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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
Laury, J., Abrahamsson, L. & Bollen, M. (2019). A rotary frequency converter model for electromechanical transient studies of 16 (2/3) Hz railway systems. International Journal of Electrical Power & Energy Systems, 106, 467-476
Open this publication in new window or tab >>A rotary frequency converter model for electromechanical transient studies of 16 (2/3) Hz railway systems
2019 (English)In: International Journal of Electrical Power & Energy Systems, ISSN 0142-0615, E-ISSN 1879-3517, Vol. 106, p. 467-476Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Low frequency railways, 16 (2/3)  Hz, Modelling, Simulations, Transient stability, Rotary frequency converter, Motor generator set, Multi machine system
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electric Power Engineering
Identifiers
urn:nbn:se:ltu:diva-71471 (URN)10.1016/j.ijepes.2018.10.017 (DOI)000454377000043 ()2-s2.0-85055732778 (Scopus ID)
Funder
Swedish Transport Administration
Note

Validerad;2018;Nivå 2;2018-11-07 (inah)

Available from: 2018-11-06 Created: 2018-11-06 Last updated: 2019-09-13Bibliographically 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
Lennerhag, O., Lundquist, J., Engelbrecht, C., Karmokar, T. & Bollen, M. (2019). An Improved Statistical Method for Calculating Lightning Overvoltages in HVDC Overhead Line/Cable Systems. Energies, 12(16), Article ID 3121.
Open this publication in new window or tab >>An Improved Statistical Method for Calculating Lightning Overvoltages in HVDC Overhead Line/Cable Systems
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2019 (English)In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 12, no 16, article id 3121Article in journal (Refereed) Published
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. 

Place, publisher, year, edition, pages
MDPI, 2019
Keywords
HVDC, cable, overhead line, lightning, overvoltage, MTBF
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electric Power Engineering
Identifiers
urn:nbn:se:ltu:diva-75965 (URN)10.3390/en12163121 (DOI)000484454000084 ()2-s2.0-85071227522 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-09-11 (johcin)

Available from: 2019-09-11 Created: 2019-09-11 Last updated: 2019-10-01Bibliographically 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
Abrahamsson, L., Laury, J. & Bollen, M. (2019). Evaluating a constant-current load model through comparativetransient stability case studies of a synchronous-synchronous rotary frequencyconverter fed railway. In: : . Paper presented at Proceedings of the 2019 IEEE/ASME Joint Rail Conference.
Open this publication in new window or tab >>Evaluating a constant-current load model through comparativetransient stability case studies of a synchronous-synchronous rotary frequencyconverter fed railway
2019 (English)Conference paper, Published 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.

National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:ltu:diva-71801 (URN)
Conference
Proceedings of the 2019 IEEE/ASME Joint Rail Conference
Note

Submitted to JRC 2019. Not yet accepted. /20181205

Available from: 2018-11-28 Created: 2018-11-28 Last updated: 2018-12-13
Laury, J., Abrahamsson, L. & Bollen, M. (2019). Impact of reduced share of rotary frequency converter in a low-frequency synchronous railway grid: A transient stability study.. In: : . Paper presented at Proceedings of the 2019 IEEE/ASME Joint Rail Conference.
Open this publication in new window or tab >>Impact of reduced share of rotary frequency converter in a low-frequency synchronous railway grid: A transient stability study.
2019 (English)Conference paper, Published paper (Refereed)
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electric Power Engineering
Identifiers
urn:nbn:se:ltu:diva-71798 (URN)
Conference
Proceedings of the 2019 IEEE/ASME Joint Rail Conference
Note

Accepted.

Available from: 2018-11-28 Created: 2018-11-28 Last updated: 2019-01-08
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/0000-0003-4074-9529

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