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  • 101.
    Meier, Stephan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    System Aspects and Modulation Strategies of an HVDC-based Converter System for Wind Farms2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

     

    In this thesis, a new HVDC-based converter system for wind farms is investigated. It is based on a mutually commutated soft-switching converter system and provides a unique integrated solution for the wind turbine generator drive systems, the wind turbine interconnection, and the power conversion for HVDC transmission.

    In a wind farm, the mutually commutated converter system is a distributed system. A medium-frequency collection grid connects the converter station, equipped with a single-phase voltage source converter and a medium-frequency transmission transformer, with the wind turbines, each containing a cycloconverter and a medium-frequency distribution transformer. In this thesis, various system aspects regarding the application of a distributed mutually commutated converter system in a wind farm are investigated. Special attention is paid to the design of a medium-frequency collection grid that has an acceptable level of transient overvoltages, the design of medium-frequency transformers with suitable magnetic, electric and thermal properties, and the development of a strategy to commutate the voltage source converter during low power generation.

    In order to adapt the mutually commutated converter system for an application in a wind farm, it had to be further developped. Different carrier-based and space-vector oriented modulation methods have been investigated. It turns out that for any load angle there is a quasi-discontinuous pulse width modulation strategy that can produce the same pulse patterns as space vector modulation. In addition, a modulation strategy has been developed that allows to replace the IGBTs in the cycloconverter with cheap, robust, and reliable fast thyristors, despite their absence of turn-off capability. The feasibility of different modulation strategies for mutually commutated converter systems has been verified on a down-scaled prototype converter system with both IGBT- and thyristor-based cycloconverters.

    Finally, a feasible wind farm layout is proposed, which considerably reduces the energy generation costs for large winds farms distant to a strong grid connection point. As a consequence, the proposed solution may facilitate the establishment of remotely located wind farms.

     

  • 102.
    Meier, Stephan
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Kjaer, Philip C.
    Benchmark of annual energy production for different wind farm topologies2005In: PESC Record - IEEE Annual Power Electronics Specialists Conference, 2005, Vol. 2005, no 1581918, p. 2073-2080Conference paper (Refereed)
    Abstract [en]

    Wind power generation has become an established alternative power source. Especially large wind farms in remote or offshore locations are emerging strongly. Their grid connection demands new transmission solutions as distances increase. A newly proposed voltage source converter (VSC) based HVDC transmission system looks promising compared to conventional AC and DC transmission systems. This paper presents a benchmark of the estimated annual energy production (AEP) of a 200 MW wind farm depending on the transmission distance and the average wind speed. The proposed system is compared to two state-of-the-art wind farm topologies: Variable-speed wind turbines with doubly-fed induction generators (DFIG) and either AC or DC transmission systems. The benchmark comprises detailed drive-train, converter, transformer, distribution and transmission loss models. The total system losses as well as the loss distribution between the different components as a function of the transmission distance and the average wind speed allows important conclusions for future wind farm projects.

  • 103.
    Meier, Stephan
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Kjellqvist, Tommy
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Norrga, Staffan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Design Considerations for Medium-Frequency Power Transformers in Offshore Wind Farms2009In: 2009 13th European Conference on Power Electronics and Applications, EPE '09, IEEE , 2009, p. 757-768Conference paper (Refereed)
    Abstract [en]

    In a recently proposed converter system for offshore wind farms, single-phase medium-fire (MF) transformers replace the conventional three-phase line-frequency transformers that convert the electricity from the wind turbine generators to high voltage. MF operation allows a reduction of the transformer size and weight, thus leading to a compact and efficient design, which minimizes the installation and maintenance costs, This paper presents design considerations for dry-type single-phase MF power transformers in offshore wind farms. Recent transformer problems in large wind turbines have shown that a thorough and careful magnetic, electric, and thermal design is required to ensure the reliability and performance of the transformers. As a result, a suitable design for a 3 MW wind turbine transformer is proposed.

  • 104.
    Meier, Stephan
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Kuschke, Maren
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Norrga, Staffan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Space Vector Modulation for Mutually Commutated Isolated Three-Phase Converter Systems2008In: 39th IEEE Power Electronic Specialists Conference (PESC 08) Rhodes, GREECE, JUN 15-19, 2008, 2008, p. 4465-4471Conference paper (Refereed)
    Abstract [en]

    Converter systems consisting of a voltage source converter and a cycloconverter connected by a medium-frequency transformer have several attractive properties. They offer bidirectional AC/DC conversion as well as voltage transformation and isolation by the transformer. Furthermore, it is possible to achieve soft-switching conditions for all semiconductor devices by consistently commutating the two converters in alternation; hence the name "mutually commutated converter system". Such a commutation scheme, however, imposes certain restrictions on the modulation of the converter system. A newly proposed space vector oriented modulation method promises superior performance compared to carrier-based modulation methods. This paper describes the implementation of the considered space vector modulation on the example of a 40 WA prototype converter system. The experimental results show that the evaluated space vector modulation is particularly beneficial at low output voltages due to its inherent nature of maximizing the zero voltage vectors.

  • 105.
    Meier, Stephan
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Norrga, Staffan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Control Strategies for Mutually Commutated Converter Systems without Cycloconverter Turn-off Capability2008In: EEE POWER ELECTRONICS SPECIALISTS CONFERENCE RECORDS, 2008, p. 1344-1350Conference paper (Refereed)
    Abstract [en]

    Mutually commutated converter systems consisting of a voltage source converter and a cycloconverter connected by a medium-frequency transformer allow bidirectional AC/DC conversion as well as voltage transformation and isolation by the transformer. However, such converter systems require an extra power conversion stage compared to conventional converter systems, which may result in low system efficiency despite the soft-switching commutation scheme. In order to reduce the power losses in the cycloconverter, it is desirable to utilize fast thyristors instead of IGBTs. As a consequence, the cycloconverter valves lack turn-off capability because a thyristor can not be turned off by its gate. This paper describes and evaluates the most common control strategies in order to control a thyristor-based cycloconverter in a mutually commutated converter system. The behaviour of the cycloconverter depends strongly on the chosen control strategy when one of the output currents approaches zero, which may inherently affect the harmonic properties of the output voltages and currents. Experimental results from a 20 kVA prototype show that it is possible to successfully operate a mutually commutated converter system without turn-off capability.

  • 106.
    Meier, Stephan
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Norrga, Staffan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Modulation strategies for a mutually commutated converter system in wind farms2007In: 2007 European Conference on Power Electronics and Applications, EPE, 2007, p. 1221-1230Conference paper (Refereed)
    Abstract [en]

    A novel mutually commutated converter (MCC) system consisting of a voltage source converter (VSC) and a cycloconverter connected by a medium-frequency (MF) transformer is adapted for the power collection and conversion in large wind farms. Different modulation strategies based on space vectors are described and evaluated with regard to the very restrictive constraints on the modulation and commutation of the thyristor valves in the cycloconverter. This paper shows that a feasible and effective modulation strategy can be found in order to provide the desired reference voltage vector during every single modulation interval and under all operating conditions. The proposed current clamping control strategy is based on stopping the gate pulses of the conducting thyristor valve during a certain dead-time whenever the current in the corresponding phase leg becomes zero.

