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  • 1.
    Alvarez Perez, Manuel Alejandro
    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.
    Bermúdez, Juan
    Universidad Simón Bolívar.
    Zhong, Jin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science. The University of Hong Kong.
    Bollen, Math
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    A Generic Storage Model Based on a Future Cost Piecewise-Linear Approximation2019In: IEEE Transactions on Smart Grid, ISSN 1949-3053, E-ISSN 1949-3061, Vol. 10, no 1, p. 878-888Article in journal (Refereed)
    Abstract [en]

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

  • 2.
    Laury, John
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Abrahamsson, Lars
    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.
    A rotary frequency converter model for electromechanical transient studies of 16 (2/3) Hz railway systems2019In: International Journal of Electrical Power & Energy Systems, ISSN 0142-0615, E-ISSN 1879-3517, Vol. 106, p. 467-476Article in journal (Refereed)
    Abstract [en]

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

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

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

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

  • 3.
    Nömm, Jakob
    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.
    An analysis of voltage quality in a nanogrid during islanded operation2019In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 12, no 4, article id 614Article in journal (Refereed)
    Abstract [en]

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

  • 4.
    Lennerhag, Oscar
    et al.
    Independent Insulation Group Sweden AB, Ludvika, Sweden.
    Lundquist, Jan
    Independent Insulation Group Sweden AB, Ludvika, Sweden.
    Engelbrecht, Christiaan
    Engelbrecht Consulting B.V., The Netherlands.
    Karmokar, Tanumay
    NKT HV Cables AB, Lyckeby, Sweden.
    Bollen, Math
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science. Engineering Sciences and Mathematics, Luleå University of Technology, Skellefteå, Sweden.
    An Improved Statistical Method for Calculating Lightning Overvoltages in HVDC Overhead Line/Cable Systems2019In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 12, no 16, article id 3121Article in journal (Refereed)
    Abstract [en]

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

  • 5.
    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. 

  • 6.
    Ravindran, Vineetha
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Busatto, Tatiano
    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.
    Meyer, Jan
    Technische Universität, Dresden, Germany.
    Charactizations of interactions between PV and Energy efficient lighting (LED) in a mixed installation.2019Conference paper (Refereed)
    Abstract [en]

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

  • 7.
    Ravindran, Vineetha
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Busatto, Tatiano
    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.
    Comparison of a non-parametric and parametric method for interharmonic estimation in PV systems2019Conference paper (Refereed)
    Abstract [en]

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

  • 8.
    Abrahamsson, Lars
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Laury, John
    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.
    Evaluating a constant-current load model through comparativetransient stability case studies of a synchronous-synchronous rotary frequencyconverter fed railway2019Conference paper (Refereed)
    Abstract [en]

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

  • 9. Laury, John
    et al.
    Abrahamsson, Lars
    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 reduced share of rotary frequency converter in a low-frequency synchronous railway grid: A transient stability study.2019Conference paper (Refereed)
  • 10.
    Busatto, Tatiano
    et al.
    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.
    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.
    Including Uncertainties from Customer Connections in Calculating Low-Voltage Harmonic Impedance2019In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 34, no 2, p. 606-615Article in journal (Refereed)
    Abstract [en]

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

  • 11.
    Sakar, Selcuk
    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.
    Interferences in AC-DC LED Drivers Exposed to Voltage Disturbances in the Frequency Range 2 kHz - 150 kHz2019In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 34, no 11, p. 11171-11181Article in journal (Refereed)
    Abstract [en]

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

  • 12.
    Ravindran, Vineetha
    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.
    Interharmonics in PV systems: A Review of analysis and estimation methods; considerations for selection of an apt method2019In: IET Renewable Power Generation, ISSN 1752-1416, E-ISSN 1752-1424, Vol. 13, no 12, p. 2023-2032Article, review/survey (Refereed)
    Abstract [en]

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

  • 13.
    Mulenga, Enock
    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.
    Etherden, Nicholas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science. Vattenfall AB.
    Overvoltage due to single-phase and three-phase connected PV2019In: 25th International Conference on Electricity Distribution, Madrid, 3-6 June 2019., CIRED - Congrès International des Réseaux Electriques de Distribution, 2019, p. 1-5, article id No 370Conference paper (Refereed)
    Abstract [en]

