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Large Scale Solar Power Integration in Distribution Grids: PV Modelling, Voltage Support and Aggregation Studies
KTH, School of Electrical Engineering (EES), Electric Power Systems.
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 [en]
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: urn:nbn:se:kth:diva-154602ISBN: 978-91-7595-303-8 (print)OAI: oai:DiVA.org:kth-154602DiVA: diva2:758167
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
List of papers
1. Reactive Power Dynamic Assessment of a PV System in a Distribution Grid
Open this publication in new window or tab >>Reactive Power Dynamic Assessment of a PV System in a Distribution Grid
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
Keyword
PV system modelling, instantaneous model, reactive power control
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-99050 (URN)10.1016/j.egypro.2012.03.012 (DOI)000309468500011 ()2-s2.0-84897134411 (Scopus ID)
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
2. Comparison of a Three-Phase Single-Stage PV System in PSCAD and PowerFactory
Open this publication in new window or tab >>Comparison of a Three-Phase Single-Stage PV System in PSCAD and PowerFactory
Show others...
2012 (English)In: Proceedings of the 2nd International Workshop on Integration of Solar Power into Power Systems, Energynautics GmbH , 2012, 237-244 p.Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
Energynautics GmbH, 2012
Keyword
Photovoltaic, PSCAD, PowerFactory, Reactive power support
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
SRA - Energy
Identifiers
urn:nbn:se:kth:diva-107175 (URN)978-3-9813870-6-3 (ISBN)
Conference
2nd International Workshop on Integration of Solar Power into Power Systems. 12-13 November. Lisbon Portugal
Funder
StandUp
Note

QC 20121221

Available from: 2012-12-21 Created: 2012-12-07 Last updated: 2017-03-02Bibliographically approved
3. Evaluation of Reactive Power Support Interactions Among PV Systems Using Sensitivity Analysis
Open this publication in new window or tab >>Evaluation of Reactive Power Support Interactions Among PV Systems Using Sensitivity Analysis
2012 (English)In: 2nd International Workshop on Integration of Solar Power into Power Systems, 2012, 245-252 p.Conference paper, Oral presentation only (Refereed)
Keyword
Photovoltaic, Voltage sensitivity matrix, RGA, SVD
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
SRA - Energy
Identifiers
urn:nbn:se:kth:diva-107169 (URN)978-3-98-13870-6-3 (ISBN)
Conference
2nd International Workshop on Integration of Solar Power into Power Systems. 12-13 November 2012, Lisbon, Portugal
Funder
StandUp
Note

QC 20130109

Available from: 2013-01-10 Created: 2012-12-07 Last updated: 2014-10-28Bibliographically approved
4. Coordinated Active Power-Dependent Voltage Regulation in Distribution Grids With PV Systems
Open this publication in new window or tab >>Coordinated Active Power-Dependent Voltage Regulation in Distribution Grids With PV Systems
Show others...
2014 (English)In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 29, no 3, 1454-1464 p.Article in journal, Editorial material (Refereed) Published
Abstract [en]

High penetrations of photovoltaic (PV) systems in distribution grids have brought about new challenges such as reverse power flow and voltage rise. One of the proposed remedies for voltage rise is reactive power contribution by PV systems. Recent German Grid Codes (GGC) introduce an active power dependent (APD) standard characteristic curve, Q(P), for inverter-coupled distributed generators. This study utilizes the voltage sensitivity matrix and quasi-static analysis in order to locally and systematically develop a coordinated Q(P) characteristic for each PV system along a feeder. The main aim of this paper is to evaluate the technical performance of different aspects of proposed Q(P) characteristics. In fact, the proposed method is a systematic approach to set parameters in the GGC Q(P) characteristic. In the proposed APD method the reactive power is determined based on the local feed-in active power of each PV system. However, the local voltage is also indirectly taken into account. Therefore, this method regulates the voltage in order to keep it under the upper steady-state voltage limit. Moreover, several variants of the proposed method are considered and implemented in a simple grid and a complex utility grid. The results demonstrate the voltage-regulation advantages of the proposed method in contrast to the GGC standard characteristic.

Keyword
German grid codes, photovoltaic, reactive power control.
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-154577 (URN)10.1109/TPWRD.2014.2298614 (DOI)000337137900053 ()2-s2.0-84901391468 (Scopus ID)
Note

QC 20141029

Available from: 2014-10-23 Created: 2014-10-23 Last updated: 2017-12-05Bibliographically approved
5. Optimal Coordination of Q(P) Characteristics for PV Systems in Distribution Grids for Minimizing Reactive Power Consumption
Open this publication in new window or tab >>Optimal Coordination of Q(P) Characteristics for PV Systems in Distribution Grids for Minimizing Reactive Power Consumption
2014 (English)In: AORC Technical Meeting 2014, 2014Conference paper, Published paper (Refereed)
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-154580 (URN)
Conference
AORC Technical meeting 2014, Japan
Note

NQC 20141029

Available from: 2014-10-23 Created: 2014-10-23 Last updated: 2014-10-29Bibliographically approved
6. Multi-objective coordinated droop-based voltage regulation in distribution grids with PV systems
Open this publication in new window or tab >>Multi-objective coordinated droop-based voltage regulation in distribution grids with PV systems
Show others...
2014 (English)In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 71, 315-323 p.Article in journal (Refereed) Published
Abstract [en]

High penetrations of photovoltaic (PV) systems in distribution grids have caused new challenges such as reverse power flow and voltage rise. Reactive power contribution by PV systems has been proposed by grid codes and literature as one of the remedies for voltage profile violation. Recent German Grid Codes (GGC), for instance, introduce a standard active power dependent reactive power characteristic, Q(P), for inverter-coupled distributed generators. Nevertheless, the GGC recommends a voltage dependent reactive power characteristic Q(V) for the near future, recognizing that the Q(P) characteristic cannot explicitly address voltage limits. This study utilizes the voltage sensitivity matrix and quasi-static analysis in order to develop a coordinated Q(V) characteristic for each PV system along a radial feeder using only the local measurement and drooping technique concepts. The aim of this paper is using a multi-objective design to adjust the parameters of the Q(V) characteristic in the proposed droop-based voltage regulation in order to minimize the reactive power consumption and line losses. On the other hand, it is also possible to adjust the parameters in order to reach equal reactive power sharing among all PV systems. A radial test distribution grid, which consist of five PV systems, is used to calculate power flow and, in turn, the voltage sensitivity matrix. The comparison of results demonstrates that both approaches in the proposed droop-based voltage regulation can successfully regulate the voltage to the steady-state limit. Moreover, it is shown that the profile of reactive power consumption and line losses are considerably reduced by the multi-objective design.

Keyword
Droop control, German grid codes, Photovoltaic, Reactive power control
National Category
Energy Systems
Identifiers
urn:nbn:se:kth:diva-152552 (URN)10.1016/j.renene.2014.05.046 (DOI)000340976600035 ()2-s2.0-84902327546 (Scopus ID)
Note

QC 20140930

Available from: 2014-09-30 Created: 2014-09-29 Last updated: 2017-12-05Bibliographically approved
7. Static Equivalent of Distribution Grids with High Penetration of PV Systems
Open this publication in new window or tab >>Static Equivalent of Distribution Grids with High Penetration of PV Systems
(English)Manuscript (preprint) (Other academic)
Keyword
Photovoltaic systems, load modeling, system identification, reactive power control
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-154579 (URN)
Note

QS 2014

Available from: 2014-10-23 Created: 2014-10-23 Last updated: 2014-10-29Bibliographically approved

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Output format
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