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  • 1.
    Ahmed, Kazi Main Uddin
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Alvarez, Manuel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math H.J.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Reliability Analysis of Internal Power Supply Architecture of Data Centers in Terms of Power Losses2021Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 193, artikkel-id 107025Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The number of data centers and the energy demand are increasing globally with the development of information and communication technology (ICT). The data center operators are facing challenges to limit the internal power losses and the unexpected outages of the computational resources or servers. The power losses of the internal power supply system (IPSS) increase with the increasing number of servers that causes power supply capacity shortage for the devices in IPSS. The aim of this paper is to address the outage probability of the computational resources or servers due to the power supply capacity shortage of the power distribution units (PDUs) in the IPSS. The servers outage probability at rack-level defines the service availability of the data center since the servers are the main computational resource of it. The overall availability of the IPSS and the power consumption models of the IPSS devices are also presented in this paper. Quantitative studies are performed to show the impacts of the power losses on the service availability and the overall availability of the IPSS for two different IPSS architectures, which are equivalent to the Tier I and Tier IV models of the data center.

  • 2.
    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 Approximation2018Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 155, s. 184-195Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 3.
    Bagheri, Azam
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Gu, Irene Y.H.
    Chalmers University of Technology.
    Improved characterization of multi-stage voltage dips based on the space phasor model2018Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 154, s. 319-328Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 4.
    Bollen, Math
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Gil de Castro, Aurora
    The University of Cordoba, Cordoba, Spain.
    Rönnberg, Sarah
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Characterization methods and typical levels of variations in rms voltage at the time scale between 1 second and 10  minutes2020Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 184, artikkel-id 106322Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Voltage magnitude deviation from its nominal value varies over a range of time scales. This paper concentrates on the range between 1 s and 10 min as part of the long-term aim of obtaining a complete picture of voltage magnitude variations at time scales below ten minutes. Time series of voltage with 1-s time resolution are obtained at 57 locations around the world. The main contributions of the paper are: the definition of additional indices in the sub-10-minute time scale from the 1-s rms voltages; statistics on the values of these indices for different locations; identifying the need for further research through a set of recommendations to the research community. It is shown, among others, that for the available data set, the voltage typically varies between 0.5 V and 5 V within a 10-min window; a range exceeding 1 or 2 V is common; a range exceeding 5 V is uncommon.

    The need for the indices proposed in this paper is justified as equipment connected to the grid is changing and to help managing and for storing the huge amount of data resulting from power-quality measurements at many sites during several years.

  • 5.
    Bracale, Antonio
    et al.
    Department for Technologies, University of Naples Parthenope.
    Carpinelli, Guido
    Department of Electrical Engineering, University of Naples Federico II.
    Gu, Irene
    Chalmers University of Technology, Department of Signals and Systems.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    A new joint sliding-window ESPRIT and DFT scheme for waveform distortion assessment in power systems2012Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 88, nr 7, s. 112-120Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper proposes a novel scheme that jointly employs a sliding-window ESPRIT and DFT for estimating harmonic and interharmonic components in power system disturbance data. In the proposed scheme, separate stages are utilized to estimate the voltage fundamental component, harmonics and interharmonics. This includes the estimation of the fundamental component from lowpass filtered data using a sliding-window ESPRIT, of harmonics from a sliding-window DFT with a synchronized window, and of interharmonics from the residuals by applying the sliding-window ESPRIT. Main advantages of the approach include high resolution and accuracy in parameter estimation and significantly reduced computational cost. Experiments and comparisons are made on both synthetic and measurement data. Results have shown the effectiveness and efficiency of the proposed scheme.

  • 6.
    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.
    Rönnberg, Sarah
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Meyer, Jan
    Electric Power Engineering, Technische Universität Dresden.
    Deviations between the commonly-used model and measurements of harmonic distortion in low-voltage installations2020Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 180, artikkel-id 106166Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Harmonic analysis studies of modern power systems commonly employ Norton and Thévenin equivalents at harmonic frequencies for the nonlinear devices. This approach neglects the so-called nonlinear interaction phenomenon. This paper addresses the difference between the results from the commonly-used model and the actual harmonic distortion measured in a low-voltage installation. A number of indices are introduced to quantify the nonlinear interaction. These indices allow a quantification of the extent to which the commonly-used model is also to predict harmonic voltages and currents in a modern low-voltage installation. The proposed model and the subsequent mathematical analysis are illustrated through measurements from different combinations of PV inverters and LED lamps using different technologies. The results show that deviation is dependent on the used technology, network impedance, and source voltage waveform. Other findings are that nonlinear interaction happens mainly in the low harmonic orders and impacts are more perceived on the harmonics phase angle. Possible explanations for these observations are discussed.

  • 7.
    de Oliveira, Roger Alves
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Magnification of Transients at the Voltage Dips Starting and its Impacts on DFIG-based Wind Power Plants2022Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 211, artikkel-id 108244Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This work shows that transients at voltage dips starting impact fault-ride-through of wind turbines. For fault-ride-through studies and manufacturer tests, it is therefore important to consider these transients and their magnification from the transmission grid through the collection grid to the wind turbines. Fault-ride-through studies in the literature do not consider the transient as a dip characteristic and employ overly-simplified models that do not consider the collection grid. This work studies in detail how the dip-starting transient changes during the propagation from the transmission grid to the wind-turbine terminals. It is also studied how this transient impacts the dynamic behaviour of the wind turbines in terms of the overvoltage on the DC-link of wind turbines based on doubly-fed induction generator (DFIG). The analyses are performed for several realistic configurations of a wind-power plant, all based on an existing installation. The results show that the magnitude of the transient is magnified when the resonant frequency of the collection grid is similar to the oscillation frequency of the transient. Moreover, the higher magnitude of the transient results in a significantly higher overvoltage on the DC-link. This work is the first in power quality literature to cover the collection and internal grid as a factor for the magnification of dip-staring transient. The main finding of this work is that the detailed models of the collection grid and the transients at the voltage dips starting must be not neglected when accessing the LVRT of wind turbines. It is strongly recommended to consider the details of the dip-starting transients and of the collection grid to assess the impact of dips on the wind turbines properly.

