bluuebunny/crossref_metadata_2025_split huggingface dataset:
Robust control of PMSM system using the structure of MFC
Authors: Pajchrowski Tomasz 
Published: June 2011

PurposeThe purpose of the paper is to find a speed control structure with two degrees of freedom robust against drive parameters variations. Application of structure model following control (MFC) and fuzzy technique in the controller of PI type creates proper non‐linear characteristics, which ensures controller robustness.Design/methodology/approachThe use of proper structure with two degrees of freedom and non‐linear characteristic introduced by fuzzy technique ensures the robustness of the speed control system. The paper proposes a novel approach to MFC synthesis to be performed in two stages. The first stage consists in the set value of P type controller of model and the process controller simultaneously should be designing by fuzzy technique. At the second stage of the synthesis consist in tuning parameters of process fuzzy controller by the swarm of particles method (particle swarm optimization) on the basis of a defined quality index formulated in the paper. The synthesis is performed using simulation techniques and subsequently the behavior of a laboratory speed control system is validated in the experimental setup. The control algorithms of the system are performed by a microprocessor floating point DSP control system.FindingsUse of proper structure with two degrees of freedom of the non‐linear fuzzy controller guarantees expected robustness and improves the dynamics of speed control significantly.Research limitations/implicationsThe proposed structure of MFC was tested on a single machine under well‐defined conditions. Further investigations are required before any industrial applications.Practical implicationsThe proposed controller synthesis and its results may be very helpful in robotic system where changing of system parameters is characteristic for many industrial robots and manipulators.Originality/valueThe paper proposes an original method of synthesis of robust system with two degrees of freedom system validated by simulation and experimental investigations.
Calculation of copper losses in resistance spot welding transformer with space‐ and time‐dependent current density distribution, FEM and measurements
Authors: Popović Jelena , Dolinar Drago , Štumberger Gorazd , Klopčič Beno 
Published: June 2011

PurposeSo far the proposed analytical methods for calculation of copper losses are rather simplified and do not include the time component in the basic partial differential equations, which describe current density distribution. Moreover, when the physical parameters of the transformer (wire dimensions) are out of the certain range, the current density distribution approaches infinity. The purpose of this paper is to offer a generally applicable analytical method. The main goal of the proposed modification of the solution to the current density is improvement of the accuracy and stability of the analytical results.Design/methodology/approachThis paper deals with the calculation of copper losses with various methods, which are based on a time‐dependent electromagnetic field. Analytical method is based on Maxwell equations and Helmholtz equation. Numerical calculation is performed with finite element method (FEM).FindingsAnalytical method is a very accurate and it gives results, which are very similar to the actual behaviour of the current density in the winding. However, the FEM analysis is easier to comprehend, but yet very dependent on input parameters.Research limitations/implicationsThe numerical analysis may not be accurate enough, because of the problems with the oscillation of the output welding current amplitude. To calculate copper losses correctly, the output welding current must be equal in all test cases, especially during the measurements.Originality/valueWhen the physical properties exceed a certain range, the copper losses of the analyzed welding transformer cannot be calculated with existing analytical methods. The new analytical approach gives a far more realistic solution to the current density distribution and improves the accuracy and stability of the results.
Determination of flux density produced by multilevel inverters in CM voltage filter
Authors: Smoleński Robert , Kempski Adam , Bojarski Jacek , Leżyński Piotr 
Published: June 2011

PurposeThe purpose of this paper is to evaluate the conditions in which a saturation of the common mode (CM) choke might appear to be essential for proper design of the CM voltage filters. This paper presents a method for the determination of a CM choke flux density produced by multilevel inverters with carrier‐based modulations.Design/methodology/approachThe proposed combination of secant and tangent methods allows efficient and high‐resolution determination of the CM voltage waveforms produced at the output of the multilevel inverters with commonly used carrier‐based modulations.FindingsThe presented results show that the application of a five‐level inverter with specific modulation causes a decrease of the maximum flux density, down to 15 per cent of the maximum level of the flux density reached in a two‐level inverter. The proposed, dedicated approximation method provides an accuracy of the root estimation better by about three orders for a comparable number of the function calls in comparison with Brent's method.Practical implicationsThe presented theoretical evaluations make possible the determination of the maximum expected value of the flux density produced by multilevel inverters with various types of carrier‐based modulations, which allows a reduction in dimensions, weight and cost of CM chokes applied in CM voltage compensators.Originality/valueIn the paper, the new formulas that describe the placement of triangular carrier functions for commonly used multilevel inverters have been presented. In order to avoid accumulation of the estimation error, during determination of the CM voltage time integral, a dedicated, efficient method of roots approximation has been developed.
Rotor surface losses in an I‐converter‐fed synchronous generator considering saturation
Authors: Vogel Roman , Kulig Stefan 
Published: June 2011

