Robust Control Method for LCL-Type Grid-Connected Inverters Based on Adaptive Correction of Grid Voltage Feedforward Considering Digital Control Delay

The coupling effect between the grid voltage feedforward and the current loop under weak grid reduces the stability margin of the grid-connected inverter. Meanwhile, the risk of instability will be further increased in the case of the grid voltage feedforward parameters are not designed properly. To solve the problem, this article analyzes the stability of the grid-connected inverter under different grid impedances with grid voltage full feedforward control strategy. Second, to improve the stability of the grid-connected inverter in a wide range of grid impedance variations, this articles first proposes a grid voltage feedforward parameter design method with the phase margin as the index. Then, to further suppress the influence of digital control delay, different algorithms are introduced based on the grid voltage feedforward parameters to obtain an adaptive robust control strategy. Finally, it is verified that the proposed control strategy based on adaptively corrected grid voltage feedforward LCL type considering the delay link can improve the adaptability of the grid-connected inverter under the weak grid.