Self-Tuning Finite-State Model Predictive Control with Grid Impedance Estimation in a Grid-Tied Inverter

This paper presents an embedded finite state Model Predictive Control (MPC) algorithm for a grid connected three phase inverters with LCL-filter. The objective of the MPC is to control the active and reactive power exchanged with the grid. A grid impedance estimation method is proposed and integrated into the finite state MPC using an embedded signal injection. The resulting voltage and current transient are recorded and the Fast Fourier Transform (FFT) is applied to estimate the grid impedance seen at the point of common coupling (PCC). The grid impedance estimation is also used to estimate the grid voltage, allowing to reduce the number of sensors used in LCL-filter. The impedance and grid voltage estimation are then updated in the model predictive controller. The proposed algorithm is tested in simulation and its robustness against changes in grid impedance values will be proved.