Economic and technical comparison of static voltage stability

Project state
Zentrum für Netzintegration und Speichertechnologien der RWTH Aachen.
Testing Center Electric Mobility at RWTH Aachen University. | Image: RWTH Aachen

Ensuring voltage stability in the distribution network is a key technical challenge in integrating decentralised, renewable energy sources such as photovoltaics, onshore wind and biogas. Up until a few years ago, voltage problems were often resolved through expensive conventional grid expansion measures. In the meantime, individual innovative concepts for static voltage stability such as controllable secondary substation transformers (rONT) or the more active power-dependent reactive power consumption with photovoltaic inverters (for example, cosϕ(P) control) are often employed.

Studies on the decentralised provision of reactive power and controllable secondary substation transformers have proven the effectiveness and cost-efficiency of these concepts. However, a comprehensive analysis of all available innovative voltage stability concepts and their interaction during grid operation is still missing.

For the first time, the joint project U-Control will therefore focus on the following research questions with the aid of simulations, laboratory tests and field trials:

  • How effective are the various voltage stability methods in the distribution network?
  • How robust are these methods during grid operation, especially given their interaction with other voltage stability methods?
  • Which requirements must be imposed on the method parameters in terms of stability?
  • What are the economic costs?
  • Which properties must the verification procedures have in order to ensure a wide area of application in the distribution grids?
  • Which parameter set of the characteristic-curve method for voltage stability is optimal in terms of the various targeted functions?

The interplay between simulations, laboratory tests at various university locations (round robin tests) and field trials ensures a high level of practical relevance and validates the findings.

Auflistung der im Projekt „U-Control“ untersuchten innovativen Spannungshaltungskonzepte.
Auflistung der im Projekt „U-Control“ untersuchten innovativen Spannungshaltungskonzepte. | Grafik: TU Braunschweig

In the future, the developed solutions and results will give operators an effective and understandable toolbox to address static voltage stability problems. In addition, the brains trust and standardisation committees would be given an information and decision-making basis for the further development of the regulatory framework for the connection of distributed electricity generation systems in the low and medium voltage grids. The consortium is working on the existing solutions that are relevant to the problem, and is evaluating these based on technical and economic criteria.

Aufbau des Forschungsprojektes „U-Control“. Hauptschwerpunkte bilden die Simulationen, die Laborversuche und die Feldversuche bei den assoziierten Netzbetreibern
Structure of the research project “U-Control”. Main priorities include simulations, laboratory experiments and field trials at the associated grid operators. | Image: TU Braunschweig

Project schedule and work packages

In the first work package, a variety of grid data of the participating grid operators for medium and low voltage grids will be evaluated, and based on that, template grids for simulations will be created. The research partners TU Braunschweig, TU München, RWTH Aachen University and FGH e.V. are working on the simulations, each with different goals. First results are expected by mid-2016. There will be an economic evaluation once the simulation results are available. Concurrently with the simulations and the economic evaluation, laboratory tests in the test fields at TU Braunschweig, TU München and RWTH Aachen University are being carried out. First results are expected by mid-2016 as well. The conclusion of this work package will be the so-called round robin tests that permit a benchmark of three experimental laboratories.

Netzintegrationslabor an der TU Braunschweig. Laborumgebung zur Untersuchung des dynamischen Verhaltens von Spannungshaltungskonzepten.
Grid integration laboratory at TU Braunschweig. Laboratory environment to study the dynamic behaviour of voltage stability concepts. | Image: TU Braunschweig

In the middle of 2016, the simulation and laboratory results will be validated in three concurrent field trials at the involved distribution network operators Netze BW GmbH, Bayernwerk AG and Infrawest GmbH. The field trials and the laboratory tests are being supported by the two industry partners SMA Solar Technology AG and Maschinenfabrik Reinhausen GmbH.

The findings of the individual work packages are then combined in the sixth work package (AP6) and used to prepare recommendations for action for grid operators and members of the brains trust and standardisation committees, and to create test procedures. Finally, there will be an overall economic and technical evaluation of the benefits of the investigated voltage stability concepts taking into consideration the results of the economic assessment.

Project duration

11/2014 - 10/2017


Prof. Dr.-Ing. Bernd Engel
Project co-ordinator
TU Braunschweig
Institut für Hochspannungstechnik und
elektrische Energieanlagen
38106 Braunschweig
+49 531 391-7740
+49 531 391-8106

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