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  • 151.
    Cai, Yangjian
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Zhang, Lei
    Propagation of a hollow Gaussian beam through a paraxial misaligned optical system2006In: Optics Communications, ISSN 0030-4018, E-ISSN 1873-0310, Vol. 265, no 2, p. 607-615Article in journal (Refereed)
    Abstract [en]

    Based on the generalized diffraction integral formula for treating the propagation of a laser beam through a paraxial misaligned optical system in the cylindrical coordinate system, we obtain an analytical formula for a hollow Gaussian beam passing through a paraxial misaligned optical system. Furthermore, we also obtain the approximate analytical formula for a hollow Gaussian beam passing through a paraxial circularly apertured misaligned optical system by expanding the hard aperture function into a finite sum of complex Gaussian functions. As a numerical example, the propagation properties a hollow Gaussian beam through a misaligned thin lens are studied numerically.

  • 152. Camacho, Miguel
    et al.
    Mitchell-Thomas, Rhiannon C.
    Hibbins, Alastair P.
    Sambles, J. Roy
    Quevedo-Teruel, Oscar
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Designer surface plasmon dispersion on a one-dimensional periodic slot metasurface with glide symmetry2017In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 42, no 17, p. 3375-3378Article in journal (Refereed)
    Abstract [en]

    In this Letter, we explore the dispersion of spoof surface plasmons supported by a single-layer glide-symmetric structure. This structure consists of an infinitely long double-notched slot perforated in a metal layer. The presence of a degeneracy of the two lowest-order modes at the Brillouin zone boundary, which have non-zero group velocity is explained and experimentally demonstrated. Further, the dependence of the band structure when glide-symmetric configuration is broken is also explored.

  • 153. Camacho, Miguel
    et al.
    Mitchell-Thomas, Rhiannon C.
    Hibbins, Alastair P.
    Sambles, J. Roy
    Quevedo-Teruel, Oscar
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Mimicking glide symmetry dispersion with coupled slot metasurfaces2017In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 111, no 12, article id 121603Article in journal (Refereed)
    Abstract [en]

    In this letter, we demonstrate that the dispersion properties associated with glide symmetry can be achieved in systems that only possess reflection symmetry by balancing the influence of two sublattices. We apply this approach to a pair of coupled slots cut into an infinite perfectly conducting plane. Each slot is notched on either edge, with the complete two-slot system having only mirror symmetry. By modifying the relative size of the notches on either side of the slots, we show that a linear dispersion relation with a degeneracy with non-zero group velocity at the Brillouin zone boundary can be achieved. These properties, until now, only found in systems with glide symmetry are numerically and experimentally validated. We also show that these results can be used for the design of ultra-wideband one-dimensional leaky wave antennas in coplanar waveguide technology.

  • 154.
    Carrander, Claes
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Magnetizing Currents in Power Transformers: Measurements, Simulations, and Diagnostic Methods2017Doctoral thesis, monograph (Other academic)
    Abstract [en]

    This thesis demonstrates a method for transformer core diagnostics. The method uses the no-load current of the transformer as an indicator, and gives different characteristic signatures for different types of faults or defects. Using the no-load current for the diagnostic gives high sensitivity. The method is therefore able to detect defects that are too small to have an impact on the losses. In addition to different types of fault, the method can in some cases also distinguish between faults in different locations within the core.

    Both single-phase and three-phase transformers can be diagnosed using this method, and the measurements can be easily performed at any facility capable of measuring the no-load loss. There are, however, some phenomena that occur in large transformers, and in transformers with high rated voltages. Examples include capacitive resonance and magnetic remanence. This thesis proposes and demonstrates techniques for compensating for these phenomena. With these compensating techniques, the repeatability of the measurements is high. It is shown that units with the same core steel tend to have very similar no-load behavior.

    The diagnostics can then be performed either by comparing the transformer to another unit, or to simulations. The thesis presents one possible simulation method, and demonstrates the agreement with measurements.

    This topological simulation method includes both the electric circuit and an accurate model of the magnetic hysteresis. It is therefore also suitable for other, related, studies in addition to core diagnostics. Possible subjects include ferroresonance, inrush, DC magnetization of transformers, and transformer core optimization.

    The thesis also demonstrates that, for three-phase transformers, it is possible to compare the phases to each other. This technique makes it possible to diagnose a transformer even without a previous measurement to compare to, and without the data required to make a simulation.

  • 155.
    Carrander, Claes
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    On methods of measuring magnetic properties of power transformers2015Licentiate thesis, monograph (Other academic)
    Abstract [en]

    The core of a power transformer can weigh hundreds of tons, and represents a significant part of the total ownership cost of the transformer, in terms of both the construction cost and of the monetary cost of losses. It is therefore desirable to have a method of diagnosing the core to ensure optimal performance, and to enable the operator to plan repairs of damaged or defective cores. This study shows that measuring the magnetizing current gives an amplification effect, compared to measuring just the no-load loss, that allows even small variations in the state of the core to be detected. The measurement is performed on several large power transformers, demonstrating that the method is easy to use and that it gives reliable results that are comparable between different transformer designs, though further experiments are necessary in order to fully validate it. Experiments performed on small-scale transformer models show that different types of core faults give different characteristic changes in the magnetizing current, thus making it possible to diagnose the core.

    The large scale does, however, introduce other phenomena that must be taken into account. The most important of these is that, at high voltages, the capacitances in the transformer become noticeable and must be compensated for. This study describes a method of approximating the capacitive part of the no-load current using naturally occurring harmonics in the supply voltage.

    Additionally, there is, at present, no satisfactory method of describing the magnetizing current of a three-phase transformer. Because of the non-linearity of the core steel, there is a large difference between the measured no-load current and the actual magnetizing current. Three methods for measuring the magnetizing current in a three-phase transformer are described. However, these methods are only applicable under very special circumstances, and are generally not useful under real conditions. As an alternative, a simulation method is outlined. Measurement results from a transformer can then be compared to the simulation result, and any differences between the two can be interpreted to make a diagnosis of the transformer core. The method is used to simulate a large three-phase transformer, and produces a qualitative agreement. An improvement to the hysteresis model used in the simulation, which could potentially make it possible to make quantitative predictions as well, is discussed.

