Hybrid Active Damping and Grid-Injected Current Regulation for a PV Array Power Conditioning System Under Weak-Grid Conditions

This paper presents a hybrid active damping strategy for single-phase grid-connected photovoltaic (PV) inverters with LCL filters, combining capacitor current feedback (CCF) and PCC-voltage feedforward within a unified control framework. A detailed small-signal and frequency-domain model is derived in which both mechanisms are represented as equivalent virtual impedances, enabling explicit characterization of positive and negative damping regions as functions of sampling frequency, grid inductance, and LCL parameters. Based on this model, a systematic design procedure is proposed for the current PI controller and CCF gain that ensures minimum-phase behavior and robust stability by enforcing stringent gain- and phase-margin constraints and impedance-based stability criteria under weak-grid conditions. Parameter uncertainties and wide grid-inductance variations are analyzed using an impedance-ratio approach, and a simple gain-attenuation scheme for PCC feedforward is introduced to maintain stability in extremely weak grids. The proposed method is validated on a ۵ kW PV system through detailed MATLAB/Simulink simulations, demonstrating accurate DC-link voltage regulation, effective maximum power point tracking under irradiance transients, and high-quality grid current with total harmonic distortion below ۲% in stiff grids and about ۳% in distorted weak grids, complying with IEEE ۵۱۹.