Effect of single-current-feedback active damping on the output impedance of grid-connected inverter

LCL-filter is commonly used as an output-side filter in a grid-connected converter due to its good attenuation capability at the switching harmonic frequencies. LCL-filter creates several resonances in the converter dynamics which shall be damped for ensuring robust performance of the converter. The resonant behavior introduced by the LCL-filter can be attenuated with active damping (AD) instead of passive damping to improve the conversion efficiency. The active damping affects the output impedance of the converter, and the impedance should be accurately predicted in order to allow analyzing impedance-based stability of power electronics-based power systems. This paper presents the small-signal model for inverter-current-feedback (ICF) converter using only the inverter-side inductor current feedback for both control and active damping. Additionally, the output impedance properties are comprehensively analyzed. Experimental measurements from 3-kW prototype are presented to verify the analysis.