Time delay consideration for robust capacitor-current-inner-loop active damping of LCL-filter-based grid-connected converters

Abstract

Due to its higher switching frequency current harmonics attenuation, the LCL filter is extensively adopted in Grid connected Converters (GcCs). To cope with its inherent resonance phenomena, the Capacitor Current Inner Loop Active Damping (CCIL-AD) is typically employed to actively damp the LCL filter resonant peak. However, the time delay (td) related to digital controllers modifies the Active Damping (AD) characteristics, resulting in reduced phase margin as well as poor dynamic and steady-state performances of the system. Moreover, high variations in the grid inductance, mainly under weak grid conditions, may threaten the system stability. In view of this, this paper proposes a robust design approach for voltage oriented PI control associated to CCIL-AD for LCL-filter-based Grid-connected Converters (LCL-GcCs). The aim of the considered approach is to ensure robust stability margins, fast transient response and reduced steady-state error even under severe grid inductance changes, digital time delay and LCL filter parameters variations. The proposed approach has been validated by simulation and experimental tests based on a 4-kW three-phase converter laboratory prototype. The obtained simulation and experimental results indicate the efficiency and the robustness of the proposed design approach.