim of the paper is to present a simple approach to modelling minor hysteresis loops in grain-oriented steel sheets under quasi-static and dynamic conditions. The hysteresis phenomenon is described with a recently developed hybrid model, which combines ideas inherent in the product Preisach model and the Jiles-Atherton description. The dynamic effects due to eddy currents are taken into account in the description using a lagged response with respect to the input. Design/methodology/approach – It is assumed that some model parameters might be dependent on the level of relative magnetization within the material. Their dependencies could be given as power laws. The values of scaling coefficients in power laws are determined. Findings – A satisfactory agreement of experimental and modelled quasi-static and dynamic hysteresis loops is obtained. Research limitations/implications – The present study provides a starting point for further verification of the approach for other classes of soft magnetic materials, which could be described with the developed model. At present, the approach to model minor loops by the update of model parameters is verified for the B-sine excitation case. Practical implications – The “branch-and-bound” optimization algorithm is a useful tool for recovery of the values of both model parameters and scaling coefficients as well. Originality/value – The recently developed hybrid description of hysteresis phenomenon can be successfully extended to take into account symmetric minor loops. The developed approach could be a framework to develop a comprehensive description of magnetization phenomena in the future.

Broken rotor bar impact on sensorless control of induction machine : Table of Contents

Piotr Kolodziejek, Elzbieta Bogalecka — Sun May 17 14:15:04 BST 2009

Abstract:
Purpose – The purpose of this paper is analysis of the sensorless control system of induction machine with broken rotor for diagnostic purposes. Increasing popularity of sensorless controlled variable speed drives requires research in area of reliability, range of stable operation, fault symptoms and application of diagnosis methods. Design/methodology/approach – T transformation used for conversion of instantaneous rotor currents electrical circuit representation to space vector components is investigated to apply with closed-loop modeling algorithm. Evaluation of the algorithm is based on analysis of asymmetry influence to the orthogonal and zero components of space vector representation. Multiscalar model of the machine and selected structures of state observers are used for sensorless control system synthesis. Proposed method of frequency characteristics calculation is used for state observers analysis in open-loop operation. Findings – New algorithm of applying the T transformation allows for closed-loop and sensorless control system simulation with asymmetric machine due to broken rotor. Compensating effect of the closed-loop control system with speed measurements and diagnosis information in control system variables are identified. Proposed frequency analysis of state observers is presented and applied. Variables with amplified characteristic frequency components related to rotor asymmetry are compared for selected structures of state observers and with closed-loop and open-loop operation. Method of improving the sensorless system stability is proposed. Practical implications – In closed-loop and sensorless control system rotor fault can be diagnosed by using PI output controllers variables. Compensating effect of mechanical variables sets limitation to specified diagnosis methods. Rotor asymmetry affects sensorless control system stability depending on estimator structure. Originality/value – This paper concentrates upon sensorless control system operation with machine asymmetry and indicates rotor fault symptoms.

Numerical modelling of non-linear coupled thermo-electric problems: A comparative study : Table of Contents

Igor O. Golosnoy, Jan K. Sykulski — Sun May 17 14:15:04 BST 2009

Abstract:
Purpose – The purpose of this paper is to access performance of existing computational techniques to model strongly non-linear coupled thermo-electric problems. Design/methodology/approach – A thermistor is studied as an example of a strongly non-linear diffusion problem. The temperature field and the current flow in the device are mutually coupled via ohmic heating and very rapid variations of electric conductivity with temperature and applied electric field, which makes the problem an ideal test case for the computational techniques. The finite volume fully coupled and fractional steps (splitting) approaches on a fixed computational grid are compared with a fully coupled front-fixing method. The algorithms' input parameters are verified by comparison with published experiments. Findings – It was found that fully coupled methods are more effective for non-linear diffusion problems. The front fixing provides additional improvements in terms of accuracy and computational cost. Originality/value – This paper for the first time compares in detail advantages and implementation complications of each method being applied to the coupled thermo-electric problems. Particular attention is paid to conservation properties of the algorithms and accurate solutions in the transition region with rapid changes in material properties.

