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  • 201.
    Bagheri, Azam
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Artificial Intelligence-Based Characterization and Classification Methods for Power Quality Data Analytics2018Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    One of the important developments in the electric power system is the fast increasing amount of data. An example of such data is formed by the voltages and currents coming from power-quality measurements. Power quality disturbances like voltage dips, harmonics and voltage transient can have a serious negative impact on the performance of equipment exposed to such disturbances. Voltage dips, short duration reductions in voltage magnitude, are especially considered as important disturbances because they regularly lead to stoppages in industrial process installations and subsequently to high costs.

    The overall aim of this dissertation is the development of automatic analysis methods and other methods for extracting information from large amounts of power-quality data. This includes, methods to detect and extract event characteristics from recorded data and classify the events, for instance, based on their origins or their impact on equipment. The classification facilitates further analysis steps including reasoning and interpretation. Once the data corresponding to each class is available, a proper characterization method can be used to create more semantic data useful for information extraction. The resulting information can be used to improve the performance of the whole system, e.g., updating grid-codes, or immunity requirements of sensitive installations or processes.

    This dissertation proposes different methods to fulfil each one of the above-mentioned steps. It proposes particularly a space-phasor model (SPM) of the three phase-to-neutral voltages as basis for analytic methods. The SPM is especially suitable as it is a time-domain transform without loss of any information. Another important contribution of the work is that most of the developed methods have been applied to a large dataset of about 6000 real-world voltage dips measured in existing HV and MV power networks.

    The main contributions of this dissertation are as follows:

    A complete framework has been proposed for automatic voltage quality analysis based on the SPM. The SPM has been used before, but this is the first time it has been used in a framework covering a range of voltage quality disturbances. A Gaussian-based anomaly detection method is used to detect and extract voltage quality disturbances. A principal component analysis (PCA) algorithm is used for event characterization. The obtained single-event characteristics are used to extract additional information like origin, fault type and location. 

    Two deep learning-based voltage dip classifier has been developed. In both classifier a 2D convolutional neural network (2D-CNN) architecture has been employed to perform automatic feature extraction task. The soft-max activation function fulfills supervised classification method in first classifier. The second classifier uses a semi-supervised classification method based on generative-discriminative model pairs in active learning context.

    The same SPM was shown to enable the effective extraction of dip characteristics for multi-stage voltage dips. Applying the k-means clustering algorithm, the event is clustered into its individual stages. For each stage of the dip, a logistic regression algorithm is used to characterize that stage. The proposed method offers a new solution to the problem with transition segments that is one of the main challenges of existing methods for characterization of multi-stage dips.  

    It is also shown in the dissertation that the SPM is an effective method for voltage transient analysis. It is possible to extract corresponding sample data and get appropriate single-event characteristics.

    A systematic way has been developed and applied for comparing different sets of voltage dip characteristics. With this method, both measured and synthetic voltage dips are applied to generic models of sensitive loads. The best set of characteristics is the one most accurately reproducing the behavior of equipment when exposed to measured voltage dips.

    The dissertation further contains a number of practical applications of the before-mentioned theoretical contributions: a proposal to an international standard-setting group; energy storage for voltage-dip ride-through of microgrids; impact of different voltage dips on wind-power installations.

  • 202.
    Bagheri, Azam
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Extracting Information from Voltage-Dip Monitoring2016Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    A voltage dip is a short duration reduction in voltage magnitude due to a short duration increase in current magnitude. Causes of dips are, among others, electrical faults, large motor starting, transformer energizing and failure of power-electronic converters.

    Voltage dips are considered as a very important power quality issue because they lead to trip or malfunction of sensitive loads especially in industrial process installations and subsequently they lead to high costs.

    In this thesis the overall aim is extracting additional information from large voltage dip monitoring databases. An important step to this end is providing efficient characterization methods for voltage dips. Voltage dip characterization aids by describing voltage dip events (a set of voltage waveforms with high time resolution) as a limited number of values such that this set gives as much as possible information about the dip. This thesis contributes to the voltage dip characterization development through three different methods.

    The first method consists of a systematic way for comparison different sets of voltage dip characteristic. With this method, both real-measured and synthetic voltage dips are applied to generic models of sensitive loads. The best set of characteristics, for representing the voltage dip, is the one best enables the reproduction of the behaviour of equipment when exposed to real-measured voltage dips.

    The second method compares 12 different sets of characteristics for describing three-phase single-events.. The method determines the most efficient and feasible way that gives more realistic characteristics as well as comparable with existing standard methods. The proposed set of characteristics has been proposed for inclusion in international standard documents.

    The third method enables the extraction of dip characteristics based on machine learning approaches. It is applicable for characterization of multi-stage voltage dips in particular and for single-stage (normal) voltage dips as well. The proposed method uses the space-phasor model of three-phase voltages as an input data for k-means clustering algorithm. Then the calculated data are modeled as a general form of an ellipse by exploiting logistic regression algorithm. Finally the optimized obtained ellipse parameters are applied to calculate single-segment characteristics for each individual stage of a multi-stage voltage dip.

    Further, all proposed methods are implemented in an Matlab environment and validated by applying them to a large number of real-measured voltage dips in actual HV and MV power networks and some suitable synthetic voltage dips.

  • 203.
    Bagheri, Azam
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Additional information from voltage dips2016Inngår i: 17th International Conference on Harmonics and Quality of Power, Piscataway, NJ, 2016, s. 326-332, artikkel-id 7783434Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper presents some methods to extract additional information from voltage dip recordings, beyond residual voltage and duration. Additionally it discusses some issues related to the massive amount of data obtained from modern measurements that, is referred to as Big Data. The paper proposes some Deep Learning based algorithms as good candidates to extract complex features from big data as a step towards additional information. The applications of the information include predicting individual equipment performance, fault type and location, protection operation, and overall load behavior. Individual equipment and overall load include production as well as consumption

  • 204.
    Bagheri, Azam
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Characterizing three-phase unbalanced dips through the ellipse parameters of the space phasor model2018Inngår i: 2017 IEEE PES Innovative Smart Grid Technologies Conference Europe, ISGT-Europe 2017: proceedings, New York: Institute of Electrical and Electronics Engineers (IEEE), 2018Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper verifies the potential of ellipse parameters as voltage dip characteristics. The space-phasor model (SPM) of three phase voltages is generally in form of an ellipse in the complex plane. Mathematical relations are derived between the single-event characteristics (Characteristic Voltage; PN factor and Dip Type), and the ellipse parameters (semi-major axis, Semi-minor axis and major axis direction). The relations are validated by applying them to several actual recorded voltage dips and synthetic voltage dips.

