Fixed Switching Frequency Model Predictive Control for Grid-Forming Inverters

Abstract

This paper proposes a Fixed Switching Frequency Model Predictive Control (FSF-MPC) for Grid-Forming Inverters (GFIs) in microgrids. The inner voltage and current loops are implemented by means of the proposed FSF-MPC, and the primary control is composed by an outer Droop and a PQ controller. Such a PQ control allows a better steady-state response and enhanced power management. The performance of the proposed FSF-MPC for grid-tied and islanded modes is demonstrated using as an example an ac microgrid equipped with 50kVA grid-forming inverters with output LC filters and different loads. The microgrid is implemented in a Hardware-in-the-Loop (HIL) device, and HIL case studies are presented for grid-tied and islanded modes, with load and parametric variations and weak grid conditions. The results demonstrate the good performance of the proposed FSF-MPC approach for GFIs in microgrids, such as fast dynamic response, multi variable control, adequate load sharing between the inverters and robustness to parametric variations and unmodeled dynamics.