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  • 51.
    Eriksson, Sture J A
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    125 years running2008In: ABB Review, ISSN 1013-3119, no 1, p. 81-86Article in journal (Refereed)
    Abstract [en]

    ABB has contributed significantly for the development of electrical machines and motors for industrial and infrastructure application in its 125 years of business. The electrical machines are subjected to various types of stresses such as electrical, mechanical, thermal, and chemical. The company's 125 years of development has focused on customer's need for more reliable and cost-effective machines. The company has also developed very efficient systems such as hydrogen-cooling and direct water-cooling systems, used for very large machines. The electrical machines developed by ABB are more cost-effective with an increased specific output. The largest synchronous motor built by the company is rated at 55MW. ABB has also launched a radically different type of synchronous generator for very high voltages and is aimed to develop electrical machines with superconducting excitation windings.

  • 52.
    Fischer de Toledo, Paulo
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Modelling and control of a line-commutated HVDC transmission system interacting with a VSC STATCOM2007Doctoral thesis, monograph (Other scientific)
    Abstract [en]

    The interaction of an HVDC converter with the connected power system is of complex nature. An accurate model of the converter is required to study these interactions. The use of analytical small-signal converter models provides useful insight and understanding of the interaction of the HVDC system and the connected system components.

    In this thesis analytical models of the HVDC converters are developed in the frequency-domain by calculating different transfer functions for small superimposed oscillations of voltage, current, and control signals. The objective is to study the dynamic proprieties of the combined AC-DC interaction and the interaction between different HVDC converters with small signal analysis.

    It is well known that the classical Bode/Nyquist/Nichols control theory provides a good tool for this purpose if transfer functions that thoroughly describe the 'plant' or the 'process' are available. Thus, there is a need for such a frequency-domain model.

    Experience and theoretical calculation have shown that voltage/power stability is a very important issue for an HVDC transmission link based on conventional line-commutated thyristor-controlled converters connected to an AC system with low short circuit capacity. The lower the short circuit capacity of the connected AC system as compared with the power rating of the HVDC converter, the more problems related to voltage/power stability are expected.

    Low-order harmonic resonance is another issue of concern when line-commutated HVDC converters are connected to a weak AC system. This resonance appears due to the presence of filters and shunt capacitors together with the AC network impedance. With a weak AC system connected to the HVDC converter, the system impedances interact through the converter and create resonances on both the AC- and DC-sides of the converter. In general, these resonance conditions may impose limitations on the design of the HVDC controllers.

    In order to improve the performance of the HVDC transmission system when it is connected to a weak AC system network, a reactive compensator with a voltage source converter has been closely connected to the inverter bus. In this thesis it is shown that the voltage source converter, with an appropriate control strategy, will behave like a rotating synchronous condenser and can be used in a similar way for the dynamic compensation of power transmission systems, providing voltage support and increasing the transient stability of the converter.

  • 53.
    Fischer de Toledo, Paulo
    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.
    Frequency-domain modelling of sub-synchronous torsional interaction of synchronous machines and a high voltage direct current transmission link with line-commutated converters2010In: IET GENERATION TRANSMISSION & DISTRIBUTION, ISSN 1751-8687, Vol. 4, no 3, p. 418-431Article in journal (Refereed)
    Abstract [en]

    The authors describe a model of a system that includes a high voltage direct current (HVDC) transmission link with line-commutated current source converters (LCC) closely connected to a synchronous generator used to perform analysis of sub-synchronous torsional interaction (SSTI) in the frequency domain. The model of the HVDC transmission link adequately represents the converters in the frequency domain and includes all essential controls for the operation of the converters, including a new sub-synchronous damping control used to mitigate interaction between the recti. er LCC and the shaft of the synchronous machine. The frequency domain model has been validated against time domain simulations showing good agreement.

  • 54.
    Grop, Henrik
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Investigation of AC electrical machine stators with fractional conductor windings2010Licentiate thesis, monograph (Other academic)
    Abstract [en]

    Industry always searches the least expensive solution for a machine design. Therefore, there is a need for integrating different customer ordered machines within the same frame, while keeping the foundation of the mechanical design constant. Since the winding design in electrical machines is essential for the performance and relatively inexpensive to adapt, it can be used to meet different customer demands. This thesis investigates the foundations of a special winding named fractional conductor winding. An expression for winding factors for certain kinds of these windings is developed. Calculations showed that the selection of the winding distribution has effect on the air gap space harmonics produced by the winding. In some cases, the fifth and seventh space harmonics can be eliminated by the use of fractional conductor windings in combination with short pitching. The construction of a prototype fractional conductor wound induction motor was documented and is presented in this thesis. The air gap flux density in a dual slotted fractional conductor wound induction motor running at no load is studied. Analytical models are compared to results obtained by finite elements and measurements. It was found that analytical results overestimated the peak of the fundamental flux density by 13.5%. The overestimation was caused by the iron reluctance of the main flux path as well as saturation. Leakage was found to be a minor cause of this overestimation. Slot leakage and differential leakage in machines having these windings are studied. The analytical models were evaluated, with mostly good agreements, compared to finite element modeling as well as measurements.

  • 55.
    Grop, Henrik
    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.
    Persson, H.
    Stator Slot Leakage in AC-Machines Equipped With Fractional Conductor Windings2009In: 2009 INTERNATIONAL CONFERENCE ON ELECTRICAL MACHINES AND SYSTEMS, 2009, p. 168-173Conference paper (Refereed)
    Abstract [en]

    This paper presents a slot leakage model for stator windings having a fractional number of turns per slot. The results are compared with finite element simulations and measurements using search coils in a prototype machine. Although the slot leakage model predicts the leakage correctly in the slot bottom, the model cannot be used on its own for the slot top since the zig-zag leakage was very pronounced just below the slot wedge.

  • 56.
    Grop, Henrik
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Soulard, Juliette
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Persson, Holger
    Theoretical Investigation of Fractional Conductor Windings for AC-Machines: Definition, Air-gap m.m.f. and Winding Factors2008In: ICEM: 2008 International Conference on Electrical Machines, NEW YORK: IEEE , 2008, p. 529-534Conference paper (Refereed)
    Abstract [en]

    This paper introduces the concept of fractional conductor windings for AC-machines. They allow to obtain fractional equivalent number of conductors per slot. Different arrangements of windings are presented. The harmonic spectrum of the armature magneto-motive force in the air-gap is then analyzed in order to derive rules for choosing suitable combinations using winding factors.

