ERCOT MQT requirements and the as-left model match: from plant settings to PSS®E and PSCAD parameters

Executive Summary

ERCOT’s Model Quality Tests (MQT) are a formal set of dynamic simulations and evidence reports that show (1) your phasor-domain (RMS) model in PSS®E and your electromagnetic transient (EMT) model in PSCAD behave consistently, and (2) both reflect the plant’s as-left settings—the real controller gains, limits, protection thresholds, and ride-through logic the site will run on. Since 2024, ERCOT tightened this loop with PGRR-109: before commissioning, Inverter-Based Resources (IBRs) must submit an “as-built” model alongside the quarterly stability assessment (QSA) model and overlay their MQT plots to prove alignment. After commissioning (and after any settings change), parameter verification and overlays are required on a defined timeline. In practice, this means disciplined extraction of controller settings from OEM tools and relays; a traceable parameter-mapping into PSS®E (e.g., REGC_A/REEC_A/REPC_A for IBRs, GGOV1/ESST4B/IEEEST/REPCA for synchronous and hybrid plants); a high-fidelity PSCAD build with inner-loop controls and protection; and a test suite (faults, ride-through, ramps, phase jump, etc.) that matches ERCOT’s DWG Procedure Manual. Getting the mapping right avoids late QSA entry, commissioning delays, and performance events—and it ensures the models remain decision-grade for planning and operations. (ERCOT)

What follows is a deep dive into the regulatory requirements, the technical content of MQT/UMV/parameter verification, and concrete, step-by-step guidance for building the mapping from plant settings to PSS®E and PSCAD, with plain-language explanations and tangible examples throughout. (ERCOT)

1. Foundations

1.1 Why MQT exists and what problem it solves

MQT verifies that the model you submit behaves like the real plant and that the two main simulation domains agree: RMS (PSS®E) for system-wide stability and EMT (PSCAD) for fast control, asymmetrical faults, and low-strength grids. In short: same plant, same settings, same response—no surprises across tools. (ERCOT)

Plain-language translation: Think of PSS®E as the “map” and PSCAD as the “street-view.” MQT checks that the landmarks line up when you switch views and that both match what’s actually built. If the map shows a highway but the street-view shows a river, your directions (studies) won’t work.
Example: A solar plant’s frequency droop is 5% in the field. If PSS®E has 3% and PSCAD has 7%, their post-fault active-power recovery will differ—studies could over- or under-estimate frequency support.

1.2 Who set the rules and how they evolved

ERCOT DWG Procedure Manual defines MQT content, Unit Model Validation (UMV, a hardware benchmark for EMT models), and parameter verification. PGRR-075 introduced MQT, PGRR-085 added UMV and parameter verification, and PGRR-109 requires “as-built” model overlays before commissioning and for post-COD modifications. (ERCOT)
The Nodal Operating Guides (NOGRR-245) updated voltage and frequency ride-through requirements, aligning with IEEE 2800 for IBRs; ride-through capability must be maximized and demonstrated in models. (ERCOT)
NERC guidelines on EMT model quality and verification provide structure for hardware benchmarking and consistency checks between model and equipment. (NERC)

Plain-language translation: ERCOT raised the bar over time: first show the models are good (MQT), then prove the PSCAD model matches real hardware (UMV), then keep the model synced with any plant setting changes (parameter verification).
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Example: Before May 1, 2024, you could finish “as-built” models after COD. Now you must provide them—and the MQT overlays—before the Resource Commissioning Date. (ERCOT)

1.3 Key vocabulary (with simple examples)

As-left settings: The controller gains, limits, and protection thresholds actually enabled at the end of commissioning or after a change. Think of this as the “golden config” snapshot. (ERCOT)
MQT overlays: Side-by-side plots of the same test in PSS®E and PSCAD (and sometimes TSAT if a user-defined PSS®E model is used) showing they track closely. (ERCOT)
UMV (Unit Model Validation): EMT model benchmark against hardware/bench tests at the unit level (e.g., inverter controller), often OEM-led. (ERCOT)
Parameter verification: A report/table proving every tunable model parameter equals the plant setting, with evidence (screenshots, relay settings, OEM exports). (ERCOT)