PurposeOperation of synchronous machines in the power range of several 10 MW with variable speed up to 7,000 rpm using a current converter is, thanks to the development of power switches, possible and economically reasonable today. However, current harmonics, produced by converter, generate additional losses, especially eddy current losses on the rotor surface are produced by the converter, which strongly depend on the rotor permeability. The purpose of this paper is to show that an accurate machine modeling is required, in order to consider the nonlinearity of electromagnetic processes inside.Design/methodology/approachThis paper concentrates on the determination of the rotor surface losses in a three‐phase turbogenerator feeding a current converter. Saturation of rotor steel is taken into account using a transient finite element method model of the machine, coupled with a converter model.FindingsA detailed analysis of the damper currents and losses in a turbogenerator operating with a frequency converter is presented. The effectivenes of damper winding modifications, concerning the eddy current loss reduction in the rotor surface, is depicted.Practical implicationsThe introduced modelling technique presents an accurate electromagnetic modelling of an I‐converter‐fed synchronous generator with massiv poles, which is fed by a current converter and so has to sustain additional eddy current losses in the rotor surface. In this way, the amount and distribution of these losses are evaluated more accurately which allows a more efficient design of the damper winding as well as machine cooling system.Originality/valueSome researchers have made contributions to the analysis of current converter‐fed synchronous machine, regarding terminal behaviour of the machine. This paper focuses on eddy current losses on the rotor surface, considering the time and space dependent saturation aspect in the machine, particularly in the rotor.
Transport properties and current flow patterns in homogeneous strongly anisotropic materials
Authors: Chippendale Richard D. , Golosnoy Igor O. , Lewin Paul L. , Sykulski Jan K. 
Published: June 2011

PurposeThe purpose of this paper is to investigate and explain the unexpected current flow patterns and twisting equipotential surfaces observed in strongly anisotropic materials.Design/methodology/approachPotential distributions and current flow paths in highly anisotropic composite materials were studied via numerical simulation and experimentally. Simplified composite panels with two plyes were analysed using a finite‐element model; the predictions were then confirmed experimentally.FindingsThe unexpected twisting equipotential surfaces and current flow patterns were found to be consistent with minimising of Joule heat release in the material. Numerical modelling suggests that the twisted profiles of the potential are highly sensitive to the anisotropic electrical conductivity.Originality/valueThis paper discusses the reverse current flows witnessed in a two‐layer anisotropic system. Such behaviour has never been predicted or observed experimentally before. The reported results will be of interest to anyone who is considering using anisotropic materials such as carbon fibre composites which might experience applied potential difference, such as lightning strikes.
Optimisation of a tubular linear machine with permanent magnets for wave energy extraction
Authors: Parel Thomas S. , Rotaru Mihai D. , Sykulski Jan K. , Hearn Grant E. 
Published: June 2011

PurposeThe purpose of this paper is to optimise the cost‐based performance of a tubular linear generator and to minimise cogging forces.Design/methodology/approachOptimisation of a tubular linear generator with longitudinal flux topology has been undertaken using a finite element method. The computational models used have been verified experimentally.FindingsThe use of an oversized stator linear generator design as opposed to an oversized translator design has the potential to increase the output electromotive force per unit material cost by 25 per cent for slotless iron core topologies and approximately 14 per cent for air core topologies. For cogging force minimisation, optimisation of the length of the stator core is an effective technique for both oversized stator and oversized translator constructions. Comparisons of magnet materials also indicate that the higher cost of rare earth magnets to ferrites is compensated by their superior specific performances.Originality/valueIn this paper, a broader range of design parameters than in previous investigations has been optimised for the slotless iron core and air core topologies. The result relating to cogging force reduction and cost savings (in particular) has the potential to make direct drive wave energy extraction a more competitive technology in terms of reliability and cost.
A new DTC control for PMSM with torque ripple minimization and constant switching frequency
Authors: Sikorski Andrzej , Grodzki Rafał 
Published: June 2011