  • 8.
    Ehnberg, S.G. Jimmy
    et al.
    Department of Electric Power Engineering, Chalmers University of Technology, Gothenburg, Sweden.
    Bollen, Math H.J.
    STRI AB, Ludvika, Sweden.
    Reliability of a small power system using solar power and hydro2005Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 74, nr 1, s. 119-127Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper studies the availability of the electricity supply when the sources consist of a combination of solar energy and a small hydro installation. Instead of flow-of-river, a small reservoir is used. By not using the hydro energy during sunny periods, the natural flow-of-river fills up the reservoir for later use. A model for global solar radiation is proposed with an astronomical part (deterministic) and a meteorological part (stochastic). The meteorological part is based on a Markov model of the cloud coverage. The solar model does not require solar radiation measurements, just cloud observations. A case study has been performed for Timbuktu (16.75°N, 0.07°W) in which generation availability is simulated for four different cases: solar power only; solar power with storage; solar and hydro power and solar and hydro power with storage. To be able to use exclusively renewable energy sources, a combination of sources is needed to secure the reliability of the supply. Using solar cells in combination with a small reservoir is favorable. Even with a weak flow the affect of the flow on the day time reliability is minor, but great benefits can be found for reliability during low load hours (night time).

  • 9.
    Espin Delgado, Angela
    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.
    Ravindran, Vineetha
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Summation law for supraharmonic currents (2–150 kHz) in low-voltage installations2020Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 184, artikkel-id 106325Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The development of methods to study the propagation of supraharmonics in LV and even MV grids is a current research topic among the power quality community, which has been motivated by the efforts to establish limits for non-intentional supraharmonic emissions and planning levels. The assessment of how much distortion a bulk use of power electronics devices can inject into the grid is necessary before stating emission limits and planning levels for supraharmonics. To address this issue, the development of suitable models that can predict the supraharmonic emission from a low-voltage installation as a whole is required. This article presents a comparison of models for the summation of supraharmonics. An improved model for the summation of supraharmonics is proposed, which is validated experimentally. It is shown that by using the proposed model, predictions of supraharmonic propagation can be accomplished. Furthermore, it is demonstrated experimentally that, with the increasing number of supraharmonic emitting devices, the supraharmonic current distortion injected into a grid by an installation increases up to a maximum value and then decreases due to the capacitive nature of power electronics appliances existing in low-voltage networks.

  • 10.
    Espín-Delgado, Ángela
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Rönnberg, Sarah
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Sudha Letha, Shimi
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Diagnosis of supraharmonics-related problems based on the effects on electrical equipment2021Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 195, artikkel-id 107179Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Supraharmonics (SH) have proliferated in low-voltage (LV) and medium-voltage (MV) grids due to the increasing use of technologies emitting distortion in the range 2–150 kHz. Currently, no recommended practices to assess the effects of SH on the electrical system exist. The propagation of SH through LV and MV grids leads to interference with the elements for power delivery and end-user equipment, e.g., light flicker, aging of capacitors and cable terminations, audible noise, and interruption of electric vehicle (EV) charging. As such incidents happen more often, the need for guidelines that facilitate the diagnosis of problems related to SH arises. Different features of the SH distortion are responsible for different interferences. This article introduces guidelines for the evaluation of the impact of SH based on the morphology of the interference. The evaluation is performed with easy-to-use methods and formulas directly related to the characteristics of the SH distortion. The adverse effects of SH considered are audible noise, light flicker, tripping of LV residual current devices (RCDs), and MV cable termination failure. This work interests field engineers and researchers facing problems related to SH; it also serves as a guide for further research.

  • 11.
    Etherden, Nicholas
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Overload and overvoltage in low-voltage and medium-voltage networks due to renewable energy: some illustrative case studies2014Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 114, s. 39-48Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents the use of curtailment to allow more wind or solar power to be connected to a distribution network when overcurrent or overvoltage set a limit. Four case studies, all based on measurements, are presented. In all cases the hosting capacity method is used to quantify the gain in produced energy for increased levels of distributed renewable energy resources. A distinction is made between “hard curtailment” where all production is disconnected when overcurrent and overvoltage limits are exceeded and “soft curtailment” where the amount of production to be disconnected is minimized. It is shown that the type of curtailment method used has a large impact on the amount of delivered energy to the grid. The paper further discusses details of the curtailment algorithm, alternatives to curtailment, the communication needs and risks associated with the use of curtailment

  • 12.
    Ferreira, Danton D.
    et al.
    Federal University of Lavras.
    de Seixas, Jose M.
    Federal University of Rio de Janeiro, COPPE/Poli.
    Cerqueira, Augusto S.
    Department of Electrical Circuits, Federal University of Juiz de Fora, Campus Universitário.
    Duque, Carlos A.
    Department of Electrical Circuits, Federal University of Juiz de Fora, Campus Universitário.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Ribeiro, Paulo F.
    Federal University of Itajubá.
    A new power quality deviation index based on principal curves2015Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 125, s. 8-14, artikkel-id 4289Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, a new power quality deviation index based on principal curves is proposed. The index provides a quantitative measure, which gives an idea of how much the monitored electrical signal has deviated from the nominal one. Differently of existing indices, the proposed index is a general index, i.e., it can be used for any type of disturbance in the monitored signal. In addition, the proposed index is used to perform a direct approach for detecting disturbances in power signals. This approach is able to detect the beginning and localize the disturbance by analyzing non-overlapping signal windows of one cycle of the fundamental component, leading to a simple method in terms of computational complexity

