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  • 151.
    Svechkarenko, Dmitry
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Cosic, Alija
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Soulard, Juliette
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Sadarangani, Chandur
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Transverse flux machines for sustainable development - Road transportation and power generation2007In: 2007 INTERNATIONAL CONFERENCE ON POWER ELECTRONICS AND DRIVE SYSTEMS, 2007, p. 1301-1307Conference paper (Other academic)
    Abstract [en]

    The higher specific torque and power density of a transverse flux machine (TFM) in comparison to a conventional machine makes it a promising energy converter in various applications. In this paper, a free piston energy converter and a direct-driven wind turbine are considered. The analytical investigation of the novel TFM topology applied in these two cases is presented. The cogging torque is evaluated by use of a three-dimensional finite element method. The results of simulating generators rated in the range of 3-12 MW are discussed. Manufacturing of a linear prototype is presented.

  • 152.
    Svechkarenko, Dmitry
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Soulard, Juliette
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Sadarangani, Chandur
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Parametric Study of a Transverse Flux Wind Generator at No-load using Three-dimensional Finite Element Analysis2009In: 2009 INTERNATIONAL CONFERENCE ON ELECTRICAL MACHINES AND SYSTEMS, 2009, p. 49-54Conference paper (Refereed)
    Abstract [en]

    This paper deals with the three-dimensional static and dynamic finite element analysis of a transverse flux generator at no-load conditions used in offshore wind turbines. Two transverse flux topologies, namely the basic topology and that utilizing iron bridges are analyzed. The parametric study with respect to the flux linkage and pole-to-pole flux leakage is conducted for various combinations of dimensions in static finite element analysis. The magnitudes and waveforms of the flux linkage and the induced emf obtained in the dynamic finite element simulations are compared with the analytical and static simulation results.

  • 153.
    Svechkarenko, Dmitry
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Soulard, Juliette
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Sadarangani, Chandur
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Performance Evaluation of a Novel Transverse Flux Generator with 3D Finite Element Analysis2009In: 2009 INTERNATIONAL CONFERENCE ON ELECTRICAL MACHINES AND SYSTEMS, 2009, p. 55-60Conference paper (Refereed)
    Abstract [en]

    The calculation of the power factor and the electromagnetic force of a transverse flux generator with the use of three-dimensional finite element analysis is presented in this paper. At first, the analysis is performed for two different single-phase transverse flux topologies. The influence of the dimensions in the peripheral plane on the force production and power factor is estimated. The power factor is calculated by three different methods and results are compared. The alternative way to estimate the electromagnetic force based on the static simulations is described as well.

  • 154.
    Tolstoy, Georg
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Peftitsis, Dimosthenis
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Lim, Jang-Kwon
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Bakowski, Mietek
    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.
    Circuit Modeling of Vertical Buried-Grid SiC JFETs2010In: SILICON CARBIDE AND RELATED MATERIALS 2009, PTS 1 AND 2   / [ed] Bauer AJ; Friedrichs P; Krieger M; Pensl G; Rupp R; Seyller T, 2010, Vol. 645-648, p. 965-968Conference paper (Refereed)
    Abstract [en]

    The main problem when the conventional PSpice JFET model is used to simulate a vertical short-channel buried-grid JFET is caused by the constant values of Threshold Voltage (VTO) and Transconductance (BETA). This paper presents a new model for the vertical short-channel buried-grid 1200V JEET, where both VTO and BETA vary with respect to the Drain-Source voltage. Simulation data from Medici have been analyzed in order to extract the analytical equations for VTO and BETA. Also other PSpice parameters are extracted from these data. The proposed circuit model has been simulated in Matlab by optimizing the same algorithm that PSpice uses. A variety of results are shown and discussed in this paper.

  • 155.
    Tolstoy, Georg
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Peftitsis, Dimosthenis
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Rabkowski, Jacek
    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.
    Performance tests of a 4, 1x4, 1mm(2) SiC LCVJFET for a DC/DC boost converter application2011In: SILICON CARBIDE AND RELATED MATERIALS 2010 / [ed] Monakhov EV; Hornos T; Svensson BG, 2011, Vol. 679-680, p. 722-725Conference paper (Refereed)
    Abstract [en]

    A 4.1x4.1mm(2), 100m Omega 1,2kV lateral channel vertical junction field effect transistor (LCVJFET) built in silicon carbide (SiC) from SiCED, to use as the active switch component in a high-temperature operation DC/DC-boost converter, has been investigated. The switching loss for room temperature (RT) and on-state resistance (Ron) for RT up to 170 degrees C is investigated. Since the SiC VJFET has a buried body diode it is also ideal to use instead of a switch and diode setup. The voltage drop over the body diode decreases slightly with a higher temperature. A short-circuit test has also been conducted, which shows a high ruggedness.

  • 156.
    Wallmark, Oskar
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Harnefors, Lennart
    Carlson, Ola
    Control algorithms for a fault-tolerant PMSM drive2007In: IEEE transactions on industrial electronics (1982. Print), ISSN 0278-0046, E-ISSN 1557-9948, Vol. 54, no 4, p. 1973-1980Article in journal (Refereed)
    Abstract [en]

    This paper proposes control algorithms for a fault-tolerant permanent-magnet synchronous motor (PMSM) drive. In order to improve the reliability of the drive, an algorithm for achieving a sensorless control that operates properly also in fault mode is proposed. Furthermore, it is shown how a closed-loop field-weakening controller needs to be modified in order to operate properly in fault mode. Automotive applications are in mind and the algorithms presented are verified with experimental results using an in-wheel PMSM. With the proposed modifications, the reliability of the drive can be improved.