  • 205.
    Bagheri, Azam
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Developments in voltage dip research and its applications, 2005-20152016Inngår i: 17th International Conference on Harmonics and Quality of Power, Piscataway, NJ, 2016, s. 48-54, artikkel-id 7783428Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper presents a review of literature on voltage dips, from several points of view, throughout the last decade. It also summarizes the results related to voltage dip mitigation in both AC and DC power systems whereas it shows the remaining challenges that requires further research on voltage dips.

  • 206.
    Bagheri, Azam
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Generative Adversarial Model-Guided Deep Active Learning for Voltage Dip Labelling2019Konferansepaper (Fagfellevurdert)
  • 207.
    Bagheri, Azam
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Simple diagnostic technique of switch failure modes of VSI power converter2018Inngår i: 2017 IEEE PES Innovative Smart Grid Technologies Conference Europe, ISGT-Europe 2017: proceedings, New York: Institute of Electrical and Electronics Engineers (IEEE), 2018Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper presents a diagnostic method to detect switch failure of PWM power converters. The proposed method uses space phasor model (SPM) of three voltages measured at terminal of the power converter, then it applies principal component analysis to detect and localize the failure mode. The SPM results in one unique rotated ellipse or semi ellipse for every failure mode of every faulty leg. The quadrants occupied by the ellipse or semi ellipse also determine the faulty switch location in the leg. The proposed method is validated through comprehensive simulations.

  • 208.
    Bagheri, Azam
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Space Phasor Model Based Monitoring of Voltages in Three Phase Systems2018Inngår i: Proceedings of International Conference on Harmonics and Quality of Power, ICHQP, Piscataway, NJ: Institute of Electrical and Electronics Engineers (IEEE), 2018Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper proposes a method for monitoring of voltages in three-phase systems using parameters of the ellipse, correspondent to the space phasor model of three-phase voltages. Three main parameters, semi-minor axis, semi-major axis and rotating angle of the ellipse are calculated as single-cycle characteristics. Once these characteristics exceed predefined threshold values, different voltage events are detected. Given whole event data the parameters of the corresponding ellipse are calculated as ‘single-event characteristics’. The proposed method is applied to different measured voltage waveforms. The simulation results confirm that the ellipse parameters are a good basis for both detecting and characterizing voltage events.

  • 209.
    Bagheri, Azam
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    The impact of voltage dips to low-voltage-ride-through capacity of doubly fed induction generator based wind turbine2019Konferansepaper (Fagfellevurdert)
  • 210.
    Bagheri, Azam
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    The Novel Method for Voltage Transient Detection and Characterization2019Konferansepaper (Fagfellevurdert)
  • 211.
    Bagheri, Azam
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Gu, Irene Y.H.
    Signal Processing group, Chalmers University of Technology.
    Big data from smart grids2018Inngår i: 2017 IEEE PES Innovative Smart Grid Technologies Conference Europe, ISGT-Europe 2017: proceedings, New York: Institute of Electrical and Electronics Engineers (IEEE), 2018Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper gives a general introduction to “Big Data” in general and to Big Data in smart grids in particular. Large amounts of data (Big Data) contains a lots of information, however developing the analytics to extract such information is a big challenge due to some of the particular characteristics of Big Data. This paper investigates some existing analytic algorithms, especially deep learning algorithms, as tools for handling Big Data. The paper also explains the potential for deep learning application in smart grids.

  • 212.
    Bagheri, Azam
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Gu, Irene Y.H.
    Chalmers University of Technology.
    Improved characterization of multi-stage voltage dips based on the space phasor model2018Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 154, s. 319-328Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper proposes a method for characterizing voltage dips based on the space phasor model of the three phase-to-neutral voltages, instead of the individual voltages. This has several advantages. Using a K-means clustering algorithm, a multi-stage dip is separated into its individual event segments directly instead of first detecting the transition segments. The logistic regression algorithm fits the best single-segment characteristics to every individual segment, instead of extreme values being used for this, as in earlier methods. The method is validated by applying it to synthetic and measured dips. It can be generalized for application to both single- and multi-stage dips.

  • 213.
    Bagheri, Azam
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Gu, Irene Y.H.
    Department of Electrical Engineering, Chalmers University of Technology.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Balouji, Ebrahim
    Department of Electrical Engineering, Chalmers University of Technology.
    A Robust Transform-Domain Deep Convolutional Network for Voltage Dip Classification2018Inngår i: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 33, nr 6, s. 2794-2802Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper proposes a novel method for voltage dip classification using deep convolutional neural networks. The main contributions of this paper include: (a) to propose a new effective deep convolutional neural network architecture for automatically learning voltage dip features, rather than extracting hand-crafted features; (b) to employ the deep learning in an effective two-dimensional transform domain, under space-phasor model (SPM), for efficient learning of dip features; (c) to characterize voltage dips by two-dimensional SPM-based deep learning, which leads to voltage dip features independent of the duration and sampling frequency of dip recordings; (d) to develop robust automatically-extracted features that are insensitive to training and test datasets measured from different countries/regions.

    Experiments were conducted on datasets containing about 6000 measured voltage dips spread over seven classes measured from several different countries. Results have shown good performance of the proposed method: average classification rate is about 97% and false alarm rate is about 0.50%. The test results from the proposed method are compared with the results from two existing dip classification methods. The proposed method is shown to out-perform these existing methods.

  • 214.
    Bahramirad, S
    et al.
    ComEd, Chicago.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Khodaei, A
    University of Denver, Colorado.
    Smart distribution applications – some contributions to P18542014Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Rapid and wide-spread deployment of newtechnologies in the electric power distribution network under theconcept of smart grids has resulted in a growing need to newstandards and guidelines specifically designed to addressemerging technological challenges and further streamline the useof new technology. This document is prepared as part of theactivities to develop the IEEE Power and Energy Society’s“smart distribution application guide”, to give guidance toutilities and network operators in the use of new technology inelectric power distribution. The document will provide adescription of the available new technology based on itsapplication, followed by a more detailed description of thetechnologies and associated supporting solutions. The topicsdiscussed in this document include improving the reliability ofsupply, improving the power quality, improving the efficiency ofdistribution-system operation, increasing hosting capacity fornew production or for new consumption, and allowing marketfunctioning and participation of all network users. This papercontains some examples of texts as they are currently beingdiscussed within the smart distribution working group