  • 13.
    Filho, J.M.C.
    et al.
    Universidade Federal de Itajubá, Brazil.
    Leborgne, R.C.
    Chalmers University of Technology, Sweden.
    da Silveira, P.M.
    Universidade Federal de Itajubá, Brazil.
    Bollen, Math H.J.
    STRI AB, Sweden.
    Voltage sag index calculation: Comparison between time-domain simulation and short-circuit calculation2008Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 78, nr 4, s. 676-682Artikkel i tidsskrift (Fagfellevurdert)
  • 14.
    Ge, Chenjie
    et al.
    Department of Electrical Eng, Chalmers University of Technology, 412 96 Göteborg, Sweden.
    Oliveira, Roger A.D.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Gu, Irene Y.H.
    Department of Electrical Eng, Chalmers University of Technology, 412 96 Göteborg, Sweden.
    Bollen, Math H.J.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Unsupervised deep learning and analysis of harmonic variation patterns using big data from multiple locations2021Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 194, artikkel-id 107042Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper addresses the issue of automatically seeking and identifying daily, weekly and seasonal patterns in harmonic voltage from measurement data at multiple locations. We propose a novel framework that employs deep autoencoder (DAE) followed by k-mean clustering. The DAE is used for extracting principal features from time series of harmonic voltages. A new strategy is used for training the encoder in DAE from data at one selected location that is effective for subsequent feature extraction from data at multiple locations. To analyze the patterns, several empirical analysis approaches are applied on the clustered principal features, including the distribution of daily patterns over the week and the year, representative waveform sequences of individual classes, and feature maps for visualizing high-dimensional feature space through low-dimensional embedding. The proposed scheme has been tested on a dataset containing harmonic measurements at 10 low-voltage locations in Sweden for the whole year of 2017. Results show distinct principal patterns for most harmonics that can be related to the use of equipment causing harmonic distortion. This information can assist network operators in finding the origin of harmonic distortion and deciding about mitigation actions. The proposed scheme is the first to provide a useful analysis tool and insight for finding and analyzing underlying patterns from harmonic variation data at multiple locations.

  • 15.
    Gil de Castro, Aurora
    et al.
    Electronics Technology, University of Cordoba.
    Rönnberg, Sarah
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Light intensity variation (flicker) and harmonic emission related to LED lamps2017Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 146, s. 107-114Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper discusses two power-quality aspects of LED lamps: harmonics and flicker. Measurements have been performed of 24 different LED lamps: the harmonic current spectrum and light intensity variations have been measured. To enable an objective comparison, the light intensity variations were measured for all the lamps when exposed to the same voltage magnitude variations. Results show a large variety in harmonic emission between different LED lamps indicating that different technologies or different components are being used within the LED lamps. Moreover the results show a large variety in light intensity variations when different LED lamps are subjected to the same voltage fluctuations. A clear correlation was found between harmonic emission and sensitivity to voltage magnitude variations. Lamps with low light intensity variations are also the ones with the highest harmonic current emission. No clear relation between active power or price and sensitivity to voltage magnitude variations was found.

  • 16.
    Gil-de-Castro, Aurora
    et al.
    Departamento de Ingeniería Electrónica y de Computadores, Universidad de Cordoba, Cordoba, Spain.
    Bollen, Math H.J.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Rönnberg, Sarah K.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Variations in harmonic voltage at the sub-10-minute time scale2021Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 195, artikkel-id 107163Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents the statistical analysis of variations in harmonic voltage in the time scale between 1 second and 10 min, a time scale that is rarely considered in studies but that is of relevance for incorrect operation of end-user equipment. The paper also introduces a set of novel power-quality indices quantifying these variations and it gives recommendations on how to include these indices in the power-quality-monitoring framework provided by IEC 61000–4–30. The statistics and the illustration of the novel indices are based on measurements of harmonic 2 through 40 with 1-second time resolution at 154 locations in 16 countries. The proposed power-quality indices are a compromise between storing large amounts of raw data with high time resolution, resulting in the different big-data challenges, and completely neglecting this time scale. Two important findings from this paper are that this time scale should not be completely neglected and that information on this time scale can be recorded without excessive increase in the need for data transmission and storage.

  • 17.
    Hajeforosh, Seyede Fatemeh
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bakhtiari, Hamed
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Risk Assessment Criteria for Utilizing Dynamic Line Rating in Presence of Electric Vehicles Uncertainty2022Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 212, artikkel-id 108643Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Dynamic line rating (DLR) is a grid enhancing technology to enable a more effective use of transmission capacity of existing infrastructure.~The growth in load consumption along with a high integration of electric vehicles (EV) highlights the potential of DLR utilization for reducing the congestion costs and overloading risks.~Selecting the proper lines for DLR implementation is necessary to exploit optimally the benefits of DLR. In this paper, we propose risk assessment criteria to select proper lines for DLR implementation to minimize the system operation costs and the risk of overloading caused by high EV integration.A stochastic method is introduced to model the uncertain behavior of EV in charging stations. Furthermore, we analyze the impact of inherent uncertainties in DLR by comparing different DLR percentiles. The benefits of using DLR in different percentiles are then quantified in terms of supply and interruption costs.The results show improvements in system supply cost, system reliability, and operation risks. 

  • 18.
    Hajeforosh, SeyedeFatemeh
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math H.J.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Uncertainty analysis of stochastic dynamic line rating2021Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 194, artikkel-id 107043Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents an uncertainty analysis of lines equipped with dynamic line rating (DLR) that are exposed to operational overloading. Multiple sources of uncertainties are taken in to account to model the line rating probabilistically. The superiority of dynamic rating above static rating is confirmed in this paper. However, it is shown in this paper that when the uncertainties in line rating are not considered, DLR can result in a high probability of undetected overloading. Based on assumptions for the uncertainties in relevant weather parameters, the probability of overloading is calculated for three different loading profiles of a line, for each hour during an eight-year period. Guaranteeing a low probability of overloading, with a deterministic dynamic rating, will require a large margin and result in many hours during which unnecessary measures against overloading will be taken. A stochastic dynamic rating, as introduced in this paper, allows for a more transparent and hour-by-hour trade-off between failure to take measures and unnecessary measures against overloading.

