IEEE Electrification Magazine - December 2019 - 68

TABLE 2. A summary of control techniques

for the emulation of inertia.

Synchro- Inherent
nization Current
Technique Unit
Limitation Complexity Flexibility
ac
systems
IE

✓

Low

Medium

Low

CCVSM

✓

Medium

High

VCVSM

✓

High

✓

Low

Medium

DVC

Low

VC2

✓

High

VDCM

✓

Medium

High

SIE

DIE

✓*

✓

Medium

High

dc
systems

ICs

*Only if connected to an ac grid.
** Depending on which technique is used, the properties will be different.

xx
Analysis of the effects of synchronization units in IE tech-

niques for ICs: Synchronization units are required in ac
grids to measure frequency. Such units are not needed,
however, for measuring dc voltage. Challenges arise
when the IC is interfacing an ac and a dc grid and using
a DIE technique, because the IC might react to the voltage and the frequency derivatives at different instants
because of the synchronization unit. One approach to
avoid this problem might be to employ IE techniques
that do not rely on the measurement of the voltage or
the frequency. Another approach is to compensate the
delays of the synchronization unit so that the IE at the
ac and dc part are carried out adequately.
xx
Development of the implementation aspects of DIE techniques for their integration into IC microcontrollers: It is
important to identify and address the challenges that
arise on a real implementation when an IC is connecting different types of grids because the characteristics
of such grids can condition an adequate control.
xx
Adaptation of synchronous machine model-based techniques (such as SV, VSM, or MC techniques) to consider
dynamic perturbations on both sides of ICs: It would be
interesting to use this type of technique for the emulation of inertia at both sides of the IC instead of
employing an IE technique based on the derivative of
the voltage or the frequency. In addition to avoiding

I E E E E l e c t r i f i cati o n M agaz ine / DECEMBER 2019

the derivative terms and excessive filtering in the controllers, in some cases, it would also be possible to
avoid the necessity to synchronize with the grid to
carry out the emulation of inertia.
xx
Evaluation of parallel-connected ICs with IE techniques:
Usually control techniques for the emulation of inertia have been studied for systems interfacing a generation or a storage system connected to the grid.
However, the interactions between parallel-connected
ICs equipped with IE techniques also need to be thoroughly analyzed. Moreover, new methodologies or
criteria are still required for determining the size of
ICs and the tuning of their control algorithms.
xx
Improvement of stability boundaries by emulating inertia
at ICs: Power systems with a high penetration of
power electronic converters, including ICs, need to be
studied in detail from a point of view of stability to
measure how their integration and control affect the
stability boundaries of the system.

Acknowledgments
This work was partially funded by the European Regional
Development Fund/Ministry of Science, Innovation, and
Universities-State Research Agency (MTM2017-82996-C22-R) and by the Basque government under the project
Road2DC (KK-2018/00083).

For Further Reading
F. Milano, F. Dörfler, G. Hug, D. J. Hill, and G. Verbic, "Foundations and challenges of low-inertia systems," in Proc. 20th
Power Systems Computation Conf. (PSCC), 2018, p. 25. doi:
10.23919/PSCC.2018.8450880.
E. Unamuno and J. A. Barrena, "Equivalence of primary
control strategies for AC and DC microgrids," Energies, vol. 10,
no. 1, p. 91, Jan. 2017. doi: 10.3390/en10010091.
X. Wang and F. Blaabjerg, "Harmonic stability in power
electronic based power systems: concept, modeling, and
analysis," IEEE Trans. Smart Grid, vol. 10, no. 3, pp. 2858-5870,
May 2019. doi: 10.1109/TSG.2018.2812712.
P. Tielens, D. Van Hertem, and D. Van Hertem, "The relevance of inertia in power systems," Renew. Sustain. Energy Rev.,
vol. 55, pp. 999-1009, Mar. 2016. doi: 10.1016/j.rser.2015.11.016.
A. Ordono, E. Unamuno, J. A. Barrena, and J. Paniagua,
"Interlinking converters and their contribution to primary
regulation: A review," Int. J. Electr. Power Energy Syst., vol. 111,
pp. 44-57, Oct. 2019. doi: 10.1016/j.ijepes.2019.03.057.

Biographies
Eneko Unamuno (eunamuno@mondragon.edu) is with the
Electronics and Computing Department, Mondragon
Unibertsitatea, Spain.
Julen Paniagua ( jpaniagua@mondragon.edu) is with
the Electronics and Computing Department, Mondragon
Unibertsitatea, Spain.
Jon Andoni Barrena ( jabarrena@mondragon.edu) is
with the Electronics and Computing Department, Mondragon Unibertsitatea, Spain.

IEEE Electrification Magazine - December 2019

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