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Multi-objective coordinated droop-based voltage regulation in distribution grids with PV systems
KTH, School of Electrical Engineering (EES), Electric Power Systems.
KTH, School of Electrical Engineering (EES), Electric Power Systems.
KTH, School of Electrical Engineering (EES), Electric Power Systems.
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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.

Place, publisher, year, edition, pages
2014. Vol. 71, 315-323 p.
Keyword [en]
Droop control, German grid codes, Photovoltaic, Reactive power control
National Category
Energy Systems
URN: urn:nbn:se:kth:diva-152552DOI: 10.1016/j.renene.2014.05.046ISI: 000340976600035ScopusID: 2-s2.0-84902327546OAI: diva2:750815

QC 20140930

Available from: 2014-09-30 Created: 2014-09-29 Last updated: 2014-10-28Bibliographically 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.
TRITA-EE, ISSN 1653-5146 ; 2014:050
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
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)

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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