Research on control strategy of three-phase grid-connected inverter under distorted and unbalanced voltage conditions

The proportional error resonant current control has been extensively employed to reduce the current harmonic distortion in a wide range of grid-connected distributed generation applications, including photovoltaic (PV) inverters, wind and water turbines, and fuel-cell inverters. However, the performance of these systems is deteriorated when the utility grid voltage experiences abnormal conditions such as voltage harmonics and imbalances. This paper first analyzes the limitations of the proportional error resonant current control operating under abnormal grid conditions and then introduces an advanced control scheme(proportional feedback resonant control) that improves the current harmonic distortion in such adverse conditions without increasing the computational load of the original current control. Moreover, the system of the external loop adopts power droop control and voltage loop, so the system can not only grid-connected operation, but also can run independently in the network. Finally, a prototype is built to validate the feasibility and correctness of the proposed control strategy.