Stabilization effect of virtual synchronous generators in microgrids with highly penetrated renewable energies

Because of the increasing use of renewable energy technology, distributed power sources and greatly varying loads can be critical factors in power system destabilization. This problem has hampered the adoption of renewable energy; thus, researchers have studied various control method types that enable an inverter to be operated as a synchronous generator (SG). Some of these methods, referred to as Virtual Synchronous Generators (VSGs), are designed to provide virtual inertia. Using VSG technology, we can decrease the introduction of fossil fuel-based power, which allows a variety of energy sources to be combined. In this study, we derived and analyzed the frequency system dynamics of microgrids, and show that a VSG expressed as a first-order equation can stabilize the frequency of a grid without causing resonance among the generators and loads. Furthermore, we derived excitation system dynamics, and observed that a VSG applying constant impedance can reduce the voltage fluctuations in the system. The results were verified in laboratory experiments and through a simulation using EMTP-RV. The simulation test results, which were generated using data acquired from an actual photovoltaic facility, indicated that the VSG could effectively suppress system deviations caused by sudden weather change.