Symmetrization of asymmetrical nonlinear three-phase load supplied from non-ideal sinusoidal voltage source : Table of Contents

Krzysztof Debowski, Marian Pasko — Sun May 17 14:15:04 BST 2009

Abstract:
Purpose – The purpose of this paper is to deal with the problem of symmetrization of asymmetrical three-phase delta connected nonlinear load. In the model of the three-phase sinusoidal voltage source have also been included inner impedances. The purpose is to obtain symmetrical line currents of the voltage source, to minimize RMS values of currents and to minimize higher harmonics generated by nonlinear loads. Design/methodology/approach – This symmetrization of the system is realized by means of a symmetrizing system, which is composed of LC one-ports. In order to solve the problem the symmetrical component theory is applied. The structure of symmetrizing system is consisted of two components: parameters determined for the basic harmonic and the filter for elimination of the higher harmonics generated by nonlinear loads. Findings – After symmetrization line currents of the source will be symmetrical with lower RMS values than before symmetrization, and the source will generate the greater active power than beforehand. Research limitations/implications – This approach can be used for inertialess (non-reactive) elements in systems, where currents are periodical. Practical implications – The results of symmetrization can be useful for high-power systems where LC one-ports can be used, e.g. for arc furnaces. Originality/value – Application of presented methods makes possible to improve the working point of the system, i.e. voltage source can generate greater active power than before symmetrization and line currents can be symmetrical.

Rotor-design and on-line starting-performance analysis of a synchronous-reluctance motor : Table of Contents

Damijan Miljavec, Mykhaylo Zagirnyak, Bogomir Zidaric — Sun May 17 14:15:04 BST 2009

Abstract:
Purpose – The purpose of this paper is to derive the geometry-based equations for inductances which are used in circuit theory analysis of synchronous reluctance motor (SRM). Transient and steady state performance analyze of SRM by using the 2D time-stepping finite-element method (FEM). Design/methodology/approach – The analytical approach is used to obtain the equations which describe geometry dependent magnetizing inductances of SRM. Transient and steady state performance of the SRM is analyzed by using the 2D time-stepping FEM. The external electric circuit connected with the finite-element model of the SRM geometry allows the study of almost any of the electric and magnetic properties of the machine. Presented SRM model is also connected to the external mechanical loads (friction, rotor inertia and load torque). The use of different materials for the magnetic-pole part of the rotor and for flux barriers was analyzed. The flux barriers in the first SRM rotor were filled with a pure massive electrically conductive ferromagnetic with a proper B-H curve, whereas the rotor magnetic segments were made of non-conductive electric steel described with its B-H curve. The conductive barriers with their end rings form a squirrel cage and allow SRM to start on-line. The flux barriers of the second SRM rotor were made of aluminum but between the second and third flux barrier a massive electrically-conductive ferromagnetic was inserted which during starting-up acted as a part of the squirrel cage. All of the flux barriers of the third SRM rotor were made of electrically-conductive aluminum with iron parts axially laminated. The finite-element SRM models coupled with an electric circuit is also used to evaluate the motor performance at various asynchronous speeds. Findings – Analytical geometry-dependant equations for the d- and q-axis SRM inductances are derived. On the basis of the proposed 2D time-stepping finite-element analysis, the start-up performance for the SRM rotor design using different materials is established. The torque distribution as a function of time at any of the observed asynchronous speeds is not smooth and uniform. It consists of the stator-to-rotor tooth pulsating torque, and the synchronous and asynchronous component. Research limitations/implications – The main disadvantage of analytical geometry-dependant equations for the d- and q-axis SRM inductances is the linearization of any of the ferromagnetic parts. Practical implications – On the basis of the proposed 2D time-stepping finite-element analysis, the start-up performance, asynchronous run and synchronous torque characteristics for the SRM rotor design using different materials are established. Originality/value – The value of the paper is the closed view about happenings in rotor flux barriers of SRM, mostly regarding the time distribution of induced currents in the rotor flux barriers. On the base of 2D time-stepping FEM, the use of different materials for the magnetic-pole part of the rotor and for flux barriers was analyzed.

