In the June 4, 2024, meeting of the Interconnection Process Working Group (IPWG) stakeholders were invited to review and submit feedback on Recommended GFM BESS Requirements (PAC-2024-2).
Specifically, MISO seeks feedback on details of MISO’s proposed requirements and simulation test approach, which could include input on:
Please provide feedback by June 28, 2024.
AES Clean Energy appreciates the opportunity to comment on the Grid-Forming Battery Energy Storage Capabilities, Performance, and Simulation Test Requirements Proposal whitepaper. AES supports the initial requirements only applying to stand-alone BESS projects on a forward basis. AES also agrees that applying such requirements to hybrid projects is more complex. If MISO considers extending these requirements to hybrid projects, AES encourages MISO to consider separate requirements for DC-coupled vs AC-coupled projects, and potentially exempt some requirements for the PV inverters of an AC-coupled system. AES expects that MISO would run a similar stakeholder process to determine the requirements for hybrid systems and looks forward to engaging with MISO and other stakeholders in these future endeavors.
AES generally supports the Voltage Source Capability Requirements outlined on pages 15-16 of the whitepaper. However, AES recommends that MISO modify the requirement that “the GFM IBR should naturally respond in a few milliseconds, achieving full response time in <50 milliseconds depending on the nature of the event”. In AES’s experience, it has found that response times under 10 milliseconds are unlikely, but a response time between 20 to 50 milliseconds is. Additionally, MISO is proposing to require “the conformity test will assess simulated performance with an SCR as low as 1.25” (pg. 15). In AES’s experience, an SCR below 2.0 is highly unlikely and hasn’t been observed to date in system in which we operate assets. Has MISO observed an SCR below 2.0? What justification can MISO provide for testing at an SCR below 2.0?
AES appreciates MISO’s responsiveness and consideration of our prior comments on how IEEE 2800 requirements might need to be modified for Grid following vs Grid forming IBRs. AES supports the exemptions outlined in Table 2 on page 20 of the whitepaper. However, AES requests more details on if MISO will specify alternative standards that the resource must conform to, especially on the ride-through and voltage injections, if they are exempted from the Section 7 subclauses?
On the data requirements and documentation section on page 23, AES requests more information on the test procedure check list to be able to review and provide additional feedback on. AES also requests further clarity on the 4th bullet, “Model documentation describing functionality and operation of resource and model”, whether customers need to provide plant-level documentation?
On page 25, MISO states that “the GFM IBR protection settings shall be set as wide as possible within equipment capabilities and ratings”. Can MISO provide a more specific range/details to define “as wide as possible”? How would this requirement align with PRC 24?
For Test set-up A on page 25-26, AES requests MISO to provide more details on the synchronous machine model you would like customers to use? Could MISO provide the data file for the detailed model? For PSSE, could MISO provide the DYR with all parameters, and for PSCAD could MISO provide the library with synchronous machine/model they would like customers to utilize?
AES appreciates MISO providing more details on the conditions for each case for the loss of last synchronous machine test as summarized in Table 5. AES recommends MISO take out Case 1 from the list because several other Cases would capture the impacts of this Case. Case 2 reflects a bigger ramp up of the resource, and Case 4 would cover the discharge in range of Case 1, therefore Case 1 would not provide any additional information not already captured in other cases.
On page 28, could MISO provide more examples or clarity on “post-trip: c. Final voltage is expected based on droop and deadband settings”. What specific droop and deadband settings are MISO proposing? Could MISO provide examples of pass/fail and how to calculate the settings? AES also requests more information on how MISO plans to define “Post-trip: f. oscillations is adequately damped.” Is there a certain damping ratio MISO would like the resource to achieve? Similarly, for the ROCOF success criteria on page 29, could MISO provide more details on “d. Oscillations should be adequately damped”?
On page 30, MISO outlines the phase jump test sequence. AES requests more information on how long between each test sequence must the resource be in steady state. Can MISO be more specific on what they mean be a “a few seconds later”?
AES reiterates its prior comments that a 60-degree phase change is outside the realm of likelihood, and far beyond the IEEE 2800 requirements. AES request MISO provide further justification on why it believes a test of a 60-degree phase jump is warranted. AES believes that stopping the test at 30 degrees would provide results of more realistic grid conditions that might be observed in operations and is in compliance with IEEE 2800.
AES continues to believe that a SCR ramp down with fault test sequence below 2.0 is unnecessary, and unlikely to ever be observed in operations. AES continues to request that MISO provide justifications on why testing below 2.0 is necessary and whether it has observed an SCR below 2.0 in operations.