  • 157.
    Wallmark, Oskar
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Kjellqvist, Peter
    Meier, Florence
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Analysis of Axial Leakage in High-Speed Slotless PM Motors for Industrial Hand Tools2008In: 2008 IEEE INDUSTRY APPLICATIONS SOCIETY ANNUAL MEETING, 2008, p. 2070-2075Conference paper (Refereed)
    Abstract [en]

    This paper presents an analysis of axial leakage effects in high-speed, slotless permanent magnet (PM) motors for industrial hand-tool applications. Analytical predictions and results from a finite-element simulation model are compared to experimental results from three, series-produced PM motors. The reduction in predicted and measured flux density outside the motor's axial ends is substantial; the flux density has practically vanished only a few millimeters outside the stator lamination stack. To predict the resulting flux linkage, a simple winding model is presented where the winding is made up of a discrete number of winding layers. Using this winding model, it is verified that the reduction in flux linkage, manifested as a reduction in the back electromotive force (EMF), is dependent on the motor's axial length but also that the effect is minor for slotless PM motors with dimensions suitable for hand-tool applications. The results are also supported by no-load line-to-line voltage measurements on the three PM motors.

  • 158.
    Wallmark, Oskar
    et al.
    KTH, School of Electrical Engineering (EES), Centres, Swedish Centre of Excellence in Electric Power Engineering, EKC2. KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Kjellqvist, Peter
    Meier, Florence
    KTH, School of Electrical Engineering (EES), Centres, Swedish Centre of Excellence in Electric Power Engineering, EKC2. KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Analysis of Axial Leakage in High-Speed Slotless PM Motors for Industrial Hand Tools2009In: IEEE transactions on industry applications, ISSN 0093-9994, E-ISSN 1939-9367, Vol. 45, no 5, p. 1815-1820Article in journal (Refereed)
    Abstract [en]

    This paper presents an analysis of axial-leakage effects in high-speed slotless permanent-magnet (PM) motors for industrial hand-tool applications. Analytical predictions based on a 2-D model and results from a 3-D finite-element (3DFEM) simulation model are compared with experimental results from three series-produced PM motors. The reduction in flux density (resulting from 3DFEM simulations and measurements) outside the motor's axial ends is substantial; the flux density has practically vanished only a few millimeters outside the stator lamination stack. To predict the resulting flux linkage, a simple winding model is presented where the winding is made up of a discrete number of winding layers. Using this winding model, it is verified that the reduction in flux linkage, manifested as a reduction in the back electromotive force, is not only dependent on the motor's axial length but also that the effect is minor for slotless PM motors with dimensions suitable for hand-tool applications. The results are also supported by no-load line-to-line voltage measurements on the three PM motors.

  • 159.
    Xie, Hailian
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    On Power-system Benefits, Main-circuit Design, and Control of StatComs with Energy Storage2009Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Static synchronous compensation (StatCom) is an application that utilizes a voltage source converter (VSC) to provide instantaneous reactive power support to the connected power system. Conventionally, StatComs are employed for reactive power support only. However, with the integration of energy storage (ES) into a StatCom, it can provide active power support in addition to the reactive power support. This thesis deals with the integration of ES into StatComs. The investigation involves the following aspects: possible benefits for power systems, main circuit design, and control strategies.

    As the basis of the investigation, a control scheme is proposed for two-level VSCs. It is a novel flux modulation scheme combined with the well-known deadbeat current control. The current controller is capable of controlling the positive sequence, the negative sequence, and the offset components of the converter current. With flux modulation, all the three above-mentioned components of the bus flux are controllable. This differs from the conventional voltage modulation scheme, in which only the positive and negative sequence components of the bus voltage are controllable. The difference between the proposed flux modulation scheme and the voltage modulation scheme is investigated regarding saturation of transformers in the connected system during fault recovery. The investigation shows that by controlling the offset component of the bus flux, the transformer saturation problem can be mitigated to a certain extent.

    The possible benefits of the additional active power support of StatComs are investigated through several case studies. Different active power compensation schemes are proposed. First, active power compensation for sudden load changes in weak systems is investigated. The proposed control strategies are verified through computer simulations and through experiments in a real-time simulator. It is shown that with active power compensation, both the phase jumps and magnitude variations in the voltage at the PCC can be reduced significantly. Secondly, the power compensation of cyclic loads is investigated. The results show that the power quality at the connection point can be improved regarding both phase jumps and magnitude variations. In the third case study, the fault-recovery performance of an example system is investigated, showing that improved performance can be achieved by the additional active power support.

    ES devices such as capacitors, supercapacitors, and batteries exhibit considerable variation in the terminal voltage during a charging/discharging cycle. A direct connection of ES devices to the dc side of a VSC requires a higher voltage rating of the VSC. Thus, the cost of the VSC has to be increased. In this thesis, a dual thyristor converter topology is proposed to interface ES devices with the dc side of the VSC. First, a cost comparison is performed to compare the total cost of the whole system with and without the proposed interface topology. A cost comparison between various types of ES is also presented, providing a guideline for the choice of ES at energy levels where several alternatives exist. Then, the dynamics of systems with the proposed interface topology are investigated. Control strategies are proposed and verified by computer simulations. Two different control methods for the dual-thyristor converter are compared.