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

  • 14.
    de Oliveira, Tiago Elias Castelo
    et al.
    Electrical Energy Systems, Technological University of Eindhoven, Eindhoven, The Netherlands.
    Bollen, Math
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Ribeiro, Paulo Fernando
    Advanced Power Technologies and Innovations in Systems and Smart Grids Group, Federal University of Itajuba, Itajuba, Brazil.
    de Carvalho, Pedro M. S.
    Energy Scientific Area, Instituto Superior Tecnico, Lisbon, Portugal.
    Zambroni, Antônio C.
    Advanced Power Technologies and Innovations in Systems and Smart Grids Group, Federal University of Itajuba, Itajuba, Brazil.
    Bonatto, Benedito D.
    Advanced Power Technologies and Innovations in Systems and Smart Grids Group, Federal University of Itajuba, Itajuba, Brazil.
    The Concept of Dynamic Hosting Capacity for Distributed Energy Resources: Analytics and Practical Considerations2019In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 12, no 13, article id 2576Article in journal (Refereed)
    Abstract [en]

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

  • 15.
    Mulenga, Enock
    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.
    Etherden, Nicholas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science. Vattenfall AB.
    The Role of Aleatory and Epistemic Uncertainties in a Stochastic Hosting Capacity Approach for Solar PV2019In: IEEE PES Innovative Smart Grid Technologies (ISGT), Bucharest: IEEE, 2019, p. 1-5, article id 133Conference paper (Refereed)
    Abstract [en]

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

  • 16.
    Ravindran, Vineetha
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Busatto, Tatiano
    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
    Institute of Electrical Power Systems and High Voltage Engineering, Technische Universitaet Dresden, Dresden, Germany.
    Bollen, Math
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Time-varying interharmonics in different types of grid-tied PV inverter systems2019In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208Article in journal (Refereed)
    Abstract [en]

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

  • 17.
    Alvarez, Manuel
    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.
    Frías, Pablo
    Comillas Pontifical University, Madrid, Spain.
    Cossent, Rafael
    Comillas Pontifical University, Madrid, Spain.
    Jabr, Rabih
    American University of Beirut, Beirut, Lebanon.
    Zhong, Jin
    The University of Hong Kong, Hong Kong, China.
    A Capacity Mechanism Design for Distribution Network Expansion Planning2018In: 2018 IEEE International Conference on Environment and Electrical Engineering and 2018 IEEE Industrial and Commercial Power Systems Europe (EEEIC / I&CPS Europe), 2018, article id 8493874Conference paper (Refereed)
    Abstract [en]

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

  • 18.
    Balouji, Ebrahim
    et al.
    Department of Electrical Engineering, Chalmers University of Technology.
    Gu, Irene Y.H.
    Department of Electrical Engineering, Chalmers University of Technology.
    Bollen, Math
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Bagheri, Azam
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Nazari, Mahmood
    Department of Electrical Engineering, Chalmers University of Technology.
    A LSTM-based deep learning method with application to voltage dip classification2018In: Proceedings of International Conference on Harmonics and Quality of Power, ICHQP, Piscataway, NJ: Institute of Electrical and Electronics Engineers (IEEE), 2018Conference paper (Refereed)
    Abstract [en]

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

  • 19.
    Bagheri, Azam
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Gu, Irene Y.H.
    Department of Electrical Engineering, Chalmers University of Technology.
    Bollen, Math
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Balouji, Ebrahim
    Department of Electrical Engineering, Chalmers University of Technology.
    A Robust Transform-Domain Deep Convolutional Network for Voltage Dip Classification2018In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 33, no 6, p. 2794-2802Article in journal (Refereed)
    Abstract [en]

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

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

  • 20.
    Schwanz, Daphne
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Busatto, Tatiano
    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.
    Larsson, Anders
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    A stochastic study of harmonic voltage distortion considering single-phase photovoltaic inverters2018In: Proceedings of International Conference on Harmonics and Quality of Power, ICHQP, Piscataway, NJ: Institute of Electrical and Electronics Engineers (IEEE), 2018Conference paper (Refereed)
    Abstract [en]

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

  • 21.
    Nömm, Jakob
    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.
    An Analysis of Frequency Variations and its Implications on Connected Equipment for a Nanogrid during Islanded Operation2018In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, article id en11092456Article in journal (Refereed)
    Abstract [en]