  • 215.
    Bahramirad, Shay
    et al.
    ComEd, Chicago.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Khodaei, Amin
    University of Denver, Colorado.
    Clark, George Larry
    Alabama Power.
    Svachula, Jospeh
    ComEd, Chicago.
    Simard, Georges
    SIMARD SG Inc..
    Smart Distribution Application Guide – IEEE Project P18542014Konferansepaper (Fagfellevurdert)
  • 216.
    Baker, Mark
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Optimization of CHIMS2018Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    The CHopper (Comet Hopper) was a proposal for a NASA mission to visit comet 46P/Wirtanen. A time of flight ion and neutral mass spectrometer (CHIMS) was developed especially for the proposed mission and was to be mounted on the Chopper spacecraft. CHIMS was to establish the composition and isotopic ratios of the comet's volatile components. Since NASA selected the InSight mission, CHIMS had been proposed for other missions: LIFE, Life Investigation For Enceladus, a low-cost sample return mission to Enceladus and Castalia, an ESA medium-sized mission to explore the Main Comet Belt. CHIMS was in need of fine tuning; the scientific demand of having accurate detection efficiency, combined with high performance make it necessary to rigorously test and calibrate instruments to operate at their optimum level. The goal of this work is to improve the performance of the ion source by applying simulation and optimization techniques to the CHIMS lab prototype. The results show a positive outcome, and propose a number of future modifications that should help obtain the desired results for any future missions.

  • 217.
    Balouji, Ebrahim
    et al.
    Department of Electrical Engineering, Chalmers University of Technology.
    Gu, Irene Y.H.
    Department of Electrical Engineering, Chalmers University of Technology.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bagheri, Azam
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Nazari, Mahmood
    Department of Electrical Engineering, Chalmers University of Technology.
    A LSTM-based deep learning method with application to voltage dip classification2018Inngår i: Proceedings of International Conference on Harmonics and Quality of Power, ICHQP, Piscataway, NJ: Institute of Electrical and Electronics Engineers (IEEE), 2018Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper, a deep learning (DL)-based method for automatic feature extraction and classification of voltage dips is proposed. The method consists of a dedicated architecture of Long Short-Term Memory (LSTM), which is a special type of Recurrent Neural Networks (RNNs). A total of 5982 three-phase one-cycle voltage dip RMS sequences, measured from several countries, has been used in our experiments. Our results have shown that the proposed method is able to classify the voltage dips from learned features in LSTM, with 93.40% classification accuracy on the test data set. The developed architecture is shown to be novel for feature learning and classification of voltage dips. Different from the conventional machine learning methods, the proposed method is able to learn dip features without requiring transition-event segmentation, selecting thresholds, and using expert rules or human expert knowledge, when a large amount of measurement data is available. This opens a new possibility of exploiting deep learning technology for power quality data analytics and classification.

  • 218.
    Bangemann, Thomas
    et al.
    Ifak - Institut für Automation und Kommunikation.
    Karnouskos, Stamatis
    SAP Research, Karlsruhe.
    Camp, Roberto
    FluidHouse, Jyväskylä, Prodatec Oy.
    Carlsson, Oscar
    Midroc Electro AB, Stockholm.
    Riedl, Matthias
    Ifak - Institut für Automation und Kommunikation.
    McLeod, C. Stuart
    University of Warwick, Coventry.
    Harrison, Robert
    University of Warwick, Coventry.
    Colombo, Armando Walter
    Schneider Electric and University of Applied Sciences Emden/Leer.
    Stluka, Petr
    Honeywell, Prague.
    State of the Art in Industrial Automation2014Inngår i: Industrial Cloud-Based Cyber-Physical Systems: The IMC-AESOP Approach, Cham: Encyclopedia of Global Archaeology/Springer Verlag, 2014, s. 23-47Kapittel i bok, del av antologi (Fagfellevurdert)
    Abstract [en]

    In the last decades, industrial automation has become a driving force in all production systems. Technologies and architectures have emerged alongside the growing organisational structures of production plants. Every innovation had to start from the latest state-of-the-art systems within the respective domain. While investigating the introduction of service-oriented architectures to automation, and even down to the shop floor, one has to consider latest standards, proofed technologies, industrial solutions and latest research works in the automation domain. This chapter tries, without any claim to completeness, to provide a short summary of today’s situation and trends in automation.

  • 219.
    Barabash, Victoria
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Ejemalm, Johnny
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Kuhn, Thomas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Milz, Mathias
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Molin, Sven
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Johansson, Jonny
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Westerberg, Lars-Göran
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Masters Programs in Space Science and Engineering in Northern Sweden2017Konferansepaper (Fagfellevurdert)
  • 220.
    Barakou, Fani
    et al.
    Eindhoven University of Technology, The Netherlands.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Mousavi-Gargari, S.
    TenneT TSO B.V, The Netherlands.
    Lennerhag, Oscar
    STRI AB, Sweden.
    Wouters, Peter A A F
    Eindhoven University of Technology, The Netherlands.
    Steennis, E. Fred
    Eindhoven University of Technology, The Netherlands.
    Impact of Load Modeling on the Harmonic Impedance seen from the Transmission Network2016Inngår i: 17th International Conference on Harmonics and Quality of Power, Piscataway, NJ, 2016, s. 283-288, artikkel-id 7783466Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Traditionally when studying harmonics at transmis-sion system level the medium and low voltage grid is modeledwith either an equivalent short-circuit impedance or a fixed PQload (based on the powerflow) directly at the secondary side ofthe transmission transformer. However the recent replacement ofconventional loads with electronic loads as well as the extendeduse of power electronics in LV level will result in reductionof damping and increase of household capacitance which maychange the harmonic impedance seen from the upstream network(MV or HV) both in the dominant frequency and magnitude.In this paper a HV feeder is modeled in detail starting fromthe transmission transformer up to the household equipmentto investigate whether changes in the type of load affect theimpedance seen from the HV. The simulations are performedusing software package PSCAD/EMTDC.

  • 221.
    Barakou, Fani
    et al.
    Eindhoven University of Technology.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Mousavi-Gargari, S.
    TenneT TSO BV, Arnhem.
    Wouters, P.A.A.F.
    Eindhoven University of Technology.
    Steenis, E.F.
    Eindhoven University of Technology.
    Downstream network modeling for switching transients in EHV networks containing cables2017Inngår i: IEEE PES PowerTech Manchester 2017: towards and beyond sustainable energy systems, 2017, Piscataway, NJ: Institute of Electrical and Electronics Engineers (IEEE), 2017, artikkel-id 7980800Konferansepaper (Fagfellevurdert)
    Abstract [en]

    For the study of switching transients in Extra High Voltage (EHV) networks it is common practice to model a relatively small part of the EHV network. The downstream network is either disregarded or modeled as a parallel RC or RL circuit, based on the powerflow, directly at the secondary side of the transmission transformer. In this paper an investigation for the extent and model type of the downstream network (below 380 kV) is performed. A detailed model for an example downstream network is developed. Different simplifications and equivalent models are compared in frequency domain and in time domain, during cable energization. The impact of the lower voltage network on both the maximum overvoltage and the harmonic content during energization is assessed. Moreover, components that are of major importance are identified and proper equivalent models for the downstream network are proposed. Simulation results show that in particular the type of the 150 kV network (underground cable or overhead line) affects greatly both the maximum overvoltage and the harmonic content during energization. On the other hand, the parameters of end customer loads have only minor effect.

