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  • 201. Alfier, A.
    et al.
    Pasqualotto, R.
    Spizzo, G.
    Canton, A.
    Fassina, A.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Electron temperature profiles in RFX-mod2008In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 50, no 3, p. 035013-Article in journal (Refereed)
    Abstract [en]

    Electron temperature profiles have been measured by the main Thomson scattering ( TS) diagnostic on the RFX-mod reversed field pinch experiment in Padova, Italy. The increased accuracy and spatial and temporal resolution permits one to measure in detail the improvements in T-e profiles, obtained with the active saddle coil system, which allows one to obtain core temperature 30% higher and scaling stronger with plasma current, steeper gradients in the core (+30%) and at the edge (+60%). 1D power balance calculations show that the active control of MHD modes largely reduces the values of electron heat diffusivity along the whole plasma radius, with similar to 50% reduction at the edge and similar to 30% in the core. The resulting electron energy confinement time is doubled. Further improvements occur during quasi-single helicity (QSH) states: the new TS allows one to study in detail the hot island that develops in the core. A characterization of the island electron thermal profile is presented, in terms of width, temperature increase, gradients and asymmetry; the effect on density profile is also discussed. A 2D transport code has been applied to calculate the heat diffusivity inside the magnetic island corresponding to the QSH state, also considering the correlation between temperature increase and pressure gradient with the chaos level around the island. Finally, electron energy confinement time during QSH states is compared with that in MH states.

  • 202.
    Alfonsetti, Elisabetta
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Privacy preserving car-parking: adistributed approach2012Student paper other, 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    There has been a substantial interest recently in privacy preserving problems in various application domains, including data publishing, data mining, classication, secret voting, private querying of database, playing mental poker, and many others. The main constraint is that entities involved in the system are unwilling to reveal the data they hold or make them public. However, they may want to collaborate and nd the solution of a bigger computational problem without revealing the privately held data. There are several approaches for addressing such issues, including cryptographic methods, transformation methods, and parallel and distributed computation techniques. In this thesis, these three methods are highlighted and a greater emphasis is placed on the last one. In particular, we discuss the theoretical backgrounds of optimization decomposition techniques. We further point out key literature associated with the privacy preserving problems and provide basic classications of their treatments. We focus to a particular interesting application, namely the car parking problem, or parking slot assignment problem. To solve the problem in a privacy preserving manner, a new parallel and distributed computation method is proposed. The goal is to allocate the parking slots to the cars, but without revealing anyone else the intended destinations. We apply decomposition techniques together with projected subgradient method to address this problem and the result is a decentralized privacy preserving car parking algorithm. We compare our algorithm with three other methods and numerically evaluate the performance of the proposed algorithm, in terms of optimality and as well as the computational speed. Despite the reduced computational complexity of the proposed algorithm, it provides close-to-optimal performance.

  • 203.
    Alfonsetti, Elisabetta
    et al.
    KTH, School of Electrical Engineering (EES).
    Weeraddana, P. C.
    Fischione, Carlo
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Min-max fair car-parking slot assignment2015In: Proceedings of the WoWMoM 2015: A World of Wireless Mobile and Multimedia Networks, IEEE conference proceedings, 2015Conference paper (Refereed)
    Abstract [en]

    Empirical studies show that cruising for car parking accounts for a non-negligible amount of the daily traffic, especially in central areas of large cities. Therefore, mechanisms for minimizing traffic from cruising directly affect the dynamics of traffic congestions. One way to minimizing cruising traffic is efficient car-parking-slot assignment. Usually, the related design problems are combinatorial and the worst-case complexity of optimal methods grows exponentially with the problem sizes. As a result, almost all existing methods for parking slot assignment are simple and greedy approaches, where each car or the user is assigned a free parking slot, which is closer to its destination. Moreover, no emphasis is placed to optimize any form of fairness among the users as the a social benefit. In this paper, the fairness as a metric for modeling the aggregate social benefit of the users is considered. An algorithm based on Lagrange duality is developed for car-parking-slot assignment. Numerical results illustrate the performance of the proposed algorithm compared to the optimal assignment and a greedy method.

  • 204. Alfsen, K. H.
    et al.
    Bonifazi, C.
    Pedersen, A.
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Electric field and plasma observations near the magnetopause and bow shock during a rapid compression.1984In: Achievements of the International Magnetospheric Study (IMS), p. 99-104Article in journal (Refereed)
    Abstract [en]

    A fast compressional motion of the magnetopause resulting from the interaction of an interplanetary shock and the Earth's magnetosphere is discussed. The ISEE-1 and 2 satellites were in the frontside magnetosphere before the shock. A magnetosonic wave front, the magnetopause, and the bow shock passed them in a very short time. By a combination of electric and magnetic field data it is possible to determine the magnetosonic and the magnetopause velocity. -from STAR, 23(14), 1985

  • 205. ALFSEN, KH
    et al.
    BONIFAZI, C
    PEDERSEN, A
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    INTERACTION BETWEEN AN INTERPLANETARY SHOCK AND THE EARTHS MAGNETOSPHERE ON AUGUST 27, 1978 - ISEE-1 ELECTRIC-FIELD AND ISEE-2 PLASMA OBSERVATIONS1984In: JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol. 89, no NA10, p. 8863-8871Article in journal (Refereed)
  • 206. ALFVEN, H
    et al.
    AXNAS, I
    BRENNING, N
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    VOYAGER SATURNIAN RING MEASUREMENTS AND THE EARLY HISTORY OF THE SOLAR-SYSTEM1986In: PLANETARY AND SPACE SCIENCE, ISSN 0032-0633, Vol. 34, no 2, p. 145-154Article in journal (Refereed)
  • 207.
    Al-Ghazu, Nader
    KTH, School of Electrical Engineering (EES), Signal Processing.
    A Study of the Next WLAN Standard IEEE 802.11ac Physical Layer2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This thesis studies the Physical Layer (PHY) of the new IEEE 802.11acWireless Local Access Network (WLAN) standard. The 11ac is built basedon the 11n successful standard. The standard is expected to be completedby the end of 2013. And it promises a Very High Throughput (VHT),and robust communication. In order to achieve that, the 11ac uses morebandwidth, it employs higher numbers of Multiple-Input Multiple-Output(MIMO) spatial streams, and higher orders of modulations. The 11ac PHYframe structure is studied in details. The transmitter and receiver blocks areexplained and implemented by MATLAB. Bit Error Rate (BER) and ErrorVector Magnitude (EVM) simulations of the PHY were run. The effectof different Modulation and Coding Scheme (MCS), and bandwidths werestudied. The performance of MIMO and Space-Time Block Coding (STBC)was investigated. The simulation results shows how the 11ac benefits fromthe new employed features. The created MATLAB simulation program canbe used for further tests and research.

  • 208.
    Alhaj Moussa, Obada
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Li, Minyue
    Kleijn, W. Bastiaan
    KTH, School of Electrical Engineering (EES), Communication Theory. Victoria University of Wellington, New Zealand .
    PITCH ENHANCEMENT MOTIVATED BY RATE-DISTORTION THEORY2014Conference paper (Refereed)
    Abstract [en]

    A pitch enhancement filter is designed with the objective to approach the optimal rate-distortion trade-off. The filter shows significant perceptual benefits, restating that information-theoretical and perceptual criteria are usually consistent. The filter is easy to implement and can be used as a complement to existing audio codecs. Our experiments show that it can improve the reconstruction quality of the AMR-WB standard.