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

  • 22.
    Bagheri, Azam
    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.
    Gu, Irene Y.H.
    Signal Processing group, Chalmers University of Technology.
    Big data from smart grids2018In: 2017 IEEE PES Innovative Smart Grid Technologies Conference Europe, ISGT-Europe 2017: proceedings, New York: Institute of Electrical and Electronics Engineers (IEEE), 2018Conference paper (Refereed)
    Abstract [en]

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

  • 23.
    Bagheri, Azam
    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.
    Characterizing three-phase unbalanced dips through the ellipse parameters of the space phasor model2018In: 2017 IEEE PES Innovative Smart Grid Technologies Conference Europe, ISGT-Europe 2017: proceedings, New York: Institute of Electrical and Electronics Engineers (IEEE), 2018Conference paper (Refereed)
    Abstract [en]

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

  • 24.
    Bollen, Math
    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.
    Zavoda, Francisc
    IREQ (HQ), Varennes.
    Langella, Roberto
    Second University of Naples.
    Djokic, Sasa
    University of Edinburgh.
    Cuifo, Philip
    University of Wollongong.
    Meyer, Jan Christian
    Technische Universitaet Dresden.
    Cuk, Vladimir
    Eindhoven University of Technology.
    Consequences of Smart Grids for Power Quality Overview of the Results from CIGRE Joint Working Group C4.24/CIRED2018In: 2017 IEEE PES Innovative Smart Grid Technologies Conference Europe, ISGT-Europe 2017: proceedings, New York: Institute of Electrical and Electronics Engineers (IEEE), 2018Conference paper (Refereed)
    Abstract [en]

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

  • 25.
    Busatto, Tatiano
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Ravindran, Vineetha
    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.
    Estimation of the Consumer Electronics Capacitance for Harmonic Resonance Studies by a Non-Invasive Measurement Method2018In: Proceedings of International Conference on Harmonics and Quality of Power, ICHQP, Piscataway, NJ: Institute of Electrical and Electronics Engineers (IEEE), 2018, , p. 6Conference paper (Refereed)
    Abstract [en]

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

  • 26.
    Abrahamsson, Lars
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Laury, John
    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.
    Further studies on the transient stability of synchronous-synchronous rotary frequency converter fed railways with low-frequency AC high-voltage transmission2018In: International Journal of Energy Production and Management, ISSN 2056-3272, E-ISSN 2056-3280, Vol. 3, no 4, p. 266-276Article in journal (Refereed)
    Abstract [en]

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

  • 27.
    Nömm, Jakob
    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.
    Harmonic Voltage Measurements in a Single House Microgrid2018In: Proceedings of International Conference on Harmonics and Quality of Power, ICHQP, Piscataway, NJ: Institute of Electrical and Electronics Engineers (IEEE), 2018Conference paper (Refereed)
    Abstract [en]

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

  • 28.
    Cundeva, Snezana
    et al.
    University Ss. Cyril and Methodius Faculty of Electrical Engineering and IT Skopje.
    Krkoleva Mateska, Aleksandra
    University Ss. Cyril and Methodius Faculty of Electrical Engineering and IT Skopje.
    Bollen, Math
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Hosting capacity of LV residential grid for uncoordinated ev charging2018In: Proceedings of International Conference on Harmonics and Quality of Power, ICHQP, Piscataway, NJ: Institute of Electrical and Electronics Engineers (IEEE), 2018Conference paper (Refereed)
    Abstract [en]

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

  • 29.
    Bollen, Math
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Mulenga, Enock
    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.
    Etherden, Nicholas
    Hosting Capacity of the Grid for Photovoltaic Installations: a Stochastic Approach Applied to Single-phase Connections2018In: 8th Solar Integration Workshop, 2018, p. 1-7, article id 6A_1_SIW18_046Conference paper (Refereed)
    Abstract [en]

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

  • 30.
    Sakar, Selcuk
    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.
    Immunity Test of LED Lamps Based on IEC 61000-4-19 and Unexpected Consequence2018In: Proceedings of International Conference on Harmonics and Quality of Power, ICHQP, Piscataway, NJ: Institute of Electrical and Electronics Engineers (IEEE), 2018Conference paper (Refereed)
    Abstract [en]

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

  • 31.
    Mulenga, Enock
    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.
    Impact of Service and Feeder Cable Upgrade on Hosting Capacity for Single Phase Connected Photovoltaics2018In: Proceedings of International Conference on Harmonics and Quality of Power, ICHQP, Institute of Electrical and Electronics Engineers (IEEE), 2018Conference paper (Refereed)
    Abstract [en]

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

  • 32.
    Bagheri, Azam
    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.
    Gu, Irene Y.H.
    Chalmers University of Technology.
    Improved characterization of multi-stage voltage dips based on the space phasor model2018In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 154, p. 319-328Article in journal (Refereed)
    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.

