| 11. |
- Nakhodchi, Naser, et al.
(författare)
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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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Ingår i: Electric power systems research. - : Elsevier. - 0378-7796 .- 1873-2046. ; 214
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Tidskriftsartikel (refereegranskat)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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| 12. |
- Nakhodchi, Naser, et al.
(författare)
-
Measurements of Harmonic Voltages at Multiple Locations in LV and MV Networks
- 2020
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Ingår i: 2020 19th International Conference on Harmonics and Quality of Power (ICHQP). - : IEEE.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This paper presents harmonic voltage measurements for a part of a distribution network including low-voltage (400 V) and medium-voltage (10 kV). Measurements were performed during 2017 and 2018 in the north of Sweden. This paper shows correlations between different harmonic orders in low voltage and the correlation between low and medium-voltage harmonics. This information can be used for harmonic propagation studies in distribution networks. The results showed significant correlation between the 5 th and 7 th harmonics for low-voltage side and very high correlation between 5 th harmonic order in low-voltage and medium-voltage. It is also observed that 5 th harmonic has almost the same values for all transformers connected to the same 40 kV network.
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| 13. |
- Nakhodchi, Naser, 1981-
(författare)
-
On Harmonics in Low-voltage Networks
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- On the road to reducing global warming, the use of renewable energy sources and efficient use of electricity are among the key aspects. The increasing number of energy efficient appliances such as LED lamps, booming demand for electric vehicles (EVs), and growing penetration of distributed energy resources such as photovoltaic (PV) systems in low-voltage (LV) networks are expected to affect the power quality in the entire electric power system and specifically in the LV network, where such new devices are connected. Waveform distortion, mainly expressed by the harmonic components, is one of the topics within power quality that is highly affected by the introduction of such new devices. However, there is a lack of publications discussing the existing level of voltage harmonics in LV networks or addressing the origin and transfer of harmonics in LV and MV distribution networks. This highlights the need for more research in this field.To evaluate the ability of the network to host new sources of harmonics, the existing harmonic voltage and current levels as well as the impact of these new sources on those levels should be investigated. Harmonic levels are determined by emission from harmonic sources, the propagation from other harmonic sources, and the aggregation between the contributions from different sources. Studies on harmonic emission from a variety of different individual devices under different conditions have already been carried out. However, limited knowledge is available about the harmonic aggregation and propagation in LV networks. This study aims to improve the understanding about the behaviour of harmonics in LV networks covering both aggregation and propagation.In the first part of this work, the impact of the MV network and remote LV loads on the harmonic voltage in the LV network are examined. Simulation results have revealed that for frequencies below the resonant frequency of the local LV network the harmonic voltage levels mainly are determined by aggregated emission of the whole distribution network (both LV and MV) rather than by the emission from local LV loads. Furthermore, a graphical method is introduced for harmonic propagation studies, using measurements but without the need for accurate synchronized measurements.In the second part of this work, the aggregated emission from a group of EV fast chargers is examined. A stochastic method, based on Bayesian statistics and harmonic correlation, was used to include uncertainties in harmonic hosting capacity calculation for an EV charging station equipped with fast chargers. The impact of MV network and remote LV loads on harmonic hosting capacity is investigated. It is also shown that harmonic hosting capacity studies are needed; and details of the distribution network must be included to get an accurate estimation of the harmonic hosting capacity.Finally, an alternative method for time aggregation of harmonic phase angle is proposed in this work.In general, this work contributes to reducing the research gaps recognized in harmonic analysis in the LV networks considering propagation and aggregation utilizing both simulation and measurement.
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| 14. |
- Nakhodchi, Naser, et al.
(författare)
-
Time Aggregation of Harmonic Phase Angle based on Park Transform
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- This Paper proposes an alternative method for defining and aggregating the complex harmonic components (magnitude and phase-angle) in a three-phase system. Instead of using the DFT to define the harmonic components, the Park or dq-transform is used. This results in a natural method for aggregation, for both magnitude and phase angle. The method is evaluated utilizing generated signals and two sets of measured signals as normal case and extreme case. Some aspects of the method, including a set of indicators, are discussed in the paper.
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| 15. |
- Nakhodchi, Naser, et al.
(författare)
-
Transfer of Harmonics in Distribution Networks
- 2022
-
Ingår i: IEEE Transactions on Power Delivery. - : IEEE. - 0885-8977 .- 1937-4208. ; 37:3, s. 1617-1626
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents the role of the medium-voltage network and low-voltage loads in harmonic voltages with low-voltage customers and harmonic propagation. A general model, as well as a detailed transfer function-based model, are used. By applying them to an existing network, it is shown that remote low-voltage loads have a significant impact on the source and transfer impedance. The main impact occurs for a specific range of frequencies below the resonant frequency of the low-voltage network. The general model is able to estimate this frequency range with an acceptable level of accuracy. Furthermore, by utilizing the concept of overall transfer impedance, it is shown that voltage harmonic levels for harmonic orders around this frequency range are determined mainly by aggregated remote emission rather than local emission.