  • 107.
    Modéer, Tomas
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Norrga, Staffan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Loss comparison of different sub-module implementations for modular multilevel converters in HVDC applications2011In: Proceedings of the 2011-14th European Conference on Power Electronics and Applications (EPE 2011) / [ed] EPE Association, 2011Conference paper (Refereed)
    Abstract [en]

    This paper presents a loss calculation and comparison between different submodule topologies and semiconductor choices for a Modular Multilevel Converter in a 1.1GW, ±320kV HVDC application.

  • 108.
    Moghaddam, Reza Rajabi
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Magnussen, Freddy
    Sadarangani, Chandur
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    A FEM INVESTIGATION ON THE SYNCHRONOUS RELUCTANCE MACHINE ROTOR GEOMETRY WITH JUST ONE FLUX BARRIER AS A GUIDE TOWARD THE OPTIMAL BARRIER'S SHAPE2009In: EUROCON 2009: INTERNATIONAL IEEE CONFERENCE DEVOTED TO THE 150 ANNIVERSARY OF ALEXANDER S. POPOV, VOLS 1- 4, PROCEEDINGS, NEW YORK: IEEE , 2009, p. 663-670Conference paper (Refereed)
    Abstract [en]

    The Synchronous Reluctance Machine (SynRM) is studied. A brief comparison of the SynRM and its correspondent Induction Machine based on their physical nature as well as measurements from efficiency point of view is presented. The finite element method is used to investigate the most important geometrical parameters effect on the SynRM performance by studying the simplest rotor structure with just one flux barrier. The SynRM overload capacity is shown as well.

  • 109.
    Moghaddam, Reza Rajabi
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Magnussen, Freddy
    Sadarangani, Chandur
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Theoretical and Experimental Reevaluation of Synchronous Reluctance Machine2010In: IEEE transactions on industrial electronics (1982. Print), ISSN 0278-0046, E-ISSN 1557-9948, Vol. 57, no 1, p. 6-13Article in journal (Refereed)
    Abstract [en]

    This paper theoretically introduces and develops a new operation diagram (OPD) and parameter estimator for the synchronous reluctance machine (SynRM). The OPD demonstrates the behavior of the machine's main performance parameters, such as torque, current, voltage, frequency, flux, power factor (PF), and current angle, all in one graph. This diagram can easily be used to describe different control strategies, possible operating conditions, both below- and above-rated speeds, etc. The saturation effect is also discussed with this diagram by finite-element-method calculations. A prototype high-performance SynRM is designed for experimental studies, and then, both machines' [corresponding induction machine (IM)] performances at similar loading and operation conditions are tested, measured, and compared to demonstrate the potential of SynRM. The laboratory measurements (on a standard 15-kW Eff1 IM and its counterpart SynRM) show that SynRM has higher efficiency, torque density, and inverter rating and lower rotor temperature and PF in comparison to IM at the same winding-temperature-rise condition. The measurements show that the torque capability of SynRM closely follows that of IM.

  • 110.
    Moghaddam, Reza Rajabi
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Magnussen, Freddy
    Sadarangani, Chandur
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Lendenmann, Heinz
    New Theoretical Approach to the Synchronous Reluctance Machine Behavior and Performance2009In: ICEM: 2008 INTERNATIONAL CONFERENCE ON ELECTRICAL MACHINES, NEW YORK: IEEE , 2009, p. 144-149Conference paper (Refereed)
    Abstract [en]

    This paper introduces and develops a new operating diagram and parameter estimator for the synchronous reluctance machine, based on the machine equivalent vector model in the synchronous reference frame. The operating diagram demonstrates the machine main performance parameters, like torque, current, voltage, frequency, power factor and current angle, behavior all together in one graph. This diagram can easily be used to describe different control strategies, possible operating conditions below and above rated speed, etc. The saturation effect is also discussed with this diagram by FEM calculations.

  • 111.
    Monge, Mauro
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Johansson, Nicklas
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Ängquist, Lennart
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Adaptive control for power oscillation damping by means of a Thyristor Controlled Series Capacitor (TCSC)2008In: 2008 PROCEEDINGS OF THE 43RD INTERNATIONAL UNIVERSITIES POWER ENGINEERING CONFERENCE, NEW YORK: IEEE , 2008, p. 37-41Conference paper (Refereed)
    Abstract [en]

    This paper describes an adaptive method for control of a TCSC device for power oscillation damping. The aim is to mitigate power oscillations in power systems with one dominating oscillation mode. To design the controller, a simple generic model of the power system with only a few variables is used. Initially, a fixed-parameter controller which is based on a pole-placement technique is designed. The controller is then implemented in a digital simulator and tested in a four-machine power system. The fixed-parameter controller performs well in most cases but in some contingencies, a performance decay is seen. To improve the controller performance, an adaptive control design has been investigated. The investigated controller is a Self-Tuning Regulator and a Recursive Least-Squares method is used to estimate the system model parameters. An open-loop controller for transient stability improvement and a closed-loop PI-controller for power flow control are also presented. The adaptive controller has been validated with good results by means of simulations of a number of contingencies in different operating conditions of the four-machine system.

  • 112.
    Nordlund, Erik
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Eriksson, Sture
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Test and verification of a four-quadrant transducer for HEV applications2005In: 2005 IEEE Vehicle Power and Propulsion Conference (VPPC), 2005, p. 37-41Conference paper (Refereed)
    Abstract [en]

    This work concerns the design, building and testing of a prototype four-quadrant energy transducer (4QT) for hybrid electric vehicles [1], [6]. The paper describes the test and verification of the 4QT prototype concerning machine parameters, efficiency and thermal performance. The 4QT consists of two different electric radial flux machines: one double rotor machine (DRM) and one conventional machine. In this paper, the conventional machine will simply be referred to as the stator machine (SM). The prototype is designed for a power of 30kW in each of the double rotor machine and the stator machine [2]. The double rotor machine has an inner rotor with a 3-phase winding fed through sliprings and an outer rotor with inner permanent magnets. The outer rotor has also a set of magnets on its outside and serves therefore as rotor for the stator machine. The input shaft is connected to the inner rotor and the output shaft to the outer rotor. Both machines are designed to work as motors and generators. The 4QT is mounted between the internal combustion engine (ICE) and the final reduction gear in a hybrid vehicle; the ICE is connected to the input shaft and the final gear to the output shaft. The function of the 4QT is to keep the operation of the ICE at optimum efficiency at all speeds and torques required by the vehicle. To do so, the speed is controlled with the DRM and the torque with the SN'll.

