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  • 101.
    Schwanz, Daphne
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Möller, Friedemann
    Technische Universität Dresden.
    Rönnberg, Sarah
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Meyer, Jan Christian
    Technische Universität Dresden.
    Bollen, Math
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Stochastic assessment of voltage unbalance due to single-phase-connected solar power2017In: 2017 IEEE PowerTech, Piscataway, NJ: Institute of Electrical and Electronics Engineers (IEEE), 2017Conference paper (Refereed)
    Abstract [en]

    A stochastic method is presented in this paper to estimate the future voltage unbalance in a low-voltage distribution network with high-penetration of single-phase photovoltaic inverters (PVIs). The location and phase allocation of the PVIs are considered as input parameters for the stochastic simulation. The method has been applied to three different low-voltage networks: two in Sweden and one in Germany. In the Swedish networks, for 6-kW single-phase PVIs, it is likely that the contribution from single-phase photovoltaic inverters to the voltage unbalance exceeds 1%. The 2% value is unlikely to be exceeded. In the German network, for 4.6-kW single-phase PVIs, the voltage unbalance is between 1.35% and 2.62%. The risk of high-voltage unbalance can be reduced by a combination of controlled distribution over the phases and a reduction of the maximum size for a single-phase PVI.

  • 102.
    Schwanz, Daphne
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Rönnberg, Sarah
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Bollen, Math
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Hosting capacity for photovoltaic inverters considering voltage unbalance2017In: 2017 IEEE PowerTech, Piscataway, NJ: Institute of Electrical and Electronics Engineers (IEEE), 2017, article id 7981274Conference paper (Refereed)
    Abstract [en]

     In this paper the hosting capacity considering voltage unbalance is estimated for single-phase photovoltaic inverters (PVIs) in low-voltage distribution networks in Sweden. A stochastic approach is used to calculate the negative-sequence voltage unbalance for each of the possible locations in the network. The method has been applied to 6 and 28-customer networks for the connection of 6-kW single-phase PVIs. The impact of three-phase motors on the unbalance was also studied. From the results, it was observed that the contribution from single-phase photovoltaic inverters to the voltage unbalance likely exceeds 1%, but unlikely that it will reach 2% of voltage unbalance.

  • 103.
    Schwanz, Daphne
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Rönnberg, Sarah
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Bollen, Math
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Voltage unbalance due to single-phase photovoltaic inverters2017In: CIRED - Open Access Proceedings Journal, ISSN 2515-0855, Vol. 2017, no 1, p. 906-910Article in journal (Refereed)
    Abstract [en]

    In this study, the negative-sequence voltage unbalance is calculated for increasing numbers of single-phase photovoltaic inverters (PVIs) connected to low-voltage distribution networks. The transfer impedance matrix is used to calculate the negative-sequence voltage for each of the possible locations in the networks and a stochastic method is applied to estimate the voltage unbalance. The method has been applied to six- and 28-customer networks for the connection of 6 kW single-phase PVIs. Furthermore, the hosting capacity for each network has also been estimated. From the results, it was observed that it is likely that the contribution from single-phase PVIs to the voltage unbalance exceeds 1%, but unlikely that it will reach 2%.

  • 104.
    Sierra-Fernández, J.-M.
    et al.
    University of Cádiz, Algeciras, Spain.
    Rönnberg, Sarah
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    De La Rosa, J.-J.G
    University of Cádiz, Algeciras, Spain.
    Bollen, Math
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Palomares-Salas, J.-C.
    University of Cádiz, Algeciras, Spain.
    Application of spectral kurtosis to characterize amplitude variability in power systems' harmonics2019In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 12, no 1, article id en12010194Article in journal (Refereed)
    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. 

  • 105.
    Singh, Gaurav
    et al.
    Department of Electrical and Computer Engineering, Clemson University.
    Collins Jr., Randolph
    Department of Electrical and Computer Engineering, Clemson University.
    Rönnberg, Sarah
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Larsson, Anders
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Bollen, Math
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Impact of high frequency conducted voltage disturbances on LED driver circuits2017In: IEEE Power and Energy Society General Meeting, Piscataway, NJ: Institute of Electrical and Electronics Engineers (IEEE), 2017Conference paper (Refereed)
    Abstract [en]

    Increasingly, consumer electronic devices utilize power supplies that have switching frequencies up to several tens of kilohertz. Consequently, emission in the frequency range 2 to 150kHz ('supraharmonics') is continuously increasing. Cases of conducted interference in LED lamps using switched mode power supplies, from supraharmonics have been reported over the past three years. This paper presents results from experiments where supraharmonic voltage distortion was applied to commercially available LED driver circuits. Variations of light output were obtained in some cases, along with evidence pointing to reduced converter efficiency and influence of point on wave of the distortion, on the light output. Importantly, it was shown that electromagnetic compatibility is not converter topology dependent, nor influenced by galvanic isolation. The results demonstrate that converters with similar topology can have vastly different behavior and there is a marked dissimilarity in performance among different topologies.

