Ändra sökning
Avgränsa sökresultatet
1234567 1 - 50 av 383
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf
Träffar per sida
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sortering
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
Markera
Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
  • 1.
    Alvarez Perez, Manuel Alejandro
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Rönnberg, Sarah
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bermúdez, Juan
    Universidad Simón Bolívar.
    Zhong, Jin
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap. The University of Hong Kong.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    A Generic Storage Model Based on a Future Cost Piecewise-Linear Approximation2019Ingår i: IEEE Transactions on Smart Grid, ISSN 1949-3053, E-ISSN 1949-3061, Vol. 10, nr 1, s. 878-888Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This work presents a generic storage model (GSM) inspired by the scheduling of hydraulic reservoirs. The model for steady state short-term (ST) operational studies interlaces with the long-term (LT) energy scheduling through a piecewise-linear Future Cost Function (FCF). Under the assumption that a Stochastic Dual Dynamic Programming (SDDP) approach has been used to solve the energy schedule for the LT, the FCF output from that study will be processed to obtain an equivalent marginal opportunity cost for the storage unit. The linear characteristic of a segment of the future cost function (FCF) will allow a linear modeling of the storage unit production cost. This formulation will help to coordinate the renewable resource along with storage facilities in order to find the optimal operation cost while meeting end-point conditions for the long-term plan of the energy storage. The generic model will be implemented to represent a battery storage and a pumped-hydro storage. A stochastic unit commitment (SUC) with the GSM will be formulated and tested to assess the day-ahead scheduling strategy of a Virtual Power Plant (VPP) facing uncertainties from production, consumption, and market prices.

  • 2.
    Lennerhag, Oscar
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    A power system model for resonance studies2019Konferensbidrag (Refereegranskat)
  • 3.
    Laury, John
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Abrahamsson, Lars
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    A rotary frequency converter model for electromechanical transient studies of 16 (2/3) Hz railway systems2019Ingår i: International Journal of Electrical Power & Energy Systems, ISSN 0142-0615, E-ISSN 1879-3517, Vol. 106, s. 467-476Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Railway power systems operating at a nominal frequency below the frequency of the public grid (50 or 60 Hz) are special in many senses. One is that they exist in a just few countries around the world. However, for these countries such low frequency railways are a critical part of their infrastructure.

    The number of published dynamic models as well as stability studies regarding low frequency railways is small, compared to corresponding publications regarding 50 Hz/60 Hz public grids. Since there are two main type of low frequency railways; synchronous and asynchronous, it makes the number of available useful publications even smaller. One important reason for this is the small share of such grids on a global scale, resulting in less research and development man hours spent on low frequency grids.

    This work presents an open model of a (synchronous-synchronous) rotary frequency converter for electromechanical stability studies in the phasor domain, based on established synchronous machine models. The proposed model is designed such that it can be used with the available data for a rotary frequency converter.

    The behaviour of the model is shown through numerical electromechanical transient stability simulations of two example cases, where a fault is cleared, and the subsequent oscillations are shown. The first example is a single-fed catenary section and the second is doubly-fed catenary section.

  • 4.
    Nömm, Jakob
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Rönnberg, Sarah
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    An analysis of voltage quality in a nanogrid during islanded operation2019Ingår i: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 12, nr 4, artikel-id 614Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Voltage quality data has been collected in a single house nanogrid during 48 weeks of islanded operation and 54 weeks of grid-connected operation. The voltage quality data contains the voltage total harmonic distortion (THD), odd harmonics 3 to 11 and 15, even harmonics 4 to 8, voltage unbalance, short-term flicker severity (Pst) and long-term flicker severity (Plt) values, and voltage variations at timescales below 10 min. A comparison between islanded and grid-connected operation values was made, were some of the parameters were compared to relevant grid standard limits. It is shown that some parameters exceed the defined limits in the grid-standards during islanded operation. It was also found that the islanded operation has two modes of operation, one in which higher values of the short circuit impedance, individual harmonic impedance, harmonic voltage distortion and voltage unbalance were reached.

  • 5.
    Lennerhag, Oscar
    et al.
    Independent Insulation Group Sweden AB, Ludvika, Sweden.
    Lundquist, Jan
    Independent Insulation Group Sweden AB, Ludvika, Sweden.
    Engelbrecht, Christiaan
    Engelbrecht Consulting B.V., The Netherlands.
    Karmokar, Tanumay
    NKT HV Cables AB, Lyckeby, Sweden.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap. Engineering Sciences and Mathematics, Luleå University of Technology, Skellefteå, Sweden.
    An Improved Statistical Method for Calculating Lightning Overvoltages in HVDC Overhead Line/Cable Systems2019Ingår i: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 12, nr 16, artikel-id 3121Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    HVDC cable systems connected to HVDC overhead lines are subject to fast front overvoltages emanating from the line when lightning strikes a shield wire (backflashover) or a pole conductor (shielding failure). Representative fast front overvoltage levels for HVDC cable systems are usually established without considering their statistical characteristics. A statistical method to determine overvoltages related to the acceptable mean time between failure (MTBF) for the cable system was developed previously. The method accounts for the statistical distribution of lightning current magnitudes as well as the attenuation of the overvoltage wave due to corona discharges on the line, since this effect dominates for system voltages up to about ±320 kV. To make the method suitable for higher system voltages as well, this article introduces an improved statistical method which also accounts for surge attenuation through resistive effects, soil ionization, and statistical treatment of overvoltages due to shielding failures. To illustrate the improved method, it is applied to a case study for a ±525 kV DC line. 

