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Reactive Power Dynamic Assessment of a PV System in a Distribution Grid
KTH, School of Electrical Engineering (EES), Electric Power Systems.
KTH, School of Electrical Engineering (EES), Electric Power Systems.ORCID iD: 0000-0002-6431-9104
KTH, School of Electrical Engineering (EES), Electric Power Systems.ORCID iD: 0000-0002-8189-2420
2012 (English)In: Energy Procedia, ISSN 1876-6102, E-ISSN 1876-6102, Vol. 20, 98-107 p.Article in journal (Refereed) Published
Abstract [en]

Accommodating more and more PV systems in grids has raised new challenges that formerly had not been considered and addressed in standards. According to recently under-discussed standards, each PV unit is allowed to participate in reactive power contributions to the grid to assist voltage control. There are some PV models in the literature however those models mostly assumed unity power factor operation for PV systems owing to the contemporary standards. Therefore, there is a need to develop a PV model considering the reactive power contribution and its dynamic influence on power system. This paper describes non-proprietary modeling of a three-phase, single stage PV system consisting of controller scheme design procedure and coping with the important aspects of three different reactive power regulation strategies and their impact assessment studies. The model is implemented in PSCAD to examine the behavior of the proposed model for recently codified reactive power strategies. Furthermore, this model is integrated in a distribution grid with two PV systems in order to effectively investigate consequences of the different reactive power control strategies on the distribution network.

Place, publisher, year, edition, pages
Elsevier, 2012. Vol. 20, 98-107 p.
Keyword [en]
PV system modelling, instantaneous model, reactive power control
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-99050DOI: 10.1016/j.egypro.2012.03.012ISI: 000309468500011Scopus ID: 2-s2.0-84897134411OAI: oai:DiVA.org:kth-99050DiVA: diva2:540913
Conference
2nd Technoport Renewable Energy Research Conference (RERC) Location: Trondheim, Norway Date: APR 16-18, 2012
Funder
StandUp
Note

QC 20120730

Available from: 2013-01-21 Created: 2012-07-12 Last updated: 2017-06-15Bibliographically approved
In thesis
1. Large Scale Solar Power Integration in Distribution Grids: PV Modelling, Voltage Support and Aggregation Studies
Open this publication in new window or tab >>Large Scale Solar Power Integration in Distribution Grids: PV Modelling, Voltage Support and Aggregation Studies
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Long term supporting schemes for photovoltaic (PV) system installation have led to accommodating large numbers of PV systems within load pockets in distribution grids. High penetrations of PV systems can cause new technical challenges, such as voltage rise due to reverse power flow during light load and high PV generation conditions. Therefore, new strategies are required to address the associated challenges.

Moreover, due to these changes in distribution grids, a different response behavior of the distribution grid on the transmission side can be expected. Hence, a new equivalent model of distribution grids with high penetration of PV systems is needed to be addressed for future power system studies.

The thesis contributions lie in three parts. The first part of the thesis copes with the PV modelling. A non-proprietary PV model of a three-phase, single stage PV system is developed in PSCAD/EMTDC and PowerFactory. Three

different reactive power regulation strategies are incorporated into the models and their behavior are investigated in both simulation platforms using a distribution system with PV systems.

In the second part of the thesis, the voltage rise problem is remedied by use of reactive power. On the other hand, considering large numbers of PV systems in grids, unnecessary reactive power consumption by PV systems first increases total line losses, and second it may also jeopardize the stability of the network in the case of contingencies in conventional power plants, which supply reactive power. Thus, this thesis investigates and develops the novel schemes to reduce reactive power flows while still keeping voltage within designated limits via three different approaches:

  1. decentralized voltage control to the pre-defined set-points
  2. developing a coordinated active power dependent (APD) voltage regulation Q(P)using local signals
  3. developing a multi-objective coordinated droop-based voltage (DBV) regulation Q(V) using local signals

 

In the third part of the thesis, furthermore, a gray-box load modeling is used to develop a new static equivalent model of a complex distribution grid with large numbers of PV systems embedded with voltage support schemes. In the proposed model, variations of voltage at the connection point simulate variations of the model’s active and reactive power. This model can simply be integrated intoload-flow programs and replace the complex distribution grid, while still keepingthe overall accuracy high.

The thesis results, in conclusion, demonstrate: i) using rms-based simulations in PowerFactory can provide us with quite similar results using the time domain instantaneous values in PSCAD platform; ii) decentralized voltage control to specific set-points through the PV systems in the distribution grid is fundamentally impossible dueto the high level voltage control interaction and directionality among the PV systems; iii) the proposed APD method can regulate the voltage under the steady-state voltagelimit and consume less total reactive power in contrast to the standard characteristicCosφ(P)proposed by German Grid Codes; iv) the proposed optimized DBV method can directly address voltage and successfully regulate it to the upper steady-state voltage limit by causing minimum reactive power consumption as well as line losses; v) it is beneficial to address PV systems as a separate entity in the equivalencing of distribution grids with high density of PV systems.

 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. 72 p.
Series
TRITA-EE, ISSN 1653-5146 ; 2014:050
Keyword
Photovoltaic systems, PV system modelling, reactive power control, droop control, voltage sensitivity analysis, German Grid Codes, relative gain array (RGA), singular value decomposition (SVD), load modeling, system identification
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-154602 (URN)978-91-7595-303-8 (ISBN)
Public defence
2014-11-13, F3, Lindstedtsvägen 26 (02 tr), KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

The Doctoral Degrees issued upon completion of the programme are issued by Comillas Pontifical University, Delft University of Technology and KTH Royal Institute of Technology. The invested degrees are official in Spain, the Netherlands and Sweden, respectively. QC 20141028

Available from: 2014-10-28 Created: 2014-10-24 Last updated: 2014-10-28Bibliographically approved

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Ghandhari, MehrdadSöder, Lennart

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