Guidelines for Using Real-Code in EMT Models for HVDC, FACTS, and Inverter-Based Resources

Introduction

As power systems rapidly transition toward inverter-based resources (IBRs), high-fidelity modeling has become a regulatory, operational, and planning necessity rather than a luxury. Utilities, ISOs, and developers increasingly require Electro-Magnetic Transient (EMT) studies that accurately reflect the real behavior of HVDC systems, FACTS devices, and inverter-based generators under normal and abnormal grid conditions.

The IEEE/CIGRE real-code EMT modeling methodology (Technical Brochure 958, February 2025) represents a major step forward in this space. It establishes a standardized, tool-agnostic framework that allows actual controller firmware (“real-code”)—the same code running in field hardware—to be executed directly within EMT and RMS simulation environments.

At Keentel Engineering, we actively support utilities, generation owners, and developers in implementing IEEE/CIGRE-compliant EMT models for interconnection studies, NERC compliance, and advanced grid performance assessments.

Why Real-Code EMT Modeling Matters

Traditional EMT and transient stability models often rely on:

• Simplified block diagrams
• Generic control representations
• Tool-specific implementations

While these approaches can be sufficient for high-level studies, they fall short when:

• Grid codes demand accurate fault-ride-through and control response
• Multiple vendors’ equipment must interact realistically
• Protection, PLLs, current limiters, and fast controls dominate system behavior



The IEEE/CIGRE approach solves these issues by enabling controller source code reuse without exposing intellectual property and without tying models to a single simulation platform.

Overview of the IEEE/CIGRE DLL Modeling Method

The IEEE/CIGRE methodology defines a standardized Dynamic Link Library (DLL) interface that acts as a bridge between:

• Manufacturer or model-writer controller code, and
• Any compliant EMT or RMS simulation tool

Key characteristics:

• Black-box implementation
• Self-documenting model structure
• Fixed-step, real-time controller execution
• Support for EMT and RMS tools
• Snapshot and multi-instance capability



Although commonly referred to as a “DLL” method, the same concept applies to Linux shared objects (.so), making it suitable for real-time simulators and Linux-based EMT platforms.

Core Benefits of the IEEE/CIGRE Real-Code Approach

1. Highest Possible Model Fidelity

Sector integration enables renewable electricity to displace fossil fuels in transport, heating, and industry through electrification and power-to-X technologies. This is critical because electricity alone accounts for only ~20% of final energy consumption, while heat and transport together exceed 70% globally 

2. Tool Independence

The same DLL model can run in multiple EMT or RMS tools without recompilation, ensuring consistent results across platforms.

3. Intellectual Property Protection

• Manufacturers retain full control of proprietary code while still delivering high-quality models to utilities and system operators.
  

4. Long-Term Compatibility

• Unlike static linking (.lib or .obj files), dynamically linked models avoid compiler and version dependency issues.
  

5. Regulatory and Compliance Alignment

High-fidelity EMT models are increasingly expected for:

• Interconnection studies
• NERC MOD, PRC, and TPL analyses
• ISO-specific EMT requirements (ERCOT, WECC, CAISO, PJM, etc.)
  

Architecture of an IEEE/CIGRE DLL Model

Static Model Information

Each model contains a static data structure that defines:

• Model name, version, and description
• Input and output signals
• Parameters, units, limits, and defaults
• Fixed controller sampling rate
• Supported EMT/RMS modes
• Required state variable counts

This makes the model self-describing, allowing simulation tools to automatically generate interfaces.

Dynamic Model Instance

During simulation, an instance structure is used to pass:

• Real-time inputs (voltages, currents, control signals)
• Outputs (firing pulses, current commands, trips)
• Parameters
• Time information
• State variables
• Each instance operates independently, enabling multiple identical controllers within the same study.
  

State Variables, Snapshots, and Multi-Instance Support

State variables are central to real-code modeling:

• They store integrator states, internal memory, and output history
• They enable flat-start initialization for RMS studies
• They allow EMT simulations to restart from saved snapshots

Proper state management ensures:

• No cross-talk between identical model instances
• Accurate continuation from saved simulation states
• Repeatable and auditable study results

Keentel Engineering places special emphasis on validating correct state variable grouping when reviewing OEM-supplied DLL models.

Roles Defined by the Standard

Model Writers (OEMs or Developers)

• Wrap controller firmware with a standardized interface
• Define inputs, outputs, parameters, and state variables
• Compile the complete package into a DLL or shared object

Simulation Tool Developers

• Provide DLL import utilities
• Manage sample-and-hold execution
• Allocate state variable memory
• Handle EMT/RMS solver interaction

End Users (Utilities, ISOs, Consultants)

• Import DLL models into simulation tools
• Configure parameters
• Connect models to electrical networks
• Run EMT and RMS studies

Practical Applications for HVDC, FACTS, and IBRs

IEEE/CIGRE real-code modeling is particularly valuable for:

• VSC-HVDC converters
• LCC-HVDC control and protection
• STATCOMs and SVCs
• Grid-forming and grid-following inverters
• Wind, solar PV, and BESS plant controllers

These technologies are dominated by fast digital controls that cannot be accurately represented using simplified RMS models alone.

How Keentel Engineering Supports Real-Code EMT Modeling

Keentel Engineering provides end-to-end support for IEEE/CIGRE-compliant modeling, including:

• OEM DLL model review and validation
• EMT model integration into PSCAD, EMTP, RTDS, and other tools
• Snapshot and multi-instance testing
• Interconnection and NERC compliance studies
• Independent verification for utilities and ISOs

Our engineers understand both power electronics control theory and regulatory study expectations, ensuring models are technically sound and acceptable to stakeholders.

Conclusion

The IEEE/CIGRE real-code EMT modeling methodology represents the future of high-fidelity power system analysis. By bridging real controller firmware with modern simulation tools, it enables unprecedented accuracy, repeatability, and confidence in grid studies involving HVDC, FACTS, and inverter-based resources.

Keentel Engineering is proud to support clients at the forefront of this transition—helping ensure reliable, compliant, and resilient power systems.

Frequently Asked Questions (FAQ)