  • 160.
    Xie, Hailian
    et al.
    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.
    A Converter Topology Suitable for Interfacing Energy Storage with the dc Link of a StatCom2008In: 2008 IEEE INDUSTRY APPLICATIONS SOCIETY ANNUAL MEETING, 2008, p. 1916-1919Conference paper (Refereed)
    Abstract [en]

    Voltage Source Converters (VSC) have been widely utilized to provide instantaneous reactive power support to power systems, an application referred to as Static synchronous Compensators (StatCom). Integration of energy storage (ES) into a StatCom makes it possible for the StatCom to provide a certain amount of active power as well as reactive power support. The possible benefit of the additional active power support of a StatCom can be power oscillation damping capability, mitigation of phase-jump related disturbance, etc. Direct connection of ES device to the dc link of the VSC incurs unnecessary high voltage rating of the VSC due to the considerable voltage swing associated with the ES device. This paper proposes a thyristor converter topology as the interface between the ES device and the VSC dc link. With the proposed interface, the dc voltage of the VSC can be kept constant and thus lower the VSC rating and cost.

  • 161.
    Xie, Hailian
    et al.
    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.
    Active power compensation of voltage source converters with energy storage capacitors2006In: 2006 IEEE/PES POWER SYSTEMS CONFERENCE AND EXPOSITION. VOLS 1-5, NEW YORK: IEEE , 2006, p. 1012-1019Conference paper (Refereed)
    Abstract [en]

    The voltage at the point of common coupling (PCC) in a weak network is very sensitive to load changes. A sudden change in active load will cause both a phase jump and a magnitude fluctuation in the bus voltage, whereas reactive load changes mainly affect the voltage magnitude. With the addition of energy storage to a static synchronous compensator (StatCom), it is possible to compensate for the active power change as well as providing reactive power support. In this paper some effective active power compensation schemes are proposed. Simulation and experimental results verify the compensation schemes by showing that a StatCom with energy storage can significantly reduce phase jumps and magnitude deviations of the bus voltage. Simulation results are also presented showing the benefits of active power compensation to certain applications with phase sensitive load.

  • 162. Xie, Hailian
    et al.
    Ängquist, Lennart
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Nee, Hans-Peter
    Comparison of Voltage and Flux Modulation Schemes of StatComs Regarding Transformer Saturation During Fault Recovery2008In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 23, no 4, p. 1653-1661Article in journal (Refereed)
    Abstract [en]

    A transformer might be driven into saturation by faults in the connected system. In a transmission system with a Static synchronous Compensator and transformers connected at the point of common coupling, different modulation schemes utilized by the voltage source converter influence the transformer saturation in different ways. This paper compares the saturation effect during fault recovery when two alternative modulation schemes are utilized: voltage modulation and flux modulation. The comparison shows that utilization of flux modulation scheme. tends to soften the saturation problem during fault recovery. However, this is achieved at a higher converter transient peak current.

  • 163.
    Xie, Hailian
    et al.
    KTH, School of Electrical Engineering (EES).
    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.
    Design and Analysis of a Controller for a Converter Interface Interconnecting an Energy Storage With the Dc Link of a VSC2010In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 25, no 2, p. 1007-1015Article in journal (Refereed)
    Abstract [en]

    Voltage source converters (VSC) have been widely utilized to provide instantaneous reactive power support to power systems, an application referred to as static synchronous compensator (StatCom). Integration of energy storage (ES) into a StatCom makes it possible for the StatCom to provide a certain amount of active power as well as reactive power support. The possible benefit of the additional active power support of a StatCom can be power oscillation damping capability, mitigation of phase-jump related disturbances, etc. Direct connection of an ES device to the dc link of the VSC incurs unnecessarily high voltage rating of the VSC due to the considerable voltage swing associated with the ES device. In order to reduce the total cost, a dual thyristor converter topology has been proposed as the interface between the ES and the dc link of the VSC. In this paper, dynamics of the proposed system are investigated. Control strategies are proposed and verified by simulations with PSCAD/EMTDC.

  • 164.
    Xie, Hailian
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Ängquist, Lennart
    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).
    Impact of energy storage on system performance under fault conditions2007In: International CIGRE Zagreb Symposium 2007: Transient Phenomena in Large Electric Power Systems, 2007Conference paper (Refereed)
    Abstract [en]

    This work investigates the impact of the energy stored in the dc side capacitor of a converter on the system performance under fault conditions. The system under investigation consists of two interconnected sources feeding a radial string of heavily loaded transmission lines. Along the lines six large induction motors are connected together with eight other loads and some capacitor banks supplying the reactive power consumption in the motors and lines. Since the system is vulnerable to faults close to the sources, additional reactive power support is necessary to improve the fault ride-through capability of the system and the performance of the motors. During a fault, the motor terminal voltage is very low. The unbalance between the electrical torque and the mechanical torque decelerates the motor. After the fault-clearance, the motor starts to accelerate if the electrical torque generated is larger than the mechanical torque. In order to produce the required torque, the motor consumes much more reactive power than under normal condition. If the reactive power support is not sufficient, the motor will keep decelerating until it stops. A StatCom can be installed to provide fast and dynamic reactive power support and voltage control to the system. In this paper, a control scheme for a StatCom with energy storage capability is proposed. The system performance, especially the motor speeds, will be analyzed through simulations carried out in PSCAD. It is shown in the paper that the scheme with active power compensation effectively helps the system to recover from faults. Although this incurs extra cost for the increased dc voltage of the converter and the dc side capacitor, the overall rating of the converter can be reduced by utilization of the proposed scheme.

