PERC Studio

A desktop studio that accelerates data center modeling for transmission planning engineers. It takes a facility's ride-through standard and equipment type, or measured values for an as-built facility, and produces documented, PSS/E-ready dynamic load models for a data center or similar large, power-electronics-heavy load. From one window you can build and compare models across several PSS/E load models, check them against published ride-through standards, inspect existing .dyr files, and export a .dyr file plus an HTML review report. The studio currently supports the PERC1 and PERC2 family (four variants) and conventional motor load, and is built to take on more load models.

Abstract

Large Electronic Loads (LELs), such as data centers, are rapidly becoming a dominant share of bulk power system load, with ride-through and reconnection behavior unlike conventional motor-driven load. NERC's May 2026 Level 3 Alert directs Transmission Planners and Planning Coordinators to use the PERC1 model, or an equivalent-or-better model, as the baseline for large load modeling, but these models' many parameters and cease/reconnect options make consistent parameterization difficult without facility-level power electronics data. This work presents a studio that accelerates data center modeling for transmission planning engineers. Given plain-language facility inputs (ride-through capability, trip and reconnect behavior, UPS/VFD front-end type), or full field-measured CON values for as-built facilities, the tool produces a ready-to-use PSS/E .dyr file and an HTML report documenting assumptions and plotting simulated ride-through performance live against a library of independently-sourced ride-through presets (three generic tiers plus utility-specific grid-operator standards such as ERCOT NOGRR282, MISO, SPP HILL, and NERC's own PRC-029-1/LLWG SAR proposals), letting planners quickly retrieve a defensible parameterization. This effort complements PNNL's Load Model Data Tool (LMDT), focusing on rapid model parameterization and checking for data-center-class loads.

Project status

PERC Studio is research software under active development. Work in progress (also see docs/user/roadmap.md):

• Modular CMLD as a motor-load option. Offer the modular composite load model (CMLD) as an alternative to CLOD for representing the motor share of a facility.
• Faster black-box validation. Cut the cost of a validation run, which is dominated by starting a PSS/E process for every case, by reusing processes (behind an equivalence check), scheduling searches asynchronously and using idle workers. The target is a Standard run in under 15 minutes.
• Full-facility testing in a real system. Upload a PSS/E case and test a whole facility, meaning several load models together that represent a data center, at its point of connection in that system, instead of one model on a single bus.

Future work: parameterize load models from the performance of a PSCAD (EMT) model run against a benchmark.

The PSS/E validation libraries behind the models (several thousand cases on PSS/E 35.6 and 36.7) are not part of this repository. Their results are summarized in the model pages under docs/user/.

Features

Feature	What it gives you
Ride-through preset library	Nine explicit, cited presets: three generic tiers (Extended, Standard, Minimal) and utility or grid-operator standards (ERCOT NOGRR282, PJM, MISO, SPP HILL, NERC PRC-029-1 and the NERC LLWG SAR proposal). Each preset has a page with its source, envelope plots and CON mapping.
Multiple load models	Four PSS/E models today: PERC1 DLL (PSS/E 34/35), PERC1 standard (PSS/E 36.5+), PERC2 standard (36.7) and PERC2 DLL v2.3 (34-36). Choose one per block; presets are carried over to each model as fully as the model allows, and the editor says what is left out.
Facility composition	Split a facility across IT/UPS, cooling VFD, conventional cooling motors and other load. Each block has its own model, preset, operating mode and editable parameters.
Full parameter editing	Every CON is editable, grouped into voltage ride-through, frequency ride-through, trip and reconnect fractions, ZIP exponents, current limits and other. Edited rows are marked and revert individually. Hovering a label shows its CON name.
Live response chart	A fast simulation of the block under a voltage sag/swell or a frequency excursion, shown against the selected preset's voltage envelope (and frequency table where the standard has one), with a TRIPS / RIDES THROUGH verdict, reconnect timing and a facility-wide response. It follows rules measured in PSS/E; it is not PSS/E.
.dyr import	Load a record from an existing .dyr file to see what it does before simulating it. Values are kept as written, and out-of-range values are flagged, not clamped.
Exports	A .dyr file in the exact CON layout of the vendor model, and an HTML report with the load, the assumptions, the preset citation, every parameter against its real mnemonic, a data-confidence label per block and the response plots.
Built-in documentation	A Documentation tab with a model comparison, a parameter reference, the PSS/E behaviors and limitations found in testing, and a page per preset.
Validated against PSS/E	Every model was run in real PSS/E (over 2,000 runs across the four models), and every shipped preset was run against the real model. The editor warns about each reproduced pitfall, such as a reconnect voltage that strands the load. The results are summarized in each model's page.
Black-box validation	Tests any PSS/E load model, with no knowledge of its internals, by searching for the voltage and frequency boundaries where it rides through, trips or never reconnects, and compares them with a standard. See docs/black_box/.
Automation CLI	perc-studio generates, runs and validates parameterizations from scripts (install from source). See src/dev/cli/README.md.

