PSCAD Models for Inverter OEMs: What Manufacturers Need to Know About EMT Model Development

Power Systems Modeling & NERC Compliance

Summary

If you manufacture grid-connected power electronics — solar inverters, battery inverters, wind converters, STATCOMs, electrolyser rectifiers, EV charging power units, or data centre power systems — you will be asked for a PSCAD model. Not by a regulator, but by your own customers, because their interconnection studies cannot proceed without one.

Most OEMs encounter this requirement for the first time when a sale is already in motion. The developer's consultant asks for the EMT model, the OEM has nothing to send, and the project stalls. Sometimes the developer switches to a vendor who has one.

This article explains what an EMT model is, why the requirement exists, what a manufacturer-grade PSCAD model actually contains, what data is needed to build one, how long it takes, and where these projects go wrong. It is written for OEM engineering and product managers who need to understand the scope before committing to it.

1. Why OEMs are suddenly being asked for PSCAD models

The requirement is not new, but it has hardened considerably.

ERCOT began requiring EMT models for all new inverter-based resource interconnections in 2016, initially driven by subsynchronous resonance and subsynchronous control interaction concerns. What started as a regional response to a narrow stability problem has become a general expectation across North America.

Three things drove the expansion.

Real disturbances with real consequences

A sequence of events across the Western and Texas Interconnections showed inverter-based resources tripping or entering momentary cessation during faults that they should have ridden through. The June 2022 Odessa Disturbance in Texas is the reference case: a single transmission fault resulted in the unexpected loss of roughly 1,711 MW of solar PV output. Post-event analysis found that positive-sequence models had not predicted the observed behaviour, because the behaviour originated in fast inner-loop control and protection logic that RMS models do not represent.

Regulatory response

FERC Order No. 901, issued in October 2023, directed NERC to close reliability gaps for inverter-based resources across data sharing, model quality, model validation and performance. That directive produced the PRC-028 / PRC-029 / PRC-030 standards family and NERC Project 2022-04 on EMT modelling. PRC-029-1, approved by FERC in Order 909 in July 2025, establishes performance-based frequency and voltage ride-through requirements for IBRs and adopts the IEEE 2800-2022 performance curves. It becomes effective 1 October 2026 for Bulk Electric System facilities and 1 January 2027 for non-BES facilities. The applicability threshold dropped from 75 MVA to 20 MVA.

Falling system strength

As synchronous generation retires, short-circuit ratios at interconnection points fall. Converter control loops that are stable at SCR 5 can become unstable at SCR 2. Positive-sequence simulation cannot reliably predict this. EMT simulation can.

The net effect for an OEM: your equipment cannot be studied without an EMT model, and increasingly it cannot be sold without one either.

Who gets asked

• Manufacturers of utility-scale PV and BESS inverters
• Wind turbine converter suppliers
• STATCOM and SVC vendors
• HVDC and MVDC converter suppliers
• Electrolyser and industrial rectifier manufacturers
• Data centre power system suppliers, as large-load ride-through expectations tighten
• EV charging power unit manufacturers at megawatt scale
• Plant controller (PPC) vendors, whose control layer must be represented alongside the converter
  

2. EMT versus positive-sequence: why both exist

Power system simulation operates in two domains, and the distinction matters because ISOs generally want models in both.

Positive-sequence (RMS / phasor domain)

Tools: PSS®E, PSLF, TSAT, PowerFactory RMS. Typical timestep: 4–10 milliseconds. The network is represented as balanced positive-sequence phasors at fundamental frequency. Fast switching, harmonics, and unbalance are not represented. These models run large networks quickly, which is why they remain the backbone of planning studies.

Electromagnetic transient (EMT)

Tools: PSCAD/EMTDC, EMTP-RV, PowerFactory EMT, RSCAD. Typical timestep: 1–20 microseconds — roughly a thousand times finer. Instantaneous three-phase quantities are solved, so switching behaviour, unbalance, harmonics, DC offset, saturation and control-loop dynamics down to the current regulator are all represented.

