NERC MOD-026-2: Verification and Validation of Dynamic Models and Data

Broadening model verification obligations across all generating facility types

What Is MOD-026-2?

As the generating mix on the bulk electric system has diversified (with synchronous machines retiring and IBRs growing rapidly), planning models have struggled to keep pace. Dynamic models developed for one generation type don't translate directly to another, and the rapid deployment of new IBR technology has outpaced the modeling standards that were written with synchronous generators in mind.

MOD-026-2 extends model verification requirements across all generating facility types, building on the framework of MOD-026-1 and applying it to the broader range of generating technologies now connected to the BES. The standard requires that dynamic models used in planning studies are validated against real-world test data and kept current as facility configurations change.

For IBR facilities in particular, this means developing and validating both positive-sequence and, in some cases, electromagnetic transient (EMT) models that accurately capture the control system behavior that drives IBR response during grid disturbances.

Who Must Comply?

MOD-026-2 applies broadly to Generator Owners across all generating facility types connected to the BES, with applicability determined by the standard's requirements table. This includes:

Synchronous generators subject to excitation system and governor model verification
IBRs (solar, wind, and battery storage) with positive-sequence and EMT modeling requirements
Facilities that have undergone equipment changes affecting model parameters
Facilities whose models have not been verified against field data within the required re-verification interval

Contact your transmission planner or regional entity to confirm specific applicability for your facility, as requirements can vary by interconnection and facility type.

Key Requirements

Field Testing

Perform staged field tests appropriate for the generating facility type. For synchronous generators this typically involves voltage and governor response tests. For IBRs, testing may include voltage step tests, reactive power ramps, and fault ride-through validation depending on the applicable requirements.

Model Validation

Compare the recorded field response to the model response under the same test conditions. Models that don't match the field data within acceptance criteria must be updated and re-validated until the match is achieved.

Ongoing Model Currency

Models must be updated when facility configurations change: inverter firmware updates, control system modifications, equipment replacements, or changes to plant-level control settings that affect the modeled response. A change log documenting model updates is part of the evidence record.

Planning Data Submission

Submit validated model data to the applicable transmission planner in the required format and on the required schedule. Different planners use different simulation platforms; model format compatibility must be confirmed before submission.

Common Compliance Challenges

IBR Models That Don't Match Field Behavior

Generic IBR models (the REGC, REEC, REPC model families) are approximations. For facilities where the actual inverter control behavior deviates significantly from the generic model structure, achieving a validated match within tolerance may require developing user-defined models (UDMs) or working directly with the inverter manufacturer to obtain proprietary model files.

Firmware Updates That Invalidate Existing Models

When inverter firmware is updated (which happens routinely for security patches, performance improvements, or grid code compliance), the control system behavior can change. A model that was validated against the previous firmware version may no longer be valid, and re-verification may be required.

EMT Modeling Requirements for Weak Grid Connections

IBRs connecting to areas with high IBR penetration or weak grid characteristics are increasingly required to provide EMT models in addition to positive-sequence models. EMT model development is substantially more complex, requires different simulation tools and expertise, and often requires close coordination with the inverter manufacturer.

Cross-Planner Format Compatibility

Generator owners who sell into multiple markets or have facilities in different transmission planning areas may need to provide models in multiple formats (PSSe, PSLF, PowerWorld) and verify that each version produces consistent results. Managing this across a fleet is a significant ongoing administrative and engineering effort.

How TWC Can Help

TWC performs dynamic model verification for both synchronous generators and IBRs, with experience in positive-sequence and EMT modeling across the major simulation platforms.

Field Testing

We plan and execute staged field tests for the facility type, coordinating with the system operator and capturing the high-resolution data needed for model comparison.

Model Development and Validation

We develop or update the dynamic model in the required simulation tool, simulate the test conditions, and perform the field-to-model comparison. For IBRs, we work with manufacturer data and UDMs where generic models are insufficient.

EMT Modeling

We develop and validate EMT models in PSCAD for IBRs where positive-sequence models alone don't meet planning requirements, including plant-level aggregation and cross-validation against positive-sequence results.

Planning Submission Support

We prepare model submissions in the format required by the applicable transmission planner and maintain compliance documentation covering the verification process and submission records.

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