Improved Droop Control Strategy Based on Adaptive Virtual Impedance in a Microgrid System

In a microgrid system with multiple inverters operating in parallel, due to the resistive-inductive nature of the line impedance and the mismatch between line impedance and inverter rated reactive power, inverters cannot share reactive power load in proportion to their rated reactive power when droop control is used. To address the reactive power distribution issue caused by line impedance, the conditions for different inverters to share reactive power load according to capacity ratio are analyzed. An improved droop control strategy based on adaptive virtual impedance is proposed. A static virtual impedance tuning method is provided based on the estimated line impedance, de-coupling active and reactive power control and improving the reactive power distribution issue. Further, dynamic virtual impedance based on the consistency algorithm is introduced to achieve accurate reactive power distribution. For the AC bus voltage drop caused by virtual impedance, a communication-free virtual impedance voltage compensation method is employed, improving the bus voltage drop. Simulation results validate the effectiveness of the proposed improved droop control strategy.