  • 165.
    Xie, Hailian
    et al.
    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.
    Investigation of StatComs With Capacitive Energy Storage for Reduction of Voltage Phase Jumps in Weak Networks2009In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 24, no 1, p. 217-225Article in journal (Refereed)
    Abstract [en]

    The voltage at the point of common coupling (PCC) in a weak network is very sensitive to load changes. A sudden change in active load will cause both a phase jump and a magnitude fluctuation in the bus voltage (voltage at the PCC), whereas reactive load changes mainly affect the voltage magnitude. With the addition of energy storage to a static synchronous compensator (StatCom), it is possible to compensate for the active power change as well as providing reactive power support. In this paper effective active power compensation schemes are proposed. Simulation and experimental results verify the compensation schemes by showing that a StatCom with energy storage can significantly reduce phase jumps and magnitude deviations of the bus voltage under load disturbances.

  • 166.
    Xie, Hailian
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Ängquist, Lennart
    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).
    Investigation of the Control of a Converter Topology Interfacing an Energy Storage with the dc Link of a VSC2009In: 2009 13th European Conference on Power Electronics and Applications, EPE '09, IEEE , 2009, p. 5289-5298Conference paper (Refereed)
    Abstract [en]

    Integration of energy storage (ES) into a static synchronous compensator (StatCom) makes it possible for the StatCom to provide a certain amount of active power as well as reactive power support. The possible benefit of the additional active power support of a StatCom can be power oscillation damping capability, mitigation of phase-jump related disturbances, etc. Direct connection of an ES device to the dc link of the VSC incurs high voltage rating of the VSC due to the considerable voltage swing associated with the ES device. In order to reduce the total cost, a dual thyristor converter topology has been proposed as the interface between the ES and the dc link of the voltage Source Converter. In this paper, the dynamics of the proposed system are investigated. Control strategies are proposed and verified by simulations with PSCAD/EMTDC. A comparison is made between two control methods.

  • 167.
    Xie, Hailian
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Ängquist, Lennart
    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).
    Novel flux modulated positive and negative sequence deadbeat current control of voltage source converters2006In: IEEE POWER ENG SOC GEN MEETIN, 2006, p. 533-540Conference paper (Refereed)
    Abstract [en]

    Voltage source converters are widely used in the power system to enhance the power system performance. In the conventional converter control, the control system usually takes the voltage measured at the point where the converter is connected and calculates the reference voltage for the converter; with a modulation system the converter then produces the required 'average voltage'. In this paper, a novel flux modulation scheme, combined with the deadbeat current control strategy, is proposed. The current controller is capable of controlling both positive and negative sequence currents. With flux modulation, the control system measures the bus flux and commands the converter to generate the required flux. The simulation and experimental results presented show a good performance of this converter control system.

  • 168.
    Zhang, Lidong
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Modeling and Control of VSC-HVDC Links Connected to Weak AC Systems2010Doctoral thesis, monograph (Other academic)
    Abstract [en]

    For high-voltage direct-current (HVDC) transmission, the strength of the ac system is important for normal operation. An ac system can be considered as weak either because its impedance is high or its inertia is low. A typical high-impedance systemis when an HVDC link is terminated at a weak point of a large ac system where the short-circuit capacity of the ac system is low. Low-inertia systems are considered to have limited number of rotating machines, or no machines at all. Examples of such applications can be found when an HVDC link is powering an isand system, or if it is connected to a wind farm. One of the advantages of applying a voltage-source converter (VSC) based HVDC systemis its potential to be connected to very weak ac systems where the conventional linecommutated converter (LCC) based HVDC system has difficulties.

    In this thesis, the modeling and control issues for VSC-HVDC links connected to weak ac systems are investigated. In order to fully utilize the potential of the VSC-HVDC system for weak-ac-system connections, a novel control method, i.e., powersynchronization control, is proposed. By using power-synchronization control, the VSC resembles the dynamic behavior of a synchronous machine. Several additional functions, such as high-pass current control, current limitation, etc. are proposed to deal with  issues during operation.

    For modeling of ac/dc systems, the Jacobian transfer matrix is proposed as a unified modeling approach. With the ac Jacobian transfer matrix concept, a synchronous ac system is viewed upon as one multivariable feedback system. In the thesis, it is shown that the transmission zeros and poles of the Jacobian transfer matrix are closely related to several power-system stability phenomena. The similar modeling concept is extended to model a dc system with multiple VSCs. It is mathematically proven that the dc system is an inherently unstable process, which requires feedback controllers to be stabilized.

    For VSC-HVDC links using power-synchronization control, the short-circuit ratio (SCR) of the ac system is no longer a limiting factor, but rather the load angles. The righthalf plane (RHP) transmission zero of the ac Jacobian transfer matrix moves closer to the origin with larger load angles, which imposes a fundamental limitation on the achievable bandwidth of the VSC. As an example, it is shown that a VSC-HVDC link using powersynchronization control enables a power transmission of 0.86 p.u. from a system with an SCR of 1.2 to a system with an SCR of 1.0. For low-inertia systemconnections, simulation studies show that power-synchronization control is flexible for various operation modes related to island operation and handles the mode shifts seamlessly.

