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International Review of Electrical Engineering - February 2006 - Preface and acknowledgments



International Review of Electrical Engineering - February 2006 - Papers





International Review of Electrical Engineering - Preface and acknowledgments


go to top    Preface and acknowledgments

        by Santolo MEO

   Vol. 0. n. 0, pp. 1-2



International Review of Electrical Engineering - Papers


go to top    Modelling, Analysis and Control of a DC-connected Wind Farms to Grid
        by F. Iov, A. D. Hansen, P. Sørensen, F. Blaabjerg

   Vol. 0. n. 0, pp. 3-13


Abstract - Nowadays, there is an increasing trend to connect large MW wind farms to the transmission system. Requirements that focus on the influence of the farms on the grid stability and power quality, and on the control capabilities of wind farms have already been established. The main trends of modern wind turbines/farms are clearly the variable speed operation and a grid connection through a power electronic interface, especially using doubly-fed induction generators. Using power electronics the control capabilities of these wind turbines/farms are extended and thus the grid requirements are fulfilled. However, the traditional squirrel-cage generators based wind turbines/wind farms directly connected to the grid have less control capabilities. These wind turbines/farms cannot regulate their production and contribute to power system stability. A DC transmission system for connection of the active stall wind farms to the grid can provide these features and also maximize the produced power especially at low wind speeds by using variable voltage/frequency for the wind farm. The focus in this paper is in studying the variable speed operation for the active stall wind farms using a voltage source converter based DC transmission system.

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Keywords: wind power, active stall wind farms, DC transmission system, variable frequency operation.



go to top    Winding functions theory and Maxwell's equations coupled analytical modeling of an axial flux PM synchronous machine

        by N. Adbelkarim, J. Azzouzi, G. Barakat

   Vol. 0. n. 0, pp. 14-22


Abstract - In this paper, a complete analytical model of an axial flux permanent magnet synchronous machine (AFPMSM) is investigated. This modeling is based on an exact 2D solution of the magnetic field in the machine derived from the Maxwell's equations and coupled with the winding function theory to calculate the back emf, the self and mutual inductances. The developed analytical model is then used to simulate a 10 kW / 130 rpm, 28-poles, AFPMSM dedicated to wind energy application (WEA). According to the simulation results, it is possible to evaluate the performance of the AFPMSM with reasonable accuracy via the developed analytical model.

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Keywords: Disc-type machine, Permanent magnet, magnetic field, analytical method.



go to top    Adaptive Speed Observers for Sensorless Control of Induction Motors : a New Criterion of Stability
        by E. Etien, N. Bensiali, C. Chaigne, G. Champenois

   Vol. 0. n. 0, pp. 23-26


Abstract - A new criterion of stability for the study of adaptive speed observer is presented. It proves to be a good alternative to the classical transfer function analysis and allows to simplify the determination of the regions of stability and to provide a power full tool for observer design.

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Keywords: Induction motor drive, adaptive observer, regenerating mode, stability analysis.



go to top    Stator Faults Diagnosis In Induction Machines
        by S. Bachir, S. Tnani, G. Champenois

   Vol. 0. n. 0, pp. 27-35


Abstract - In this paper, authors proposes a new monitoring technique of inter turns short circuit windings under fixed speed. This method is based on introduction of sinusoidal extra-signals to input voltage delivered by power inverter. For diagnosis, we propose a model of squirrel cage induction motors under stator faults. This model takes into account the effects of inter turn faults resulting in the shorting of one or more circuits of stator phase winding. Experimental test results show the good agreement between the real faults and their estimations.

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Keywords: Induction motor, Estimation technique, Modelling, Excitation system, Diagnostics.



go to top    A Tool for Phase Spectrum Retrieval from Impedance Amplitude Spectrum

        by J. Ahola, E. Vartiainen, T. Lindh, V. Särkimäki, R. Tiainen

   Vol. 0. n. 0, pp. 36-43


Abstract - The estimation of load impedance spectrum is required in the research and applications of electrical engineering. Some of the current applications are the grid   impedance estimation of active filters, the research of the propagation of EMI (Electro Magnetic Interference) and power line communication. The direct measurement of load impedance, in the frequency range in question, requires synchronous voltage and current measurement, which can be difficult. Compared to the direct impedance spectrum measurement, the measurement of impedance amplitude spectrum is a simple and low-cost method since e.g. only peak or RMS (Root-Mean-Square) value of current and voltage for each measured frequency is required. This article presents a method and a tool based on the method that allows one to compute the phase spectrum estimate for the impedance amplitude spectrum. The method is based on the maximum entropy model (MEM). The applicability of the tool is demonstrated with input impedance measurements of a low voltage power cable and a low voltage electric motor, where both the amplitude and the phase spectrum of input impedance were measured in the frequency range of 100 kHz – 30 MHz.

