Institut für Energiesysteme und Elektrische Antriebe, Arbeitsgruppe Elektrische Anlagen
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SmartDCGrid - a research project to analyze advantages and possibilities on realization for low voltage grids

Synopsis

A lot of electrical devices have to transform alternating current (AC) into direct current (DC) because they work on direct current. Besides that a lot of decentralized energy sources and electrochemical storage produce or work on direct current. To check whether there is a possibility for realization and to show up advantages, we are going to do research on low voltage dc-power grids. We will investigate the feasibility and the necessary components as well as algorithms to operate and control such a DC-grid. With extended algorithms it should be possible to realize a “smart DC-grid”. The economical evaluation will indicate the possibility for realization or the additional demand for research in this area.

Project Objectives

Nowadays a significant amount of electric devices work on direct current (DC) but the power is supplied via an alternating current (AC)-grid, thus making it necessary to convert AC into DC for the devices. On the other hand, decentralized generation like photovoltaic, fuel cells or electro chemical storage used for energy optimization are all working with DC, which has to be converted to AC to be feed into the power grid.

Figure 1: Example of a state of the art low voltage AC grid: a lot of components work with DC. The arrows indicate the direction of the (active) power flow.

The project is based on the idea to substitute or amend the low voltage AC-grid with a DC-grid inside a building or residential area to reduce the necessary transformations from DC to AC and back to DC.

Figure 2: PV system, fuel cell and storage are part of a DC-grid, with direct connected consumers (electric vehicle, suitable devices). AC devices can still be directly connected to the AC-Grid (lighting, washing mashine) or connected to DC with an suitable inverter.
Figure3: DC grid only: low voltage supply only with DC. With smart DC componentns, reacting on the load situatuion in the grid, or to support the external AC grid.

To find out in which areas further know-how is necessary to realize a DC-grid it is important to check the following five questions in this feasibility study:

1. Which components are needed for a smart-DC-grid?

2. How could such a smart-DC-grid be operated?

3. How could, as an additional functionality, such a smart-DC-grid be operated as an island?

4. Is a smart-DC-grid economically feasible?

5. Which concept could lead to a realization?

Investigation on State-of-the-Art for components, designing of exemplary grids for different scenarios (AC-DC-combined grid, standalone DC-grid, DC-grid for residential area, DC-grid for an office building …) will make it possible with the developed simulation tool to gather information on the design and operation of a smart-DC-gird. Simple exemplary algorithms for operation combined with Demand Side Management (DSM) should be developed and tested, for instance by using the voltage magnitude for signaling information about the current energy production and state of charge of storage in the SmartDCGrid. Furthermore the advantages and disadvantages compared to a conventional AC-grid should be investigated. 

Simulations for the exemplary grids will be done with and without a connection to the AC-grid. If the AC-grid is not available, DC-grids might be economically feasible because the costs for not delivered energy are much higher than usual energy costs.

Figure 4: AC/DC hybrid grid with a blackout of the AC grid: with the pv system and the storage (possible including the storage of electric vehicles) a limited supply in DC is possible. So for example ligthing and the frige are still working but the TV is not supplied.
Figure 5: SmartDCGrid as an island: voltage is used as information on prodcution and storage. The devices react on that (red = no usage possible, yellow = limited usage possible, green = full usage possible or necessary)

The exemplary grids are going to be compared to “business-as-usual” scenarios to find the maximum of costs for the components. This economical evaluation will indicate whether it makes sense to do further research or not.

This project will deliver a large knowledge base for future work on smart-DC-grids. That will make it is possible to develop concepts for a realization with the project partners and external partners.

Project Members

Project Lead:

  • TU Vienna - Institute for Energy Systems and Electrical Drives

    • Workgroup Energy Systems

Project Partners:

  • TU Vienna - Institute for Energy Systeme and Electrical Drives

    • Workgroup Electrical Machines - Power Electronics
    • Workgroup Energy Economics Group

  • Swimsol GmbH

Contact

Dipl.-Ing. Franz Zeilinger

Dipl.-Ing. Michael Chochole

Dipl.-Ing. Markus Heimberger

Dipl.-Ing. Thomas Kaufmann

Dipl.-Ing. Jürgen Marchgraber

Dipl.-Ing. Alexander Winter

Duration/ Funding

From 07/2014 to 06/2015

This project is funded by the "Klima- und Energiefonds" and is conducted within the research programme "e!MISSION.at – 4.Ausschreibung".