PLL-less robust active and reactive power controller for single phase grid-connected inverter with LCL filter

Grid connected inverters, especially those used in DG (Distributed Generation) system, are expected with decoupled and flexible power control ability. Many existing power control methods are based on synchronous reference frame transformation, which requires the phase angle information provided by Phase-Locked Loop (PLL). This creates additional drawbacks of the system and makes the system complex. This paper presents a controller for single-phase grid connected inverter system with LCL filter in stationary reference frame. And PLL is avoided. Compared with traditional power control scheme for single phase grid-connected inverter controller, this control scheme has faster response, higher reliability and decoupled real and reactive power control ability. Moreover, the proposed controller has good robustness under different distorted grid conditions. Since the controller is totally implemented in stationary reference frame, the control algorithm comes to be simpler and easier. The designed current controller, combining the active damping technique, helps restrain the high resonant peak value. Compared with traditional PI based current controller, the designed current controller, which is based on the Proportional & Resonant (PR) controller, provides the system with high gain in wide range of frequency to track given reference value fast and output excellent grid current with low THD.