IEEE Power & Energy Magazine - November/December 2021 - 49

At what point is it better to break from trying to replicate
synchronous machine features and exploit the wider
flexibility of inverters?
methods that underpin their power system planning and operating
decisions. They also will dictate the development of new tools and
methods to ensure the system's reliability, security, and stability.
Therefore, analytical tools must be developed to help evaluate the
operation of a power system with a large number of IBRs.
IBR models pose a challenge in that there are various proprietary
control schemes across manufacturers. Depending on the
type of stability modeling conducted, existing generic models
may not be adequately detailed to capture their behavior under
a variety of grid conditions. As IBR penetrations increase, the
converging issues of appropriately designing and modeling IBR
responses and integrating these tools into planning and operation
practices will become increasingly pressing.
Even in high-IBR scenarios with no fossil-fueled generation,
many power systems will still operate with synchronous
machines at least part of the time (e.g., with nuclear, hydropower,
geothermal, or hydrogen-fired plants). New stability
tools and methods will need to be fully integrated into existing
ones, which are part of the system operator " toolbox, "
to conduct analyses in planning and operating time frames.
Such stability tools must be configured to allow system operators
to switch seamlessly from synchronous to asynchronous
analyses as generation shifts over time.
The use of these tools in long-term planning and online
applications may face computational limitations that require
additional hardware, software, refinements, and approximations
to make them tractable while maintaining accuracy.
Ensuring that proposed solutions are scalable and that they
adequately cover the diversity of power system contexts and
IBR designs are two of the main issues to be solved as new
methods and tools are developed.
The Stability Tools and Methods Research Program (Table 3)
focuses on understanding the limitations of existing tools and
methods. It also deals with developing new and/or improved
tools and methods to identify potential reliability, security,
and stability issues and the associated least-cost solutions in
future power systems. These tool sets will focus on core stability
issues with the ability to evaluate small- and large-signal
stability. Ultimately, they would have to cover an entire suite of
prospective issues, including frequency stability, frequencydomain
profile (eigenvalue analysis), protection equipment
performance in reduced short circuit power systems, network
reduction, power quality assessment, and other dimensions.
The research program attempts to yield both 1) new
methods that can be implemented as new capabilities within
existing tools for detecting incipient instabilities and 2) new
analytical tools for detecting instabilities and other foreseen
november/december 2021
power system issues, using both legacy and new methods for
assessment. New tools would need to take traditional concepts,
related to dynamic stability, plus newer concepts, related to
IBR control interactions and system strength, and merge them
with concepts of economic dispatch and unit commitment.
A Much More Complex System
to Control
The increasing roles of inverters, highly distributed VRE generation,
storage, and DERs bring a complex control challenge
unlike anything seen before in the bulk power system. Many
variables need to be observed at faster rates and controlled in a
much more dynamic and stochastic environment, including the
potential for large-scale common-mode failures. The control
room of the future thus must be able to manage significantly
higher volumes of data to be quickly converted into actionable
information (via novel tools and methods). Furthermore,
table 3. Stability Tools and Methods Research
Program questions.
12) What approaches can be taken to near real-time system
modeling with large quantities of IBR that make design for
system stability sufficiently accurate and still tractable?
13) What methods can be used for offline and online
monitoring tools for detecting incipient instabilities? What
new capabilities are needed to address these limitations?
14) What type of online contingency and stability analyses
should be conducted at changing levels of IBRs?
15) What analytical tools and models should be provided
to planners and operators for robust assessment of system
performance?
16) What tools are needed for operational analysis of higherimpedance
grids?
17) What analytical methods and tools should be used to
determine the appropriate mix and capabilities of gridforming
and grid-following inverters to mitigate low-inertia
conditions for a given power system?
18) What are the appropriate analytical methods and tools
to determine-for a given power system-the extent to
which very fast frequency response can substitute for inertia.
Relatedly, what tools and methods are needed to effectively
compose a mix of Tf and df/dt responses?
19) What tools and methods are needed to identify the
best mitigation strategies for voltage-collapse problems
under high-IBR conditions? And how effective is the IBR in
recovering from deep voltage dips (bearing in mind lack of
short-term overload current)?
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IEEE Power & Energy Magazine - November/December 2021

Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - November/December 2021