  • 169.
    Zhang, Lidong
    et al.
    ABB Power Systems.
    Harnefors, Lennart
    ABB Power Systems.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Interconnection of Two Very Weak AC Systems by VSC-HVDC Links Using Power-Synchronization Control2011In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 26, no 1, p. 344-355Article in journal (Refereed)
    Abstract [en]

    In this paper, voltage-source converter (VSC) based high-voltage dc (HVDC) transmission is investigated for interconnection of two very weak ac systems. By using the recently proposed power-synchronization control, the short-circuit capacities of the ac systems are no longer the limiting factors, but rather the load angles. For the analysis of the stability, the Jacobian transfer matrix concept has been introduced. The right-half plane (RHP) transmission zero of the ac Jacobian transfer matrix moves closer to the origin with larger load angles. The paper shows that, due to the bandwidth limitation imposed by the RHP zero on the direct-voltage control of the VSC, high dc-capacitance values are needed for such applications. In addition, the paper proposes a control structure particularly designed for weak-ac-system interconnections. As an example, it is shown that the proposed control structure enables a power transmission of 0.86 p.u. from a system with the short-circuit ratio (SCR) of 1.2 to a system with an SCR of 1.0. This should be compared to previous results for VSC based HVDC using vector current control. In this case, only 0.4 p.u. power transmission can be achieved for dc link where only one of the ac systems has an SCR of 1.0.

  • 170. Zhang, Lidong
    et al.
    Harnefors, Lennart
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Modeling and Control of VSC-HVDC Links Connected to Island Systems2011In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 26, no 2, p. 783-793Article in journal (Refereed)
    Abstract [en]

    The recently proposed power-synchronization control for grid-connected voltage-source converters (VSCs) has been shown to be a feasible solution for high-voltage direct-current (HVDC) transmission connected to high-impedance weak ac systems. In this paper, power-synchronization control is investigated for VSC-HVDC links connected to another type of weak ac system, i.e., low-inertia or island systems. As an example, a linear model of a typical island system feeding by a VSC-HVDC link, including a synchronous generator, an induction motor, and some passive loads, is developed for tuning the control parameters of the VSC-HVDC link. Time simulations in PSCAD/EMTDC demonstrate that VSC-HVDC systems using power-synchronization control are flexible for various network conditions, such as large-ac-system connection, island systems, or passive networks. The time simulations also show that power-synchronization control can seamlessly handle transitions between operation modes, as well as ride through ac-system faults in all network conditions.

  • 171.
    Zhang, Lidong
    et al.
    ABB power Systems, Ludvika.
    Harnefors, Lennart
    ABB Power Systems, Ludvika.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Modelling and control of VSC-HVDC connected to island systems2010In: IEEE Power and Energy Society General Meeting, IEEE , 2010Conference paper (Refereed)
    Abstract [en]

    The recently proposed power-synchronization control for grid-connected voltage-source converters (VSCs) has been shown to be a feasible solution for high-voltage dc (HVDC) transmission connected to high-impedance weak ac systems. In this paper, power-synchronization control is investigated for VSC-HVDC connected to another type of weak ac system, i.e., low-inertia or island systems. As an example, a linear model of a typical island system feeding by a VSC-HVDC link, including a synchronous generator, an induction motor and some passive loads, is developed for tuning the control parameters of the VSCHVDC. Time simulations in PSCAD/EMTDC demonstrate that VSC-HVDC using power-synchronization control is flexible for various network conditions, such as large-ac-system connection, island systems, or passive networks. The time simulations also show that power-synchronization control can seamlessly handle transitions between the operation modes, as well as ride through ac-system faults in all network conditions.

  • 172. Zhang, Lidong
    et al.
    Harnefors, Lennart
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Power-Synchronization Control of Grid-Connected Voltage-Source Converters2010In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 25, no 2, p. 809-820Article in journal (Refereed)
    Abstract [en]

    In this paper, a novel control method of grid-connected voltage-source converters (VSCs) is proposed. The method can be generally applied for all grid-connected VSCs but may be of most importance in high-voltage dc (HVDC) applications. Different from the previous control methods, the proposed method utilizes the internal synchronization mechanism in ac systems, in principle, similar to the operation of a synchronous machine. By using this type of power-synchronization control, the VSC avoids the instability caused by a standard phase-locked loop in a weak ac-system connection. Moreover, a VSC terminal can give the weak ac system strong voltage support, just like a normal synchronous machine does. The control method is verified by both analytical models and time simulations.

  • 173.
    Zhao, Shuang
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Modeling and Control of a PMSynRel Drive for a Plug-InHybrid Electric Vehicle2011Licentiate thesis, monograph (Other academic)
    Abstract [en]

    This thesis presents two transient models for a prototype integrated charger for use in a plug-in hybrid-electrical vehicle application. The models can be useful in order to develop control algorithms for the system or to recommend improvements to the machine design.

    A flux map based method, obtaining input data from simulations using the finite element method (FEM) is used to model the grid synchronization process. The grid side voltage can then be predicted by incorporating spatial flux linkage harmonics. The model is implemented in Matlab/Simulink and compared to stand alone FEM simulations with good agreement.

    The charging process is modeled using an inductance based model also requiring FEM simulations as input data. Since the flux linkages in the grid and inverter side windings are dependent on each other, the presented transient model is linearized around a specific operating point. This model is also implemented in a Matlab/Simulink environment.

    Sensorless control of a PMSynRel drive is also studied in this thesis. Focus is put on operating limits due to magnetic saturation when operating at low speeds. The rotating and pulsating voltage vector injection methods for sensorless control are studied in detail. A technique to map the feasible sensorless control region is proposed which utilizes the resulting position error signal rather than data of differential inductances. This technique is implemented experimentally and compared to corresponding FEM simulations with good agreement.

    The impact of spatial inductance harmonics on the quality of the position estimates is also studied. A method to predict the maximum position estimation error due to the inductance harmonics is proposed based on simplified analytical models. A technique is presented and experimentally verified which can compensate for this effect by injecting a modified rotating voltage carrier. Lastly, the impact of saturation in the rotor structure on the initial magnet polarity detection is investigated. The experimental results, in good agreement with the corresponding FEM simulations, indicate that the impact of saturation in the magnet bridges of rotor is the dominant phenomenon at lower peak current magnitudes.

