Understanding ISO-NE’s DDMS: A Technical Guide to Dynamic Modeling & Model Lifecycle

Accurate and validated dynamic models are essential for reliable power system planning and operational decision-making across the ISO-NE region. As inverter-based resources (IBRs) continue to grow and the grid transitions toward more complex, fast-acting dynamics, the need for high-fidelity transient stability models has become critical. ISO New England addresses this requirement through its Dynamics Data Management System (DDMS)—a structured, secure platform used to collect, validate, correct, approve, and manage the full lifecycle of dynamic stability models.

DDMS serves as the central system through which all generator owners, transmission operators, consultants, and project developers must submit and maintain models required for transient stability simulations. These include machine models, excitation systems, governor controls, PSS models, and inverter-based resource models that must be accurate to remain compliant with regional and NERC modeling standards.

This technical guide provides a clear, engineering-focused overview of DDMS—covering its purpose, workflow, approval process, required file formats, submission responsibilities, and its relationship to NERC MOD-032, MOD-026, and MOD-027. It is written for power system engineers, transmission planners, consultants, and generator owners who need a practical understanding of how DDMS supports model accuracy, model governance, and ISO-NE stability case development.

Introduction: Why DDMS Matters

ISO-NE requires high-quality dynamic models for all generators, synchronous condensers, static VAR compensators (SVCs), HVDC converters, FACTS devices, and other dynamic grid components that influence transient stability and system reliability. The Dynamics Data Management System (DDMS) provides a controlled, standardized environment to store, validate, and manage these models across the ISO-NE region.

Through DDMS, ISO-NE ensures:

• Centralized and secure storage of dynamic model data for transient stability simulations
• Version control and traceability, allowing engineers to track parameter changes and equipment updates
• A structured submission and review workflow aligned with ISO-NE’s modeling requirements
• Compliance with NERC MOD-032, MOD-026, and MOD-027 standards, ensuring validated and accurate models. See our NERC Compliance Services.
• Annual recertification to maintain long-term model accuracy as equipment ages or control settings change
• A transparent, auditable lifecycle from draft creation to final approval
  

ISO-NE’s official PSS®E stability cases, used for operational planning, interconnection studies, and reliability assessments, are populated exclusively with approved and system-modeled DDMS submissions. This means no dynamic model can enter ISO-NE master stability cases unless it successfully passes through the DDMS workflow.

Purpose and Scope of DDMS

According to ISO-NE’s official User Guide, the Dynamics Data Management System (DDMS) functions as the central repository for all dynamic stability models required for ISO-NE planning and operational transient stability studies. The platform securely manages and validates the full range of dynamic model data needed for accurate simulation in tools such as PSS®E.

DDMS supports submission, tracking, and lifecycle management of the following model categories:

• Synchronous machine models
• Excitation systems
• Governor models
• Power System Stabilizers (PSS models)
• HVDC converter dynamic models
• FACTS device models
• User-defined model DLLs or FLX files
• Supporting test, tuning, and validation documentation (e.g., MOD-026 & MOD-027 evidence)
  

These files and parameters directly feed into ISO-NE’s transient stability simulation cases, ensuring that generator owners and project developers maintain compliance with NERC MOD-032 data submission requirements.

DDMS does not store steady-state modeling parameters. The following datasets must be provided through ISO-NE’s separate steady-state data systems:

• NX-9 transmission line impedances
• NX-12 transformer parameters
• Real/reactive capability curves

These steady-state elements typically form part of broader power system studies.

When Model Submissions Are Required

ISO-NE requires updated dynamic model submissions through the DDMS platform at several key project milestones to maintain accuracy in transient stability simulations and ensure compliance with NERC MOD-032, MOD-026, and MOD-027.

1. New Generation or ETU (Elective Transmission Upgrade) Projects

A DDMS submission is required after the System Impact Study (SIS) is completed and formally presented. The assigned ISO-NE Technical Lead will notify the Lead Market Participant when the modeling package is due.

2. All Other New Equipment

A submission is required once the Proposed Plan Application (PPA) is approved by the NEPOOL Reliability Committee, ensuring the new asset can be accurately represented in ISO-NE’s stability cases.

