A novel two degrees of freedom grid current regulation for single-phase LCL-type photovoltaic grid-connected inverter

For single-phase LCL-type photovoltaic (PV) grid-connected system installed at the end of the grid, a novel two degrees of freedom grid current regulation (2DOFGCR) is proposed, which includes the synchronous reference frame quasi-proportional-integral (SRFQPI) controller and grid-current-feedback active damping (GCFAD) controller. The SRFQPI controller compensate reactive power quickly and regulate the instantaneous output grid current with zero steady-state errors regardless of the fluctuation range of fundamental frequency. The GCFAD controller not only damps LCL-resonance, but also improves both transient and steady-state performances. Finally, the optimized design of 2DOFGCR is proposed with the careful examinations of the system dynamic performance, stability margin and amplitude error. Simulation and experimental results verified the validity of the proposed method.