  • 19.
    Jesus, P. M. De Oliveira-De
    et al.
    Energy Institute and Department of Conversion and Energy Delivery, Simon Bolivar University, Caracas.
    Alvarez, Manuel
    Energy Institute and Department of Conversion and Energy Delivery, Simon Bolivar University, Caracas.
    Yusta, J. M.
    Department of Electrical Engineering, University of Zaragoza.
    Distribution power flow method based on a real quasi-symmetric matrix2013Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 95, s. 148-159Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents a new load flow formulation to solve active and passive electric distribution networks. The fundamental idea discussed here is how to obtain the power flow solution by using the elements of a unique quasi-symmetric matrix called TRX in the iterative process. The method is formulated for single-phase balanced and three-phase unbalanced radially operated networks. It works with real variables as opposed to complex variables used in previous backward/forward sweep algorithms discussed in literature. The proposed TRX matrix constitutes a complete database by including information of network topology structure as well as branch impedances of the distribution feeder. Data arrangement is suitable to be exchanged under standard Common Information Model (CIM) under Distribution Management Systems (DMS) environment allowing an efficient computation of the state of the system for on-line and off-line study applications. The proposed methodology was applied on a group of IEEE test systems and a real distribution system of 49,000 nodes. © 2012 Elsevier B.V. All rights reserved.

  • 20.
    Leborgne, Roberto Chouhy
    et al.
    Federal University of Rio Grande do Sul (UFRGS), Porto Alegre.
    de Oliveira, Thiago Clé
    Itajuba Federal University, Brazil.
    de Carvalho Filho, José Maria
    Itajuba Federal University, Brazil.
    de Oliveira, Jeder Francisco
    CEMIG, Belo Horizonte.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    New approach for power lines performance estimation based on load variation due to voltage sags2011Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 83, nr 1, s. 35-40Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The power line performance has traditionally been assessed in terms of its efficiency and reliability. The increase of the effect of voltage sags on sensitive loads, maybe located far away from the faulted line, is the reason to carry out a new analysis of power line's performance. A new method to evaluate the power line performance, based on voltage sag indices, is proposed. The voltage sag indices suggested to assess power lines performance are the load variation, the non delivered energy and the total cost due to voltage sags. The proposed power line performance is compared with the traditional performance based on power line outages. The results show that the proposed method can change the assessment of power lines performance and therefore the utility focus for investment.

  • 21.
    Lennerhag, Oscar
    et al.
    Independent Insulation Group, Ludvika, Sweden.
    Bollen, Math H.J.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Impact of uncertainties on resonant overvoltages following transformer energization2020Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 187, artikkel-id 106503Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [sv]

    A number of changes in the power system have increased the risk for more serious resonances in the harmonic frequency range. The changes also result in an increased uncertainty with regard to the frequency and damping of those resonances. Uncertainties could be related to variations with time, uncertain future developments in the grid, and the modelling of individual components. This article investigates uncertainties affecting resonant overvoltages caused by transformer energization. Several study cases investigating the impact of different uncertainties on resonances and resonant overvoltages, performed in PSCAD, are presented. The results show that some uncertainties may have a significant impact on the resulting impedance characteristics and on the resulting overvoltage levels.

  • 22.
    Mohammadi, Younes
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Leborgne, Roberto C.
    Universidade Federal do Rio Grande do Sul, Osvaldo Aranha, 99, 90035-190, Porto Alegre, RS, Brazil.
    Polajžer, Boštjan
    University of Maribor, Koroška c. 46, 2000 Maribor, Slovenia.
    Modified methods for voltage-sag source detection using transient periods2022Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 207, artikkel-id 107857Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Real-time detection of the voltage sag sources' relative location requires fast and accurate methods. Therefore, in this paper, the transient period of voltage sags is used with useful detection information, which is not considered in the literature. In this context, this work firstly analyses the main positive-sequence phasor-based (PB) and instantaneous-based (IB) methods within both transient and steady-state periods of voltage sags caused by network faults and transformer energizing. Secondly, new methods are proposed using five different modifiers, applied in the transient period of voltage sags, i.e., half and one cycle time windows, to achieve a faster and more accurate response. These modifiers use the PB/IB criteria obtained from the existing methods, such as power, impedance, and current, and are applied as: The mean of the criterion changes, the first largest peak (FLP) on the criterion changes, the mean of the zero-mean criteria during a sag, the FLP of the zero-mean criteria during a sag, and the Trend (slope) of criteria's trajectories versus time. Voltage sag source detection methods are evaluated by applying 1992 simulated voltage sag events in a Brazilian regional power network. The results reveal that the proposed modifiers, used in the new methods, improve the ineffective existing methods by taking half/one cycle within a transient period of voltage sags. The modifiers also show an accuracy equal to other existing enhanced methods due to employing them within the transient period, thus evidencing their appropriateness. Correspondingly, a selection is made amongst the new modified methods in order to choose the most accurate time window (half or one cycle) for the methods. The selected modified methods are also tested by applying field measurements in a Slovenian power network to confirm their effectiveness in the transient short periods. According to a recommendation of the fastest and most accurate new methods in this study, an important application can be using the recommended methods as the directional function in the relays, along with an accurate voltage sag/fault inception time detection algorithm in real-time.

  • 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.
    Distribution networks measured background voltage variations, probability distributions characterization and Solar PV hosting capacity estimations2021Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 192, artikkel-id 106979Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Solar photovoltaics in electricity distribution networks is often limited by the rise in voltage magnitude. The pre-connection voltage magnitude is an important factor that determines the hosting capacity.