2. Core Concepts & Mechanics

2.1 The three pillars: RMS vs EMT vs evidence

RMS (PSS®E): Positive-sequence stability. Uses generic modules for IBRs (REGC_A + REEC_A/B + REPC_A), synchronous machines (GENROU/GENSAE), exciters (ESST4B), governors (GGOV1), power system stabilizers (IEEEST), and plant controllers (REPCA_A). (ESIG)
EMT (PSCAD): Full electromagnetic details where inner current loops, PLLs, protection, unbalance, and weak-grid dynamics matter. ERCOT prefers models that embed real firmware or fully represent inner controls. (ERCOT)
Evidence pack: MQT report (plots + pass/fail), UMV report (hardware benchmark rationale/data), Parameter Verification Report (PVR) mapping each plant parameter to each model field and showing equality. (ERCOT)

Plain-language translation: PSS®E is your “whole-grid zoom-out,” PSCAD is the “millisecond zoom-in,” and your verification artifacts are the receipts.

Example: An SCR≈2 POI may seem OK in PSS®E but show PLL hunting in PSCAD unless inner-loop bandwidth and limits are exact.

2.2 What is in scope for MQT/UMV and parameter verification

Typical MQT test families include: three-phase and single-line-to-ground faults at the POI; voltage ride-through bands; frequency steps/ramps; reactive/active power ramps; and phase-jump tests. UMV focuses on unit-level benchmarks (e.g., current limit behavior, PLL response, protection blocking/unblocking). Parameter verification focuses on tunable controls and protection that materially change dynamic behavior. (ERCOT)

Plain-language translation: You “poke” the model in repeatable ways and check whether it flinches like the real control would.

Example: For IBRs, you must show current-priority behavior (reactive vs real), low-voltage power logic (LVPL), and post-fault active-power recovery within specified times. (ESIG)

2.3 Why PSS®E and PSCAD must match—and how close is close

ERCOT expects “consistency” in shape and key metrics across domains. That means if the control prioritizes reactive current during a sag and limits Ip/Iq by a current circle, both models must show the same current split, ramp recovery, and ride-through logic. Overlays should use identical axes and time windows, presented side-by-side. (ERCOT)

Plain-language translation: If your PSCAD shows a sharp reactive-current burst then settles, your PSS®E model must show the same story in slower time.

Example: A 25° phase jump test shouldn’t trigger PLL loss of sync in either model if the plant won’t trip in the field. (NERC)

2.4 PSS®E model components and what real settings feed them (IBR focus)

REGC_A (converter interface): Parameters for current limits (Iqmax, Ipmax), ramp rates (rrpwr), and crowbar/limit logic proxy. Maps to inverter current limit frames and ramp-rate setpoints. (ESIG)
REEC_A/B (electrical controller): Q-V droop (\(Kqv\)), \(Vref/Vmax/Vmin\), P-f droop (\(Kpf/Kpi\) equivalents via plant controller), \(LV/HV\) ride-through logics (\(LVPL/HVRCM\)), and deadbands. Maps to PPC and inverter controller gains/limits. (ESIG)
REPC_A (plant controller): Voltage or reactive-power control mode; Volt/VAR curve, Q limits vs P (D-curve), and remote-bus control with line drop compensation. Maps to PPC mode, Vref, droop, LDC R/X. (ESIG)
For wind: add WT* modules (e.g., WTGTRQ, WTGPT) with pitch/torque gains and limits, driven by turbine PLC settings. (ESIG)

Plain-language translation: REGC_A is the inverter’s “muscle”; REEC_A is the inverter’s “reflexes”; REPC_A is the “plant brain.”