  • 222.
    Barf, Jochen
    Luleå tekniska universitet, Institutionen för system- och rymdteknik.
    Development and Implementation of an Image-Processing-Based Horizon Sensor for Sounding Rockets2017Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
  • 223. Barracó, Marc
    et al.
    Fernández, Enrique
    Torres, Ricardo
    López, José
    Bosch, Ricard
    Carlson, Johan
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Ultrasound monitoring of the setting of injectable bone cement biomaterials for spinal surgery applications2005Inngår i: Proceedings 2nd Annual European Rheology Conference, 2005, s. 133-133Konferansepaper (Fagfellevurdert)
  • 224. Bask, Michael
    Dynamic threshold generators for robust fault detection2005Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Detection of faults, such as clogged valves, broken bearings or biased sensors, has been brought more and more into focus during the last few decades. There are two main reasons why faults are important to detect at an early stage. Firstly, faults in safety critical applications, such as aircraft, nuclear reactors, cars and trains, may create risks of personal injuries. Secondly, faults in the manufacturing or process industry, e.g. flotation processes and steel plants, may cause decrease in quality or interruptions of production. A fault detection algorithm consists of two parts, the residual generator, which generates a residual, and the residual evaluator, which compares the residual, or a function of it, with a threshold to determine if a fault is present. The residual generation contains a process model and the residual can be described as a filtered difference between the measured and estimated process outputs. When no fault is present, the residual will be nonzero due to residual disturbances, i.e. measurement disturbances, process disturbances and model uncertainties. Therefore, the residual evaluation must be robust against these disturbances to avoid false alarms. Due to the model uncertainties, the residual is affected by the known input signals, which are, in general, time varying. To achieve a threshold that is as tight to the residual as possible, the threshold should also depend on the known input signals. To make this possible, parametric uncertainty in the process model is considered in this thesis. The dynamic threshold generator is introduced, a dynamic system whose output is the threshold and the inputs are the known process inputs. A dynamic threshold generator is developed for full-state measurement systems, assuming that the residual disturbances are constant and unknown but bounded. This dynamic threshold generator is then generalized to non-full state measurement systems with time-varying but bounded residual disturbances. Both generators depend on the unknown upper bounds of the residual disturbances. These upper bounds are replaced by design parameters, which are determined by minimizing the threshold for a set of fault free data. A nonlinear optimization solution is discussed. It is also shown that the residual generator state vector can always be parameterized such that the designing of the parameters can be done by linear optimization. A part of the generalized dynamic threshold generator is a system whose impulse response is an upper bound to another impulse response. Automatic methods to find realizable upper bounds are derived. To validate the methods in this thesis, two applications have been considered, detection of clogging in the valves of a flotation process and detection of faults in the compressor inlet temperature sensor of a jet engine.

  • 225. Bask, Michael
    On external model controller of vibrations2001Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    A promising way to increase the suppression of vibration in mechanical systems is to apply active damping instead of passive damping, which is most widespread today. An active damper system consists of an actuator, a controller and at least one sensor, usually an accelerometer. The sensor measures the vibration and sends the measurements further to the controller in order to calculate the necessary damping force to be fed back to the mechanical system. A number of questions arises regarding active damper design, namely how to construct the active damper, what kind of sensors to use and where to place them, how to model the vibration and the mechanical system itself, and, last but not least, how to design the controller. This licentiate thesis deals with the controller design issue. The most widely used controller in active vibration control is the Filtered-X Least Mean Square Controller and it is briefly reviewed in this thesis. The main focus of the thesis is however on another structure, the External Model Controller (EMC). The EMC has much more degrees of freedom than the Filtered-X Controller but lacks performance and robust stability analysis as well reliable design methods. The four papers included in the thesis contribute to bridging this gap.

  • 226. Bask, Michael
    et al.
    Johansson, Andreas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Linear optimization of parameters in dynamic threshold generators2005Inngår i: Proceedings of 16th IFAC World Congress: Prague, Czech Republic, July 3 - 8, 2005, Oxford: Elsevier, 2005Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A model-based fault detection algorithm for linear systems with uncertain parameters is treated. An error system, bilinear in the uncertainties, generates the residual. The residual is compared to a threshold, which is generated by a linear system with the unknown uncertainty upper bounds as parameters. These unknown uncertainty upper bounds can be substituted by design parameters and this article suggests an algorithm to choose design parameter values such that the threshold is larger than the residual when no fault is present. This parameter design algorithm is applied to a sensor fault detection algorithm for a jet engine.

  • 227. Bask, Michael
    et al.
    Johansson, Andreas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Model-based supervision of valves in a flotation process2003Inngår i: 42nd IEEE International Conference on Decision and Control, Piscataway, NJ: IEEE Communications Society, 2003, s. 744-749Konferansepaper (Fagfellevurdert)
    Abstract [en]

    An observer based approach for detecting clogging in valves in flotation processes is investigated. Integral action and linear feedback applied to a nonlinear process model constitutes the observer for which local stability is shown. The integral terms give estimates of the clogging in the valves of the process and this estimate is compared to a constant threshold. Experiments on real data from Boliden's flotation series at the Boliden Area Concentrator, Sweden, show no false alarm during any of the two working conditions, PI control and LQ control. It is also shown that cloggings, simulated by manipulating measurement data, are promptly detected. The observer based fault detection algorithm is compared to an algorithm based on parameter estimation and advantages of the two approaches are highlighted.

  • 228. Bask, Michael
    et al.
    Johansson, Andreas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Realizable upper bounds for the modulus of impulse responses2005Inngår i: SICE 2005 proceedings: SICE annual conference in Okayama : August 8-10, 2005 Okayama University, Japan, Tokyo: Society of Instrument and Control Engineers , 2005, s. 2045-2050Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This article treats the problem of finding a linear system whose impulse response is an upper bound for the modulus of the impulse response of another given system. These upper bounds are required for a newly developed fault detection algorithm1). Three different methods to calculate a realizable upper bound for an impulse response, which contains multiple real poles and distinct complex poles, are presented. The triangular inequality and linear optimization are used in the first and second method, respectively. In the third method, the original impulse response is used combined with time-delays. The upper bounds are calculated for a fictitious impulse response and compared with its modulus.