An inverter's response to a fault is governed by control loops with bandwidths in the hundreds of hertz to low kilohertz. A 4 ms timestep cannot see them. That is the entire reason EMT models are required: the phenomena that caused the disturbances are invisible in the phasor domain.

Where EMT is specifically required:

• Weak grid and low-SCR stability assessment
• Subsynchronous resonance and subsynchronous control interaction
• Phase angle jump response
• Unbalanced fault response and negative-sequence current injection
• Harmonic interaction and control instability between adjacent plants
• Detailed ride-through verification against IEEE 2800 curves
• Series-compensated line applications
• Grid-forming behaviour and islanding

Where positive-sequence remains sufficient: bulk transient stability, large-area planning, most contingency screening.

Because the two must agree, cross-validation between the EMT and RMS models is now a formal deliverable in its own right — and often the item that exposes errors in both.

3. Model types: black box, white box, and real code

OEMs face a genuine tension. The model must be detailed enough to reproduce controller behaviour, but the controller is the product. Three approaches manage that tension differently.

Black box (compiled, encrypted)

The control logic is implemented in the EMT tool, then compiled into a library and encrypted. Third parties can run the model, set parameters and view terminal quantities, but cannot inspect or extract the control code.

• Protects IP: strongly
• Fidelity: high, limited by the accuracy of the implementation
• Accepted by ISOs: yes, this is the standard commercial form
• Maintenance: must be rebuilt when firmware changes

This is what the overwhelming majority of OEM models are, and what most manufacturers should build.

White box (open source)

Control logic visible and editable. Rare in commercial practice — used internally, in research, or where a utility contractually demands full visibility.

• Protects IP: no
• Fidelity: high
• Use case: internal development, academic collaboration

Real code (firmware-derived)

The production controller source — typically C running on a DSP, sometimes with an FPGA layer — is converted into the EMT environment rather than re-implemented from block diagrams. The simulated controller executes the same logic as the physical controller.

• Protects IP: yes, when compiled and encrypted
• Fidelity: highest available in software
• Cost and effort: substantially higher
• Advantage: tracks firmware releases with much lower revalidation effort
• Requirement: sustained access to firmware source and the build toolchain



Real-code models are becoming the expectation in some markets and for some equipment classes. For most OEMs entering the space, a well-built black-box model is the correct first deliverable, with real-code conversion considered later if market pressure justifies it.

4. What a manufacturer-grade PSCAD model actually contains

"A PSCAD model" is not a single artefact. A model package that will survive ISO review has several layers, and OEMs consistently underestimate the ones below the surface.

4.1 Power stage

• Converter topology and switching representation — two-level, three-level, NPC, ANPC, modular multilevel as applicable
• Modulation scheme, carrier arrangement, dead time
• DC link capacitance, pre-charge circuit, DC bus operating window
• AC filter topology and component values, including damping
• Interface transformer: rating, vector group, impedance, X/R, tap range, and saturation characteristic where relevant
• Internal impedances between modules, cabinet and point of connection
• DC-side source or load representation — battery, PV array, wind generator, rectifier load — with its own dynamics

An important practical point: full switching representation is expensive to simulate. Many production models use an averaged or hybrid switching representation that reproduces terminal behaviour accurately at a manageable timestep. Whether that is acceptable depends on the study type, and the choice must be documented, not silently made.

4.2 Control system

This is where the effort concentrates.