Numerical modeling of 3-D comb drive electrostatic accelerometers structure (method of levitation force reduction) : Table of Contents

Slawomir Wiak, Krzysztof Smólka — Sun May 17 14:15:04 BST 2009

Abstract:
Purpose – The purpose of this paper is to discuss the numerical modelling of 3D structure of micro-electro-mechanical systems (MEMS) accelerometers. The general idea being discussed is the method of levitation force reduction, as the main source of incorrect mathematical model of comb drive structure. Design/methodology/approach – Accelerometers design is a highly interdisciplinary area and, therefore, different methods and tools have to be exploited. Dynamic accelerometer behaviour modelling has been performed by use of a new object-oriented model (NOOM), based on complex computer field and mechanical models. Findings – The paper describes methods of levitation force reduction in electrostatic comb drive structures based on electrostatic structural models and finite elements method. Research limitations/implications – In the present work, the authors limit themselves to the electrostatic energy domains. Practical implications – Both, mechanical and electric models of accelerometers give the input data for defining the object-oriented model, based on Matlab-Simulink platform, fulfilling the general demand of dynamic behaviour simulation of comb drive structure. The proposed by authors methodology could give valuable contribution to MEMS design methodology. Originality/value – A new methodology has been successfully applied to calculation of levitation force in different geometries of comb drive. This methodology could be useful for multidisciplinary MEMS systems.

Scattering by a two-dimensional doped photonic crystal presenting an optical Kerr effect : Table of Contents

Pierre Godard, Frédéric Zolla, André Nicolet — Sun May 17 14:15:04 BST 2009

Abstract:
Purpose – The purpose of this paper is to discuss two-dimensional electromagnetic diffraction by a finite set of parallel nonlinear rods (optical Kerr effect). To point out the versatility of this approach, a nonlinear (Kerr-effect) finite crystal is considered. Design/methodology/approach – In this paper, a new route for obtaining the scattered field by nonlinear obstacles is proposed. The basic idea consists in simulating the real incident field (e.g. plane waves) by a virtual field emitted by an appropriate antenna, located in a meshed domain, and encompassing or lying above the obstacles. This latest problem is then solved by a finite element method that is well suited to take into account the material inhomogeneities due to the nonlinearity of the permittivity. Findings – The transmission through a finite Kerr crystal doped by a microcavity is given and a resonant wavelength is obtained. At this resonant wavelength, it is shown that the nonlinearity has a large influence on the behaviour of the electromagnetic wave. Originality/value – Introducing the concept of virtual antenna, the paper proposes a rigorous treatment of the scattering of an electromagnetic wave by a bounded nonlinear obstacle of arbitrary shape.

The influence of magnetic hysteresis on magnetorheological fluid clutch operation : Table of Contents

