Investigation of Virtual Synchronous Machine (VISMA) and Voltage Controlled Inverter (VCI) under grid fault cases

Inhalt:
With the ongoing energy transition, the power grid is increasingly moving towards inverter-based resources, such as wind and solar power, which are replacing conventional plants with synchronous machines. In the future, inverters will therefore have to provide the same grid-stabilizing properties as synchronous machines. This will require new control concepts to enable an inverter-connected decentralized unit to take over these tasks, the so-called grid-forming inverters. For this purpose, various control concepts have been developed. This paper analyses two promising concepts for grid-forming inverters: the Virtual Synchronous Machine (VISMA) and the Voltage Controlled Inverter (VCI). Both exhibit grid-supporting behavior in parallel grid operation by providing momentary reserve, frequency support via primary control and voltage maintenance. In addition, errors must be safely controlled in future networks. The focus of this paper is on two particular faults cases: grid outage and short circuit. Simulations show that both approaches can continue to supply a load during a grid failure without changing the controls. A short circuit in the grid causes more difficulties, only the VISMA can cope with this for a limited time. Since the VISMA behaves more robustly than the VCI, only the simulation results of the VISMA are verified by real measurements in a real-time-hardware test bench.