  • 57. Hagbin, Saeid
    et al.
    Alukula, Mats
    Khan, Kashif
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Lundmark, Sonja
    Leksell, Mats
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Wallmark, Oskar
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Carlson, Ola
    An integrated charger for plug-in hybrid electric vehicles based on a special interior permanent magnet motor2010Conference paper (Refereed)
    Abstract [en]

    For a plug-in hybrid electric vehicle (PHEV), the battery needs to be charged from the grid while the vehicle is parked. The traction system components are normally not engaged during the charging time so there is a possibility to use them in the charger system to develop an integrated charger. An innovative high power isolated three-phase bi-directional integrated charger with unit power factor operation is introduced for PHEVs based on a special configuration of the ac motor. The winding of the machine is re-arranged in charging mode to have a three-phase boost based high power battery charger. The system configuration, the device model (machine with multiple windings), traction and charging system functionality and charger control are presented in this paper.

  • 58. Hagbin, Saeid
    et al.
    Khan, Kashif
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Lundmark, Sonja
    Alukula, Mats
    Carlson, Ola
    Leksell, Mats
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Wallmark, Oskar
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Integrated chargers for EV's and PHEV's: Examples and new solutions2010Conference paper (Refereed)
    Abstract [en]

    The battery is an important component in an electric vehicle (EV) or a plug-in hybrid electric vehicle (PHEV) and it should be charged from the grid in a cost efficient, preferably fast and definitely safe way. The charger could be an on board or an off board charger. For an on board charger it is possible to use available hardware of the traction system, mainly the inverter and the electric motor, in the charger circuit. This is called an integrated charger. In this paper, different examples of integrated chargers are reviewed and explained. Additionally, other possible solutions of integrated chargers are described.

  • 59.
    Haider, Arif
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Ahmed, Noman
    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).
    Open-loop approach for control of multi-terminal DC systems based on modular multilevel converters2011In: Proceedings of the 2011-14th European Conference on Power Electronics and Applications (EPE 2011) / [ed] EPE Association, 2011Conference paper (Refereed)
    Abstract [en]

    In this paper a multi-terminal direct current (MTDC) system with modular multilevel converters (M2Cs) is suggested. An open loop control method is used for the control of the converters. Each converter is modeled with 36 sub-modules per arm with a total of 216 sub-modules consisting of half bridges. Power-synchronization control is used instead of a phase-locked loop (PLL) for synchronization. Thus, the short circuit capacities of the ac systems are no longer limiting factors and the instability caused by the PLL in weak ac systems is avoided [10]. A direct voltage controller is implemented with power-synchronization control as an inner loop in one station. Several scenarios are analyzed to demonstrate control flexibility and ride-through capability for grid transients. By means of analytical calculations and time simulations in PSCAD/EMTDC, the validity of the proposed MTDC system is confirmed.

  • 60.
    Hansson, Jörgen
    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.
    Performance of a Series Hybrid Electric Vehicle with a Free-Piston Energy Converter2006In: 2006 IEEE VEHICLE POWER AND PROPULSION CONFERENCE, NEW YORK, NY: IEEE , 2006, p. 108-113Conference paper (Refereed)
    Abstract [en]

    The free-piston energy converter (FPEC), consists of an internal combustion engine and a linear electrical machine. It is characterised by high efficiency and rapid transient response, which makes it suitable for hybrid electric vehicles. In this paper we investigate the performance gain of utilising the FPEC in a medium sized series hybrid electric vehicle (SHEV), compared to a conventional diesel-generator. First, we utilise optimisation to find a lower limit on the SHEVs fuel consumption for a given drive cycle. In addition, we develop a control strategy based on the ideas of an equivalent consumption minimisation (ECM) proposed earlier in the literature. The results show a potential decrease in fuel consumption of up to 19% compared to a diesel-generator SHEV. The ECM control strategy behaves as desired, and a 13% reduction of fuel consumption compared to a traditional load-following strategy is achieved.

  • 61.
    Ilves, Kalle
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Antonopoulos, Antonios
    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).
    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).
    Controlling the ac-side voltage waveform in a modular multilevel converter with low energy-storage capability2011In: Proceedings of the 2011-14th European Conference on Power Electronics and Applications (EPE 2011) / [ed] EPE Association, 2011, p. 1-8Conference paper (Refereed)
    Abstract [en]

    During nominal operation of a modular multilevel converter the stored energy in the submodule capacitors will vary with time. If the energy storage capability of the capacitors is relatively small compared to the energy variations, this will give large variations in the capacitor voltages. These voltage variations will distort the ac-side voltage waveform and induce harmonic components in the current that is circulating between the dc terminals. The adverse effects on the ac-side voltage can be compensated for by identifying the factors that cause the distortion. It is shown that the compensation can be done by means of feed forward control while maintaining stable operating conditions and thus eliminating the need of additional stabilizing controllers. It is also shown that the voltage controller can be combined with a circulating current controller that removes the harmonics in the current that is circulating between the dc terminals. The functionality of the proposed controller is verified by both simulations and experimental results from a 10 kVA laboratory prototype. The simulations illustrate how the proposed controller successfully removes the distortion from the ac-side voltage waveform. The experimental results demonstrate stable operation during a step transient when the output power is increased by 125%.

  • 62. Jansson, Magnus
    et al.
    Harnefors, L.
    Wallmark, Oskar
    Leksell, Mats
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Synchronization at startup and stable rotation reversal of sensorless nonsalient PMSM drives2006In: IEEE transactions on industrial electronics (1982. Print), ISSN 0278-0046, E-ISSN 1557-9948, Vol. 53, no 2, p. 379-387Article in journal (Refereed)
    Abstract [en]

    In this paper, a variant of the well-known voltage model is applied to rotor position estimation for sensorless control of nonsalient permanent-magnet synchronous motors (PMSMs). Particular focus is on a low-speed operation. It is shown that a guaranteed synchronization from any initial rotor position and stable reversal of rotation can be accomplished, in both cases under load. Stable rotation reversal is accomplished by making the estimator insensitive to the stator resistance. It is also shown that the closed-loop speed dynamics are similar to those of a sensored drive for speeds above approximately 0.1 per unit, provided that the model stator inductance is underestimated. Experimental results support the theory.

