Overview on Grid-Forming Inverter Control Methods Peter Unruh * , Maria Nuschke *, Philipp Strauß * and FriedrichWelck-Power System Stability and Converter Technology Division, Fraunhofer Institute for Energy Economics and Energy System Technology IEE, 34119 Kassel, Germany

Concept Paper Overview on Grid-Forming Inverter Control Methods Peter Unruh * , Maria Nuschke *, Philipp Strauß * and FriedrichWelck Power System Stability and Converter Technology Division, Fraunhofer Institute for Energy Economics and Energy System Technology IEE, 34119 Kassel, Germany; friedrich.welck@sma.de

 Abstract: In this paper, dierent control approaches for grid-forming inverters are discussed and compared with the grid-forming properties of synchronous machines. Grid-forming inverters are able to operate AC grids with or without rotating machines. In the past, they have been successfully deployed in inverter dominated island grids or in uninterruptable power supply (UPS) systems. It is expected that with increasing shares of inverter-based electrical power generation, grid-forming inverters will also become relevant for interconnected power systems. In contrast to conventional current-controlled inverters, grid-forming inverters do not immediately follow the grid voltage. They form voltage phasors that have an inertial behavior. In consequence, they can inherently deliver momentary reserve and increase power grid resilience 

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