  • 209.
    Alhaj Moussa, Obada
    et al.
    KTH, School of Electrical Engineering (EES), Sound and Image Processing.
    Li, Minyue
    KTH, School of Electrical Engineering (EES), Sound and Image Processing.
    Kleijn, W. Bastiaan
    KTH, School of Electrical Engineering (EES), Sound and Image Processing.
    Predictive Audio Coding Using Rate-Distortion-Optimal Pre-and-Post-Filtering2011In: Applications of Signal Processing to Audio and Acoustics (WASPAA), 2011 IEEE Workshop on, IEEE conference proceedings, 2011, p. 213-216Conference paper (Refereed)
    Abstract [en]

    A natural approach to audio coding is to use a rate-distortion optimal design combined with a perceptual model. While this approach is common in transform coding, existing predictive-coding based audio coders are generally not optimal and they benefit from heuristically motivated post-filtering. As delay requirements often force the use of predictive coding, we consider audio coding with a pre- and post-filtered predictive structure that was recently proven to be asymptotically optimal in the rate-distortion sense [1]. We show that this audio coding is efficient in achieving the state-of-the-art performance. We also show that the pre-filter plays a relatively minor role. This leads to an analytic approach for optimizing the post-filter and the predictor at each rate, eliminating the need for manual re-tuning whenever a different rate is called for. In a subjective test, the theoretically optimized post-filter provided a better performance than a conventional post-filter.

  • 210. Al-Hammouri, A.T.
    et al.
    Nordström, Lars
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Chenine, Moustafa
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Honeth, Nicholas
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Leelaruji, Rujiroj
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Virtualization of synchronized phasor measurement units within real-time simulators for smart grid applications2012In: Power and Energy Society General Meeting, 2012 IEEE, IEEE , 2012, p. 6344949-Conference paper (Refereed)
    Abstract [en]

    Synchronized phasor measurement units (PMUs) provide GPS-time tagged high-sampling rate positive-sequence voltage and current phasors. When placed in high-voltage substations in power networks, PMUs can provide real-time information that is necessary for the development of Smart Transmission Grid software applications for improving power system monitoring, control and protection. The development of these applications, particularly for use within control centers for on-line purposes, is limited by the availability of and access to real-time PMU data and other information. One attractive approach for application development is the use of real-time simulators to which PMUs can be interfaced as hardware-in-the-loop (HIL) devices to harvest PMU data. However, this approach has technical and economical limitations, which can be tackled by the virtualization of PMU devices. This article describes the development of an entirely software-based synchronized phasor measurement unit for use within real-time simulators that will allow the emulation of a large number of real-life PMUs, which in turn can be used for creating new phasor-based applications.

  • 211. Ali Khan, N.
    et al.
    Ali, S.
    Jansson, Magnus
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Direction of arrival estimation using adaptive directional time-frequency distributions2018In: Multidimensional systems and signal processing, ISSN 0923-6082, E-ISSN 1573-0824, Vol. 29, no 2, p. 503-521Article in journal (Refereed)
    Abstract [en]

    Time-frequency distributions (TFDs) allow direction of arrival (DOA) estimation algorithms to be used in scenarios when the total number of sources are more than the number of sensors. The performance of such time-frequency (t-f) based DOA estimation algorithms depends on the resolution of the underlying TFD as a higher resolution TFD leads to better separation of sources in the t-f domain. This paper presents a novel DOA estimation algorithm that uses the adaptive directional t-f distribution (ADTFD) for the analysis of close signal components. The ADTFD optimizes the direction of kernel at each point in the t-f domain to obtain a clear t-f representation, which is then exploited for DOA estimation. Moreover, the proposed methodology can also be applied for DOA estimation of sparse signals. Experimental results indicate that the proposed DOA algorithm based on the ADTFD outperforms other fixed and adaptive kernel based DOA algorithms.

  • 212. Ali, Muhammad
    et al.
    Matevosyan, Julija
    Milanovic, J. V.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Effect of wake consideration on estimated costs of wind energy curtailments2009In: 8th International Workshop on Large Scale Integration of Wind Power into Power Systems as well as on Transmission Networks of Offshore Wind Farms, 14-15 Oct. 2009 Bremen, 2009Conference paper (Refereed)
    Abstract [en]

    Measures such as energy curtailment or gridreinforcement are required to integrate the upcoming windgeneration in parts of the power system with existing transmissionbottlenecks. In order to choose between these two measurespotential wind energy curtailments and its costs need to becarefully evaluated. The paper analyzes the effect of wakeconsideration on the overall energy curtailment cost. For thispurpose detailed wake model was used taking into account partialand multiple shading of wind turbines. It is shown that not onlywind speed but also wind direction of the incoming wind affects theamount of energy produced by a wind farm. A comparison ofcurtailment cost with cost for grid reinforcement in areas withlimited transmission capacity was carried out with and withoutconsideration of wake effect. The effect on curtailment cost due toavailability of wind turbines is also investigated both with andwithout wake effect consideration. The results have proven thatwith consideration of wake effect and availability potential windenergy curtailments are reduced and hence curtailment costs arelowered, making curtailment a cheaper option than gridreinforcement. The method illustrated in the paper can be used inpre-feasibility study to compare the costs of wind curtailment withthe costs of grid reinforcement in order to make sound economicdecision. The method can also be applied in wind farm energy yield estimation.

  • 213.
    Ali, Muhammad Taha
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Ghandari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Harnefors, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Mitigation of Sub-Synchronous Control Interaction in DFIGs using a Power Oscillation Damper2017In: 2017 IEEE Manchester PowerTech, Powertech 2017, Institute of Electrical and Electronics Engineers (IEEE), 2017, article id 7980941Conference paper (Refereed)
    Abstract [en]

    The aim of this research work is to analyse subsynchronous control interaction (SSCI) in doubly-fed induction generators (DFIGs) and to design a supplementary control technique for the mitigation of SSCI. A mathematical model of the DFIG is derived and linearized in order to perform an eigenvalue analysis. This analysis pinpoints the parameters of the system which are sensitive in making sub-synchronous modes unstable and hence are responsible for causing SSCI. A power oscillation damper (POD) is designed using a residue method to make the DFIG system immune to the SSCI. The POD control signal acts as a supplementary control, which is fed to the controller of the grid-side converter (GSC). The POD signal is applied to different summation junctions of the GSC controller in order to determine the best placement of the POD for effective mitigation of SSCI and for the increased damping of the system.

  • 214.
    Ali, Muhammad Taha
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Harnefors, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Effect of control parameters on infliction of sub-synchronous control interaction in DFIGs2016In: 2016 IEEE International Conference on Power and Renewable Energy (ICPRE), IEEE conference proceedings, 2016, p. 72-78, article id 7871175Conference paper (Refereed)
    Abstract [en]

    This research work deals with the analysis of sub-synchronous control interaction (SSCI) in doubly-fed induction generators (DFIGs). The time-invariant model of the DFIG is linearized to perform eigenvalue analysis and to obtain the participation factor of each state variable for unstable modes. The sensitivity of system eigenvalues related to sub-synchronous modes is analyzed with respect to all the proportional and integral parameters of the controllers in the rotor-side-converters and grid-side-converters. The major contribution of this research work is the outcomes based on eigenvalue analysis that clearly point out the control parameters to which sub-synchronous modes are highly sensitive. The effect of series compensation level on DFIG system and on the sensitivity of converter control parameters is also studied.