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Keywords: Impedance measurements, phase retrieval, load impedance, active filters, power line communication, electromagnetic interference.



go to top    Analysis of non-Linear Inductors with the Use of Generalized Rayleigh Relations

        by Z. Włodarski, A. Brykalski, J. Włodarska

   Vol. 0. n. 0, pp. 44-48


Abstract - Evaluation of currents in circuits containing ferromagnetic cores involves troublesome graphical or numerical procedures. For materials with narrow hysteresis loops satisfactory good results may be obtained by the use of inductance determined from the analytical approximation of main magnetization curve based on the generalized Rayleygh relations. Extension of this formula to hysteresis loops enables further improvement of computed characteristics.

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Keywords: Modeling, Magnetization Curves, Non-Linear circuits, Hysteresis.



go to top    Speed Synchronized Control of Permanent Magnet Synchronous Motors distributed system with field-weakening capability

        by L. Samaranayake, Y.K. Chin

   Vol. 0. n. 0, pp. 49-56


Abstract - A vast amount of attentions has been given to permanent magnet synchronous motors (PMSMs) in a variety of automotive applications as these motors present higher efficiency, power factor and better dynamic performance than asynchronous motors without sacrificing reliability. It has also been shown that they can be operated over a wide constant power speed range (CPSR) with the field weakening capability. This paper presents a theoretical study on speed synchronized control of the permanent magnet synchronous motors (PMSMs) in both the constant torque and the field-weakening (or constant power) operation regions. Promising applications of this can be found in aero dynamic, naval, material processing etc., industries.

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Keywords: Field-weakening, Permanent Magnet Synchronous Motor, Speed Synchronization.



go to top    A Novel Three-Phase UPS System with a Single-Phase Resonant HF Link

        by M. K. Darwish

   Vol. 0. n. 0, pp. 57-65


Abstract - This paper presents a new three-phase uninterruptible power supply (UPS) system based on a single-phase resonant high frequency (HF) link and a single-phase transformer. The three-phase output voltage is constructed and regulated from a three-phase cycloconverter fed from the constant amplitude, constant frequency link voltage. The generation of a novel switching stategy for the three-phase cycloconverter is presented. The simulation of the proposed system is carried out and verified with experimental results.

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Keywords: UPS, PWM converters, Resonant inverters, HF transformers.



go to top    Linear model and H∞ Control of Shunt Active Power Filter
        by T. Al Chaer, J.P. Gaubert, L. Rambault, C. Dewez

   Vol. 0. n. 0, pp. 66-73


Abstract - This paper presents a shunt active power filter which is intended for eliminating the unwanted harmonics generated by non-linear loads in power distribution systems. An original linear model of a three phase network with a parallel active filter is described as a complex state space representation. Next, the objective of this work is to synthesize a robust static feedback controller for controlling this three phase shunt active power filter. The synthesis of such controller is realized by using H∞ robust control based on a Linear Matrix Inequality (LMI) approach. Theoretical analyses and a complete simulation of the system are presented to confirm the validity of the proposed technique.

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Keywords: Active filters, Harmonics, H Control, Linear model, State space representation.



go to top    Characteristics and Comparison of Output Voltage Non-Idealities of Direct and Indirect Matrix Converters
        by M. Jussila, M. Eskola, H. Tuusa

   Vol. 0. n. 0, pp. 74-82


Abstract - This paper compares the voltage transfer characteristics of direct and indirect matrix converter topologies. Knowledge of the real voltage transfer capability of a converter is essential, especially in sensorless motor drives. The comparison is based on the analysis of non-idealities caused by real semiconductor devices and safe commutation methods. The effects of on-state voltage losses and commutation methods are modeled with equations. The analysis is verified in measurements and simulations. The direct matrix converter follows the reference more accurately than the indirect matrix converter. Thus direct topology is also found to be a more suitable converter solution for sensorless motor drives if no compensation methods of voltage inaccuracies are used. The results show that analysis of voltage transfer inaccuracies in direct and indirect matrix converter topologies can be used as a basis to develop the compensation methods needed in high performance motor drives without speed sensors.

