IEEE Power & Energy Magazine - January/February 2014 - 53

higher power transfers but still not the full 200 mW. several
factors contributed to the use of a back-to-back dc link with
vscs. These included the weak ac connection, the need for
dynamic voltage support, the potential for wind generation in
the eastern UP, and the possibility of system separation, resulting in islanded operation in the eastern UP, which is not interconnected with neighboring ontario in canada. Black-start
capability was therefore an important selection criterion.
installing a vsc-based BtB hvdc link in line with the
138-kv transmission between the upper and lower peninsulas
provides the needed flow control, adds dynamic voltage support
from each terminal, and permits transmission lines between the
central and eastern UP to be closed and operated at their rated
voltages. This solves the loop flow problem without degrading
reliability. it is interesting to note that mackinac is a BtB hvdc
application embedded in a synchronous network. in other words,
mackinac is not normally an asynchronous interconnection, but
it can become one if there is a network separation between the
central and eastern parts of the UP following network contingencies. The hvdc link controls are therefore designed to transition
smoothly from synchronous to islanded or quasi-islanded operation. furthermore, to mitigate the chance of cascading outages
following loss of transmission lines, the dc link is controlled to
automatically alter its power flow in response to changes in the
measured phase angle differential across its terminals. This is
accomplished by emulating the ac line power flow characteristic. figure 9 shows the relative position of the dc link in the ac
network, along with a possible separation locus.

Conclusions
system restoration from black-start generation resources or
by connection to intact neighboring grid locations requires
advance planning, careful coordination, and close communication. The more widespread the area affected, the greater the
need for prioritized coordination among generators, transmission providers, load-serving entities, and system operators.
situational awareness is essential, not only to avoid or limit
the scope of such events but also to carefully manage the restoration process in a secure and timely manner. anything that
can be done to limit the outage extent or ease return to service
should be considered. This could include use of vscs for their
dynamic voltage support, controllability, and ability to connect asynchronously to adjacent grids or with intact islands
within the larger system. strategically placed and intelligently
controlled transmission elements with vscs can offer system
operators additional flexibility during network restoration.

For Further Reading
P. fairley. (2013, apr. 29). germany takes the lead in
hvdc-New developments in high voltage dc electronics
could herald an epic shift in energy delivery, IEEE Spectrum [online]. available: http://spectrum.ieee.org/energy/
renewables/germany-takes-the-lead-in-hvdc
m. marz. mackinac vsc hvdc flow control project design. presented at minnesota Power systems conf.,
january/february 2014

Nov. 2012. [online]. available: http://www.cce.umn.edu/
documents/cPe-conferences/miPsycoN-Papers/2012/
mackinacvschvdcflowcontrolProjectdesign.pdf
T. g. magg, m. manchen, e. Krige, e. Kandjii, r. Pålsson, and J. Wasborg. (2012). caprivi link hvdc interconnector: comparison between energized system testing and
real-time simulator testing. cigrÉ Paper B4 107 [online].
available: http://www05.abb.com/global/scot/scot221.nsf/
veritydisplay/c3e48f84c5ba0947c1257a8600268e61/$f
ile/caprivi%20link%20hvdc%20interconnector%20
comparison%20between%20energized%20system.pdf
P. lundberg, m. callavik, m. Bahrman, and P. sandeberg,
"Platforms for change: high-voltage dc converters and
cable technologies for offshore renewable integration and
dc grid expansions," IEEE Power Energy Mag., vol. 10, no.
6, pp. 30-38, Nov./dec. 2012.
d. a. N. Jacobson, P. Wang, c. Karawita, r. ostash, m.
mohadded, and B. Jacobson. (2012). Planning the next Nelson
river hvdc development phase considering lcc vs. vsc
technology. cigrÉ Paper B4-103 [online]. available: http://
www05.abb.com/global/scot/scot221.nsf/veritydisplay/51fb
b859a1d9aaf7c1257a860028e10b/$file/Planning%20the%20
Next%20Nelson%20river%20hvdc%20development%20
Phase%20considering%20lcc.pdf
y. Jiang-hafner and m. manchen. stability enhancement
and blackout prevention by vsc based hvdc. presented at
232 CIGRÉ Electric Power System Future Symp., Bologna,
italy, sept. 2011. [online]. available: http://www05.abb.
com/global/scot/scot221.nsf/veritydisplay/4de68025f7a4320
dc125791f003c1626/$file/0232_bologna_2011.pdf
P. l. francos et al, "first hvdc link between france and
spain," in Proc. CIGRÉ B4-5, SCB4 Colloq. 2011.
J. Pan, r. Nuqui, B. Berggren, s. Thorburn, and B. Jacobson. (2009, mar.). The balance of power. ABB Rev. [online].
pp. 27-32. available: http://www05.abb.com/global/scot/
scot271.nsf/veritydisplay/7bdc4f3d304cac51c125762d00457
f50/$file/aBB%20review_3_2009_72dpi.pdf
h. clark, a.-a. edris, m. el-gasseir, and K. epp "softening the blow-segmentation with grid shock absorbers
for reliability of large transmission interconnections," IEEE
Power Energy Mag., vol. 6, no. 1, pp. 30-41, Jan./feb. 2008.
y. Jiang-hafner, h. duchen, m. Karlsson, l. ronstrom, and
B. abrahamsson. hvdc with voltage source converters-a
powerful black start facility. presented at IEEE/PES Transmission Distribution Conf. Expo., apr. 2008. [online]. available:
http://search.abb.com/library/download.aspx?documentid=0
8Td0083&languagecode=en&documentPartid=&action=
launch&content=external

Biographies
Michael Bahrman is with aBB, raleigh, North carolina.
Per-Erik Bjorklund is with aBB, ludvika, sweden.
p&e
ieee power & energy magazine

http://www.cce.umn.edu/ http://www05.abb.com/global/scot/scot221.nsf/ http://http:// http://www05.abb.com/global/scot/scot221.nsf/veritydisplay/51fb http://www.www05.abb http://www05.abb.com/global/scot/ http://search.abb.com/library/download.aspx?documentid=0 http://spectrum.ieee.org/energy/

Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - January/February 2014