  • 229. Bask, Michael
    et al.
    Johansson, Andreas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Robust time-varying thresholds for supervision of valves in a flotation process2004Inngår i: 2004 43rd IEEE Conference on Decision and Control: Nassau, Bahamas, 14 - 17 December 2004, Piscataway, NJ: IEEE Communications Society, 2004, s. 4305-4310Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Robust thresholds for observer-based residuals are developed for the purpose of detecting clogging in the valves of a flotation process. The observer in the residual generator is a linear model of the flotation process extended with integrators and corrected with a linear feedback term. The integral states in the observer constitute the residual. Contribution to the residual comes not only from the faults but also from uncertainties in measurements, estimates and working point To avoid false alarms generated by these uncertainties, robust time-varying thresholds depending on the uncertainties are derived. Experiments on a froth flotation process with four cascade coupled tanks are carried out successfully. The data was provided by Boliden Area Concentrator in Boliden, Sweden.

  • 230. Bask, Michael
    et al.
    Medvedev, Alexander
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Analysis of least-squares state estimators for a harmonic oscillator2000Inngår i: Proceedings of the 39th IEEE Conference on Decision and Control: December 12 - 15, 2000, Sydney Convention and Exhibition Centre, Sydney, Australia, Piscataway, NJ: IEEE Communications Society, 2000, Vol. 4, s. 3819-3824Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The concept of least-squares observer is revisited. Robustness properties of this class of observers with respect to norm-bounded measurement noise are investigated and shown to be very much dependent on the operator chosen for the observer implementation. For the case of a harmonic oscillator, an explicit observer parameterization in terms of the implementation operator and the oscillator frequency is obtained, and observer's existence conditions are proven and analyzed

  • 231. Bask, Michael
    et al.
    Medvedev, Alexander
    External model controller for active vibration isolation1998Konferansepaper (Fagfellevurdert)
  • 232. Bask, Michael
    et al.
    Medvedev, Alexander
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    External model repetitive controller for active vibration isolation1999Inngår i: Proceedings of Active 99: International Symposium on Active Control of Sound and Vibration : an international INCE symposium, Fort Lauderdale, Florida, USA, 1999 December 02-04 / [ed] Scott Douglas, Washington, DC: Institute of noise control engineering , 1999, s. 177-188Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper deals with the External Model Repetitive Controller, a structure that combines the classical repetitive disturbance model (in the form of a time delay with a unit feedback) with a feedback of a disturbance estimate. The latter is often termed the External Model Controller and has a broad spectrum of technical applications, e.g., active vibration control. By analyzing the controller performance under the assumption of a disturbance period modeling error, it is shown that an unacceptable performance degradation might occur even for very small values of the modeling error

  • 233.
    Basu, Supratim
    et al.
    Bose Research (P) Ltd., Bangalore.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    A novel common power factor correction scheme for homes and offices2005Inngår i: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 20, nr 3, s. 2257-2263Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper explores the approach of having a common Power Factor Correction circuit for domestic and commercial loads. This leads to lower harmonic distortion without the need to install (expensive) active rectifiers in each end-user device. The need for power-factor correction as well as a number of design options is discussed in this paper. The design and cost estimation of a common Power Factor Correction scheme and some reliability issues are discussed

  • 234.
    Bazzocchi, Michael C. F.
    et al.
    University of Toronto, Institute for Aerospace Studies.
    De Decker, Nathan
    University of Liège.
    Emami, Reza
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Application of pseudo-equinoctial shaping to Near-Earth asteroid orbital transfer2017Inngår i: IEEE Aerospace Conference Proceedings, Piscataway, NJ: Institute of Electrical and Electronics Engineers (IEEE), 2017, artikkel-id 7943777Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper determines the near-optimal transfer trajectory of a Near-Earth Asteroid (NEA) to an orbit in the Earth-Moon system through the use of an ion beam redirection method. The ion beam method is a hovering approach to asteroid redirection. The method operates through the use of two diametrically opposed thrusters. The redirection mission targets Arjuna-type asteroids, and uses a sample asteroid, 2013 RZ53, to demonstrate the applicability of the pseudo-equinoctial shaping to asteroid orbital transfer. The asteroid transfer from its initial orbit about the Sun to its final orbit in the Earth-Moon system is divided into two phases using a patched conics approximation. The first phase includes the transfer of the asteroid from its initial orbit to an optimized rendezvous point with Earth. The second phase begins as soon as the asteroid arrives within the Earth's sphere of influence and ends with the transfer of the asteroid into a stable orbit about Earth and Moon. The pseudo-equinoctial shaping approach is employed during each phase, and determines the near-optimal solution for the lowest combined delta-v required to complete the orbital transfer. The pseudo-equinoctial method is a shape-based approach to trajectory design which assumes the trajectory transfer can be modelled as a variation of a conic arc. The transfer considers the eccentricity, inclination, and semi-major axis, as well as optimizes several free parameters, such as the thrust, the start of transfer and the rendezvous point with Earth. The optimization is completed using a genetic algorithm, and the results of the optimization are presented in terms of time of flight, thrust, number of revolutions, and delta-v. Lastly, the results are detailed and the feasibility of a redirection mission for an Arjuna-type asteroid is discussed.

  • 235.
    Bazzocchi, Michael C. F.
    et al.
    University of Toronto, Canada.
    Emami, M. Reza
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. University of Toronto, Canada.
    A Systematic Assessment of Asteroid Redirection Methods for Resource Exploitation2015Konferansepaper (Fagfellevurdert)
  • 236.
    Bazzocchi, Michael C. F.
    et al.
    Institute for Aerospace Studies, University of Toronto, Canada.
    Emami, M. Reza
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Institute for Aerospace Studies, University of Toronto, Canada.
    An Assessment of Multiple Spacecraft Formation for Asteroid Redirection2016Inngår i: Transactions of the Japan Society for Aeronautical and Space Sciences, Aerospace Technology Japan, E-ISSN 1884-0485, Vol. 14, nr ists30, s. Pk_137-Pk_146Artikkel i tidsskrift (Fagfellevurdert)
  • 237.
    Bazzocchi, Michael C. F.
    et al.
    Institute for Aerospace Studies, University of Toronto.
    Emami, M. Reza
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Institute for Aerospace Studies, University of Toronto.
    Asteroid Redirection Mission Evaluation Using Multiple Landers2018Inngår i: The Journal of the astronautical sciences, ISSN 0021-9142, Vol. 65, nr 2, s. 183-204Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, a low-thrust tugboat redirection method is assessed using multiple spacecraft for a target range of small near-Earth asteroids. The benefits of a landed configuration of tugboat spacecraft in formation are examined for the redirection of a near-Earth asteroid. The tugboat method uses a gimballed thruster with a highly collimated ion beam to generate a thrust on the asteroid. The target asteroid range focuses on near-Earth asteroids smaller than 150 m in diameter, and carbonaceous (C-type) asteroids, due to the volatiles available for in-situ utilization. The assessment focuses primarily on the three key parameters, i.e., the asteroid mass redirected, the timeframe for redirection, and the overall system cost. An evaluation methodology for each parameter is discussed in detail, and the parameters are employed to determine the expected return and feasibility of the redirection mission. The number of spacecraft employed is optimized along with the electrical power needed for each spacecraft to ensure the highest possible return on investment. A discussion of the optimization results and the benefits of spacecraft formation for the tugboat method are presented.

