With the growing shift toward renewable energy, attention focused on the disadvantages of current control inverter-based distributed generators, such as lack of grid-forming ability and inertia. To provide inertia support and grid-forming ability, virtual synchronous generators (VSGs) have been proposed. Various control methods related to VSGs have been reported, and various research challenges have been evaluated. However, only a few experimental demonstrations have been addressed. Recommended practices for VSGs were launched as IEEE Standard Project 2988 on March 25, 2021, with VSGs considered to be a new technology that is nearly ready to be put into practical use. Therefore, experimental demonstrations on a real-scale grid are important for establishing a technical standard for VSGs. In this study, a grid was built by simulating an actual microgrid on an approximately 1:1 power capacity scale. In the simulated grid, 125 kVA was provided by a diesel SG, five 20 kVA inverters with a battery energy system (BES) were used, and the power generation penetration of the inverter BES units achieved 44.4%. Six different penetration scenarios for operation of a grid forming inverter with BES (GFM-BES) and a grid following inverter with BES (GFL-BES) were evaluated comparatively. System inertia, and transient and steady state power sharing characteristics affected by different degrees of GFM-BES penetration under a sudden load change were demonstrated. Moreover, characteristics related to grid forming, synchronization, frequency regulation, and power regulation were demonstrated through field tests. The simulations and experiments also evaluated the inertia constant of a diesel SG, which is expected to be helpful for future simulations on this topic. The findings of this paper provide important instructions for engineers to model, design, and test distributed generators.INDEX TERMS Distributed power generation, microgrid, diesel synchronous generator, virtual synchronous generator (VSG), parallel operation, grid-forming, inertia, experiment demonstration.