  • 63.
    Johansson, Nicklas
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Aspects on Dynamic Power Flow Controllers and Related Devices for Increased Flexibility in Electric Power Systems2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis studies different aspects of Flexible AC Transmission System (FACTS) devices which are used to improve the power transfer capability and increase the controllability in electric power systems. In the thesis, different aspects on the usage and control of Dynamic Power Flow Controllers (DPFC) and related FACTS devices are studied. The DPFC is a combination of a Phase Shifting Transformer (PST) and a Thyristor Switched Series Capacitor (TSSC)/Thyristor Switched Series Reactor (TSSR).

    The thesis proposes and studies a new method, the Ideal Phase-Shifter (IPS) method, for selection and rating of Power Flow Controllers (PFC) in a power grid. The IPS method, which is based on steady-state calculations, is proposed as a first step in the design process for a PFC. The method uses the Power controller plane, introduced by Brochu et al in 1999. The IPS method extends the usage of decoupling methods in the Power controller plane to a power system of arbitrary size. The IPS method was in the thesis used to compare the ratings of different PFC:s required to improve the power transfer capability in two test systems. The studied devices were here the PST, the TSSC/TSSR and the DPFC.

    The thesis treats control of ideal Controlled Series Capacitors (CSC), TCSC, TSSC/TSSR, and DPFC. The goals of the FACTS controllers which are developed are Power Oscillation Damping (POD), fast power flow control, and transient stability improvement in the power system. New adaptive control strategies for POD and power flow control are proposed and studied in different models of power systems by time-domain simulations. A strategy for transient stability improvement is also proposed and studied.

    Additionally, different methods for study of Subsynchronous Resonance (SSR), which is associated with series compensation in power systems, are investigated. Here, four of the most common methods for frequency scanning to determine the electrical damping of subsynchronous oscillations in a power grid are studied. The study reveals significant differences of the electrical damping estimates of the studied standard methods when applied to a four-machine test system.

  • 64.
    Johansson, Nicklas
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Control of Dynamically Assisted Phase-shifting Transformers2008Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this thesis, controllers for power oscillation damping, transient stability improvement and power flow control by means of a Controlled Series Compensator (CSC) and and a Dynamic Power Flow Controller (DPFC) are proposed. These devices belong to the group of power system components referred to as Flexible AC Transmission System (FACTS) devices. The developed controllers use only quantities measured locally at the FACTS device as inputs, thereby avoiding the risk of interrupted communications associated with the use of remote signals for control.

    For power systems with one dominating, poorly damped inter-area power oscillation mode, it is shown that a simple generic system model can be used as a basis for damping- and power flow control design. The model for control of CSC includes two synchronous machine models representing the two grid areas participating in the oscillation and three reactance variables, representing the interconnecting transmission lines and the FACTS device. The model for control of DPFC is of the same type but it also includes the phase shift of the internal phase-shifting transformer of the DPFC.

    The key parameters of the generic grid models are adaptively set during the controller operation by estimation from the step responses in the FACTS line power to the changes in the line series reactance inserted by the FACTS device. The power oscillation damping controller is based on a time-discrete, non-linear approach which aims to damp the power oscillations and set the desired power flow on the FACTS line by means of two step changes in the line reactance separated in time by half an oscillation cycle.

    A verification of the proposed controllers was done by means of digital simulations using power system models of different complexities. The CSC and DPFC controllers were shown to significantly improve the small-signal- and transient stability in one four-machine system of a type commonly used to study inter-area oscillations. The CSC controller was also tested for 18 different contingencies in a 23-machine system, resulting in an improvement in both the system transient stability and the damping of the critical oscillation mode.

  • 65.
    Johansson, Nicklas
    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.
    Ängquist, Lennart
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    An adaptive model predictive approach to power oscillation damping utilizing variable series reactance FACTS devices2006In: PROCEEDINGS OF THE 41ST INTERNATIONAL UNIVERSITIES POWER ENGINEERING CONFERENCE, 2006, p. 790-794Conference paper (Refereed)
    Abstract [en]

    This paper describes an adaptive method of controlling FACTS devices for power oscillation damping. The method is based on step-wise series reactance modulation. Here, a reduced model of the power system with only two rotating masses is used as a basis for the control design. The model parameters are updated using local measurements of the active power on the controlled line. An adaptive closed loop controller is developed based on the principle that it is possible to stabilize an oscillation in a power system which is characterized by one major mode of oscillation by switching a reactance in series with one transmission line in a small number of steps. The reduced model parameters are recomputed when new information of the system response is known making the control scheme an adaptive one. The paper also includes the derivation of a damping controller with a power flow control feature and a verification of the controllers using digital simulations of power system models of different complexities.

  • 66.
    Johansson, Nicklas
    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.
    Ängquist, Lennart
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Discrete open loop control for power oscillation damping utilizing variable series reactance FACTS devices2006In: PROCEEDINGS OF THE 41ST INTERNATIONAL UNIVERSITIES POWER ENGINEERING CONFERENCE, 2006, p. 785-789Conference paper (Refereed)
    Abstract [en]

    This paper describes an open loop method of controlling FACTS devices for power oscillation damping. The method is based on step-wise series reactance modulation. The principle of the method is to stabilize an oscillation in a power system which is characterized by one major mode of oscillation by switching a reactance in series with one transmission line, thereby changing the total reactance between the areas participating in the oscillation. In order to stabilize the system during an oscillation, the stationary voltage angle difference between the areas is changed to coincide with the present angle at a point where the speed of the lumped machine representations of the areas is nominal. This is the case at the peaks of the oscillation. To determine the required size of the reactance step, a reduced model of the power system is used. The model parameters are continuously updated using local measurements of the active power on the reactance controlled line. Several approaches for damping with different numbers of steps are presented and verified using digital simulations of power system models.

