Improved Current Composite Control Strategy for Single-Phase LCL Grid-Connected Inverters

To address the issue that the traditional grid-connected inverter control system has poor grid-connected current quality under weak power grids and non-ideal grid voltages with abundant background harmonics, an improved capacitive current active damping control strategy is proposed. Firstly, by utilizing the different frequency characteristics of the proportional and integral feedback of the capacitive current in digital control, a composite feedback is carried out. By selecting the optimal value based on the constraint conditions, the frequency characteristics of the equivalent virtual damping can be improved, enabling it to maximize the positive resistance characteristics within the Nishikawa frequency range, thereby enhancing the robustness of the grid-connected inverter. At the same time, to suppress the influence of the background harmonics of the power grid on the system, a multi-resonance controller is introduced to suppress the low-order harmonics of the grid-connected current. Ultimately, a computer model was constructed for a six-kilowatt single-phase LCL grid-connected inverter system. The experimental results verified that the proposed control strategy can operate stably under complex conditions and output high-quality waveforms.