PurposeThe aim of the paper is to conduct an analytical study of the two new methods of the permanent magnet synchronous motor torque and flux direct control with the predictive non‐linear torque and flux controller.Design/methodology/approachThe method is based on the prediction of the torque and flux error vector in order to minimize the torque ripple and ensure the constant switching frequency.FindingsThe proposed methods ensure the torque and flux error vector minimization, reduction of the torque ripples, and constant switching frequency without deterioration of the dynamic properties of the standard direct torque control (DTC).Originality/valueAn innovative predictive DTC method is presented. The correctness of the analysis and main assumptions, as well as the expected final results have been verified in simulation.
Adaptive stabilization for generator excitation system
Authors: Ritonja Jožef 
Published: June 2011

PurposeThe purpose of this paper is to develop a controller for damping of oscillations of a synchronous generator connected to the electric network. The goal is to determine the configuration of the controller and to set up the procedure for determination of the controller parameters.Design/methodology/approachOn the basis of the analytical and numerical analysis of the so‐far proposed stabilizers, the new directions towards improved and efficient stabilizer have been established. The advantage of the proposed approach has been confirmed with simulations and experimental results.FindingsThree main contributions can be highlighted: on the basis of the synchronous generator analysis, it is shown that the conventional power system stabilizer is inappropriate for optimal oscillation damping through the entire operating range; the possibility of application of the model reference adaptive control theory for stabilizer design is confirmed; and the rules have been set up for selection of the stabilizer parameters.Research limitations/implicationsThe power system control is rather conservative and does not allow new approaches to the control concepts.Originality/valueThe paper's originality lies in the fact that the proposed adaptive approach for realizing the control system for damping of oscillations is presented completely. The configuration of the controller is presented, as well as the method for determining the adaptation mechanism parameters.
Improved accuracy of electro‐quasistatic simulations of large‐scale 3D high voltage insulators with nonlinear material layers
Authors: Weida Daniel , Steinmetz Thorsten , Clemens Markus 
Published: June 2011

PurposeThe purpose of this paper is to analyze the accuracy of finite element method simulations for high voltage equipment featuring resistive field grading.Design/methodology/approachIn such simulations, the order of the mesh used and the polynomial order of the ansatz functions are varied while maintaining mesh and simulation parameters. The resulting accuracy of the simulations is analyzed by an error convergence study which shows the relative errors against the number of degrees of freedom the computational time and the memory consumption.FindingsSimulation results of simplified benchmark geometry and applications to large‐scale 3D high voltage equipment are presented herein.Originality/valueThe impact of the order of the mesh and the Ansatz functions are studied for realistic high voltage setups. The paper helps the user of simulation software to choose adequate simulation parameters.
Spectral inductance of the linear motor‐space harmonic analysis
Authors: Utrata Grzegorz , Kaplon Andrzej 
Published: June 2011

PurposeThe aim of the paper is to present the methodology of obtaining an approximate equivalent circuit composed of lumped parameters which describes an electromagnetic state of induction machines (IMs) with solid secondary. Higher space harmonic field components are taken into account. The proposed method of machine model constructing is useful for solving electrodynamics states of solid secondary IMs, as well linear machines.Design/methodology/approachA determination of equivalent circuit parameters of a polyharmonic machine is divided into two steps. In the first step, frequency plots of the spectral inductances are derived – for each of the space harmonic components – from an electromagnetic field distribution calculated by means of the finite element method. In the second step, each of the spectral inductances are represented by the operational inductances which corresponds to the equivalent circuit composed of parallel connected the magnetizing inductance and branches consisting of resistance and inductance connected in series.FindingsThe proposed method allows the construction of the approximate equivalent circuit with lumped parameters which enables to solve electrodynamic states of solid secondary IMs, as well linear machines. The machine model has been derived with consideration of the higher space harmonic field components.Research limitations/implicationsSaturation effects of a magnetic circuit and an unbalance of phase currents have not been taken into account.Originality/valueThe paper shows the method of constructing a machine field‐circuit model. Lumped parameters of the model have been derived using frequency characteristics of the stator spectral inductance with consideration of the higher space harmonic field components.
Completely online group formation and development: small groups as socio‐technical systems
Authors: Goggins Sean P. , Laffey James , Gallagher Michael 
Published: June 2011