  • 6.
    Sierra-Fernández, J.-M.
    et al.
    University of Cádiz, Algeciras, Spain.
    Rönnberg, Sarah
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    De La Rosa, J.-J.G
    University of Cádiz, Algeciras, Spain.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Palomares-Salas, J.-C.
    University of Cádiz, Algeciras, Spain.
    Application of spectral kurtosis to characterize amplitude variability in power systems' harmonics2019Ingår i: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 12, nr 1, artikel-id en12010194Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The highly-changing concept of Power Quality (PQ) needs to be continuously reformulated due to the new schemas of the power grid or Smart Grid (SG). In general, the spectral content is characterized by their averaged or extreme values. However, new PQ events may consist of large variations in amplitude that occur in a short time or small variations in amplitude that take place continuously. Thus, the former second-order techniques are not suitable to monitor the dynamics of the power spectrum. In this work, a strategy based on Spectral Kurtosis (SK) is introduced to detect frequency components with a constant amplitude trend, which accounts for amplitude values' dispersion related to the mean value of that spectral component. SK has been proven to measure frequency components that follow a constant amplitude trend. Two practical real-life cases have been considered: Electric current time-series from an arc furnace and the power grid voltage supply. Both cases confirm that the more concentrated the amplitude values are around the mean value, the lower the SK values are. All this confirms SK as an effective tool for evaluating frequency components with a constant amplitude trend, being able to provide information beyond maximum variation around the mean value and giving a progressive index of value dispersion around the mean amplitude value, for each frequency component. 

  • 7.
    Ravindran, Vineetha
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Busatto, Tatiano
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Rönnberg, Sarah
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Meyer, Jan
    Technische Universität, Dresden, Germany.
    Charactizations of interactions between PV and Energy efficient lighting (LED) in a mixed installation.2019Konferensbidrag (Refereegranskat)
    Abstract [en]

    The possible interactions between grid-tied powerelectronicbased PV systems and energy efficient LEDlighting systems in terms of current and voltage, fordifferent combinations of the inverter and LED lamp typesunder different grid conditions, are studied in a laboratoryenvironment. In this paper, the interactions arecharacterized in terms of the power quality disturbanceslike harmonics, interharmonics, supraharmonics,overvoltage, undervoltage, and rapid voltage changes.

  • 8.
    Ravindran, Vineetha
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Busatto, Tatiano
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Rönnberg, Sarah
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Comparison of a non-parametric and parametric method for interharmonic estimation in PV systems2019Konferensbidrag (Refereegranskat)
    Abstract [en]

    A comparative analysis of ‘Desynchronized processing technique’ (non-parametric) and ‘Sliding window ESPRIT method’ (parametric) for interharmonic estimation in PV systems is carried out. Both methods were applied to field measurements and semi-measured signals to test their feasibility under different conditions. In Desynchronized processing technique, in the second stage of estimation, a Short-term Fourier transform was used to address the time-varying nature of interharmonics. In Sliding window ESPRIT method, the signal subspace dimension was fixed in all analysed cases. An adaptive algorithm was used to find the best rank of the Hankel matrix and apt order of the filter to ensure stability. A set of critical parameters affecting the performance of these methods in interharmonic estimation are identified. This paper emphasizes the significance of using appropriate methods for accurate interharmonic estimation and also demonstrates through the illustrated results that different inferences can be drawn for the same measurements analysed using different methods.

  • 9.
    Hajeforosh, Seyede Fatemeh
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Abrahamsson, Lars
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Dynamic Line Rating Operational Planning: Issues and Challenges2019Ingår i: Proc. of the 25th International Conference on Electricity Distribution (CIRED 2019), AIM , 2019, artikel-id 1957Konferensbidrag (Refereegranskat)
    Abstract [en]

    Network operational planning aims to provide smart and cost effective solutions to postpone conventional transmission and sub-transmission expansion. One emerging measure of improving the efficiency of power lines utilization is Dynamic Line Rating (DLR). DLR has to deal with different uncertainties ranging from production and consumption to meteorological variabilities. This paper presents the application of DLR from operational planning viewpoints and reviews relevant works. It also addresses DLR protection and challenges that the power system has to cope with.

  • 10.
    Ahmed, Kazi Main Uddin
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Sutaria, Jil
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Rönnberg, Sarah
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Electrical Energy Consumption Model of Internal Components in Data Centers2019Konferensbidrag (Refereegranskat)
    Abstract [en]

    In the context of modern information technology (IT) industry, cloud computing is gaining popularity for big data handling. Therefore, IT service providers like Google, Facebook and Amazon are expanding their technical resources by building data centers to improve the data processing and data storage facilities under cloud service pattern. However, data centers consume a large amount of electrical energy. In recent years, a lot of research has been done to reduce the electrical energy consumption of data centers by high performance computing. However, very few researchers have focused on the electrical energy consumption by the electrical components inside the data center. In this paper, a component based electrical energy consumption modelling approach is presented to identify the losses of different components as well as their interactions to the total electrical energy consumption of the data center. The electrical energy consumption models of servers and other components are presented as a function of server utilization.