  • 113.
    Norrga, Staffan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Experimental study of a soft-switched isolated bidirectional AC-DC converter without auxiliary circuit2006In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 21, no 6, p. 1580-1587Article in journal (Refereed)
    Abstract [en]

    An isolated ac-dc converter topology includes a capacitively snubbered. voltage source converter (VSC) and a cycloconverter, coupled by a medium frequency transformer. The topology offers the possibility of bilateral power flow as well as three-level pulse width modulation on the ac side. It is shown that by alternately commutating the VSC and the cycloconverter it is possible to achieve either zero-voltage or zero-current switching conditions for all semiconductor devices in all points of operation. This is the case without any need for auxiliary semiconductor devices. At low load the transformer current may be insufficient for recharging the VSC snubber capacitors. In this case, however, it is possible to utilize the cycloconverter for providing a current path by which a quasi-resonant commutation can be made. The design and operation of a 40-kVA prototype converter system is described. It is shown how the rather complex switching logic required for implementing the chosen algorithm for commutation and modulation can be realized by using modern programmable logic devices [field programmable gate array (FPGA)]. Measurement results from the prototype converter are presented and analyzed. The measurements indicate that the,studied commutation algorithm works well in practice.

  • 114.
    Norrga, Staffan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    On soft-switching isolated AC/DC converters without auxiliary circuit2005Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    The thesis is concerned with a class of power electronic converter systems that permit bidirectional AC/DC conversion with galvanic separation of the AC and DC sides by a transformer operating at elevated frequency. The systems consist of a capacitively snubbered voltage source converter and a cycloconverter, separated by the mentioned transformer. The use of a medium-frequency transformer permits considerable reduction of the transformer weight and size. Both systems with single-phase and three-phase AC terminal are conceivable.

    It is shown that the converter concept is compatible with soft switching of the semiconductor valves, which considerably reduces the switching losses and the stress on the valves. This can be achieved in all points of operation without any need for auxiliary valves dedicated to the commutation process. A resonant mode of commutation, which is vital for extending the soft-switching operating region also to low load conditions, is described in detail.

    The demand for soft switching imposes certain important constraints on the possibilities for pulse width modulation of the AC side voltage. These tend to result in low-order harmonics in the output voltages that are not negligible. The impact of the constraints on the resulting pulse patterns is analysed by analytical derivation of the harmonic spectra. This way the low-order harmonics were found to originate from sidebands around multiples of the switching frequency. Furthermore, advanced modulation schemes, both for single-phase and three-phase systems are described and analysed. These schemes allow for improved harmonic performance and overall loss reduction. The improvement in harmonic performance is most pronounced at low modulation index.

    A down-scaled prototype converter with a rated power of 40 kVA was designed and built up. The prototype can be configured for operation with single-phase or three-phase AC terminal. In the thesis special emphasis is put on the implementation of the commutation and modulation methods in the digital control system. Experimental results from the prototype verify the intended operating principles. Measurements made on the prototype indicate an overall efficiency of up to 92%.

    The envisaged applications are found in the high power range, where the advantages of soft switching are most significant. Two examples of possible applications are outlined: line side power conversion in rail vehicles and systems for energy capture from offshore wind power parks.

  • 115.
    Norrga, Staffan
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Meier, Stephan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    A three-phase soft-switched isolated AC/DC converter without auxiliary circuit2008In: IEEE transactions on industry applications, ISSN 0093-9994, E-ISSN 1939-9367, Vol. 44, no 3, p. 836-844Article in journal (Refereed)
    Abstract [en]

    This paper describes an ac/dc converter system consisting of a voltage-source converter (VSC) with purely capacitive snubbers and a two-phase by three-phase cycloconverter, connected via a medium-frequency (MF) transformer. By alternately commutating the two converters, it is possible to achieve beneficial switching conditions for all semiconductor devices. A commutation and modulation algorithm is described, which allows for pulsewidth-modulation control of the output voltage while maintaining soft switching. Low-load operation of the converter is a potential difficulty because the load current may be insufficient for recharging the snubber capacitors of the VSC. However, if the cycloconverter is used to momentarily short circuit the transformer, a quasi-resonant commutation mode of the VSC can be achieved, making a fast and soft commutation of the VSC down to zero load possible, without an auxiliary circuit. Furthermore, the design and operation of a 40-kVA prototype converter system are described. The experimental results from the prototype clearly show the practical feasibility of the studied concept.

  • 116.
    Peftitsis, Dimosthenis
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Adamidis, Georgios
    Fyntanakis, Athanasios
    Modulation of Three Phase Rectifier in Connection With PMSG for Maximum Energy Extraction2009In: 2009 13th European Conference on Power Electronics and Applications, EPE '09, IEEE , 2009, p. 1197-1206Conference paper (Refereed)
    Abstract [en]

    This paper presents a Maximum Power Point Tracking (MPPT) method which is applied on a Wind Turbine with Permanent Magnet Synchronous Generator (PMSG). A three-phase Switched Mode Rectifier (SMR) is connected with the three phase output of the PMSG. The SMR employs a modulation strategy which is based on the Space Vector Modulation (SVM) technique. Thus, the three phase input voltage is divided in six equal intervals with respect to the zero crossing of the phase voltage and only two switches are switching in each one. A duty ratio D is introduced for each switch and is able to vary by Delta D in order to control the peak current through each phase. By controlling the three phase currents, it is possible to adjust the rotational speed of the PMSG and consequently the extracted power. The "Hill Climbing" algorithm has been used for achieving operation on the Maximum Power Point (MPP). The whole system has been designed and simulated using Matlab/Simulink and simulation results are shown for a variety of Delta D. Finally, a short discussion about the results is given.

  • 117.
    Peftitsis, Dimosthenis
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Baburske, Roman
    Technische Universität Chemnitz.
    Rabkowski, Jacek
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Lutz, Josef
    Technische Universität Chemnitz.
    Tolstoy, Georg
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Challenges regarding parallel-connection of SiC JFETs2011In: IEEE 8th International Conference on Power Electronics and ECCE Asia (ICPE & ECCE), 2011: 'Green World with Power Electronics' / [ed] IEEE, 2011, p. 1095-1101Conference paper (Refereed)
    Abstract [en]

    Considering the present development of the available Silicon Carbide switches, their current ratings are so low that they cannot be used for high-power converters. It is therefore necessary to connect several switches in parallel in order to obtain sufficient current ratings. An investigation of parallel-connected normally-on Silicon Carbide Junction Field Effect Transistors is presented in this paper. The parameters that play the most important role for the parallel connection are the pinch-off and the gate-source breakdown voltages. The temperature dependency of those two voltages is analyzed based on the pnp structure of the device. If the spread in these parameters is sufficiently large there might be no possibility for a stable off-state operation of a pair of transistors without forcing one of the gate voltages to exceed the breakdown voltage, especially at high temperatures. A solution to this problem is given. The switching performance of two pairs of parallel-connected devices is compared with respect to their pinch-off voltages, and it is found that differences of approximately 25% in switching losses could result from a difference in the pinch-off voltage of 0.5 V.

