Single-Loop MPC-Based Voltage Control for Grid-Forming Inverters with Adaptive Virtual Impedance

Grid-forming inverters (GFM) integrated with the capabilities of traditional synchronous generators (SGs) are emerging as a promising solution for the grids dominated by inverter-based resources (IBR). However, the GFM inverters require several cascaded control loops to effectively emulate the qualities and functionalities of the SGs. Since GFMs lack inherent inertia to support the grid, the entire process of frequency and voltage regulation relies substantially on the control structure implemented. Therefore, it is crucial to develop advanced control methods that are both simple and capable of providing better dynamic response. At present, the inner control loops are predominantly dual-loop configurations, where interaction between the control loop bandwidths leads to instability. To address this, this paper proposes a single loop Model Predictive based voltage control for the inner loop, combined with an outer primary Droop controller. Additionally, a modified adaptive virtual impedance scheme is incorporated to enable current limiting during symmetrical fault-induced voltage sags. The effectiveness of the proposed control is evaluated across a range of short circuit ratio (SCR) values using PLECS simulations.