IEEE Power & Energy Magazine - May/June 2019 - 39

Strengthening the Security
of Power System Stability
systems are only moderately controllable and typically sluggish to respond, while the worldwide adoption of variable
resources increases system response speed. Grid-scale
power electronics devices employing modern switching and
control technology increase the speed at which large power
flows may be modified, allowing for increased flexibility and
overall grid resilience.
however, increased reliance on digital systems for switching command signals and wide-area sensor networks, for
example, consequently increases cyberattack vulnerabilities. a review of the most recent attacks on transmission
and generation systems reveals several concerns related to
current supervisory control and data acquisition (Scada)
systems, programmable logic controllers (plcs), and
may/june 2019

operator errors due to lack
of situational awareness.
coupled with the possibility
of misconfigured protection
equipment, these issues raise
important concerns regarding the stability of modern
power systems, which rely
heavily on digital systems.
one particular technology that benefits greatly
from increased digitalization is high-voltage direct
current (hvdc) transmission. as an enabling technology developed in the
mid- and late-20th century,
hvdc interconnects between
ac transmission systems
became economically and
technically feasible. the
first commercial hvdc interconnect was the Gotland
link in Sweden, which used
mercury arc-based switching devices. the system was
commissioned in 1954, and
it became one of the first systems to use thyristor technology when it was upgraded in
1970. as thyristor technologies have developed since
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then, the converter voltage
and current ratings have
increased. the performance and sophistication of control technologies have seen rapid developments over the
same period. voltage source converter (vSc) hvdc
schemes that have come into application in the last 20
years have taken advantage of more flexible power control schemes.
hvdc systems have advantages over ac transmission
for very long transmission distances when lines must be submerged and when two separate ac systems that are not otherwise synchronized are interconnected. Modulated power
transfers through hvdc systems may also be used to damp
potentially destabilizing oscillations between system areas.
in addition, the exceptional flexibility provided by hvdc has
been investigated and used in many existing applications,
including transient stability and transfer capability improvement, renewable energy development, and black start.
the hvdc transmission schemes and back-to-back converter installations deployed worldwide rely on control
systems that vary greatly based on manufacturer, service
requirements, and recent equipment upgrades. Modern processor-based digital systems have replaced older, less flexible
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IEEE Power & Energy Magazine - May/June 2019

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