  • 118.
    Peftitsis, Dimosthenis
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Rabkowski, Jacek
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Tolstoy, Georg
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Experimental comparison of dc-dc boost converters with SiC JFETs and SiC bipolar transistors2011In: Proceedings of the 2011-14th European Conference on Power Electronics and Applications (EPE 2011) / [ed] EPE Association, 2011Conference paper (Refereed)
    Abstract [en]

    An experimental performance comparison between SiC JFET and SiC BJT switches which are used as the main switch for a 2 kW dc/dc converter is presented. In order to perform a fair comparison and due to the different chip areas of these two SiC devices, they both operate under the same on-state losses. Moreover, the switching speeds of the gate and base drivers are approximately equal. It is experimentally shown that the SiC BJT is switching slightly faster than the SiC JFET under the same circuit conditions, while the driver loss for the SiC BJT is higher than for the JFET, especially at relatively low switching frequencies. Various experimental results dealing with the switching performance of the SiC devices and the power losses at different switching frequencies are presented. It is found that the BJT converter has a higher efficiency (99.0% measured at 50 kHz) that the JFET converter.

  • 119. Pietiläinen, K. D.
    et al.
    Leksell, Mats
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Voltage sag ride-through for active rectifiers2005In: Proceedings of the Eighth IASTED International Conference on Power and Energy Systems, ACTA Press, 2005, p. 1-6Conference paper (Refereed)
    Abstract [en]

    In this paper we design a converter control for voltage sag ride-through with good load disturbance rejection. The algorithm is intended to improve the performance of the standard industrial motor drive with intermediate dc-voltage link. There are four options for ride-through, dependent on the strength of the supply grid. A further improvement of the ride-through has been achieved by also considering the driven load.

  • 120.
    Rajabi Moghaddam, Reza
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Synchronous Reluctance Machine (SynRM) in Variable Speed Drives (VSD) Applications2011Doctoral thesis, monograph (Other academic)
    Abstract [en]

    This thesis is comprehensively dedicated to the theoretical and experimental reevaluation of the Synchronous Reluctance Machine (SynRM). A simple approach to derive the SynRM main characteristics and behavior is followed. An introduction to an evaluation of the different control strategies in is given. Finding suitable rotor geometry for the SynRM has been a subject for major investigation since 1923. This thesis will investigate the interior barrier rotor structure of the SynRM using the Finite Element Method (FEM) based sensitivity analysis. The Permanent Magnet assisted SynRM (PMaSynRM) is studied. The main aim here is to address accurately, qualitatively and quantitatively the main characteristics of such a machine. A heat-run test has been done on a prototyped SynRM and its corresponding IM and Interior Permanent Magnet (IPM) Machine to investigate the potential of the SynRM, under variable speed drive (VSD) supply conditions. This gives the state-ofart based on these measurements on the prototype SynRM and benchmarks its performance. The main behavior and characteristics of an anisotropic structure, suitable for high performance SynRM rotor geometry design, is distinguished and discussed. The carefully selected general rotor shape and some optimum distribution rules are used to develop a novel FEM-aided fast rotor design optimization for SynRM. Torque ripple minimization of SynRM is discussed. This is done by the development of a general method that minimizes the ripple independent of the stator structure. The torque ripple and interconnection to iron losses are briefly discussed. Based on these design tools, a design that is a compromise between the final machine?s performance and simplicity of the rotor structure is studied as the improved machine design. The fine tuned most promising design is prototyped and its performance compared with IM. Naturally, to have an anisotropic structure the q-axis flux must be blocked and simultaneously the d-axis flux must flow smoothly. One possibility is to align the barrier edges along the d-axis natural flux lines in the solid rotor. A prototype of the final optimized machine design SynRM is manufactured. The performance of this machine is measured and compared with the improved machine design. The effect of the number of poles on SynRM performance is discussed. Some of the most important secondary effects in SynRM are studied. Skew and torque quality, the possible effects of alternative voltage or current source supplies on torque and iron losses, the start-up and short-circuit locked rotor tests performed on the standard IM and the prototype SynRM and the effect of eccentricity are investigated. An overview comparison between IM and SynRM is given. For this purpose, a high performance rotor structure for SynRM with standard sizes of 3kW, 15kW and 90kW is designed. The thermal performance of the SynRM is discussed by analyzing the measured machine temperatures. A detailed picture regarding the thermal performance of the SynRM machine is presented. A full scale performance evaluation of the SynRM in comparison to its counterpart the IM is given. All IM and SynRM motors have the same standard stator for each size. The MTPA control strategy is used. Finally, all reported measurements in this thesis are summarized and analyzed.

  • 121.
    Ranstad, Per
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Control and Design Aspects of Components and Systems in High-Voltage Converters for Industrial Applications2010Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    High-frequency dc-dc converters are widely used in power electronic applications, both in consumer products and industrial products. By operating the converter at higher frequencies both a smaller size and better control characteristics can be obtained.

    It is the objective of this work to investigate how high-frequency power converters can be optimized for high-voltage industrial applications. Specifically, power supplies for electrostatic precipitators (ESP) are considered. The work refers to operating frequencies higher than 20 kHz and load voltages reaching 100 kV and above. The power handling capability ranges from 10 to 200 kW.

    High-frequency power supplies were originally introduced on the ESP market in 1993. An evaluation of the experiences gained during the first decade of operation is presented. It was found that the dust emissions have been reduced at the majority of the installations.

    Efficiency aspects like IGBT losses in soft-switching operation with a sinusoidal collector current and the influence of different control methods have been analyzed. Dynamic properties of the IGBT such as: dynamic conduction losses and dynamic tail charges are presented and experimentally verified. The IGBT losses have been evaluated for LCC-converters operating above the resonance frequency. The losses have been measured and compared for different control methods and for different turn-off strategies, zero-current-switching and zero-voltage-switching, respectively. It is shown experimentally that the LCC-converter is more efficient than the series-loaded resonant converter for a range of values of the parallel capacitance. This is because the LCC-converter allows a lower turns ratio of the transformer.

    The high-voltage high-frequency transformer has been analysed with respect to its parasitic elements. A method is presented, integrated rectification, which enables a sub-division of the winding capacitance into an AC-part and a DC-part. It is validated experimentally that they may be utilized as circuit elements and that the ratio of these capacitances may be varied within a wide range. This method is considered to be of importance when optimizing converters utilizing topologies where the output rectifier is followed by a capacitive filter.

  • 122.
    Ranstad, Per
    et al.
    Alstom Power.
    Nee, Hans Peter
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Linner, Jörgen
    Alstom Power.
    A novel control strategy applied to the series loaded resonant converter2005In: 2005 European Conference on Power Electronics and Applications, Dresden, 2005, Vol. 2005, p. 1665918-Conference paper (Refereed)
    Abstract [en]

    An novel control strategy of the series loaded resonant converter is presented. The main objective of the control strategy is to minimize the switching losses in the main switching elements (IGBT). The results are experimentally verified on a 60kW/25kHz prototype converter. The IGBT losses obtained with the proposed control strategy are compared with those of the commonly used frequency control and phase-shift control strategies. With the proposed control strategy it is found that the losses are reduced in the entire operating range compared to phase-shift control. The same statement is valid also for frequency control, except for the highest output voltage.

