The central research question addressed by the “Fuchstal leuchtet” project is whether and how stable grid operation can be achieved within a purely inverter-based island grid (grid-forming and grid-following converters) based on their applicable technical connection rules (TCR). This includes island grid operation as well as the transition between synchronous and island mode, and vice versa. Given recent advancements (e.g., VDE FNN Guideline “Technical requirements for grid-forming capabilities including provision of inertia”), operational requirements now define the synchronous control behavior of grid-forming (GFM) inverters, supplementing the established TCRs for grid-following (GFL) systems. While another paper examines the process of intentional islanding with GFM and GFL inverters, which will be examined practically in the 3rd field trial, a field test was conducted focusing on the evaluation of the synchronous grid operation capability of the two GFM inverters, based on the manufacturer's parameterization according to the VDE FNN Guideline.
Within the field test their grid behavior was examined regarding the following GFM requirements:
- Voltage source behavior
- Phase jump power
- Effective impedance
- Voltage source control –set‑point tracking behavior
- Voltage source control – Disturbance response and linearity of the effective impedance
- Damping of power-frequency-oscillations
- Provision of inertia (TA)
The full paper provides a detailed explanation of the individual tests according to the VDE FNN guideline and their possible implementation in the field lab. Using the generated field measurement data, the reliable synchronous operation of the GFM inverters in the distribution network and their compliance with these requirements is demonstrated.