    Much work remains before the methods described in this thesis can become fully functional diagnostic tools, but the work shows the feasibility of the project, and the potential benefits. By measuring the magnetizing current it is possible to obtain valuable information about the status of the core. This makes it easier for the transformer operator to plan maintenance, or for the manufacturer to assess the quality of the core, and increases operational reliability and efficiency.

  • 156.
    Carrander, Claes
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Engdahl, Göran
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    A semi-empirical approximation of static hysteresis for high flux densities in highly grain-oriented silicon iron2017In: 8th Joint European Magnetic Symposia (JEMS2016), Institute of Physics (IOP), 2017, article id UNSP 012039Conference paper (Refereed)
    Abstract [en]

    In calculations and simulations regarding magnetic materials, it is important to have a have an accurate model of the hysteresis loop. The major loop, in particular, is used in many simulations. However, it is generally not possible to measure the true major loop, and it must therefore be approximated using a minor loop. There are several methods available for approximating magnetization curves, but they are primarily designed for paramagnetic materials, and are poorly suited to the highly grain-oriented steels used in modern transformers. Therefore, we propose two expressions for approximating the magnetization curves of grain-oriented silicon-iron steels. Both methods give close agreement with measurements and can be extrapolated to in order to describe the major loop.

  • 157.
    Carrander, Claes
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Engdahl, Göran
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Magnetizing current measurements on full scale power transformers2015In: International journal of applied electromagnetics and mechanics, ISSN 1383-5416, E-ISSN 1875-8800, Vol. 48, no 2-3, p. 159-162Article in journal (Refereed)
    Abstract [en]

    The magnetic properties of a power transformer core are generally held to be quite similar to those of the core steel itself. Due mainly to it being rare and practically difficult to acquire a transformer for testing and verification, testing of large units is usually only performed concerning no-load losses. However, other parts of the magnetic hysteresis loop are more sensitive to variations in material and geometry and could be used for more detailed diagnostics. This paper shows that measurements of magnetic hysteresis can be performed with good results on large power transformers. Methods to compensate for capacitive currents and to calculate the effective magnetic length of the core are shown and the results are compared to standard material measurements. The results show good agreement with Epstein frame measurements on annealed samples.

  • 158.
    Carrander, Claes
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Mousavi, Seyedali
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Engdahl, Göran
    KTH, School of Electrical Engineering (EES).
    An application of the time-step topological model for three-phase transformer no-load current calculation considering hysteresis2017In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 423, p. 241-244Article in journal (Refereed)
    Abstract [en]

    In many transformer applications, it is necessary to have a core magnetization model that takes into account both magnetic and electrical effects. This becomes particularly important in three-phase transformers, where the zero-sequence impedance is generally high, and therefore affects the magnetization very strongly. In this paper, we demonstrate a time-step topological simulation method that uses a lumped-element approach to accurately model both the electrical and magnetic circuits. The simulation method is independent of the used hysteresis model. In this paper, a hysteresis model based on the first-order reversal-curve has been used. © 2016 Elsevier B.V.

  • 159.
    Casselbrant, Gustav
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Domain Decomposition Methods for Finite Periodic Structures in Electromagnetics2012Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Long computational times persist on being a limiting factor when designing complex electromagnetic structures. Even though computers get more and more powerful, the most efficient improvement for reducing the necessary time when solving a numerical problem is to change or optimise the used numerical method. One numerical method introduced lately is the domain decomposition method (DDM).

    This thesis explores the available algorithms for computational electromagnetics which are based on DDM. The study is concentrated on algorithms available for computational electromagnetics. The aim of the study is to find and further study one appropriate method for analysing finite periodic electromagnetic structures like frequency selective surfaces and array antennas.

    After an introducing study of DDM, the FACTOPO method, is selected and studied in detail. The study includes an implementation of the method, which is performed in three versions. The first deals with a 1-Dimensional waveguide problem which follows the FACTOPO method for determining the scattering parameters of a subdomain using admittance parameters of the corresponding domain. By limiting the subdomain with perfect electric conductor (PEC) the computational problem is efficiently reduced. The second implementation continues to explore the 1-Dimensional problem but introduces the ability of importing scattering parameters of a specific domain from an electromagnetic simulation software. The third, and last, implementation is an extension of the second version which introduces a 2-D structure based on a 4-port unit cell.

    The theoretical study and the results from the implementation show that that domain decomposition is a promising numerical technique which, when used properly, can improve the numerical simulation software for electromagnetic structures. It is also concluded that domain decomposition is especially promising for periodic electromagnetic structures.

  • 160.
    Cederlöf, Mikael
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Inductive Charging of Electrical Vehicles - System Study2012Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    A prerequisite of a fast increasing market of the electrical vehicles is the access to charging and reliability/accessibility of the charging systems. Wireless charging i.e. charging without a cord, is an interesting alternative that has been put forward during recent years.

    In this work a system study of topologies for inductively coupled power transfer over an air gap oftens of centimetres has been investigated. In order to obtain an effective power transfer compensation capacitors are used to achieve resonance circuits.

    In the thesis four different compensation topologies for inductively coupled power transfer are examined. Expressions for the compensation capacitances and the output voltage or current are derived.

    An example design for each of the four topologies capable of handling a transfer of 3 kW of power over an air gap of 20 cm with an efficiency of at least 96% is examined. These designs use an outer radius for both coils of 30 cm, and an operating frequency of 20 kHz. The efficiency only encompasses the windings, and does not take into account the efficiency of any power electronics before or after the coils.

    Prototype housing for the primary coil has been designed and built using basalt fibre reinforced high performance concrete, and magnetic measurements on the materials used are included in the report.