  • 67.
    Johansson, Nicklas
    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.
    Ängquist, Lennart
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Estimation of grid parameters for the control of variable series reactance FACTS devices2006In: 2006 POWER ENGINEERING SOCIETY GENERAL MEETING, VOLS 1-9, 2006, p. 105-111Conference paper (Refereed)
    Abstract [en]

    For high performance control of Flexible AC Transmission System (FACTS) devices with controllable reactances, a representation of the surrounding grid is essential. Using such a model, an adaptive control strategy can be developed which optimizes the control in real time as the grid parameters change. This paper proposes such a generic grid model and derives the theory of how to estimate the main parameters using measurements of the line active power response from small step reactance changes. The estimation methods are verified using simple grid models in PSCAD simulations and more advanced grid models using SIMPOW simulations of a modified version of the CIGRE Nordic 32 grid. This work should be thought of as a foundation for developing control systems for variable series reactance FACTS devices.

  • 68.
    Johansson, Nicklas
    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 Comparison of Different Frequency Scanning Methods for Study of Subsynchronous Resonance2011In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 26, no 1, p. 356-363Article in journal (Refereed)
    Abstract [en]

    This paper compares four different methods for determining the electrical damping of a power system seen from one generator as a function of frequency. This information is useful when the risk for subsynchronous resonance (SSR) in the system is evaluated. The study compares one frequency scanning method which is implemented in a time-domain digital simulation program with three methods of different complexity based on analytical calculations. The time-domain simulation method is easily implemented with a detailed model of the power system including complex load and generator models, whereas the analytical methods are based on simpler models of the power system. The computational effort is much larger for the time-domain method than for the analytical methods. In the study, all methods were used to determine the damping characteristics of a four-machine power system in different configurations. The study shows that fast analytical methods may provide results which closely agree with the detailed method of time-domain simulation. However, the study also shows that the level of accuracy in the analytical model is very important.

  • 69.
    Johansson, Nicklas
    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.
    Adaptive control of controlled series compensators for power system stability improvement2007In: 2007 IEEE LAUSANNE POWERTECH, 2007, p. 355-360Conference paper (Refereed)
    Abstract [en]

    This paper describes the design and verification of a time-discrete adaptive controller for damping of inter-area power oscillations, power flow control, and transient stability improvement Only locally measured signals are used as inputs to the controller. The controller may be used with any FACTS device which operates as a variable series reactance in the power grid, such as for example the TCSC. The controller is based on a reduced system model which relies on the assumption of one dominating inter-area oscillation mode in the power system where the FACTS device is placed. Verification of the controller is performed by means of digital simulations of a four-machine system commonly used to study inter-area oscillations.

  • 70.
    Johansson, Nicklas
    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.
    An Adaptive Controller for Power System Stability Improvement and Power Flow Control by Means of a Thyristor Switched Series Capacitor (TSSC)2010In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 25, no 1, p. 381-391Article in journal (Refereed)
    Abstract [en]

    In this paper, a controller for a thyristor switched series capacitor (TSSC) is presented. The controller aims to stabilize the power system by damping interarea power oscillations and by improving the transient stability of the system. In addition to this, a power flow control feature is included in the controller. The power oscillation damping controller is designed based on a nonlinear control law, while the transient stability improvement feature works in open loop. The damping controller is adaptive and estimates the power system parameters according to a simplified generic model of a two-area power system. It is designed for systems where one poorly damped dominant mode of power oscillation exists. In the paper, a verification of the controller by means of digital simulations of one two-area, four-machine power system, and one 23-machine power system is presented. The results show that the controller improves the stability of both test systems significantly in a number of fault cases at different levels of interarea power flow.

  • 71.
    Johansson, Nicklas
    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.
    An Adaptive Controller for Power System Stability Improvement and Power Flow Control by Means of a Thyristor Switched Series Capacitor (TSSC) (vol 25, pg 381, 2010)2010In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 25, no 2, p. 1200-1200Article in journal (Refereed)
  • 72.
    Johansson, Nicklas
    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).
    Aspects on Power Flow Control by means of a Dynamic Power Flow ControllerArticle in journal (Other academic)
    Abstract [en]

    This paper, which is focused on steady-state power flow control, investigates the capability of three different Power Flow Controllers (PFC) to control power flows in two test systems. The studied devices are the Dynamic Power Flow Controller (DPFC), the Phase Shifting Transformer (PST) and the Thyristor Switched Series Capacitor (TSSC). The DPFC is actually a combination of the PST and the TSSC and the study thus attempts to solve the power flow control problems either by a PST, a TSSC or a combination of these devices. The different PFC:s are designed using the Power controller plane where it is possible to decouple the surrounding grid characteristics from the PFC characteristics in a convenient way. It is found that the installation of a PFC can improve the power transfer capacity significantly in the studied test systems. In some of the studied cases, it is found that the power flow control problem can only be solved by a PST or a DPFC. One main conclusion of the study is that a DPFC may be an attractive alternative to a traditional PST installation in some cases due to a lower required rating, a better voltage control capability and a higher speed of control.

  • 73.
    Johansson, Nicklas
    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).
    Berggren, Bertil
    ABB AB, Corporate research.
    A dynamic power flow controller for power system stability improvement and loss reduction2008In: The 16th Power Systems Computation Conference, Power Systems Computation Conference ( PSCC ) , 2008Conference paper (Refereed)
    Abstract [en]

    In this paper, a novel FACTS device denoted Dynamic Power Flow Controller (DPFC) is described. The device consists of a Phase-Shifting Transformer (PST) connected in series with a set of thyristor-switched capacitive and/or inductive elements. When compared to a normal PST, this device has faster dynamic properties and in addition to the normal PST functions, it also allows for power oscillation damping, transient stability improvement, and voltage stability improvement in a power grid. The DPFC is believed to be less costly than other FACTS devices with the same functionalities. In this paper, the benefits and functions of the DPFC are discussed. Additionally, an adaptive controller for DPFC power oscillation damping, transient stability improvement, and power flow control is presented and verified by means of digital simulations.

