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Bollen, M., Gil de Castro, A. & Rönnberg, S. (2020). Characterization methods and typical levels of variations in rms voltage at the time scale between 1 second and 10  minutes. Electric power systems research, 184, Article ID 106322.
Open this publication in new window or tab >>Characterization methods and typical levels of variations in rms voltage at the time scale between 1 second and 10  minutes
2020 (English)In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 184, article id 106322Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Elsevier, 2020
Keywords
Electricity distribution grids, Power quality, Power-quality monitoring, Rapid voltage changes, Supply voltage variations
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electric Power Engineering
Identifiers
urn:nbn:se:ltu:diva-78296 (URN)10.1016/j.epsr.2020.106322 (DOI)2-s2.0-85081650800 (Scopus ID)
Note

Validerad;2020;Nivå 2;2020-04-02 (alebob)

Available from: 2020-04-02 Created: 2020-04-02 Last updated: 2020-04-02Bibliographically approved
Busatto, T., Ravindran, V., Larsson, A., Rönnberg, S., Bollen, M. & Meyer, J. (2020). Deviations between the commonly-used model and measurements of harmonic distortion in low-voltage installations. Electric power systems research, 180, Article ID 106166.
Open this publication in new window or tab >>Deviations between the commonly-used model and measurements of harmonic distortion in low-voltage installations
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2020 (English)In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 180, article id 106166Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Elsevier, 2020
Keywords
Power quality, Power system harmonics, Power electronics, Harmonic analysis, Nonlinear systems
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electric Power Engineering
Identifiers
urn:nbn:se:ltu:diva-77661 (URN)10.1016/j.epsr.2019.106166 (DOI)000514015200052 ()2-s2.0-85076840939 (Scopus ID)
Funder
Swedish Energy Agency
Note

Validerad;2020;Nivå 2;2020-03-03 (alebob)

Available from: 2020-02-06 Created: 2020-02-06 Last updated: 2020-03-13Bibliographically approved
Espin Delgado, A., Rönnberg, S., Busatto, T., Ravindran, V. & Bollen, M. (2020). Summation law for supraharmonic currents (2–150 kHz) in low-voltage installations. Electric power systems research, 184, Article ID 106325.
Open this publication in new window or tab >>Summation law for supraharmonic currents (2–150 kHz) in low-voltage installations
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2020 (English)In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 184, article id 106325Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Elsevier, 2020
Keywords
Supraharmonics, High-frequency distortion, Summation, Power quality
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electric Power Engineering
Identifiers
urn:nbn:se:ltu:diva-78295 (URN)10.1016/j.epsr.2020.106325 (DOI)2-s2.0-85082135782 (Scopus ID)
Note

Validerad;2020;Nivå 2;2020-04-02 (alebob)

Available from: 2020-04-02 Created: 2020-04-02 Last updated: 2020-04-02Bibliographically approved
Alvarez Perez, M. A., Rönnberg, S., Bermúdez, J., Zhong, J. & Bollen, M. (2019). A Generic Storage Model Based on a Future Cost Piecewise-Linear Approximation. IEEE Transactions on Smart Grid, 10(1), 878-888
Open this publication in new window or tab >>A Generic Storage Model Based on a Future Cost Piecewise-Linear Approximation
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2019 (English)In: IEEE Transactions on Smart Grid, ISSN 1949-3053, E-ISSN 1949-3061, Vol. 10, no 1, p. 878-888Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Institute of Electrical and Electronics Engineers (IEEE), 2019
Keywords
Schedules, Uncertainty, Load modeling, Production, Energy storage, GSM, Stochastic processes
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electric Power Engineering
Identifiers
urn:nbn:se:ltu:diva-60774 (URN)10.1109/TSG.2017.2754288 (DOI)000455180900080 ()2-s2.0-85030639335 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-01-25 (inah)

Available from: 2016-11-29 Created: 2016-11-29 Last updated: 2019-08-27Bibliographically approved
Nömm, J., Rönnberg, S. & Bollen, M. (2019). An analysis of voltage quality in a nanogrid during islanded operation. Energies, 12(4), Article ID 614.
Open this publication in new window or tab >>An analysis of voltage quality in a nanogrid during islanded operation
2019 (English)In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 12, no 4, article id 614Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
MDPI, 2019
Keywords
harmonics, islanded operation, nanogrids, power quality, voltage unbalance
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electric Power Engineering
Identifiers
urn:nbn:se:ltu:diva-73155 (URN)10.3390/en12040614 (DOI)000460667700040 ()2-s2.0-85061970485 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-03-11 (johcin)

Available from: 2019-03-11 Created: 2019-03-11 Last updated: 2019-04-11Bibliographically approved
Sierra-Fernández, J.-M., Rönnberg, S., De La Rosa, J.-J., Bollen, M. & Palomares-Salas, J.-C. (2019). Application of spectral kurtosis to characterize amplitude variability in power systems' harmonics. Energies, 12(1), Article ID en12010194.
Open this publication in new window or tab >>Application of spectral kurtosis to characterize amplitude variability in power systems' harmonics
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2019 (English)In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 12, no 1, article id en12010194Article in journal (Refereed) Published
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. 

