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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: 2019-01-29Bibliographically 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: 2019-01-29Bibliographically 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
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: 2019-04-11Bibliographically approved
Sakar, S., Rönnberg, S. & Bollen, M. (2019). Interferences in AC-DC LED Drivers Exposed to Voltage Disturbances in the Frequency Range 2 kHz - 150 kHz. IEEE transactions on power electronics
Open this publication in new window or tab >>Interferences in AC-DC LED Drivers Exposed to Voltage Disturbances in the Frequency Range 2 kHz - 150 kHz
2019 (English)In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107Article in journal (Refereed) Published
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.

Keywords
AC-DC power converters, Electromagnetic compatibility, immunity testing, LED lamps, Lighting, Power-system harmonics, Power quality, Supraharmonics, Switching converters
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electric Power Engineering
Identifiers
urn:nbn:se:ltu:diva-73679 (URN)10.1109/TPEL.2019.2899176 (DOI)
Note

This work was sponsored by the Swedish Energy Agency

Available from: 2019-04-16 Created: 2019-04-16 Last updated: 2019-04-16
Ravindran, V., Busatto, T., Rönnberg, S., Meyer, J. & Bollen, M. (2019). Time-varying interharmonics in different types of grid-tied PV inverter systems. IEEE Transactions on Power Delivery
Open this publication in new window or tab >>Time-varying interharmonics in different types of grid-tied PV inverter systems
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2019 (English)In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208Article in journal (Refereed) Epub ahead of print
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

Place, publisher, year, edition, pages
IEEE, 2019
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)
Funder
Swedish Energy Agency
Available from: 2019-03-29 Created: 2019-03-29 Last updated: 2019-04-10
Alvarez, M., Rönnberg, S., Bollen, M., Frías, P., Cossent, R., Jabr, R. & Zhong, J. (2018). A Capacity Mechanism Design for Distribution Network Expansion Planning. In: 2018 IEEE International Conference on Environment and Electrical Engineering and 2018 IEEE Industrial and Commercial Power Systems Europe (EEEIC / I&CPS Europe): . Paper presented at 2018 IEEE International Conference on Environment and Electrical Engineering and 2018 IEEE Industrial and Commercial Power Systems Europe (EEEIC / I&CPS Europe), 12-15 June, Palermo, Italy. , Article ID 8493874.
Open this publication in new window or tab >>A Capacity Mechanism Design for Distribution Network Expansion Planning
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2018 (English)In: 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, Published 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.

Keywords
Power system planning; capacity planning; power distribution.
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electric Power Engineering
Identifiers
urn:nbn:se:ltu:diva-72033 (URN)10.1109/EEEIC.2018.8493874 (DOI)000450163701017 ()2-s2.0-85056522960 (Scopus ID)978-1-5386-5186-5 (ISBN)978-1-5386-5187-2 (ISBN)
Conference
2018 IEEE International Conference on Environment and Electrical Engineering and 2018 IEEE Industrial and Commercial Power Systems Europe (EEEIC / I&CPS Europe), 12-15 June, Palermo, Italy
Available from: 2018-12-13 Created: 2018-12-13 Last updated: 2019-03-27Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-4074-9529

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