  • 74.
    Johansson, Niklas
    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).
    Designing power flow control devices using the power controller plane: An improved methodArticle in journal (Other academic)
    Abstract [en]

    This paper introduces an improved method for design of Power Flow Controllers (PFC) in the power controller plane where the active power of the PFC line is plotted versus the difference in voltage angle between the PFC terminals. The power controller plane makes it possible to graphically visualize the working area of a PFC in a power grid and thus determine the grid situations which are dimensioning for the PFC. The paper extends the existing methods for design of PFC:s in the power controller plane by introducing a method to decouple the power grid- and PFC characteristics in a power system of arbitrary size. With this approach, it is possible to graphically compare and design PFC:s of different types and with different characteristics in the same plot by simple geometrical considerations. The method is intended to provide additional insight into how the power flow control capabilities of different PFC:s depend on the selected PFC characteristics and the grid conditions. Additionally, the method has the potential to simplify the process for selection and design of a PFC. The paper includes a study of the accuracy of the proposed method in two test systems of different complexity.

  • 75.
    Khan, Kashif
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Haghbin, Saeid
    Leksell, Mats
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Wallmark, Oskar
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Design and performance analysis of a permanent-magnet assisted synchronous reluctance machine for an integrated charger application2010In: 19th International Conference on Electrical Machines, ICEM 2010, 2010, p. 5607905-Conference paper (Refereed)
    Abstract [en]

    In a plug-in hybrid electric vehicle equipped with an integrated charger, the electric machine and the inverter, which in traction mode are used to propel the vehicle and recover energy during braking, are also used to charge the battery from the grid while the vehicle is at rest [1]. This paper studies the design and performance of a permanent-magnet assisted synchronous reluctance machine (PMaSynRM) both in traction and charging mode. Designing a PMaSynRM in order to obtain optimal reluctance and magnetic torque components is a complex task since rotor dimensioning for one torque component (magnet or reluctance torque) limits the possibility to optimize the other torque component. This paper identifies and relates the design parameters that influence these torque components and the performance of the machine using simulations based on the finite element method. The results are compared based on developed torque, torque ripple and relative values of the resulting magnet and reluctance torque.

  • 76.
    Khan, Kashif
    et al.
    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).
    Wallmark, Oskar
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Design aspects on magnet placement in permanent-magnet assisted synchronous reluctance machines2010In: IET Conference Publications, Institution of Engineering and Technology, 2010Conference paper (Refereed)
    Abstract [en]

    The design of permanent-magnet assisted synchronous reluctance machines (PMRSMs) for optimum reluctance and magnetic torque components is a complex task since rotor dimensioning for one torque component (magnet or reluctance torque) limits the possibility to optimize the other torque component. This paper identifies and relates the design parameters that influence these torque components. It describes the influence of insulation ratio, magnet size and magnet placement on the performance of the machine using finite element (FEM) based simulations. The results are compared based on developed torque, torque ripple and relative values of the resulting magnet and reluctance torque.

  • 77. Kjaer, P. C.
    et al.
    Kjellqvist, Tommy
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Delaloye, C.
    Estimation of field current in vector-controlled synchronous machine variable-speed drives employing brushless asynchronous exciters2005In: IEEE transactions on industry applications, ISSN 0093-9994, E-ISSN 1939-9367, Vol. 41, no 3, p. 834-840Article in journal (Refereed)
    Abstract [en]

    In wound-rotor synchronous machine variable-speed drives, accurate information about the field winding current is paramount to obtain high dynamic and steady-state performance, such as unity power factor. When brushless excitation is employed and no direct measurement of field winding current is available, it must be estimated. This is a topic which has not received much attention in the literature, despite its importance in high-power synchronous motor drives. This paper presents two different methods for field current estimation, applied in a vector-controlled voltage-source converter-fed drive. Experimental results illustrate the steady-state accuracy and dynamic performance.

  • 78.
    Kjaer, Philip
    et al.
    ABB Corporate Research.
    Norrga, Staffan
    ABB Corporate Research.
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    A primary-switched converter using zero-voltage switching2000In: Proccedings of the IEEE Industry Applications Society Annual Meeting 2000, 2000Conference paper (Refereed)
  • 79.
    Kjellqvist, Peter
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Carlsson, Fredrik
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Control and design requirements of an electromechanical actuator for active suspension of rail vehicles1999Conference paper (Refereed)
  • 80.
    Kjellqvist, Peter
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Carlsson, Fredrik
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Electromechanical actuator for active suspension in rail vehicles1999Conference paper (Refereed)
  • 81.
    Kjellqvist, Tommy
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    On Design of a Compact Primary Switched Conversion System for Electric Railway Propulsion2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this thesis, a compact and light primary switched conversion system for AC-fed railway propulsion is investigated. It is characterized by soft switching of all converter stages and a source commutated primary converter comprising series connected valves. Both weight and volume of the conversion system are reduced significantly compared to a conventional system with a low frequency transformer.

    The conversion system is made up of N isolated AC/DC conversion cells, each comprising a cycloconverter and a voltage source converter (VSC) coupled by a medium frequency transformer. The cells are series connected on the AC side and connected to a common DC-link. Thus, 2N+1 voltage levels can be synthesized at the AC terminal and the voltage stress on the transformer and line filter is reduced compared to a one cell solution. Series connection of semiconductor valves allows independent choice of blocking voltage and number of converter cells. Choosing two converter cells is an attractive compromise. Five level output reduces the harmonic distortion and simplify transformer and line filter design while keeping the complexity of the conversion system low.

    The mutually commutated converter (MCC) allows a transformer frequency in the range of 4 to 8 kHz without derating the line side converter due to zero voltage switching of the VSC. Modern magnetic materials, like high silicon steel, amorphous and noncrystalline materials allow design of the transformer with high efficiency at elevated frequencies.

    In a 15 kV system, the peak voltage at the catenary is typically beyond 32 kV which is far beyond the voltage capability of currently available semiconductors. Therefore, several semiconductors are connected in series. Favourable commutation conditions and a new gate drive arrangement allow snubberless commutation of the primary converter stage. Thus, the primary converter can be highly integrated, reducing both weight and volume. The conversion system can be placed on the roof or in the underframe without compromising efficiency or vehicle performance.

    The feasibility of the conversion concept has been demonstrated by means of a down-scaled prototype. Snubberless commutation of series connected valves is demonstrated.