  • 215.
    Ali, Raja Hashim
    et al.
    KTH, School of Computer Science and Communication (CSC), Computational Science and Technology (CST).
    Bark, Mikael
    KTH, School of Information and Communication Technology (ICT).
    Miro, Jorge
    KTH, School of Information and Communication Technology (ICT).
    Muhammad, Sayyed Auwn
    KTH, School of Computer Science and Communication (CSC), Computational Science and Technology (CST).
    Sjöstrand, Joel
    Stockholm University.
    Zubair, Syed Muhammad
    KTH, School of Electrical Engineering (EES), Communication Networks. University of Balochistan, Pakistan.
    Abbas, Raja Manzar
    Arvestad, Lars
    KTH, School of Computer Science and Communication (CSC), Computational Science and Technology (CST).
    VMCMC: a graphical and statistical analysis tool for Markov chain Monte Carlo tracesManuscript (preprint) (Other academic)
    Abstract [en]

    Motivation: MCMC-based methods are important for Bayesian inference of phylogeny and related parameters. Although being computationally expensive, MCMC yields estimates of posterior distributions that are useful for estimating parameter values and are easy to use in subsequent analysis. There are, however, sometimes practical diculties with MCMC, relating to convergence assessment and determining burn-in, especially in large-scale analyses. Currently, multiple software are required to perform, e.g., convergence, mixing and interactive exploration of both continuous and tree parameters.

    Results: We have written a software called VMCMC to simplify post-processing of MCMC traces with, for example, automatic burn-in estimation. VMCMC can also be used both as a GUI-based application, supporting interactive exploration, and as a command-line tool suitable for automated pipelines.

    Availability: VMCMC is available for Java SE 6+ under the New BSD License. Executable jar les, tutorial manual and source code can be downloaded from https://bitbucket.org/rhali/visualmcmc/.

  • 216.
    Ali, Raja Hashim
    et al.
    KTH, School of Computer Science and Communication (CSC), Computational Science and Technology (CST). KTH, Centres, Science for Life Laboratory, SciLifeLab. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Bark, Mikael
    KTH, School of Information and Communication Technology (ICT).
    Miró, Jorge
    KTH, School of Information and Communication Technology (ICT).
    Muhammad, Sayyed Auwn
    KTH, School of Computer Science and Communication (CSC), Computational Science and Technology (CST). KTH, Centres, Science for Life Laboratory, SciLifeLab. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Sjöstrand, J.
    Zubair, Syed M.
    KTH, School of Electrical Engineering (EES), Communication Networks. University of Balochistan, Pakistan.
    Abbas, R. M.
    Arvestad, L.
    VMCMC: A graphical and statistical analysis tool for Markov chain Monte Carlo traces2017In: BMC Bioinformatics, ISSN 1471-2105, E-ISSN 1471-2105, Vol. 18, no 1, article id 97Article in journal (Refereed)
    Abstract [en]

    Background: MCMC-based methods are important for Bayesian inference of phylogeny and related parameters. Although being computationally expensive, MCMC yields estimates of posterior distributions that are useful for estimating parameter values and are easy to use in subsequent analysis. There are, however, sometimes practical difficulties with MCMC, relating to convergence assessment and determining burn-in, especially in large-scale analyses. Currently, multiple software are required to perform, e.g., convergence, mixing and interactive exploration of both continuous and tree parameters. Results: We have written a software called VMCMC to simplify post-processing of MCMC traces with, for example, automatic burn-in estimation. VMCMC can also be used both as a GUI-based application, supporting interactive exploration, and as a command-line tool suitable for automated pipelines. Conclusions: VMCMC is a free software available under the New BSD License. Executable jar files, tutorial manual and source code can be downloaded from https://bitbucket.org/rhali/visualmcmc/.

  • 217.
    Ali, Sadiq
    et al.
    Universitat Autònoma de Barcelona (UAB),.
    Jansson, Magnus
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Seco-Granados, Gonzalo
    Universitat Autònoma de Barcelona (UAB),.
    López-Salzedo, José A.
    Universitat Autònoma de Barcelona (UAB),.
    Novel collaborative spectrum sensing based on spatial covariance structure2013In: 2013 Proceedings of the 21st European Signal Processing Conference (EUSIPCO), 2013, p. 6811678-Conference paper (Refereed)
    Abstract [en]

    In collaborative spectrum sensing, spatial correlation in the measurements obtained by sensors can be exploited by adopting Generalized Likelihood Ratio Test (GLRT). In this process the GLRT provides a test statistics that is normally based on the sample covariance matrix of the received signal samples. Unfortunately, problems arise when the dimensions of this matrix become excessively large, as it happens in the so-called large-scale wireless sensor networks. In these circumstances, a huge amount of samples are needed in order to avoid the ill-conditioning of the GLRT, which degenerates when the dimensionality of data is equal to the sample size or larger. To circumvent this problem, we modify the traditional GLRT detector by decomposing the large spatial covariance matrix into small covariance matrices by using properties of the Kronecker Product. The proposed detection scheme is robust in the case of high dimensionality and small sample size. Numerical results are drawn, which show that the proposed detection schemes indeed outperform the traditional approaches when the dimension of data is larger than the sample size.

  • 218. Alinia, Bahram
    et al.
    Yousefi, Hamed
    Talebi Mazraeh Shahi, Mohammad Sadegh
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Khonsari, Ahmad
    Maximizing Quality of Aggregation in Delay-Constrained Wireless Sensor Networks2013In: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558, Vol. 17, no 11, p. 2084-2087Article in journal (Refereed)
    Abstract [en]

    In this letter, both the number of participating nodes and spatial dispersion are incorporated to establish a bi-objective optimization problem for maximizing the quality of aggregation under interference and delay constraints in tree-based wireless sensor networks (WSNs). The formulated problem is proved to be NP-hard with respect to Weighted-sum scalarization and a distributed heuristic aggregation scheduling algorithm, named SDMAX, is proposed. Simulation results show that SDMAX not only gives a close approximation of the Pareto-optimal solution, but also outperforms the best, to our knowledge, existing alternative proposed so far in the literature.

  • 219.
    Alizadeh, Mahmoud
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. Univ Gavle, Sweden.
    Amin, Shoaib
    KTH, School of Electrical Engineering (EES), Signal Processing. Univ Gavle, Sweden.
    Ronnow, Daniel
    Measurement and Analysis of Frequency-Domain Volterra Kernels of Nonlinear Dynamic 3 x 3 MIMO Systems2017In: IEEE Transactions on Instrumentation and Measurement, ISSN 0018-9456, E-ISSN 1557-9662, Vol. 66, no 7, p. 1893-1905Article in journal (Refereed)
    Abstract [en]

    Multiple-input multiple-output (MIMO) frequencydomain Volterra kernels of nonlinear order 3 are experimentally determined in bandwidth-limited frequency regions. How the effect of higher nonlinear orders can be reduced and how this affects the estimated errors are discussed. The magnitude and the phase of the kernels are Kramers-Kronig consistent. The self-kernels and cross-kernels have different symmetries, and the kernels are therefore determined and analyzed in different regions in the 3-D frequency space. By analyzing the properties along certain paths in the 3-D frequency space, the block structures for the respective kernels are determined. These block structures contain the significant blocks of the general block structures for the third-order kernels. The device under test is an MIMO transmitter for radio frequency signals.

  • 220.
    Alizadeh, Mahmoud
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Amin, Shoaib
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Rönnow, Daniel
    ATM, University of Gävle.
    Measurement and analysis of frequency-domainVolterra kernels of nonlinear dynamic 3x3 MIMO systems2016In: IEEE Transactions on Instrumentation and Measurement, ISSN 0018-9456, E-ISSN 1557-9662Article in journal (Refereed)
    Abstract [en]

    Multiple-input multiple-output (MIMO) frequency-domain Volterra kernels of nonlinear order 3 are experimentally determined in bandwidth-limited frequency regions. How the effect of higher nonlinear orders can be reduced and how this affects the estimated errors are discussed. The magnitude and phase of the kernels areKramers-Kronig consistent. The self- and cross-kernels have different symmetries and the kernels are therefore determined and analyzed in different regions in the 3D frequency space. By analyzing the properties along certain paths in the 3D frequency space, the block structures for the respective kernels are determined. These block structures contain the significant blocks of the general block structures for third-order kernels. The device under test is a MIMO transmitter for radio frequency signals.

