Single-Feedback Based Inverter-Current-Controlled LCL-Type Grid-Connected Inverters with Capacitor-Current Active Damping: Robust Design and Single-Feedback Implementation

The dual-feedback control combining inverter current control and capacitor-current active damping is widely applied for LCL-type grid-connected inverters. This paper investigates the operation cases of this dual-feedback control, paving a path for a robust design. Theoretical analysis is presented to provide a design guideline. A robust damping gain is derived which can ensure robustness against the grid inductance variation. However, it is found that this property is subjected to both filter parameter fluctuations and the lagging phase of the current regulator. To address these issues, extra phase-lead compensation is suggested to be embedded with the current regulator. On top of these, a robust single-feedback inverter current control is developed, where the capacitor current is extracted from the sensed inverter current for active damping, and the proportional-integral-resonant current regulator is used for avoiding the dc bias. The proposed strategy combines high robustness and cost-efficiency. Experimental results from a 6-kW prototype are finally provided to confirm the theoretical analysis and expectations.