Design of a robust grid-forming control for low-voltage grids

To ensure future dynamic grid stability, short-term installation of the largest possible grid-forming plant capabilities at all levels of the grid is required. This will partly shift responsibility for ensuring dynamic stability from transmission grid level to all levels, including the distribution grid. Here, this means a shift from the previously passive, consumer-oriented levels to active grid-forming inverters. Operation at highly resistive grid connection points poses a particular challenge to controller stability in the low-voltage grid. A novel approach is presented to ensure high-performance inverter behaviour even under such conditions. An extended control concept of the Voltage-Controlled Inverter is presented and underlying mechanisms are explained. Afterwards, several approaches to designing the controllers to comply with current grid requirements are introduced. The controller is then tested under disturbances for typical and extreme grid conditions in simulation and the laboratory to ensure robust operation, even under changing grid conditions. The introduction of a comprehensible methodology achieves a significant gain in knowledge for future controller designs.