Low-Loss Active Grid Impedance Cancellation in Grid-Connected Inverters with LCL Filter

Abstract

Distributed power inverters with inductive capacitive−inductive (LCL) filters have become popular in distributed power generation system. However, due to unknown grid impedance, the inverters are confronted with challenges of local filter resonance, poor power quality, and multiple interactive resonance. This paper proposes a low-loss active compensator that can counteract effects of the grid impedance on the current control performance of single-phase grid-connected inverter with an LCL filter. The compensator utilizes dual unit point-of-common-coupling voltage feedforward control mechanisms (VFFC), in which one is integrated with the inverter controller, and the other is generated through an extra low voltage source converter (LV-VSC) in series with the filter capacitor. The LV-VSC has no additional passive inductive-capacitive filtering elements and provides very low volt-ampere. To confirm its validity, a single-phase inverter testbed integrated with the compensator was built. The experimental results validate the current-controlled performance enhancement of the proposed inverter system operating under different grid conditions.

Keywords

• inverters
• lcl filter
• grid impedance
• weak grid
• active compensator