• Phase-locked loop: structure, bandwidth, and behaviour under unbalanced and distorted supply
• Inner current regulator: reference frame, bandwidth, decoupling, anti-windup
• Outer loops: DC voltage, active power, reactive power, AC voltage, power factor
• Current limiting strategy and active/reactive priority under fault
• Negative-sequence current injection behaviour
• Ride-through logic: momentary cessation behaviour, blocking and de-blocking thresholds, recovery ramp rates
• Autonomous grid support functions: volt-VAR, volt-watt, frequency-watt
• Sample rates, computation delays, actuation delays, measurement filter time constants
• Start-up, synchronisation, soft-start, pre-charge, shutdown sequences

Delays and filter time constants deserve special mention. They are routinely omitted from OEM documentation and routinely decisive in weak-grid stability results. A model with correct gains and wrong delays will look right in a strong grid and be wrong where it matters.

4.3 Protection

Protection is not optional detail. It determines whether the model trips, and tripping behaviour is precisely what ISOs are trying to assess.

• AC and DC over/under voltage and over/under current, with pickup levels and time delays
• Over and under frequency
• Phase jump, RoCoF and vector shift protection, and whether these are user-defeatable
• Thermal, ground fault, insulation monitoring
• Anti-islanding scheme where applicable

PRC-029-1 recommends disabling phase-jump protection that trips unnecessarily during permissible phase angle excursions. A model that does not represent the protection cannot demonstrate compliance either way.

4.4 Plant controller interface

Most ISOs require that the model accept external setpoints in the way the real plant does. SPP's PSCAD model requirements, for example, specify that the plant power controller accept an external active power setpoint and a voltage setpoint, implement a settable voltage droop, and that the model initialise to the setpoints specified in the PPC. Communication latency and setpoint update rate must be represented.

4.5 Aggregation

A plant contains many inverters. Simulating each one individually is impractical. The model must support a documented aggregation approach — typically a single-unit equivalent scaled to plant rating, sometimes with a small number of representative units where diversity matters. The aggregation basis and its limitations belong in the documentation.

4.6 Numerical behaviour

The least visible layer, and the one that most often causes rejection.

• Timestep: models are generally expected to run at 10–20 µs. Some ISOs accept smaller timesteps where the penalty is not significant, but a model that only runs at 1 µs will be unwelcome in a large study case.
• Initialisation: the model must reach steady state cleanly from a flat start and initialise to the specified setpoints, without manual intervention.
• Snapshot capability: studies rely on saving and restoring a converged state. A model that cannot snapshot forces every run to re-initialise.
• Multi-instance: dozens of instances in one case, each with independent parameters and no shared-state collisions.
• Parallel and multi-core execution: required for large study cases.
• Compiler compatibility: typically Intel Fortran, against the PSCAD versions the ISO and the consultant are running.

4.7 Documentation and packaging



• Encrypted compiled library, installer, and licence file where used
• User manual: installation, parameters with ranges and units, control modes, aggregation guidance
• Parameter data sheet mapping model parameters to real product settings
• Validation report
• Model quality test conformance record
• Release note recording model version, firmware version modelled, and known limitations
  

5. Model quality testing: what reviewers actually run

Model quality tests exist because reviewers were receiving models that would not run. They are basic in concept and unforgiving in practice.

ERCOT introduced model quality test requirements effective May 2020, initially for PSS®E dynamic models, and requires MQT reports for all new and updated models — PSS®E and PSCAD. Since 2024, PGRR-109 has required IBRs to submit an as-built model alongside the quarterly stability assessment model and overlay the MQT plots before commissioning. ERCOT's NOGRR-245 updated voltage and frequency ride-through requirements to align with IEEE 2800, and ride-through capability must be demonstrated in models.



Typical test content across ISOs:

A model that fails MQT is returned for retuning and resubmission. For an OEM, that means the customer's schedule slips and the OEM is visibly responsible.

6. Validation: the part that determines everything

A model that has not been validated against hardware is an assertion, not evidence. Validation is also, consistently, the item that determines whether a modelling project runs to schedule.

What is needed

The distinction that matters most: test certificates are not validation data. A UL 1741 SB or IEC 61851 certificate states that a test was passed. It does not contain the waveform. Validation requires raw records — COMTRADE or equivalent — showing the measured response.