  • 33.
    Ravindran, Vineetha
    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.
    Busatto, Tatiano
    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.
    Inspection of Interharmonic emissions from a Grid-tied PV Inverter in North Sweden2018In: Proceedings of International Conference on Harmonics and Quality of Power, ICHQP, Piscataway, NJ: Institute of Electrical and Electronics Engineers (IEEE), 2018Conference paper (Refereed)
    Abstract [en]

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

  • 34.
    Sakar, Selcuk
    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.
    Light Intensity Behavior of LED Lamps within theThermal Stabilization Period2018In: Proceedings of International Conference on Harmonics and Quality of Power, ICHQP, Piscataway, NJ: Institute of Electrical and Electronics Engineers (IEEE), 2018Conference paper (Refereed)
    Abstract [en]

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

  • 35.
    Lennerhag, Oscar
    et al.
    Independent Insulation Group Sweden AB.
    Bollen, Math
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Power system impacts of decreasing resonance frequencies2018In: Proceedings of International Conference on Harmonics and Quality of Power, ICHQP, Piscataway, NJ: Institute of Electrical and Electronics Engineers (IEEE), 2018Conference paper (Refereed)
    Abstract [en]

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

  • 36.
    Alvarez Perez, Manuel Alejandro
    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.
    Bermúdez, Juan
    Department of Energy Conversion and Transport, Simón Bolívar University.
    Zhong, Jin
    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.
    Reservoir-Type Hydropower Equivalent Model Based on a Future Cost Piecewise Approximation2018In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 155, p. 184-195Article in journal (Refereed)
    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.

  • 37.
    Tang, Yuchen
    et al.
    Department of Electrical and Electronic Engineering, The University of Hong Kong.
    Zhong, Jin
    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.
    Schedule of air-conditioning systems with thermal energy storage considering wind power forecast errors2018In: International Journal of Electrical Power & Energy Systems, ISSN 0142-0615, E-ISSN 1879-3517, Vol. 95, p. 592-600Article in journal (Refereed)
    Abstract [en]

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

  • 38.
    Bagheri, Azam
    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.
    Simple diagnostic technique of switch failure modes of VSI power converter2018In: 2017 IEEE PES Innovative Smart Grid Technologies Conference Europe, ISGT-Europe 2017: proceedings, New York: Institute of Electrical and Electronics Engineers (IEEE), 2018Conference paper (Refereed)
    Abstract [en]

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

  • 39.
    Schwanz, Daphne
    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.
    Larsson, Anders
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Some methods for harmonic emission determination in wind power plants2018In: Proceedings of International Conference on Harmonics and Quality of Power, ICHQP, Piscataway, NJ: Institute of Electrical and Electronics Engineers (IEEE), 2018Conference paper (Refereed)
    Abstract [en]

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

  • 40.
    Bagheri, Azam
    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.
    Space Phasor Model Based Monitoring of Voltages in Three Phase Systems2018In: Proceedings of International Conference on Harmonics and Quality of Power, ICHQP, Piscataway, NJ: Institute of Electrical and Electronics Engineers (IEEE), 2018Conference paper (Refereed)
    Abstract [en]

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

  • 41.
    Laury, John
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Abrahamsson, Lars
    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.
    Transient Stability of a Rotary Frequency Converter fed railway, interconnected with a parallel low frequency high voltage transmission system2018In: WIT Transactions on the Built Environment, ISSN 1746-4498, E-ISSN 1743-3509, Vol. 181, p. 15-24Article in journal (Refereed)
    Abstract [en]

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

  • 42.
    Laury, John
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Abrahamsson, Lars
    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.
    Transient stability of rotary frequency converter fed low frequency railway grids: The Impact of Different Grid Impedances and Different Converter Station Configurations2018Conference paper (Refereed)
    Abstract [en]

    One method of strengthening low frequency AC railway grids is to upgrade Booster Transformer (BT) catenary systems, to Auto Transformer (AT) catenary systems. An AT catenary system has lower equivalent impedance compared to a BT system. Thus, an upgrade makes the existing converter stations electrically closer.

    Converter stations may have different types of Rotary Frequency Converters (RFCs) installed in them, and it is not well explored how different RFCs behaves and interact during and after a large disturbance.