  • 11.
    Abrahamsson, Lars
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Laury, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Evaluating a constant-current load model through comparativetransient stability case studies of a synchronous-synchronous rotary frequencyconverter fed railway2019Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper continues the pursuit of getting a deeperunderstanding regarding the transient stability of lowfrequencyAC railway power systems operated at 162⁄3 Hzsynchronously to the public grid. The focus is set on theimpact of different load models. A simple constant-currentload model is proposed and compared to a previously proposedand studied load model in which the train’s activepower is regulated.The study and comparison is made on exactly the samecases as and grid as with the already proposed and moreadvanced load model. The railway grid is equipped witha low-frequency AC high-voltage transmission line whichis subjected to a fault. The study is limited to railwaysbeing fed by different distributions of RFC (Rotary FrequencyConverter) types. Both AT (auto transformer) andBT (booster transformer) catenaries are considered.The RFC dynamic models are essentially Anderson-Fouad models of two synchronous machines coupled mechanicallyby their rotors being connected to the same shaft.The differences in load behaviour between the proposedconstant-current load model and the previously proposedand studied voltage-dependent active power load model areanalyzed and described in the paper.

  • 12.
    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 Labelling2019Konferensbidrag (Refereegranskat)
  • 13. Laury, John
    et al.
    Abrahamsson, Lars
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Impact of reduced share of rotary frequency converter in a low-frequency synchronous railway grid: A transient stability study.2019Konferensbidrag (Refereegranskat)
  • 14.
    Busatto, Tatiano
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Larsson, Anders
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Rönnberg, Sarah
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Including Uncertainties from Customer Connections in Calculating Low-Voltage Harmonic Impedance2019Ingår i: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 34, nr 2, s. 606-615Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A method is proposed in this paper to determine the harmonic impedances in low-voltage networks in a stochastic way. The consequences of resonances for harmonic propagation and stability of power converters are summarized. By using Monte Carlo simulation, the method includes the uncertainties in customer impedances, specifically due to electronic loads and local generation. The uncertainty in customer impedance is included by considering probability distribution for the resistive, inductive and capacitive parts of the impedance. The concept of transfer impedance is used for phase-to-neutral connections. A method is developed and applied to two existing low-voltage networks in Sweden. Results show that, for these two networks, the resonant frequencies decrease around 28 % once PV panels are installed. The paper includes a discussion of some of the practical aspects of applying the proposed method.

  • 15.
    Sakar, Selcuk
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Rönnberg, Sarah
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Interferences in AC-DC LED Drivers Exposed to Voltage Disturbances in the Frequency Range 2 kHz - 150 kHz2019Ingår i: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 34, nr 11, s. 11171-11181Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    LED lamps are both potential victims and sources of electromagnetic disturbances in the frequency range between 2 kHz and 150 kHz (“supraharmonics”). Immunity tests for this frequency range are important due to possible performance degradation of light intensity with LED lamps. In this paper, the impact of supraharmonics (SHs) on light intensity from LED lamps has been analyzed. LED lamps have been exposed to supraharmonic test profiles based on IEC 61000-4-19. Three phenomena that impact light intensity metrics have been observed and explained by models: (1) earlier conduction/later blocking caused by supraharmonic voltage, (2) intermittent conduction depending on the supraharmonic impedance of the LED driver and (3) reverse-recovery current of the diodes at higher frequency. It is observed that impact on the light intensity metrics shows up around the beginning and end of the conduction period. The results reveal that the profile of the supraharmonic voltage could cause deviations in the modulation depth and the average light intensity. The immunity of LED lamps against SHs shall be further studied and discussed by research groups and standard committees.

  • 16.
    Ravindran, Vineetha
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Rönnberg, Sarah
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Interharmonics in PV systems: A Review of analysis and estimation methods; considerations for selection of an apt method2019Ingår i: IET Renewable Power Generation, ISSN 1752-1416, E-ISSN 1752-1424, Vol. 13, nr 12, s. 2023-2032Artikel, forskningsöversikt (Refereegranskat)
    Abstract [en]

    A comprehensive reviewing of existing interharmonic analysis and estimation methodologies irrespective of application is carried out. The paper is enlisting the characteristics of an appropriate method to analyse and estimate interharmonics in PV systems, and linking these characteristics with the features of the reviewed methodologies. The distinctive characteristics of interharmonic emissions related to PV systems are therefore presented. The various methodologies are classified, summarized, and a checklist is prepared to emphasize the areas to be paid attention to while establishing an apt method for interharmonic analysis in PV systems. The priorities for selection of a method by a practicing engineer vary case by case. This paper will serve as a guideline for selection and further development of a suitable method for interharmonic analysis in a PV included power system.

  • 17.
    Sakar, Selcuk
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Rönnberg, Sarah
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Light intensity immunity performance of LED street lamps under power quality disturbances2019Konferensbidrag (Refereegranskat)
    Abstract [en]

    An increasing application of LED street lamps brings out an important question regarding their immunity against power quality disturbances. The behaviour of commonly used lighting equipment such as incandescent lamps, compact fluorescent lamps (CFL), and gas-discharge lamps is known. However, knowledge on immunity of LED based lighting equipment is still limited, particularly in street lighting aspect. In this paper, immunity of LED street lamps is determined for voltage dips, short interruptions, voltage fluctuations and supraharmonics. A series of experiments has been performed with respect to test levels defined in IEC 61000-4-11, IEC 61000-4-15 and IEC 61000-4-19. Voltage dips and short interruptions cause higher short-term light flicker severity values that might lead to unintended consequences for car drivers and pedestrians. Interharmonics can result in light flicker, but the impact is very limited, only one lamp exceeds the limits. Supraharmonics impact the current but have minor impact on the visible light. The supraharmonic current can be 25 times nominal. This could decrease the lifetime of equipment