How to use it

1. Launch the app (installer, portable ZIP, or uv run perc-studio from source; see Install).
2. Choose a starting point. Use Screening for a quick single-block estimate, or Post-Commissioning for a full facility.
3. Pick a model version and a ride-through preset (for example ERCOT NOGRR282 or the generic Standard tier). Enter the load name, bus and MW/Mvar. For a facility, set the load split across blocks.
4. Review and adjust. Open any parameter row to edit it. Watch the live chart: choose a voltage or frequency event, set its depth and duration, and check the verdict and the position against the preset's envelope.
5. Export the .dyr with Save .dyr... and the HTML report with Save report.... To inspect an existing model instead, use Import .dyr....
6. Run it in PSS/E. Add a matching static Load record (same bus and ID) to your power-flow case, load the .dyr, and confirm the model ordering against your installed Model Library. The app does not include PSS/E or the PERC DLLs.

docs/user/getting_started.md walks through each screen in detail.

What the app does

A data center's load is not a single lump of MW - it is a mix of IT/compute load behind UPS power electronics, cooling load behind VFDs, conventional cooling motors, and other miscellaneous load, each of which responds differently to a voltage sag on the bulk power system. This studio helps a transmission planning engineer:

1. Describe each block of the facility with a ride-through preset - one of three generic tiers or a specific utility/RTO/ISO standard (ERCOT, SPP, PJM, MISO, NERC) from an explicit, cited library - and its equipment type (UPS operating mode, VFD front end), or with field-measured values.
2. Have those choices translated into numeric PSS/E model parameters by a documented, inspectable rule set (src/presets/ridethrough.py, each model's cons.py and presets.py under src/load_models/).
3. Get back a ready-to-use .dyr file - built to the exact CON layout of the vendor model, not an approximation - plus an HTML report that documents every assumption, shows the parameters against their real model mnemonics, and plots the block's simulated response to a voltage sag/swell or a frequency excursion live against the selected standard's own voltage envelope and (where the standard publishes one) frequency ride-through table.

It is an engineering aid for constructing a documented, defensible starting model - not a certified vendor export. Confirm CON ordering against your installed PSS/E Model Library and treat placeholder values as placeholders until field-validated (the app tracks and displays this confidence level explicitly).

Workflows

The app bar at the top of the window switches between:

• Screening - a single-page form (load, bus, ride-through preset) for a quick, preliminary estimate with a live response chart.
• Post-Commissioning - the full facility (IT/UPS, cooling VFD, conventional motors), with every block's parameters editable in its parameter rows.
• Documentation - the user documentation library (docs/user/); each block's Preset docs link opens its page there. A source checkout adds a Developers group with the contributor documentation.
• Black-Box Validation - runs any PSS/E load model through a ride-through test protocol in your own PSS/E; see docs/black_box/BLACK_BOX_VALIDATION.md.

Requirements

• Python 3.13 to run from source. The app is developed and tested on Windows; the installer and portable ZIP are Windows 10/11 (64-bit) only.
• PSS/E is not required to build, edit and export models. Only black-box validation and the real PSS/E runner need a licensed PSS/E (35.x or 36.x).
• The PERC1 and PERC2 user-defined model DLLs belong to ISO-NE and are not distributed with this app; PERC1 standard and PERC2 standard are built into PSS/E 36.

Install

Windows portable ZIP. Download it from the Releases page, extract it to a folder you keep, and run Create Desktop Shortcut.cmd once. It is the full desktop app and needs no Python. (An installer, PERC-Studio-<version>-Setup.exe, is attached to a release when one is built.) Releases are not yet code-signed, so Windows SmartScreen asks for confirmation on first run: click More info, then Run anyway.

From source, with uv:

git clone https://github.com/TimThacker/perc-studio.git
cd perc-studio
uv sync
uv run pytest -q

Or without uv:

git clone https://github.com/TimThacker/perc-studio.git
cd perc-studio
python -m venv .venv
.venv\Scripts\activate          # Windows
source .venv/bin/activate       # macOS/Linux
pip install -e .
pip install pytest ruff
pytest -q

Running the app

uv run perc-studio                            # opens on Screening
uv run perc-studio --mode post-commissioning  # opens on Post-Commissioning
uv run python src/main.py                     # the same app, as a script

Without uv, run perc-studio (or python src/main.py) with the virtual environment activated.

