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  • 1.
    Demetriades, Georgios D.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    On small-signal analysis and control of the single- and the dual-active bridge topologies2005Doctoral thesis, monograph (Other scientific)
    Abstract [en]

    High-frequency dc-dc converters are nowadays widely used in a diversity of power electronic applications. High operating frequencies entail a reduction in size of the passive components, such as inductors, capacitors and power transformers. By operating the converter at higher frequencies with conventional hard-switching topologies, the transistor switching losses increase at both turn-on and turn-off. High-voltage converters in the power range of 1-10MW will therefore have excessive switching losses if the switching frequency is higher than 4 kHz. In order to achieve a high-frequency operation with moderate switching losses a number of soft-switched topologies have been studied in [Dem1]. The favourable DC-DC converter was found to be the Dual-Active Bridge when a bi-directional power flow is demanded. Additionally, the Single-Active Bridge (SAB) topology was introduced for the first time.

    In this thesis the two topologies are thoroughly studied. The dynamic small-signal models are presented and the dynamic behaviour of the converters is discussed in deep. Different control strategies are presented concerning the two converters and the advantages and the disadvantages of the different control strategies are stated.

    Critical issues as efficiency and stability are presented separately for the two converters.

  • 2. Demetriades, Georgios D.
    et al.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Characterization of the Dual-Active Bridge Topology for High-Power Applications Employing a Duty-Cycle Modulation2008In: 2008 IEEE POWER ELECTRONICS SPECIALISTS CONFERENCE, VOLS 1-10, NEW YORK, NY: IEEE , 2008, p. 2791-2798Conference paper (Refereed)
    Abstract [en]

    In the present paper the Dual-Active Bridgetopology employing a duty-cycle modulation is studied. Thebehavior of the converter at steady-state is examined.Additionally, the small-signal model of the topology ispresented and the dynamic behavior is examined.Simulations and experimental results are presented. It isworth noticing that the converter is operated under softswitchingconditions in a wide load range.

  • 3. Demetriades, Georgios D.
    et al.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Dynamic Modeling of the Dual-Active Bridge Topology for High-Power Applications2008In: 2008 IEEE POWER ELECTRONICS SPECIALISTS CONFERENCE, VOLS 1-10, NEW YORK: IEEE , 2008, p. 457-464Conference paper (Refereed)
    Abstract [en]

    In the present paper the staedy-state and thedynamic behavior of the Dual-Active Bridge topology havebeen studied. The small-signal model of the converter hasbeen derived and theoretical and experimental results arepresented.The Dual-Active Bridge is an attractive solution for highpowerapplications where a bi-directional operation is needed.

  • 4.
    Demetriades, Georgios
    et al.
    ABB.
    Manias, S. N.
    National Technical University of Athens- Greece.
    Ranstad, Per
    National Technical University of Athens- Greece.
    High-frequency oscillations in a power transformer: 32ND ANNUAL POWER ELECTRONICS SPECIALISTS CONFERENCE, VOLS 1-4, CONFERENCE PROCEEDINGS2001In: IEEE POWER ELECTRON SPEC CONF, IEEE , 2001, p. 612-616Conference paper (Refereed)
    Abstract [en]

    Power transformers are widely used as step-up or step-down devices and they can offer galvanic isolation between the input of the power supply and the output. When the operating frequency is considerably high, transformer parasitics are of importance. Interleaving of the transformer windings causes a reduction of the leakage inductance. However, the winding capacitance and the stray capacitance increases due to the good proximity of the windings achieved by interleaving.

  • 5.
    Demetriades, Georgios
    et al.
    ABB Environmental Systems.
    Ranstad, Per
    ABB Environmental Systems.
    Sadarangari, C.
    KTH, Superseded Departments, Electrical Systems.
    Three elements resonant converter: The LCC topology by using MATLAB2000In: PESC Record: IEEE Annual Power Electronics Specialists Conference, Galway, UK, 2000, Vol. 2, no Piscataway, NJ, United States, p. 1077-1083Conference paper (Refereed)
    Abstract [en]

    The behaviour of a series-parallel resonant power converter is analysed by means of MATLAB simulations. PSPICE and experimental results are also presented. Stress parameters are calculated and compared with those of the series-loaded resonant power converter.

  • 6.
    Ranstad, Per
    et al.
    Alstom Power Environmental Systems.
    Demetriades, Georgios D.
    ABB Corporate Research.
    On conversion losses in SLR and LCC-topologies2002Conference paper (Other academic)
    Abstract [en]

    A methodto improve the efficiency of the SLR-converter is presented. By adding a capacitor the overall component stresses can be lowered. Simulation and experimental results are presented. A 60kW converter is tested in order to verify the theoretical results. Substantial improvements can be obtained by the proposed method.

  • 7.
    Ranstad, Per
    et al.
    Alstom Power Serv.
    Linner, Jorgen
    Alstom Power Serv.
    Demetriades, Georgios
    ABB.
    On Cascading of the Series Loaded Resonant Converter2008In: 2008 IEEE POWER ELECTRONICS SPECIALISTS CONFERENCE, IEEE , 2008, p. 3857-3860Conference paper (Refereed)
    Abstract [en]

    In this paper a novel method for cascading H-bridge and resonant tanks in a SLR, series loaded resonant, converter is presented. The main focus is on load sharing. Different methods are discussed. Their robustness regarding variations in operating frequency, values of the components and parasitic elements are evaluated. The results are validated both by simulations and by experiments. For the experimental part a 120kW/70kV system has been designed and tested. The measurements confirm the simulations, where the proposed method shows an equal sharing of the load (current) even when operating the system close to resonance with a +/- 10% worst-case variation of the resonant tank components. The method is derived for two subsystems, but can be generalised to any number of subsystems. Thus, enabling the use of compact, standardised modules connected together forming very powerful systems.

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