  • 18.
    Mulenga, Enock
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Etherden, Nicholas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap. Vattenfall AB.
    Overvoltage due to single-phase and three-phase connected PV2019Ingår i: 25th International Conference on Electricity Distribution, Madrid, 3-6 June 2019., CIRED - Congrès International des Réseaux Electriques de Distribution, 2019, s. 1-5, artikel-id No 370Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper presents the overvoltage caused by single and three-phase connected PV to a low-voltage distribution grid. Statistics are obtained based on source-impedance data for 40 000 customers. A stochastic approach is applied to a 28-customer low-voltage network and the probability of overvoltage is assessed. It is shown that the voltage rise due to single-phase connected PV is six times the rise for three-phase connected PV.To mitigate the overvoltage, grid-reinforcement, reactive power compensation, curtailment and coordinated connection of PV can be used. It is shown that reactive compensation is not effective in LV grids due to high R/X ratio. Coordinated connection helps in reducing the overvoltages caused by single-phase PV.Policy suggestions towards three-phase PV installations and coordinated single-phase PV connections are included in the paper.

  • 19.
    Sutaria, Jil
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Ahmed, Kazi Main Uddin
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Rönnberg, Sarah
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Propagation of Supraharmonics through EMI Filters with Varying Loads2019Konferensbidrag (Refereegranskat)
  • 20.
    Schwanz, Daphne
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Larsson, Anders
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Secondary Harmonic Emission in Wind Power Plants,2019Konferensbidrag (Refereegranskat)
  • 21.
    de Oliveira, Tiago Elias Castelo
    et al.
    Electrical Energy Systems, Technological University of Eindhoven, Eindhoven, The Netherlands.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Ribeiro, Paulo Fernando
    Advanced Power Technologies and Innovations in Systems and Smart Grids Group, Federal University of Itajuba, Itajuba, Brazil.
    de Carvalho, Pedro M. S.
    Energy Scientific Area, Instituto Superior Tecnico, Lisbon, Portugal.
    Zambroni, Antônio C.
    Advanced Power Technologies and Innovations in Systems and Smart Grids Group, Federal University of Itajuba, Itajuba, Brazil.
    Bonatto, Benedito D.
    Advanced Power Technologies and Innovations in Systems and Smart Grids Group, Federal University of Itajuba, Itajuba, Brazil.
    The Concept of Dynamic Hosting Capacity for Distributed Energy Resources: Analytics and Practical Considerations2019Ingår i: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 12, nr 13, artikel-id 2576Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The hosting capacity approach is presented as a planning, improving, and communication tool for electrical distribution systems operating under specific uncertainties, such as power quality issues, power stabilities, and reliability, among others. In other words, it is an important technique, when renewable sources are present, to answer the amount of power that is possible to supply to the system without trespassing power performance limits. However, the power flow in a distribution system, for instance, can change throughout time due to the penetration of distributed generation, as well as load consumption. Based on the dynamic nature existing in distribution grids nowadays, it is important to highlight that the hosting capacity should not be calculated in a specifically chosen time only, but must be analyzed throughout a period of time. Thus, this paper introduces an extended concept of hosting capacity in relation to an integrated impact of harmonic voltage distortion and voltage rise as a function of time for daily, weekly, monthly, or even yearly periods. This extended concept is named as Dynamic Hosting Capacity (DHC(t)). General aspects of DHC(t) are demonstrated via measured data on a photovoltaic system (PV) connected at a low-voltage (LV) side of a university building.

  • 22.
    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 turbine2019Konferensbidrag (Refereegranskat)
  • 23.
    Mulenga, Enock
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Etherden, Nicholas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap. Vattenfall AB.
    The Role of Aleatory and Epistemic Uncertainties in a Stochastic Hosting Capacity Approach for Solar PV2019Ingår i: IEEE PES Innovative Smart Grid Technologies (ISGT), Bucharest: IEEE, 2019, s. 1-5, artikel-id 133Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper introduces the terms aleatory and epistemic uncertainties for use in a stochastic hosting capacity method. The role these uncertainties play in the hosting capacity determination is illustrated. It is shown that distinction between aleatory (statistical) and epistemic (systematic) uncertainties is helpful to characterize the probability distributions correctly. For epistemic uncertainties, it is often challenging to obtain information on the probability distribution function. For aleatory uncertainties, a method for characterizing the probability distribution is presented. Aleatory uncertainties’ data measurements are used to obtain a distribution best-fit. The background voltage measurement for a customer in a low-voltage distribution network is used to illustrate the method. Values were obtained for the distribution functions of the three-phase voltages. The used distribution functions are found to influence the resulting hosting capacity. This entails that there is need for measurements and data collection. A research challenge remaining concerns the stochastic model of epistemic uncertainty.

  • 24.
    Ravindran, Vineetha
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Busatto, Tatiano
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Rönnberg, Sarah
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Meyer, Jan
    Institute of Electrical Power Systems and High Voltage Engineering, Technische Universitaet Dresden, Dresden, Germany.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Time-varying interharmonics in different types of grid-tied PV inverter systems2019Ingår i: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Widely existing circuit topologies and inverter control strategies for PV systems allow customer flexibility but also introduce different kinds of interharmonics into the grid. A complete understanding of interharmonics from PV systems, with reasons behind their origin, remains needed. In addition, the timevarying nature of interharmonics and the potential impacts on other equipment are yet to be understood. In this paper, laboratory and field measurements are presented of seven different inverter types at multiple locations. A comprehensive analysis is performed to understand the existence, persistence, and propagation of interharmonics in PV systems on the DC side as well as grid side for different power levels. The origins of the interharmonics are established with experimental evidence and through a comparative analysis. A rural low voltage 6 customer network, with two different impedance profiles caused by the installation of PV, is considered to show the potential impact on customer voltage. To address the time-varying nature of interharmonics, a sliding window ESPRIT method is preferred over FFT based methods