  • 174.
    Zhao, Shuang
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Haghbin, S.
    Wallmark, Oskar
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Leksell, Mats
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Lundmark, S.
    Carlson, O.
    Transient modeling of an integrated charger for a plug-in hybrid electric vehicle2011In: Proceedings of the 2011 14th European Conference on Power Electronics and Applications, EPE 2011, IEEE conference proceedings, 2011, p. 1-10Conference paper (Refereed)
    Abstract [en]

    This paper considers a permanent magnet assisted synchronous reluctance (PMSynRel) machine for an integrated charger application for use in a plug-in hybrid electric vehicle (PHEV). The integrated charger functionality means that the machine is also used when the battery is charged from the electrical grid. A finite element model (FEM) is presented from which a transient model of the complete system is derived. The resulting model can be used for simulating and tuning the algorithms needed to synchronize the machine to the electrical grid and controlling the charging process.

  • 175. Zheng, P.
    et al.
    Nordlund, Erik
    KTH, School of Electrical Engineering (EES).
    Thelin, Peter
    KTH, School of Electrical Engineering (EES).
    Sadarangani, Chandur
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Investigation of the winding current distribution in a 4-quadrant-transducer prototype machine2005In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 41, no 5, p. 1972-1975Article in journal (Refereed)
    Abstract [en]

    The 4-quadrant energy transducer (4QT) is a solution to realize both the torque and speed control of the internal combustion engine (ICE) for hybrid electric vehicles. Since the base frequency of the prototype 4QT is much higher than the industrial one, the effect of eddy current on winding current distribution is considered in this paper. A two-dimensional (2-D) eddy-current FEM model is established and used for analysis. Current density and strand current distribution are given. It is pointed out that owing to the effect of eddy current, the conductor currents are unevenly distributed within the strands of the same turn. According to the 2-D FEM analysis, when the uneven current distribution is considered, the average rms turn current is increased by 1.05 times for the stator and 1.65 times for the inner rotor, and the copper loss is increased by 1.1 times for the stator and 3.16 times for the inner rotor. Since the inner rotor slots are much deeper than the stator slots, the inner rotor current distribution is more uneven than the stator. It means that for high-frequency deep slot machine the eddy current effect should be considered seriously. Because of the increased current and copper loss, more ventilation will be needed for the 4QT, especially for the inner rotor. The average torques of stator machine and double rotor machine meet the requirements, and the torque ripples are small owing to the skewed slots.

  • 176. Zheng, P.
    et al.
    Thelin, P.
    Nordlund, E.
    Sadarangani, Chandur
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Two-dimensional finite element method simulation of a four-quadrant transducer prototype machine considering skewed slots2006In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 99, no 8Article in journal (Refereed)
    Abstract [en]

    A four-quadrant transducer (4QT) electric machine is an integrated electric machine used for hybrid electric vehicles. In this article a 4QT prototype machine that is radially integrated by two permanent-magnet synchronous machines is analyzed. Skewed slots are adopted for the two machines, and the multislice two-dimensional time-stepping finite element method is used to calculate the performance. The dividing method of the 4QT, the choice of calculated cutplanes and the determination of the number of slices are discussed. The no-load and load performance of the 4QT are calculated. The 4QT prototype machine was tested. The tested no-load line-to-line back electromotive force curves are in good agreement with the calculated ones, which verifies the feasibility of the proposed method.

  • 177. Zheng, Ping
    et al.
    Chen, Anyuan
    Thelin, Peter
    Arshad, Waqas M.
    Sadarangani, Chandur
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Research on a tubular longitudinal flux PM linear generator used for free-piston energy converter2007In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 43, no 1, p. 447-449Article in journal (Refereed)
    Abstract [en]

    The free-piston energy converter (FPEC) is used for a series hybrid electric vehicle scheme, which may have the advantages of high efficiency, compact structure, and reliable operation. The linear generator is an important part in the FPEC, and a tubular longitudinal flux permanent-magnet (PM) linear generator scheme is investigated in this paper. The electromagnetic and thermal properties of the generator are analyzed with commercial software Flux 2D. The generator is optimized from the aspects of material selection and structure optimization. Rare-earth PM material VACODYM 655HR is selected for the permanent magnets, and low-performance low-loss material M235-35A is chosen for the stator lamination. The pole number and machine size are optimized, and the optimum scheme with efficiency of 0.935 and specific power of 1.49 kW/kg is obtained, which meets the requirements of FPEC application.

  • 178. Zheng, Ping
    et al.
    Liu, Ranran
    Thelin, Peter
    Nordlund, Erik
    Sadarangani, Chandur
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Research on the cooling system of a 4QT prototype machine used for HEV2008In: IEEE transactions on energy conversion, ISSN 0885-8969, E-ISSN 1558-0059, Vol. 23, no 1, p. 61-67Article in journal (Refereed)
    Abstract [en]

    A four-quadrant transducer (4QT.) is a hybrid electric vehicle (HEV) power train concept. It can enable the internal combustion engine (ICE) to operate at optimum efficiency during all driving conditions with both torque and speed control. The thermal property is a vital problem due to its special configuration. Aiming to find the hot spot and investigate the cooling system of the 4QT, the thermal field is calculated with finite-element method (FEM). The simulation is validated by the comparisons with the experiment. The influences of the forced-air cooling, water cooling, and the distribution of the cooling channels on the cooling performance are discussed, respectively. The stator air ducts; are removed, and 12 water channels evenly distributed in the housing are employed. The design principle of the cooling system is presented. The speed impacts of air flow and water flow are discussed and provide a parameter reference for choosing the forced-air cooling fan and water pump properly.

