Federal regulators took steps that could lead to new mandatory standards for inverter-based resources (IBRs) in an effort to enhance the reliability of the bulk electric system.

IBRs are solar photovoltaic, wind, fuel cell and battery storage resources that use power electronic devices to change direct current power to alternating current power, to be transmitted on the bulk-power system.

In its November 17 action, the Federal Energy Regulatory Commission (FERC) issued orders that focused on three IBR-relateded actions:

• An order directing the North American Electric Reliability Corp. (NERC) to develop a plan to register the entities that own and operate IBRs;
• A Notice of Proposed Rulemaking to direct NERC to develop reliability standards for IBRs that cover data sharing, model validation, planning and operational studies, and performance requirements; and
• An order approving reliability standards that are related to IBRs, which NERC proposed earlier in 2022.

Common mode failures

Until recently, the bulk power system’s generation fleet was made up almost exclusively of synchronous generation, such as hydropower, nuclear, coal, or natural gas-fired resources. But, according to NERC, the rapid integration of IBRs is “the most significant driver of grid transformation” on the bulk power system. 

In certain circumstances, IBRs can behave differently than synchronous generation. While IBRs produce power like synchronous generators, they do not react to grid disturbances in the same way. 

For example, FERC said that where synchronous resources not connected to a fault would automatically ride through a disturbance, IBRs must be programmed to do so. There have been at least 12 events on the bulk power system – with an average loss of approximately 1,000 MW of IBRs – which have demonstrated common mode failures of IBRs acting together unexpectedly in response to normally cleared transmission line faults, FERC said. 

“Such common mode failures of IBRs exacerbated the reliability impacts of the underlying disturbances,” it said.

The NERC-documented events demonstrate that the potential for IBRs to have a material impact on the bulk power system is not limited to larger IBRs that are typically required to register with NERC. They also “demonstrate the challenges to transmission planning and operations” posed by IBRs that may not currently be required to register with NERC. Further, these events demonstrate the challenges to planning and operating the bulk power system posed by gaps in reliability standards specific to IBRs.

Inverter-based resources do not reaction to grid disturbances the same way as synchronous generating resources do.

FERC said directives in the draft order, and proposed directives in the draft notice of proposed rulemaking, are supported by at least seven NERC event reports, two NERC Alerts, three NERC-issued reliability guidelines, as well as other technical reports and white papers.

Proposed actions

FERC said its actions would address both “observed and future impacts” of IBRs on the reliable operation of the bulk power system. 

Item E-1 is a draft order directing NERC to submit within 90 days a work plan for FERC approval describing how NERC plans to identify and register owners and operators of bulk power systemystem-connected IBRs that are not currently required to register with NERC but that have a material impact on the grid’s reliable operation. It said that many IBRs connecting to the grid do not meet the current bulk electric system definition and, thus, are not registered with NERC. This means that those IBRs are not required to comply with mandatory reliability standards or respond to NERC Alerts. 

The draft order directs NERC to do three things. 

First, to complete modifications to its registration processes no later than 12 months after FERC approves the work plan. 

Second, to identify all owners and operators of Bulk-Power System-connected IBRs that in the aggregate affect the reliable operation of the bulk power system no later than 24 months of FERC approval of the work plan. 

And third, to register owners and operators of grid-connected IBRs that “in the aggregate have a material impact on the reliable operation” of the grid no later than 36 months after FERC approval of the work plan. 

FERC said its draft order recognizes that smaller IBRs may not present the same reliability impact in all circumstances as generation that has historically been registered. It said that NERC “may determine that the full set of Reliability Standard Requirements otherwise applicable to generator owners and operators need not apply” to all newly registered grid-connected IBR generator owners or operators.

Inverter-based resources are an increasingly visible component on the bulk power system.

Item E-2 is a draft notice of proposed rulemaking preliminarily finding that the reliability standards do not fully address the impacts of IBRs on the reliable operation of the grid. It proposes to direct NERC to develop new or modified Reliability Standards that address four reliability gaps related to IBRs. 

First, data sharing: currently, IBR owners and operators do not consistently share IBR planning and operational data, and the information that is shared is often inaccurate or incomplete. 

Second, model validation: once planners have IBR data, they must ensure the accuracy of such data to create valid system models. 

Third, planning and operational studies: once planners and operators validate system models, they must include those models in planning and operational studies to assess the reliability impacts—both of individual and collective IBRs—on Bulk-Power System performance. 

And finally, performance requirements, such as IBRs’ ability to ride through system disturbances. 

The draft notice of proposed rulemaking proposes to direct NERC to submit a compliance filing within 90 days of the effective date of the final rule detailing a comprehensive standards development and implementation plan explaining how NERC will prioritize the development and implementation of new or modified Reliability Standards to address these four reliability gaps. 

The draft notice of proposed rulemaking explains that NERC’s plan should take into account the risks posed to the reliable operation of the Bulk-Power System, standard development projects already underway, resource constraints, and other factors as necessary.  Comments in response to the draft proposed rule would be due 60 days after the date of publication in the Federal Register, with reply comments due 30 days later.

More information is available here.