Stability analysis and improvement of three-phase grid-connected power converters with virtual inertia control

The lack of inertia issue challenges the frequency control and stability of small-scale modern power systems. To alleviate adverse effects from inertia reduction, three-phase grid-connected power converters are increasingly being used to provide virtual inertia upon system demands. This can be achieved by directly linking the grid frequency and voltage references of DC-link capacitors/ultracapacitors. However, this paper reveals that the virtual inertia control may possibly induce instabilities to power converters under weak grid conditions, which is caused by the coupling between the d- and q-axis as well as the inherent differential operator introduced by the virtual inertia control. To tackle the instability issue, this paper proposes a modified virtual inertia control to mitigate the differential effect. Experimental verifications are provided, which demonstrate the effectiveness of the proposed control in stabilizing three-phase grid-connected power converters for inertia emulation even when connected to weak grids.