  • 123.
    Ranstad, Per
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    On dynamic effects influencing IGBT losses in soft switching converters2011In: IEEE Transactions on Power Electronics, ISSN 0885-8993, Vol. 26, no 1, p. 260-271Article in journal (Refereed)
    Abstract [en]

    Two different dynamic effects influencing the IGBT losses in soft switching converters are demonstrated. The first one, The Dynamic tail-charge effect shows that the tail-charge is dependent not only on the absolute value of the current at turn-off but also on the dynamics of the current. This effect may have a significant impact on the optimization of zero-current-switching converters. The Dynamic conduction losses originate from the conductivity modulation lag of the IGBT. It is shown by experiments that the on-state losses depend on the operating frequency. Different methods to accurately determine the on-state losses are evaluated. It was found that the best method is an indirect measurement where the stray inductance is identified by the use of an oscillating circuit. The experiments are performed under a sinusoidal current excitation at a fixed amplitude (150 A) for different frequencies (up to 104 kHz). The switching devices used are IGBT-modules rated 300-400 A/1200 V in a bridge-leg configuration. From the experiments performed it is found that IGBTs of a modern PT design have the lowest losses in the series-loaded resonant converters studied in the present paper.

  • 124.
    Ranstad, Per
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    On the distribution of AC and DC winding capacitances in high-frequency power transformers with rectifier loads2011In: IEEE Transactions on Industrial Electronics, ISSN 0278-0046Article in journal (Refereed)
    Abstract [en]

    In this paper a method to adjust the AC winding capacitance of high-voltage high-frequency transformers by means of a winding-rectifier integration is described. First a theoretical background to the method is given. From the theory, an equivalent circuit describing the characteristics of the combination of the transformer and the rectifier is derived. The derived circuit introduces the concept of a DC-capacitance. Finally, the equivalent circuit and the method itself are verified by means of experiments on a transformer-rectifier system from an industrial application with the ratings 70 kV, 30 kW, 25 kHz. The results from the experiments show that it is possible to vary the AC component of the winding capacitance from a few percent up to 95 percent of the total winding capacitance. This means that it is virtually free to choose between AC or DC capacitance during the design stage. This is very important in applications such as resonant converters with transformers having secondary windings connected to rectifiers with capacitive output filters.

  • 125.
    Sadarangani, Chandur
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Electrical Machines- Design and Analysis of Introduction and permanent Magnet Motors2006 (ed. 2)Book (Refereed)
  • 126. Salminen, Pia
    et al.
    Libert, Florence
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Pyrhönen, J.
    Soulard, Juliette
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Torque Ripple of Permanent Magnet Machines with Concentrated Windings2005In: Proceedings of the 6th International Symposium on Electromagnetic Fields in Mechatronics, Electrical and Electronic Engineering, (ISEF 2005), 2005Conference paper (Refereed)
    Abstract [en]

    In the present paper, the torque ripples of surface mounted PM machines with different concentrated windings are investigated. The goal is to analyze the torque ripple for different concentrated windings and check how the ripple can be minimized by changing the geometry of the design. The slot number and pole number are varied. The effect of the magnet width and the slot opening width on the torque ripple of these motors is investigated.

  • 127.
    Samaranayake, Lilantha
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Leksell, Mats
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Alahakoon, S
    Distributed control of an XY board via Ethernet2005In: Proceedings of the Eighth IASTED International Conference on Intelligent Systems and Control, CALGARY: ACTA PRESS , 2005, p. 216-221Conference paper (Refereed)
    Abstract [en]

    With the recent IPv6, Power over Ethernet (PoE) and robust hardware designs, Switched Ethernet technology is currently reaching the status of a complete fieldbus system for harsh factory floor applications. However, the investors still hesitate on its field level operation for time critical applications, due to the non-deterministic delays in the closed world of a switched network. The objective of this paper is to practically prove an adaptive sampling scheme to handle network delays and to highlight the potential of Switched Ethernet in implementing time critical real-time distributed control system applications. Experiments are carried out on a distributed XY board, in which the speed and position control loops on each axis, are closed through a 100Mbps Switched Ethernet network.

  • 128. Samaranayake, Lilantha
    et al.
    Leksell, Mats
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Alahakoon, S
    Relating sampling period and control delay in distributed control systems2005In: Eurocon 2005: The International Conference on Computer as a Tool, Vol 1 and 2 , Proceedings, NEW YORK: IEEE , 2005, p. 274-277Conference paper (Other academic)
    Abstract [en]

    The control delay in distributed control systems may be compensated on-line or off-line depending on the required quality of the output, available computational power of the controller node, time stamping and clock synchronizing facilities etc. Irrespective of the compensation technique, there is an upper bound to the constant or variable control delay, which is decided by the plant, controller and the selected sampling period of the distributed computer controlled system. It is shown that in general, if the control delay exceeds the sampling period, the system becomes multi-rate; deteriorate performance as the plant updates do not correspond to the output samples. This paper introduces an adaptive sampling scheme to ensure the control delay is less than the sampling period in steady state and uses the maximum tolerable delay of the system at a particular sampling interval to ensure stable transform from one sampling period to another.

  • 129.
    Samaranayake, Lilantha
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Leksell, Mats
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Vijayananda, T
    Alahakoon, S
    Ethernet ready sensor actuator module for distributed control applications2005In: Eurocon 2005: The International Conference on Computer as a Tool, Vol 1 and 2 , Proceedings, NEW YORK: IEEE , 2005, p. 342-345Conference paper (Refereed)
    Abstract [en]

    Ethernet today is the most widely used information carrier and the service provider for many important applications in the routine life such as e-mail, voice-image data and web based information. It is also emerging strongly into the area of industrial communication covering even sensors and actuators at the factory floor level. However, obtaining network connectivity for existing machinery is still an open question on which many research interests are being focused. This paper presents the hardware development of a general purpose Ethernet Ready Sensor Actuator (ERSA) module and its usage in closing the speed control loop of a Brushless DC motor over a standard Switched Ethernet network. The module is subsequently used to compare connection oriented TCP with connectionless UDP for the same Distributed Control Application under constant network traffic but at different sampling rates.

  • 130.
    Shisha, Samer
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Analysis of Inverter-fed Losses on the Solid Rotor of Large-scale Synchronous Machines2008Licentiate thesis, monograph (Other academic)
  • 131.
    Shisha, Samer Badie
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Analysis of Losses in Inverter-fed Synchronous Machines with Salient-pole Solid Rotors2011Doctoral thesis, monograph (Other academic)
    Abstract [en]

    The work that is presented here considers loss analysis of inverter-fed field-excited synchronous machines. The project was initiated, as a co-operation between indus­trial partners and KTH, with the aim of providing knowledge about the losses that take place in inverter-fed large scale synchronous machines. The use of inverter con­trolled machines is becoming prominent in heavy industry, as VSD (Variable Speed Drives) allow for energy savings compared to the more primitive methods of process control (such as throttling). The machines being considered have a solid rotor and rotor pole-plates and are driven by a DTC (Direct Torque Control) inverter. DTC has several advantages over other, more conventional control techniques. However its main disadvantage, from an analysis point of view, is its stochastic nature. This means that DTC lacks a fixed switching frequency, and hence a predictable pattern. One of the challenges that are faced in dealing with DTC controlled machines is modelling their operation in FEM (Finite Element Method) software. The use of FEM has become an inseparable part of machine design and analysis, as it provides for a detailed insight into the machine and its various components.

