UNIFI members are leading the industry with publications pertaining to GFM IBRs covering a wide spectrum. Here, you can UNIFI specifications for GFM IBRs that are leading the industry forward with guidelines for modeling, analysis, installation, and verification. You can also access modeling & simulation libraries / software, technical publications from our academic and research-lab members that appear in top journals and conferences, and educational tutorials that have been delivered in conferences around the world.

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Specifications v2

Cover of Unifi's "Specifications for Grid-forming Inverter-based Resources, Vol 1."

This document defines a set of specifications for GFM IBRs that provides requirements from both a power system-level as well as functional requirements at the inverter level that are intended to provide means for vendor-agnostic operation of GFM IBRs at any scale in electric power systems. The specifications are clearly identified and attributed to an IBR plant or an IBR unit throughout the document, where applicable. The specifications are authored by stakeholders from across the industry.

modeling & simulation libraries / software

Models developed by the UNIFI modeling & simulation team continue to be adopted across the industry. You can find our GitHub Repository with UNIFI open-source guidelines, policies, covenants, and other important documents here. Some examples of electromagnetic-domain and positive-sequence models for GFM IBRs are given below:

PS CAD logo.

EMT models of PV inverter based resource in GFL and GFM mode.  Model includes an interoperable primary control grid forming system architecture that is designed for use with both individual IBRs and aggregations.  The design is intended to coexist with vendor specific proprietary controls that exchange standardized signals with the system operator to regulate frequency and voltages, or to manage black start.

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WECC logo.

The model specifications of droop-based GFM (REGFM_A1) and VSM-based GFM (REGFM_B1) have been adopted by WECC. The model specifications can be accessed through the following links. The REGFM_A1 model has already been released in major commercial transient stability simulation tools including PTI-PSS®E, GE-PSLF, PowerWorld Simulator, and TSAT. The REGFM_B1 model is expected to be released in those tools soon.

Download Model Specification – REGFM_A1 PDF →

Download Model Specification – REGFM_B1 PDF →

EMTP logo.

Generic EMTP model for a three-phase aggregated grid-forming inverter (GFM inverter).  Applications include stability, fault, harmonic, dynamic, and interconnection studies.  The GFM inverter can be modeled as: droop- based, virtual synchronous machine (VSM)-based, dispatchable virtual oscillator (dVOC)-based, or a PLL-based.

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Power World Corporation logo.

Control blocks of REGFM_A1 and REGFM_B1.

reports

See below for technical reports and other documents authored by UNIFI.

Universal Input-Output Model of GFM Functions and Data-Driven Verification Methods

Towards answering the key question of how to translate high-level requirements and principles into rigorous specifications that can be enforced and validated for a wide range of IBRs.

Universal Input-Output Model of GFM Functions and Data-Driven Verification Methods

Towards answering the key question of how to translate high-level requirements and principles into rigorous specifications that can be enforced and validated for a wide range of IBRs.

Value Proposition for GFM Inverters

An overview of value that can be unlocked with the choice of GFM inverter technology in renewable integration projects across scales.

GFM Technology Specifications: A Review of Research Reports & Roadmaps

Recently, there has been pronounced interest by system operators, regulators, and national labs in GFM technology. This has translated to a slew of reports and roadmaps that are critically reviewed in this work.

Large Scale Field Demonstration Evaluation Plan

Defines commissioning tests for GFM inverters/plants. These commissioning tests can be used by plant owner/operators to exercise GFM control and operation without significant cost in testing architecture for evaluation equipment (e.g., load banks, grid simulators).

Publications

See below for a few of our highlighted publications covering GFM technology.See below for a few of our highlighted publications covering GFM technology.

Cover of "Stabilizing Inverter-based Transmission Systems" white paper.

Inverter-Based Transmission Systems: Power hardware-in-the-loop experiments with a megawatt-scale grid-forming inverter
A. Hoke, P. Koralewicz, R. W. Kenyon, B. Wang, L. Yu, K. Kawamura, J. Tan

View on IEEE Xplore →

Cover of "Transient Simulations with a Large Penetration of Converter-Interfaced Generation" white paper.

Transient Simulations With a Large Penetration of Converter-Interfaced Generation
Rodrigo Henriquez-Auba, Jose Daniel Lara, Duncan S. Callaway, Clayton Barrows

Download (PDF) →

Cover of "Model Reduction for Inverters with Current Limiting and Dispatchable Virtual Oscillator Control" white paper.

