Reduction of Voltage Deviation Induced by Virtual Impedance in Droop Control of Parallel Inverters

Virtual impedance is widely used in the microgrid since it can change line impedance as required and achieve the favorable effect when combined with the droop control. However, the virtual impedance will bring about the voltage deviation, which cannot be solved by using present methods. Aiming at this problem, this paper combines virtual impedance and power coordinate transformation to implement power coordinate transformation for active power P and reactive power Q, by which general active power P_d and reactive power Q_d is got. Virtual impedance angle is chosen according to power factor of microgrid's total load so as to eliminate the longitudinal component of voltage drop deviation due to virtual impedance, by which voltage deviation is reduced greatly. Droop control P_df is adopted and Q_dU is abandoned while droop coefficients are chosen in inverse proportion to rated capacity of inverters and impedance virtual magnitude is chosen in inverse proportion to rated capacity of inverters. In this way, proportional sharing of active power P and reactive power Q are realized while voltage deviation is reduced. The simulation confirms the effectiveness of the proposed method in this paper.