    This paper studies to which extent details of the pre-connection voltage magnitude impact the hosting capacity. Extensive measurements of voltage magnitude and solar power production were obtained for a number of distribution networks with 10-minute resolution. The measured background voltage during the sunny-hours from the two-year measurements was used to obtain representative probability distribution functions. A guide for selecting the time-of-day (ToD) used is presented.

    The obtained probability distribution functions are applied to estimate the stochastic hosting capacity for a low-voltage distribution network with 83 customers. The impact of various details on the hosting capacity are studied.

    The results show that general knowledge about the range of the pre-connection voltage are essential for the hosting capacity estimation. Measurements over one year were shown to be sufficient to estimate the hosting capacity. The hosting capacity considering the entire day was underestimated by 11 % when compared to the 10 am – 2 pm sunny-hours. The proposed method is general and can be applied to other aleatory uncertainties and other types of hosting capacity studies.

  • 24.
    Mulenga, Enock
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math H.J.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Etherden, Nicholas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Limits set by component loadability on solar power integration in distribution networks2022Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 209, artikkel-id 107951Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper proposes a deterministic and stochastic approach to quantify the hosting capacity that is often limited by the loadability limit of the cable cabinet or transformers due to customers with solar photovoltaics (PV) units. Distribution networks from two areas in Sweden supplying 309 MV/LV distribution transformers with 12,000 customers downstream have been studied. Using a deterministic model, a method is proposed and applied to assess the cable overvoltage against the loadability while considering the voltage rise margin. In addition, measurements have been applied to the methods and the loadability limits assessed. Illustrations for the concepts and important results for the guide to DSOs decision-making guide has been obtained. It is shown in the paper the hosting capacity anticipated at the end of a distribution network cable with a particular size is determined more often by the loadability at larger voltage rise margin and by overvoltage at smaller voltage rise margins. The results obtained for the data used show that the overload limit is exceeded more often for transformers than for cable supplying the cable cabinets at smaller solar PV sizes. For larger solar PV sizes, the feeder cable loadability limit is likely to be exceeded first before that of the transformers. The stochastic approach applied to the yields a small probability to exceed the hosting capacity and depend on the two epistemic uncertainties.

  • 25.
    Nakhodchi, Naser
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bakhtiari, Hamed
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math H. J.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Rönnberg, Sarah K.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Including uncertainties in harmonic hosting capacity calculation of a fast EV charging station utilizing Bayesian statistics and harmonic correlation2023Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 214, artikkel-id 108933Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The harmonic emission from an electric vehicle fast charger depends on factors like charger topology, EV type, initial state of charge of EV battery, as well as supply voltage and background distortion. This paper presents the results from harmonic current measurement of a fast charger for a period of one month in Sweden that has charged a variety of EVs from different brands under different state of charge and background distortion. Besides the common harmonic emission pattern, a high level of variation in emission is observed that can affect the aggregation of the emission from multiple chargers. To include such uncertainties, the harmonic hosting capacity is obtained for a fast EV charging station in a stochastic way. A new method, based on Bayesian statistics and the correlation between harmonic magnitude and fundamental magnitude, is proposed for the generation of stochastic samples. It is shown that the proposed method, to a high extent, can model the stochastic behavior of harmonic emission from a fast charger. Furthermore, the results show that neglecting the correlation between harmonic magnitude and fundamental magnitude can underestimate the harmonic hosting capacity.

    Fulltekst (pdf)
    fulltext
  • 26.
    Oliveira, Roger Alves de
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math H.J.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Deep learning for power quality2023Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 214, artikkel-id 108887Artikkel, forskningsoversikt (Fagfellevurdert)
    Abstract [en]

    This paper aims to introduce deep learning to the power quality community by reviewing the latest applications and discussing the open challenges of this technology. Publications covering deep learning to power quality are stratified in terms of application, type of data, and learning technique. This work shows that the majority of the deep learning applications to power quality are based on unrealistic synthetic data and supervised learning without proper labelling. Some applications with deep learning have already been solved by previous machine learning methods or expert systems. The main barriers to implementing deep learning to power quality are related to lack of novelty, low transparency of the deep learning methods, and lack of benchmark databases. This work also discusses that even with automatic feature extraction by deep learning methods, power quality expert knowledge is still needed to implement and analyse the results. The main research gaps identified in this work are related to the applications of semi-supervised learning, explainable deep learning and hybrid approaches combining deep learning with expert systems. Suggestions for overcoming the present limitations are: providing a stronger collaboration among the grid stakeholders and academy to keep track of power quality events; proper labelling and enlarging of datasets in deep learning methods; explaining the end-to-end decision making of deep learning methods; providing open-access databases for comparison purposes.

  • 27.
    Ravindran, Vineetha
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Sakar, Selcuk
    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.
    Characterization of the impact of PV and EV induced voltage variations on LED lamps in a low voltage installation2020Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 185, artikkel-id 106352Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Photovoltaic (PV) systems, Electric vehicles (EV) and LED lamps have gained significant popularity in our current society. It is therefore common to find customer installations with all three operating together. PV and EV are known sources of voltage variations on the grid. The impact of these voltage variations on LED lamps situated in close proximity to PV or EV in a low voltage installation, in terms of overvoltage, undervoltage, and rapid voltage changes is systematically studied in a laboratory environment in this paper. Such variations can cause malfunctioning of the lamp based on its immunity and tolerance level or be disturbing to the end-user based on the intensity of variations and rate of recurrence of being subjected to such variations. In this work, the observed impacts on LED lamps are illustrated as 15 different cases. The scope of this work is to identify the possible impacts due to voltage variations induced by PV and EV systems on LED lamps and the potential problems that could happen long term due to recurrent subjection of such voltage variations.

