Current-Limiting VSG for Renewable Energy Applications

In this paper, an improved nonlinear controller structure, which inherits both virtual inertia (VI) and current-limiting properties in grid-connected voltage-source converters (VSCs), is proposed. The proposed method inherits the Vdc ~ ω droop control for inertia emulation and frequency control, and Q ~ V droop control for AC voltage support. The current-limiting property, which is a critical issue for the protection of grid interface inverters throughout the whole operation including the grid faults is proven analytically for VI-based VSCs using nonlinear control theory. Furthermore, small-signal stability of the system is examined considering the effects of different controller gains in order to provide guidance for the selection of their values. To validate both the small-signal stability and nonlinear current limitation proof, extensive Matlab/Simulink simulations are performed.