Stability Assessment of Multiple Virtual Synchronous Machines for Microgrid Frequency Stabilization

Due to the lack of system inertia driven by the increasing integration of renewable energy, a virtual synchronous machine (VISMA) concept has been developed to provide backup inertia, maintaining microgrid stability and resiliency. To enhance an inertia support in regards to frequency stability, this paper proposes a novel control approach using multiple VISMAs with different P-f droop characteristics. This approach can effectively enhance frequency stability of the microgrid under the situation of low system inertia. The stability difference and efficacy between single VISMA and multiple VISMAs are investigated over microgrid performance with contrastive scenarios. Transient and steady-state responses are also compared. The analysis results reveal that the multiple-VISMA configuration suppresses frequency oscillation better than the single VISMA configuration, maintaining stable microgrid operation. This work also provides a recent overview of a practical multiple-VISMA system in regards to frequency stability improvement.