Example: If the site volt/VAR droop is 4% at the POI with remote-bus control, REPC_A must use the measured R/X path and droop that replicate that behavior in base-MVA units.

2.5 PSCAD models and what must be “real”

ERCOT expects EMT models to represent inner current controllers (d-q PI gains and bandwidth), PLL (\(kp/ki\) and filters), DC-link and AC protection (OV/UV, OF/UF, current blocking and restart timers), and crowbar/ride-through logic as implemented in firmware. Using embedded code or meticulously ported logic is recommended; “block-by-block approximations” that omit key loops are discouraged. (ERCOT)

Plain-language translation: The PSCAD model should be the “true personality” of the controls—not a simplified caricature.

Example: A 150-Hz PLL bandwidth with a 2-Hz low-pass on \(Vq\) will react differently to a 100-ms three-phase fault than a 50-Hz bandwidth. Your PSCAD PLL must use the as-left bandwidth and filters.

2.6 Ride-through and protection (what must appear in both models)

ERCOT’s NOG updates require maximizing voltage and frequency ride-through and documenting curves and control behaviors to meet them; models must enforce the same trip thresholds, blocking logic, and post-disturbance recovery. (ERCOT)

Plain-language translation: If the field won’t trip until 0.15 pu for 0.15 s, your models shouldn’t trip earlier; and if real power must restore within 1 s after voltage recovers, both models need to show it.

Example: Frequency ride-through 59.4–60.6 Hz continuous with time-varying tolerances: represent the same curve and primary frequency response (droop, deadband) in both models. (ERCOT)

Summary: MQT is the “same-story” check; UMV is the “is it the real device?” check; parameter verification is the “show your work” check. PSS®E needs the plant-level picture; PSCAD needs the inner-loop guts; both must match as-left settings and the ride-through curves you’re obligated to meet. (ERCOT)

3. Applications & Practical Process

3.1 The regulatory thread you must follow

Before QSA entry: submit models that pass MQT; meet DWG templates; include PSCAD for IBRs. (ERCOT)
Before Resource Commissioning Date (PGRR-109): submit “as-built” PSS®E and PSCAD, plus overlay of as-built vs QSA responses (same tests, same axes) and a concise table of changed parameters. (ERCOT)
After Part III approval/after any settings change: submit parameter verification and updated MQT overlays within ERCOT timelines. (ERCOT)
If PSS®E uses a user-defined model, include TSAT overlays as well. (ERCOT)

Plain-language translation: You need an MQT-ready “QSA model,” then an “as-built model” before you energize, and then keep them current every time you tweak a setting.

Example: You increase Q droop from 2% to 4% to improve voltage stability. Update REPC/REEC droop, regenerate PSS®E and PSCAD cases, re-run MQT tests, overlay, and submit an explanation plus the parameter table.

3.2 Extracting settings from the plant: what, where, and how

Collect and archive:

PPC settings (mode, Vref, droop %, deadbands, LDC R/X, VAR/PF limits; Volt-VAR curve points).
Inverter settings (current limit circle, Ip/Iq priority, ramp rates, LVPL/HV ride-through logic, PLL bandwidth, current controller gains, DC-link OVP/UVP).
Protection (OV/UV/OF/UF setpoints vs time, phase-jump logic, current blocking thresholds/timers, breaker/fuse coordination).
Synchronous equipment (governor droop and deadband; exciter gains/limits; PSS gains; AVR/PSS limiting).
Relay settings (voltage/frequency elements, ride-through timers, permissive logic).
Evidence: screenshots, CSV exports, OEM configuration reports, relay setting files (.RRT, .XRIO, etc.), with timestamps.

Plain-language translation: Download the “truth files” from each controller and relay; don’t rely on emails or spreadsheets.

Example: For a BESS, pull GFL mode parameters (PLL, current loops), primary frequency response (droop/ deadband), and state-of-charge-dependent active-power limits.

