Adaptive active damping method of grid-connected inverter based on model predictive control in weak grid

The LCL-type grid-connected inverter based on finite control set model predictive control (FCS-MPC) is suitable for weak grids because of its good robustness and fast dynamic response. However, in an FCS-MPC-based system, the variable switching frequency causes the spread of the inverter-side current harmonic spectrum. Thus, the grid-side current may be distorted because the harmonics are amplified to the grid side due to the resonance peak of the LCL filter. To solve the above problem, this paper proposes an adaptive active damping (AD) method to eliminate the resonant effects. First, the system based on an MPC controller is regarded as a closed-loop system of the grid-side current, and the resonance peak is suppressed effectively by an AD, which consists of a virtual resistor and a virtual capacitor. Second, to balance the resonance suppression and dynamic performance of the system under weak grid conditions, the grid impedance is measured and the optimal AD values for different grid impedance are calculated online. Compared with the fixed-value AD, the proposed method has better resonance suppression and higher bandwidth. The effectiveness and feasibility of the proposed control strategy are verified by simulations and experiments.