Fraunhofer Institute for Energy Economics and Energy System Technology
Fraunhofer Institute for Energy Economics and Energy System Technology

Research PnP Grids

PnP grids - Grid-forming control for distributed power converters

The Committee on Education, Research and Technology Assessment of the German Bundestag dealt with the threat to modern societies posed by large-scale and long-lasting power outages. It was emphasized that regional island grids with decentralized energy suppliers are of great importance for disaster management, especially for the supply of central infrastructure elements such as authorities and hospitals.

Fraunhofer IEE presented an innovative solution for the construction of stand-alone grids, which used grid-forming power converters that could operate locally autonomously, modular and without higher-level communication. These power converters were also intended to improve power quality and were used in industrial plants, emergency power supplies for public facilities and hospitals. In order to increase redundancy and modularity in island grids and interconnected grids, it was crucial that the grid-forming power converters could be distributed flexibly in the grid. The social benefit of this control method was considered to be high, as it offered solutions to the challenges of island and future supply grids.

Validation of new Plug & Play concept for grid-forming inverters

Overview of the Fraunhofer IEE Test Center SysTec, with schematic representation of the PNP networks test setup in the SGLV area (intelligent low-voltage network laboratory area).
© Fraunhofer IEE
Overview of the Fraunhofer IEE Test Center SysTec, with schematic representation of the PNP networks test setup in the SGLV area (intelligent low-voltage network laboratory area).
43.5 kVA RCP power converter developed in the project.
© Farunhofer IEE
43.5 kVA RCP power converter developed in the project.

The project PnP Grids "Validation of new Plug & Play concept for grid-forming inverters" followed the primary goal to validate a grid-forming control method patented by Fraunhofer IEE. The control method is particularly suitable for the use of locally distributed, decentral installed grid-forming battery converters in especially resistive grids (low-voltage or medium-voltage grid) .

For validation, a microgrid ecosystem was set up at Fraunhofer IEE, which is characterized by several locally distributed 43.5 kVA RCP power converters (rapid-control prototyping) developed in the project, on which the grid-forming control methods were implemented.

In order to address the plug and play capability, the control was parameterized in a generally valid manner, without adaptation to the respective network topology. The methods were implemented on fast-switching grid-forming converters developed in the project, which are particularly representative of future converter generations due to the use of hardware design.

Innovative current limiting methods and applications of grid-forming converters

Grid-Forming converter using SelfLim in LVRT operation.
© Fraunhofer IEE
Grid-Forming converter using SelfLim in LVRT operation.
Decentralized Operation of Grid-Forming Converters.
© Farunhofer IEE
Decentralized Operation of Grid-Forming Converters.

In the further course of the project, the patent* for an innovative current limiting method with grid-forming properties for interconnected and isolated grid operation was one of the major outcomes. Together with the validation of the current limiting method in grid-connected operation and in island grid operation, the potential of using converters with the validated grid-forming control was demonstrated, which can be used locally autonomously and modular and can act in an equal operation with other similar decentralized distributed converters.

The applications of the grid-forming converters include operation in remote island grids, in dynamic grid islands in the interconnected grid (if provided for in the standardization) and use as UPS applications for industrial plants, emergency power supplies for public facilities (e.g. fire departments, town halls, THW, ...) or hospitals.

 

* Current limitation for grid-forming power inverters (DE102021206502)

Funding: Federal Ministry of Education and Research 

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