By: Faizan Hassan Hajam
ERCOT convened its scheduled Inverter-Based Resource Working Group (IBRWG) meeting on September 12, 2025. The sessions mainly focused on two critical technical issues affecting inverter-based resources (IBRs): VRT/PFR Control Coordination and Dynamic Model Accuracy. Additionally, the meeting discussed the regulatory requirements for reactive power capability at zero-megawatt output, clarifying the application of IEEE 2800-2022 standard for resources.
Key Discussion Items from ERCOT IBRWG
- IBR Performance and Control Coordination
- Strict Dynamic Model Requirements
- Reactive Power Capability at Zero Output
IBR Performance and Control Coordination:
One of the key themes of the meeting was the interaction between voltage-ride through (VRT) and primary frequency response (PFR).
- ERCOT has observed that during voltage ride-through events caused by high frequency calculations or PPC interactions during fault conditions. These high-frequency spikes, although not indicative of actual system frequency, can cause a power plant controller (PPC) to misinterpret these spikes and incorrectly trigger a PFR response, reducing the plant’s active power output.
- Multiple industry stakeholders including Mortenson, Sungrow, and Vestas presented their perspectives on this issue.
- Some options outlined by stakeholders include
- Pause responses to PPC dispatch commands during a VRT event.
- Implement configurable delays before applying a new power reference once frequency crosses a deadband; this will help filter out short disturbances and reduce unnecessary oscillations.
- Introduce hysteresis bands and various other PPC features, including latch, hold, and counter
Strict Dynamic Model Requirements
ERCOT presented an urgent reminder about dynamic model submission requirements.
- ERCOT mentioned that they have observed that models submitted at FIS and QSA stages often contain unrealistic assumptions, such as controllers with extremely high reactive gains and zero communication delay.
- PPC vendors are often selected after QSA; therefore, as-built models may demonstrate different MQT response than that submitted during FIS and QSA. This may delay the commissioning schedule for the interconnecting entity (IE).
- To avoid the above unnecessary delays, ERCOT recommended:
- IEs must declare the assumed PPC vendor and model for FIS studies. Any subsequent change to the PPC vendor or model may trigger an FIS restudy. The vendor details must be filled out in the relevant section of Dynamic Model Template.
- All model submissions should be as “REASONABLE and ACCURATE as possible” and must be submitted both to ERCOT and the interconnecting TSP as per Planning Guide 6.2, 6.2.1, and DWG Procedure Manual 3.2.2.
- Updated models must be promptly submitted whenever changes occur.
- Resource entities (REs) must study not only AVR/PFR performance but also MQT in simulation prior to synchronization to confirm that planned settings are able to pass AVR and PFR tests and to avoid excessive retuning.
- Field technicians must consult with the IE/RE’s dynamic modeling engineer before adjusting settings, especially reactive power limits (Q-limits), as improper changes have caused facilities to fail performance tests.
Reactive Power Capability at Low or Zero Output
ERCOT clarified the adoption of the IEEE 2800-2022 for satisfying reactive power requirements of inverter-based resources (IBRs). The IEEE 2800-2022 standard requires an IBR to satisfy minimum reactive power capability requirements at all active power levels, including zero, whereas the existing ERCOT protocols require this requirement to be satisfied for MW output above 10% of the nameplate capacity. ERCOT clarified this rule depends on the standard generation interconnection agreement (SGIA):
- If SGIA is signed before 08/01/2024, the 10% MW threshold (existing protocol) needs to be satisfied for reactive capability.
- If SGIA is after 08/01/2024, Section 5 of IEEE 2800-2022 needs to be satisfied, that is, an IBR must satisfy the 0% threshold requirement.
Future Plans:
ERCOT plans to propose a new Nodal Protocol Revision Request (NPRR) and Nodal Operating Guide Revision Request (NOGRR) to clarify the power reactive requirements for IBRs.
