Design and Analysis of LCL-type Grid-Connected PV Power Conditioning System Based on Positive Virtual Impedance Capacitor-Current Feedback Active Damping

In recent years, grid-connected solar systems have become increasingly common on low-voltage grids to promote renewable energy sources. In these systems, LCL filters are commonly used to eliminate high-frequency harmonics produced by switching grid-connected inverters. However, the resonance frequency of LCL filters is highly dependent on network impedance. Variations in network impedance can shift the resonance frequency, causing instability in the system. To address this issue, this paper proposes a new method for attenuating resonance using capacitor-current feedback with positive virtual impedance shaping. It can provide a positive equivalent resistance almost within the Nyquist frequency, i.e., the entire controllable frequency range. The proposed method maintains system stability against changes in network impedance and offers good performance against changes in the production capacity of the solar array. For maximum power point tracking, the incremental conductance method and integral regulator are used. Simulation results using MATLAB/Simulink software demonstrate the effectiveness of the proposed method in injecting high-quality current into the network and maintaining stability against changes in network impedance. The proposed method can lead to improved power quality and increased efficiency of grid-connected solar systems, which can help to promote the adoption of renewable energy sources and reduce carbon emissions.