3.3 Translating settings → PSS®E model parameters (IBR example)

Below is a practical map (units and per-unit bases matter—convert to generator MVA base consistently):

Volt/VAR droop at PPC (e.g., 4% at POI) → REPC_A: \(Vref\), \(Kpv/Kiv\) tuned to achieve 4% slope; set Rcomp/Xcomp for remote bus/line drop compensation equal to collector + GSU path used by PPC. (ESIG)
Volt-VAR curve points (Volt vs Qcap/Qcap_min) → Implement as Q limits in REEC_A with V-dependent logic (via \(LV/HV\) logic or external limiter block), ensuring curve points are scaled to mvab. (ESIG)
Active-power ramp limits (MW/s) → REGC_A rrpwr (per-unit/s on mvab) and, if plant-wide, REPC_A p-ramp limits to reflect PPC pacing. (ESIG)
Current limit circle and priority → REGC_A Ipmax/Iqmax and REEC_A current-priority flags; ensure PSS®E limiters emulate inverter hardware (reactive priority by default unless ERCOT-approved real-priority). (ESIG)
Frequency droop/deadband → REPC_A frequency-power loop or REEC_A P control elements; convert site droop (%) and deadband (Hz) to per-unit (on 60 Hz) gains and thresholds. (ESIG)
\(LVPL/HVRCM\) behavior → REEC_A \(LVPL/HV\) logic parameters (e.g., \(Lvpnt0/Lvpnt1\), hvrc thresholds/timers) matching inverter ride-through assistance behavior. (ESIG)
Remote-bus voltage control → REPC_A flags and \(R/X\) compensation equal to measured path; verify against steady-state Q output at different loading. (ESIG)

Plain-language translation: Every knob in the PPC/inverter UI has a home in REGC/REEC/REPC; convert MW, MVAr, Hz, and volts to per-unit on the model’s MVA base and make sure the limiters and priorities match.

Example: A 100-MW plant with 110-MVA inverters: rrpwr of 20 MW/s becomes rrpwr = (20/110) pu/s ≈ 0.182 pu/s.

3.4 Translating settings → PSCAD parameters

Copy inner-loop PI gains and bandwidths directly; don’t “retune” to fit plots.
Implement PLL (kp/ki, filters, washout) exactly; include phase-jump and loss-of-sync logic.
Current limit circle/priority and anti-windup must match firmware; include blocking/restart timers (e.g., 5 cycles restart after permissive region).
Protection: OV/UV/OF/UF curves and timers; DC link protections; AC OCP; island detection disabled unless permitted; event latches/reset.
PPC: replicate V control mode, droop, deadbands, LDC; consider communication and sampling delays used by OEM—if present, include them.
Network: represent collector impedances, padmount/GSU taps, and POI exactly; for asymmetrical tests, include sequence impedances.

Plain-language translation: PSCAD should be a “wiring-accurate twin” of how the code runs—including delays and timers—not just a look-alike.

Example: A PLL with kp=75, ki=500 (rad/s units) and a 2-ms sampling delay will ride through a 200-ms 0.2 pu sag differently than a 0-ms delay; your MQT phase-jump result will reveal mismatches immediately.

3.5 Building the parameter verification report (PVR) that passes first time

One row per parameter: Plant Source → Value/Units → Convert to PU on mvab → PSS®E field name & value → PSCAD variable & value → Evidence link (screenshot, file) → Notes.
Include non-obvious defaults (e.g., anti-windup limits, saturation blocks, deadband implementations) and unit conversions.
End with a “changed since QSA” summary table (PGRR-109 request) and a list of which MQT tests are sensitive to each change. (ERCOT)

Plain-language translation: Make it easy to audit: “this is the setting, here’s where it lives in each model, and here’s the proof.”

