LAUSR

The wide bandwidth impedance of grid and inverter are the critical parameters for small-signal stability analysis and control optimization of grid-tied inverter systems. The impedance measurement is an effective way to obtain the grid and inverter impedance by injecting a series of perturbations into the measured system. However, previous studies fail to fully consider the adverse grid voltage conditions; including harmonics, unbalance, frequency deviation, voltage sag, and phase jump; which may bring errors to the measured impedance. In this article, a cascaded delayed signal cancellation (CDSC)-based method is proposed to accurately obtain the impedance of the measured system under adverse grid voltage conditions. The proposed CDSC-based method is mainly composed of the perturbation extraction module (PEM) and frequency adaptive module (FAM). Different CDSC blocks are applied to implement the PEM and FAM to extract the injected perturbations adaptively, under various adverse grid voltage conditions. Simulation and hardware-in-the-loop experiment results are presented to validate the effectiveness and feasibility of the proposed impedance measurement method.