  • 25.
    Bollen, Math
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Rönnberg, Sarah
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Typical harmonic levels and spectra with low-voltage customers2019Konferensbidrag (Refereegranskat)
  • 26.
    Alvarez, Manuel
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Rönnberg, Sarah
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Frías, Pablo
    Comillas Pontifical University, Madrid, Spain.
    Cossent, Rafael
    Comillas Pontifical University, Madrid, Spain.
    Jabr, Rabih
    American University of Beirut, Beirut, Lebanon.
    Zhong, Jin
    The University of Hong Kong, Hong Kong, China.
    A Capacity Mechanism Design for Distribution Network Expansion Planning2018Ingår i: 2018 IEEE International Conference on Environment and Electrical Engineering and 2018 IEEE Industrial and Commercial Power Systems Europe (EEEIC / I&CPS Europe), 2018, artikel-id 8493874Konferensbidrag (Refereegranskat)
    Abstract [en]

    Capacity remuneration mechanisms have been originally oriented to ensure availability and continuity of supply on the power generation pool. Equivalent generation-based capacity mechanisms could be implemented to enhance and prolong the usability of the distribution grid. In particular, such capacity mechanisms would provide an alternative to traditional expansion options leading to investment deferral. In this work, a distribution capacity mechanism to fit within a distribution network planning methodology will be proposed and discussed. The capacity mechanism will be outlined following similar guidelines as for the design of capacity mechanisms used in the energy only market. The result of the design is a volume based capacity auction for a capacity-constrained system, oriented to both the active and the reactive power provision.

  • 27.
    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 classification2018Ingår i: Proceedings of International Conference on Harmonics and Quality of Power, ICHQP, Piscataway, NJ: Institute of Electrical and Electronics Engineers (IEEE), 2018Konferensbidrag (Refereegranskat)
    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.

  • 28.
    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 Classification2018Ingår i: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 33, nr 6, s. 2794-2802Artikel i tidskrift (Refereegranskat)
    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.

  • 29.
    Schwanz, Daphne
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Busatto, Tatiano
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Larsson, Anders
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    A stochastic study of harmonic voltage distortion considering single-phase photovoltaic inverters2018Ingår i: Proceedings of International Conference on Harmonics and Quality of Power, ICHQP, Piscataway, NJ: Institute of Electrical and Electronics Engineers (IEEE), 2018Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper, the hosting capacity considering harmonic distortion is estimated for single-phase-connected photovoltaic inverters (PVIs) in low-voltage distribution networks. A stochastic approach is used to calculate the harmonic voltage distortion with each customer in the network. The method has been applied to a 6-customer network for the connection of 2.5-kW single-phase PVIs with and without harmonic voltage background. From the results, it was observed that the contribution from 2.5 kW single-phase photovoltaic inverters to the individual harmonic distortion will not cause the established limits to be exceeded. Also, that the harmonic voltage background is often dominating and should be continuously observed.

  • 30.
    Nömm, Jakob
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Rönnberg, Sarah
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    An Analysis of Frequency Variations and its Implications on Connected Equipment for a Nanogrid during Islanded Operation2018Ingår i: Energies, ISSN 1996-1073, E-ISSN 1996-1073, artikel-id en11092456Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Frequency, voltage and reliability data have been collected in a nanogrid for 48 weeks during islanded operation. Frequency values from the 48 week measurements were analyzed and compared to relevant limits. During 19.5% of the 48 weeks, the nanogrid had curtailed the production due to insufficient consumption in islanded operation. The curtailment of production was also the main cause of the frequency variations above the limits. When the microgrid operated on stored battery power, the frequency variations were less than in the Swedish national grid. 39.4% of all the interruptions that occurred in the nanogrid are also indirectly caused by the curtailment of solar production. Possible solutions for mitigating the frequency variations and lowering the number of interruptions are also discussed.

  • 31.
    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 grids2018Ingår i: 2017 IEEE PES Innovative Smart Grid Technologies Conference Europe, ISGT-Europe 2017: proceedings, New York: Institute of Electrical and Electronics Engineers (IEEE), 2018Konferensbidrag (Refereegranskat)
    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.

  • 32.
    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 model2018Ingår i: 2017 IEEE PES Innovative Smart Grid Technologies Conference Europe, ISGT-Europe 2017: proceedings, New York: Institute of Electrical and Electronics Engineers (IEEE), 2018Konferensbidrag (Refereegranskat)
    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.

  • 33.
    Bollen, Math
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Rönnberg, Sarah
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Zavoda, Francisc
    IREQ (HQ), Varennes.
    Langella, Roberto
    Second University of Naples.
    Djokic, Sasa
    University of Edinburgh.
    Cuifo, Philip
    University of Wollongong.
    Meyer, Jan Christian
    Technische Universitaet Dresden.
    Cuk, Vladimir
    Eindhoven University of Technology.
    Consequences of Smart Grids for Power Quality Overview of the Results from CIGRE Joint Working Group C4.24/CIRED2018Ingår i: 2017 IEEE PES Innovative Smart Grid Technologies Conference Europe, ISGT-Europe 2017: proceedings, New York: Institute of Electrical and Electronics Engineers (IEEE), 2018Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper gives an overview of the expected unintended (negative) consequences for power quality of several on-going developments in the power system. Four developments directly related to smart-grid technology are covered: microgrids; advanced voltage control; feeder reconfiguration; and demand-side management. Four developments indirectly related are also covered: new sources of electricity production; increased used of active power-electronic converters; shift from overhead lines to cables; and new types of lighting. The paper summarizes the discussions in an international working group and presents the main findings are recommendations.

