A Gray-Box Impedance Reshaping Method of Grid-Connected Inverter for Resonance Damping

Oscillation phenomenon of grid-connected inverter can be caused due to time-varying grid impedance. Terminal output impedance of inverter can be reshaped by re-tuning internal parameters of inverter to mitigate the oscillation issue. However, it's not easy to obtain internal parameters of grid-connected inverter in practical operation. This paper presents a gray-box parameters identification method to identify the parameters of LCL filter, the proportional coefficient of current controller and capacitor-current-feedback coefficient from the measured terminal impedance frequency responses by using vector fitting algorithm. When instability phenomenon of multiple-paralleled inverters system occurs, the internal parameters of each inverter are first identified by using the proposed method. Then, the capacitor-current-feedback coefficients are re-tuned to stabilize the studied power system according to the impedance-based stability criterion. The re-designed parameters for the specific grid condition can be delivered to the manufacturers for further parameters modification. Simulation results are given to validate the proposed gray-box parameter identification and corresponding impedance reshaping method.