  • 161.
    Chen, C
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Bissal, Ara
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Salinas, E
    Numerical modelling and experimental testing of eddy-current dampers2014In: ACTUATOR14, Bremen: MESSE BREMEN , 2014Conference paper (Refereed)
    Abstract [en]

    A contact system driven by a high energetic Thomson actuator requires to be decelerated from full speed down to zero. The forces originated from the interaction between a stationary copper tube and a moving array of magnets combined with plastic separators or ferromagnetic material are used to generate eddy-current damping. Five different configurations of small but strong neodymium magnets and spacers were benchmarked for simple free-fall damping. A comparison between experimental results and simulations (using COMSOL) shows that the most effective damping is reached by two consecutive permanent magnets with opposite magnetization directions, separated by low-carbon content steel concentrators. The proposed damper design is the result of the balance between various parameters such as magnet orientation topology in the array, spacer material and its dimensions, copper tube thickness and the air gap between copper tube and array. Furthermore, the design was scaled up and an actuator-drive system was added to perform more realistic tests, which demonstrated the damping effectiveness on a fast moving armature actuated by a Thomson coil energized by a capacitor bank. The results of these tests validated the numerical model with a good degree of accuracy.

  • 162.
    Chen, Chen
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Simulation, design and experimental validation of a passive magnetic damper for ultra-fast actuators2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    A contact system driven by a high energetic Thomson actuator requires to be decelerated from

    full speed down to zero. The forces originated from the interaction between a stationary

    copper tube and a moving array of magnets combined with plastic or ferromagnetic material

    are used to generate eddy-current damping. Five different configurations of small but strong

    (N52) neodymium magnets and spacers were benchmarked for simple free-fall damping. A

    comparison between experimental results and simulations (using COMSOL) has shown that

    the most effective damping is reached by two consecutive permanent magnets with opposite

    magnetization directions ,separated by low-carbon content steel concentrators(SN - Fe

    concentrator- NS).

    The proposed damper design is the result of the balance between various parameters such as

    magnet orientation topology in the array, spacer material and its dimensions, copper tube

    thickness and the air gap between copper tube and array.

    Furthermore, the design was scaled up and an actuator-drive system was added to perform

    more realistic tests, which demonstrated the damping effectiveness on a fast moving armature

    actuated by a Thomson coil energized by a capacitor bank. All models in the simulation

    predicted the damping effect in advance. Investigations were conducted with two cases: (1) A

    solid copper rod was supposed to pass through the magnet array; (2) A plastic shaft was

    applied to support the magnet array.

    Finally a damping prototype with a plastic shaft was built for completing damping tests. The

    results of these tests validated the numerical model with a high degree of accuracy.

  • 163. Chen, D.
    et al.
    Fu, H.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Novel microwave photonic filter based on a mode-locked fiber laser2007In: Laser Physics Letters, ISSN 1612-2011, Vol. 4, no 8, p. 597-600Article in journal (Refereed)
  • 164. Chen, D. R.
    et al.
    Liu, W. S.
    Jiang, M.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    High-Resolution Strain/Temperature Sensing System Based on a High-Finesse Fiber Cavity and Time-Domain Wavelength Demodulation2009In: Journal of Lightwave Technology, ISSN 0733-8724, E-ISSN 1558-2213, Vol. 27, no 13, p. 2477-2481Article in journal (Refereed)
    Abstract [en]

    A high-resolution strain/temperature sensing system based on a fiber Bragg grating-Fabry-Perot cavity (FBG-FPC) and a wavelength-swept single-longitudinal-mode laser diode (modulated by a sawtooth signal) is proposed. The high-finesse (similar to 627) FBG-FPC formed by two uniform FBGs of high reflectivity (similar to 99.5%) is used both as a strain/temperature sensor and a FPC with ultranarrow (similar to 0.12 pm) transmission bands. Using a photodetector to detect the transmissive light of the laser diode through the FBG-FPC, wavelength demodulation is achieved by mapping wavelength measurement to time measurement. Both strain sensing and temperature sensing with a resolution of 0.11 mu epsilon and 0.014 degrees C, respectively, have been demonstrated.

  • 165. Chen, Daru
    et al.
    Qin, Shan
    Gao, Ying
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Wavelength-spacing tunable multi-wavelength fiber lasers based on hybrid gain medium and Mach-Zehnder interferometer2007In: 2007 Pacific Rim Conference on Lasers and Electro-Optics, IEEE , 2007, p. 4391428-Conference paper (Refereed)
    Abstract [en]

    Wavelength-spacing continuously tunable multi-wavelength fiber lasers based on a Mach-Zehnder interferometer comb filter are achieved. Stable multi-wavelength lasing based on hybrid gains of Erbium-doped fiber amplification and fiber Raman amplification (semiconductor optical amplification) is demonstrated.

  • 166. Chen, Daru
    et al.
    Qin, Shan
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Channel-spacing-tunable multi-wavelength fiber ring laser with hybrid Raman and erbium-doped fiber gains2007In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 15, no 3, p. 930-935Article in journal (Refereed)
  • 167.
    Chen, Daru
    et al.
    KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Qin, Shan
    KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Yu, Zhangwei
    KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Tunable and injection-switchable erbium-doped fiber laser of line structure2007In: Microwave and optical technology letters (Print), ISSN 0895-2477, E-ISSN 1098-2760, Vol. 49, no 4, p. 765-768Article in journal (Refereed)
    Abstract [en]

    A tunable and injection-switchable erbium-doped fiber (EDF) laser is proposed based on a line structure formed by a fiber Sagnac loop reflector and an fiber Bragg grating (FBG). Wavelength switching is achieved by controlling the power of the tunable injection laser. The self-seeded wavelength corresponding to the Bragg wavelength of the FBG can be tuned by, for example, heating the FBG, and the injection wavelength can be tuned over a wide range of about 50 nm. The characteristics of the wavelength switching for different levels of the EDF pump power and different wavelengths of the injection laser are studied experimentally. The present fiber laser has the advantages of tunability, stability, low amplified spontaneous emission noise, and high injection efficiency when compared with a fiber ring laser. Rapid wavelength switching is expected and the transient switching response of the laser is also studied.

  • 168.
    Chen, Daru
    et al.
    KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Yu, Zhangwei
    KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Qin, S.
    KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP. KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Switchable dual-wavelength Raman erbium-doped fibre laser2006In: Electronics Letters, ISSN 0013-5194, E-ISSN 1350-911X, Vol. 42, no 4, p. 202-204Article in journal (Refereed)
    Abstract [en]

    A fibre Bragg grating feedback fibre laser with both Raman and erbium-doped fibre pumps is proposed. Dual-wavelength switching is achieved by controlling the power of the Raman pump. The characteristics of the dual-wavelength switching are studied experimentally, and the mechanism is explained physically.