Required records typically include:

• Low and high voltage ride-through, balanced and unbalanced, across the applicable envelope
• Frequency ride-through and RoCoF events
• Phase angle jump
• Reference step responses: active power, reactive power, AC voltage, DC voltage
• Weak grid stability tests with the tested SCR stated
• Harmonic emission and power quality records
• Hardware-in-the-loop results, where available
• Field disturbance records from operating installations, where available

Sources of validation data



1. Type test campaigns. UL 1741 SA/SB, IEEE 1547.1, IEC 61400-21, IEC 62116 and equivalents generate exactly the disturbance responses needed — but only if raw captures were retained. Many were not.
2. Hardware-in-the-loop. The most efficient source. A real controller running against a simulated grid can produce any test case on demand.
3. Factory test records. Useful for control response, usually not for ride-through.
4. Field records. Highest credibility for post-event validation, but opportunistic.

When the data does not exist

This is common, particularly for products that were certified before EMT modelling became a commercial requirement. Options, in descending order of preference:

• Run a targeted HIL campaign against the specific test cases the model needs
• Run a supplementary laboratory campaign at a grid simulator facility
• Validate against a subset and document the unvalidated envelope explicitly
• Proceed on documented assumptions, accepting reduced defensibility under review

The last option is legitimate but should be a conscious decision. Every assumption belongs in an assumptions register reproduced in the validation report. Reviewers do not object to assumptions; they object to discovering them later.

7. The PSS®E companion model

Most OEMs asking for a PSCAD model actually need two models.

Transmission providers run planning studies in the phasor domain and detailed studies in EMT. Both need to reflect the same equipment, and the requirement to show they agree is now explicit — ERCOT's MQT includes benchmarking PSCAD against PSS®E, and NERC's EMT modelling work formalises cross-validation practice.

Two routes exist for the positive-sequence model:

Generic library models. The WECC/IEEE second-generation renewable energy models — REGC_A/B/C, REEC_A/B/C/D, REPC_A/B, and their equivalents — parameterised to represent the product. Fast, widely accepted, and adequate for many products. The limitation is real: generic models cannot represent behaviour their structure does not contain.

User-written models. A custom compiled dynamic model. Higher fidelity, higher effort, higher maintenance burden.



Whichever route is taken, developing the EMT and RMS models in parallel is materially more efficient than sequentially, because cross-validation failures usually indicate an error in one of them, and finding that error early is cheaper than finding it at submission.

8. Grid-forming: the emerging second requirement

Conventional inverters are grid-following: they synchronise to a measured voltage through a PLL and inject current. This works while the grid is strong. As system strength falls, PLL-based control approaches its stability limit.

Grid-forming control instead regulates voltage magnitude and angle directly, presenting as a voltage source behind an impedance. Grid-forming inverters can support islanded operation, contribute to system strength, and provide inertial response.

For OEMs, three implications:

1. Tender requirements are shifting. Grid-forming capability is increasingly requested for BESS, microgrid and backup power applications, and is being specified in some interconnection requirements.
2. Grid-forming models require different validation. The relevant tests are weak-grid and no-grid cases, black start, load steps in islanded operation, and parallel operation with other grid-forming units — not the standard grid-following test matrix.
3. Dual-mode products need dual-mode models. If the product can operate in either mode, the model must represent both, including the transition.

Modelling a grid-forming mode is not a small increment on a grid-following model. Budget for it separately.

9. Schedule: what actually drives it

A manufacturer-grade PSCAD model for a single product, grid-following, black box, with a companion positive-sequence model, is realistically a 650 to 900 hour engagement. On a standard programme that is 18 to 24 weeks. Compressed with parallel workstreams and a dedicated team, 12 weeks is achievable. A project-specific model for one named study can be delivered in around 5 weeks.