Model Reduction for Inverters with Current Limiting and Dispatchable Virtual Oscillator Control
Olaoluwapu Ajala, Minghui Lu, Sairaj Dhople, Brian Johnson, Alejandro Domínguez-García

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Cover of "Model Reduction for Inverters with Current Limiting and Dispatchable Virtual Oscillator Control" white paper.

Compensating Network Dynamics in Grid-Forming Control
Dominic Groß

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Cover of "Open-Circuit Submodule Fault Diagnosis in MMCs Using Support Vector Machines" white paper.

Open-Circuit Submodule Fault Diagnosis in MMCs Using Support Vector Machines
Ardavan Mohammadhassani, Ali Mehrizi-Sani

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Cover of "Simulation of 100% Inverter-Based Resource Grids With Positive Sequence Modeling" white paper.

Simulation of 100% Inverter-Based Resource Grids With Positive Sequence Modeling
Deepak Ramasubramanian, Pouyan Pourbeik, Evangelos Farantatos, Anish Gaikwad

View on IEEE Xplore →

Cover of "Integrated System Models for Networks with Generators & Inverters" white paper.

Integrated System Models for Networks with Generators & Inverters
D. Venkatramanan, Manish K. Singh, Olaoluwapo Ajala, Alejandro Domínguez-García, and Sairaj Dhople

View on Website →

Cover of "Sparse and Safe Frequency Regulation for Inverter Intensive Microgrids" white paper.

Sparse and Safe Frequency Regulation for Inverter Intensive Microgrids
Junhui Zhang, Lizhi Ding, Xiaonan Lu, Wenyuan Tang

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Cover of "A Generic Primary-control Model for Grid-forming Inverters: Towards Interoperable Operation & Control" white paper.

A Generic Primary-control Model for Grid-forming Inverters: Towards Interoperable Operation & Control
B. Johnson, T.G. Roberts, O. Ajala, A. Domínguez-García, S. Dhople, D. Ramasubramanian, A. Tuohy, D. Divan, B. Kroposki

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Cover of "Unified Virtual Oscillator Control for Grid-Forming and Grid-Following Converters" white paper.

Unified Virtual Oscillator Control for Grid-Forming and Grid-Following Converters
M. A. Awal, Iqbal Husain

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Cover of "Modeling of Grid-Forming and Grid-Following Inverters for Dynamic Simulation of Large-Scale Distribution Systems" white paper.

Modeling of Grid-Forming and Grid-Following Inverters for Dynamic Simulation of Large-Scale Distribution Systems
Wei Du, Francis K. Tuffner, Kevin P. Schneider, Kevin P. Schneider, Jing Xie, Jing Xie, Bishnu Bhattarai

View on IEEE Xplore →

Cover of "Definition and Classification of Power System Stability - Revisited & Extended" white paper.

Definition and Classification of Power System Stability – Revisited & Extended
Nikos Hatziargyriou, Jovica Milanovic, Claudia Rahmann, Venkataramana Ajjarapu, Claudio Canizares, Istvan Erlich, David Hill, Ian Hiskens, Innocent Kamwa, Bikash Pal, Bikash Pal, Juan Sanchez-Gasca, Aleksandar Stankovic, Thierry Van Cutsem, Thierry Van Cutsem, Costas Vournas

View on IEEE Xplore →

Educational Material

See below for a few of our educational tutorials and videos created by our consortium members.

EPRI Grid Forming Inverters Tutorial (2023)

IEEE PES Tutorial (2023)

Deepak Ramasubramanian, Sairaj Dhople, Dominic Gross, Brian Johnson, Wenzong Wang, Duncan Callaway, Philip Hart: Grid Forming Inverter Technology

IEEE IAS Tutorial (2023)

Iqbal Husain: Grid Interactive Power Converter Controls and their Fault Ride-Through Capability

EPRI Grid Forming Inverters Tutorial (2022)

Power Electronics Educational Videos

Educational videos of about 10 to 20 minutes duration each on various topics in power electronics, solar PV, wind and energy systems by Dr. Raja Ayyanar of Arizona State University.

Videos

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Meet the Inverter

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From follower to former

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Understanding Inertia without the Spin