    Using the Anderson-Fouad model of synchronous machines to describe the dynamics of RFCs, several case studies have been performed through numerical simulations. The studies investigate the interactions within and between converter stations constituted with different RFC types, for BT as well AT catenary systems.

    The numerical studies reveal that replacing BT with AT catenary systems, results in a more oscillatory system behaviour. This is seen for example in the power oscillations between and inside converter stations, after fault clearance.

  • 43.
    Alvarez Perez, Manuel Alejandro
    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.
    Bermúdez, Juan
    Universidad Simón Bolívar.
    Zhong, Jin
    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.
    A Hydro-Reservoir Generic Storage Model for Short-Term Hydrothermal Coordination2017In: IEEE PES PowerTech Manchester 2017: towards and beyond sustainable energy systems, 2017, Piscataway, NJ: Institute of Electrical and Electronics Engineers (IEEE), 2017, article id 7980882Conference paper (Refereed)
    Abstract [en]

    This work presents a linear solution for the short-term hydro-thermal scheduling problem linked to long-term conditions through a piecewise-linear Future Cost Function (FCF). Given end-point conditions to conform long-term water releases, and given actual reservoir conditions, a segment of a pre-built piecewise future cost function will be chosen. The linear characteristic of the FCF segment will allow a linear modeling of the hydro-power plant, in a similar fashion as a thermal unit with an equivalent marginal opportunity cost. A short-term hydro thermal coordination problem will be formulated considering parallel and cascaded hydro-reservoirs. Three study cases involving different reservoir configurations and scenarios will be computed to test the model. The results of this model mimics coherently the future-cost hydro-thermal coordination problem for the different configurations tested. Given similarities with other forms of energy storage, a new theoretical model for generic storage will be proposed and discussed.

  • 44.
    Abrahamsson, Lars
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Serrano Jimenez, Daniel
    University Carlos III.
    Laury, John
    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.
    AC cables strengthening railway low frequency AC power supplysystems2017In: ASME/IEEE 2017 Joint Rail Conference, ASME Press, 2017Conference paper (Refereed)
    Abstract [en]

    In present-day railway power supply systems using an AC frequency lower than the one in the public power system of 50/60 Hz, high voltage overhead transmission lines are used as one measure of strengthening the railway power supply system grids. This option may be economically beneficial, compared to strengthening the grid purely by increasing the density of converter stations or increasing the cross section areas of the overhead catenary wires. High voltage AC transmission lines in the railway power supply system allow larger distances between converter stations than would otherwise be possible for a given amount of train traffic. Moreover, the introduction of AC transmission lines implies reduced line losses and reduced voltage level fluctuations at the catenary for a given amount of train traffic. However, due to the increased public and government resistance for additional overhead high voltage AC transmission lines in general, different alternatives will be needed for the future improvements and strengthening of railway power systems. For a more sustainable transport sector, the share and amount of railway traffic needs to increase, in which case such a strengthening becomes inevitable. Earlier, usage of VSC-HVDC transmission cables has been proposed as one alternative to overhead AC transmission lines. One of the main benefits with VSC-HVDC transmission is that control of power flows in the railway power systems is easier and that less converter capacity may be needed. Technically, VSC-HVDC transmission for railway power systems is a competitive solution as it offers a large variety of control options. However, there might be other more economical alternatives reducing the overall impedance in the railway power system. In public power systems with the frequency of 50/60 Hz, an excess of reactive power production in lowly utilized cables imposes an obstacle in replacing overhead transmission lines with cables. In low frequency AC railway power system, the capacitive properties are less significant allowing longer cables compared to 50/60 Hz power systems. Moreover, in converter-fed railways, some kind of reactive compensation will automatically be applied during low-load. At each converter station, voltage control is already present following the railway operation tradition. Therefore, in this paper, we propose AC cables as a measure of strengthening low-frequency AC railway power systems. The paper compares the electrical performances of two alternative reinforcement cable solutions with the base case of no reinforcement. The options of disconnecting or toggling the cables at low load as well as the automatic reactive compensation by converter voltage control are considered. Losses and voltage levels are compared for the different solutions. Investment costs and other relevant issues are discussed.