3. Existing Equipment

A new or updated model must be submitted when any of the following occurs:

• Model parameters are corrected or updated
• Physical equipment (generator, inverter, controls) is modified
• Plant-level or unit-level control settings change
• A more accurate or validated model becomes available
• ISO-NE identifies deficiencies during technical review
• The existing model becomes obsolete or no longer reflects as-built performance

In addition, annual model recertification is required for all equipment to maintain continuous compliance with ISO-NE processes and NERC modeling standards.

Overview of the DDMS Process

DDMS manages the complete lifecycle of a dynamic model from initial draft creation through final approval and inclusion in ISO-NE’s transient stability libraries. The structured workflow consists of:

• Draft creation by the Lead Market Participant
• Submission and certification
• ISO-NE assignment to a Technical Lead
• Technical review of parameters and model behavior
• Iterative corrections, when required
• Formal approval
• System modeling, where the approved model is added to ISO-NE stability cases
• Annual recertification to maintain ongoing accuracy
  

DDMS uses standardized status codes to ensure transparency and full traceability:

• Draft – Initial stage; not visible to ISO-NE analysts
• Submitted – Certified by the Lead Market Participant
• Pending Review – Assigned to an ISO Technical Lead
• ISO Review – Verification of parameters and simulation accuracy
• Correction Required – ISO-NE requests updates; submitter uses “Resubmit & Recertify”
• Correction Submitted – Corrections provided and under re-evaluation
• Approved Pending System Model – Approved but not yet inserted into master stability cases
• Approved & System Modeled – Fully accepted and included in ISO-NE stability libraries
• Approved & Modeled Pending Recertification – Approved, awaiting annual recertification
• Terminated / Rejected / Superseded – For canceled, obsolete, or replaced models
  

These DDMS status codes provide a consistent, auditable framework for model governance across the ISO-NE footprint.

See More About: Power System Modeling Services

Access, User Roles, and Security

DDMS access is managed through ISO-NE’s CAMS (Customer and Asset Management System), ensuring controlled and secure handling of all dynamic model data. Users can gain access through two pathways:

Market Participants

Their Security Administrators assign the DDMS Compliance Officer role directly within CAMS.

Non-Market Participants

Project developers request access through ISO-NE’s “Ask ISO” portal to participate in model submission or NERC MOD-related processes.

Creating and Editing a Draft Submission

Once logged in, engineers can create new dynamic model records in DDMS using the Create Issue function. Each draft entry must include the following required fields to support ISO-NE’s dynamic modeling and transient stability requirements:

Key Data Elements

• Summary and Description
• Submission Reason (e.g., New, Data Correction, As-Built/Tested)
• Equipment Name
• Equipment Type
• Effective Model Start/End Dates
• Whether User-Defined Models are included
• Applicable PSS®E version information
  

Engineers must upload all relevant model files to ensure a complete and accurate submission, including:

• .RAW files for steady-state data
• .DYR files for dynamic model parameters
• User-defined DLLs or FLX files when applicable
• Supporting documentation such as factory test reports, tuning reports, and MOD-026/027 validation evidence

DDMS automatically applies validation rules to maintain data quality, consistency, and compliance with ISO-NE modeling standards. Draft submissions remain editable and may be updated as needed before final certification.

For engineering teams seeking support with preparing or validating RAW/DYR files, see Power System Modeling Services.

Submitting and Certifying the Model

Certification is required before ISO-NE will begin its technical review within the Dynamics Data Management System (DDMS). The Lead Market Participant must formally attest that:

• The dynamic model data is accurate and reflects the actual equipment configuration.
• All required attachments—including RAW, DYR, and supporting documentation—have been uploaded.
• All parameters have been validated against commissioning data, system tests, and applicable NERC MOD-026/027 requirements.

Additional required fields include:

• Certification = Yes
  
• Original Certification Date
  

Once these steps are completed, the model automatically transitions from Draft to Submitted, allowing ISO-NE to assign it to a Technical Lead for review.

