MISO adopts NERC's inverter-based resource recommendations in interconnection process

Washington — The Federal Energy Regulatory Commission cleared Midcontinent Independent System Operator to amend its generator interconnection procedures to adopt the North American Electric Reliability Corp.'s recommendations on interconnection requirements for inverter-based resources.

The NERC recommendations reflected in MISO's tariff revisions (ER20-2621) were accepted with an Oct. 6 effective date. MISO's revised pro forma generator interconnection agreement includes improvements tied to momentary cessation, phase jump immunity, monitoring and protection settings, as laid out in NERC's September 2019 Reliability Guideline on bulk power system-connected inverter-based resources.

NERC first released such a guideline in 2018, following discovery of the reliability risk posed by inverter-based resource controls tripping and disconnecting from the BPS during California wildfires in 2016 and 2017 that caused transmission fault-induced losses of solar photovoltaic generation.

Given growing penetrations of renewable energy sources, the reliability watchdog updated that voluntary guideline in 2019 to better reflect how the guidance can be translated into interconnection requirements for newly interconnecting generating resources, and to assist utilities with further development of those interconnection requirements.

"Unlike synchronous generators that predominantly respond to grid events with classical mechanics, inverter-based resource response is driven by advanced controls," the September 2019 guideline said. "These controls are configurable and capable of providing similar [essential reliability services] as synchronous generating resources; however, the industry is faced with providing sufficient guidance during the interconnection process to clearly describe what capabilities and control settings are desired."

As such, inverter-based resources like wind and solar PV facilities need "flexible yet clear requirements for how [they] should behave," NERC said in the report. "Leaving requirements vague or incomplete can lead to abnormal or even adverse behavior for the reliability of the BPS."

FERC approval

FERC's independent entity variation standard grants grid operators flexibility to propose variations to pro forma interconnection procedures and agreements. "We find that MISO's proposal satisfies that standard and, therefore, is just, reasonable, and not unduly discriminatory or preferential," FERC staff said in an Oct. 5 letter order approving the tariff changes.

"We agree with MISO that including these provisions in MISO's pro forma GIA will aid in the protection of the BPS by: prohibiting momentary cessations by inverter-based resources, establishing the conditions under which an inverter must not trip, requiring the collection of specific data to monitor resource performance and event analysis, and specifying inverter protection settings," the order delegated to staff said.

MISO's new pro forma GIA replaces references to wind generating plants with the term "non-synchronous generating facilities." It also replaces the term "low voltage ride-through" with the term "abnormal voltage ride-through," which "more accurately describes the type of voltage events that may occur," the order said.

And staff agreed with MISO's decision to remove from the pro forma GIA a "provision that generating facilities must incorporate the requirements directed by the applicable Reliability Council, as this requirement is no longer necessary given other proposals in the instant filing."