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On Transfer Functions for Power Quality Studies in Wind Power and Solar PV Plants
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
2019 (English)Doctoral thesis, comprehensive summary (Other academic)Alternative title
Överföringsfunktioner förElkvalitetstudier i vindkraft- och Solcellsanläggningar (Swedish)
Abstract [en]

As part of the decarbonisation of the energy system, wind and solar power are expected to play an important role. However, together with their growth, new challenges appear in the electric power system; this requires further research, development, and often studies before connection is possible. Two of those challenges, both impacts on the quality of power, are the subject of this dissertation: harmonic distortion and voltage unbalance.

The growing use of solar power for electricity generation, especially in distribution systems, will result in increased voltage unbalance due to single-phase photovoltaic inverters (PVIs). Regulation on power quality and potential impact on other equipment, place a limit to the number of PVIs that can be connected to the system, the so-called “hosting capacity”. To include different uncertainties in the planning stage, a stochastic method based on the transfer-impedance matrix is proposed for quantifying this hosting capacity, with respect to voltage unbalance. The method has been illustrated by applying it to two typical Swedish low-voltage networks.

Wind power plants (WPPs) consist of a collection grid and a number of wind turbines. These are known to be a harmonic source as power electronic devices are used to connect them to the power system. Earlier studies have shown that the actual emission at harmonic frequencies is low, but that the main issue is related to the spread of harmonics through the collection grid, especially the role of resonances. Regulation setting emission limits and the potential adverse impact of harmonics on equipment make that studies are needed to predict harmonic voltages and currents in and around a WPP. These studies are based on measurements performed on individual turbines under certain operating conditions. The main issue related to this determination is distinguishing the emission originating within the WPP (primary emission) from the emission originating elsewhere (secondary emission). A critical review has been performed on methods used for harmonic emission determination (i.e. distinguishing between primary and secondary emission) in WPPs. It was concluded that this determination cannot be solved without making assumptions. Transfers functions are independent of the emission from the individual turbines and can be obtained with less assumptions. These transfer functions have been used to estimate the spread of harmonics through a WPP and towards the public grid. Transfer functions were shown to be a suitable tool to quantify amplifications due to resonances and identify which harmonic orders can be an issue.

Furthermore, information on the different transfer functions allows the selection of proper mitigation methods. This application of transfer functions has been illustrated for a specific advanced mitigation method: the use of inverter control techniques to emulate a “virtual resistor”. In this way it is possible to damp resonances without increasing fundamental-frequency losses.

The ultimate aim of harmonic studies is to avoid interference between the grid and equipment connected to it, in this case between the power-electronics in the wind turbine and other equipment. However, these studies rarely address actual cases of interference, instead of this, measured or calculated harmonic voltages and/or currents are compared with limits set in regulations. These and regulations differ strongly between countries and even between individual network operators. A comparative study of regulatory methods has been performed presenting their advantages and disadvantages from the viewpoint of the network operator and from the viewpoint of the owner or operator of the WPP.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2019.
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
National Category
Electrical Engineering, Electronic Engineering, Information Engineering Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electric Power Engineering
Identifiers
URN: urn:nbn:se:ltu:diva-71826ISBN: 978-91-7790-278-2 (print)ISBN: 978-91-7790-279-9 (electronic)OAI: oai:DiVA.org:ltu-71826DiVA, id: diva2:1266963
Public defence
2019-02-15, A193, Hörsal A, Skellefteå, 10:00 (English)
Opponent
Supervisors
Available from: 2018-11-30 Created: 2018-11-29 Last updated: 2019-03-04Bibliographically approved
List of papers
1. A Review of Solutions for Harmonic Mitigation
Open this publication in new window or tab >>A Review of Solutions for Harmonic Mitigation
2016 (English)In: 2016 17th International Conference on Harmonics and Quality of Power, Piscataway, NJ: IEEE Computer Society, 2016, p. 30-35, article id 7783422Conference paper, Published paper (Refereed)
Abstract [en]

With the increasing of non-linear equipments connected in the network, mitigation solutions are needed to avoid and solve harmonic and resonance problems that may damage equipments and avoid their connection into the grid. Several are the solutions given to this problem; however, not all them are suitable for all situations. For it, in this paper a review of the most used harmonic solutions and some new technologies are presented. The advantages and disadvantages are described and the most used passive, active and hybrid solutions are described

Place, publisher, year, edition, pages
Piscataway, NJ: IEEE Computer Society, 2016
Series
International Conference on Harmonics and Quality of Power, ISSN 1540-6008
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electric Power Engineering
Identifiers
urn:nbn:se:ltu:diva-60505 (URN)10.1109/ICHQP.2016.7783422 (DOI)000391424200006 ()2-s2.0-85009507997 (Scopus ID)9781509037926 (ISBN)
Conference
17th International Conference on Harmonics and Quality of Power (ICHQP), Belo Horizonte, Brasil, 16-19 October 2016
Available from: 2016-11-17 Created: 2016-11-17 Last updated: 2019-02-07Bibliographically approved
2. Some methods for harmonic emission determination in wind power plants
Open this publication in new window or tab >>Some methods for harmonic emission determination in wind power plants
2018 (English)In: Proceedings of International Conference on Harmonics and Quality of Power, ICHQP, Piscataway, NJ: Institute of Electrical and Electronics Engineers (IEEE), 2018Conference paper, Published paper (Refereed)
Abstract [en]

