IEEE Power & Energy Magazine - March/April 2015 - 31

Generators (RfG) network code aims not only at pan-European harmonization of the requirements
but guaranteeing system security with a growing share of dispatchable as well as variable DERs.
As in Europe, renewable and distributed resources in many areas of the United States have
reached-or are presently reaching-levels at which conventional methods of interconnection are no
longer adequate. Because of this, codes and standards designed more than a decade ago to ensure safe
and reliable grid operation at low DER penetrations require updates. In an effort to learn from the
European experience, work is under way to update standards and codes to allow or require DERs to
support the grid rather than simply trip off-line at the first sign of trouble.
In California, where renewable penetrations
are the highest in the mainland United States,
electric utilities and industry stakeholders have
collaborated to develop new recommendations
for updates to California Public Utilities Commission Electric Rule 21 that would require
inverter-based DERs to support the grid in
various ways. IEEE has also passed an amendment to IEEE Standard 1547, which governs
U.S. DER grid interconnection systems. The
amendment, known as IEEE Standard 1547a,
permits DERs to remain connected to the grid over a much wider range of voltage and frequency levels
for much longer intervals than was previously permitted, effectively allowing voltage and frequency
ride-through. IEEE 1547a also permits DERs to contribute to grid voltage regulation for the first time. In
addition, a full revision of IEEE 1547 is under way; many stakeholders expect it will not just allow but
require DERs to ride through a range of faults and assist with grid voltage and frequency regulation. In
response to both Rule 21 and the IEEE 1547 updates, efforts are under way to update UL 1741-the test
standard most DERs are required to comply with-to include testing of advanced grid support functions.
This article describes the advanced functions and control modes currently being implemented in
DER power converters. It presents the facilities and features of new test labs that have recently been
built in Europe as well as the United States to facilitate the testing and certification of new DERs with
advanced grid support functions. Case studies from three different labs highlight the testing methods
and principles applied for the validation of key functionalities. Last, the collaborative work being undertaken within the Smart Grid International Research Facility Network (SIRFN) is presented. This global
network of laboratories coordinates international efforts to design harmonized test protocols to characterize the interoperability and advanced functionality of DERs.

images licensed byingram publishing

Verifying That Smart
Grid Power Converters
Are Truly Smart

New Features of DER Power Converters
Traditionally, DER inverters (dc to ac) and power converters (dc to ac and vice versa) were designed to
convert the primary dc power provided by sources such as solar photovoltaics (PVs) or batteries to gridsynchronized ac. The main design goal was to achieve this fundamental purpose as efficiently as possible, meeting the standard limits for harmonic and other disturbances to avoid any detrimental effects on
the local distribution system. In addition, the inverters were required by local standards and grid codes to
provide safety and protection features such as interface protection and anti-islanding. The protection settings were commonly determined so as to achieve an immediate disconnection of the DER system from
the grid under any abnormal condition, an approach known as "disconnecting at the first sign of trouble."
At low DER penetration levels, these basic functionalities were still adequate to ensure safe and
reliable operation of the DERs and the distribution system. But with massively increasing numbers
and growing capacity, unmanaged DERs increasingly challenge traditional power system management.
To resolve these issues, new grid codes and interconnection agreements increasingly demand that
DERs provide advanced control capabilities and defined responses during critical grid conditions. In
this context, "smart" DERs inverters that provide a wide range of advanced functions will be the key
enabling technology for increasing the hosting capacity of distribution systems and ensuring stable
and reliable operation of the overall power system even with a massive share of DERs.
State-of-the-art DER inverters can provide a broad range of features, supporting the grid through
autonomously controlled and remotely commanded operating modes. Today, their capabilities already
go far beyond what is actually required by interconnection specifications.
march/april 2015

ieee power & energy magazine

Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - March/April 2015