    One of the initial aspects as part of this project was the development of a method in which DTC could be modelled using commercially available FEM software. Ini­tially the method developed relied on analytical simulations to produce DTC switch­ing signals, which were then inserted in FEM. This was later developed further to allow switching signals obtained from measurements to be used. Apart from eval­uating simulation methods and results, the research has also involved intensive measurements. The focus of the research is on analysing the losses that take place in the machine due to the inverter drive (time harmonic losses). As the rotor and its pole-plates are solid, it would be expected that a significant portion of the time harmonic losses would take place on the rotor. Furthermore it is expected that, since the time harmonics are of a high frequency, the pole-plate will act to shield the rest of the rotor. Hence most of the rotor losses will be in the pole-plates. The fact that the pole-plates are solid also means that the eddy currents will compose the majority of the losses in the rotor.

    The thesis gives a detailed overview of how the time, as well as the space, harmonic losses are located on the pole-plates. Moreover, the research also considers the effect of varying material properties on the different losses that take place in the machine as a whole and in the pole-plates in particular. Qualitative explanations are given to how these different losses vary with material property. The research covers the effect of different variables - such as switching frequency and material properties - on the losses in the machine, with specific focus on the time harmonics. The study is conducted using both measurements as well as simulations. The knowledge acquired from the evaluations carried out, reveal that significant power savings are possible by modifications to the machine structure, material as well as to the control technique. Various methods are investigated and recommendations provided into how these benefits can be attained.

  • 132.
    Shisha, Samer
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Sadarangani, Chandur
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Analysis of losses in inverter fed large scale synchronous machines using 2D FEM software2007In: 2007 INTERNATIONAL CONFERENCE ON POWER ELECTRONICS AND DRIVE SYSTEMS, 2007, p. 1012-1016Conference paper (Refereed)
    Abstract [en]

    This paper presents a study of eddy current rotor losses in solid pole synchronous machines, fed by a voltage source inverter. The main emphasis is on DTC (Direct Torque Control) application. The DTC operation loss analysis is carried out using FEM (Finite Element Method)-software. The article considers a novel modelling technique that can be used when simulating inverter-fed machines in 2D-FEM application. In addition this article includes a brief introduction into how DTC operates.

  • 133.
    Shisha, Samer
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Sadarangani, Chandur
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Evaluation of Zero Vectors in DTC Control of Synchronous Machines and its Effect on Losses2009In: 2009 IEEE Energy Conversion Congress and Exposition, ECCE 2009, IEEE , 2009, p. 2552-2556Conference paper (Refereed)
    Abstract [en]

    This paper evaluates the effects of using zero voltage vectors in DTC (Direct Torque Control) applications. The evaluation considers a DTC-driven field wound synchronous motor, where the analysis is carried out using a combination of analytical and FEM (Finite Element Method) simulations. The simulations are assessed against a background of measurement results. The main emphasis of the analysis is placed on finding the losses in the motor, with a particular focus on those occurring in the solid rotor pole-plates. The paper will also utilise an innovative power difference method to estimate the time harmonic power losses in the machine.

  • 134.
    Shisha, Samer
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Sadarangani, Chandur
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Modelling for Loss Analysis of Inverter-fed Synchronous Machines2009In: ICEM: 2008 INTERNATIONAL CONFERENCE ON ELECTRICAL MACHINES, NEW YORK: IEEE , 2009, p. 1457-1462Conference paper (Refereed)
    Abstract [en]

    This paper presents a novel method in which eddy current losses in a solid rotor direct torque controlled synchronous machine are found by utilizing a combination of analytical and FEM (Finite Element Method) simulations. The method is presented along with the results obtained. The article also briefly presents a new method in which 3D (three dimensional) current flows can be modelled using a 2D (two dimensional) FEM model.

  • 135.
    Shisha, Samer
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Sadarangani, Chandur
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Testing and Simulation for Loss Evaluation in Field Wound Synchronous Motors Driven by Voltage Source Inverters2009In: 2009 INTERNATIONAL CONFERENCE ON ELECTRICAL MACHINES AND SYSTEMS, 2009, p. 1759-1762Conference paper (Refereed)
    Abstract [en]

    This paper presents the results obtained from testing of a Direct Torque Controlled (DTC) Field excited synchronous motor. The results obtained from testing will be compared to their equivalents obtained from simulation of the machine model using Finite Element Method (FEM) software.

  • 136. Skoglund, M.
    et al.
    Bark, P.
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Dual mode locomotives systems study of new freight locomotives for Sweden2008Conference paper (Refereed)
    Abstract [en]

    A conceptual study for a Swedish dual-mode locomotive is presented. The primary energy sources are AC electricity from an overhead catenary system or a diesel-electric generator system. The study focuses on analysing how freight operations and locomotive utilisation can be improved and how it can affect environmental aspects of freight operations. Based on project experiences and operative demands, a system proposal has been presented. The rated power output is considerably higher in electric mode compared to diesel mode. The reason for this being higher power demand on electrified main lines compared to branch lines and yards lacking overhead catenary where the power need is lower. The starting tractive effort will however be the same regardless of electric mode or diesel mode, making it possible to haul the same train weight in both propulsion modes. The study has shown that dual-mode locomotives for Swedish freight operations are most interesting in order to improve operations, degree of utilisation and environmental performance.

  • 137.
    Skoglund, Mattias
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Evaluation of test cycles for freight locomotives2011Licentiate thesis, monograph (Other academic)
    Abstract [en]

    Diesel locomotives provide versatility to the railway system as they do not depend on electric feeding. Worldwide they constitute important parts of locomotive fleets used for various tasks such as mainline services, shunting and terminal operations. The main drawbacks are emissions of CO2, NOx and other pollutants. The emissions to air are in general controlled by legislation.

    The European testing and approval procedure for locomotive engines is performed with the ISO 8178-F test cycle. It is alone meant to resemble all European locomotives. Good correlation was found between mainline operations and the ISO 8178-F test cycle. A good correlation was furthermore found between shunting operations and North American shunting test cycles. However, this thesis has shown that this results in inadequate description of for instance shunting operations. Typical characteristics for shunting are relatively high ratio of transient loading, low mean power output and high amount of idling. Therefore important aspects of diesel locomotive usage are thereby disregarded in certifications. Deficient correlation between test cycle and intended operations may lead to locomotives that are not properly optimised for the type of operation they are intended for. Improperly dimensioned and optimised locomotives cause impaired fuel economy and more emissions emitted. Many Swedish diesel locomotives are to a large extent used in shunting-like conditions in yards and industries for instance. Therefore, it is recommended to supplement the present ISO test cycle with a test cycle that includes the characteristic of shunting.

