Unified Active Damping Strategy Based on Generalized Virtual Impedance in LCL-Type Grid-Connected Inverter

Abstract

Extensive solutions have been proposed to damp <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> filter resonance. However, the time delay caused by computation and modulation process aggravates the complexity of current loop analysis. In this paper, a generalized virtual impedance model for six kinds of commonly used active damping methods is proposed, and the physical meaning is established by introducing the metric of “damping factor”. To ensure system robustness in a wide range of grid conditions, a hybrid active damping strategy that combines inverter current feedback and capacitor voltage feedforward is proposed. Importantly, this method only requires inverter current and capacitor voltage sensors, which are the basic variables for over-current protection, power control and synchronization. The superposition theorem is also utilized to analyze the damping capability provided by parasitic resistances, current feedback loop and voltage feedforward loop. Finally, experimental results verify the feasibility and robustness of the proposed damping method.