  • 34.
    Busatto, Tatiano
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Ravindran, Vineetha
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Larsson, Anders
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Estimation of the Consumer Electronics Capacitance for Harmonic Resonance Studies by a Non-Invasive Measurement Method2018Ingår i: Proceedings of International Conference on Harmonics and Quality of Power, ICHQP, Piscataway, NJ: Institute of Electrical and Electronics Engineers (IEEE), 2018, , s. 6Konferensbidrag (Refereegranskat)
    Abstract [en]

    Harmonic resonances in distribution systems are mainly between network inductances and shunt capacitances from capacitor banks and consumer loads. In this paper, particular attention is devoted to the evaluation of capacitances from domestic equipment, serving as a reference for resonance frequency studies. The assessment is performed by simulation and measurements of common low power electronic loads. From the analysis of EMI filters topologies used in AC/DC converters, a non-invasive capacitance measurement estimation method is presented. The method is verified after correlating capacitances with the resonance frequencies obtained from a frequency sweep method. From experimental measurements, the results show that the equivalent shunt capacitances for a set of 24 LED lamps are between 10 and 135 nF.

  • 35.
    Abrahamsson, Lars
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Laury, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Further studies on the transient stability of synchronous-synchronous rotary frequency converter fed railways with low-frequency AC high-voltage transmission2018Ingår i: International Journal of Energy Production and Management, ISSN 2056-3272, E-ISSN 2056-3280, Vol. 3, nr 4, s. 266-276Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper continues the pursuit of getting a deeper understanding regarding the transient stability of low-frequency AC railway power systems operated at 16 2/3 Hz that are synchronously connected to the public grid. Here, the focus is set on such grids with a low-frequency AC high-voltage transmission line subject to a fault. The study here is limited to railways being fed by different distributions of Rotary Frequency Converter (RFC) types. Both auto transformer (AT) and booster transformer (BT) catenaries are considered. No mixed model configurations in the converter stations (CSs) are considered in this study. Therefore, only interactions between RFCs in different CSs and between RFCs, the fault, and the load can take place in this study. The RFC dynamic models are essentially two Anderson-Fouad models of synchronous machines coupled mechanically by their rotors being connected to the same mechani- cal shaft. Besides the new cases studied, also a new voltage-dependent active power load model is presented and used in this study.

  • 36.
    Nömm, Jakob
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Rönnberg, Sarah
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Harmonic Voltage Measurements in a Single House Microgrid2018Ingår i: Proceedings of International Conference on Harmonics and Quality of Power, ICHQP, Piscataway, NJ: Institute of Electrical and Electronics Engineers (IEEE), 2018Konferensbidrag (Refereegranskat)
    Abstract [en]

    The harmonic voltage distortion have been measured in a single house microgrid in Sweden. The microgrid can operate in both islanded mode and grid connected mode. A comparison of the voltage harmonic magnitudes has been made between the two operation states and also against relevant standards. Both the 10 minute average and the 3 second average values are presented in the paper. The harmonic voltage magnitudes are higher during island mode and the difference between the 10 minute value and 3 second value is also greater compared to when the microgrid is connected to the grid. At some instances the magnitudes of both total harmonic distortion and of individual harmonics exceed the limits described in the standards.

  • 37.
    Cundeva, Snezana
    et al.
    University Ss. Cyril and Methodius Faculty of Electrical Engineering and IT Skopje.
    Krkoleva Mateska, Aleksandra
    University Ss. Cyril and Methodius Faculty of Electrical Engineering and IT Skopje.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Hosting capacity of LV residential grid for uncoordinated ev charging2018Ingår i: Proceedings of International Conference on Harmonics and Quality of Power, ICHQP, Piscataway, NJ: Institute of Electrical and Electronics Engineers (IEEE), 2018Konferensbidrag (Refereegranskat)
    Abstract [en]

    The envisaged large penetration of electric vehicles (EVs) in the near future, brings new challenges to low voltage (LV) and medium voltage (MV) grids. For uncoordinated EV charging, the impact on the LV grid may be significant, due to the simultaneity between the residential power peak and the charging of EVs. The amount of EV chargers that can be connected to the grid without endangering the reliability or voltage quality for other customers is called the hosting capacity. This paper presents the analyses of the hosting capacity of a realistic LV residential network with 160 households for EV chargers. A stochastic approach is used, assuming that the EV chargers are randomly distributed over the households and the phases. For different EVs penetration rates in the network, the hosting capacity for slow chargers is determined. The results show that the EV penetration rate that the network can safely accept is 45%.

  • 38.
    Bollen, Math
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Mulenga, Enock
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Rönnberg, Sarah
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Etherden, Nicholas
    Hosting Capacity of the Grid for Photovoltaic Installations: a Stochastic Approach Applied to Single-phase Connections2018Ingår i: 8th Solar Integration Workshop, 2018, s. 1-7, artikel-id 6A_1_SIW18_046Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper discusses the voltage rise due to PV installations connected to a low-voltage network. The connection of individual installations is studies for both single-phase and three-phase connection. A stochastic method is presented to estimate the hosting capacity. This method is illustrated for random and coordinated connection of single-phase installations. It is shown, in a number of ways, that the installation of large (e.g. 6 kW) single-phase connected units can easily result in unacceptable overvoltages.