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| 16. |
- Ravindran, Vineetha, 1987-, et al.
(författare)
-
Assessing time-varying harmonic interactions in a wind park
- 2021
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Ingår i: IEEE Access. - : IEEE. - 2169-3536. ; 9, s. 68151-68160
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Tidskriftsartikel (refereegranskat)abstract
- The harmonic interaction mechanism in a wind park is examined in this paper. The paper investigates the feasibility of a solution to the yet challenging harmonic contribution estimation from multiple sources in a wind park with limited available information, via an extension of a simple modeling approach as well as from detailed analysis of field measurements. The paper has two distinct objectives in assessing harmonic interactions (a) one to extend the classical Norton equivalent model to a multi-measurement wind park system and to suggest potential areas for further model developments from field measurement analysis, and (b) second to draw inferences from field measurements and to develop a new independent concept of analysis from long-term field measurements in the wind park. From practical experience, a new concept of analysis with a ‘harmonic interaction break-even point’ is introduced. With the help of it, one could identify whether the primary emission (emission from considered source) or secondary emission (emission from a distant source) dominates in the analysis period. In this way, the highest responsibility between different interacting time-varying harmonic sources is evaluated. It was concluded that from long-term measurements one can define a magnitude of power production where a certain harmonic order is canceled or reaches its lowest magnitude. If one finds this cancellation point, one can define a level of secondary/primary emission or at least a feasible range. This knowledge is a step forward towards harmonic contribution analysis.
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| 17. |
- Sudha Letha, Shimi, et al.
(författare)
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Power Quality Issues of Electro-Mobility on Distribution Network—An Overview
- 2023
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Ingår i: Energies. - : MDPI. - 1996-1073. ; 16:13
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Forskningsöversikt (refereegranskat)abstract
- The journey towards sustainable transportation has significantly increased the grid penetration of electric vehicles (EV) around the world. The connection of EVs to the power grid poses a series of new challenges for network operators, such as network loading, voltage profile perturbation, voltage unbalance, and other power quality issues. This paper presents a coalescence of knowledge on the impact that electro-mobility can impose on the grid, and identifies gaps for further research. Further, the study investigates the impact of electric vehicle charging on the medium-voltage network and low-voltage distribution network, keeping in mind the role of network operators, utilities, and customers. From this, the impacts, challenges, and recommendations are summarized. This paper will be a valuable resource to research entities, industry professionals, and network operators, as a ready reference of all possible power quality challenges posed by electro-mobility on the distribution network.
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| 18. |
- Sutaria, Jil, et al.
(författare)
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Comparing Harmonic Unbalance At Multiple Locations To Characterize The Unbalance
- 2021
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Ingår i: CIRED 2021 - The 26th International Conference and Exhibition on Electricity Distribution. - : Institution of Engineering and Technology. ; , s. 728-732
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Konferensbidrag (refereegranskat)abstract
- Harmonic emission at any point of connection (PoC) depends on the loads connected there and the background voltage distortion at that point. Under balanced supply voltage and load, the harmonics adhere to the rule that third harmonics are zero sequence, fifth harmonic are negative sequence, etc. However, under unbalance in either load or supply voltage, this assumption is no longer true. A phasor analysis of the voltage and current measured at different locations in a city is presented in this paper. Individual harmonics are decomposed into their sequence components, and the results are presented in terms of polar plots. The components are further quantified in terms of balanced and unbalanced THD, which is an indicator of the impact of unbalance. The harmonics do not follow the defined norm of sequence component in presence of unbalance in the system. The triplen harmonics were shown to have higher unbalanced sequence components than non-triplen harmonics.
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| 19. |
- Zabihi, Mohsen, et al.
(författare)
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Power Quality Assessment of a Single Customer Micro Grid-Case Study
- 2019
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Ingår i: CIRED 2019 Proceedings. - : AIM.
-
Konferensbidrag (refereegranskat)abstract
- Mashhad Electric Energy Distribution Company has designed and implemented its first local micro-grid in Mashhad which is called "Mehrsun". This paper presents the results of field measurement of power quality indices and energy flow for a single customer micro-grid in Mashhad, Iran. Measurements performed during a week in spring for both grid-connected and islanded mode. Power and energy parameters as well as current and voltage THD, voltage fluctuations, power factor are illustrated and their consistency with power quality standards and limits are investigated.
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