  • 82.
    Kjellqvist, Tommy
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Norrga, Staffan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Active snubber circuit for source commutated converters utilizing the IGBT in the linear region2007In: 2007 EUROPEAN CONFERENCE ON POWER ELECTRONICS AND APPLICATIONS, VOLS 1-10, PISCATAWAY: IEEE SERVICE CTR , 2007, p. 2679-2688Conference paper (Refereed)
    Abstract [en]

    This paper describes a gate control method where an IGBT is controlled in its linear region by means of a closed control loop in order to regulate the voltage slope during turn-on and to clamp the voltage of an anti-parallel diode in a source commutated converter. Controlling the voltage slope may be necessary in a high voltage converter to avoid emission of EMI or to avoid triggering oscillations which may cause insulation failure. Controlling the switching trajectory without influence from the device characteristics is important where series-connection is necessary to increase the overall blocking voltage. The control method has been verified by means of a prototype.

  • 83.
    Kjellqvist, Tommy
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Norrga, Staffan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Harmonic Mitigation in Single Phase Mutually Commutated Converter Systems2006In: Proceedings of the 37th Annual IEEE Power Electronics Specialists Conference, PESC 2006, NEW YORK, NY: IEEE , 2006, p. 1542-1548Conference paper (Refereed)
    Abstract [en]

    An AC/DC converter comprising a cycloconverter and a capacitively snubbered voltage source converter (VSC), coupled by a medium frequency transformer, offers significant advantages. Bidirectional AC/DC power flow as well as voltage transformation and isolation can be achieved. By mutual commutation of the converters, soft switching can be achieved for all semiconductors, thus, link frequency can be increased, allowing smaller transformer and reduced filter components. However, the mutual commutation scheme imposed by the soft switching requirement puts constraints on the PWM pattern causing low frequency harmonics in certain operating points. It is shown that the low frequency harmonics can be eliminated for all points of operation, both in a single bridge configuration and interlaced configuration, common in AC-fed propulsion. A sub-optimal harmonic mitigation method based on a regularly sampled modulator is proposed. By proper oversampling of the reference waveforms substantial reduction of the low frequency harmonic contents can be achieved. The mitigation method is verified by circuit simulation and the feasibility to propulsion is demonstrated.

  • 84.
    Kjellqvist, Tommy
    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.
    Norrga, Staffan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Switching Frequency Limit for Soft-Switching MF Transformer System for AC-fed Traction2005In: Proceesings of the 36th Annual IEEE Power Electronics Specialist Conference, PESC 2005, IEEE , 2005, p. 1678-1684Conference paper (Refereed)
    Abstract [en]

    The migration to line side power conversion topologies comprising a medium frequency transformer in AC-fed propulsion systems may reduce size and weight of the conversion system. The switching frequency is a crucial factor affecting the viability of such a conversion system. An increased switching frequency of a mutually commutated conversion system comprising a medium frequency transformer employing soft switching is verified by single pulse measurements. A test bench to characterize standard IGBT modules under soft switching has been build and loss measurements on a 3.3 kV IGBT module are presented for hard and soft switching. A loss model of the investigated topology is developed and the maximum switching frequency for a converter equipped with the investigated module is estimated for hard and soft switching.

  • 85.
    Kjellqvist, Tommy
    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.
    Norrga, Staffan
    ABB AB, Sweden .
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Ilves, Kalle
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Thermal Evaluation of a Medium Frequency Transformer in a Line Sider Conversion System2009In: Proceedings of the 13th International European Electronics Conference and Exhibition, EPE '09, IEEE , 2009, p. 2517-2526Conference paper (Refereed)
    Abstract [en]

    A central part of a medium frequency conversion system is the transformer. A medium frequency transformer for railway propulsion may be stressed beyond 30kV with voltage slopes around 50kV/mu s depending on topology while the geometric dimensions are small. A 170kVA transformer prototype operated at 4 kHz has been developed and tested.

    A transient thermal model of the transformer is developed and verified experimentally. The transient thermal behavior is important in propulsion applications where the conversion system is often heavily overloaded. Simulations indicate that the overloading capability of the transformer is comparable to a conventional traction transformer. Experimental results are in good agreement with the model.

  • 86.
    Kjellqvist, Tommy
    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.
    Östlund, Stefan
    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).
    Active Snubber Circuit for Source Commutated Converters Utilizing the IGBT in the Linear Region2008In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 23, no 5, p. 2595-2601Article in journal (Refereed)
    Abstract [en]

    This paper describes a gate control method where an IGBT is controlled in its linear region by means of closed loop control in order to regulate the voltage slope during turn-on and to clamp the voltage of an anti-parallel diode in a source commutated converter. Controlling the voltage slope may be necessary in a high voltage converter to avoid emission of EMI or to avoid triggering oscillations which may cause insulation failure. Controlling the switching trajectory without influence from the device characteristics is important where series-connection is necessary to increase the overall blocking voltage. The control method has been verified by means of a prototype.

  • 87.
    Larsson, Tomas
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Active DC Link Filter for AC-AC Converters1995Conference paper (Refereed)
  • 88.
    Larsson, Tomas
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    An active DC link filter for two frequency electric locomotives1994Conference paper (Refereed)
  • 89.
    Libert, Florence
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Soulard, Juliette
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Manufacturing Methods of Stator Cores with Concentrated Windings2006In: The 3rd IET International Conference on Power Electronics, Machines and Drives, 2006, p. 676-680Conference paper (Other academic)
    Abstract [en]

    The purpose of this paper is to investigate the difficulties in manufacturing a stator core with concentrated windings. The existing solutions are compared in terms of cost, required equipment for the production and performance of the permanent-magnet (PM) motor. A 1 kW 28-pole PM motor with an outer diameter of 400mm, designed for a low-speed direct-driven application is taken as an example

  • 90.
    Lim, Jang-Kwon
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Bakowski, M.
    Analysis of 1.2 kV SiC buried-grid VJFETs2010In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T140, p. 014008-Article in journal (Refereed)
    Abstract [en]

    1.2 kV buried-grid vertical 4H-SiC JFET structures with normally-on (N-on) and normally-off (N-off) designs were investigated by simulation. The static and dynamic characteristics of the devices were determined over a wide range of current, voltage and gate drive conditions in the temperature range -50 degrees C to 250 degrees C. In this paper, the properties of the N-on designs with threshold voltages (V-th) -50 and -10 V are compared with the properties of the N-off design (V-th = 0). For constant V-th, on-resistance decreases and output current increases with increasing channel doping and decreasing channel width. Simulations show that an on-resistance lower than 2 m Omega cm(2) at 250 degrees C can be obtained provided the channel width is smaller than 1.5 and 0.5 mu m for N-on JFETs with V-th = -50 V and V-th = -10 V, respectively, and lower than 3 m Omega cm(2) provided the channel width is smaller than 0.3 mu m for the N-off JFET. At the same time, E-on decreases and E-off increases with increased channel doping concentration and reduced channel width. It is shown that E-on decreases with increasing channel doping concentration due to the reduced channel resistance for the faster turn-on process. E-off increases with increasing channel doping concentration due to the increase in gate-drain capacitance, C-GD.