  • 106.
    Smith, Jeff W.
    et al.
    Distribution Planning, Operations and Studies, EPRI, Knoxville.
    Rönnberg, Sarah
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Bollen, Math
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Meyer, Jan
    TU Dresden, Institute of Electrical Power Systems and High Voltage Engineering.
    Blanco, Ana Maria
    TU Dresden, Institute of Electrical Power Systems and High Voltage Engineering.
    Koo, Kah Leong
    National Grid, Power Quality and Modelling, System Design, Warwick.
    Mushamalirwa, Daudi
    GE Grid Solutions, Technical Institute - Network Consulting, Paris.
    Power quality aspects of solar power: Results from CIGRE JWG C4/C6.292017In: CIRED - Open Access Proceedings Journal, ISSN 2515-0855, Vol. 2017, no 1, p. 809-813Article in journal (Refereed)
    Abstract [en]

    The increasing use of solar power connected to the public grid and the associated concern for deteriorating power quality triggered the formation of a joint working group with the aim to describe and quantify this impact. The WG formed in 2012 as a joint C4/C6 effort, formed to examine the power quality aspects of solar power, specifically addressing a number of phenomena, all which will be discussed in this study

  • 107.
    Tjäder, Anna
    et al.
    AT Power, 43539 Mölnlycke.
    Gu, Irene
    Chalmers University of Technology, Department of Signals and Systems.
    Bollen, Math
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Rönnberg, Sarah
    Performance evaluation for frequency estimation of transients using the ESPRIT: measured noise versus white noise2008In: 2008 13th International Conference on Harmonics and Quality of Power: [ICHQP 2008] ; Wollongong, Australia, 28 September - 1 October 2008, Piscataway, NJ: IEEE Communications Society, 2008Conference paper (Refereed)
    Abstract [en]

    A number of papers have proposed to use the ESPRIT method for estimating some power system transients. The mathematical model for using the ESPRIT requires that the additive noise be white. Fail to satisfy this could lead to degraded performance of frequency estimation. However, in practical situations the noise is often non-white. In this paper we study the performance of the ESPRIT frequency estimation method when the additive noise is measured from power systems. It is shown that tests using synthetic white noise are not sufficient for realistic power-system scenarios, as the noise is often non-white and not i.i.d. distributed. First, a set of measured voltage waveforms is superimposed to synthetic transients with known frequencies. This yields a set of semi-measured transients. The ESPRIT method is then applied to estimate the frequencies. The performance of the ESPRIT is then evaluated in term of the mean value and standard deviation. Our experiments show that, for a transient contains one sinusoid, the ESPRIT of sinusoidal model order K=2 results in an acceptable accuracy if the amplitude of the transient is well above the noise level and the transient frequency is not too close to the powersystem frequency. This is sufficient for most practical applications. A better performance for higher noise levels is obtained by significantly increasing the sinusoidal model order in the ESPRIT.

  • 108.
    Wahlberg, Mats
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Rönnberg, Sarah
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Case study on electrical conductivity in wood poles2017Report (Other academic)
  • 109.
    Wahlberg, Mats
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Rönnberg, Sarah
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Currents in power line wood poles2011In: Proceedings of CIRED 21st International Conference on Electricity Distribution, 2011, article id 0347Conference paper (Refereed)
    Abstract [en]

    Over the last few years some rather severe problems have arisen for poles used to support overhead power lines. A wooden power line pole is assumed to be a good electric insulator because of the basic properties of wood with its porous structure and cellulose compounds forming the major part of the cell walls. A fault during which an insulator is broken or a phase conductor has loosened, normally poses no danger. In rare cases a fire has started, but this has not been seen as a sufficiently dangerous situation to change maintenance practice. However, it has been noticed that under certain circumstances such poles can get conductive enough to result in hazardous or even lethal current for power line maintenance workers climbing the pole.