Example: “Q droop: 4.0% (field PPC screenshot #12) → REPC_A droop = 0.04 pu; PSCAD: ppc.droop=0.04; affects VRT, \(3φ/1LG\) fault tests, and voltage steps.”

3.6 Running the MQT—tests, tolerances, and overlays

Minimum recommended set (tune to DWG template in force):

3φ and 1LG POI faults at multiple clearing times (e.g., 4–6 cycles); compare VPOI, IPOI, P, Q, frequency, PLL angle.
Voltage steps/ramps and consecutive sags to validate ride-through and LVPL/HVRCM.
Frequency steps (±0.03 Hz) and ramps to validate droop and deadband.
Active and reactive ramp limits (up/down).
Phase jump (e.g., +25°) without losing sync.
Post-fault active-power recovery time. (ERCOT)

Overlay guidance: same axes/scales, side-by-side on the same page; annotate key metrics (peak Iq, minimum V, recovery times). If PSS®E uses a user-defined model, include TSAT overlays. (ERCOT)

3.7 Common pitfalls and how to avoid them

Inconsistent MVA bases between models (mvab mismatch) → standardize on generator base and document. (ESIG)
Plant-level vs unit-level droop double-counting → ensure only PPC or unit loop owns primary control.
Missing inverter timers/filters in PSCAD → add all delays and time constants per firmware. (ERCOT)
Remote-bus control mis-implementation in PSS®E → set correct \(R/X\) compensation and verify against steady-state.
Protection curves not mirrored → implement identical setpoints and timers in both domains, including blocking/restart. (ERCOT)

3.8 Why the mapping matters (beyond compliance)

QSA entry and schedule: bad overlays or missing PVR delay your planned energization window. (ERCOT)
Grid performance: mismatched models lead to poor dispatch/voltage plans and can increase the risk of abnormal performance flags (APFs). (ERCOT)
Change management: parameter verification makes later troubleshooting faster—engineers can see what changed and why. (ERCOT)

Summary: Treat the mapping as an engineering product, not a spreadsheet chore. With clean extraction, precise conversion, and curated overlays, approvals are smoother and the models will hold up in real events.

4. Integration & Broader Context

4.1 How ERCOT’s requirements connect to IEEE 2800 and NERC

ERCOT’s ride-through and control expectations reflect a broader North American shift: IEEE 2800 sets IBR performance baselines; NERC EMT guidelines specify model content and verification; ERCOT operationalizes both with MQT/UMV/parameter verification and pre-commissioning as-built submissions. (NERC)

Plain-language translation: IEEE says “what good performance looks like,” NERC says “what good models look like,” and ERCOT says “prove yours do both—before you go live.”

Example: Consecutive voltage deviations and post-disturbance ramp-rates now feature in multiple regions; ERCOT requires you to model and test them explicitly. (ERCOT)

4.2 From theory to practice: code → controller → model

Controller code/firmware defines the truth; OEM tools export settings.
PSCAD embeds or faithfully reproduces that code for EMT.
PSS®E captures the same behavior in aggregate via generic modules and limiters.
MQT overlays confirm fidelity; UMV anchors the EMT to hardware. (ERCOT)

4.3 Adjacent domains this touches

Protection engineering: ride-through curves, permissive blocking, and breaker timing directly affect dynamic response—coordinate settings and models. (ERCOT)
Planning and operations: flat-start cases (DWG/SSWG) and QSA rely on dynamic data being realistic; poor models distort transfer limits and remedial action plans. (ERCOT)
Future trends: grid-forming controls, very low SCR interconnections, and hybrid plants increase the value of EMT and require richer model-to-settings traceability. (NREL)

4.4 Open questions & frontiers

Grid-forming model standards and how to represent inner loops and virtual impedance consistently across RMS/EMT. (EPRI)
Robust handling of unbalanced faults and sequence-dependent protections in RMS surrogates (beyond current practice). (NERC)
Automated consistency checks (e.g., DMView, scripted overlays, parameter diff tools) embedded in submission workflows. (ERCOT)

Summary: ERCOT’s MQT framework stands at the intersection of evolving performance standards and maturing EMT practice; traceability from firmware to models is becoming the norm.

