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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
Ravindran, V., Sakar, S., Rönnberg, S. & Bollen, M. (2020). Characterization of the impact of PV and EV induced voltage variations on LED lamps in a low voltage installation. Electric power systems research, 185, Article ID 106352.
Open this publication in new window or tab >>Characterization of the impact of PV and EV induced voltage variations on LED lamps in a low voltage installation
2020 (English)In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 185, article id 106352Article in journal (Refereed) Published
Abstract [en]

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

Place, publisher, year, edition, pages
Elsevier, 2020
Keywords
Electric vehicle, LED lamps, Light emitting diodes, Photovoltaic systems, Harmonic analysis, Power quality, Voltage variations
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electric Power Engineering
Identifiers
urn:nbn:se:ltu:diva-78984 (URN)10.1016/j.epsr.2020.106352 (DOI)
Note

Validerad;2020;Nivå 2;2020-05-26 (johcin)

Available from: 2020-05-26 Created: 2020-05-26 Last updated: 2020-05-26Bibliographically approved
Khokhlov, V., Meyer, J., Grevener, A., Busatto, T. & Rönnberg, S. (2020). Comparison of Measurement Methods for the Frequency Range 2-150 kHz (Supraharmonics) based on the present Standards Framework. IEEE Access
Open this publication in new window or tab >>Comparison of Measurement Methods for the Frequency Range 2-150 kHz (Supraharmonics) based on the present Standards Framework
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2020 (English)In: IEEE Access, E-ISSN 2169-3536Article in journal (Refereed) Epub ahead of print
Abstract [en]

Advances in power electronics, increasing share of renewables in the energy system and e-mobility cause an increase of disturbances in the frequency range 2-150 kHz, also known as supraharmonics. A rigorous, credible and agreed measurement framework is essential to evaluate electromagnetic compatibility (EMC) in this frequency range. While a normative method exists for measuring equipment emission in the laboratory, no normative method exists yet for the measurement of supraharmonic disturbance levels in the grid. The aim of this research is a detailed comparison of potential measurement methods derived from existing standards IEC 61000-4-7, IEC 61000-4-30, CISPR 16-1-1 and a critical assessment of their suitability for disturbance measurements in grid applications. Based on a comprehensive set of synthetic signals and real measurements from laboratory and field, this article studies the ability of the methods to assess the typical characteristics of supraharmonic emission with relevance to EMC coordination. It presents the benefits and drawbacks of the existing measurement methods and discusses the suitability of possible modifications for grid compliance assessment. The results and recommendations intend to be an input for the present activities of IEC SC 77A WG 9 to define a normative method for the measurement of supraharmonic disturbance levels to be included in the next edition of IEC 61000-4-30.

Place, publisher, year, edition, pages
IEEE, 2020
Keywords
Distortion measurement, electromagnetic compatibility, measurement standards, power quality, supraharmonics, frequency domain analysis
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electric Power Engineering
Identifiers
urn:nbn:se:ltu:diva-78555 (URN)10.1109/ACCESS.2020.2987996 (DOI)
Available from: 2020-04-17 Created: 2020-04-17 Last updated: 2020-04-27
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)000525770200038 ()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: 2020-05-04Bibliographically approved
Sakar, S., Bagheri, A., Rönnberg, S. & Bollen, M. (2020). Susceptibility of LED street lamps to voltage dips. Lighting Research and Technology
Open this publication in new window or tab >>Susceptibility of LED street lamps to voltage dips
2020 (English)In: Lighting Research and Technology, ISSN 1477-1535, E-ISSN 1477-0938Article in journal (Refereed) Epub ahead of print
Abstract [en]

There is an ongoing transition from high-pressure sodium lamps to LED street lamps that offer higher efficiency, cost saving and better photometric performance. This transition could lead to unintended consequences such as light flicker and extinguishing in street lighting applications when they are exposed to voltage dips. The goal of this paper is to analyse the light intensity variation of various street lamps when they are exposed to voltage dips. Several performance metrics for quantifying immunity of lamps have been proposed. Values for these metrics are obtained by applying artificial voltage dips to lamps. For voltage dips with residual voltage above 38%, lamps are immune in terms of a short-term light flicker metric. For residual voltage above 25%, light intensity reduces but without extinguishing. Compared to an incandescent lamp and high-pressure sodium lamp, LED street lamps exhibit longer zero-light intensity duration. Most of the studied LED street lamps exhibit uncoordinated light intensity drops, i.e. longer or shifted, with respect to the applied voltage dip. Individual characteristics of LED street lamps require testing before installation to prevent unexpected consequences. Recommendations are given for standardisation committees to implement an assessment method for lighting equipment.

Place, publisher, year, edition, pages
Sage Publications, 2020
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electric Power Engineering
Identifiers
urn:nbn:se:ltu:diva-78574 (URN)10.1177/1477153520917441 (DOI)000527112000001 ()2-s2.0-85083804320 (Scopus ID)
Available from: 2020-04-20 Created: 2020-04-20 Last updated: 2020-05-08
Ravindran, V., Busatto, T., Rönnberg, S. K., Meyer, J. & Bollen, M. (2020). Time-Varying Interharmonics in Different Types of Grid-Tied PV Inverter Systems. IEEE Transactions on Power Delivery, 35(2), 483-496
Open this publication in new window or tab >>Time-Varying Interharmonics in Different Types of Grid-Tied PV Inverter Systems
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2020 (English)In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 35, no 2, p. 483-496Article in journal (Refereed) Published
Abstract [en]

Widely existing circuit topologies and inverter control strategies for photovoltaic (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 time-varying nature of interharmonics and the potential impacts on other equipment are yet to be understood. In this paper, laboratory and field measurements of seven different inverter types at multiple locations are presented. 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 six 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 fast fourier transform (FFT)-based methods.

Place, publisher, year, edition, pages
IEEE, 2020
Keywords
Interharmonics, Islanding, Maximum power point tracking, Power quality, Photovoltaic systems, Reactive power control
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electric Power Engineering
Identifiers
urn:nbn:se:ltu:diva-73359 (URN)10.1109/TPWRD.2019.2906995 (DOI)000522350600004 ()2-s2.0-85063369770 (Scopus ID)
Funder
Swedish Energy Agency
Note

Validerad;2020;Nivå 2;2020-04-16 (alebob)

Available from: 2019-03-29 Created: 2019-03-29 Last updated: 2020-04-16Bibliographically 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
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ORCID iD: ORCID iD iconorcid.org/0000-0002-4004-0352

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