Installer and source install

The installer and portable ZIP contain the desktop app: every workflow, black-box validation and the user documentation. Installing from source gives the same desktop app plus the perc-studio automation CLI, the test suite and the contributor documentation (the Documentation tab's Developers group). Building the installer and ZIP: packaging/README.md.

Automation CLI

The same perc-studio command, given a command instead of options, is a scriptable command-line tool (from a source install) for generating parameterizations programmatically, running them (a built-in analytic mock, or real PSS/E once a PSS/E install is selected), and validating the result against what a ride-through preset's own envelope says should happen. perc-studio help lists the commands:

uv run perc-studio params generate --source preset --preset-id ercot_nogrr282 --out case.json
uv run perc-studio dyr to-case vendor.dyr --out vendor_case.json   # load an existing .dyr
uv run perc-studio sweep my_sweep_spec.json --output-dir output/my_run

It requires no PySide6/Qt runtime and prints structured JSON by default. See src/dev/cli/README.md for the command map, a reference page per command group, the JSON output contract, and a cookbook of worked examples.

Documentation

Indexed in docs/README.md:

Document	What's in it
docs/user/model_overview.md	Start here for load models. Every supported model compared side by side (PSS/E versions, what each can represent, pitfalls, validation), with a page per model: PERC1 DLL, PERC1 standard, PERC2 standard and PERC2 DLL v2.3.
docs/user/	The user documentation library shipped with the app: getting started, generic parameter tiers, a user-level model reference, the PSS/E model behavior and limitations page, the ride-through preset pages (one per standard, with citations, envelope plots and CON mapping) and the roadmap.
docs/developer/PERC1_MODEL.md	Deep reference for the PERC1 and CLOD models: the full 173-CON DLL layout, what each CON does, the three cease/reconnect Options, the DLL-vs-Standard variant gap, and the exported .dyr record format.
docs/developer/PERC2_MODEL.md	The PERC2 standard model (PSS/E 36.7's built-in PERCxx2U): six cease checks with their own reconnect settings, how presets map onto them, and the PSS/E 36.7.1 issues the app works around.
docs/developer/PERC2_DLL_MODEL.md	The PERC2 DLL v2.3 (ISO-NE's PERC2_v3x_v2p3.dll, PSS/E 34-36): how the app tells its PERCBL records from the PERC1 DLL's, carries presets over, and what the v35 and v36 builds do that the document does not say.
docs/developer/ADDING_A_PRESET.md	Adding or editing a ride-through preset (the whole library is one dict in src/presets/ridethrough.py) and regenerating the preset plots.
docs/developer/ADDING_A_LOAD_MODEL.md	Registering a new PSS/E load model in src/load_models/ and running it through perc-studio's generate -> export -> run -> validate -> sweep loop.
docs/developer/ARCHITECTURE.md	Project layout and what each source module is responsible for - start here if you're contributing code.
docs/black_box/BLACK_BOX_VALIDATION.md	Black-box model validation: how to run it, how it works inside, how to read the results, and its limits.
src/dev/cli/README.md	The perc-studio automation CLI.
packaging/README.md	Building the production installer and portable ZIP, code signing, and the release checklist.
CONTRIBUTING.md	Set up, test, and contribute.

Notes for engineering use

• This is an engineering aid for constructing a documented starting model, not a final vendor-certified model export.
• Always confirm model ordering and assumptions against the installed PSS/E Model Library before final study use - .dyr output includes a reminder comment to this effect.
• Every IT/UPS and VFD block carries an explicit data-confidence label (Field-validated, Vendor nameplate/spec sheet, or Placeholder); the HTML report shows this per block and adds a warning banner if any block is still using placeholder values.
• The PERC and CLOD records are USRLOD/USRLODC models and carry no MW/Mvar themselves - a matching static Load record (by bus + ID) must exist in the power flow case.
• The response plots in the HTML report are an illustrative fixed scenario, not a substitute for a full EMT/stability simulation.

License

MIT; see LICENSE. Bundled third-party components and their licenses are listed in THIRD_PARTY_NOTICES.md. Neither PSS/E nor the PERC1 or PERC2 user-defined model DLLs are included.

Acknowledgements

Developed at CURENT, The University of Tennessee, Knoxville, in partnership with the Tennessee Valley Authority.

Special thanks to:

• Michael McAmis, Thomas Anderson, and Matthew Dolan (TVA)
• Dr. Yilu Liu, Stephanie Thomasik (UTK/CURENT)
• NERC LMWG

Citing

If you use PERC Studio in your work, please cite it using the metadata in CITATION.cff (GitHub's "Cite this repository" button reads it).

Contact

Point of contact: Tim Thacker, tthacke3@vols.utk.edu.

Bug reports and feature requests: GitHub Issues. For security issues, see SECURITY.md.