减小逆变器下垂控制中虚拟阻抗所致电压偏差的方法研究

虚拟阻抗可以灵活改变线路阻抗,和下垂控制结合可取得较好效果,在微网中应用广泛。但虚拟阻抗会导致电压偏差,目前该问题尚无有效的解决方法。针对这一问题,本文将虚拟阻抗和功率坐标变换结合,对有功P及无功Q进行功率坐标变换,得到广义有功P_d和广义无功Q_d。根据微网总负荷的功率因数选取虚拟阻抗角,使虚拟阻抗造成的电压降落的纵分量为零,从而大幅减小电压偏差。采用P_df下垂,舍弃Q_dU下垂,按照逆变器容量的反比选择下垂系数和虚拟阻抗值的大小。通过上述措施实现了有功P和无功Q的按比例分担并大幅减小了电压偏差,仿真证明了本文所提方法的有效性。

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.