Research on Harmonic Suppression Based on LCL-type Grid-connected Inverter

The harmonics of the grid-connected inverter mainly come from the high-frequency harmonics generated by the SPWM and the low-frequency harmonics generated by the fluctuation of the voltage side of the grid. For high-frequency harmonics, the LCL filter is used to provide a low-impedance path for the high-frequency harmonics. The parameters of the LCL filter are conditionally constrained, and the power loss of the damping branch is used as the objective function, and the constraint range of the parameters is traversed by the enumeration method to obtain the optimal solution of the relevant parameters at the minimum power loss. For low-frequency harmonics, the composite control scheme of proportional resonance（PR） control and repetitive control in parallel is adopted, and the parameters of the composite controller are designed by establishing a mathematical model and using the open-loop amplitude and frequency characteristics of the system. Finally, the simulation model is built, and the full-load and half-load experiments are carried out on the grid-connected current, and the total harmonic distortion rate of the output current is 2.05%, the overshoot is 36.7%, and the adjustment time is about 2 ms. The simulation results verify the rationality of the design, which can make the grid-connected inverter have good harmonic suppression ability and achieve the effect of fast response during dynamic time.