  • 238.
    Bazzocchi, Michael C. F.
    et al.
    Institute for Aerospace Studies, University of Toronto.
    Emami, Reza
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Application of asteroid redirection methods to orbital debris removal2016Inngår i: 2016 IEEE Aerospace Conference: AERO 2016, Big Sky, United States, 5 - 12 March 2016, Piscataway, NJ: IEEE Communications Society, 2016, artikkel-id 7500750Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper discusses the applicability of some of the asteroid redirection methods, prominently studied in the literature, to orbital debris removal. The tasks of asteroid redirection and orbital debris removal share the common goal of controlled redirection of an uncooperative target. Three asteroid redirection methods are systematically compared and analyzed to assess their viability for an orbital debris reentry mission, i.e., ion beam shepherd, laser sublimation, and tugboat. These methods are investigated in terms of the characteristics of the orbital debris population and based on the major criteria for mission design of controlled reentry of uncooperative objects. In addition, the uncertainty intrinsic to the orbital debris population is quantified through the use of a Monte Carlo simulation, which provides insight into the robustness of the methods for various ranges of orbital debris. The Analytical Hierarchy Process will be employed to assess the viability of each method in a logically consistent fashion, namely, through aggregation of the relative preference (of each method) and relative importance (of each criterion). The advantages and drawbacks of each redirection method are discussed in light of the assessment results for orbital debris reentry

  • 239.
    Bazzocchi, Michael C. F.
    et al.
    University of Toronto, Institute for Aerospace Studies.
    Emami, Reza
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. University of Toronto.
    Asteroid detumbling for redirection missions2018Inngår i: 2018 IEEE Aerospace Conference, IEEE Computer Society, 2018Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In order to accomplish most asteroid redirection missions, rotational control of the asteroid body is required. Small near-Earth asteroids tend to exhibit a significant range of rotational and tumbling properties. This work provides an analysis of asteroid detumbling using a formation of spacecraft. Through an orbiter and three landed thruster spacecraft, a low-thrust detumbling maneuver is performed on two illustrative asteroids. The asteroid scenarios are designed such that they reflect the characteristics of possible redirection scenarios. In particular the geometries, densities, angular velocities, and masses of the asteroids are adjusted according to available asteroid data to provide two unique redirection scenarios. The asteroid and spacecraft specifications are outlined, as well as the formulations for the detumbling maneuver. The results of the maneuver are discussed along with the key detumbling parameters and timeframe required.

  • 240.
    Bazzocchi, Michael C. F.
    et al.
    Institute for Aerospace Studies, University of Toronto.
    Emami, Reza
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Institute for Aerospace Studies, University of Toronto.
    Formation of Multiple Landers for Asteroid Detumbling2018Inngår i: Advances in Space Research, ISSN 0273-1177, E-ISSN 1879-1948, Vol. 62, nr 3, s. 732-744Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This work develops a method for ascertaining the landing locations and thruster orientations of a formation of multiple spacecraft on an irregular asteroid for discrete time optimal detumbling control, as a prerequisite to asteroid redirection. Asteroid geometries are known to be extremely irregular, especially for small asteroids, which are the typical targets for redirection missions. The method entails the modelling of asteroids as convex polyhedra with triangular facets, and computing the mass and inertial properties through the divergence theorem and Green’s theorem. Given the asteroid geometry, mass, and inertial properties, the feasible lander locations and thruster orientations are determined. The model ensures full attitude control of the asteroid, using multiple spacecraft with fixed-orientation, low-thrust modules, through measures imposed on the location and orientation of each thruster. A linear control scheme is employed to assess the time and fuel requirements of the asteroid detumbling maneuver, given feasible spacecraft formation configurations and thruster orientations. The method then assesses the detumbling time performance of each formation configuration to determine the discrete optimal landed formation configuration for a given asteroid. Simulations are performed to demonstrate the method using an irregular asteroid with characteristics derived from available asteroid data. Extensions of the method are further discussed in light of the results.

  • 241.
    Bazzocchi, Michael C. F.
    et al.
    Institute for Aerospace Studies, University of Toronto.
    Emami, Reza
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Institute for Aerospace Studies, University of Toronto.
    Low-thrust orbit transfer of Arjuna-type asteroids2016Inngår i: AIAA/AAS Astrodynamics Specialist Conference, 2016, American Institute of Aeronautics and Astronautics, 2016Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper investigates the accessible low-thrust transfer trajectories for a near-Earth asteroid transfer mission. The target asteroids considered are Arjuna type asteroids, which are characterized by their Earth-like orbital paths including low-eccentricity and low-inclination. The asteroid range is characterized by specific semi-major axes and transfer angles to provide an overall assessment of the potential Arjuna transfer domain. A single hovering ion beam spacecraft is employed for the task of asteroid redirection. The method utilizes a continuous thrust over the duration of the transfer maneuver to redirect the asteroid to an Earth bound orbit. The transfer model employs a minimized form of Gauss's variational equations to determine the available trajectories for asteroid redirection. The transfer model employs, in addition to the aforementioned orbital equations, spacecraft thruster and sizing metrics, as well as mission cost analysis formulae. The system parameters and orbital transfer paths are assessed with regards to key mission parameters, namely, timeframe for redirection, number of orbital revolutions, system mass, propellant mass, thrust, power, system cost, and financial return rate

