A circulating current suppression strategy of VSG based on adaptive virtual complex impedance

Abstract

By adding inertia and damping elements in droop control, virtual synchronous generators (VSG) can simulate the output characteristics of synchronous generators and effectively reduce the impact of power electronic equipment connected to the power grid. Since the capacity and spatial distribution of each VSG is random, the output impedance of VSG and line impedance are mismatched, which will cause circulating current between VSGs. Considering the influence of line resistance, the traditional dynamic virtual inductance control strategy can be enhanced. A circulating current suppression strategy based on adaptive virtual complex impedance is proposed after analyzing the composition and causes of the circulating current between VSGs. The proposed strategy compensates the line impedance adaptively according to VSG's output reactive power, thus to reduce the reactive power sharing errors and suppress the circulating current between VSGs. The scheme is reliable and robust under fault as there is no need for measurement of line impedance or communication modules. The simulation results are presented to verify the effectiveness of the proposed strategy.