IEEE Power & Energy Magazine - November/December 2021 - 27

Power System Needs
From the various examples around the world, it is clear that
the observed stability issues are due to increasing GFL IBR
penetrations combined with specific local system characteristics.
These challenges can be addressed by various means
as described in the previous sections. Moving forward, a
more holistic approach is necessary to lay out a process for
developing grid services based on system needs.
First, system requirements change with IBR penetration
levels and should be identified based on penetration
scenarios, considering changes in policy targets and economic
assumptions, future load composition, and network
topology. System operators must also identify critical disturbances
that a system has to withstand. Such reference
scenarios are driven by system characteristics, such as
the RoCoF, inertia, and system strength, which may be
determined on a network, regional, and local level. Reliability
studies using suitable tools should then determine
the scope of the minimum performance requirements and
functionalities to operate the system stably and within
expected voltage and frequency limits during normal and
contingency events.
Second, the identified functionalities should be specified
in a technology-neutral manner, translating system
needs into quantifiable contributions that can be provided by
resources and network components, including the following:
✔ physical quantities to detect disturbances, for which
a device should only ride through or provide support
(how this quantity should be measured and during
what period)
✔ robustness requirement (conditions under which a device
should ride through)
✔ grid support requirement (conditions under which grid
support services should be provided)
✔ response characteristics (magnitude and duration)
✔ compliance verification requirements (how the specified
performance should be tested).
Establishing these performance requirements in a technology-neutral
and quantifiable manner enables network
participants to provide the necessary support services. A technical
and commercial tradeoff is needed between marketbased
solutions and mandatory requirements. In all cases,
clear, consistent, and justified performance requirements are
critical for ensuring reliable BPS operation to keep up with
changing system needs and new technologies.
Tools
New modeling practices and tools are needed to ensure
that the reliability and security of the grid evolve. Declining
system strength, inverter control interactions, and
control instabilities necessitate advanced modeling techniques,
such as EMT, real-time simulators, and hardwarein-the-loop
simulators. These tools are emerging for
modeling larger portions of the grid and even entire interconnections.
Australia is using an EMT model of its entire
november/december 2021
network for operational planning studies. Similarly, Texas
and New England have developed EMT models of large
portions of their networks with high IBR concentrations
to evaluate stability limits. Real-time simulators are being
used by the New York Power Authority to study control
and protection elements.
New approaches are emerging, such as the use of " real
code " models incorporating the exact code used in equipment.
IEEE and the International Council on Large Electrical
Systems are leading an effort to standardize real code
models to ensure confidentiality and improve usability, compatibility,
and interoperability. The need to harness these
tools is driving the necessity for improved models, study
techniques, and hardware and software capabilities. The
first step in enabling the use of these tools is establishing
requirements for necessary models early in the interconnection
process. Once suitable models are provided and verified,
they can be employed to identify stability issues. Entities
around the world are improving their requirements for models
and study processes to enable advanced, computationally
intensive, yet necessary study techniques at transmission
and distribution levels. Australia is continuously improving
such requirements, and there is a significant effort in North
America to develop similar practices.
One such achievement is a " virtual EMT lab " facility.
This is where the grid is modeled in EMT for parallel
computing on multicore computers. Various suppliers can
remotely add black-boxed EMT models of their IBR(s) to
the EMT grid connection buses and have full remote control
over their IBR settings and operation. IBR suppliers usually
cannot obtain nondisclosure agreements with competitors,
but this provides a way for them to remotely optimize their
application. No one can change the model but the supplier,
and other suppliers cannot see one another's IBRs and performance.
An independent operator in the lab coordinates
IBR operations with each supplier. This enhances rapid solutions
to grid instability and adverse interactions and maintains
security for the IBR suppliers.
Another advance in simulation techniques is the use of
cosimulation methods, where different tools (for example, phasor
domain and EMT simulations) are coupled and exchange
information to effectively study time frames of interest. These
methods are computationally intensive and call for highperformance
computing. Improvements to and the standardization
of these techniques are being researched. Conventional
simulation methods should still be used where appropriate.
Summary and Recommendations
As the generation mix evolves, system services that were
inherently provided by synchronous generators are becoming
scarce. The reduction of these intrinsic services tends
to weaken the grid, making it less able to tolerate the disturbances
that accompany the operation of any power system.
This may lead to stability concerns, primarily related
to low-system-strength conditions and a high RoCoF after
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IEEE Power & Energy Magazine - November/December 2021

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