Effects of suppressing frequency fluctuations by parallel operation of virtual synchronous generator in microgrids

When a greatly varying load is connected to a weak power system, stability of the system becomes a problem. In these days, because the use of renewable energy is accelerating, not only the loads but also the distributed generators can be critical factors in destabilizing the system. A virtual synchronous generator (VSG) control allows a static inverter to behave similar to a synchronous generator (SG). Using this VSG technology, we can increase the introduction ratio of renewable sources, and thus, we can combine various types of power sources. Simultaneously, if the combination of governor and rotor inertia is represented in a first-order lag element, the VSG can suppress the frequency fluctuations in microgrids. In this paper, the oscillation mechanism in parallel operations of generators is clarified, and we present the effects of suppressing the frequency fluctuations using the VSG. The results are verified by simulation using EMTP-RV and in laboratory experiments.