  • 242.
    Bazzocchi, Michael C. F.
    et al.
    University of Toronto, Toronto, ON, Canada; Institute for Aerospace Studies, 4925 Dufferin Street, Canada.
    Emami, Reza
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. University of Toronto, Toronto, ON, Canada; Institute for Aerospace Studies, 4925 Dufferin Street, Canada.
    Study of Arjuna-Type Asteroids for Low-Thrust Orbital Transfer2018Inngår i: Journal of Spacecraft and Rockets, ISSN 0022-4650, E-ISSN 1533-6794, Vol. 55, nr 1, s. 37-48Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper investigates the accessible low-thrust transfer trajectories for a near-Earth asteroid transfer mission. The target asteroids considered are Arjuna-type asteroids, which are characterized by their Earth-like orbital paths including low eccentricity and low inclination. The asteroid range is characterized by a specific range of semimajor axes and transfer angles to provide an overall assessment of the potential Arjuna transfer domain. A single hovering ion beam spacecraft is employed for the task of asteroid redirection. The method uses a continuous thrust over the duration of the transfer maneuver to redirect the asteroid to an Earth-bound orbit. The transfer model employs a minimized form of Gauss's variational equations to determine the available trajectories for asteroid redirection. The transfer model employs, in addition to the aforementioned orbital equations, spacecraft thruster and sizing metrics as well as mission cost analysis formulae. The system parameters and orbital transfer paths are assessed with regard to key mission parameters, namely, time frame for redirection, number of orbital revolutions, system mass, propellant mass, thrust, power, system cost, and financial return rate

  • 243.
    Bazzocchi, Michael C.F.
    et al.
    Institute for Aerospace Studies, University of Toronto.
    Emami, Reza
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Comparative analysis of redirection methods for asteroid resource exploitation2016Inngår i: Acta Astronautica, ISSN 0094-5765, E-ISSN 1879-2030, Vol. 120, s. 1-19Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An in-depth analysis and systematic comparison of asteroid redirection methods is performed within a resource exploitation framework using different assessment mechanisms. Through this framework, mission objectives and constraints are specified for the redirection of an asteroid from a near-Earth orbit to a stable orbit in the Earth-Moon system. The paper provides a detailed investigation of five redirection methods, i.e., ion beam, tugboat, gravity tractor, laser sublimation, and mass ejector, with respect to their capabilities for a redirection mission. A set of mission level criteria are utilized to assess the performance of each redirection method, and the means of assigning attributes to each criterion is discussed in detail. In addition, the uncertainty in physical characteristics of the asteroid population is quantified through the use of Monte Carlo analysis. The Monte Carlo simulation provides insight into the performance robustness of the redirection methods with respect to the targeted asteroid range. Lastly, the attributes for each redirection method are aggregated using three different multicriteria assessment approaches, i.e., the analytical hierarchy process, a utility-based approach, and a fuzzy aggregation mechanism. The results of each assessment approach as well as recommendations for further studies are discussed in detail.

  • 244.
    Bazzocchi, Michael C.F.
    et al.
    Institute for Aerospace Studies, University of Toronto, Toronto, Ontario, Canada.
    Emami, Reza
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Stochastic optimization of asteroid three-dimensional trajectory transfer2018Inngår i: Acta Astronautica, ISSN 0094-5765, E-ISSN 1879-2030, Vol. 152, s. 705-718Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this work, an approach to designing near-optimal nonplanar transfer trajectories for asteroids is introduced, taking into account the uncertainty in asteroid parameters. The approach is demonstrated using a specific known Near-Earth Asteroid (NEA) as a model for the transfer scenario. The designed trajectory redirects the NEA from its current orbit about the Sun to a new orbit in the Earth-Moon system. The approach utilizes a low-thrust redirection method, namely the ion beam method, to execute the transfer; however, the work can be extrapolated to most low-thrust redirection methods. Asteroid parameters, such as absolute magnitude, albedo and density, are modelled, and a Monte Carlo analysis is employed to investigate the redirection maneuver in light of the expected variation in parameters. The trajectory transfer is modelled in three dimensions through the use of pseudo-equinoctial shaping, and is subsequently optimized. Due to the large design space created by the 21 decision variables, the optimization is parsed into two main steps; first, a global optimization that employs a genetic algorithm, followed by a local optimization that utilizes sequential quadratic programming to refine the result from the global optimization. Lastly, the results of the Monte Carlo analysis for the near-optimal trajectory transfer of the NEA are discussed.

  • 245.
    Becker, Tova
    Luleå tekniska universitet, Institutionen för system- och rymdteknik.
    Etiska och moraliska dilemman vid hantering av personlig information.2016Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
    Abstract [sv]

    I många tusen år har vad som anses vara etiskt försvarbart diskuterats. Allt fler perspektiv beaktas

    bland annat beroende på den tekniska utvecklingen. På senare tid har utvecklingen av de

    digitala medierna inneburit att personlig information värderas och hanteras på nya sätt. Tekniken

    innebär att nya möjligheter skapas samtidigt som det finns en risk att personlig information

    missbrukas. Detta kan påverka vad som är etiskt försvarbart.

    Detta arbete handlar om hur personlig information hanteras med hjälp av digital teknik. Det

    undersöks om användare av IT är medvetna om att deras personliga information samlas in,

    sprids och används för att skapa en mängd nya individuella tjänster. Det utforskas om denna

    hantering, samt de nya möjligheterna att individualisera tjänster, är något som skapar dilemma.

    Till sist sammanställs rekommendationer som framkommit under studien gällande

    vad enskilda individer kan göra om de vill minska riskerna för att personlig information missbrukas.

    Studien inleds med en litteraturgenomgång vilken belyser hur IT påverkat vårt samhälle samt

    hur personlig information hanteras med den nutida teknikens möjligheter.

    Det beskrivs bland annat:

     Hur företag samlar in användardata i bakgrunden utan att tydligt informera om det

     Att det finns profiler om oss alla

     Att den information vi får är anpassad till oss som individer

     Att personlig information finns lättillgänglig och sökbart för alla bland annat för arbetsgivare

    Etik och moral bör ligga till grund för alla resonemang som avser avgöra vad som är rätt och

    fel. Företagen har riktlinjer för hur de bör handla enligt etiska och moraliska principer. Det

    finns lagstiftning och regelverk som styr men informationshantering utvecklas snabbt och är

    global vilket gör situationen komplex. Tekniken utvecklas ofta snabbare än regelverket.

    Metoden för insamlande av empiri bestod av två delar. Primärdata samlades in via intervjuer

    och sekundärdata söktes via nätet och medier för att få aktuell data som underlag till intervjuerna.

    Intervjuerna genomfördes som semikonstruerade intervjuer där datorer användes som

    hjälpmedel för att exemplifiera data som fanns tillgänglig om respondenten. Den empiri som

    framkom från intervjuerna innehåller en bred beskrivning av ämnesområdet även om urvalsgruppen

    var liten. Insamlad data analyserades genom att notera och sammanställa svaren samt

    söka mönster och samband mellan olika teman i intervjun.