Cezary Jedryczka, Piotr Sujka, Wojciech Szelag — Sun May 17 14:15:04 BST 2009

Abstract:
Purpose – The purpose of this paper is to elaborate upon the mathematical model of coupled electromagnetic, fluid dynamic and motion phenomena that will allow for investigation of the magnetic hysteresis influence on the axial symmetry magnetorheological fluid (MRF) clutch operation. Design/methodology/approach – To solve the partial differential equations describing magnetic vector and fluid velocity potential distributions in axial symmetry MRF electromechanical transducers the finite-element methods have been applied. To solve model equations in the time domain, the time stepping method have been adopted. To introduce magnetic hysteresis phenomenon to presented approach the Jiles-Atherton model have been applied. The physical properties of MRFs have been modeled by means of the Bingham model. Owing to high nonlinearity of the considered problem to solve obtained matrix equations systems the iterative Newton-Raphson combined with the block over relaxation method have been applied. Findings – The proposed model of coupled phenomena and the elaborated algorithm for solving the nonlinear model equations can be successfully applied in the analysis of transients in the MRF transducers taking fluid dynamics and magnetic hysteresis into account. Comparison of the measured and calculated clutch characteristics proves the model accuracy. Moreover, it has been shown that the residual magnetic flux density of the ferromagnetic core has significant impact on both to yield stresses forming in MRFs as well as the torque in disengagement clutch operation. Originality/value – Development of the method for analysis of transients electromagnetic and fluid flow phenomena in MRF transducers taking magnetic hysteresis, electric circuits and motion into account. The presented approach is universal and can be successfully applied in other types of MRF electromechanical transducers such as clutch, brakes, rotary and linear dampers.

Phenomena of additional cogging torque components influenced by stator lamination stacking methods in PM motors : Table of Contents

Lovrenc Gašparin, Andrej Cernigoj, Rastko Fišer — Sun May 17 14:15:04 BST 2009

Abstract:
Purpose – The purpose of this paper is to estimate and evaluate how cogging torque in permanent magnet (PM) motor designs is sensitive to the number of applied interlocks in stator back-iron, which is a standard method for stator lamination stacking. Design/methodology/approach – The PM motors exhibit inherent cogging torque, which creates torque ripple and prevents smooth rotation of the rotor resulting in undesirable vibration and noise. While cogging torque minimization is necessary to improve PM motor performance, several FEM models have been developed to study and present data demonstrating sensitivity of the cogging torque to the applied interlocks. A procedure that would predict and evaluate cogging torque components relative to chosen number and positions of interlocks was proposed. Findings – On the basis of theoretical considerations, which were verified by numerous performed simulations using different FEM models, it was found out and proved that interlocks in the stator back-iron cause the phenomenon of additional cogging torque harmonic components (AHC). Taking into account presented theoretical aspects motor designers can predict, which AHC will comprise the cogging torque. Each motor design has its own optimal value of interlocks, therefore a precise study should be performed during the design process. Practical implications – By utilizing presented method and considering recommendations, advanced designers of PM motors will have a reliable tool for predicting the order and the level of AHC in total cogging torque due to the stator lamination stacking methods. Originality/value – The paper presents theoretical aspects and analytical equations of AHC of PM motors. So far, the authors dealing with the cogging torque of the PM motors did not take into account the influence of the stator lamination stacking method on the level of torque oscillations. The new contribution is also the study of the sensitivity of different motor designs to the number and position of interlocks, which enables the minimization of the AHC in order to fulfil stringent market demands for low-cogging torque level.

Amorphous modular transformers and their 3D magnetic fields calculation with FEM : Table of Contents

K. Zakrzewski, B. Tomczuk, D. Koteras — Sun May 17 14:15:04 BST 2009

Abstract:
Purpose – The purpose of this paper is to examine the calculation of magnetic field distribution in the modular amorphous transformers under short-circuit state including the flux by the voltage supplying. The magnetically asymmetrical transformer (amorphous asymmetrical transformer – AAT) has been compared also with the symmetrical one (amorphous symmetrical transformer – AST). Design/methodology/approach – 3D field problems were analyzed with total ? and reduced f potentials within the finite element method (FEM). The calculated fluxes have been verified experimentally. Findings – The field method which includes voltage excitation is helpful for flux density (B) calculation and winding reactances determination, as well. Calculations and tests yield similar flux distributions in both AST and AAT constructions. One should emphasize that AAT is better for manufacturing and repairing. Research limitations/implications – Owing to very thin (80?µm) amorphous ribbon, the solid core has been assumed for computer simulations. Originality/value – Employment of a field method for calculation of the innovative three-phase amorphous modular transformers. New construction of amorphous transformer, i.e. AAT, has been manufactured at Opole University of Technology.

