The zero sequence circulating current suppression based on virtual impedance

Abstract

There are zero sequence circuits, when inverters work in parallel directly, and zero sequence circulating current would flow, when zero sequence voltage of the inverter is different with that of the gird. The mechanism of the zero sequence circulating current is analyzed. By the analysis of the influence of the power switch tube voltage-drop, the dead time of PWM and the most common two PWM methods on the zero sequence voltage, the zero sequence voltage is a periodic signal the frequency of which is triple of the fundamental frequency. A novel zero sequence circulating current suppression method based on virtual impedance is proposed by the analysis of the zero sequence output impedance of the inverter, and the zero sequence voltage harmonic impedance is increased to improve the performance. The results of simulations and experiments show that the circulating current is suppressed effectively.