  • 39.
    Sakar, Selcuk
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Rönnberg, Sarah
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Immunity Test of LED Lamps Based on IEC 61000-4-19 and Unexpected Consequence2018Ingår i: Proceedings of International Conference on Harmonics and Quality of Power, ICHQP, Piscataway, NJ: Institute of Electrical and Electronics Engineers (IEEE), 2018Konferensbidrag (Refereegranskat)
    Abstract [en]

    ED lighting technology is the most efficient way oflighting service and its usage has increased rapidly. Although,LED lamps are potential victim and source of electromagneticinterference in the frequency range between 2 kHz and 150 kHz(“supraharmonics”). Therefore, immunity test for this frequencyrange is necessary to analyze its performance variations. In thisstudy, Test profiles described in IEC 61000-4-19 have beenapplied to LED lamps and the results have been analyzedaccording to implemented algorithm that uses the relative lightintensity variation index. The results show that bothsupraharmonics and modulation of the test profiles can reveallight flicker. In addition, some potential drawbacks of thestandard have been found that deviation of the mains’ frequencyis also another factor causes intermodulation/nonsynchronizationon the applied test signal, so this can be seen aslight flicker. This issue better be clarified with more details in theIEC 61000-4-19, particalulary for lighting equipment.

  • 40.
    Mulenga, Enock
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Impact of Service and Feeder Cable Upgrade on Hosting Capacity for Single Phase Connected Photovoltaics2018Ingår i: Proceedings of International Conference on Harmonics and Quality of Power, ICHQP, Institute of Electrical and Electronics Engineers (IEEE), 2018Konferensbidrag (Refereegranskat)
    Abstract [en]

    The addition of photovoltaics (PV) to a grid impacts the performance of that grid in a number of ways. These impacts limit how much PV can be connected, termed ‘hosting capacity (HC)’. The impacts include overvoltage and overloading. Mitigation of impacts can be achieved in different ways: in this paper, upgrade of service cable and feeder cable has been considered, one of the classical solutions. Cable size upgrades to 16, 25 and 35 mm2 from 10 mm2 have been studied to mitigate overvoltages in a 28-customer Swedish suburban grid. A stochastic planning-based approach has been used to obtain a performance parameter that can be used to compare the mitigation methods. The results showed an improvement in overvoltage and hosting capacity with cable upgrade. The hosting capacity is also shown to be sensitive to the risk chosen and to the PV size.

  • 41.
    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 model2018Ingår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 154, s. 319-328Artikel i tidskrift (Refereegranskat)
    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.

  • 42.
    Ravindran, Vineetha
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Rönnberg, Sarah
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Busatto, Tatiano
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Inspection of Interharmonic emissions from a Grid-tied PV Inverter in North Sweden2018Ingår i: Proceedings of International Conference on Harmonics and Quality of Power, ICHQP, Piscataway, NJ: Institute of Electrical and Electronics Engineers (IEEE), 2018Konferensbidrag (Refereegranskat)
    Abstract [en]

    The main objective of the paper is to investigate theexistence of interharmonic emissions from an MPPT drivengrid-connected PV inverter, identify their severity andpersistence. The presence of interharmonics in the measuredcurrent from a PV installation is linked to direct and diffusedsolar irradiation as well as a high ramping rate of theirradiation causing variations in both active and reactive power.The paper sets forth a set of observations and inferences, whichis an appendage to the ongoing research on the power qualityaspects of solar power. Three different case studies areevaluated in detail using signal processing tools like STFT andFFT.

  • 43.
    Sakar, Selcuk
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Rönnberg, Sarah
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Light Intensity Behavior of LED Lamps within theThermal Stabilization Period2018Ingår i: Proceedings of International Conference on Harmonics and Quality of Power, ICHQP, Piscataway, NJ: Institute of Electrical and Electronics Engineers (IEEE), 2018Konferensbidrag (Refereegranskat)
    Abstract [en]

    Visible changes in the light intensity of lamps, referredto as flicker, are quantified based on definitions such asnormalized gain factor and relative light intensity variation.However, those values also change depending on the time after anLED lamp has been switched on. An experiment has been carriedout to analyze this phenomenon. A new metric, a “thermalstabilization time”, has been proposed to identify the time toreach steady state light intensity. Although rare, the change inlight intensity can reach up to 68% during the thermalstabilization time. Consequently, acquiring data at differentintervals can lead to incorrect estimation of critical metrics.Stabilization is an essential factor that should be taken intoconsideration in LED lamps’ measurement. It is recommended bythe authors that 60-minute operation is required before acquiring data.

  • 44.
    Lennerhag, Oscar
    et al.
    Independent Insulation Group Sweden AB.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Power system impacts of decreasing resonance frequencies2018Ingår i: Proceedings of International Conference on Harmonics and Quality of Power, ICHQP, Piscataway, NJ: Institute of Electrical and Electronics Engineers (IEEE), 2018Konferensbidrag (Refereegranskat)
    Abstract [en]

    As the energy system is transitioning to a more sustainable one several of the related changes will affect the power system in different ways. Renewable electricity sources, energy efficiency measures and increased operational flexibility lead to more serious resonances in the electricity network and an increased uncertainty in terms of frequency and damping of those resonances. This could have a large impact on the spread of harmonics and on temporary overvoltages. In this paper, some examples of changes in the grid are presented and their impact on the spread of harmonics and temporary overvoltages, as a consequence of changes in resonances, is discussed.

