IEEE Power & Energy Magazine - September/October 2020 - 63

To get to the final numbers, relevant capital expenditures
for the additional converter capacity must be compared to
the relevant operational expenditures, hence, a reduction
in total redispatch cost over the operational lifetime. The
important parameters for an initial assessment are
✔ the converter cost in euros per additional megavolt amp
✔ the redispatch volume in megawatt hours and cost
in euros per megawatt hour and operational lifetime in years.
Redispatch energy volume and cost vary from year to
year and strongly depend on how the actual power grid
infrastructure can keep pace with changing power generation assets. For instance, in Germany, during 2014-2017,
the total redispatch volume ranged from 11.5 to 18.5 TWh,
and the average cost ranged from 19.40 to €26.70/MWh. In
this study, a constant redispatch cost of €23/MWh is taken
considering the average value of the time period from 2014
to 2017. If the grid development is fully deployed, the redispatch volume should decrease significantly (1.9-2.6 TWh is
projected for 2030 in the current network development plan,
when all of the HVdc links are scheduled to be in service).
The HVdc links have a conservative operational lifetime
of 25 years.
Additional converter ratings could be assumed to be roughly
€70,000 per additional mega volt-ampere. For higher active
power transfer by HVdc, the cables or overhead lines must
be designed accordingly to carry the higher currents, which
was not considered in our cost estimate.
From the case study the following recommendations can
be made.
✔ In highly congested grids, as currently experienced in
Germany, reactive power of up to roughly 25-30% of
the converter rating would help reduce congestion-related costs. Beyond that, it is more interesting to invest
in either additional active power capacity or a combination of active and reactive power.
✔ For less-congested grids, as projected for Germany in
2030, the benefit is lower than the additional converter
costs associated with the extra reactive power capacity. However, a minimum amount of reactive power
capability is required.
✔ In general, the case study confirmed the initial assessment that the steady-state reactive power capability
benefits are medium to low for redispatch reduction
from long, embedded HVdc systems. Depending on
the generation/load/reactive power and grid scenario,
extra active power capacity or a combination of both
active and reactive power capability is advantageous.

Summary
This article highlighted the various features an embedded
HVdc system brings to the legacy ac grid. Among others,
reactive power support from embedded HVdc can boost
active power transfer through the existing ac system. The
possible benefits from reactive power supply by HVdc termiseptember/october 2020

nal stations were discussed for cases of lack of local reactive
power and for cases of varying degrees of meshing, parallelism, and distance. Furthermore, the article described a fullyear simulation for 2030 for the German transmission grid
with the planned embedded HVdc links. The outcome was
that a minimum reactive power capability is vital; however,
extensive requirements should be avoided.

Acknowledgments
The authors gratefully acknowledge funding by the German Federal Ministry of Education and Research within the
Kopernikus Project ENSURE. The corresponding author is
Kevin Schönleber.

For Further Reading
M. P. Bahrman and B. K. Johnson, "The ABCs of HVDC
transmission technologies," IEEE Power Energy Mag., vol. 5,
no. 2, pp. 32- 44, Mar.-Apr. 2007. doi: 10.1109/MPAE.
2007.329194.
J. Pan, R. Nuqui, K. Srivastava, T. Jonsson, P. Holmberg,
and Y. Hafner, "AC grid with embedded VSC-HVDC for
secure and efficient power delivery," in Proc. 2008 IEEE
Energy 2030 Conf., Atlanta, GA, pp. 1-6. doi: 10.1109/
ENERGY.2008.4781042.
J. Danielsson, S. Patel, J. Pan, and R. Nuqui, "Transmission grid reinforcement with embedded VSC-HVDC," in
Proc. CIGRE U.S. Nat. Committee Conf., 2015. [Online].
Available: http://cigre-usnc.org/wp-content/uploads/2015/10/
G r id-Rei n for c ement-w it h-E mb e dd e d-VSC-H V D C
_2015-10-12.pdf
T. Meridji, F. Ceja-Gomez, J. Restrepo, and R. Azar,
"High-voltage dc conversion: Boosting transmission capacity in the grid," IEEE Power Energy Mag., vol. 17, no. 3, pp.
22-31, May-June 2019. doi: 10.1109/MPE.2019.2896689.
"Influence of embedded HVDC transmission on system security and AC network performance," CIGRE, Paris,
France, Tech. Rep. 536, CIGRE JWG C4/B4/C1, 2013.
"Commission Regulation (EU) 2016/1447 of 26 August
2016 establishing a network code on requirements for grid
connection of high voltage direct current systems and direct current-connected power park modules," European
Commission, Brussels, Belgium, 2016. [Online]. Available:
https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=
CELEX:32016R1447&from=EN

Biographies
Kevin Schönleber is with Hitachi ABB Power Grids
Research, Germany.
Alexandre Oudalov is with Hitachi ABB Power Grids,
Switzerland.
Athanasios Krontiris is with Hitachi ABB Power Grids,
Germany.
Peter Lundberg is with Hitachi ABB Power Grids,
Sweden.
p&e

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IEEE Power & Energy Magazine - September/October 2020

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