An Extension of Grid-Forming: A Frequency-Following Voltage-Forming Inverter

The grid-forming inverter (GFM) is widely acknowledged for its capabilities of forming both grid frequency and voltage. This letter investigates an extension of GFM, which decouples the capabilities of forming grid frequency and voltage. Based on the GFM inverter with matching control, a virtual resistor in series with the dc-link capacitor is added, so that the inverter can stably and quickly respond to outer grid frequency variations [i.e., frequency-following (FFL)], and meanwhile enhance the voltage stiffness of power grids [i.e., voltage-forming (VFM)]. The dc-link voltage regulation is also integrated into the synchronization control, making this inverter fit for short-term constant power inputs such as renewable energy resources. A full-order state-space model is established to assess the stability of the inverter. Control parameters are properly tuned. A 3 kW grid-tided inverter experiment platform is tested and a modified IEEE 68-bus power system is simulated to validate the decoupled FFL and VFM features of the inverter.