  • 169.
    Chen, Feng
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Taylor, Nathaniel
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Balieu, Romain
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Kringos, Niki
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Dynamic application of the Inductive Power Transfer (IPT) systems in an electrified road: Dielectric power loss due to pavement materials2017In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 147, p. 9-16Article in journal (Refereed)
    Abstract [en]

    Inductive Power Transfer (IPT) technology is seen as a promising solution to be applied in an electrified road (eRoad) to charge Electric Vehicles (EVs) dynamically, i.e. while they are in motion. Focus in this study was placed on the dielectric loss effect of pavement surfacing materials on the inductive power transfer efficiency, induced after the integration of the technology into the physical road structure. A combined experimental and model prediction analysis was carried out to calculate this dielectric loss magnitude, based on which some preliminary conclusions as well as a prioritization of future focus needs were summarized in detail.

  • 170.
    Chen, Feng
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Taylor, Nathaniel
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Kringos, Nicole
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Dynamic application of the Inductive Power Transfer (IPT) systems in an electrified road: Dielectric power loss due to pavement materials2016In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526Article in journal (Other academic)
    Abstract [en]

    It is well-known that the high cost and limited performance of existing energy storage systems have significantly constrained the commercialization of the Electric Vehicle (EV) at large scale. In recent years, attention has been given not only to the improved energy storage systems but also to develop appropriate charging infrastructures that would allow the EVs to be powered in an easier way. Inductive Power Transfer (IPT) technology, also known as a near-field wireless power transfer technology, is capable of delivering electricity wirelessly with large power and high efficiency at a given gap distance. It is therefore seen as a promising solution to be applied in an electrified road (eRoad) to charge EVs dynamically, i.e. while they are moving. Various technical aspects of this contactless charging solution have been studied actively by system developers, such as the charging power, its efficiency, the optimum gap distance as well safety issues. Focus in this study is placed on the effect of pavement surfacing materials on the wireless power transfer efficiency, after the integration of the technology into the physical road structures. Specifically, a combined experimental and model prediction analysis has been carried out to investigate this potential energy loss in a quantitative way, based on which some preliminary conclusions as well as a prioritization of future focus needs are summarized in detail. This work provides thus an important beginning for understanding the pavement materials’ influence on the IPT systems that may be used for dynamic applications in an eRoad.

  • 171.
    Chen, Feng
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Taylor, Nathaniel
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Kringos, Nicole
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Electrification of Roads: Opportunities and Challenges2015In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 150, p. 109-119Article in journal (Refereed)
    Abstract [en]

    The Electrical Vehicle (EV) has become a potential solution for enhancing the sustainability of our road transportation, in view of the environmental impacts traditional vehicles have regarding emissions and use of fossil fuel dependence. However, the widespread use of EVs is still restrained by the energy storage technologies, and the electrification of road transportation is still in its early stages. This paper focuses on the technical aspects related to the ‘electrification of roads’ (called ‘eRoads’) infrastructure that aims to diminish the limitations for using EVs. A historical overview of the technology development towards the electrification of road transportation is presented, along with an overview of prospective technologies for implementing an eRoad charging infrastructure. Of these, the Inductive Power Transfer (IPT) technology is examined in further details. The main objective of this paper is to explore the potential knowledge gaps that need to be filled for a successful integration of IPT technology within actual road infrastructure. As such, this paper can be used as an overview of the current state-of-the-art of eRoad infrastructure and also as guidance towards future research directions in this domain.  

  • 172.
    Chen, Feng
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Taylor, Nathaniel
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Kringos, Nicole
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Birgisson, Björn
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    A study on dielectric response of bitumen in the low-frequency range2015In: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402, Vol. 16, p. 153-169Article in journal (Refereed)
    Abstract [en]

    From the current state of literature, the dielectric property of bitumen has not been understood extensively, nor its relation with other properties such as polarity and rheology. In this study, dielectric spectroscopy measurement in a low-frequency range (10−2–106 Hz) was performed on both pure bitumen in different grades and wax-modified bitumen (WMB). From the performed tests we found the following: (i) the dielectric response of base bitumen is strongly temperature and frequency dependent, which is also highly linked to the rheology of the system. (ii) No remarkable differences in the dielectric constant (Formula presented.) among different grades of bitumen from the same crude oil source can be seen. (iii) Regular changes of dielectric loss tangent (tan δ) among the different grades of bitumen can be observed, which can be a good indicator for the linkage between the dielectric and rheological responses. In addition, it can also be perceived that the dielectric spectroscopy may have the potential to become a new approach for the multi-scale characterisation of road infrastructure materials.

  • 173.
    Chen, Jiajia
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Lu, Xiang
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Analytical Formulas for Calculating the Blocking Probability of a Dynamic Star Network2005In: Chinese Optics Letters, ISSN 1671-7694, Vol. 3, no 10, p. 579-582Article in journal (Refereed)
    Abstract [en]

    For a dynamic routing and wavelength assignment (RWA) a star topology is shown to be more efficient in comparison with a ring topology. Analytical formulas for a dynamic RWA in a star network are presented and verified with virtual simulation.

  • 174.
    Chen, Jiajia
    et al.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Wosinska, Lena
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics. KTH, School of Information and Communication Technology (ICT), Centres, Kista Photonics Research Center, KPRC.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    A novel protection scheme for a hybrid WDM/TDM PON2007In: NETWORK ARCHITECTURES, MANAGEMENT, AND APPLICATIONS V, 2007, Vol. 6784, p. F7840-F7840Conference paper (Refereed)
    Abstract [en]

    This paper proposes a novel protection scheme based on the cyclic property of an array waveguide grating (AWG) and neighboring connection pattern between two adjacent optical network units (ONUs) for the hybrid WDM/TDM passive optical networks (PONs). Our scheme uses 50% fewer wavelengths while offering one order of magnitude better connection availability than the existing scheme.