PurposeThis paper has two purposes. First, to provide insight into the formation of completely online small groups, paying special attention to how their work practices develop, and how they form identity. Second, to pursue conceptual development of a more multi‐level view of completely online group experience, which can be made visible through analysis of the unique interaction logging system used in this study.Design/methodology/approachThe authors conduct a mixed methods study that integrates interviews, grounded theory analysis, case study methods and social network analysis to build a multi‐layered view of completely online group and community development.FindingsCompletely online group formation is explicated as a socio‐technical system. The paper identifies themes of tool uptake and use, and patterns of interaction that accompany group formation and development of completely online group practices. These patterns show little respect for the boundaries of space and time. It then shows how groups who are paired together for two non‐sequential activities develop a common internal structural arrangement in the second activity, and are viewable as groups in the larger course context in four of six cases.Research limitations/implicationsThe time bounded nature of the group and community, combined with the educational context limit the generalizability of these findings.Practical implicationsThe study shows how completely online group development can be made visible. Managers of work teams and teachers who work with classrooms in completely online contexts need to recognize the dynamic structure and interaction practices of completely online teams.Originality/valueFirst, little research has been conducted on completely online group formation. Second, a conceptual understanding of how group members relate to one another and how groups interact with other groups in the same socio‐technical context is not explored in prior work. Third, the paper performs this analysis including data from rich, contextualized usage logs, which enables greater insight into online group interactivity than prior research.
Employee management and service provision: a conceptual framework
Authors: Blount Yvette 
Published: June 2011

PurposeThe purpose of this paper is to provide a way of thinking about the technical and social subsystems in the context of e‐commerce adoption.Design/methodology/approachAn interpretive research approach was used to investigate the employee management issues in service industries as they implemented B2C e‐commerce. Two case studies were selected, both retail banks in Australia. One case study was a major bank, the other a smaller bank in a niche market.FindingsEmployees who interact with customers using B2C technologies require different levels of skill and capability than those required in face‐to‐face interactions. This has implications for human resource management processes such as job design, recruitment and retention, performance management and training.Research limitations/implicationsThe study was small in scale and therefore limited in scope. Other service organisations and industries may have quite different information ecologies and business strategies.Practical implicationsThe coactive commerce system provides a concrete way for researchers and practitioners to better align technology, customers and employees to achieve competitive advantage.Social implicationsThis research shows that it is important to understand B2C e‐commerce technologies in conjunction with business practices and in their broader context. It is important to understand how a service organisation's business strategy, technology strategy, business processes and employee management work together to provide an appropriate level of service to customers and achieve sustainable competitive advantage and strategic positioning. This is a complex set of factors.Originality/valueThe coactive commerce system extends the socio‐technical framework to provide a more explicit way to analyse both the social and technical subsystems in an organisation by integrating the human resource management aspects into the theoretical mix in the electronic commerce and information systems literature. This is important because the employee interaction with the customer is the way the customer perceives the organisation.
Why don't more women major in information systems?
Authors: Croasdell David , McLeod Alexander , Simkin Mark G. 
Published: June 2011

PurposeIncreasing enrollments in colleges of business have not been matched by women majoring in the field of information systems (IS). This paper aims to explore reasons why women choose not to major in information technology disciplines and to suggest potential solutions.Design/methodology/approachThe authors used a behavioral model based on the theory of reasoned action and a survey of the students enrolled in six sections of a college‐wide MIS course to help them answer the fundamental question “Why don't more women major in information systems?” They also used partial least squares analysis to estimate the parameters of the model and the results of several open‐ended survey questions to validate their statistical findings, leading to a richer triangulation of study results.FindingsThe study found that a “genuine interest in IS” and the “influence of family” most account for a woman's decision to major in information systems. Equally important are those items that did not appear to attract females, including such matters as “job‐related factors” or the “influence of fellow students or friends”. These findings have important recruitment and retention implications as well as suggesting some avenues for further study.Originality/valueThe analyses suggest that there is much faculty and business recruiters can do to encourage more females to major in IT‐related disciplines. One is to encourage women to develop more interest in the field. Another is to create more study options for women with hard‐science talents who want to pursue technologically‐intensive careers. Finally, teachers, academic institutions, and employers might find it useful to address some of the misconceptions that women might have about IT‐related jobs – for example, that IT jobs are only for males or computer geeks – and stress the many positive dimensions of IT career paths.