A Hybrid-Frame Control Based Impedance Shaping Method to Extend the Effective Damping Frequency Range of the Three-Phase Adaptive Active Damper

The grid-connected inverter may get unstable due to variation of grid impedance. To improve the system stability, an adaptive active damper, which emulates an adaptive tuning virtual resistor, can be introduced at the point of common coupling. However, subject to the control bandwidth, the virtual resistor is actually a frequency- dependent impedance, and its damping performance is impaired. In this article, we propose an impedance shaping method to make the virtual impedance be resistive in a wider frequency range, and it is implemented under hybrid frame for directly controlling the active power of the active damper and eliminating the influence of the cross-coupling terms on the emulation of a virtual resistor. Finally, the prototypes of a 3-kVA three-phase active damper and a 6-kVA three-phase LCL- type grid-connected inverter are fabricated and tested in the lab. The experimental results are provided to verify the effectiveness of the proposed control methods for the three-phase adaptive active damper.