Small-Signal Disturbance Compensation Control for LCL-Type Grid-Connected Converter in Weak Grid

When the three-phase LCL-type converter is attached to a weak grid, its grid current control will interact with a phase-locked loop (PLL), via the point of common coupling voltage. And, the PLL dynamic has a negative influence on the current control, rendering an undesired performance to grid current control, even leading to the instability issue, if no effective measure is employed. To mitigate this problem, this article proposes a simple and visualized small-signal disturbance compensation control method for the LCL-type grid-connected converter. First, the effect mechanism of PLL dynamic on the current control is analyzed, and the root of the small-signal disturbance caused by PLL dynamic is identified subsequently. Based on this, an improved control method is proposed to compensate the aforesaid PLL-introduced small-signal disturbance terms in current loop, and then, the negative effect of PLL dynamic on the grid current control can be effectively reduced in the weak grid, without modifying the PLL parameters and structure. Moreover, the method is not influenced by the circuit parameters change, and it is robust to the variation of grid impedance. Finally, the proposed method is validated by the experiment.