  • 175.
    Chen, Jiajia
    et al.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Wosinska, Lena
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    High utilization of wavelengths and simple interconnection between users in a protection scheme for passive optical networks2008In: IEEE Photonics Technology Letters, ISSN 1041-1135, E-ISSN 1941-0174, Vol. 20, no 5-8, p. 389-391Article in journal (Refereed)
    Abstract [en]

    A novel protection architecture for passive optical networks (PONs) is presented and evaluated. It is based on the cyclic property of arrayed waveguide gratings (AWGs) and the interconnection between two adjacent optical network units. The proposed scheme is compatible with both wavelength-division-multiplexing (WDM) PONs and hybrid WDM/time-division-multiplexing PONs. It is compared with two existing schemes and shown to have several advantages: 1) 50% less wavelengths is needed; 2) the fiber interconnections are simplified; 3) the connection availability is improved by one order of magnitude.

  • 176. Chen, Li-li
    et al.
    Jiang, Li
    Wang, Ya-lun
    Qian, Jun
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Multilayered polyelectrolyte-coated gold nanorods as multifunctional optical contrast agents for cancer cell imaging2010In: Journal of Zhejiang University: Science B, ISSN 1673-1581, Vol. 11, no 6, p. 417-422Article in journal (Refereed)
    Abstract [en]

    We report the application of multilayered polyelectrolyte-coated gold nanorods (GNRs) as multifunctional optical contrast agents for cancer cell imaging. The surface modification of GNRs improves their chemical stability and facilitates them to be taken up by cancer cells through electrostatic interaction. The unique longitudinal surface plasmon resonance property of GNRs makes them suitable as both "scattering contrast agents" and "Raman contrast agents". In our experiments, the staining of GNRs in cells was further confirmed by dark field microscopy and Raman microscopy. Our experiment results indicated that GNRs have great potential as multifunctional "optical contrast agents" for future in vivo animal imaging.

  • 177. Chen, Rui-Pin
    et al.
    Chen, Zhaozhong
    Chew, Khian-Hooi
    Li, Pei-Gang
    Yu, Zhongliang
    Ding, Jianping
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Structured caustic vector vortex optical field: manipulating optical angular momentum flux and polarization rotation2015In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 5, article id 10628Article in journal (Refereed)
    Abstract [en]

    A caustic vector vortex optical field is experimentally generated and demonstrated by a caustic-based approach. The desired caustic with arbitrary acceleration trajectories, as well as the structured states of polarization (SoP) and vortex orders located in different positions in the field cross-section, is generated by imposing the corresponding spatial phase function in a vector vortex optical field. Our study reveals that different spin and orbital angular momentum flux distributions (including opposite directions) in different positions in the cross-section of a caustic vector vortex optical field can be dynamically managed during propagation by intentionally choosing the initial polarization and vortex topological charges, as a result of the modulation of the caustic phase. We find that the SoP in the field cross-section rotates during propagation due to the existence of the vortex. The unique structured feature of the caustic vector vortex optical field opens the possibility of multi-manipulation of optical angular momentum fluxes and SoP, leading to more complex manipulation of the optical field scenarios. Thus this approach further expands the functionality of an optical system.

  • 178. Chen, Rui-Pin
    et al.
    Chew, Khian-Hooi
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Dynamic Control of Collapse in a Vortex Airy Beam2013In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 3, p. 1406-Article in journal (Refereed)
    Abstract [en]

    Here we study systematically the self-focusing dynamics and collapse of vortex Airy optical beams in a Kerr medium. The collapse is suppressed compared to a non-vortex Airy beam in a Kerr medium due to the existence of vortex fields. The locations of collapse depend sensitively on the initial power, vortex order, and modulation parameters. The collapse may occur in a position where the initial field is nearly zero, while no collapse appears in the region where the initial field is mainly distributed. Compared with a non-vortex Airy beam, the collapse of a vortex Airy beam can occur at a position away from the area of the initial field distribution. Our study shows the possibility of controlling and manipulating the collapse, especially the precise position of collapse, by purposely choosing appropriate initial power, vortex order or modulation parameters of a vortex Airy beam.

  • 179. Chen, Rui-Pin
    et al.
    Chew, Khian-Hooi
    Zhou, Guoquan
    Dai, Chao-Qing
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. Zhejiang University, China.
    Vectorial effect of hybrid polarization states on the collapse dynamics of a structured optical field2016In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 24, no 24, p. 28143-28153Article in journal (Refereed)
    Abstract [en]

    The collapse dynamics of a structured optical field with a distribution of spatially-variant states of polarization (SoP) and a spiral phase in the field cross section is studied using the two-dimensional coupled nonlinear Schrodinger equations. The self-focusing of a structured optical field with an inhomogeneous SoP distribution can give rise to new phenomena of collapse dynamics that is completely different from a scalar field. The collapse patterns are closely related to the topological charges of the vortexas well as the polarization, the initial power, and the SoP distribution in the field cross section. A single on-axis collapse or multiple off-axis partial collapses may occur due to the self-focusing effects of linearly, elliptically and circularly polarized components located at different positions of the field cross-section. The polarization in the core of the collapsing beam is always linearly polarized. The structured collapsing beams, which are driven by the vortex, propagate along a spiral trajectory in a saturated medium.

  • 180. Chen, Tuo
    et al.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. Zhejiang University, Hangzhou, China.
    Frequency-tunable circular polarization beam splitter using a graphene-dielectric sub-wavelength film2014In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 22, no 16, p. 19748-19757Article in journal (Refereed)
    Abstract [en]

    Manipulating the circular polarization of light is of great importance in chemistry and biology, as chiral molecules exhibit different physiological properties when exposed to different circularly polarized waves. Here we suggest a graphene/dielectric-stacked structure, which has both the properties of an epsilon-near-zero material and the high Hall conductivity of graphene. The proposed sub-wavelength structure demonstrates efficient manipulation of circular polarization properties of light. In a quite broad frequency range and at a large oblique incidence angle, the present magnetically active structure is transparent for one circularly polarized wave, and opaque for another. Such an effect can be further tuned by changing the magnitude of the applied magnetic field and chemical potential of graphene.