    Knowledge about duty cycles for specific operations can be of importance in locomotive acquisition, dimensioning of new locomotives or when estimating emissions and/or fuel consumption. It is essential to make proper dimensioning of propulsion systems as it can imply lower life cycle costs as well as fewer emissions. Appropriate dimensioning of the propulsion system is particularly important for non-conventional propulsion systems.

    If the application range of a test cycle is narrow, its emulating capability ought to be better at describing and representing the indented application. Today's test cycles state fractional power or torque as a function of engine speed. This may result in misleading duty cycles when the same kind of operation is undertaken with different locomotives that have widespread power ratings. A more powerful locomotive used for the very same load as a less powerful locomotive will result in a different duty cycle.

    Non-conventional propulsion systems are gaining popularity also in the railway industry where implementation of new technology usually is slow. Dual mode and hybrid systems are two examples. Related to test and duty cycles the build-up of these new propulsion systems change the prerequisites of the propulsion systems. From a duty cycle perspective it is reasonable to implement an additional test cycle for non-conventional propulsion systems if the popularity rises.

  • 138.
    Skoglund, Mattias
    et al.
    TFK - Transport Research Institute.
    Bark, Peter
    TFK - Transport Research Institute.
    Östlund, Stefan
    KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group. KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Dual mode locomotives - System studies of new freight locomotives for Sweden2008In: Proceedings of IEEE/ASME Joint Railroad Conference, 2008, p. 263-268Conference paper (Refereed)
    Abstract [en]

    A conceptual study for a Swedish dual-mode locomotive is presented. The primary energy sources are AC electricity from an overhead catenary system or a diesel-electric generator system. The study focuses on analysing how freight operations and locomotive utilisation can be improved and how it can affect environmental aspects of freight operations. Based on project experiences and operative demands, a system proposal has been presented. The rated power output is considerably higher in electric mode compared to diesel mode. The reason for this being higher power demand on electrified main lines compared to branch lines and yards lacking overhead catenary where the power need is lower. The starting tractive effort will however be the same regardless of electric mode or diesel mode, making it possible to haul the same train weight in both propulsion modes. The study has shown that dual-mode locomotives for Swedish freight operations are most interesting in order to improve operations, degree of utilisation and environmental performance.

  • 139. Skoglund, Mattias
    et al.
    Bark, Peter
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    The Swedish T43H Hybrid Locomotive2009In: 16th ITS World Congress, 2009Conference paper (Refereed)
    Abstract [en]

    Experiences from the Swedish hybrid locomotive (T43H) are presented. The locomotive has a series hybrid propulsion system with a comparatively small diesel engine and a large battery pack. Original layout was a traditional diesel-electric power train. Indications from switch operations show fuel savings of 37 to 50 % with the hybrid locomotive. The Swedish experiences are thus in parity with North American experiences showing savings between 30 and 80 %. The evaluation showed that hybrid locomotives in switch duty have significant advantages compared to conventional diesel locomotives in terms of reducing fuel consumption and improving environmental performance.

  • 140. Smeets, Johan
    et al.
    Soulard, Juliette
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Lomonova, Elena
    Thermal Analysis of a Winding Turn-to-Turn Fault in PM Synchronous Machine2010In: 19th International Conference on Electrical Machines, ICEM 2010, 2010Conference paper (Refereed)
    Abstract [en]

    This paper presents a detailed lumped parameter (LP) thermal model of an armature slot in a permanent magnet synchronous machine for traction applications. The model is used to investigate the temperature distribution in the slot after a turn-to-turn failure occurs. Steady-state analyses are conducted and a good agreement is found with FEM thermal simulations. The LP model is modified into a transient model and transient thermal analysis are conducted to predict the processing damage in the slot, which eventually might lead to a turn-to-tooth (ground) failure.

  • 141.
    Soulard, Juliette
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Framtidens elektriska maskiner skapas (nästan) direkt i datorn2007In: ERA : elektricitetens rationella användning, ISSN 0013-9939, no 1, p. 70-Article in journal (Other academic)
  • 142.
    Soulard, Juliette
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Permanentmagnetiserade drivsystem minskar energiförbrukningen i industrin2005In: ERA : elektricitetens rationella användning, ISSN 0013-9939, no 6-7, p. 48-Article in journal (Other academic)
  • 143.
    Soulard, Juliette
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Meier, Florence
    Design guidelines and models for PMSMs with non-overlapping concentrated windings2011In: Compel, ISSN 0332-1649, Vol. 30, no 1, p. 72-83Article in journal (Refereed)
    Abstract [en]

    Purpose - The purpose of this paper is to present a general review of design guidelines and analytical models for permanent-magnet synchronous machines (PMSMs) with non-overlapping concentrated windings, including the authors' own experience. Design/methodology/approach - The deign features specific to three-phase PMSMs with non-overlapping concentrated windings are presented following the proposed chronology for the different choices to be made by motor designers. Findings - It is shown that the selections of the stator core manufacturing method, the number of winding layers, the combination of pole and slot numbers, and the geometry of the tooth tips are crucial during the design stage of the machine. Comprehensive lists of references introducing useful analytical models and prototypes presented in literature are provided. Practical implications - By following the guidelines provided in the paper, motor designers are able to avoid the known drawbacks of PMSMs with non-overlapping concentrated windings, and have a ready list of sources describing useful analytical models. Originality/value - PMSMs with non-overlapping concentrated windings have recently been widely investigated. This paper provides an overview of the main results; pinpointing the choices encountered by the motor designers.

  • 144.
    Soulard, Juliette
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Meier, Florence
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    PMSMs with Non-Overlapping Concentrated Windings: Design Guidelines and Model References2009In: EVER, International conference on ecologic vehicles and renewable energies, 2009Conference paper (Refereed)
    Abstract [en]

    Because of their numerous advantages but also of some undesirable effects, permanentmagnetsynchronous machines (PMSMs) with non-overlapping concentrated windings have recentlybeen widely investigated. In this paper, the design features specific to 3-phase PMSMs with nonoverlappingconcentrated windings are presented. Especially, it is shown that the selections of thestator core manufacturing method, the number of winding layers, the combination of pole and slotnumbers, and the geometry of the tooth tips are crucial during the design stage of the machine.

  • 145.
    Soulard, Juliette
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Suriano, Giuseppe
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Arshad, W. A.
    Investigation of the Power Factor and the Specific Torque Trade-off in a Double-sided Flux-concentrated Transverse-flux Machine2003In: Electromotion, ISSN 1223-057X, E-ISSN 2247-8663, Vol. 10, no 4, p. 400-405Article in journal (Other academic)
    Abstract [en]

    A double-sided flux-concentrated transverse-flux machine (TFM) is investigated by using analytical models and three-dimensional finite-element methods (3D-FEM) for application as a 500 kW wind generator and as a 5 kW servomotor. The validity of the analytical models is first assessed with both electrical steel and iron powder (soft magnetic composite) for the iron parts. Analytical parametrical studies are subsequently made in order to study the relationship between the specific torque and power factor. It is found that the discussed TFM is quite superior to a surface-mounted TFM. Finally, the results are also compared with other TFM topologies and other types of electrical machines, like the axial and radial flux permanent-magnet machines and induction machines.

