LCL Grid-connected Inverter Control Strategy Based on Two-degree-of-freedom Internal Model Control

The grid-connected inverter is required to have extremely high power factor and extremely low total harmonic distortion of output current. In the grid-connected inverter system, the LCL filter can suppress the high-frequency harmonics. However, the LCL filter is a low-damping three-order system, and easy to resonate. In this paper, a control strategy of LCL grid-connected inverter based on two-degree-of-freedom (2DOF) internal model control (IMC) is proposed to suppress the resonant peak of LCL. The controller has only two tunable parameters. By means of tuning parameters,the designed controller has the good performances on tracking the set value and suppressing the disturbance. No additional sensors are needed to be equipped and the system cost is reduced. Finally, the simulation model of LCL grid-connected inverter system is built on Matlab / Simulink platform, and the two control strategies are simulated and compared. The simulation results show that the total harmonic distortion of the grid current em_g is only 1.4%, which is far lower than the national standard of 5% with good tracking performance and improves the robustness of the system.