Stationary Frame Current Control Evaluations for Three-Phase Grid-Connected Inverters with PVR-based Active Damped LCL Filters

Grid-connected inverters (GCIs) with LCL output filter have the ability of attenuating high-frequency (HF) switching ripples. However, by using only grid-current control, the system is prone to resonances if it is not properly damped, and the current distortion would be amplified significantly under highly distorted grid conditions. In this paper, a synchronous reference frame equivalent proportional-integral (SRF-EPI) controller in αβ stationary frame using the parallel virtual resistance-based active damping (PVR -AD) strategy for grid-interfaced distributed generation (DG) systems to suppress the LCL resonance is proposed. Although both proportional-resonant (PR) controller in αβ stationary frame and PI controller in dq synchronous frame achieve zero steady-state error, the amplitude- and phase-frequency characteristics differ greatly from each other except for the reference tracking at fundamental frequency. Therefore, an accurate SRF-EPI controller in αβ stationary frame is established to achieve precise tracking accuracy. Moreover, the robustness, harmonic rejection capabilities, and influence of control delay are investigated by the Nyquist stability criterion when the PVR-based AD method is adopted. Furthermore, the grid voltage feed-forward and multiple PR controllers are integrated in the current loop to mitigate the current distortion introduced by the grid background distortion. Besides, the parameters design guidelines are presented to show the feasibility and effectiveness of the proposed strategy. Finally, simulation and experimental results are provided to validate the feasibility of the proposed control approach.