  • 221.
    Alizadeh, Mahmoud
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Rönnow, Daniel
    A two-tone test for characterizing nonlinear dynamic effects of radio frequency amplifiers in different amplitude regions2016In: Measurement, ISSN 0263-2241, Vol. 89, p. 273-279Article in journal (Refereed)
    Abstract [en]

     A new two-tone test method for radio frequency power amplifiers is presented. The test signal is a two-tone probing-signal superimposed on large-signals of different amplitude. The amplifier is, thus, excited in different amplitude regions. The amplitude and phase of the 3rd order intermodulation (IM) products are measured vs. frequency spacing and probing-signal amplitude in each region. The IM magnitude is a measure of the nonlinearity, while the frequency dependence and asymmetry are measures of the memory effects in the different regions. A Doherty and a class-AB amplifier were tested. For both amplifiers the IM magnitude increased by ~15 dB from the lowest to the highest amplitude region. For the Doherty amplifier the behavior of the IM products vs. frequency spacing was similar in all regions, indicating similar memory effects. For the class-AB amplifier the IM vs. frequency spacing was significantly different in the different regions, which indicates different memory effects.

  • 222.
    Alizadeh, Razieh
    et al.
    ShahidBahonar Univ Kerman, Dept Elect Engn, Kerman, Iran..
    Saneei, Mohsen
    ShahidBahonar Univ Kerman, Dept Elect Engn, Kerman, Iran..
    Ebrahimi, Masoumeh
    KTH, School of Electrical Engineering (EES).
    Fault-Tolerant Circular Routing Algorithm for 3D-NoC2014In: 2014 INTERNATIONAL CONGRESS ON TECHNOLOGY, COMMUNICATION AND KNOWLEDGE (ICTCK), IEEE , 2014Conference paper (Refereed)
    Abstract [en]

    ExpandingNetworks-on-Chip (NoCs) to the third dimension (3D-NoC) has been known as a promising solution for the latency challenges of future many-core Systems-on-Chip. 3D-NoC may take advantages of TSVsfor vertical links which are shorter and faster than horizontal ones. Faults may occur in TSVs as well as the horizontal links though faults inTSVs are more costly. In this paper, we present a fault-tolerant routing algorithm targeting faults in both TSVs and horizontal links. The proposed routing algorithm is based on defining some circular routing paths which offers a deadlock-free routing for packets in mesh-based topologies. In addition to tolerating faults, these circular pathshelp in reducing congestion in the centralpart of the network at high injection rates. The proposed circular routing algorithm is able to tolerate all one-faulty links. In addition, it is shown that its performance is better than those of traditional methods.

  • 223. Alizai, Muhammad Hamad
    et al.
    Landsiedel, Olaf
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Wehrle, Klaus
    Exploiting the Burstiness of Intermediate-Quality Wireless Links2012In: International Journal of Distributed Sensor Networks, ISSN 1550-1329, p. 826702-Article in journal (Refereed)
    Abstract [en]

    We address the challenge of link estimation and routing over highly dynamic links, thats is, bursty links that rapidly shift between reliable and unreliable periods of transmissions. Based on significant empirical evidence of over 100,000 transmissions over each link in 802.15.4 and 802.11 testbeds, we propose two metrics, expected future transmissions (EFT) and MAC(3), for runtime estimation of bursty wireless links. We introduce a bursty link estimator (BLE) that based on these two metrics, accurately estimates bursty links in the network rendering them available for data transmissions. Finally, we present bursty routing extensions (BRE): an adaptive routing strategy that uses BLE for forwarding packets over bursty links if they offer better routing progress than long-term stable links. Our evaluation, comprising experimental data from widely used IEEE 802.15.4-based testbeds, reveals an average of 19% and a maximum of 42% reduction in the number of transmissions when routing over long-range bursty links typically ignored by routing protocols. Additionally, we show that both BLE and BRE are not tied to any specific routing protocol and integrate seamlessly with existing routing protocols and link estimators.

  • 224.
    Aljure, M.
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Becerra, M.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Pallon, L. K. H.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Electrical conduction currents of a mineral oil-based nanofluid in needle-plane configuration2016In: 2016 IEEE CONFERENCE ON ELECTRICAL INSULATION AND DIELECTRIC PHENOMENA (IEEE CEIDP), IEEE conference proceedings, 2016, p. 687-690Conference paper (Refereed)
    Abstract [en]

    We present experiments and simulations on the electrical conduction currents of purified transformer oil with and without surface-modified MgO nanoparticles. Results show that on the injection regime of the voltage-current characteristics, nanoparticles increase the charge production in the fluid. It is also found that the conduction currents in the space-charge-limited regime increased at a lower rate as a function of the voltage in the presence of nanoparticles. The numerical simulations suggest electron attachment is increased due to the nanoparticles, leading to larger accumulation of negative ionic space charge close to the needle in the space-charge-limited regime. It is concluded that electron attachment may be significantly increased with nanoparticles, becoming an important process of electrical conduction in nanofluids.

  • 225.
    Aljure, Mauricio
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Becerra, Marley
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. ABB Corporate Research, Sweden.
    Jonsson, B. Lars G.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Simulation of the electrical conduction of cyclohexane with TiO2 nanoparticles2014In: Proceedings of the 2014 IEEE 18th International Conference on Dielectric Liquids, ICDL 2014, IEEE , 2014, p. 6893119-Conference paper (Refereed)
    Abstract [en]

    Nanoparticles mixed with transformer oil can potentially increase the breakdown strength of the base liquid. Unfortunately, the basic physical mechanisms leading to such improvement are still not clear. This paper implements two existing theories to model the electrical conduction of cyclohexane with TiO2 nanoparticles in a needle to plane configuration. The generation and drift of carriers in the liquid are simulated by coupling the continuity equations for electrons, positive ions, negative ions, and nanoparticles with Poisson's equation for the electric field. The current-voltage characteristics are simulated and compared with the case of pure cyclohexane. The nanoparticles are modeled as either absorbers of electrons or as source of shallow traps in the fluid, according to the existing theories. The simulations show that the considered theories predict no significant effect of nanoparticles added to cyclohexane on the conduction current from a negative point electrode in steady state or under transient conditions.

  • 226. Allen, S. L.
    et al.
    Wampler, W. R.
    McLean, A. G.
    Whyte, D. G.
    West, W. P.
    Stangeby, P. C.
    Brooks, N. H.
    Rudakov, D. L.
    Phillips, V.
    Rubel, Marek J.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics. KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Matthews, G. F.
    Nagy, A.
    Ellis, R.
    Bozek, A. S.
    C-13 transport studies in L-mode divertor plasmas on DIII-D2005In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 337-39, no 03-jan, p. 30-34Article in journal (Refereed)
    Abstract [en]

    (CH4)-C-13 was injected with a toroidally-symmetric gas system into 22 identical lower-single-null L-mode discharges on DIII-D. The injection level was adjusted so that it did not significantly perturb the core or divertor plasmas, with a duration of similar to 3 s on each shot, for a total of similar to 300 T L of injected particles. The plasma shape remained very constant; the divertor strike points were controlled to similar to 1 cm at the divertor plate. At the beginning of the subsequent machine vent, 29 carbon tiles were removed for nuclear reaction analysis of C-13 content to determine regions of carbon deposition. It was found that only the tiles inboard of the inner strike point had appreciable 1 3 C above background. Visible spectroscopy measurements of the carbon injection and comparisons with modeling are consistent with carbon transport by means of scrape-off layer flow.

