Performance Evaluation of Multi-Vendor Grid-Forming Inverters for Grid-Connected Operation Through Hardware Experimentation

Existing real-world projects of grid-forming (GFM) inverters that operate in parallel with power grids are typically sized between dozens and a few hundred megawatts, according to a recent white paper on GFM inverters by the North American Electric Reliability Corporation. These large systems are often difficult to evaluate prior to deployment because of their large size. The performance of smaller GFM inverters (from dozens to a few hundred kVA) that operate in parallel with power grids (distribution systems) is even less understood. There is an opportunity to better understand these systems through hardware testing under controlled laboratory conditions. Therefore, this paper presents the functional performance evaluation tests of multiple (three) commercial GFM inverters when they operate in parallel with the grid through hardware experiments. The goal of these tests is to explore and benchmark the GFM inverters' functionalities and dynamic response when they are operated in parallel with power grids to eventually develop universal specifications for GFM inverters. Both steady-state (changing the inverters' frequency and voltage droop) and transient (adding step changes to the grid's frequency/voltage) tests are performed for each GFM inverter with the same testing circuit and testing protocol. The experimental results indicate that 1) the GFM inverters can be dispatched through frequency and voltage droop intercepts to output the target power when they are operated in parallel with the grid; and 2) the GFM inverters automatically respond to system frequency and voltage events to output the needed power; however, all the GFM inverters show stability issues when absorbing reactive power from the grid.