Place, publisher, year, edition, pages
MDPI, 2019
Keywords
harmonics, constant amplitude trend, fourth-order statistics, detection, spectral kurtosis
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electric Power Engineering
Identifiers
urn:nbn:se:ltu:diva-72718 (URN)10.3390/en12010194 (DOI)000460665000194 ()2-s2.0-85059981926 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-01-28 (svasva)

Available from: 2019-01-28 Created: 2019-01-28 Last updated: 2019-04-12Bibliographically approved
Ravindran, V., Busatto, T., Rönnberg, S., Bollen, M. & Meyer, J. (2019). Charactizations of interactions between PV and Energy efficient lighting (LED) in a mixed installation.. In: : . Paper presented at CIRED 2019, 25th International Conference on Electricity Distribution Madrid, 3-6 June 2019 (pp. 1-5). , -, Article ID 237.
Open this publication in new window or tab >>Charactizations of interactions between PV and Energy efficient lighting (LED) in a mixed installation.
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2019 (English)Conference paper, Oral presentation with published abstract (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.

Keywords
LED PV interactions harmonics supraharmonics interharmonics
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering Energy Engineering Signal Processing
Research subject
Electric Power Engineering
Identifiers
urn:nbn:se:ltu:diva-73887 (URN)
Conference
CIRED 2019, 25th International Conference on Electricity Distribution Madrid, 3-6 June 2019
Available from: 2019-05-09 Created: 2019-05-09 Last updated: 2019-05-20
Ravindran, V., Busatto, T., Rönnberg, S. & Bollen, M. (2019). Comparison of a non-parametric and parametric method for interharmonic estimation in PV systems. In: : . Paper presented at 13th IEEE PowerTech 2019.
Open this publication in new window or tab >>Comparison of a non-parametric and parametric method for interharmonic estimation in PV systems
2019 (English)Conference paper, Published 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.

Keywords
Interharmonics, power system measurements, time-frequency analysis, Photovoltaic systems, Power quality.
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electric Power Engineering
Identifiers
urn:nbn:se:ltu:diva-73360 (URN)
Conference
13th IEEE PowerTech 2019
Funder
Swedish Energy Agency
Available from: 2019-03-29 Created: 2019-03-29 Last updated: 2019-05-20
Ahmed, K. M., Sutaria, J., Bollen, M. & Rönnberg, S. (2019). Electrical Energy Consumption Model of Internal Components in Data Centers. In: : . Paper presented at 2019 IEEE PES Innovative Smart Grid Technologies Europe (ISGT-Europe). Bucharest, Romania: IEEE
Open this publication in new window or tab >>Electrical Energy Consumption Model of Internal Components in Data Centers
2019 (English)Conference paper, Published paper (Refereed)
Abstract [en]

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

Place, publisher, year, edition, pages
Bucharest, Romania: IEEE, 2019
Keywords
server utilization, component loss modelling, PDU and UPS, data center
National Category
Engineering and Technology
Research subject
Electric Power Engineering
Identifiers
urn:nbn:se:ltu:diva-76858 (URN)10.1109/ISGTEurope.2019.8905595 (DOI)
Conference
2019 IEEE PES Innovative Smart Grid Technologies Europe (ISGT-Europe)
Projects
Data center innovation
Available from: 2019-11-25 Created: 2019-11-25 Last updated: 2019-11-25
Busatto, T., Larsson, A., Rönnberg, S. & Bollen, M. (2019). Including Uncertainties from Customer Connections in Calculating Low-Voltage Harmonic Impedance. IEEE Transactions on Power Delivery, 34(2), 606-615
Open this publication in new window or tab >>Including Uncertainties from Customer Connections in Calculating Low-Voltage Harmonic Impedance
2019 (English)In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 34, no 2, p. 606-615Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
IEEE, 2019
Keywords
Power Quality, power system harmonics, resonance, stochastic processes, Monte Carlo methods
National Category
Electrical Engineering, Electronic Engineering, Information Engineering Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electric Power Engineering
Identifiers
urn:nbn:se:ltu:diva-72659 (URN)10.1109/TPWRD.2018.2881222 (DOI)000462414900022 ()
Funder
Swedish Energy Agency
Note

Validerad;2019;Nivå 2;2019-04-11 (oliekm)

Available from: 2019-01-23 Created: 2019-01-23 Last updated: 2019-04-24Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-4004-0352

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