  • 28.
    Renders, B.
    et al.
    Electrical Energy Laboratory (EELAB), Department of Electrical Energy, Systems and Automation (EESA), Ghent University, Gent, Belgium.
    Vandevelde, L.
    Electrical Energy Laboratory (EELAB), Department of Electrical Energy, Systems and Automation (EESA), Ghent University, Gent, Belgium.
    Degroote, L.
    Electrical Energy Laboratory (EELAB), Department of Electrical Energy, Systems and Automation (EESA), Ghent University, Gent, Belgium.
    Stockman, K.
    Electrical Energy Laboratory (EELAB), Department of Electrical Energy, Systems and Automation (EESA), Ghent University, Gent, Belgium;Provinciale Industriële Hogeschool, Hogeschool West-Vlaanderen, Kortrijk, Belgium.
    Bollen, Math H. J.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap. STRI AB, Ludvika, Sweden.
    Distributed generation and the voltage profile on distribution feeders during voltage dips2010Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 80, nr 12, s. 1452-1458Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The presence of distributed generators in the distribution network results in an increase of the voltage magnitude close to these generators, during a fault elsewhere in the distribution system or in the transmission system. This voltage dip mitigation capability of converter-connected distributed generation (DG) units is dependent on the control strategy of the converter. To compare the influence of different types of converter-connected distributed generators on the voltage profile along distribution feeders during a fault, the quantity,"voltage ratio" is used. This voltage ratio is obtained by division of the voltage during the voltage dip by the voltage just before the voltage dip. The different converter types are modelled, and the influence on the voltage ratio is analysed.

  • 29.
    Rönnberg, Sarah
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Estimating system indices for short interruptions from data obtained by a limited number of monitors2017Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 146, s. 63-70Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents an estimation of the number of monitoring locations needed to get an accurate estimation of system indices for short interruptions. The study uses data from 11 Swedish distribution network operators, where the number of short interruptions is available for every single costumer. The error range in the estimated system parameters is obtained as a function of the number of monitor locations by obtaining mean and spread of the estimations from 10 000 randomly-selected sets of monitor locations.

    To obtain a rough estimation of the system average or 95-percentile (error margin less than 50%), about 200 monitors are needed. For system 99-percentile, about 400 monitors are needed. For a reasonably accurate estimation, with an error margin less than 10%, a few thousand monitors are needed for both system average and system 95-percentile. Several thousand monitors are needed for the system 99-percentile. The paper also presents some system statistics for the 11 distribution network operators and compares the requirements with recommendations given by the Council of European Energy Regulators.

  • 30.
    Rönnberg, Sarah
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Amaris, Hortensia
    University Carlos III, Madrid.
    Chang, Gary W.
    National Chung Cheng University, Taiwan.
    Gu, Irene Y.H.
    Chalmers University of Technology.
    Kocewiak, Łukasz Hubert
    DONG Energy Wind Power, Fredericia.
    Meyer, Jan Christian
    Technische Universitaet Dresden.
    Olofsson, Magnus
    Swedish Energy Institute.
    Ribeiro, Paulo F.
    Federal University of Itajubá, Brazil.
    Desmet, Jan
    Gent University, Campus Kortrijk.
    On waveform distortion in the frequency range of 2 kHz–150 kHz: Review and research challenges2017Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 150, s. 1-10Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The frequency range between 2 and 150 kHz has recently gained significant attention, triggered by standardization needs and increased emission in this wide frequency range. This paper gives an overview of the state-of-the-art concerning these so-called supraharmonics, and noticeably indicates the research challenges associated with waveform distortion in this frequency range, with emphasis on the following aspects: emission; propagation; interference; measurements; standardization; modelling and simulation.

  • 31.
    Sakar, Selcuk
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Balci, Murat E.
    Electrical and Electronics Engineering, Balikesir University.
    Abdel Aleem, Shady H.E.
    15th of May Higher Institute of Engineering, Mathematical and Physical Sciences, Helwan, Cairo.
    Zobaa, Ahmed F.
    College of Engineering, Design & Physical Sciences, Brunel University London.
    Increasing PV hosting capacity in distorted distribution systems using passive harmonic filtering2017Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 148, s. 74-86Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Adding new capacity expansion alternatives using distributed generation (DG) technologies, particularly penetration of renewable energy, has several economical, and technical advantages such as the reduced system costs, the improved voltage profile, lower line loss and enhanced system’s reliability. However, the DG units may lead to power quality, energy efficiency, and protection problems in the system when their penetration exceeds a particular value, generally called as the system’s hosting capacity (HC) in the literature. In this paper, the HC determination of a distorted distribution system with Photovoltaic (PV)-based DG units is handled as an optimization problem by considering over and under voltage limitations of buses, current carrying capabilities of the lines, and harmonic distortion limitations as constraints. It is seen from simulation results that the HC is dramatically decreased with the increment of the load’s nonlinearity level and the utility side’s background voltage distortion. Accordingly, a C-type passive filter is designed to maximize the harmonic-constrained HC of the studied system while satisfying the constraints. The results indicate that higher HC level can be achieved using the proposed filter design approach compared to three conventional filter design approaches as voltage total harmonic distortion minimization, line loss minimization and power factor maximization.

