I. Introduction
With the increase of the distributed generation (DG) integration, the virtual synchronous generator (VSG) has been extensively investigated. The VSG adds inertia and damping to the conventional droop control, providing effective frequency and voltage support for the power systems. Currently, research on VSG mainly focuses on inertia, damping, and other dynamic characteristics. Little research has been done regarding the power quality issues of VSG-based systems. For distributed power generation system, the grid current can be easily distorted by harmonic problems. These harmonics can create complex interaction problems between distributed generation networks and control systems, and even cause unpredictable equipment trips, especially in weak-grid situations [1]. The VSG should therefore take more responsibility in injecting high-quality power into the grid.