  • 146.
    Stening, Alexander
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    On Inter-bar Currents in Induction Motors with Cast Aluminium and Cast Copper Rotors2010Licentiate thesis, monograph (Other academic)
    Abstract [en]

    This thesis presents a study of the effects of inter-bar currents on inductionmotor starting performance and stray-load losses. The work is focused on theperformance differences between aluminium and copper casted rotors.A method to predict the stator current when starting direct-on-line isdeveloped. This includes modelling of skin-effect, saturation of the leakageflux paths and additional iron losses. The results are verified by measurements.An analytical model accounting for inter-bar currents is derived, andthe dependency of the harmonic rotor currents on the inter-bar resistivity isinvestigated. It is found that the inter-bar currents can have considerableeffect on motor starting performance and stray-load losses, the amount beingstrongly dependent on the harmonic content of the primary MMF.Based on measurements of inter-bar resistivity, the starting performanceof an aluminium and a copper casted rotor is simulated. The results indicatea higher pull-out torque of the aluminium rotor than for the equivalent copperrotor. This is rather due to an increase of the fundamental starting torque ofthe aluminium rotor, than due to braking torques from the space harmonicsin the copper rotor. The results are verified by measurements. It is foundthat the difference between the pull-out torques is even larger than calculatedfrom the model. Thereby, it can be concluded that the inter-bar currents havea considerable effect on motor starting performance.At rated speed the braking torques are larger in the aluminium rotor thanin the copper rotor. This is seen as increased harmonic joule losses in the rotorcage. Simulations have shown, that these losses can be as large as 1% ofthe output power for the studied machine.

  • 147.
    Stening, Alexander
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Sadarangani, Chandur
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Performance Analysis of Asymmetrical Rotor Induction Motors2011In: Proceedings of Portuguese-Spanish Conferenceon Electrical Engineering, 2011Conference paper (Other academic)
    Abstract [en]

    Inter-bar currents can form a considerable part of stray-load losses in a skewed induction motor. A substantial reduction of these losses can be obtained by removal of the rotor skew. Removing the rotor skew will introduce parasitic effects such as increased noise level and increased magnitude of the harmonic torques during motor start. By introducing modulated rotor slots these negative effects can be reduced. In this paper, two different concepts of modulated slot rotors are studied. The starting performance and the losses at rated speed are simulated and compared with a standard motor using the Finite Element Method (FEM). The losses due to inter-bar currents in a skewed rotor are calculated from an analytical model. It is found that the additional losses introduced by the modulated rotor slots are small compared to the possible inter-bar current losses in the skewed rotor. Hence, an increased efficiency can be obtained by introducing modulated non-skewed rotor slots.

  • 148.
    Stening, Alexander
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Sadarangani, Chandur
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Starting performance of induction motors with cast aluminium and copper rotors including the effects of saturation and inter-bar currents2009In: 2009 INTERNATIONAL CONFERENCE ON ELECTRICAL MACHINES AND SYSTEMS, 2009, p. 159-163Conference paper (Refereed)
    Abstract [en]

    In this paper, a study of the starting performance of induction machines with aluminium and copper casted rotors is presented. Models are developed to predict the starting current. Based on measurements of inter-bar resistivity, an analytical model is used to predict the influence of inter-bar currents on machine starting performance and stray-load losses. The results are verified by measurements. It is found that the inter-bar currents increase the pull-out torque in the aluminium rotor, but at the expense of increased stray-load losses.

  • 149.
    Stening, Alexander
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Sadarangani, Chandur
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    The effects of inter-bar currents in cast aluminium and cast copper rotors2009In: ICEM: 2008 INTERNATIONAL CONFERENCE ON ELECTRICAL MACHINES, NEW YORK: IEEE , 2009, p. 2381-2385Conference paper (Refereed)
    Abstract [en]

    In this paper, a study of the influence of inter-bar currents on induction machines with aluminium and copper casted rotors is presented. The resistance between the rotor bars and the iron core is measured on five different rotors. An analytical model to predict the influence of inter-bar currents on machine performance is developed, and the results are verified by measurements. It is found that the measured inter-bar resistance is lower in cast copper rotors than in cast aluminium rotors. This leads to a reduced pull-out torque and increased stray-load losses.

  • 150.
    Svechkarenko, Dmitry
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    On Design and Analysis of a Novel Transverse Flux Generator for Direct-driven Wind Application2010Doctoral thesis, monograph (Other academic)
    Abstract [en]

    This thesis deals with the analysis of a permanent magnet synchronous generator suited for direct-drivenwind turbines inmegawatt class. The higher specific torque and power density of a transverse flux permanent magnet machine in comparison to conventional radial-flux machines make it a promising solution for direct-driven wind turbine generators. The novel transverse flux generator investigated in this work would allow a better utilization of the available nacelle space due to its more compact construction.

    The major part of the thesis deals with the finite element analysis and analytical calculations of transverse flux generators. The computations are performed for single units of the basic transverse flux topology (BTFM) and the one utilizing iron bridges (IBTFM). As the selection of the pole length in a transverse flux machine affects the pole-to-pole flux leakage and thus its performance, the topologies have been analyzed with respect to the varying dimensions in the direction of movement. The topologies utilizing IBTFM have been found to be superior to the BTFM with respect to the flux linkage (by 110%) and utilization of the magnets (by 84%). The machines with longest magnets gave the largest flux linkage, while machines with short magnets should be preferred for better magnet utilization. The four sets of dimensions have been selected for a dynamic finite element analysis.

    The power factor is evaluated for the topologies with the varying dimensions in the peripheral plane in static finite element analysis. The performance of the topologies with the best power factor in the studied range (0.62 in the BTFM and 0.57 in the IBTFM), as well as the topologies that give the highest power factor to magnet volume ratio, is compared with the dynamic simulations.The electromagnetic and cogging forces of the transverse-flux generator are estimated. The IBTFM is superior to the BTFM with respect to the force production, where the three-phase electromagnetic force is twice as large as in the BTFM. The force ripples of the three-phase electromagnetic force are found to be insignificant in both topologies.

    An analytical procedure based on the results from the finite element simulations is applied for evaluation of the transverse flux generators with different shapes and topologies. The effectiveness of each topology is investigated based on the estimation of the torque production in a certain nacelle volume. A toroidal generator with the iron-bridge topology is the most compact alternativefor a wind turbine as it has the highest torque-per-volume ratio.

    Furthermore, the analyticalmodel, including evaluation of the synchronous inductance, is developed and compared with the results obtained in the threedimensional finite element analysis. Themodel provides a good agreement for the studied set of dimensions.

1234 101 - 150 of 196
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