On the Stability of Virtual Inertia Control Implemented by Grid-Connected Power Converters with Delay Effects

The limit inertia contribution from renewable energy sources develops into a challenge to small-scale power systems. For the purpose of allaying the negative influence on frequency regulation performance, the concept of virtual inertia control used in three-phase grid-connected power converters has been proposed. The system inertia improvement could be realized by linking the grid frequency and voltage reference of DC-link capacitors/ultracapacitors. This paper intends to reveal that the effects of delay, which are caused by frequency measurements and DC-link voltage regulation during the inertia emulation, are nonnegligible in small-scale low inertia power systems with virtual inertia control implementations. The delay effects may even induce instabilities. To track this issue, a modified virtual inertia control is proposed in this paper. Experimental verifications are provided, which are consistent with the theoretical analysis.