Effect of Active Damping on Output Impedance of Three-Phase Grid-Connected Converter

LCL-filter is commonly used to attenuate the switching harmonics of grid-connected converters. LCL-filter creates resonances in the converter dynamics which shall be damped for ensuring robust performance of the converter. Active damping methods can be used to attenuate the resonant behavior effectively. Accordingly, the output impedance is affected and the grid-interaction sensitivity of the converter varies with the active damping design. In order to carry out impedance-based stability analysis or assessment of the harmonic rejection capability, an accurate analytical model to predict the output impedance is necessary. This paper investigates the output impedance properties of capacitor-current-feedback active damping, which are so far not considered thoroughly in the literature. The output impedance modification with the active damping design is explained, thus, the stability and harmonic rejection capability of the converter can be improved. Furthermore, in order to validate the model, experimental measurements of the output impedance with active damping are presented for the first time in literature.