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Keywords: Matrix converter, Output voltage non-ideality, PMSM drive.



go to top    Redundancy and basic switching rules in multilevel converters
        by Ó. López, J. Doval-Gandoy, C. M. Peñalver, J. Rey, F. D. Freijedo

   Vol. 0. n. 0, pp. 83-89


Abstract - This paper studies the per-phase redundancy in three basic multilevel topologies: diode-clamped converter, flying capacitor converter and cascaded bull-bridge converter. Redundancy in switching states provides some flexibility in multilevel systems and may be used to achieve some control objectives: capacitors voltage balancing, current control of dc-sources, switches power looses balancing, fault tolerant systems, etc. This study gives the basic switching rules for each topology taking advantage of redundancy. The similarities between these rules allow the design of a general switching generator useful for these three topologies. The implementation of a switching strategy for the achievement of certain goals consists on adding constrains to these basic rules. The knowledge of the number of different redundant switches states for each level facilitates this implementation. The design of controllers in accordance with the rules proposed in this paper increase the reliability of multilevel converters without adding new devices.

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Keywords: Multilevel converter, per-phase redundancy, switching generator.



go to top    A new single phase single stage high frequency AC-DC converter with CPLD controller
        by S. Mekhilef, A. M. Omar, K. S. Muhammad

   Vol. 0. n. 0, pp. 90-96


Abstract - A new single phase single stage high frequency AC-DC converter with CPLD controller is presented. The digital controller is developed using Complex Programmable Logic Devices (CPLD). The proposed system utilizes a single-phase AC input supply. The power switching devices in the controlled bridge are controlled by the multiple-pulse Pulse Width Modulation (PWM) switching technique to minimize the low order harmonics present on the AC side of the converter. A low pass filter is incorporated in the circuit to filter out unwanted harmonics and provide a sinusoidal AC supply current. A high frequency transformer with 1:1 ratio is used in the design to provide galvanic isolation for better circuit performance and protection. The optimum operation of transformer core in four quadrant of B-H curve is also considered in the proposed converter topology. A laboratory prototype of the converter is developed and tested. Experimental results are compared with the simulation results to illustrate the effectiveness of the proposed technique.

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Keywords: AC-DC converter, CPLD controller, digital controller, multiple-pulse PWM.



go to top    Frequency converter control in single FPGA circuit
        by O. Laakkonen, K. Rauma, A. Penttinen, T. Härkönen, J. Luukko, O. Pyrhönen

   Vol. 0. n. 0, pp. 97-103


Abstract - Modern frequency converters use ASIC (Application Specific Integrated Circuit) circuits to handle fastest operations and microprocessors or DSPs (Digital Signal Processor) for slower operations. By using FPGA (Field Programmable Gate Array) circuits it is possible to implement a powerful microcontroller inside the FPGA circuit and replace the combination of ASIC and microprocessor with a single chip solution. The FPGA implementation allows more flexible modification of the used algorithms and control methods. Single chip implementation of the control algorithms needs efficient and modular architecture to be used in industrial applications. A novel control electronics architecture for frequency converters is presented in this paper. The architecture consists of a single FPGA circuit which consists of a software processor, IP-blocks (Intellectual Property) and an internal bus connecting the IP-blocks. A modern small DC-link capacitor frequency converter is used as a test case. The whole control structure and measurements with a prototype are presented.

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Keywords: Field programmable gate array, RTOS, Frequency converter, single chip, control system, bus architecture.



go to top    Modeling Ferrite Core Losses in Power Electronics
        by A. Van den Bossche, V. C. Valchev

   Vol. 0. n. 0, pp. 104-111


Abstract - The paper summarizes the research of the authors dedicated to ferrite core losses under conditions specific for Power Electronics. Models named NSE and DNSE and models of the losses with DC bias are fully presented and validated. The models are checked with measurements on two different ferrite grades, with square voltage waves with a large variation in duty ratio. The model NSE is extended and improved to DNSE (Double Natural Steinmetz Extension). The dependency of the core looses in half bridge and full bridge configurations of the waveforms are well modeled using a hysteresis part and a part dependent on dB/dt. A model for ferrite loss under DC bias was proposed It is found the relative sensitivity to DC bias is mainly present in the low frequency component of the losses and that the higher frequency losses show an almost quadratic loss dependency on the peak induction.

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Keywords: Ferrite core losses, Modeling and measuring core losses.


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