  • 227.
    Alli Idd, Pazi
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Channel estimation in mobile wireless systems2012Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The demands of multimedia services from mobile user equipment (UE) for achieving high data rate, high capacity and reliable communication in modern mobile wireless systems are continually ever-growing. As a consequence, several technologies, such as the Universal Mobile Telecommunications System (UMTS) and the 3rd Generation Partnership Project (3GPP), have been used to meet these challenges. However, due to the channel fading and the Doppler shifts caused by user mobility, a common problem in wireless systems, additional technologies are needed to combat multipath propagation fading and Doppler shifts. Time-variant channel estimation is one such crucial technique used to improve the performance of the modern wireless systems with Doppler spread and multipath spread.

    One of vital parts of the mobile wireless channel is channel estimation, which is a method used to significantly improve the performance of the system, especially for 4G and Long Term Evolution (LTE) systems. Channel estimation is done by estimating the time-varying channel frequency response for the OFDM symbols. Time-variant channel estimation using Discrete Prolate Spheroidal Sequences (DPSS) technique is a useful channel estimation technique in mobile wireless communication for accurately estimating transmitted information. The main advantage of DPSS or Slepian basis expansion is allowing more accurate representation of high mobility mobile wireless channels with low complexity. Systems such as the fourth generation cellular wireless standards (4G), which was recently introduced in Sweden and other countries together with the Long Term Evolution, can use channel estimation techniques for providing the high data rate in modern mobile wireless communication systems.

    The main goal of this thesis is to test the recently proposed method, time-variant channel estimation using Discrete Prolate Spheroidal Sequences (DPSS) to model the WINNER phase II channel model. The time-variant sub-carrier coefficients are expanded in terms of orthogonal DPS sequences, referred to as Slepian basis expansions. Both Slepian basis expansions and DPS sequences span the low-dimensional subspace of time-limited and band-limited sequences as Slepian showed. Testing is done by using just two system parameters, the maximum Doppler frequency Dmax v and K, the number of basis functions of length N = 256.

    The main focus of this thesis is to investigate the Power spectrum and channel gain caused by Doppler spread of the WINNER II channel model together with linear fitting of curves for both the Slepian and Fourier basis expansion models. In addition, it investigates the Mean Square Error (MSE) using the Least Squares (LS) method. The investigation was carried out by simulation in Matlab, which shows that the spectrum of the maximum velocity of the user in mobile wireless channel is upper bounded by the maximum normalized one-sided Doppler frequency. Matlab simulations support the values of the results. The value of maximum Doppler bandwidth vDmax  of the WINNER model is exactly the same value as DPS sequences. In addition to the Power spectrum of the WINNER model, the fitting of Slepian basis expansion performs better in the WINNER model than that of the Fourier basis expansion.

  • 228.
    Alm, Erik
    et al.
    KTH, School of Electrical Engineering (EES).
    Gren, Lilian
    KTH, School of Electrical Engineering (EES).
    Real-time Scheduling in Smart Buildings2016Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
  • 229. Alm, L.
    et al.
    Argall, M. R.
    Torbert, R. B.
    Farrugia, C. J.
    Burch, J. L.
    Ergun, R. E.
    Russell, C. T.
    Strangeway, R. J.
    Khotyaintsev, Y. V.
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Marklund, Göran
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Giles, B. L.
    Shuster, J.
    EDR signatures observed by MMS in the 16 October event presented in a 2-D parametric space2017In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, no 3, p. 3262-3276Article in journal (Refereed)
    Abstract [en]

    We present a method for mapping the position of satellites relative to the X line using the measured B-L and B-N components of the magnetic field and apply it to the Magnetospheric multiscale (MMS) encounter with the electron diffusion region (EDR) which occurred on 13:07 UT on 16 October 2015. Mapping the data to our parametric space succeeds in capturing many of the signatures associated with magnetic reconnection and the electron diffusion region. This offers a method for determining where in the reconnection region the satellites were located. In addition, parametric mapping can also be used to present data from numerical simulations. This facilitates comparing data from simulations with data from in situ observations as one can avoid the complicated process using boundary motion analysis to determine the geometry of the reconnection region. In parametric space we can identify the EDR based on the collocation of several reconnection signatures, such as electron nongyrotropy, electron demagnetization, parallel electric fields, and energy dissipation. The EDR extends 2-3km in the normal direction and in excess of 20km in the tangential direction. It is clear that the EDR occurs on the magnetospheric side of the topological X line, which is expected in asymmetric reconnection. Furthermore, we can observe a north-south asymmetry, where the EDR occurs north of the peak in out-of-plane current, which may be due to the small but finite guide field.

  • 230.
    Alm, Love
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Cluster investigations of the extent and altitude distribution of the auroral density cavity2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The auroral density cavity constitutes the boundary between the cold, dense ionospheric plasma and the hot, tenuous plasma sheet plasma. The auroral density cavity is characterized by low electron density and particle populations modified by parallel electric fields. Inside the cavity the electron densities can be as much as a factor 100-1000 lower than same altitude outside the cavity.The Cluster mission's wide range of instruments, long lifetime and ability to make multi-spacecraft observations has been very successful. Over its 15 year lifespan, the Cluster satellites have gathered data on auroral density cavities over a large altitude range and throughout an entire solar cycle, providing a vast data material.The extent of the density cavity and acceleration region is large compared to the typical altitude coverage of a satellite crossing the cavity. This makes it difficult to produce a comprehensive altitude/density profile from a single crossing. In order to facilitate comparisons between data from different events, we introduce a new reference frame, pseudo altitude. Pseudo altitude describes the satellites' position relative to the acceleration region, as opposed to relative to the Earth. This pseudo altitude is constructed by dividing the parallel potential drop below the satellite with the total parallel potential drop. A pseudo altitude of 0 corresponds to the bottom of the acceleration region and a pseudo altitude of 1 to the top of the acceleration region. As expected, the pseudo altitude increases with altitude. The electron density exhibits an anti-correlation with the pseudo altitude, the density becomes lower close to the upper edge of the acceleration region. The upper edge of the acceleration region is located between a geocentric altitude of 4.375 and 5.625 RE. Above the upper edge of the acceleration region, the electron density continues to decrease for the entire range of the study, 3.0-6.5 RE. This is much further than the geocentric altitude range of 2-3 RE which is suggested by previous models. We can conclude that the auroral density cavity is not confined by the auroral acceleration region, as suggested by previous models, and may extend all the way to the plasma sheet.

  • 231.
    Alm, Love
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Li, Bin
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Marklund, Göran
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Karlsson, Tomas
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Statistical altitude distribution of the auroral density cavity2015In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 120, no 2, p. 996-1006Article in journal (Refereed)
    Abstract [en]

    The statistical altitude distribution of auroral density cavities located between 3.0 and 6.5 R-E is investigated using in situ observations from flux tubes exhibiting auroral acceleration. The locations of the observations are described using a pseudo altitude derived from the distribution of the parallel potential drop above and below the satellite. The upper edge of the auroral acceleration region is observed between 4.375 and 5.625 R-E. Above 6.125 R-E, none of the events exhibit precipitating inverted V electrons, though the upward ion beam can be observed. This indicates that the satellites are located inside the same flux tube as, but above, the auroral acceleration region. The electron density decreases as we move higher into the acceleration region. The spacecraft potential continues to decrease once above the acceleration region, indicating that the density cavity extends above the acceleration region. From 3.0 to 4.375 R-E the pseudo altitude increases by 0.20 per R-E, consistent with a distributed parallel electric field. Between 4.375 and 5.625 R-E the pseudo altitude increases weakly, by 0.01 per R-E, due to an increasing number of events per altitude bin, which are occurring above the acceleration region. Above 5.625 R-E the pseudo altitude increases by 0.28 per R-E, due to a rapid increase in the number of events per altitude bin occurring above the acceleration region, indicating that the remaining parallel potential drop is concentrated in a narrow region at the upper edge of the acceleration region, rather than in a distributed parallel electric field.