  • 32.
    Salles, Rafael S.
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Ribeiro, Paulo F.
    Federal University of Itajuba, Av. BPS 1303, 37500 903 Itajuba, Brazil.
    The use of deep learning and 2-D wavelet scalograms for power quality disturbances classification2023Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 214, nr Part A, artikkel-id 108834Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This work investigates the use of advanced signal processing and deep Learning for pattern recognition and classification of signals with power quality disturbances. For this purpose, the continuous wavelet transform is used to generate 2-D images with the time–frequency representation from signals with voltage disturbances. The work aims to use convolutional neural networks to classify this data according to the images’ distortion. In this implementation of artificial intelligence, specific stages of design, training, validation, and testing were carried out for a model elaborated from the scratch and a transfer learning technique with the pre-trained networks SqueezeNet, GoogleNet, and ResNet-50. The work was developed in the MATLAB/Simulink software, all signal processing stages, CNN design, simulation, and the investigated data generation. All steps have their objectives fulfilled, culminating in the excellent execution and development of the research. The results sought high precision for the model from scratch and ResNet-50 in classify the test set. The other two models obtained not-so-high accuracy, and the results are consistent when compared with different methodologies. The main contributions of the paper are: (i) developing a methodology to use DL and transfer learning on the classification of voltage disturbances; (ii) using a 2-D representation that incorporates time and frequency information that characterizes several PQ issues; (iii) conducting a study case that shows the suitability of CNN as a tool for voltage disturbance classification, with specific application for 2-D images. Considerations about the results were pointed out.

  • 33.
    Santos, Ivan Nunes
    et al.
    Federal University of Uberlândia.
    Ćuk, Vladimir
    Eindhoven University of Technology.
    Almeida, Pedro M.
    Federal University of Juiz de Fora, Minas Gerais.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Ribeiro, Paulo Fernando
    Federal University of Itajubá, Universidade Federal de Pernambuco, Recife, Calvin College, Grand Rapids, MI.
    Considerations on hosting capacity for harmonic distortions on transmission and distribution systems2015Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 119, s. 199-206Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The increasing penetration of renewable/distributed sources with non-linear characteristics demands a clear methodology for determining the amount of generation which can be connected to the system without deteriorating the performance (the hosting capacity). This paper proposes a methodology for determining the hosting capacity regarding harmonic distortions. The method includes aggregation effects of harmonic currents, the influence of harmonic distortion limits and harmonic generation profile. To exemplify an application of the proposed procedure, a simple case study is performed and analyzed.

  • 34.
    Sutaria, Jil
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Espin Delgado, Angela
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Rönnberg, Sarah
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Measurements and modeling of the frequency behavior of residual current devices- from 4 Hz to 40 kHz2022Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 209, artikkel-id 108052Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Residual current devices (RCDs) are a common means of protection against shock due to indirect contact in low voltage (LV) systems. Due to the increasing penetration of power electronics equipment in LV systems, higher amounts of waveform distortion at a broad range of frequencies, from dc, subharmonics up to hundreds of kHz (supraharmonics), are expected to be present both during normal operation and during faults. The standardization committees and manufacturers have responded to this challenge by proposing different types of RCDs that are expected to function under given conditions of fault current waveform. However, subharmonic and supraharmonic frequency components are not considered in the standards for most of the RCD types. This article studies the effect of these frequency components on RCDs type AC, A, B and F. An assessment is made in terms of two types of RCD failure: blinding and nuisance tripping, for which both magnitude of the current and breaking time is considered. A frequency mapping of the RCDs is performed, and an assessment of these results based on the frequency-dependent response of the human body to currents is performed. Finally, a frequency model for RCDs type A, F and B is developed.

  • 35.
    Sutaria, Jil
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Rönnberg, Sarah
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Espin Delgado, Angela
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Factors influencing the induced primary emission and induced secondary emission in the frequency range of 2 to 150 kHz2023Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 224, artikkel-id 109725Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The induced primary emission leads to changes in the primary emission of a device and the induced secondary emission leads to changes in the propagation of supraharmonics in the adjacent phase due to the connection of single-phase loads spread over three phases in an installation. The induced primary emission and induced secondary emission are shown to give a significant contribution to the total emission measured at a given point in an installation. The induction of the emission is caused by the inductive and capacitive coupling among the conductors within the cables. This paper presents an analysis of four parameters that impact the magnitude of the induced emissions. Simulations carried out in COMSOL, show that the type of cable used impacts the induced emission and studies show that shielded cable with a stranded conductor with the shield grounded will lead to a reduction in the induced emissions. Among the other parameters, i.e., the load and transformer impedance and the length of the cable, the length of the cable is dominating in deciding the magnitude of the induced emissions. Analysis is carried out using Monte Carlo simulation and varying parameters stochastically. For all investigated parameters there is a strong frequency dependency. The stochastic variation of the load impedance in one phase causes a variation of 5% whereas the change in length of the cable leads to a maximum 40% variation in the considered frequency range for induced primary emission. Measurement results are presented to validate the results.

    Fulltekst (pdf)
    fulltext
  • 36.
    Sutaria, Jil
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Rönnberg, Sarah
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Espín-Delgado, Ángela
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Analysis of supraharmonics in a three-phase frame2022Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 203, artikkel-id 107668Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Interaction in the supraharmonic range of 1-ϕ device connected in 1-ϕ or 3-ϕ installations will differ according to the design of the installation. Power factor corrected devices employing switched mode power supplies produce supraharmonics in the range 2–150 kHz. The impact of e.g. voltage unbalance, load unbalance and conductor crosstalk on supraharmonics from these devices connected in a 3-ϕ installation are still somewhat unknown. The paper aims to show with measurements and mathematical models the impact of voltage unbalance, load unbalance, and conductor crosstalk on supraharmonics. The impact of voltage unbalance for constant power loads was seen to increase the emission of supraharmonics. Two new terms induced primary and induced secondary emission showing the impact of conductor crosstalk have been introduced. The induced primary emission leads to an increase in the self-emission of the device. The induced secondary emission on the other hand influences the propagation of the emission. The impact of the voltage unbalance, load unbalance, and conductor crosstalk on the addition of supraharmonics emission in the neutral conductor is shown.

