| 11. |
- Gil-de-Castro, Aurora, et al.
(author)
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Variations in harmonic voltage at the sub-10-minute time scale
- 2021
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In: Electric power systems research. - : Elsevier. - 0378-7796 .- 1873-2046. ; 195
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Journal article (peer-reviewed)abstract
- This paper presents the statistical analysis of variations in harmonic voltage in the time scale between 1 second and 10 min, a time scale that is rarely considered in studies but that is of relevance for incorrect operation of end-user equipment. The paper also introduces a set of novel power-quality indices quantifying these variations and it gives recommendations on how to include these indices in the power-quality-monitoring framework provided by IEC 61000–4–30. The statistics and the illustration of the novel indices are based on measurements of harmonic 2 through 40 with 1-second time resolution at 154 locations in 16 countries. The proposed power-quality indices are a compromise between storing large amounts of raw data with high time resolution, resulting in the different big-data challenges, and completely neglecting this time scale. Two important findings from this paper are that this time scale should not be completely neglected and that information on this time scale can be recorded without excessive increase in the need for data transmission and storage.
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| 12. |
- Giri, Manav, et al.
(author)
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Observed Harmonic Levels on the Low Voltage Grid during EV DC Fast Charging
- 2022
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In: 2022 20th International Conference on Harmonics & Quality of Power (ICHQP) Proceedings. - : IEEE.
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Conference paper (peer-reviewed)abstract
- The paper contains a set of observations on the fast charging of electric vehicles (EV’s) on Swedish low voltage networks in rural/commercial and urban areas. The emphasis of the study has been to analyze the impact of EV charging on the electric grid and particularly on the observed waveform distortion. The paper focuses on the observation of harmonics on the grid and the variation in the observed harmonics with time as the charging current increases from a small value associated with limiting the inrush current, to the value required by the EV’s for the fast charging of the battery pack. Observations from a bus charging station at Gothenburg are also discussed.
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| 13. |
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| 14. |
- Nakhodchi, Naser, et al.
(author)
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Including uncertainties in harmonic hosting capacity calculation of a fast EV charging station utilizing Bayesian statistics and harmonic correlation
- 2023
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In: Electric power systems research. - : Elsevier. - 0378-7796 .- 1873-2046. ; 214
-
Journal article (peer-reviewed)abstract
- The harmonic emission from an electric vehicle fast charger depends on factors like charger topology, EV type, initial state of charge of EV battery, as well as supply voltage and background distortion. This paper presents the results from harmonic current measurement of a fast charger for a period of one month in Sweden that has charged a variety of EVs from different brands under different state of charge and background distortion. Besides the common harmonic emission pattern, a high level of variation in emission is observed that can affect the aggregation of the emission from multiple chargers. To include such uncertainties, the harmonic hosting capacity is obtained for a fast EV charging station in a stochastic way. A new method, based on Bayesian statistics and the correlation between harmonic magnitude and fundamental magnitude, is proposed for the generation of stochastic samples. It is shown that the proposed method, to a high extent, can model the stochastic behavior of harmonic emission from a fast charger. Furthermore, the results show that neglecting the correlation between harmonic magnitude and fundamental magnitude can underestimate the harmonic hosting capacity.
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| 15. |
- Nömm, Jakob, et al.
(author)
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Techno-economic analysis with energy flow modeling for investigating the investment risks related to consumption changes within a standalone microgrid in Sweden
- 2021
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In: Energy. - : Elsevier. - 0360-5442 .- 1873-6785. ; 225
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Journal article (peer-reviewed)abstract
- A techno-economic energy flow model for a standalone microgrid was developed to investigate the investment risks related to consumption changes and compare the results to a conventional grid-connection in Sweden. Two different design strategies for a standalone microgrid was used, one with the objective to minimize the life-cycle cost and the other to provide a lower investment risk. The largest contributor to an increased investment risk for both design strategies was an increase in annual energy consumption within the standalone microgrid. The design strategy with the objective to reduce the investment risk eliminated the influence on the life-cycle cost from an increase in peak consumption and reduced the overall investment risk in comparison to the design strategy with the objective to minimize the life-cycle cost. However, a larger life-cycle cost was the drawback of that design strategy. It was concluded that locations with larger annual mean capacity factors reduced the investment risk for standalone microgrids due to lower diesel fuel dependence. It was also concluded that a conventional grid-connection had a lower investment risk than a standalone microgrid, since adverse changes in consumption always increased the life-cycle cost less for a conventional grid-connection than for a standalone microgrid.
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| 16. |
- Ravindran, Vineetha, 1987-, et al.
(author)
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Time-Varying Interharmonics in Different Types of Grid-Tied PV Inverter Systems
- 2020
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In: IEEE Transactions on Power Delivery. - : IEEE. - 0885-8977 .- 1937-4208. ; 35:2, s. 483-496
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Journal article (peer-reviewed)abstract
- 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.
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| 17. |
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| 18. |
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| 19. |
- Sakar, Selcuk, et al.
(author)
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Interharmonic Emission in AC–DC Converters Exposed to Nonsynchronized High-Frequency Voltage Above 2 kHz
- 2021
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In: IEEE transactions on power electronics. - : IEEE. - 0885-8993 .- 1941-0107. ; 36:7, s. 7705-7715
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Journal article (peer-reviewed)abstract
- More and more devices connected to low voltage networks inject currents in the frequency range above 2 kHz up to 150 kHz, so called supraharmonics. Supraharmonics can appear as synchronized or nonsynchronized to the power system frequency. A device exposed to a fixed supraharmonic frequency are here shown to generate interharmonics when the power system frequency deviates from the ideal 50/60 Hz. Resulting interharmonic frequency and magnitude are determined by three factors, the frequency at which a supraharmonic component exist, the voltage magnitude of that component, and the deviation from 50/60 Hz of the power system frequency. Formation of interharmonics is confirmed in a functional model and validated through the measurements and numerical simulations.
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| 20. |
- Salles, Rafael De Souza, et al.
(author)
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Review of Waveform Distortion Interactions Assessment in Railway Power Systems
- 2023
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In: Energies. - : MDPI. - 1996-1073. ; 16:14
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Research review (peer-reviewed)abstract
- This work aims to cover the measurement, modeling, and analysis of waveform distortions in railway power systems. It is focused on waveform distortion as a phenomenon that includes harmonic distortion, interharmonic distortion, and supraharmonics. A comprehensive view of the interactions of waveform distortions in railway systems is needed, together with a grid perspective of power quality incorporating all aspects, sources, propagation, requirements, and effects. It is understood that the communities interested or involved in the subject of railway power systems would benefit from an integrated overview of the literature on the complex problem of waveform distortion. The literature review is divided into four categories: characterization and measurements, modeling, the application of artificial intelligence, and specific issues. For each category of work, the contributions are highlighted, and a discussion on opportunities, gaps, and critical observations is provided. The work successfully builds a framework for the subject with two main characteristics; the review is informative and propositional, providing a road map of opportunities for future works. Some aspects and recommendations can be highlighted. Suggestions for future works and research practices on waveform distortion in electrical transportation are offered.
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