Impedance-Based Stability Analysis and Design of a Fractional-Order Active Damper for Grid-Connected Current-Source Inverters

Due to its voltage boosting capability and current controllability, the current-source inverter (CSI) is a strong candidate for interfacing high-power photovoltaic (PV) systems with the utility grid. However, low-order harmonics from semiconductor switching or grid voltage give rise to resonance and render the converter unstable. Active damping techniques can modify the control algorithm to mitigate the resonance. However, digital control delays and grid-impedance variations complicate the active damping design and result in poor robustness. Notwithstanding recent research advancements, the technology of the CSI-based PV systems is still in its infancy, needing more attention to the control aspects. This paper proposes a fractional-order active damping control with a more tuning parameter for grid-connected CSI-based PV systems. A sound design strategy further has been presented for the fractional-order damper taking into account the digital control delay. The proposed active damper robustly mitigates the passive filter resonance and guarantees the power quality despite the grid-impedance variations. Simulation and experimental results demonstrate that the fractional-order active damper offers a superior response in comparison with a standard active damper.