The connection of new installations, as wind power plants, into the public grid requires that some conditions are fulfilled. Their aim is among others to ensure a proper power quality in the grid and to ensure a high probability of electromagnetic compatibility. The harmonic emission of individual sources is one of the power quality concerns, because they can damage and increase heating in devices. However, as there are other power electronics loads are connected, the correct assessment of the harmonic emission from one specific source is not straightforward. in this paper, a review of the most used methods for harmonic emission determination is presented and some considerations are discussed regarding their use in wind power plants harmonic contribution. Depending on the application, one method is more suitable than the other. However, assumptions are necessary with any method, especially for the harmonic impedances. For wind power plants not all the presented methods are suitable. Also, further investigations are needed to determine the harmonic impedance of the wind power plant and public grid, especially around resonant frequencies.

Place, publisher, year, edition, pages
Piscataway, NJ: Institute of Electrical and Electronics Engineers (IEEE), 2018
Series
International Conference on Harmonics and Quality of Power, E-ISSN 1540-6008
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electric Power Engineering
Identifiers
urn:nbn:se:ltu:diva-69528 (URN)10.1109/ICHQP.2018.8378934 (DOI)000444771900123 ()2-s2.0-85049249859 (Scopus ID)978-1-5386-0517-2 (ISBN)
Conference
18th International Conference on Harmonics and Quality of Power (ICHQP 2018), Ljubljana, Slovenia, May 13–16 2018
Available from: 2018-06-14 Created: 2018-06-14 Last updated: 2019-02-07Bibliographically approved
3. Stochastic Assessment of Voltage Unbalance due to Single-Phase-Connected Solar Power
Open this publication in new window or tab >>Stochastic Assessment of Voltage Unbalance due to Single-Phase-Connected Solar Power
Show others...
2017 (English)In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 32, no 2, p. 852-861, article id 7488998Article in journal (Refereed) Published
Abstract [en]

A stochastic method is presented in this paper to estimate the future voltage unbalance in a low-voltage distribution network with high-penetration of single-phase photovoltaic inverters (PVIs). Location and phase allocation of the PVIs are considered as input parameters for the stochastic simulation. The method has been applied to three different low-voltage networks: two in Sweden and one in Germany. In the Swedish networks, for 6-kW single-phase PVIs, it is likely that the contribution from single-phase photovoltaic inverters to the voltage unbalance exceeds 1%. The 2% value is unlikely to be exceeded. In the German network, for 4.6-kW single-phase PVIs the voltage unbalance is between 1.35% and 2.62%.The risk of high voltage unbalance can be reduced by a combination of controlled distribution over the phases and reduction of the maximum size for a single-phase PVI.

Place, publisher, year, edition, pages
IEEE, 2017
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electric Power Engineering
Identifiers
urn:nbn:se:ltu:diva-7911 (URN)10.1109/TPWRD.2016.2579680 (DOI)000398907100029 ()2-s2.0-85017651944 (Scopus ID)65608cd0-3d7c-42f3-a987-7b5aa293d825 (Local ID)65608cd0-3d7c-42f3-a987-7b5aa293d825 (Archive number)65608cd0-3d7c-42f3-a987-7b5aa293d825 (OAI)
Note

Validerad; 2017; Nivå 2; 2017-03-29 (andbra)

Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2019-02-07Bibliographically approved
4. Hosting capacity for photovoltaic inverters considering voltage unbalance
Open this publication in new window or tab >>Hosting capacity for photovoltaic inverters considering voltage unbalance
2017 (English)In: 2017 IEEE PowerTech, Piscataway, NJ: Institute of Electrical and Electronics Engineers (IEEE), 2017, article id 7981274Conference paper, Published paper (Refereed)
Abstract [en]

 In this paper the hosting capacity considering voltage unbalance is estimated for single-phase photovoltaic inverters (PVIs) in low-voltage distribution networks in Sweden. A stochastic approach is used to calculate the negative-sequence voltage unbalance for each of the possible locations in the network. The method has been applied to 6 and 28-customer networks for the connection of 6-kW single-phase PVIs. The impact of three-phase motors on the unbalance was also studied. From the results, it was observed that the contribution from single-phase photovoltaic inverters to the voltage unbalance likely exceeds 1%, but unlikely that it will reach 2% of voltage unbalance.

Place, publisher, year, edition, pages
Piscataway, NJ: Institute of Electrical and Electronics Engineers (IEEE), 2017
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electric Power Engineering
Identifiers
urn:nbn:se:ltu:diva-65642 (URN)10.1109/PTC.2017.7981274 (DOI)000411142500480 ()2-s2.0-85034731977 (Scopus ID)978-1-5090-4237-1 (ISBN)
Conference
2017 IEEE Manchester PowerTech, Manchester, 18-22 June 2017
Available from: 2017-09-14 Created: 2017-09-14 Last updated: 2019-02-07Bibliographically approved

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Schwanz, Daphne

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