What sets the position within that range is rarely engineering difficulty. It is:

• Documentation quality. Complete control block diagrams with gains, time constants and per-unit bases put a project at the fast end. Marketing datasheets put it at the slow end.
• Whether documentation matches shipping firmware. The most expensive discovery in this work is that the block diagrams describe a control structure that was superseded two firmware revisions ago.
• Validation data availability. Raw waveforms available: fast. Certificates only: add substantial time or a test campaign.
• OEM responsiveness. Query turnaround is the single largest schedule variable in practice. A 48-hour response cadence and a 10-day response cadence produce very different delivery dates from identical scopes.
• Number of variants. Each hardware variant and each firmware baseline is a separate modelling exercise, not a parameter change.

Accelerating delivery

Two techniques genuinely compress the critical path:

Interim model release. A numerically stable, functionally complete model can be issued before formal validation and packaging are complete. The customer begins preliminary study work weeks before formal release, under a clear limitation statement, and receives the validated model when it is ready. From the customer's perspective the schedule halves.

Parallel workstream execution. Power stage and control development run concurrently; documentation is drafted alongside validation rather than after it; the positive-sequence model is developed in parallel with the EMT model throughout.

10. Where these projects go wrong

Patterns that recur across OEM engagements.



Treating it as a documentation exercise. It is a development project with its own validation, version control and release management.

Underestimating numerical hardening. A model that reproduces every waveform correctly but cannot snapshot, cannot run multi-instance, or requires a 1 µs timestep will be rejected. This layer routinely consumes 15 to 20 percent of total effort.

Certificates instead of waveforms. Discovering at week eight that no raw records exist.

No version control. A model released without recording which firmware version it represents becomes unmaintainable within two release cycles.

No maintenance plan. Every firmware release touching grid-facing control or protection invalidates the released model. An OEM with a two-year-old model and four firmware releases since has a model that misrepresents its own product — a genuine liability once customers have submitted it to regulators.

Modelling one variant and issuing it for all. Different hardware ratings and different firmware baselines require separate models or, at minimum, a documented validity statement.

Firmware and modelling teams not talking. The model is derived from control logic. If the firmware team is not directly engaged, the model is being built from documentation, and documentation drifts.

11. Maintenance and versioning

The deliverable is not one-time. A sustainable arrangement includes:

• A defined trigger for revalidation — typically any firmware change affecting control, protection or grid-facing behaviour
• Version numbering that ties model version to firmware version explicitly
• A release note recording what changed and what was revalidated
• Migration across PSCAD major versions as they are released
• First-line support for customers and their consultants running the model



Per-release revalidation of a black-box model is typically 40 to 80 hours. An annual retainer is usually more economical than release-by-release engagement, and it avoids the situation where a customer needs an updated model faster than a procurement cycle can produce one.

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Working with Keentel Engineering

Keentel Engineering provides power systems engineering and NERC compliance services to utilities, developers, EPCs, OEMs and public agencies across the United States. Our modelling practice covers:

• PSCAD EMT model development for inverter-based resources, including black-box packaging and encryption
• PSS®E, PSLF, TSAT and PowerFactory dynamic model development and user-defined models
• EMT-to-RMS cross-validation and benchmarking
• ERCOT Model Quality Test preparation and submission support
• PRC-029-1 applicability assessment and ride-through design evaluation
• MOD-026 / MOD-027 model verification and parameter verification reporting
• Weak-grid, low-SCR and subsynchronous studies
• Model maintenance and revalidation across firmware and software releases

If you manufacture grid-connected power electronics and need a model your customers can submit, we can scope it from your existing documentation and tell you what is missing before you commit to anything.

Keentel Engineering

Head Office: 400 N Ashley Dr STE #2600, Tampa, FL 33602 — (813) 389-7871

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This article is provided for general information and does not constitute legal, regulatory or engineering advice for any specific project. Regulatory effective dates, thresholds and ISO requirements are subject to change; verify current requirements with the applicable authority. Information reflects Keentel Engineering's understanding at the date of publication.