ISO-NE Review and Correction Cycles

Once a model submission enters the ISO-NE review pipeline, the engineering team evaluates it for several key criteria to ensure dynamic model accuracy, compliance with NERC MOD standards, and proper integration into the regional PSS®E transient stability cases.

1. Parameter Validity

ISO-NE performs reasonableness checks using engineering judgment, historical data, and expected parameter ranges to confirm that all dynamic model values are technically sound.

2. Compatibility

The submitted model is reviewed for compatibility with:

• Existing PSS®E v33 dynamic model libraries
• Other units within the same facility
• Associated control systems, auxiliary equipment, and protection schemes

This prevents conflicts that may impact stability studies or IBR performance evaluations.

3. Behavioral Simulations

ISO-NE conducts simulation checks, including:

• AVR and governor step response performance
• PSS dynamic behavior
• Fault, clearing, and post-fault recovery behavior
  

These simulations verify whether the model behaves consistently with expected machine or inverter performance.

If any issues are identified, the model moves to Correction Required status.

The submitter must then:

• Review ISO-NE’s technical comments
• Update parameters, files, or documentation
• Re-upload corrected attachments
• Complete Resubmit & Recertify to re-enter the review cycle
  

The process repeats until the submission fully satisfies ISO-NE requirements and is ready for inclusion in regional stability cases used in planning and operational studies.

Annual Model Recertification

ISO-NE and NERC standards require periodic recertification to maintain dynamic model accuracy for transient stability studies. The DDMS platform enforces an annual recertification cycle to ensure each approved dynamic model continues to meet ISO-NE and NERC MOD-026 / MOD-027 compliance requirements.

When recertification is triggered:

• ISO-NE sends notifications to all associated users.
• The submitter must review all model information for accuracy.
• If the data is still valid, they select Recertify.
• If any information is outdated, they must Decline to Recertify and immediately submit a revised model.
  

Annual recertification ensures that updates in:

• Control tuning
• Firmware or logic changes
• Plant upgrades
• Wear-related performance drift
• Replacement of excitation or governor components

are correctly reflected in ISO-NE’s approved dynamic models. This process helps maintain accurate PSS®E stability case modeling across the region.

Terminating a Submission

A DDMS submission may be terminated when a project is cancelled or when a draft contains issues that cannot be corrected efficiently. The Lead Market Participant can terminate a Draft, Submitted, or Correction Required model.

An explanation must be provided, after which the submission is marked Terminated, ensuring clear lifecycle tracking within ISO-NE’s Dynamics Data Management System.

Technical Requirements for Model File Formats

DDMS submissions must include all required transient stability model files compatible with PSS®E Version 33, ensuring consistency across ISO-NE dynamic simulations and NERC MOD-032/026/027 data requirements.

1. RAW File Format

The RAW file provides essential steady-state parameters for transient stability modeling, including:

• Machine ratings
• Bus connections
• Voltage setpoints
• GSU transformer references
• Status flags
  

To maintain accuracy, engineers must ensure:

• Correct six-digit ISO-NE bus numbers
• Proper MVA base selection
• Accurate generator dispatch values
• Consistency with NX-9 steady-state equipment data
  

RAW files may be generated:

• From existing DDMS-approved models
• Directly within PSS®E
• Through internal equipment or EMS/SCADA databases
  

Only necessary steady-state parameters are included in DDMS; most full network data resides outside DDMS.

For additional reference on steady-state studies: Load Flow Studies in Electrical Power Systems.

2. DYR File Format

The DYR file contains all dynamic stability model definitions required for ISO-NE’s transient stability studies. This includes:

• Machine models (e.g., GENROU, GENCLS)
• Excitation system models (IEEE and vendor-specific)
• Governor and turbine control models (TGOV series)
• Power System Stabilizer (PSS) models
• HVDC dynamic controls
• FACTS device controllers
  

Each DYR entry must follow the standard PSS®E format: BusNumber ‘ModelName’ MachineID ParameterList /

To ensure a valid DDMS submission, engineers must verify that:

• The bus ID matches the correct ISO-NE 6-digit bus number
• The unit ID is consistent with the associated generator or device
• Parameters follow the correct order and formatting
• The model type is fully compatible with PSS®E Version 33, as required by ISO-NE
• Minor spacing or decimal formatting variations are acceptable and do not affect model execution

For reference, engineers using models for renewable resources, BESS, or HVDC systems may cross-check model expectations with related resources such as our Power System Studies page.