  • 179. Zheng, Ping
    et al.
    Liu, Ranran
    Thelin, Peter
    Nordlund, Erik
    Sadarangani, Chandur
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Research on the parameters and performances of a 4QT prototype machine used for HEV2007In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 43, no 1, p. 443-446Article in journal (Refereed)
    Abstract [en]

    A four-quadrant transducer (4QT) is a hybrid electric vehicle (HEV) power train concept. In this paper, a 4QT prototype machine, which is integrated radially by two permanent-magnet synchronous machines [one stator machine (SM) and one double-rotor machine (DRM)], is investigated. The inductances of both the SM and the DRM are calculated with a phasor-diagram based 2-D finite-element method (FEM), which can include the effects of eddy current and saturation. The calculated results show that the effect of eddy current can be neglected for both the SM and DRM inductances, and the cross-magnetization influence on the SM inductances can be ignored but is remarkable on the DRM inductances. The magnetic coupling between the SM and the DRM is calculated with 2-D FEM, and it is found that little magnetic coupling exists, so the SM and the DRM can be controlled independently, which is a very good feature for HEV applications. With the effect of skewed slots considered, the torque and no-load line-to-line back electromotive force (BEMF) curves of the SM and the DRM are calculated with multislice 2-D time-stepping FEM. The average torques of the SM and the DRM both meet the requirements, and the torque ripples are quite low. The calculated and tested no-load line-to-line BEMF curves of the SM and the DRM are both in good agreements. Both the BEMF curves of the SM and the DRM are somewhat similar to sinusoidal ones, which proves a good design of the magnetic structure.

  • 180.
    Ängquist, Lennart
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Haider, Arif
    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).
    Jiang, Hongbo
    Trafikverket, Borlänge, Sweden.
    Open-loop approach to control a Modular Multilevel Frequency Converter2011In: Proceedings of the 2011-14th European Conference on Power Electronics and Applications (EPE 2011) / [ed] EPE Association, 2011Conference paper (Refereed)
    Abstract [en]

    Frequency converters are required to supply power from the public three-phase network to railways using 16.7 Hz single-phase in their rolling stock. The emerging Modular Multilevel Converter (M2C) technology offers the possibility to make such power conversion in one step using Modular Multilevel Frequency Converters (MMFC) with full-bridge sub-modules. A detailed study of the modulation and control of such converters is presented in this paper. The voltage inserted by each arm of the MMFC is a mixture of the three-phase 50 Hz voltage and the single phase 16.7 Hz voltage. It is important that the voltage reference given to the modulator will be carefully reproduced by the converter because any deviation can introduce undesired frequency components from the single-phase side to the three-phase side and vice versa. The fact that the low frequency, single-phase load causes low-frequency ripple in the total capacitor voltage complicates the problem to generate the correct modulation pattern. In this paper it is proposed to solve that difficulty by estimating the instaneous total capacitor voltages in each arm and provide that information to the modulator. It is shown that such estimations can be performed using measured currents on the single- and three-phase sides. Stable single-phase voltage, symmetrical undistorted three-phase currents and stable converter capacitor voltages are achieved under varying loading conditions. Models in Matlab/Simulink (continuous) and EMTDC/PSCAD (discrete sub-modules) have been developed in this study.

  • 181.
    Ållebrand, Björn
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    On SiC JFET converters: components, gate-drives and main-circuit conditions2005Doctoral thesis, monograph (Other scientific)
    Abstract [en]

    This thesis deals with Silicon Carbide Junction Field Effect Transistors (SiC JFETs) - how to use them to their full potential in power electronic circuits, how to model them in a power electronic simulation program, and how a gate drive can be built.

    To fully utilize the low on-state losses of SiC JFETs it is suggested that SiC JFETs should not be equipped with anti-parallel diodes. This is possible due to that JFETs can conduct current in the reverse direction. The circuit making use of this property is called the Diode-less SiC JFET Inverter Bridge (DJIB). The DJIB was studied regarding blanking times, negative voltages, and other special cases.

    A gate drive circuit for use with SiC JFETs in industrial applications is presented. The design is with voltage controlled devices(MOSFETs) for use in industrial applications.

    Since the JFET model in PSpice had never been validated for SiC power devices, a validation of the PSpice JFET model is presented for SiC JFETs manufactured by SiCED. The PSpice JFET model shows good agreement with measured results up to saturation. For high currents the SiCED SiC JFET saturates much earlier than the PSpice model and this has to be taken into account when making simulations with PSpice.

    Due to the high gate-drain capacitance of the SiCED SiC JFETs, there are commutation transients during switching. A short-circuit of the bridge-leg appears due to the high gate-drain capacitance. This is studied and some solutions to this problem are presented.

    Simulations on a 1~MW converter utilizing possible future high-voltage SiC JFETs showed that an efficiency of 99,7% could be achieved compared to an efficiency of 98,8% for a converter with Si IGBTs. However, even though the high gate-drain capacitance was reduced in the simulation, undesired commutation transients was observed. This problem has to be considered when designing converters in the future.