  • 232.
    Alm, Love
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Marklund, Göran
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Karlsson, Tomas
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Electron density and parallel electric field distribution of the auroral density cavity2015In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 120, no 11, p. 9428-9441Article in journal (Refereed)
    Abstract [en]

    We present an event study in which Cluster satellites C1 and C3 encounters the flux tube of a stable auroral arc in the pre-midnight sector. C1 observes the mid cavity, while C3 enters the flux tube of the auroral arc at an altitude which is below the acceleration region, before crossing into the top half of the acceleration region. This allows us to study the boundary between the ionosphere and the density cavity, as well as large portion of the upper density cavity. The position of the two satellites, in relation to the acceleration region, is described using a pseudo altitude derived from the distribution of the parallel potential drop above and below the satellites.The electron density exhibits an anti-correlation with the pseudo altitude, indicating that the lowest electron densities are found near the top of the density cavity. Over the entire pseudo altitude range, the electron density distribution is similar to a planar sheath, formed out of a plasma sheet dominated electron distribution, in response to the parallel electric field of the acceleration region. This indicates that the parallel electric fields on the ionosphere-cavity boundary, as well as the mid cavity parallel electric fields, are part of one unified structure rather than two discrete entities.The results highlight the strong connection between the auroral density cavity and auroral acceleration as well as the necessity of studying them in a unified fashion.

  • 233.
    Alm, Love
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Marklund, Göran T.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Karlsson, Tomas
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    In situ observations of density cavities extending above the auroral acceleration region2014In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 119, no 7, p. 5286-5294Article in journal (Refereed)
    Abstract [en]

    The uppermost part of a stable potential structure in the auroral acceleration region was studied using simultaneous observations of Cluster satellites C1 and C3. Both satellites observe a monotonically decreasing electron density as they ascend through the auroral acceleration region. As C1 exits the top of the auroral acceleration region, the electron densities continue to decrease, and the minimum electron density is reached 14 km above the upper edge of the auroral acceleration region. The electron density does not return to noncavity values until the spacecraft exits the potential structure's flux tube. The data indicate that the auroral density cavity is not confined by the potential structure and may extend above the auroral acceleration region.

  • 234.
    Alm, Love
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Marklund, Göran T.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Karlsson, Tomas
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Masson, A.
    Pseudo altitude: A new perspective on the auroral density cavity2013In: Journal of Geophysical Research A: Space Physics, ISSN 2169-9380, Vol. 118, no 7, p. 4341-4351Article in journal (Refereed)
    Abstract [en]

    Studying the density distribution inside the auroral density cavity is complicated by the difficulties in achieving simultaneous measurements within the same flux tube at different altitudes. Comparisons between different events are complicated by variations in both the location of the density cavity and the location of the related potential structure. Describing the spacecraft's location inside the density cavity relative to the potential structure instead of the Earth offers a more practical and consistent frame of reference, a pseudo altitude. The pseudo altitude is determined by comparing the potential drop above the spacecraft, as determined from the characteristic energy of the downward electrons, with the parallel potential drop below the spacecraft, determined from the characteristic energy of the upward ions. A pseudo altitude of 0 corresponds to the bottom of the potential structure and a pseudo altitude of 1 to the top of the structure. Seven events from 2008 were selected, each of which corresponds to a Cluster crossing of a mainly quasi-static potential structure. All of the events exhibit a consistent anticorrelation between the pseudo altitude and the electron density. No upper limit of the density cavity can be observed, while all cavities have a lower limit above a pseudo altitude of 0.33. These observations show that the auroral density cavity is predominately concentrated to the upper parts of the quasi-static potential structure.

  • 235.
    Almas, M. Shoaib
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems. Statnett SF, Res & Dev, Oslo, Norway.
    RT-HIL Implementation of Hybrid Synchrophasor and GOOSE-based Passive Islanding Schemes2016In: 2016 IEEE POWER AND ENERGY SOCIETY GENERAL MEETING (PESGM), IEEE , 2016Conference paper (Refereed)
  • 236.
    Almas, Muhammad Shoaib
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Synchrophasor Applications and their Vulnerability to Time Synchronization Impairment2017Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Recent years have seen the significance of utilizing time-synchronized, high resolution measurements from phasor measurement units (PMUs) to develop and implement wide-area monitoring, protection and control (WAMPAC) systems. WAMPAC systems aim to provide holistic view of the power system and enable detection and control of certain power system phenomena to enhance reliability and integrity of the grid.

    This thesis focuses on the design, development and experimental validation of WAMPAC applications, and investigates their vulnerability to time synchronization impairment. To this purpose, a state-of-the-art real-time hardware-in-the-loop (RT-HIL) test-bench was established for prototyping of synchrophasor-based applications. This platform was extensively used throughout the thesis for end-to-end testing of the proposed WAMPAC applications. To facilitate the development of WAMPAC applications, an open-source real-time data mediator is presented that parses the incoming synchrophasor stream and provides access to raw data in LabVIEW environment.

    Within the domain of wide-area protection applications, the thesis proposes hybrid synchrophasor and IEC 61850-8-1 GOOSE-based islanding detection and automatic synchronization schemes. These applications utilize synchrophasor measurements to assess the state of the power system and initiate protection / corrective action using GOOSE messages. The associated communication latencies incurred due to the utilization of synchrophasors and GOOSE messages are also determined. It is shown that such applications can have a seamless and cost-effective deployment in the field.

      Within the context of wide-area control applications, this thesis explores the possibility of utilizing synchrophasor-based damping signals in a commercial excitation control system (ECS). For this purpose, a hardware prototype of wide-area damping controller (WADC) is presented together with its interface with ECS. The WADC allows real-time monitoring and remote parameter tuning that could potentially facilitate system operators’ to exploit existing damping assets (e.g. conventional generators) when changes in operating conditions or network topology emerges.

    Finally the thesis experimentally investigates the impact of time synchronization impairment on WAMPAC applications by designing RT-HIL experiments for time synchronization signal loss and time synchronization spoofing. It is experimentally demonstrated that GPS-based time synchronization impairment results in corrupt phase angle computations by PMUs, and the impact this has on associated WAMPAC application. 

  • 237.
    Almas, Muhammad Shoaib
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Baudette, Maxime
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems. Statnett.
    Utilizing synchrophasor-based supplementary damping control signals in conventional generator excitation systems2018In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 157, p. 157-167Article in journal (Refereed)
    Abstract [en]

    A supplementary function of Excitation Control Systems (ECSs) for synchronous generators is that of a Power System Stabilizer (PSS). The PSS implementation in these ECSs only allows the use of a limited type of pre-defined local input measurements and built-in PSS algorithms. To adapt existing ECSs to take advantage of synchrophasors technology, this paper proposes and implements a prototype wide-area damping controller (WADC) that provides synchrophasor-based damping input signals to existing ECSs. The developed WADC comprise (i) a real-time mode estimation module, (ii) synchrophasor’s communication latency computation module, and (iii) phasor-based oscillation damping algorithm executing in a real-time hardware prototype controller.

    Through Real-Time Hardware-in-the-Loop (RT-HIL) simulations, it is demonstrated that synchrophasor-based damping signals from the WADC can be utilized together with a commercial ECS, thus providing new options for selection of the best feedback signal for oscillation damping.