3. User-Defined Models

When standard PSS®E dynamic model libraries cannot represent a device, a user-defined model is required. DDMS supports the following file types:

• DLL binary files (preferred for ISO-NE compatibility)
  
• FLX source code files (accepted in limited cases)
  

However, ISO-NE specifies that:

• User-defined models are not accepted for generators whose SIS process began after January 1, 2017.
• Standard PSS®E models must be used whenever they are available and technically appropriate.
• All user-defined models must still include matching RAW and DYR files to ensure consistency across dynamic stability simulations.
  

For teams working with advanced inverter-based resources or complex dynamic controls, you may also review our Power System Modeling Services for support on PSS®E, PSCAD, and EMT-level modeling.

4. Supporting Documentation

Engineers must include all supporting documentation required for ISO-NE dynamic model verification to ensure accurate DDMS submissions. This documentation helps validate parameters and confirm compliance with NERC MOD-026, MOD-027, and ISO-NE modeling requirements. Required documents include:

• Factory test reports
• Excitation and governor tuning results
• MOD-026 and MOD-027 model validation evidence
• As-purchased and as-built equipment data sheets
• Detailed model validation reports supporting PSS®E compatibility
  

This documentation enables ISO-NE to cross-verify model accuracy against physical equipment characteristics and ensures the final dynamic model integrates correctly into regional transient stability studies.

Best Practices for High-Quality DDMS Submissions

To ensure smooth approval through ISO-NE’s Dynamics Data Management System (DDMS) and maintain compliance with NERC MOD-026, MOD-027, and MOD-032, engineers should follow these core best practices:

1. Validate Before Submission

Use PSS®E dynamic simulations to confirm:

• Reasonable AVR response
• Accurate governor droop and response behavior
• No numerical instability
• Model parameters properly aligned with commissioning and test data
  

2. Use Accurate ISO-NE Bus Numbers

Incorrect or outdated bus IDs remain one of the most common causes of DDMS rejections. Verify all six-digit ISO-NE bus assignments before attaching model files.

3. Include All Required Attachments

Ensure the RAW file, DYR file, and all supporting documentation are uploaded. Missing attachments frequently trigger Correction Required status.

4. Avoid User-Defined Models Unless Necessary

ISO-NE expects engineers to use standard PSS®E models when available. Only apply user-defined DLL/FLX models when no acceptable standard model exists.

5. Maintain Local Version Control

Track as-purchased, as-built, and as-tested model configurations internally. This helps maintain compliance and supports future recertification audits.

6. Recertify Promptly

Timely recertification ensures stability cases remain accurate and compliant with NERC modeling standards.

Engineering Value of DDMS

DDMS enhances system reliability across the ISO-NE footprint by ensuring:

• High-fidelity transient stability cases
• A logical, traceable workflow for dynamic model tracking
• Strong alignment with NERC MOD-032, MOD-026, and MOD-027 requirements
• Full transparency across the entire model lifecycle
• Accurate representation of actual New England grid behavior
  

Reliable and validated dynamic models are essential for:

• Voltage stability studies
• Transient stability simulations
• Frequency response analyses
• System planning and operational decision-making
  

By enforcing consistent data quality and lifecycle governance, DDMS ensures that ISO-NE’s dynamic models remain accurate, validated, and up-to-date for regional engineering studies.

Technical FAQ: DDMS for Power System Engineers

Related Resources for ISO-NE Modeling & NERC Compliance

Looking to strengthen your ISO-NE modeling workflows, improve dynamic model accuracy, or prepare for NERC MOD compliance? Explore our technical engineering resources and services:

Dynamic Modeling & Stability Analysis

Power System Modeling & Dynamic Studies

Power System Studies (PSS®E, PSCAD, DigSILENT)

EMT Analysis for Inverter-Based Resources (IBRs)

NERC MOD Standards & Compliance

NERC Compliance Engineering Services
MOD-026-2 Excitation System Model Verification

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