  • 182.
    Ållebrand, Björn
    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.
    Comparison of Commutation Transients of Inverters with Silicon Carbide JFETs with and without Body Diodes2004In: Proceedings of the Nordic Workshop on Power and Industrial Electronics (NORpie), 2004Conference paper (Refereed)
    Abstract [en]

    An inverter could be built by using silcon carbide power switches only. This can be done by using SiC JFETs which can conduct current in both directions. An interesting question is how an inverter using SiC JFETs with a body diode compares with an inverter using SiC JFETs without body diodes. This will be discussed in this paper.

  • 183.
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    A primary switched converter system for traction applications1992Doctoral thesis, monograph (Other academic)
  • 184.
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Dual system locomotives for future rail freight operation: Concept and preliminary ratings2005Report (Other academic)
  • 185.
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Influence of the control principle on a high-voltage inverter system for reduction of traction transformer weight1987Conference paper (Refereed)
  • 186.
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Performance of future regional high speed trains1998In: Proceedings of the 1998 ASME/IEEE Joint Railroad Conference, 1998, p. 21-28Conference paper (Refereed)
  • 187.
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Reduction of traction transformer weight by using a naturally commutated high-voltage inverter with increased frequency1988Licentiate thesis, monograph (Other academic)
  • 188.
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Vehicle performance and Technology1997In: Efficient Train Systems for Future Passenger Services / [ed] Bo Lennart Nelldal, KTH Royal Institute of Technology, 1997, p. 79-99Chapter in book (Other academic)
  • 189.
    Östlund, Stefan
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Andersson, Evert
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Railway Technology.
    Kottenhoff, Karl
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Traffic and Logistics.
    Efficient Passenger Trains for the Future1999In: Proceedings of the WCRR99, 1999Conference paper (Refereed)
  • 190.
    Östlund, Stefan
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Brokemper, Michael
    Sensorless Rotor Position Detection from Zero to Ratted Speed for an Integrated PM Synchronous Motor Drive1996In: IEEE transactions on industry applications, ISSN 0093-9994, E-ISSN 1939-9367, Vol. 32, no 5, p. 1158-1165Article in journal (Refereed)
  • 191.
    Östlund, Stefan
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930). KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group.
    Gustafsson, Anders
    Buhrkall, Lars
    Skoglund, Martin
    Condition Monitoring of Pantograph Contact Strip2008In: IET Seminar Digest, 2008Conference paper (Refereed)
    Abstract [en]

    A common issue in electric railway operation is the wearofthepantographcontact strip. This is especially pronounced with ice or rime frost on the overhead line that causes arcing between the contact strip and the contact wire. To monitor the contact strip it is possible to utilise the fact that arcing between the contact strip and the overhead line generates a DC component in the AC locomotive current. The paper presents a method forconditionbased maintenanceofthe contact strip. The wearofthe contact strip is predicted bymonitoringthe running distanceofthepantographas well as the DC componentofthe locomotive current. To evaluate the method, measurements have been carried out on a Swedish Re locomotive during winterconditions.

  • 192.
    Östlund, Stefan
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Kjellqvist, Peter
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Determining Dynamic Properties of Active Electromechanical Suspension for Rail Vehicle Performance2001Conference paper (Refereed)
  • 193.
    Östlund, Stefan
    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).
    Aronsson, Martin
    SICS.
    Bohlin, Markus
    SICS.
    Doganay, Kivanc
    SICS.
    Holst, Anders
    SICS.
    An Integrated Adaptive Maintenance Concept2010In: International Conference on Condition Monitoring and Diagnosis 2010, 2010Conference paper (Other academic)
    Abstract [en]

    In this paper, we present a novel maintenance concept based on condition monitoring and dynamic maintenance packaging, by showing how to connect the information flow from low-level sensors to high-level operations and planning under uncertainty. Today, condition-based maintenance systems are focused on data collection and custom-made rule based systems for data analysis. In many cases, the focus is on measuring "everything" without considering how to use the measurements. In addition, the measurements are often noisy and the future is unpredictable which adds a lot of uncertainty. As a consequence, maintenance is often planned in advance and not replanned when new condition data is available. This often reduces the benefits of condition monitoring. The concept is based on the combination of robust, dynamically adapted maintenance optimization and statistical data analysis where the uncertainty is considered. This approach ties together low-level data acquisition and high-level planning and optimization. The concept has been illustrated in a context of rail vehicle maintenance, where measurements of brake pad and pantograph contact strip wear is used to predict the near future condition, and plan the maintenance activities.

  • 194.
    Östlund, Stefan
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Lilliesköld, Joakim
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Assessing project courses with several teachers involved2007In: Proceedings of the 3rd annual CDIO conference, 2007Conference paper (Refereed)
  • 195.
    Östlund, Stefan
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Lilliesköld, Joakim
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Designing, implementing and maintaining a first year project course in Electrical engineering2008In: European Journal of Engineering Education, ISSN 0304-3797, E-ISSN 1469-5898, Vol. 33, no 2, p. 231-242Article in journal (Refereed)
    Abstract [en]

    Being a modern electrical engineer does not only require state of the art skills in areas such as transfer and processing of information, electronics, systems engineering, and biomedical electrical engineering; it also requires generic engineering skills such as oral and written communication, team building, interpersonal skills, and the ability to take the responsibility of solving assigned tasks. In the development of a new electrical engineering curriculum, it was considered a challenge to introduce these generic engineering skills in a more applicable way. The approach described in this paper has been very successful in implementing and maintaining a challenging first year project based engineering course with a high level of training of generic engineering skills.

  • 196.
    Östlund, Stefan
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Skoglund, Mattias
    TFK.
    Bark, Peter
    TFK.
    Experiences from the Swedish T43H Hybrid Locomotive2008Conference paper (Other academic)
1234 151 - 196 of 196
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