A Fixed Switching Frequency Direct Model Predictive Control for Grid-Tied Converters With <i>LCL</i> Filters Under Adverse Grid Conditions

This article presents a direct model predictive control (MPC) scheme for grid-tied converters (GTCs) with LCL filters operating under nominal and adverse grid conditions. Specifically, the proposed MPC algorithm achieves a high-quality grid current in steady state and fast dynamic responses that characterize direct controllers due to the absence of a dedicated modulator. Thanks to the adopted modeling approach, the control and modulation problems are formulated together as a multiple-input multiple-output (MIMO) problem. In doing so, not only the controller design process is greatly simplified, but also favorable performance in terms of controller bandwidth and robustness is achieved. This is in stark contrast to conventional linear control methods, where the existence of different cascaded and/or parallel control loops oftentimes leads to an adverse interaction with each other. Consequently, as also demonstrated by the presented experimental results, the proposed algorithm achieves superior performance for a wide range of operating conditions, rendering it as a promising control approach for the systems in question.