Research on Hierarchical Control Method of Low-Voltage AC Microgrid Based on Island Mode

When operating an island low-voltage AC micro-grid, the system exhibits instability fluctuations. Therefore, the stable control of the frequency and the voltage becomes crucial. This paper employs a hierarchical control approach utilizing a two-level control structure. Firstly, an enhanced droop control strategy in accordance with the dynamic virtual impedance is introduced in the first level control. By utilizing reactive power data from each distributed generation unit, the dynamic virtual impedance is formulated to enhance the efficiency of distributing the reactive power. Compared to traditional virtual impedance methods, the dynamic virtual impedance method proposed in this paper has stronger resistance to external disturbances. Secondly, a secondary compensation method based on the fractional-order PI control is applied in the secondary level control to control for reinstating the frequency and the voltage to their rated values. Finally, the efficiency of the suggested control strategy is validated through detailed simulation experiments employing Matlab/Simulink.