An Equivalent Differential Method for Active Damping of LCL Type Grid-Connected Inverters With Grid-Side Inductor Voltage Feedback

Abstract

The differential feedback of grid-side inductor voltage can effectively increase the damping of grid-connected inverters. Compared with proportional feedback of filter capacitor current, it can increase the output impedance of the grid-connected inverters, which is more conducive to reducing the impact of grid background harmonics on the grid-in current. However, there is a differential link in its damping branch, and existing differential implementation methods were pursuing to be ideal differential in wide frequency band, as a consequence, high frequency components of the grid-side inductor voltage are amplified, which affects the quality of grid-in current. For this reason, this paper proposes a band-pass filter in series with a lead compensation unit to replace the ideal differential. The major advantage different from the conventional methods is that the proposed strategy is only equivalent to the ideal differential around the resonance frequency band. Specifically, it features lower gain at low and high frequency bands. Finally, theoretical analysis and experiment results show that the proposed strategy can reduce the influence of the added damping path on the fundamental component of grid-in current and features better suppression effect on the harmonics.