  • 91.
    Lim, Jang-Kwon
    et al.
    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).
    Peftitsis, Dimosthenis
    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).
    Bakowski, Mietek
    Acreo, Kista.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Comparison of total losses of 1.2 kV SiC JFET and BJT in DC-DC converter including gate driver2011In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 679/680, p. 649-652Article in journal (Refereed)
    Abstract [en]

    The 1.2 kV SiC JFET and BJT devices have been investigated and compared with respect to total losses including the gate driver losses in a DC-DC converter configuration. The buried grid, Normally-on JFET devices with threshold voltage of -50 V and -10V are compared to BJT devices with ideal semiconductor and passivating insulator interface and an interface with surface recombination velocity of 4.5·104 cm/s yielding agreement to the reported experimental current gain values. The conduction losses of both types of devices are independent of the switching frequency while the switching losses are proportional to the switching frequency. The driver losses are proportional to the switching frequency in the JFET case but to a large extent independent of the switching frequency in the BJT case. The passivation of the emitter junction modeled here by surface recombination velocity has a significant impact on conduction losses and gate driver losses in the investigated BJT devices.

  • 92.
    Magnussen, Freddy
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Chin, Yung-Kang
    KTH, Superseded Departments, Electrical Systems.
    Soulard, Juliette
    KTH, Superseded Departments, Electrical Systems.
    Broddefalk, A.
    Eriksson, Sture J A
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Sadarangani, Chandur
    KTH, Superseded Departments, Electrical Systems.
    Iron losses in salient permanent magnet machines at field-weakening operation: COVERING THEORY TO PRACTICE2004In: CONFERENCE RECORD OF THE 2004 IEEE INDUSTRY APPLICATIONS CONFERENCE, VOLS 1-4: COVERING THEORY TO PRACTICE, NEW YORK, NY: IEEE , 2004, p. 40-47Conference paper (Refereed)
    Abstract [en]

    Permanent magnet machines for electric vehicles are often designed with a magnetic saliency to improve the torque generation as a result of the reluctance torque at field-weakening operation. The armature reaction is pronounced in such operation, leading to extensive magnetic field harmonics in the teeth and consequently iron losses. This paper analyses the iron losses in two designed machine topologies, inset and interior permanent magnet rotor structures, by measurements and finite element method computations. The measurements and calculations are performed on three prototypes-one with an in set design and two with an equal interior design, but different laminated stator core sheet thickness of 0,35 and 0,20 mm, respectively. The three machines have the same stator designs and water-cooled housings.

  • 93.
    Malik, Naveed Ur Rehman
    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).
    Lindmark, Magnus
    Theoretical and Experimental Investigation of the Self-Excited Rotating Power Electronic Induction Machine2011In: IECON 2011: 37TH ANNUAL CONFERENCE ON IEEE INDUSTRIAL ELECTRONICS SOCIETY, 2011, p. 2048-2053Conference paper (Refereed)
    Abstract [en]

    This paper presents the theoretical model and analysis of a novel topology of the self-excited induction machine using rotating power electronic converters. The power electronic converters are connected to the rotor of the induction machine and it is shown that the machine operates at unity power factor at variable load conditions including rated load. Special control strategy of the two converters helps in magnetization of the induction machine from the rotor. The experimental analysis is conducted in the industry using 11kW induction machine and close agreement is found between the theoretical model and the experimental results. Besides, the rotor resistance is varied and its effect on the power factor and performance of the machine is studied and analyzed.

  • 94. Meessen, K. J.
    et al.
    Thelin, P.
    Soulard, Juliette
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Lomonova, E. A.
    Inductance calculations of permanent-magnet synchronous machines including flux change and self- and cross-saturations2008In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 44, no 10, p. 2324-2331Article in journal (Refereed)
    Abstract [en]

    Accurate inductance calculation of permanent-magnet synchronous machines is a relevant topic, since the inductances determine a large part of the electrical machine behavior. However, the inductance calculation, as well as the inductance measurement, is never a completely straightforward task when saturation occurs. In this paper, the total flux in the d and q axes are obtained from finite-element method or measurements and therefore include saturation and cross-couplings. The inductances are obtained from analytical post-processing based on an equivalent magnetic circuit. The originality of this method is that it accommodates the changes in the magnet flux and the inductances with the level of saturation. The resulting inductance values are the ones seen by the converter or the grid, as found by a more accurate approach.

  • 95. Mei, Z.
    et al.
    Zou, J. -B
    Jiang, X. -T
    Fu, X. -H
    Sadarangani, Chandur
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Influence of axial length ratio of stator segment on performance of tubular transverse flux linear machine2010In: Digests of the 2010 14th Biennial IEEE Conference on Electromagnetic Field Computation, CEFC 2010, 2010, p. 5481161-Conference paper (Refereed)
    Abstract [en]

    In this paper the influence of axial length ratio of stator segment on performance of tubular transverse flux linear machine (TTFLM) is investigated. The following issues have been emphasized: cogging force, winding flux, and back-EMF. The special topology of TTFLM requires 3-D finite element analysis to accurately predict the machine performance. However, equivalent 2-D finite element analysis is performed, which is more visual from physical view and faster from computing time than 3-D finite element analysis.