  • 181. Chen, X. W.
    et al.
    Choy, W. C. H.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Efficient and rigorous modeling of light emission in planar multilayer organic light-emitting diodes2007In: Journal of Display Technology, ISSN 1551-319X, Vol. 3, no 2, p. 110-117Article in journal (Refereed)
    Abstract [en]

    In this paper, we propose a technique to enable efficient and rigorous modeling of light emission in planar organic light-emitting diodes (OLEDs) composed of an arbitrary number of layers with different permittivity (including metals of a complex permittivity). The effects of the change of exciton radiative decay rate are explicitly included in the simulation. The numerical implementation of the technique is comprehensively discussed through an illustrative example. By using the proposed method, a bottom emitting OLED with a thick glass substrate is rigorously analyzed. The calculated results show a good agreement with the experimental results. The proposed method is efficient and well suited for optimizing OLEDs with complicated device structures. As a demonstration, we optimize the two-unit tandem top-emitting OLEDs with three types of charge generating layer. The results and design guidelines are given and discussed in detail.

  • 182. Chen, X. W.
    et al.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Choy, W. C. H.
    Highly efficient and tunable fluorescence of a nanofluorophore in silica/metal dual shells with plasmonic resonance2008In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 103, no 2Article in journal (Refereed)
    Abstract [en]

    A dual-shell structure consisting of a silica buffer shell and a metallic outer shell is studied and designed for highly efficient and tunable fluorescence. The enhanced Purcell effect due to the plasmonic resonance and the dependence of the resonance on the structural parameters are analyzed and discussed through a classical electromagnetic approach. With the present dual-shell structure a fivefold enhancement of the fluorescence efficiency can be achieved for a nanofluorophore comprised of multiple tetramethylrhodamine isothiocyanate dye molecules, as compared to the nanofluorophore within a single silica shell. Furthermore, the peak wavelength of the fluorescence spectrum can be tuned easily (due to the variation of the surface plasmon resonance) by over 50 nm when the refractive index of the ambient material varies from 1.3 to 1.6.

  • 183. Chen, Xue-Wen
    et al.
    Choy, Wallace C. H.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Efficient optical modeling of spontaneous emission in a cylindrically layered nanostructure2007In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 15, no 16, p. 10356-10361Article in journal (Refereed)
  • 184.
    Chen, Xue-Wen
    et al.
    KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Choy, Wallace C. H.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Simulation of light emission from a semiconductor nanowire/nanotube2007In: 2007 IEEE LEOS ANNUAL MEETING CONFERENCE PROCEEDINGS, 2007, p. 411-412Conference paper (Refereed)
  • 185. Chen, Xue-Wen
    et al.
    Choy, Wallace C. H.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Chui, P. C.
    Highly efficient fluorescence of a fluorescing nanoparticle with a silver shell2007In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 15, no 11, p. 7083-7094Article in journal (Refereed)
  • 186. Chen, Xue-Wen
    et al.
    Choy, Wallace C. H.
    Liang, C. J.
    Wai, P. K. A.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Modifications of the exciton lifetime and internal quantum efficiency for organic light-emitting devices with a weak/strong microcavity2007In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 91, no 22Article in journal (Refereed)
  • 187. Chen, Z. -L
    et al.
    Kehn, M. N. M.
    Quevedo-Teruel, Oscar
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Artificial maxwell fisheye lens design and synthesis with using metasurface structure2015In: 2015 International Workshop on Electromagnetics: Applications and Student Innovation Competition, iWEM 2015, Institute of Electrical and Electronics Engineers Inc. , 2015Conference paper (Refereed)
    Abstract [en]

    In this paper, we use a periodic structure to produce a Maxwell's fisheye lens and investigate some important information such as power, efficiency, etc. At Chapter 1, we describe some introduction about the surface plasmon polariton (SPP), frequency selective surface (FSS), concentration power by using lens. At Chapter 2, we describe some theorem about we need to use like Transmission line modal, high impedance surface, periodic structure lens. At Chapter 3, we describe our design and we show some simulation results about the surface wave Maxwell's fisheye lens. At chapter 4, we discuss our results about the fisheye lens. At chapter 5, we will draw the conclusions. © 2015 IEEE.

  • 188. Chen, Zhe-Feng
    et al.
    Xu, Bo
    Hu, Jun
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. Zhejiang University, Chaina.
    A CPW-fed broadband circularly polarized wide slot antenna with modified shape of slot and modified feeding structure2016In: Microwave and optical technology letters (Print), ISSN 0895-2477, E-ISSN 1098-2760, Vol. 58, no 6, p. 1453-1457Article in journal (Refereed)
    Abstract [en]

    A low-profile, compact, concisely designed CPW-fed broadband circularly polarized wide slot antenna is proposed. By protruding the ground into the wide slot, the distribution of equivalent magnetic currents inside the slot is changed. Together with appropriate adjustment of the feeding structure, broad impedance bandwidth and broad axial ratio bandwidth (ARBW) can be achieved simultaneously. General design steps are given so that the antenna can be easily transplanted to other bands. The measured results show that the 3 dB ARBW is 1.85-3.15 GHz (52%) and the impedance bandwidth is 1.35-4.12 GHz (101.3%). Detailed design procedures and key parameters analysis are also given for further understanding of the antenna design. 

  • 189. Cheng, F.
    et al.
    Lin, XianQi
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Liu, X. X.
    Song, K. J.
    Fan, Y.
    A compact dual-band bandpass SIW filter2013In: Journal Electromagnetic Waves and Applications, ISSN 0920-5071, E-ISSN 1569-3937, Vol. 27, no 3, p. 338-344Article in journal (Refereed)
    Abstract [en]

    A novel method for the design of substrate integrated waveguide (SIW) dual-band bandpass filter is presented in this paper. Dual-band response is achieved by TE101 mode and diagonal TE201 (TE102) mode. The resonant frequency of TE101 mode can be adjusted by the location of perturbation vias while the resonant frequency of diagonal TE201 (TE102) mode keeps unchanged. A design example with second-order filter response is given and verified by experiments. The vertically stacked SIW resonators are used here to save the size.