  • 238.
    Almas, Muhammad Shoaib
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Baudette, Maxime
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Løvlund, S
    Gjerde, J.O
    Synchrophasor Network, Laboratory and Software Applications Developed in the STRONg2rid Project2014In: PES General Meeting Conference & Exposition, 2014 IEEE, IEEE conference proceedings, 2014, p. 1-5Conference paper (Refereed)
    Abstract [en]

    This paper presents the activities carried out in one of the work packages of the Nordic Energy Research funded project Smart Transmission Grid Operation and Control (STRONg2rid). The main objective of the work package is to deploy a state-of-the-art software and hardware for developing power system operation, protection, control and automation applications. Several PMUs have been deployed at partner universities and a network of synchrophasors has been set up. In addition the Smart Transmission System Laboratory (SmarTS-Lab) has been established. This laboratory serves as a test-bench to develop and verify smart transmission grid technologies. A software development kit (S3DK) was developed within the project. The S3DK has been used to implement PMU-based applications and deploy them in different targets, including smart phones and tablets. Several tools and software applications which utilize synchrophasor measurements (from the laboratory or the deployed university PMU network) to perform power system monitoring, sub-synchronous power oscillation detection, etc., have been developed and are presented herein.  

  • 239.
    Almas, Muhammad Shoaib
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Kilter, Jako
    Tallinn University of Technology-Estonia.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Experiences with Steady-State PMU Compliance Testing using Standard Relay Testing Equipment2014In: Electric Power Quality and Supply Reliability Conference (PQ), 2014, IEEE conference proceedings, 2014, p. -110Conference paper (Refereed)
    Abstract [en]

    This paper presents the results of steady state compliance testing of phasor measurement units (PMUs) from three different vendors in a laboratory environment. Testing is performed by providing three phase voltage and current injections to the VT and CT inputs of the PMUs through Freja-300 stand-alone protection relay test set. Testing is performed according to the standard “IEEE C37.242-2013 - IEEE Guide for Synchronization, Calibration, Testing, and Installation of Phasor Measurement Units (PMUs) for Power System Protection and Control”. The paper discusses the test setup, testing process and overall test results of this project. The limitations of stand-alone testing equipment and recommendations for utilizing real-time hardware-in-the-loop simulation for thorough testing of PMUs are also presented. 

  • 240.
    Almas, Muhammad Shoaib
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Leelaruji, Rujiroj
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Over-current relay model implementation for real time simulation & Hardware-in-the-Loop (HIL) validation2012In: IECON 2012 - 38th Annual Conference on IEEE Industrial Electronics Society, Montreal, QC: IEEE conference proceedings, 2012, p. 4789-4896Conference paper (Refereed)
    Abstract [en]

    Digital microprocessor based relays are currently being utilized for safe, reliable and efficient operation of power systems. The overcurrent protection relay is the most extensively used component to safeguard power systems from the detrimental effects of faults. Wrong settings in overcurrent relay parameters can lead to false tripping or even bypassing fault conditions which can lead to a catastrophe. Therefore it is important to validate the settings of power protection equipment and to confirm its performance when subject to different fault conditions. This paper presents the modeling of an overcurrent relay in SimPowerSystems (\textsc {matlab}/Simulink). The overcurrent relay has the features of instantaneous, time definite and inverse  definite minimum time (IDMT) characteristics. A power system is modeled in SimPowerSystems and this overcurrent relay model is incorporated in the test case. The overall model is then simulated in real-time using Opal-RT's eMEGAsim real-time simulator to analyze the relay's performance when subjected to faults and with different characteristic settings in the relay model. Finally Hardware-in-the-Loop validation of the model is done by using the overcurrent protection feature in Schweitzer Engineering Laboratories Relay SEL-487E. The event reports generated by the SEL relays during Hardware-in-the-Loop testing are compared with the results obtained from the standalone testing and software model to validate the model.

  • 241.
    Almas, Muhammad Shoaib
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems. Statnett.
    A Hybrid Synchrophasor and GOOSE-Based Power System Synchronization Scheme2016In: IEEE Access, E-ISSN 2169-3536, Vol. 4, p. 4659-4668Article in journal (Refereed)
    Abstract [en]

    The design and real-time hardware-in-the-loop implementation of a hybrid synchrophasors and GOOSE-based automatic synchronization algorithm are presented in this paper. Automatic synchronization is performed by utilizing the synchrophasor measurements from two commercial phasor measurement units (PMUs), while the coordinated control commands to automatic voltage regulator and/or turbine governor control and trip command to the circuit breaker are issued using IEC 61850-8-1 GOOSE messages. The algorithm is deployed inside the PMU using the protection logic equations, and direct communication between the PMUs is established to minimize the communication latencies. In addition, the algorithm is tested using a standard protection relay test-set, and automatic test sequences are executed to validate its performance. It is concluded that the hybrid synchrophasor and GOOSE-based automatic synchronization scheme ensures minimum communication latencies, reduces equipment cost, facilitates interoperability, and performs automatic reconnection adequately.

  • 242.
    Almas, Muhammad Shoaib
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems. Statnett.
    A method exploiting direct communication between phasor measurement units for power system wide-area protection and control algorithms2017In: MethodsX, ISSN 1258-780X, E-ISSN 2215-0161, Vol. 4, p. 346-359Article in journal (Refereed)
    Abstract [en]

    Synchrophasor measurements from Phasor Measurement Units (PMUs) are the primary sensors used to deploy Wide-Area Monitoring, Protection and Control (WAMPAC) systems. PMUs stream out synchrophasor measurements through the IEEE C37.118.2 protocol using TCP/IP or UDP/IP. The proposed method establishes a direct communication between two PMUs, thus eliminating the requirement of an intermediate phasor data concentrator, data mediator and/or protocol parser and thereby ensuring minimum communication latency without considering communication link delays. This method allows utilizing synchrophasor measurements internally in a PMU to deploy custom protection and control algorithms. These algorithms are deployed using protection logic equations which are supported by all the PMU vendors. Moreover, this method reduces overall equipment cost as the algorithms execute internally in a PMU and therefore does not require any additional controller for their deployment. The proposed method can be utilized for fast prototyping of wide-area measurements based protection and control applications. The proposed method is tested by coupling commercial PMUs as Hardware-in-the-Loop (HIL) with Opal-RT’s eMEGAsim Real-Time Simulator (RTS). As illustrative example, anti-islanding protection application is deployed using proposed method and its performance is assessed. The essential points in the method are:

    •  Bypassing intermediate phasor data concentrator or protocol parsers as the synchrophasors are communicated directly between the PMUs (minimizes communication delays).

    •  Wide Area Protection and Control Algorithm is deployed using logic equations in the client PMU, therefore eliminating the requirement for an external hardware controller (cost curtailment)

    •  Effortless means to exploit PMU measurements in an environment familiar to protection engineers

  • 243.
    Almas, Muhammad Shoaib
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Vanfretti, Luigi
    Statnett SF, Oslo, Norway.
    Experimental Performance Assessment of a Generator's Excitation Control System using Real-Time Hardware-in-the-Loop Simulation2014In: Industrial Electronics Society, IECON 2014 - 40th Annual Conference of the IEEE, IEEE conference proceedings, 2014, p. 3756-3762Conference paper (Refereed)
    Abstract [en]

    This paper presents methods and results for experimental performance assessment using Real-Time Hardware-in-the-Loop (RT-HIL) simulation of an Excitation Control System (ECS) for both terminal voltage regulation and power oscillation damping. The ECS configured for this study is Unitrol 1020 from ABB and its performance is assessed for both Automatic Voltage Regulator (Auto) and Field Current Regulator (Manual) modes. RT-HIL simulation is performed by using Opal-RT’s eMEGAsim RT Simulator using a power system model including a synchronous generator. Finally, the Power System Stabilizing feature of Unitrol 1020 is calibrated and assessed.  