  • 45.
    Alvarez Perez, Manuel Alejandro
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Rönnberg, Sarah
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bermúdez, Juan
    Department of Energy Conversion and Transport, Simón Bolívar University.
    Zhong, Jin
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Reservoir-Type Hydropower Equivalent Model Based on a Future Cost Piecewise Approximation2018Ingår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 155, s. 184-195Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The long-term (LT) scheduling of reservoir-type hydropower plants is a multistage stochastic dynamic problem that has been traditionally solved using the stochastic dual dynamic programming (SDDP) approach. This LT schedule of releases should be met through short-term (ST) scheduling decisions obtained from a hydro-thermal scheduling that considers uncertainties. Both time scales can be linked if the ST problem considers as input the future cost function (FCF) obtained from LT studies. Known the piecewise-linear FCF, the hydro-scheduling can be solved as a one-stage problem. Under certain considerations a single segment of the FCF can be used to solve the schedule. From this formulation an equivalent model for the hydropower plant can be derived and used in ST studies. This model behaves accordingly to LT conditions to be met, and provides a marginal cost for dispatching the plant. A generation company (GENCO) owning a mix of hydro, wind, and thermal power will be the subject of study where the model will be implemented. The GENCO faces the problem of scheduling the hydraulic resource under uncertainties from e.g. wind and load while determining the market bids that maximize its profit under uncertainties from market prices. A two-stage stochastic unit commitment (SUC) for the ST scheduling implementing the equivalent hydro model will be solved.

  • 46.
    Tang, Yuchen
    et al.
    Department of Electrical and Electronic Engineering, The University of Hong Kong.
    Zhong, Jin
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Schedule of air-conditioning systems with thermal energy storage considering wind power forecast errors2018Ingår i: International Journal of Electrical Power & Energy Systems, ISSN 0142-0615, E-ISSN 1879-3517, Vol. 95, s. 592-600Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    As the penetration of uncontrollable renewable energy sources (RESs) increases, energy storage and flexible demand will play a more important role in future power systems. In this paper, air-conditioning systems with thermal energy storage (A/C storage systems) are studied as a way of compensating uncertainties from wind power. Wind power forecast errors are analyzed from different perspectives in order to better assist the schedule of storage devices. An operation scheme is proposed for A/C storage systems for both day-ahead scheduling and real-time operation, based on the features of wind power forecast errors. The targets include load management and compensation of wind power forecast errors. Simulations illustrate the effectiveness of the proposed scheme to support power systems with high wind penetration.

  • 47.
    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 converter2018Ingår i: 2017 IEEE PES Innovative Smart Grid Technologies Conference Europe, ISGT-Europe 2017: proceedings, New York: Institute of Electrical and Electronics Engineers (IEEE), 2018Konferensbidrag (Refereegranskat)
    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.

  • 48.
    Schwanz, Daphne
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Larsson, Anders
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Some methods for harmonic emission determination in wind power plants2018Ingår i: Proceedings of International Conference on Harmonics and Quality of Power, ICHQP, Piscataway, NJ: Institute of Electrical and Electronics Engineers (IEEE), 2018Konferensbidrag (Refereegranskat)
    Abstract [en]

    The connection of new installations, as wind power plants, into the public grid requires that some conditions are fulfilled. Their aim is among others to ensure a proper power quality in the grid and to ensure a high probability of electromagnetic compatibility. The harmonic emission of individual sources is one of the power quality concerns, because they can damage and increase heating in devices. However, as there are other power electronics loads are connected, the correct assessment of the harmonic emission from one specific source is not straightforward. in this paper, a review of the most used methods for harmonic emission determination is presented and some considerations are discussed regarding their use in wind power plants harmonic contribution. Depending on the application, one method is more suitable than the other. However, assumptions are necessary with any method, especially for the harmonic impedances. For wind power plants not all the presented methods are suitable. Also, further investigations are needed to determine the harmonic impedance of the wind power plant and public grid, especially around resonant frequencies.

  • 49.
    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 Systems2018Ingår i: Proceedings of International Conference on Harmonics and Quality of Power, ICHQP, Piscataway, NJ: Institute of Electrical and Electronics Engineers (IEEE), 2018Konferensbidrag (Refereegranskat)
    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.

  • 50.
    Laury, John
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Abrahamsson, Lars
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Transient Stability of a Rotary Frequency Converter fed railway, interconnected with a parallel low frequency high voltage transmission system2018Ingår i: WIT Transactions on the Built Environment, ISSN 1746-4498, E-ISSN 1743-3509, Vol. 181, s. 15-24Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Using low frequency High Voltage Transmission systems (HV-T) in parallel with the catenary systemstrengthens the railway system by reducing the total impedance of the railway grid. A consequence ofthe reduced impedance is that converter stations are electrically closer to each other.Inside a converter station, different types of Rotary Frequency Converters (RFCs) are used. It is not wellexplored how different RFCs behaves and interacts with each other during and after a large disturbance,like a short circuit.The dynamics of an RFC are modelled by using the Andersson-Fouad model of a synchronous machine.The study presented in this paper investigates interactions inside and between converter stations, withdifferent types of RFC, for an HV-T system in parallel with a Booster Transformer catenary system.The numerical simulation results show, for instance, that the main power oscillation take place inside aconverter station with mixed configuration of RFC type after fault clearance.

1234567 1 - 50 av 383
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf