Research on Smooth Switching Control of Off-grid Mode and Grid-connected Mode in Micro-grid

摘要

Aiming at the problem of smooth switching between off-grid mode and grid-connected mode in low-voltage micro-grid, an improved droop control strategy is proposed. In addition, aiming at the problem of power coupling in low-voltage micro-grid, power decoupling control is realized by adding virtual impedance to the control system to change the equivalent resistance into pure inductiveness. Further, for the problem of inrush current and impulse voltage during the mode switching of the micro-grid, smooth and shock-free grid-connected is achieved by adding a grid-connected pre-synchronization control link in the droop control. Then, for the problem of large voltage and frequency fluctuations during the mode switching of the micro-grid, the designed adaptive droop control strategy achieves the voltage and frequency meet the requirements of normal operation. The proposed control strategy can realize the smooth connection of the micro-grid without impact and the off-network mode and the grid-connected mode, so as to ensure the stable operation of the micro-grid system. Finally, the results of simulation and experiment demonstrate the correctness and effectiveness of the proposed theory.