  • 190. Cheng, Hao
    et al.
    Qin, Wei
    Zhu, Zhenfeng
    Qian, Jun
    Qin, Anjun
    Tang, Ben Zhong
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Nanoparticles with aggregation-induced emission for monitoring long time cell membrane interactions2013In: Progress In Electromagnetics Research, ISSN 1070-4698, E-ISSN 1559-8985, Vol. 140, p. 313-325Article in journal (Refereed)
    Abstract [en]

    We perform the long time monitoring of nanoparticle-cell membrane interaction with high spatial and temporal resolution. The 2, 3-bis(4-(pheny1(4-(1, 2, 2-triphenylvinyl) phenyl)amino)phenyl) fumaronitrile (TPE-TPA-FN) is doped in organically modified silica (ORMOSIL) to be a biocompatible nanoprobe, which displays an aggregation-induced emission (ATE) effect. Photobleaching resistance of this synthesized nanoparticle is tested and compared with its similar counterpart, which proves its superiority and capability of long term fluorescence emission. We utilize the objective-based total internal reflection microscopy combined with the living cell incubation platform to investigate the cell uptake process of this nanoparticle in real time.

  • 191.
    Cheng, Jialu
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Broadband Dieletric Properties of Impregnated Transformer Paper Insulation at Various Moisture Contents2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The actual life of a transformer is determined by ageing of the cellulosic insulation such as transformer paper. The presence of moisture in the insulation system decreases the electrical strength of paper and accelerates the aging. It is an efficient way to monitor the moisture content in paper insulation by measuring the dielectric constant of the paper. The moisture dependent permittivity of impregnated transformer paper below 1 MHz has been widely investigated. High frequency (> 1 MHz) dielectric spectroscopy is under requirement since the loss peak information is missing. The impregnated paper is kept in desiccators with saturated salt solutions to get the samples with moisture content from 1 % to 5.5 %. Then they are placed in a coaxial line and the scattering parameters are obtained by modern Vector Network Analyzer. Full wave analysis is utilized to calculate the permittivity from the obtained S-parameters due to its high accuracy. The magnitude of the dielectric spectroscopy below 100 Hz is very dependent on the moisture content while there is a horizontal shift of curves towards higher frequencies depending on the water content over a wide frequency range. The loss peaks appear between 1 MHz and 1 GHz for the impregnated paper with moisture level less than 5.5 %. Due to the limited system accuracy, there is a blank frequency band from 1 MHz to 100 MHz.

  • 192.
    Colmenares, Juan
    et al.
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Sadik, Diane-Perle
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Hilber, Patrik
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Reliability Analysis of a High-Efficiency SiC Three-Phase Inverter2016In: IEEE Journal of Emerging and Selected Topics in Power Electronics, ISSN 2168-6777, E-ISSN 2168-6785, Vol. 4, no 3, p. 996-1006Article in journal (Refereed)
    Abstract [en]

    Silicon carbide as an emerging technology offers potential benefits compared with the currently used silicon. One of these advantages is higher efficiency. If this is targeted, reducing the on-state losses is a possibility to achieve it. Parallel-connecting devices decrease the on-state resistance and therefore reduce the losses. Furthermore, increasing the amount of components such as parallel connection of devices introduces an undesired tradeoff between efficiency and reliability, since an increased component count increases the probability of failure. A reliability analysis has been performed on a three-phase inverter rated at 312 kVA, using parallel-connected power modules. This analysis shows that the gate voltage stress has a high impact on the reliability of the complete system. Decreasing the positive gate-source voltage could, therefore, increase the reliability of the system approximately three times without affecting the efficiency significantly. Moreover, adding redundancy in the system could also increase the mean time to failure by approximately five times.

  • 193.
    Colmenares, Juan
    et al.
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Sadik, Diane-Perle
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Hilber, Patrik
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Reliability analysis of a high-efficiency SiC three-phase inverter for motor drive applications2016In: 2016 IEEE Applied Power Electronics Conference and Exposition (APEC), Institute of Electrical and Electronics Engineers (IEEE), 2016, p. 746-753, article id 7467955Conference paper (Refereed)
    Abstract [en]

    Silicon Carbide as an emerging technology offers potential benefits compared to the currently used Silicon. One of these advantages is higher efficiency. If this is targeted, reducing the on-state losses is a possibility to achieve it. Parallel-connecting devices decrease the on-state resistance and therefore reducing the losses. Furthermore, increasing the amount of components introduces an undesired tradeoff between efficiency and reliability. A reliability analysis has been performed on a three-phase inverter for motor drive applications rated at 312 kVA. This analysis has shown that the gate voltage stress determines the reliability of the complete system. Nevertheless, decreasing the positive gate-source voltage could increase the reliability of the system approximately 8 times without affecting the efficiency significantly. Moreover, adding redundancy in the system could also increase the mean time to failure approximately 5 times.

  • 194. Colombi, Davide
    et al.
    Thors, Björn
    Jonsson, B. Lars G.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Efficient Whole-Body SAR Assessments by Means of Surface Scan Measurements2014In: IEEE transactions on electromagnetic compatibility (Print), ISSN 0018-9375, E-ISSN 1558-187X, Vol. 56, no 3, p. 539-548Article in journal (Refereed)
    Abstract [en]

    In this study, an experimental method has been investigated for efficient assessments of whole-body specific absorption rates (SAR) from radio base station antennas. Using surface amplitude measurements of the electric field components together with an integral equation technique, a method is obtained which is not biased to specific antenna designs or phantom shapes. For realistic material parameters, it has been found that only the amplitude of the tangential field components over the phantom boundary is needed to accurately assess whole-body SAR, which makes the proposed method well suited for integration with commercially available SAR measurement systems. The method has been validated with simulations and measurements. Compared with a volumetric scan, and for the cases investigated, the measurement time was reduced with a factor larger than 3 while keeping the relative error smaller than 8%.