  • 244.
    Almas, Muhammad Shoaib
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems. Statnett.
    Impact of Time-Synchronization Signal Loss on PMU-based WAMPAC Applications2016In: IEEE PES General Meeting 2016, IEEE , 2016Conference paper (Refereed)
    Abstract [en]

    This paper experimentally assesses the impact of loss of time-synchronization signal on synchrophasor-based Wide-Area Monitoring, Protection and Control applications. Phase Angle Monitoring (PAM), anti-islanding protection and power oscillation damping applications are investigated. Power system models are executed using a real-time simulator with commercial PMUs coupled to them as hardware-in-the-loop. The experiments conclude that a phase angle monitoring application shows erroneous power system state whereas the operating time of an anti-islanding protection application increases due to the loss of time-synchronization signal input to PMUs. In addition, the performance of an oscillation damping controller degrades in the absence of time-synchronization input to the PMUs.

  • 245.
    Almas, Muhammad Shoaib
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Implementation of Conventional and Phasor Based Power System Stabilizing Controls for Real-Time Simulation2014In: Industrial Electronics Society, IECON 2014 - 40th Annual Conference of the IEEE, IEEE conference proceedings, 2014, p. 3770-3776Conference paper (Refereed)
    Abstract [en]

    This paper presents the implementation of three different types of Power System Stabilizers (PSS) and a Static Var Compensator with a supplementary Phasor Power Oscillation Damper (POD) control for real-time simulation. The Klein-Rogers-Kundur model is used as test case and the PSS and Phasor-POD’s performance is evaluated for both large and small disturbances.  Modeling is performed in the MATLAB/Simulink environment and is executed in real-time using Opal-RT’s eMEGAsim Real-Time Simulator. The simulation results and the developed model will be used to deploy hardware prototype based on embedded controllers to provide power oscillation damping. Real-time software in the loop (SIL) approach is used for validating developed models as a first logical step towards development of a prototype hardware controller.

  • 246.
    Almas, Muhammad Shoaib
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Methodologies for Power Protection Relay Testing: From Conventional to Real-Time Hardware-in-the-Loop (HIL) Simulation Approaches2013In: 10th International Conference on Power System Transients, 2013Conference paper (Refereed)
    Abstract [en]

    Performance testing of the protection relays ensures that a particular protection scheme will operate reliably and fast enough to disconnect a faulty zone from the rest of the network, thus mitigating the effect of fault on the power system. It is therefore important to validate the settings of power protection equipment and to confirm its performance when subject to different fault conditions. Traditionally, commissioning engineers make use of standalone protection relay test sets for analyzing the performance of relays when subjected to different voltage and current injections. With the advent of digital simulators the model of the power system can be executed in real-time and protection relays can be interfaced as hardware-in-the-loop to evaluate their performance when subjected to different faults in the simulated power system. This gives an added value of analyzing the overall behavior of the power system coupled with the relay performance under faulty conditions. In addition, the utilization of GOOSE messages for status, control and protection purposes puts an extra requirement to completely test the IEC 61850 capabilities of the protection relays.

    This article illustrates two different techniques namely standalone testing and real-time hardware-in-the-loop testing used for protection relays performance verification. Both techniques are evaluated for hardwired and IEC 61850-8-1 (GOOSE) signals. The instantaneous overcurrent protection feature of Schweitzer Engineering Laboratories Relay SEL-421 is used for complete standalone and RT-HIL testing. For RT-HIL testing, the test case is modeled in MATLAB/Simulink and executed in real-time using Opal-RT's eMEGAsim real-time simulator. The event reports generated by standalone and RT-HIL testing for both hardwired and GOOSE signals is used to verify the tripping times achieved. Finally the performance of hardwired and GOOSE tripping times are compared and the overall standalone and RT-HIL techniques are evaluated.

  • 247.
    Almas, Muhammad Shoaib
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    PERFORMANCE EVALUATION OF PROTECTION FUNCTIONS FOr IEC 61850-9-2 PROCESS BUS USING REAL-TIME HARDWARE-IN-THE-loop simulation approach2013Conference paper (Refereed)
    Abstract [en]

    With the evolution of Process Bus (IEC 61850-9-2), there is a need to assess the performance of protection schemes using process bus against those where traditional copper wires are implemented. Differential protection is the fundamental and most commonly used protection for transformers, motors and generators. In this paper a power system is modelled in SimPowerSystems and is executed in real-time using Opal-RT’s eMEGAsim real-time simulator. Hardware-in-the loop validation of a process bus implementation for differential protection for a two winding transformer is done by using the differential protection feature in ABB’s RED-670 relay. The event reports generated by the ABB relay during Hardware-in-the-Loop testing are compared for three different scenarios i.e. complete process bus, hybrid process bus and complete traditional topology.   

  • 248.
    Almas, Muhammad Shoaib
    et al.
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric power and energy systems. Statnett.
    RT-HIL Implementation of Hybrid Synchrophasor and GOOSE-based Passive Islanding Schemes2015In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 31, no 3, p. 1299-1309Article in journal (Refereed)
    Abstract [en]

    Real-time hardware-in-the-loop performance assessmentof three different passive islanding detection methodsfor local and wide-area synchrophasor measurements is carriedout in this paper. Islanding detection algorithms are deployedwithin the phasor measurement unit (PMU) using logic equations.Tripping decisions are based on local and wide-area synchrophasorsas computed by the PMU, and trips are generated usingIEC 61850-8-1 generic object-oriented substation event messages.The performance assessment compares these islanding detectionschemes for the nondetection zone and operation speed underdifferent operating conditions. The testbench that is demonstratedis useful for a myriad of applications where simulation exercises inpower system computer-aided design software provide no realisticinsight into the practical design and implementation challenges.Finally, different communication latencies introduced due tothe utilization of synchrophasors and IEC 61850-8-1 GOOSEmessages are determined.

  • 249.
    Almas, Muhammad Shoaib
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems. Statnett, Oslo.
    RT-HIL Testing of an Excitation Control System for Oscillation Damping using External Stabilizing Signals2015Conference paper (Refereed)
    Abstract [en]

    A feature of an Excitation Control System (ECS) for synchronous generators is to enable power system stabilization by providing an additional input to the Automatic Voltage Regulator (AVR) for external stabilization signals. This paper explores this feature by externally generating stabilization signals which are fed as an analog input to a commercial ECS. This allows bypassing the built-in PSS function in the ECS and gives more freedom to the end-user to utilize custom stabilizer models. ABB’s Unitrol 1020 Excitation Control System is coupled with Opal-RT’s eMEGAsim Real-Time simulator to perform Hardware-in-the-Loop simulation of the ECS. The output of several stabilizer models is fed to the ABB’s Unitrol 1020 ECS as external power system stabilization signals to analyze their performance for small signal stability enhancement.  

  • 250.
    Almas, Muhammad Shoaib
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems. Statnett.
    Baudette, Maxime
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    BabelFish—Tools for IEEE C37.118.2-compliant real-time synchrophasor data mediation2017In: SoftwareX, ISSN 2352-7110, Vol. 6, p. 209-216Article in journal (Refereed)
    Abstract [en]

    BabelFish (BF) is a real-time data mediator for development and fast prototyping of synchrophasor applications. BF is compliant with the synchrophasor data transmission IEEE Std C37.118.2-2011. BF establishes a TCP/IP connection with any Phasor Measurement Unit (PMU) or Phasor Data Concentrator (PDC) stream and parses the IEEE Std C37.118.2-2011 frames in real-time to provide access to raw numerical data in the LabVIEW environment. Furthermore, BF allows the user to select ‘‘data-of-interest’’and transmit it to either a local or remote application using the User Datagram Protocol (UDP) in order to support both unicast and multicast communication. In the power systems Wide Area Monitoring Protection and Control (WAMPAC) domain, BF provides the first Free/Libre and Open Source Software (FLOSS) for the purpose of giving the users tools for fast prototyping of new applications processing PMU measurements in their chosen environment, thus liberating them of time consuming synchrophasor data handling and allowing them to develop applications in a modular fashion, without a need of a large and monolithic synchrophasor software environment.

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