  • 37.
    Wang, Ying
    et al.
    College of Electrical Engineering and Information Technology, Sichuan University.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bagheri, Azam
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Xiao, Xian-Xong
    College of Electrical Engineering and Information Technology, Sichuan University.
    Olofsson, Magnus
    Elforsk, Energiforsk AB, Stockholm.
    A quantitative comparison approach for different voltage dip characterization methods2016Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 133, s. 182-190Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents a systematic approach to compare different methods for characterizing voltage dips in a quantitative way. A prediction error is calculated between measured and synthetic dips (reproduced from single-event characteristics for the measured dips) with respect to the way they impact the performance of a generic device. The proposed approach is illustrated by comparing seven different characterization methods and their ability to predict the minimum dc-bus voltage of a three-phase adjustable-speed drive. A generic model of such a drive is used for this. Based in this comparison it is concluded that characterization method for dips in three-phase systems should include unbalance and phase-angle jump.

  • 38.
    Yang, Kai
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Interharmonic currents from a Type-IV wind energy conversion system2017Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 143, s. 357-364Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents, for the first time, the verification of the classic model for the origin of interharmonic emission from a frequency converter, for a Type-IV wind turbine by using long-term measurements. Interharmonic variations in magnitude and in frequency are due to the difference between the generator-side and grid-side frequency of the full-power converter. The model verification consists of three parts: correlation between frequencies; relation between magnitude of interharmonics and active-power production, and relation between magnitudes of different interharmonics. The measurements are in agreement with the model predictions. The paper also introduces a novel graphical correlation method to extract information on interharmonics from long-term measurement series.

  • 39.
    Yang, Kai
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Bollen, Math
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Amaris, Hortensia
    Carlos III University of Madrid, 28911 Leganés, Madrid, Spain.
    Alvarez, Carlos
    Energy to Quality, 28046 Madrid, Spain.
    Decompositions of harmonic propagation in wind power plant2016Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 141, s. 84-90Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents harmonic propagation in a wind power plant. The two groups of propagation are distinguished based on the harmonic sources: propagation from one individual wind turbine to other turbines and to the public grid; and propagation from the public grid to the collection grid and to individual wind turbines. The paper studies the characteristics of the different harmonic propagation paths. A case with emission from all turbines, at different production levels, and from the public grid is presented as well. Also the impact of a turbine filter on the propagation is studied. The study indicates that, resonances of a wind power plant have a significant impact on the propagation. It is also shown that harmonic studies should consider both emission originating from turbines and emission originating from the public grid. It is also shown that the filter with the turbine has a significant impact on the harmonic propagation.

  • 40.
    Yang, Kai
    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.
    Wahlberg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Measurements of harmonic emission versus active power from wind turbines2014Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, nr 108, s. 304-314Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents harmonic measurements from three individual wind turbines (2 and 2.5MW size). Both harmonics and interharmonics have been evaluated, especially with reference to variations in the active-power production. The overall spectra reveal that, emission components may occur at any frequency and not only at odd harmonics. Interharmonics and even harmonics emitted from wind turbines are relatively high. Individual frequency components depend on the power production in dierent ways: characteristic harmonics are independent of power; interharmonics show a strong correlation with power; other harmonic and interharmonic components present various patterns. It is concluded that the power production is not the only factor determining the current emission of a wind energy conversion system.

    Fulltekst (pdf)
    FULLTEXT01
  • 41.
    Zhang, Tengfei
    et al.
    School of Marine Engineering, Jimei University, Xiamen 361021, PR China.
    Wu, Defeng
    School of Marine Engineering, Jimei University, Xiamen 361021, PR China; Fujian Provincial Key Laboratory of Naval Architecture and Ocean Engineering, Xiamen 361021, PR China.
    Li, Lingyu
    School of Marine Engineering, Jimei University, Xiamen 361021, PR China.
    Yamashita, Andre S.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Huang, Saifeng
    School of Marine Engineering, Jimei University, Xiamen 361021, PR China.
    A fault reconfiguration strategy based on adjustable space operator discrete state transition algorithm for ship microgrid system2022Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 205, artikkel-id 107707Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    As an independent power supply network, when the ship ring microgrid system (SRMS) fails or is damaged, the power-loss load can be reasonably distributed to other power sources through the control switch, thereby improving the reliability of the power grid. We consider the maximum power load, minimum switching action and generator efficiency as the reconfiguration goals. In order to complete the reconfiguration quickly, we present an optimization strategy based on an adjustable space operator (ASO) and the discrete state transition algorithm (DSTA), the ASODSTA. The main idea of DSTA is to use four spatial geometric operators to find the optimal solution. The optimization is completed by combining the operators with the sigmoid function, and an ASO is proposed as the variable of the sigmoid function. The spatial distribution of the candidate solutions is more widespread through the unification of the four operators. The introduction of the sigmoid function and the ASO improves the quality of the global optimal solution and shortens the running time of the algorithm. The simulation results show that the proposed method can solve the SRMS reconfiguration problem faster and more effectively by comparing with the algorithms EO, WOA, GWO and BPSO in the references.

  • 42.
    Štumpf, Martin
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB. Lerch Lab of EM Research, Faculty of Electrical Engineering and Communication, Brno University of Technology, Brno, 616 00, Czech Republic.
    Antonini, Giulio
    UAq EMC Laboratory, Department of Industrial and Information Engineering and Economics, University of L’Aquila, L’Aquila, 671 00, Italy.
    Ekman, Jonas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Pulsed electromagnetic field coupling to a transmission line with arbitrary loads—A unified methodology based on reciprocity2024Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 227, nr Part A, artikkel-id 109980Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    V.A unified description of the time-domain (TD) electromagnetic (EM) field coupling to a transmission line (TL) that is terminated by arbitrary linear time-invariant loads is presented. Closed-form expressions for the electric current induced in the loads are derived with the aid of the EM reciprocity theorem of the time-convolution type. The validity of the solution is demonstrated via illustrative numerical examples.

1 - 42 of 42
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