Gerardo Medrano and Santiago Cóbreces, researchers from the University of Valladolid in Spain, have published a study that challenges conventional wisdom in the energy sector regarding grid-forming control design principles. Their work, titled “Modal Analysis of Core Inertial Dynamics: Re-evaluating Grid-Forming Control Design Principles,” was published in the IEEE Transactions on Power Systems.
The study employs modal analysis to examine the fundamental interactions between governor-controlled synchronous generators (GC-SGs) and droop-based grid-forming (GFM) converters. The researchers found that the industry’s current approach of emulating traditional GC-SG behavior in GFM converters may not be optimal. Specifically, the prevailing strategy of using high inertia to slow down the system and large droop to increase damping could be suboptimal.
The researchers demonstrated that GC-SGs face a fundamental trade-off: achieving adequate damping of the turbine-governor mode requires large droop constants, which in turn increases steady-state frequency deviation and reliance on secondary regulation. In contrast, droop-based GFM converters invert this relationship. By decreasing the droop constant, steady-state frequency deviations are reduced, damping is increased, and virtual inertia can be independently adjusted.
When two GC-SGs are coupled, a poorly damped electromechanical swing mode emerges. The study showed that replacing one GC-SG with a GFM converter of equivalent droop and inertia significantly improves damping of both swing and turbine-governor modes. Surprisingly, further damping gains were achieved by substantially lowering the GFM virtual inertia constant.
These findings suggest that current industry trends may be limiting the potential benefits of Inverter Based Resources (IBRs). Optimal stability and performance are instead obtained with low droop and low virtual inertia, resulting in tightly bounded frequency variations and strongly-damped electromechanical modes. The researchers call for a re-evaluation of GFM control design principles and emerging grid-code requirements.
The practical implications for the energy sector are significant. As the grid increasingly integrates more inverter-based resources, understanding and optimizing their control parameters will be crucial for maintaining grid stability and performance. The study’s findings could inform the development of more effective grid-forming strategies, ultimately contributing to a more reliable and resilient energy infrastructure.
For further details, the research can be accessed in the IEEE Transactions on Power Systems.
This article is based on research available at arXiv.