Loop analysis of multi-branch, multi-node non-linear circuits using singular formulation : Table of Contents

Andrzej Demenko, Rafal Wojciechowski — Sun May 17 14:15:04 BST 2009

Abstract:
Purpose – The purpose of this paper is to find effective methods of loop analysis of multi-branch and multi-node non-linear circuits using a singular formulation. Design/methodology/approach – The classical loop analysis and the loop analysis using a singular formulation have been compared. The non-linear systems of equations have been considered and iterative procedures of solving non-linear equations have been applied. Special attention has been paid to the Newton-Raphson method combined with successive over relaxation and incomplete Cholesky conjugate gradient methods. The convergence of the methods has been discussed. Findings – It has been shown that in the case of the loop analysis of non-linear circuits it is not necessary to form fundamental loops. The system of loop equations with a singular coefficient matrix can be successfully solved iteratively. Using a singular formulation one of the infinitely many solutions can be found quicker than the only one resulting from a classical method with a non-singular coefficient matrix. Therefore, in the case of the analysis of multi-branch and multi-node non-linear circuits using iterative methods, it is beneficial to introduce superfluous loops. This results in more economical computation and faster convergence. Originality/value – The presented methods of solving multi-branch and multi-node non-linear circuits using a singular formulation are universal and may be successfully applied both in circuit analysis and the FE analysis using edge elements for non-linear problems with a large number of unknowns.

Steady and transient states modelling methods of matrix-reactance frequency converter with buck-boost topology : Table of Contents

Igor Ye. Korotyeyev, Zbigniew Fedyczak — Sun May 17 14:15:04 BST 2009

Abstract:
Purpose – The purpose of this paper is to introduce methods for calculating steady-state and transient processes in a symmetrical three-phase matrix-reactance frequency converter (MRFC). The MRFC in question makes it possible to obtain a load output voltage much greater than the input voltage. Design/methodology/approach – MRFCs based on a matrix-reactance chopper are used for both frequency and voltage transformation. The processes in a MRFC system are described by nonstationary differential equations. A two-frequency complex function method is proposed for solving non-stationary equations in steady-state. The method is applied to a state-space averaged mathematical model used in the analysis of the discussed MRFC. A two-frequency matrix transform is proposed for solving non-stationary equations. This method can be used to find both transient and steady-state processes. Findings – The two-frequency complex function method permits the reduction from 12 non-stationary differential equations to four stationary differential equations. The two-frequency matrix transform allows the transformation of non-stationary differential equations to stationary ones. By using these methods descriptions of steady-state and transient properties of buck-boost MRFCs are obtained. Originality/value – A new method of solving of nonstationary differential equations is presented. The method is useful for process analyses in nonstationary power electronic converters.

Application of MLP and RBF neural networks in the control structure of the drive system with elastic joint : Table of Contents

Teresa Orlowska-Kowalska, Marcin Kaminski — Sun May 17 14:15:04 BST 2009

Abstract:
Purpose – The purpose of this paper is to obtain an estimation of not measured mechanical state variables of the drive system with elastic coupling between the driven motor and a load machine, using neural networks (NN) of different type for the sensorless drive system. Design/methodology/approach – The load-side speed and the torsional torque are estimated using multi-layer perceptron (MLP) and radial basis function (RBF) networks. The special forms of input vectors for neural state estimators were proposed and tested in open- and closed-loop control structure. The estimation quality as well as sensitivity of neural estimators to the changes of the inertia moment of the load machine were evaluated and compared. Findings – It is shown that an application of RBF-based neural estimators can give better accuracy of the load speed and torsional torque estimation, especially for the proper choice of the input vector of NN, also in the case of a big change of the load machine time constant. Research limitations/implications – The investigation and comparison is based on simulation tests and looked mainly at the quality of state variable estimation while the realisation cost in parallel processing devices (FPGA) still need to be addressed. Practical implications – The proposed neural state variable estimators of two-mass system can be practically implemented in the control structure of two-mass drive with additional feedbacks from load machine speed and torsional torque, which results in the successive vibration damping. Originality/value – The application of RBF neural state estimators for two-mass drive and their comparison with commonly used MLP-based estimators, as well as testing of both type of NN in the closed-loop control structure with additional feedbacks based on state variables estimated by neural estimators.

