IEEE Electrification - December 2022 - 11

relationships to each other (Figure 2). For example, owners
of distributed energy resources (DERs) in California are
increasingly participating in the wholesale energy market
as aggregated entities, especially after the U.S. Federal
Energy Regulatory Commission approved Order 2222 to
enable DER aggregators to compete in all regional organized
wholesale electricity markets. As these or similar
arrangements become more common, the nature of the
challenges will evolve.
Under the current grid edge paradigm, the largest priority
at the ISO/RTO scale is the day-ahead and intrahour
forecasting of the effect of grid edge BTM resources
on the load shape observed at the T&D interface. This
includes estimating not only the output of grid edge
generators, such as photovoltaic (PV) generation, but
also the behavior of load-shifting devices, such as batteries,
or load-creating devices, such as electric vehicles
(EVs). For ISOs, grid edge forecasting can substantially
improve market efficiency by improving net load forecasting
and by enabling more efficient procurement of
ancillary services. On the other hand, errors in output
forecasting can produce invalid grid state estimates and
limit reactive power, voltage control, and dynamic
responses to grid faults.
As with transmission planning, forecasting grid edge
behavior is also important to distribution operators to
maintain distribution grid balance, although generally on a
shorter timescale than that needed for ISOs. In addition,
distribution operators require some control over DER
behavior, such as peak shaving or volt/volt-ampere reactive
(VAR) control, and therefore, they must be able to design
and send signals (possibly through pricing) to DER owners,
and they must be able to determine whether the DER owners
comply. Further, grid edge resources often respond differently
from traditional grid components to grid faults or
parameter excursions, so the visibility of their response
characteristics (e.g., whether an inverter is equipped with
voltage or frequency ride-through capability) is important
for distribution operator contingency planning.
Note that although distribution operators and ISOs/
RTOs face similar varieties of challenges, the distribution
grid is substantially larger than the transmission grid, and
typically, it has a more complex topology that can change
with time. Further, grid edge resources generally exist only
along the distribution feeder, so the scale of grid edge
visibility problems (e.g., in terms of cost) is generally
larger for distribution operators than for ISOs/RTOs.
Although engaging distribution operators will be especially
important to address the gaps outlined here, this is
complicated by the increased cost and by the fact that
the value of grid edge visibility has not been as clearly
established at the distribution operator level as at the
ISO level. The engagement of distribution operators
must devote attention to demonstrating the value proposition
of grid edge visibility and how it can be obtained
within their budget requirements.
Resource owners currently face fewer challenges
related to grid edge visibility than RTOs or distribution
operators do. As their role develops, however, and as
resource owners participate more in the wholesale
energy market (possibly under an aggregator), they will
face new demands, including service guarantees and
flexibility requirements. This will require not only the
increased visibility of their own grid edge resources (to
ensure that the resource owner is complying with their
obligations to the wholesale power market) but also of
the local distribution grid to which they are connected
to minimize deliverability risks and to maximize marketability.
For example, in the case where an RTO issues
a dispatch to a DER under the control of a resource
owner or an aggregator, it is important that the controlling
entity can determine whether meeting that dispatch
is feasible within the constraints of its
distribution grid. This will require improved communication
and coordination between not only distribution
operators and resource owners but also distribution
operators and RTOs to ensure that that the grid edge
resources are being managed safely and efficiently.
IEEE Electrification Magazine / DECEMBER 2022
11
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IEEE Electrification - December 2022

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