  • 110.
    Wahlberg, Mats
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Rönnberg, Sarah
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Currents in power line wood poles: a measuring method2010Conference paper (Refereed)
    Abstract [en]

    Recently a maintenance worker in Sweden was killed when climbing into a wood pole supporting an 11-kV overhead line. The investigating done afterwards raised the suspicion that a current flowed through the pole was sufficient to kill a person. Due to a broken insulator one of the phases of the 11-kV line had been resting on the metal crossbar. This accident triggered an investigation in order to determine if power line wood poles can conduct current and if so, whether this current can be sufficient to injure a maintenance worker climbing into the pole. The study has been made at the 11 kV level on a pole while a live wire was resting on the metal cross arm as would be the case if the insulator had broken. A proposal for a measuring method has been developed in order to determine under what conditions climbing should be prohibited. In Sweden the use of wood poles as part of 11 kV overhead lines is fairly common. A three phase system is used to distribute 11 kV, one wire for each phase, and the three wires are supported by insulators mounted on a horizontal metal (or wood) cross arm. The poles are treated with some kind of preservative to protect the wood from rot and insects. Three kinds of preservatives are commonly used in Sweden: arsenic, creosote and salt. In this study eight poles with different preservative and age varying from 50 years old to brand new have been examined in a realistic environment. The measurements presented in this paper support the earlier suspicion that a wood pole used for distributing power can conduct current if a fault occurs and a live wire comes in contact with the metal cross arm. It also shows that the current through a parallel, not connected to earth, resistor (i.e. a human climbing the pole) can reach potentially harmful amplitudes. Three main variables that affect the electrical characteristics of the pole have been identified: the preservation of the wood; the environmental temperature; and the humidity of the surroundings. There are however other variables that can have an impact on the conductivity of the pole for example how the pole was dried before preservation.

  • 111.
    Wahlberg, Mats
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Rönnberg, Sarah
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Design of power lines poles that will be safe even when a phase has come in contact with crossarm.2014Conference paper (Refereed)
  • 112. Zavoda, Francisc
    et al.
    Bollen, Math
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Rönnberg, Sarah
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    CIGRE/CIRED JWG C4.24, Power Quality and EMC Issues associated with future electricity networks: status report2016Conference paper (Refereed)
  • 113.
    Zavoda, Francisc
    et al.
    IREQ (HQ), Varennes.
    Langella, Roberto
    Second University of Naples.
    Lǎzǎroiu, George Cristian
    University Politehnica of Bucharest.
    Bollen, Math
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Rönnberg, Sarah
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Meyer, Jan Christian
    Technische Universitaet Dresden.
    Ciufo, Philip
    University of Wollongong.
    Power Quality in the Future Grid: Results from CIGRE/CIRED JWG C4.242016In: 2016 17th International Conference on Harmonics and Quality of Power, Piscataway, NJ, 2016, p. 931-936, article id 7783475Conference paper (Refereed)
    Abstract [en]

    This paper gives a status report on activities of CIGRE/CIRED JWG C4.24. The following issues are addressed in the paper: Introduction, scope of the report and terminology; New developments in power electronics (PE); Changes in probability of interference; Microgrids and PQ; Volt-VAR control and PQ; Feeder reconfiguration and PQ; Demand side management and PQ; New measurement techniques; New mitigation.

  • 114.
    Zavoda, Francisc
    et al.
    IREQ.
    Rönnberg, Sarah
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Bollen, Math
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Meyer, Jan
    Technical University Dresden.
    Desmet, Jan
    Ghent University.
    CIGRE/CIRED/IEEE working group C4.24 - New measurement techniques in the future grid2015Conference paper (Refereed)
    Abstract [en]

    One of the issues that the joint working groupCIGRÉ/CIRED/IEEE JWG C4.24 will be addressing, isthe need in future networks for new measurementtechniques, more complex and more accurate, which willbe undergoing architecture reconfiguration (due tofeeder reconfiguration) and will be witnessing old andnew phenomena affecting the power quality. This papergives a comprehensive overview and betterunderstanding of the real challenges related tomeasurement techniques in future networks

  • 115.
    Zhong, Jin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Bollen, Math
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Wei, Ming
    The University of HongKong.
    Rönnberg, Sarah
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Towards a 100% Renewable Energy Power Generation in Sweden2016In: Meeting Sweden's current and future energy challenges, Luleå: Luleå tekniska universitet, 2016, Luleå: Luleå tekniska universitet, 2016Conference paper (Other academic)
123 101 - 115 of 115
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