IEEE Electrification - September 2021 - 70

controllers. Similar stability problems can be seen in a
Banshee grid. In the next section, I briefly summarize the
modeling and control in energy space which overcome
these problems.
Microgrid Control for TEM Implementation
An interesting opportunity exists to enhance microgridenabled
controlled participation of DERs in the transactive
energy management (TEM). It was recently recognized that
this participation must account for potential voltage problems
that can be created as a high number of grid users
responds to the electricity price. The IEEE 8,500 distribution
feeder as a representative future microgrid with lots of
solar rooftops, some storage, and controllable behind-themeter
technologies, HVACs, and EVs, was used to demonstrate
how these can participate in electricity service and
help the local distribution company. In other words,
microgrid control helps administer TEM as one way of
implementing retail electricity markets. Having well-functioning
neighborhood microgrid controllers that aggregate
many small end users with a high penetration of solar
rooftops and EVs, like in California, with approximately
8 GW of such power, and Hawaii could enable seamless
integration of DERs in support of clean electricity services.
At present, these DERs are mainly considered to be an
uncertain component of system demand seen by the BPS.
The U.S. National Institute of Standards and Technology
report describes an important study, which demonstrated
the complexity of voltage control in these emerging
microgrid applications. In particular, voltage control can be
implemented by the solar rooftops themselves, if there is
additional storage at their locations (clusters of EVs, thermal
storage, controllable appliances). Notably, the most
effective-technically and economically-outcomes greatly
depend on the type of price signals sent to the DERs participating
in TEM. It was shown that the outcomes are very
different when microgrid components are given flat tariffs,
time-of-use, or dynamic pricing. The results of these
detailed studies reported by several teams should be investigated
when taking into consideration microgrid control
in support of retail markets while trying to ensure reliable
and resilient service.
Microgrid Control for Implementing Network
Optimized Distributed Energy Systems
Finally, microgrid control plays a major role as an enabler
of residential end user participation in synthetic reserve
for ancillary services. In addition to utilizing clusters of
EVs and household appliances for participating in feedforward
electric energy markets, the grid-edge components
can contribute significantly to balancing slow
hard-to-predict power imbalances. These " synthetic regulation
reserves " (SRR) could offset need for deploying new
expensive storage and for using more conventional generation
for frequency and voltage regulation. The performance
specifications for these functions are much
stricter because of time criticality and it is important to
design end-to-end microgrid control with these specifications
in mind. For example, the burden of ensuring that
the committed SRR is implementable could be put on
TABLE 2. The Potential of nonlinear plug-and-play primary controllers.
Challenge Problem
State-of-the-Art Control Primary Control
Case S1 (Sheriff, high load,
low PV power)
Stable; does not settle to the right voltage
w/o returning; induction motors when
simulated result in poor voltage profile
Case S2.1 (Sheriff, islanded feeder 1) Stable; settles to right voltage if tertiary
control set points are accurate; dynamic
loads when used result in poor voltage profile
Case S2.2 (Sheriff, islanded feeder 2) Stable; grid-forming mode requires either
lot of tuning or requires proper selection of
filter parameters to ensure current evolves
much faster than voltage; switches might hit
saturation for large disturbances
Case S2.3 (Sheriff, islanded feeder 3) Stable; short line model when used can
result in over-voltage; large in-rush current
produced by induction motors results in poor
voltage profile
Case S3 (Sheriff, reconnecting)
Stable; but the load is not served; might
also damage loads because of sudden drop
in voltage; sensitive to control gains on
generators and solar PV
Energy-Based Plug-and-Play Primary
Control (with Microgrid Control)
Stable; voltage profile around 1 p.u. is
ensured by generators readjusting their
power output
Stable; voltage profile is good irrespective
of the load model used
Stable; doesn't require any island detection
loop for different modes of operation.
Same control can be used in all of the
modes
Stable; regulates voltage irrespective of
the line/load model
Stable; desired load is always served as
the generators reschedule themselves
during sudden islanding and ensure good
voltage profile with overshoots being
within the protection limits
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IEEE Electrification Magazine / SEPTEMBER 2021
IEEE Electrification - September 2021

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