Virtual Model Predictive Control for Inverters to Achieve Flexible Output Impedance Shaping in Harmonic Interactions With Weak Grids

The impedance-based method is an effective approach to investigate harmonic interaction problems in weak grids. Modeling and shaping the inverter output impedance are two important aspects of this method. However, for the inverter under finite-control-set model predictive control (FCS-MPC), the output impedance model is difficult to develop due to the nonlinear dynamic characteristics. To explore the FCS-MPC-based solution to harmonic interaction problems in weak grids, this article first derives the mathematical output impedance model of the inverter under FCS-MPC based on the described function method. The developed inverter output impedance model is highly robust to changes in operating conditions and parameters, and the proposed modeling method provides an effective way to describe the impedance characteristics of inverters under FCS-MPC. Then, based on the virtual MPC, a flexible output impedance shaping method for the inverter is proposed. The ability to improve system stability and mitigate harmonics is evaluated through impedance-based analysis, and a design method for the control parameters is presented. Finally, the theoretical model of inverter output impedance and the impedance shaping method developed in this article are verified through simulations and experiments.