Inverter-Based Resources (IBRs) connect wind, solar, and battery-stored energy to the power grid. These resources now account for 33% of the electricity generated in MRO’s region, a significant increase from 13% in 2016. This upward trend is expected to continue, as 95% of the megawatts in the MISO and SPP interconnection queues are solar, battery, hybrid, and wind. While IBRs contribute to a resilient and sustainable energy future, this newer technology presents challenges to how the industry approaches power system design, modeling, and performance.
Traditional, synchronous coal, gas, and nuclear generators inherently respond to system disturbances in a predictable way based on physics and electromagnetic principles. The more modern IBR technology is fundamentally different in that it responds to system disturbances through human-defined software controls. Assumptions were embedded in IBR manufacturer designs that do not reflect the way that traditional synchronous generators respond to disturbances. This has led to unpredictable IBR performance when connected to the grid and inaccurate power system models. These challenges are further complicated by the restructuring of electric utilities where system planners, generation owners, transmission owners, and system operators have more separation, and therefore there are potential knowledge gaps that affect how the system is designed.
One of the primary drivers of IBR performance issues is the difference between how an IBR facility is designed and how it is installed and operated. For example, generator owners and operators primarily focus on plant-level engineering, which requires only basic power system modeling. Transmission owners, operators, and planners on the other hand, require much more detailed system-level models capable of dynamic and transient simulations that fully study grid interconnections. This separation of engineering responsibilities has worked well in the past because the rotating masses of traditional generation provided predictable inertial responses, meaning that plant-level engineers could rely on the electromagnetic characteristics that followed well established principles. The introduction of IBRs created a scenario where the manufacturer design does not have adequate system-level specifications to design an Inverter-Based Resource with expected system performance, and the models were not reflective of the actual behavior. The system design gaps that resulted could be closed by specifications in Generation Interconnection Agreements. Recently NERC issued a Level 3 Alert that starts to tackle that issue.
NERC’s Level 3 Alert: Essential Actions for Inverter-Based Resource Performance and Modeling is targeted at all registered Transmission Owners, Transmission Planners, Planning Coordinators, and Generator Owners, with an aim of enhancing the minimum requirements and study processes in order to mitigate risks posed by IBR performance during system disturbances.
Since 2016, NERC and the Regional Entities have analyzed major system disturbances totaling more than 15,000 MW of unexpected generation losses that were not predicted (or could not be replicated) through normal planning processes. The alert’s essential actions urge Transmission Owners, Operators, and Planning Coordinators to establish transparent criteria for IBRs connected to the bulk power system, including reactive power control characteristics, frequency response characteristics, ride through behaviors, post disturbance performance (including settling time), and full utilization of reactive power capability. This represents a shift towards explicit documentation of system performance expectations that were previously assumed with synchronous generation.
The alert also emphasizes the importance of model quality, performance testing, and a process to keep the models up to date and accurate between the Generator Owners and Transmission Planners and Planning Coordinators.
NERC and the Regional Entities are asking registered entities to consider the “Essential Actions” listed in the alert and respond to a survey describing any activities related to the essential actions. The survey responses are required to be submitted through the NERC Alert System by August 18, 2025.
Resolving IBR modeling and performance issues are a systems engineering effort that requires a team approach. These issues cannot be solved in isolation by inverter manufacturers, IBR generation owners/operators, or grid operators. Collaboration amongst all parties is needed to develop performance expectations that enhance the system design of IBRs.
Further coordination on the modeling of inverters and how those models are incorporated within existing system models is needed to reliably plan and operate the bulk power system.
– Lee Felter, Principal Risk Strategy Engineer, Midwest Reliability Organization