IEEE Power & Energy Magazine - January/February 2016 - 91

The smart grid is a complex system of systems,
serving the diverse needs of
many stakeholders.

FDEMS to handle DER systems located at utility sites
such as substations or power plant sites.
✔ Level 3 Third Parties: Retail Energy Provider or Aggregators (red in Figure 8) shows market-based aggregators and
retail energy providers (REP) who request or even command DER systems (either through the facility's FDEMS
or via aggregator-provided direct communication links) to
take specific actions, such as turning on or off, setting or
limiting output, providing ancillary services (e.g., volt-var
control), and other grid management functions. Aggregator DER commands would likely be price-based either to
minimize customer costs or in response to utility requirements for safety and reliability purposes. The combination
of this level and level 2 may have varying scenarios, while
still fundamentally providing the same services.
✔ Level 4 Utility Operational Grid Management (yellow in Figure 8) applies to utility applications that
are needed to determine what requests or commands
should be issued to which DER systems. Distribution
system operators (DSOs) must monitor the power system and assess if efficiency or reliability of the power
system can be improved by having DER systems modify their operation. This utility assessment involves
many utility control center systems, orchestrated by the
Distribution Management System (DMS) and including
the DER database and management systems (DERMS),
geographical information systems (GIS), transmission
bus load model (TBLM), outage management systems
(OMS), and demand response (DR) systems. Transmission system operators (TSOs), regional transmission
operators (RTOs), or independent system operators
(ISOs) may interact directly with larger DER systems,
and/or may request services for the bulk power system from aggregated DER systems through the DSO
or through the REP/aggregators. Once the utility has
determined that modified requests or commands
should be issued, it will send these either directly to a
DER system, indirectly through the FDEMS, or indirectly through the REP/aggregator.
✔ Level 5 Market Operations (purple in Figure 8) is the
highest level and involves the larger utility environment where markets influence which DER systems
will provide what services. The TSO markets are typically bid/offer transaction energy markets between
individual DER owner/operators and the TSO. At the
distribution level, the markets are not yet well formed
january/february 2016

and, over time as they evolve, may be based on individual contracts, special tariffs, demand response signalling, and/or bid/offer transaction energy markets.
The definition of these five levels does not mean that all
scenarios will use all of them. For instance, small residential PV systems may not include sophisticated local energy
management systems (FDEMS), while large industrial and
commercial sites could include multiple FDEMS and even
multiple levels of FDEMS. Some DER systems will be managed by REPs through DR programs, while others may be
managed (not necessarily directly controlled) by aggregators
and utilities through financial and operational contracts or tariffs with DER owners. Within these levels and the different
stakeholders, there are many different possible information
exchanges (as illustrated by the circled numbers in Figure 8).

Developing Distributed Resource
Information Models
As can be seen from the number of interfaces introduced with
distributed resources in the architecture, the amount and types of
data being exchanged can be huge. If standards are not provided,
then chaos could reign as different vendors and users implement
different protocols with different definitions of the data being
exchanged. Similarly, using different communication protocols
between different DER systems and different utilities or facilities
would make interoperability impossible. The first step in providing interoperability is to define a standard information model. An
information model is the standardized collection of data objects
that have well-defined names and structures (ontology). In the
power industry, two main information models have been developed: IEC 61970/61968 (the CIM) and IEC 61850. The CIM is
used primarily at the enterprise level, and IEC 61850 is used primarily between control centers and field equipment.
Initial work on the required information models for distributed resources has been done within the IEC 61850 framework,
but these information models can also become the framework
for communications with DMSs and related enterprise applications. Then, these models become the basis of information
exchanges and messaging in the CIM to facilitate integration at
the systems level. This work has been done within IEC TC57,
Working Group 17, and has been ongoing since 2004. The first
set of definitions was provided in IEC 61850-7-420:2009 for
the basic DER functions. More recently, information models
were developed that allow the integration of "smart inverters"
and published as IEC 61850-90-7. These basic information
models have been mapped to other protocols, such as IEEE
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Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - January/February 2016