AES appreciates the thought MISO has put into this whitepaper and looks forward to continuing to work with MISO staff and stakeholders to develop GFM requirements for BESS resources.
MISO presented proposed performance requirements, simulation test success criteria and IEEE 2800 integration approach for grid forming (GFM) controls for battery energy storage (BESS) at the June 4 IPWG and posted an initial whitepaper. The MISO Transmission Owners (Owners) support establishing GFM requirements for BESS and generally support the framework MISO has proposed. The Owners see value in these capabilities and support the implementation of GFM requirements for BESS as soon as practical.
The GFM requirements in this whitepaper are limited to stand-alone energy storage devices. It is unclear what “potential complexities” would need to be overcome to expand GFM requirements to include comparable systems added through hybrid and surplus interconnection processes. The Owners recommend further information to fully comprehend the problems and are in favor of requiring all BESS to have GFM functionality.
The OMS Transmission Planning Work Group (TPWG) provides this feedback to MISO on its recommended requirements for Grid-Forming (GFM) Battery Energy Storage Systems (BESS). This feedback is from an OMS work group and does not represent a position of the OMS Board of Directors.
The TPWG appreciates MISO’s issuance of the June 2024 Draft Whitepaper on GFM BESS Capabilities, Performance, and Simulation Test Requirements Proposal. The TPWG requests that MISO respond to the following questions in due course:
Clean Grid Alliance Comments on Recommended GFM BESS Requirements (PAC-2024-2)
June 28, 2024
At the June 4, 2024 meeting of the Interconnection Process Working Group (IPWG), stakeholders were invited to review and submit feedback on Recommended GFM BESS Requirements (PAC-2024-2).
Clean Grid Alliance appreciates the opportunity to further emphasize that storage is just getting started on the MISO system and is not being appropriately compensated for the many reliability services it provides. The MISO market did not initially contemplate such a fast acting reliability resource that can respond to and prevent blackouts that initiate within a fraction of a second. Battery storage provides a multitude of reliability functions and benefits that MISO does not recognize nor compensate for but will significantly benefit from.
Battery storage has been held back from coming online in the MISO system due to multiple policy barriers such as the MISO requested delays to implementation of a storage market participation model, and inaccurate dispatch in planning studies leading to unnecessarily high cost Network Upgrades that remove the arbitrage value storage depends on, among other barriers. Battery storage is a grid resource to be encouraged through financial compensation and acknowledgement of its value, not targeted for additional costs and requirements to prevent it from coming online.
CGA again emphasizes that grid forming inverters should not be mandatory for energy storage, but elective and compensated. Furthermore, any new requirements, if appropriate, should not apply to projects that have already entered the MISO queue process.
Grid forming capability, which offers near instantaneous frequency and voltage support, is not free as MISO has suggested in stakeholder meetings it might be. It comes at an additional cost and should be compensated to balance not just the cost but the benefit of the service it provides. Suppliers, such as SMA, are open about charging a higher premium for GFM inverters as they are overall more complex and require a different site sizing and hardware overbuild to offer the GFL services. Operating in Grid-Forming mode impacts the power rating, operating current, and the state of charge. MISO’s performance requirements should incorporate and consider these impacts, which are currently lacking.
Tesla has supplied GFM equipment in Australia and while an initial claim was made in a presentation at the ESIG technical workshop in March 2024 of “just a software switch”, a few slides later noted “it costs money to implement and thus requires a market and compensation”. Capabilities expected to result in hardware oversizing are short circuit current, black start, power quality support, and specified amounts of inertia, among other capabilities. Additionally, a de-rating of the unit is generally required to provide for GFM services, which also comes at a financial cost. For a BESS to run in GFM mode much more is required than just a software change and there are costs associated.
Even if capital costs were not higher, which they absolutely are higher, the testing aspect of the proposed requirement has costs associated with it.
In Australia, a location MISO has modeled some of its proposed GFM technical requirements after, all resources, regardless of type, are required to provide stability service (which can be met with GFM inverters) or they can purchase it. Energy storage is not singled out from thermal or other resources.
We encourage MISO to give serious consideration toward implementing a robust compensation mechanism that (financially) acknowledges the unique reliability services energy storage provides, and at the very least, to not further penalize or implement additional barriers to bringing storage on its system. There are additional costs associated with grid forming inverters that would be better suited for elective implementation through financial compensation, rather than singling out energy storage for required/mandatory higher costs. Energy storage in MISO has already faced significant policy barriers and hence why very little is interconnected in the MISO footprint today.
Sincerely,
Rhonda Peters, Ph.D.
Technical Consultant for Clean Grid Alliance