  • 96.
    Meier, Florence
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Permanent-Magnet Synchronous Machines with Non-Overlapping Concentrated Windings for Low-Speed Direct-Drive Applications2008Doctoral thesis, monograph (Other scientific)
    Abstract [en]

     Many geared electric drives can benefit from removing the gearbox and driving directly the load at low speed using a permanent-magnet synchronous machine (PMSM). PMSMs with non-overlapping concentrated windings are particularly attractive in low-speed direct drives since they allow, among other advantages, a high number of poles with a limited number of slots. Therefore, this thesis is dedicated to PMSMs with non-overlapping concentrated windings designed for low-speed directdrive applications.First, the design features specific to PMSMs with non-overlapping concentrated windings are presented and illustrated with examples based on finite-element (FE) simulations. Especially, 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.Second, the benefits of removing the gearbox in a 4.5 kW, 50 rpm mixer used in a waste-water treatment plant are investigated. With its PMSM having buried ferrite magnets and concentrated windings, the designed direct-drive mixer has a higher efficiency than the commercialized geared mixer, but it is also heavier and more expensive due to the larger required housing, shaft and seals. In addition, the cost of the stator core and coil assembly was also higher than expected. Therefore, the difficulties in manufacturing a stator core with concentrated windings are investigated. Mainly due to economical aspects, no prototype motor has been built for the direct-drive mixer.Finally, measurements on a prototype motor at disposal having a large constantpower speed range are performed. Three methods to measure the inductances without using a position sensor are provided and compared. One of the methods is a new test at load conditions to determine the inductance without the knowledge of the rotor position. Results from this method agree well with a conventional blocked rotor test, as well as with results from 3D-FE simulations. Furthermore, the measurements of the magnetic flux obtained with search coils placed in different parts of the stator are analyzed. The analysis allows highlighting the zigzag flux flowing from one magnet to another through a tooth tip, which is characteristic of PMSMs with non-overlapping concentrated windings. It is shown that this zigzag flux leakage causes high iron losses in the tooth tips that represent approximately 50% of the stator iron losses under field weakening operation. Using these measurements, the 3D-FE model of the prototype is also validated thoroughly.

  • 97.
    Meier, Florence
    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.
    Soulard, Juliette
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Emetor: An educational web-based design tool for permanent-magnet synchronous machines2009In: ICEM: 2008 INTERNATIONAL CONFERENCE ON ELECTRICAL MACHINES, NEW YORK: IEEE , 2009, p. 2238-2243Conference paper (Refereed)
    Abstract [en]

    An educational web-based design tool for permanent-magnet synchronous machines (PMSM) is presented in this article. This tool, named Emetor, has been developed to be used in an undergraduate course on permanent-magnet machines. The technical aspects behind the tool, such as the PMSM's design procedure and the program architecture are presented. The benefits of Emetor in an educational environment are described. Different learning activities are presented to illustrate the potential of Emetor, as well as its suitability for education.

  • 98.
    Meier, Florence
    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.
    Analysis of Flux Measurements on a PMSM With Non-Overlapping Concentrated Windings2008In: 2008 IEEE INDUSTRY APPLICATIONS SOCIETY ANNUAL MEETING, 2008, p. 2090-2097Conference paper (Refereed)
    Abstract [en]

    In this paper, measurements of the magnetic flux in a permanent-magnet synchronous machine (PMSM) with non-overlapping concentrated windings are analyzed. Flux leakage, inductances and stator iron losses are investigated from measurements performed at open-circuit, blocked-rotor, and load conditions, respectively. Comparisons of the measurements with the corresponding 3D finite-element (FE) simulations allow validating thoroughly the FE model. The zigzag leakage flux flowing from one magnet to another through a tooth tip, which is characteristic for PMSMs with concentrated windings, is highlighted and its effect on the stator iron losses is investigated.

  • 99.
    Meier, Florence
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Soulard, Juliette
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    dq Theory Applied to a Permanent Magnet Synchronous Machine with Concentrated Windings2008In: 4th IET International Conference on Power Electronics, Machines and Drives (PEMD 2008), 2008, p. 194-198Conference paper (Refereed)
    Abstract [en]

    In this paper, dq theory is applied to a surface-mounted permanent magnet synchronous machine with non-overlapping concentrated windings. Although the assumption of sine-distributed windings is violated, it is shown with theory and measurements, that the dq model is reliable for torque and voltage calculations of the loaded machine.

  • 100.
    Meier, Stephan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Novel voltage source converter based HVDC transmission system for offshore wind farms2005Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Offshore wind farms have recently emerged as promising renewable energy sources. For increasing distances between offshore generation and onshore distribution grid, HVDC transmission systems based on voltage source converters can be a feasible and competitive solution. This thesis presents a comprehensive evaluation of a novel integrated wind farm topology that includes the generator drive system, the turbine interconnection and the HVDC transmission.

    In the proposed concept, every wind turbine is connected to a single-phase medium-frequency collection grid via a distribution transformer and a cycloconverter, which allows the wind turbines to operate at variable speed. The collection grid is connected to an HVDC cable via a transmission transformer and a single-phase voltage source converter. This thesis evaluates in detail the principle of operation, which is also verified with system simulations in PSCAD.

    The proposed concept promises several potential benefits. Converter switching losses and stress on the semiconductors for example can be considerably reduced by applying a soft-switched commutation scheme in all points of operation. Single-phase medium-frequency transformers have comparably low losses and their compact size and low weight implies an important benefit in an offshore environment. In addition, the voltage source converter is considerably simplified by the reduction to one phase leg, which implies a substantial cost saving.

    Several technical challenges are identified and critically evaluated in order to guarantee the feasibility of the proposed concept. Especially the design of the medium-frequency collection grid is crucial as unwanted system resonances can cause dangerous overvoltages. Most of the technical challenges concern the specific characteristics of the proposed concept. The insulation of the single-phase medium-frequency transformers for example needs to withstand the high voltage derivatives. This thesis contains also considerations regarding the dimensioning and optimization of different system components.

    A survey of different transmission systems for the grid connection of wind farms shows the potential of the proposed concept, which addresses several problems associated with electrical systems of wind farms. Both the requirements for variable-speed operation of the wind turbines and an interface for HVDC transmission are fulfilled in a cost-effective way. Compared to conventional voltage source converter based HVDC transmission systems, the initial costs are reduced and the expected annual energy production is increased. In addition, the proposed voltage source converter based HVDC transmission system can fully comply with recent requirements regarding the grid connection of wind farms.

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