IEEE Power & Energy Magazine - May/June 2016 - 58

table 2. The definition of products.
Attribute

Wholesale/Transmission

Location

Point of receipt/point of delivery

Retail/Distribution
Street address

Products

Service delivery point (SDP)
Point of common connection (PCC)
Grid service supplied by DR-DER

Grid services by transmission
connected resources

Response time

Capacity

Milliseconds

Increase

10 min

Energy

Decrease

60 min

1 min

Both

90 min

5 min

180 min

15 min

Balancing services

1 hour

5-min energy

Day ahead

Day ahead, real time

Ancillary services
*

Nonspin, spin, regulation

Direction

Duration

Frequency response

Even at the wholesale/bulk-power level, some of the conventional grid services (ancillary services) are being revisited to
address operational issues related to increased levels of renewable generation. For example, the regulation and frequency
response service that has been a standard tradable product both
in ISO/RTO markets and in bilateral wholesale markets for the
last two decades is now bifurcated into two products, regulation and primary frequency response, per FERC Orders 794 (16
January 2014) and 819 (20 November 2015).
Regardless of standard or nonstandard distribution grid
services, the prosumer-side assets are perfectly capable of
providing these wholesale grid services. In fact the new primary frequency response service may be easily provided
through local DER controls to operate autonomously with
no need for DSO instructions.

seasonally, whereas that of a VPP may change hourly or
even subhourly. As another example, a VPP comprises
a large number of residential electric water heaters may
have a high P max in the morning hours but a low P max
during the work hours of a weekday when residents are
not home.
The same may apply to other resource parameters such
as Pmin and ramp rate. The scheduling and dispatch of a VPP
must take these variations into account but will otherwise be
similar to that of conventional resources. The deployment
of VPPs is based on economic bids and offers at the distributed resource level offered by the transactive agents. These
bids and offers may be aggregated into VPP bids and offers
on par with conventional resources being scheduled or dispatched by the system operator.

Scheduling and Dispatch of Demand-Side
Resources for the Provision of Grid Services

Distribution Constraint
Management by the DSO

One approach for the provision of grid services from distributed resources is to aggregate these distributed assets in
the form of virtual power plants (VPPs). These VPPs will
exhibit characteristics similar to conventional power plants,
while taking into account the temporal and geographical attributes and constraints of these resources, as well as
any distribution system constraints, contractual limitation
related to demand-side programs, and bids and offers from
demand-side intelligent devices or agents. This will allow
for the direct mapping and management of grid services provided by demand-side resources to established bulk-power
products and services.
The parameters of a VPP change with time more frequently compared to those of a conventional generation
resource. For example, the net dependable capacity (P max)
of a conventional generating unit or power plant changes

Transmission congestion management is central to transmission open access. Under the bilateral market paradigm,
the control area operator (balancing authorities) must resort
to schedule curtailments, when necessary, to manage transmission congestion. Transmission capacity reservations
with different priority levels provide the mechanism for
congestion management. Similar concepts may be applied
to the distribution system. For example, with the emergence
of plug-in EVs, a distribution circuit may not be able to
serve all EVs in a neighborhood simultaneously. The TE
systems paradigm attempts to resolve the situation through
the submission of bids and offers by the EV owners among
themselves for the use of limited distribution capacity. A
broader scheme may involve distribution capacity reservations administered by the DSO with different priority levels established based on various criteria such as reservation

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