5. Practical How-To: a concise, reproducible workflow

5.1 One-day field + desk protocol (repeatable)

5.1.1 Freeze the as-left: capture PPC, inverter, relay settings with timestamps; export CSVs and screenshots; record transformer taps and SCADA scaling.
5.1.2 Build the parameter ledger: one row per parameter with conversions to per-unit; fill both PSS®E and PSCAD columns; add evidence links.
5.1.3 Implement PSS®E: REGC/REEC/REPC plus relevant plant/synchronous modules; ensure mvab consistency; set remote-bus control and R/X compensation. (ESIG)
5.1.4 Implement PSCAD: paste inner-loop gains, PLL, protection, and timers; include communication delays; validate no-disturbance flat run. (ERCOT)
5.1.5 Run MQT test plan: 3φ/1LG faults, VRT/FRT, ramps, phase jump; archive input files and outputs. (ERCOT)
5.1.6 Create overlays: identical axes/time windows; annotate key KPIs. (ERCOT)
5.1.7 Write the PVR: include a “changed since QSA” table and test impacts; prepare the DMView/overlay package per ERCOT guidance. (ERCOT)
5.1.8 Submit as a package: PSS®E, PSCAD, overlays, PVR, and (for UDM) TSAT overlays if applicable. (ERCOT)

5.2 Rules of thumb (mental models)

Same knob, same number: if a setting is 0.04 (4% droop) in the field, it should be 0.04 pu in both models (after correct base conversion).
Priorities and limits dominate: get current priority and circle limits right before fine-tuning gains.
Timers matter: a 100-ms reclose or 5-cycle current-restart timer can change ride-through outcomes more than a gain tweak.
Overlay to learn: mismatches teach you which abstraction (RMS vs EMT) needs adjustment—fix causes, not symptoms.

5.3 Example parameter map (abbreviated)

PPC droop 4% at POI → REPC_A droop=0.04 pu; PSCAD ppc.droop=0.04; LDC R/X from plant test; verify Q vs V step. (ESIG)
Ipmax=1.1 pu, \(Iqmax=1.1\) pu, reactive-priority → REGC_A Ipmax/Iqmax=1.1; REEC_A priority flag; PSCAD: limit circle 1.1 pu, reactive priority true. (ESIG)
Frequency droop 5% with ±36 mHz deadband → REPC_A gains to achieve 0.05 slope; deadband=0.0006 pu; PSCAD: identical; verify ±0.03-Hz step response. (ESIG)
LVPL enables below 0.9 pu with slope S → REEC_A Lvpnt0=0.9 pu; slope per OEM spec; PSCAD: identical logic with anti-windup. (ESIG)
Phase-jump ride-through, 25° non-fault → Ensure PLL won’t force trip; PSCAD PLL limits/timers; PSS®E surrogate via no-trip logic and limiters; overlay MQT phase-jump test. (NERC)

5.4 Documentation to include with submissions

MQT report (plots, KPIs, pass/fail) with PSS®E/PSCAD overlays (and TSAT if UDM). (ERCOT)
UMV report (for IBR models) showing hardware benchmark coverage. (ERCOT)
Parameter Verification Report with evidence links; “changed since QSA” summary. (ERCOT)

5.5 Post-commissioning change management

Any firmware or setting change that affects dynamics → refresh ledger, re-run sensitive MQT tests, update overlays, submit per Planning Guide timelines. (ERCOT)
Keep “diffs” small and well-explained; include a short narrative of the operational need (e.g., improved voltage stability margin). (ERCOT)

Summary: With a standardized ledger, disciplined conversions, and curated overlays, you can go from field capture to ERCOT-ready package in a predictable cycle—before COD and during operations.