Spectral-element method for high-speed rotating cylinders : Table of Contents

Herbert De Gersem — Sun May 17 14:15:04 BST 2009

Abstract:
Purpose – The purpose of this paper is to offer a fast and reliable discretisation scheme for computing the electromagnetic fields inside a ferromagnetic cylinder, accounting for motional eddy currents under high velocities and accounting for the severe ferromagnetic saturation of the rotor surface. Design/methodology/approach – A nonlinear spectral-element (SE) formulation is developed and compared to existing analytical and finite-element approaches. Findings – The proposed SE method results in a higher accuracy, allows for smaller models, avoids upwinding and needs less computation time. Disadvantages are the dense system matrix and the bad condition number. Research limitations/implications – The SE approach is only developed and tested for 2D models with a single cylindrical domain. Practical implications – The results of the paper may improve the design and optimisation of solid-rotor induction machines and magnetic bearings. Originality/value – The paper offers an appropriate solution for a computational problem, which already has been encountered by a large community of researchers and engineers dealing with high-speed rotating devices.

Modelling of a car starter with permanent magnet commutator motor : Table of Contents

M. Ciurys, I. Dudzikowski, D. Gierak — Sun May 17 14:15:04 BST 2009

Abstract:
Purpose – The purpose of this paper is to present a developed modelling method of a car starter with permanent magnet commutator motor. Design/methodology/approach – Mathematical model, algorithm and computational program of electrical and mechanical quantities transients in the system: battery – car starter with permanent magnet commutator motor and planetary gear – combustion engine were developed. Circuit-field method was applied. Magnetic quantities determined using time-stepped finite-element method (with the help of Maxwell software) were used as the parameters of mathematical model equations in circuital part. Program was developed in the Matlab environment. Findings – The developed mathematical model, the algorithm and the program enable the computations of transients of electrical and mechanical quantities at different ambient temperature, by different swept capacity of the combustion engine as well as by different battery capacity and different charge ratio. Research limitations/implications – The analysis was carried out on an example of four-cylinder combustion engine. However, the developed modelling method can be used for analysis of different combustion engines start-up. Practical implications – The proposed modelling method is useful for analysis of car starters at the stage of design. Originality/value – The originality of the work consist in the fact that in the developed model variation of the car starter load torque as well as the variations of the entire mechanical system moment of inertia were taken into account.

Analysis of the force ripples of a current loaded PMLSM : Table of Contents

Ghislain Remy, Julien Gomand, Abdelmounaïm Tounzi, Pierre-Jean Barre — Sun May 17 14:15:04 BST 2009

Abstract:
Purpose – The purpose of this paper is to present an analysis of the force ripples of an open slot permanent magnet linear synchronous motor (PMLSM). A calculation procedure using 2D finite elements method (2D-FEM) is then evaluated with experimentations. Design/methodology/approach – First, the studied PMLSM and its main features are introduced. Then, the 2D-FEM model used to study the motor is presented. The methods used to calculate the force and the meshing procedures are also highlighted. The calculated no-load force is compared to measurements. Lastly, the validated model is used to study the influence of the current magnitude on the force ripples at load. Findings – In addition to the no-load case, the influence of the current magnitude on these forces is presented. Originality/value – The paper is orientated with a sound industrial background. For that reason, the impact of the current saturation on the thrust generation is presented via the evolution of the thrust coefficient, which is the force to the RMS currents ratio.

