This paper presents a vector fitting (VF) algorithm-based grey-box structure and controller parameters identification method for grid-connected inverter. Terminal frequency responses of inverter are first measured by frequency scanning method. Then, mathematical representation of these impedance frequency responses are fitted in a form of polynomial transfer function by using VF algorithm. Finally, the theoretical terminal impedance formulas of possible control structures are compared with the fitted transfer function. Simulation results show that the proposed method is able to identify internal control
structure and system parameters when internal parameters are unknown due to industrial secrecy or are perturbated due to variation of operation points, temperature and aging impact.