  • 195.
    Colombi, Davide
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Thors, Björn
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Jonsson, B. Lars G.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Experimental whole-body SAR assessments by means of surface scan with no phase information2011In: 33rd Annual Meeting of the Bioelectromagnetics Society, 2011Conference paper (Refereed)
  • 196.
    Condez-Godziemba, Cyril
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Transmission System Operational Risk Assessment and Mitigation2012Independent thesis Basic level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    As transmission networks are getting older and as their components are reaching their life span’s end, the number of maintenance outages for equipments reparation or replacement is destined to gradually increase in the coming years. These outages weaken system’s security and lead to highstress situations that often do not comply with N-k operation rules. Thus in-depth risk analysis have to be performed in those cases, to ensure system’s smooth operation and optimal maintenance planning. It requires a comprehensive knowledge of contingencies consequences on system and society, but also refined contingencies occurrence probability estimations. This integration of probabilistic issues in operational problematic is challenging as current doctrines are profoundly deterministic, however the methodology developed here aims to comply with those while preparing the ground for future risk-based doctrines. Finally, integration of curative and preventive risk mitigation means gives more visibility to contingency probability reduction means and measures their economic efficiency, which leads to more optimal decision-making than the only use of classic consequences reduction techniques. This easily implementable method makes accessible new information to operators, allowing them to limit the use of systematic conservative and costly risk mitigation strategies.

  • 197. Cooray, Vernon
    et al.
    Cooray, Gerald
    Becerra, Marley
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    On the streamer discharges emitted from the head of a person located in the vicinity of lightning strikes and their possible consequences2013In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 71, no 3, p. 572-576Article in journal (Refereed)
    Abstract [en]

    In this paper the currents associated with the streamer discharges generated from the head of a person located in the vicinity of a lightning strike are investigated. In the analysis the location of the person with respect to the lightning strike is selected in such a way that only a streamer burst, without the formation of a connecting leader, is emitted from the head. The current associated with these streamer bursts could exceed several hundreds of mA and may last for several hundreds of microseconds. The results of the calculation show that the passage of the streamer currents through the body of the person could create electric fields in the brain large enough to excite neurons. Depending on the strength of lightning flash and the distance to the strike point these streamer bursts can give rise to phosphenes which are a form of visual experience that occurs when the visual cortex is stimulated by electric currents.

  • 198. Corea-Araujo, Javier A.
    et al.
    Martinez-Velasco, Juan A.
    Magnusson, Jesper
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Optimum design of hybrid HVDC circuit breakers using a parallel genetic algorithm and a MATLAB-EMTP environment2017In: IET Generation, Transmission & Distribution, ISSN 1751-8687, E-ISSN 1751-8695, Vol. 11, no 12, p. 2974-2982Article in journal (Refereed)
    Abstract [en]

    The optimum design of power system components is becoming a relevant topic in power system studies. Genetic algorithms (GAs) are considered as a proper approach for optimisation problems in which non-linear elements are involved. Several trends are presently leading GAs to a new level; for instance, its combination with parallel computing can facilitate the solution of problems where individual evaluations of the fitness function require an important computational effort. This study presents a procedure based on a MATLAB-EMTP application and the usage of a multicore environment for the optimum selection of hybrid high-voltage DC (HVDC) circuit breaker parameters; the goal is to obtain a transient response of the hybrid design with voltages, currents and fault clearance times within specified limits.

  • 199.
    Court, Alexandre
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    OCPP Compatibility between a Central System and Electric Vehicle Charging Stations2015Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Nowadays, the growing CO2 emissions is one of the main international

    issues. The world is becoming aware that the current climate issues start

    being critic and that something has to be done. In parallel, Earth starts

    running out of fossil fuels so alternative energies and alternative ways of

    producing energy have to be found. Driving electric vehicles would reduce

    the CO2 emissions and the use of fossil fuels. Of course, it would not make

    it possible to solve all the current issues but it could be part of a global

    solution.

    Over the past few years, the production of electric vehicle has grown

    faster and faster and consequently so did the production of electric vehicle

    charging stations. International and European standards have been set for

    electric vehicles and electrical vehicle charging stations. Besides, the

    growing number of charging stations entails a need of supervision.

    Supervision makes it possible for instance to control the charging stations

    remotely or to manage the transaction and the energy transmissions.

    Given the large number of charging station constructors and supervision

    system suppliers, the need of a common communication protocol was

    imperative. The Open Charge Alliance (OCA) has developed a standard

    communication protocol named Open Charge Point Protocol (OCPP). This

    protocol is still in development but it enables the different actors to have a

    common communication protocol and so to possibly interconnect their

    systems.

    Given OCPP is still under construction, the communication between a

    charging station and a supervision system is not trivial and some

    adjustments usually have to be made. The aim of this Thesis is to work on

    the compatibility between a supervision system and several charging

    stations from different constructors.

  • 200.
    Couturier, Nicolas
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Transient Stability During Asymmetrical Faults2015Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This research project has been conducted at RTE in order to study the transient stability after

    asymmetrical faults. When three-phase short-circuits occur in a network, almost all the electrical

    power is lost on the relevant line(s). Among all short-circuit types, it is the most drastic event and the

    issue has to be solved very quickly. But oddly, it is also the easiest problem to solve mathematically

    speaking. This comes from the fact that the system stays balanced, and equations can be simplified.

    However with line-to-ground faults this is no longer the case, and transient stability analysis becomes

    tricky.

    Until now, unbalanced situations have not been studied much. Since this kind of trouble is less

    serious than losing all three phases, every protection devices on the network have been sized to

    counter three-phase faults in time and avoid severe consequences. They will then also work for onephase

    problems.

    Despite this, there is a desire from RTE to understand

    – physically and mathematically – what

    happens when one-phase faults occur, and it is the mission behind this master thesis. First, a

    mathematical theoretical model was derived to examine a

    network’s stability without running any

    simulation. Then, once simulation software programs were taken in hand, several tests were run on a

    very simplified network, and compared with the theory developed previously. Finally, these

    experiments were carried out on a much larger scale.

    It is important to understand that, except for the theoretical model, all the results and conclusions in

    this document come from simulations. Even if a lot of tests and models led to them, these

    conclusions must be handled with care. The goal of this work was also to have a better

    understanding of unbalanced systems, of the Fortescue representation and thus, understand more

    clearly the parameters required by simulation tools like Eurostag© for future studies.

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