  • 45.
    Meyer, Jan
    et al.
    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.
    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.
    Smith, Jeff W.
    Electric Power Research Institute (EPRI), Power System Studies, Palo Alto, CA.
    CIGRE C4/C6.29: Survey of utilities experiences on power quality issues related to solar power2017In: CIRED - Open Access Proceedings Journal, ISSN 2515-0855, Vol. 2017, no 1, p. 539-543Article in journal (Refereed)
    Abstract [en]

    Owing to the energy policies and the consequent transition to renewable energy sources, the amount of photovoltaic (PV) installations is continuously increasing in many countries. As PV inverters utilise power electronics, its impact on power quality is an important concern for manufacturers, planners, solar power operators and utilities/ network operators. The International council on large electric systems (CIGRE) working group C4/C6.29 has studied many aspects related to PV installations and its impact on power quality. To incorporate the existing experiences with power quality issues related to solar power, an international survey has been conducted by the working group. The survey has found that there is a significant lack of information among utilities/network operators with respect to the possible impact of PV installations on power quality. It is recommended to intensify the monitoring of PV installations in order to obtain sufficient information for a reliable assessment of its impact on power quality.

  • 46.
    Barakou, Fani
    et al.
    Eindhoven University of Technology.
    Bollen, Math
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Mousavi-Gargari, S.
    TenneT TSO BV, Arnhem.
    Wouters, P.A.A.F.
    Eindhoven University of Technology.
    Steenis, E.F.
    Eindhoven University of Technology.
    Downstream network modeling for switching transients in EHV networks containing cables2017In: IEEE PES PowerTech Manchester 2017: towards and beyond sustainable energy systems, 2017, Piscataway, NJ: Institute of Electrical and Electronics Engineers (IEEE), 2017, article id 7980800Conference paper (Refereed)
    Abstract [en]

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

  • 47.
    Rönnberg, Sarah
    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.
    Estimating system indices for short interruptions from data obtained by a limited number of monitors2017In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 146, p. 63-70Article in journal (Refereed)
    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.

  • 48.
    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.

  • 49.
    Bollen, Math
    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.
    Hosting Capacity of the Power Grid for Renewable Electricity Production and New Large Consumption Equipment2017In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 10, no 9, article id 1325Article in journal (Refereed)
    Abstract [en]

    After a brief historical introduction to the hosting-capacity approach, the hosting capacity is presented in this paper as a tool for distribution-system planning under uncertainty. This tool is illustrated by evaluating the readiness of two low-voltage networks for increasing amounts of customers with PV panels or with EV chargers. Both undervoltage and overvoltage are considered in the studies presented here. Probability distribution functions are calculated for the worst-case overvoltage and undervoltage as a function of the number of customers with PV or EV chargers. These distributions are used to obtain 90th percentile values that act as a performance index. This index is compared with an overvoltage or undervoltage limit to get the hosting capacity. General aspects of the hosting-capacity calculations (performance indices, limits, and calculation methods) are discussed for a number of other phenomena: overcurrent; fast voltage magnitude variations; voltage unbalance; harmonics and supraharmonics. The need for gathering data and further development of models for existing demand is emphasised in the discussion and conclusions

  • 50.
    Lu, Shengye
    et al.
    Department of Electrical Engineering, Tampere University of Technology.
    Repo, Sami
    Department of Electrical Engineering, Tampere University of Technology.
    Tjäder, Jonas
    STRI AB, Ludvika.
    Kjellström, Anders
    Luleå tekniska universiet.
    Bollen, Math
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Etherden, Nicholas
    Vattenfall AB.
    IEC 61850-based Communication and Aggregation Solution for Demand-Response Application2017In: IEEE PES Innovative Smart Grid Technologies Conference Europe: ISGT Europe 2016,  Ljubljana,  Slovenia,  9-12  October 2016, Piscataway, NJ, 2017, Vol. Part F126485, article id 7856283Conference paper (Refereed)
    Abstract [en]

    This paper presents an IEC 61850 standard-based communication and aggregation solution for Demand-Response application, which allows end devices automatically detected, configured and integrated to the overlying Demand-Response system, thereby greatly increasing the integration efficiency, and making large scale of deployment feasible. This communication solution is dedicated to one community-wide Demand-Response application designed for a residential area near an industrial installation in Sweden. The community-wide Demand-Response application will be briefly explained in the paper, however, the main focus of this paper is the communication solution and IT system implementation for this application. The communication solution is realized by the unconventional use of IEC 61850 standard, and implemented in a hierarchical structure consisting of SCADA, communication gateway and low cost micro processor-based spatial heating controllers

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