TESTCASE: a benchmark problem for coupled field-circuit simulations : Table of Contents

M. van der Giet, E. Lange, K. Hameyer — Sun May 17 14:15:04 BST 2009

Abstract:
Purpose – The purpose of this paper is to present an experimental setup for the verification of coupled electromagnetic field-circuit simulation, called TESTCASE. By means of simple and well-defined geometries, the comparison of different coupling approaches among each other and with measurements should be possible. Design/methodology/approach – The physical setup consists of a C-core in conjunction with a reluctance rotor. The TESTCASE is designed to work in static operation and with motion induced voltage. Findings – Simulation results using different approaches as well as measurement results are presented. Practical issues in measurement and simulation are discussed. It was found that particular care has to be taken concerning the modeling of the air around the TESTCASE structure. Originality/value – With the proposed approach, it is possible to evaluate the coupled field circuit problem on a defined and well-known geometry. Simulation results can be compared to measurements.

Voltage security constrained minimization of power losses in an electric power system : Table of Contents

Matjaž Dolinar, Miloš Pantoš, Drago Dolinar — Sun May 17 14:15:04 BST 2009

Abstract:
Purpose – The purpose of this paper is to present an improved approach to reactive power planning in electric power systems (EPS). It is based on minimization of a transmission network's active power losses. Several operating conditions have to be fulfilled to ensure stable operation of an EPS with minimal power losses. Some new limitations such as voltage instability detection and generator capability curve limit have been added to the existing method in order to improve the reliability of reactive power planning. The proposed method was tested on a model of the Slovenian power system. The results show the achievement of significant reduction in active power losses, while maintaining adequate EPS security. Design/methodology/approach – Optimal voltage profile has to be found in order to determine minimal possible active power losses of EPS. The objective function, used to find the optimal voltage profile, has integer and floating point variables and is non-differentiable with several local minima. Additionally, to ensure secure operation of EPS, several equality and inequality boundaries and limitations have to be applied. Differential evolution (DE) was used to solve the optimization problem. Findings – Corresponding reactive power planning can significantly reduce active power losses in EPS. However, such planning can affect the security of EPS, therefore, several additional constrains have to be considered. The presented constrains considerably improve the operational security of EPS. Research limitations/implications – DE was used to solve the minimization problem. Although this method has proven to be fast and reliable, it is theoretically possible that the obtained solution is not global minimum. Originality/value – Novel approach to voltage security constrained reactive power planning with additional nonlinear constrains, such as generator capability curves and voltage instability detection.

Modeling non-linear passive direct methanol fuel cells : Table of Contents

Piergiorgio Alotto, Massimo Guarnieri, Federico Moro — Sun May 17 14:15:04 BST 2009

Abstract:
Purpose – The purpose of this paper is to simulate micro direct methanol fuel cells (DMFCs) for portable electronic devices by means of a non-linear equivalent circuit based on a fully coupled, dynamic, electrochemical model. Design/methodology/approach – The equivalent circuit accounts for electrochemical reactions and electric current generation inside the catalyst layers, electronic and protonic conduction, fuel crossover across the membrane, mass transport of reactants inside the diffusion layers. The V-I characteristic of the device is obtained by combining mass transport and electric equations. The transient dynamics is accounted for by an equivalent capacitance, while the slow dynamics by the mass conservation equation. The equivalent circuit is embedded in the Matlab/Simulink® dynamic model of a hybrid system, consisting of a micro fuel cell and a Li-ion rechargeable battery. Findings – An original equivalent circuit of a passive DMFC suitable for static and dynamic simulations under variable loading conditions is proposed and validated. Research limitations/implications – The one-dimensional model of the micro cell does not take into account transverse mass transfer and current density variations in the cell layers, which can be due to non-homogeneous materials or to the complex dynamics of the convective mass flow in the reservoir and in the room air. Practical implications – The equivalent circuit can be used for simulating the dynamic performance in realistic operating conditions when the fuel cell is used to supply the electronic equipment through a power management unit. Originality/value – The DMFC is described from an electrical point of view as a controlled non-linear generator; such equivalent representation is particularly suited for designing power management units for electronic portable devices.