    Slutsatser sammanställdes vilka visar på att det finns oroväckande låg medvetenhet inom ämnesområdet.

    Slutsaterana innehåller också tre dilemman kopplade till hur den tekniska utvecklingen

    hanterar personlig information. Dessa är faktaresistens, kränkning av den personliga

    integriteten och utformning av lagar, avtal och normer. Sist sammanställs rekommendationer

    avsedda för de som vill minska riskerna med hantering av personlig information.

    I slutet diskuteras att det är först när allmänheten börjar reagera som en diskussion kan uppstå.

    Först då kan en eventuell förändring ske där en reglering som behandlar hur individer får beröras

    och hur tekniken får användas växer fram.

  • 246.
    Beckman, Claes
    et al.
    Department of Communications systems, School of ICT, Royal Institute of Technology, Kista.
    Borg, Johan
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Johansson, Jonny
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Tecsor, Irina
    Department of Communications systems, School of ICT, Royal Institute of Technology, Kista.
    Design considerations for the EISCAT-3D phased array antenna2014Inngår i: 2014 8th European Conference on Antennas and Propagation: (EuCAP); The Hague; Netherlands, 6 -11 April 2014, Piscataway, NJ: IEEE Communications Society, 2014, s. 1700-1704Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper presents a background and an overview of the initial design considerations for phased array antenna being designed for the New Generation multi-static, incoherent-scatter radar station - EISCAT-3D - in Northern Scandinavia. Its anticipated electrical, mechanical and environmental design requirements are given both by the physics as well as by the extreme climate in the subarctic region of northern Scandinavia

  • 247.
    Beek, Jaap van de
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Channel quality feedback schemes for 3GPP's Evolved-UTRA downlink2006Inngår i: IEEE GLOBECOM 2006: 2006 Global Telecommunications Conference; San Francisco, CA, USA, 27 November - 1 December 2006, Piscataway, NJ: IEEE Communications Society, 2006, artikkel-id 4151293Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Today's packet-based cellular systems typically are equipped with a channel quality reporting mechanism that supports scheduling and adaptive modulation/coding. When resources are scheduled not only In time but also In frequency the design of the return channel becomes intricate. The feedback signalling must balance improved cell-throughput with deteriorated spectral efficiency In the return link due to excessive signalling. In this contribution we examine system simulation results for the downlink of 3GPP's long-term evolution system equipped with various signalling schemes. The simulations results show that for a certain uplink load In bits/s/Hz, emphasizing the quality of the mobile's best channel instants (assigning these with more signalling bits) provides about 12% higher downlink throughput than capturing the quality of all channel Instants equally well. Moreover, about 95% of the throughput provided by an ideal reference feedback scheme Is obtained.

  • 248.
    Beek, Jaap van de
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Estimation of synchronization parameters1996Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This thesis deals with the estimation of synchronization parameters in {Orthogonal Frequency Division Multiplexing} (OFDM) communication systems and in active ultrasonic measuring systems. Estimation methods for the timing and frequency offset and for the attenuation taps of the frequency selective channel are presented and investigated.In OFDM communication systems the estimation of the timing offset of the transmitted data frame is one important parameter. This offset provides the receiver with a means of synchronizing its sampling clock to that of the transmitter. A second important parameter is the offset in the carrier frequency used by the receiver to demodulate the received signal.For OFDM systems using a cyclic prefix, the joint {Maximum Likelihood} (ML) estimation of the timing and carrier frequency offset is introduced. The redundancy introduced by the prefix is exploited optimally. This novel method is derived for a non-dispersive channel. Its performance, however, is also evaluated for a frequency-selective Rayleigh-fading radio channel. Time dispersion causes an irreducible error floor in this estimator's performance. This error floor is the limiting factor for the applicability of the timing estimator. Depending on the requirements, it may be used in either an acquisition or a tracking mode. For the frequency estimator the error floor is low enough to allow for stable frequency tracking.A low-complex variant of the timing offset estimator is presented allowing a simple implementation. This is the ML estimator, given a 2-bit representation of the received signal as the sufficient statistics. Its performance is evaluated for a frequency-selective Rayleigh-fading radio channel and for a twisted-pair copper channel. Simulations show this estimator to have a similar error floor as the full resolution ML estimator.The problem of estimating the propagation time of a signal is also of interest in active pulse echo systems, such as are used in, {\it e.g.}, radar, medical imaging, and geophysics. The {Minimum Mean Squared Error} (MMSE) estimator of arrival time is derived and investigated for an active airborne ultrasound measurement system. Besides performing better than the conventional {\it Maximum a Posteriori} (MAP) estimator, this method can be used to develop different estimators in situations where the system Signal to Noise Ratio (SNR) is unknown.Coherent multi-amplitude OFDM receivers generally need to compensate for a frequency selective channel in order to detect transmitted data symbols reliably. For this purpose, a channel equalizer needs to be fed estimates of the subchannel attenuations.The linear MMSE estimator of these attenuations is presented. Of all linear estimators, this estimator optimally makes use of the frequency correlation between the subchannel attenuations. Low-complex modified estimators are proposed and investigated. The proposed modifications cause an irreducible error floor for this estimator's performance, but simulations show that for SNR values up to 20~dB, the improvement of a modified estimator compared to the Least Squares (LS) estimator is at least 3~dB.

  • 249.
    Beek, Jaap van de
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    OFDM Spectral Precoding with Protected Subcarriers2013Inngår i: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558, Vol. 17, nr 12, s. 2209-2212Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A new precoder structure reduces an OFDM signal's out-of-band emission by tens of decibels while allowing a receiver to employ a classical OFDM channel estimator.

  • 250.
    Beek, Jaap van de
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Synchronization and channel estimation in OFDM systems1998Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This thesis addresses synchronization and channel estimation in OFDM communication systems. The joint maximum likliehood estimator of symbol time and carrier frequency offsets for OFDM systems using a cyclic prefix is presented. This estimator exploits the redundancy introduced by the prefix and does not require extra pilot information. Signal models, accounting for pulse shaping, channel dispersion, or slowly changing synchronization errors and the associated maximum likliehood estimators are presented. Tracking synchronization of a multiuser OFDM system, which often has been questioned, is feasible using a scheme incorporating the above estimator concept. Furthermore, this thesis analyzes channel estimators based on the discrete Fourier transform. The symbol error rate of systems employing these estimators may experience an irreducible error floor. A novel channel estimation concept using singular-value decomposition of the channel attenuations is presented. These channel estimators, designed with suitably chosen fixed design parameters, combine low-complexity and high performance.

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