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

Resonance phenomenon of grid-connected inverter may happen due to dynamic variation of grid impedance. Terminal output impedance of inverter can be reshaped by retuning internal parameters of inverter to mitigate resonance issue and stabilize grid-connected inverter system. However, it’s not easy to obtain internal parameters of grid-connected inverter in practical operation due to industrial secrecy. This paper presents a grey-box parameters identification method to extract the internal 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-parallel 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 manufacturer for further parameters modification. Simulation results are given to validate the proposed grey-box parameter identification and corresponding impedance reshaping method.