Evaluating the delay problems and solutions for active filters in Photovoltaic grid-connected

An active power filter (APF) is one of the main ways to eliminate the harmonic quality of the grid, and LCL is currently the APF connected to the grid’s common filters. To inhibit the resonance problem caused by the LCL filter, active damping based on capacitive current feedback is commonly used. Active damping can effectively inhibit the resonance caused by the LCL filter, and it can be equivalent to the resistance parallel to the filter capacitor under the simulation control, due to the stagnation of capacitive current. After that, the virtual resistance value will be negative, and the negative damping characteristics will be presented, which will affect the stability of the system. For this reason, this article aims to evaluate the delay problems and solutions for active filters in photovoltaic grid-connected, and four solutions were analyzed. The first method is modifying the sampling method, the second one is the delay compensation method for state estimation, the third one is the phase advance method and the fourth one is the Kalman Filter.