In light of recent grid disturbances involving inverter-based resources (IBRs), NERC sent a Level 2 Alert to industry June 4 seeking information on their presence on the grid and the models in use by their owners and operators while also providing recommendations to strengthen current modeling practices.
Under NERC’s alert system, recipients of a Level 2 Alert must respond to the ERO by a set time; in this case, applicable stakeholders must acknowledge their receipt of the alert by midnight ET on June 11 and respond to its questions by Sept. 2. Unlike a Level 3 Alert, action by stakeholders is recommended but not required.
Concerns about IBRs, and particularly modeling practices related to them, have risen in recent years because of a series of grid disturbances directly involving IBRs such as wind and solar generation facilities. NERC’s alert mentions 10 large-scale disturbances since 2016 totaling nearly 15 GW of “unexpected IBR output reduction.” About 10 GW worth of disturbances have occurred in the past four years.
The ERO did not mention specific disturbances in its alert, but it has documented several noteworthy events in which operators lost substantial amounts of generation from IBRs, including two separate events near Odessa, Texas, in which the Texas Interconnection lost nearly 4 GW of solar PV and synchronous generation. (See NERC Repeats IBR Warnings After Second Odessa Event.) After the second event, NERC issued a report identifying modeling as a significant challenge to maintaining grid reliability with IBRs.
“The significantly higher complexity and software-based nature of IBR modeling … necessitates an improvement in the fundamental principles of dynamic modeling to accurately capture the performance of IBR plants,” NERC said in this week’s alert.
The alert is directed at generator owners (GOs), transmission planners (TPs) and planning coordinators (PCs). GOs that own grid-connected IBRs, including solar and wind generators, battery energy storage systems and “any hybrid facilities with an IBR component” are required to complete a workbook providing a range of information about their IBRs, including:
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- manufacturers of inverters on their systems;
- model numbers for their inverters and their quantity;
- nameplate ratings for each model of inverter;
- inverter- and plant-level voltage and frequency protection settings;
- inverter- and plant-level reactive power capabilities and control information;
- model types used to represent facility model data to TPs and PCs; and
- dynamic and load-flow model files for each facility.
In addition to this information, IBR owners — along with TPs and PCs — must answer a series of questions. These include whether their organizations have publicly available model submission and quality requirements, what type of generator models are permitted during the interconnection process, and how the organizations verify accuracy of their models.
NERC also provided a set of recommendations for all stakeholders to mitigate known modeling deficiencies, such as validating models at the individual inverter and plant level and updating models throughout the life cycle of the plant. In addition, the ERO suggested implementing standard library positive sequence phasor domain models in interconnection-wide base case creation, while using equipment-specific models for generation interconnection and local reliability studies.
