OpenIWPI

A Modelica library that couples phasor-based (TS) and electromagnetic-transient (EMT) power-system models, so converter-rich grids can be simulated — and linearized — as a single hybrid EMT–TS model.

Repository archived on Zenodo — DOI: 10.5281/zenodo.20586745

This repository is the open-source companion to the paper "OpenIWPI: Open-Instance Wave-Phasor Interface Library for Power System Simulation Studies in Modelica" by M. de Castro and L. Vanfretti, presented at the 16th International Modelica & FMI Conference (Lucerne, Switzerland, September 8–10, 2025). OpenIWPI is a Modelica library that interconnects electromagnetic-transient (EMT) models with the phasor-based power-system components of OpenIPSL, so that hybrid EMT–TS systems can be simulated — and linearized — together in a single Modelica model, without co-simulation.

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Overview

Modern grids host a growing number of power-electronic, converter-based resources. Some parts of a study need a detailed electromagnetic-transient (EMT) representation (fast switching dynamics), while the bulk grid is best modeled with phasor / positive-sequence transient-stability (TS) models. Traditionally these two worlds live in separate tools and are stitched together with ad-hoc co-simulation, which is cumbersome and breaks small-signal analysis.

OpenIWPI takes a different route: a wave-phasor interface — built from a positive-sequence filtering approach (DSOGI-PLL and SOGI filters) — lets a single Modelica model contain both an EMT subsystem (modeled with the Modelica Standard Library's Electrical package) and a phasor grid (modeled with OpenIPSL). The whole hybrid model is solved with a single variable-step solver (e.g. DASSL), and — uniquely among EMT-capable tools — it can be linearized for small-signal stability analysis (e.g. with Modelica_LinearSystems2) and exported as an FMU when co-simulation is genuinely needed.

In short: model the plant you care about in EMT detail, keep the rest of the network as a phasor equivalent, and study them together.

How the interface works

flowchart LR
  A["Phasor / TS grid<br/>OpenIPSL (positive sequence)"] -- "voltage phasor &rarr; 3-phase waves" --> B["Wave-Phasor<br/>interface bus"]
  B -- "current waves &rarr; phasor<br/>(DSOGI-PLL + SOGI)" --> A
  B -- "voltage waves" --> C["EMT subsystem<br/>MSL Electrical"]
  C -- "current waves" --> B

Loading

The phasor side acts as a variable voltage source on the interface bus (phasor-to-wave); the EMT side acts as a variable current injection, whose positive-sequence phasor is recovered by filtering the three-phase current waves (wave-to-phasor).

Repository structure

Path	Contents
OpenIWPI/	The OpenIWPI Modelica library (load OpenIWPI/package.mo).
LICENSE	3-Clause BSD license.

The library (OpenIWPI/) has six sub-packages:

• Copyright — the library's copyright and license notice.
• UsersGuide — overview, getting-started notes, and references.
• Examples — runnable demos: SimpleCircuit and ConverterCircuit (a STATCOM).
• Buses — the hybrid wave-phasor bus that connects an OpenIPSL phasor node to MSL EMT pins.
• Interfaces — the filter-based wave-phasor interface model.
• Utilities — auxiliary blocks: Clarke and Park transformations, a resettable integrator, the Second-Order Generalized Integrator (SOGI), and the DSOGI-PLL.

Requirements

This is a pure Modelica library — no hardware or code-generation toolchain is required.

• A Modelica tool. Developed and tested with Dymola 2025x. Other Modelica-compliant tools may work, but have not been fully tested.
• OpenIPSL v3.1.0 — provides the phasor-domain components and the PwPin connector. Available from openipsl.org.
• Modelica Standard Library (MSL) 4.0.0 and Complex 4.0.0 — provide the EMT (Electrical/Analog) models and constants; both ship with the Modelica tool.
• (Optional) Modelica_LinearSystems2 — for small-signal / linearization studies of the hybrid model.

Getting started

1. Clone

git clone https://github.com/ALSETLab/OpenIWPI.git

2. Load the libraries (order matters)

OpenIWPI depends on OpenIPSL and the MSL, so load them first:

1. Load OpenIPSL 3.1.0 and the Modelica Standard Library.
2. Open OpenIWPI/package.mo to load OpenIWPI.

3. Initialize and simulate

Note

The library does not ship a power-flow solver. Initial guess values for the phasor (OpenIPSL) side must come from a power-flow solution — see the OpenIPSL User's Guide. The EMT side is best initialized de-energized and connected/energized at a positive time instant.

Open and simulate the bundled examples to see the interface in action:

• OpenIWPI.Examples.SimpleCircuit — a two-bus system comparing a fully phasor model against a hybrid TS–EMT model, demonstrating that the current filtering recovers the correct positive-sequence current phasor.
• OpenIWPI.Examples.ConverterCircuit — a placeholder, pending integration into the library. It is intended to demonstrate a STATCOM modeled in EMT detail connected to a phasor (SMIB) grid. That example was presented in M. de Castro and L. Vanfretti, "Multi Time-Scale Modeling of a STATCOM and Power Grid for Stability Studies using Modelica," OSMSES 2022 (IEEE Xplore), but has not yet been added to this repository.

How to cite

If you use this library, please cite the paper:

M. de Castro and L. Vanfretti, "OpenIWPI: Open-Instance Wave-Phasor Interface Library for Power System Simulation Studies in Modelica," in Proc. 16th International Modelica & FMI Conference, Lucerne, Switzerland, Sep. 8–10, 2025.

@inproceedings{deCastro2025_OpenIWPI,
  author    = {de Castro, Marcelo and Vanfretti, Luigi},
  title     = {{OpenIWPI}: Open-Instance Wave-Phasor Interface Library for Power System Simulation Studies in {Modelica}},
  booktitle = {Proceedings of the 16th International Modelica \& FMI Conference},
  address   = {Lucerne, Switzerland},
  year      = {2025},
  month     = sep
  % TODO: add pages and DOI from the published proceedings
}

You can also cite this archived release directly via its Zenodo DOI: 10.5281/zenodo.20586745.

License

Released under the 3-Clause BSD License. Copyright © 2016–2025, Luigi Vanfretti, ALSETLab (formerly SmarTS Lab) and contributors. See LICENSE.

Authors

• Marcelo de Castro — Mitsubishi Electric Power Products, Inc., USA
• Luigi Vanfretti — Rensselaer Polytechnic Institute, USA

Developed and maintained by ALSETLab. Contributions are welcome.