Single-phase Photovoltaic Grid-connected Control Strategy With LCL Filter

Single-phase photovoltaic grid-connected generator systems adopt LCL filter which is useful to restrain high-frequency switching current into the grid.However,the LCL filter increases the system order so that the design of the system stability is difficult to be realized.At present,dual-loop control strategies which consist of dc-side voltage outer loop and grid-side current inner loop have been widely used for single-phase photovoltaic grid-connected generator systems with L or LC filters.But if the dual-loop control is directly used in the photovoltaic system with the LCL filter,the system may be unstable.This paper presented a novel grid-connected control strategy composed of voltage loop,power loop,and capacitor current loop.The voltage loop stabilized the capacitor voltage at dc-side of the grid-connected inverter;the power loop regulated the power factor of photovoltaic grid-connected generating power;both the power loop and the capacitor current loop improved the system stability and suppress resonant peak caused by the LCL filter.The system closed-loop transfer function was derived and the influence of control parameters on the system stability was analyzed with the closed-loop pole distribution.Simulation and experiment results demonstrate the feasibility of the proposed control system.