POWER June 2022 Intl - 18

TRANSMISSION & DISTRIBUTION
Hitachi Energy Classic and Light references
All other Hitachi technologies
other phases, " says Siemens Energy.
" This way it is possible to achieve the
required sinusoidal AC and smooth DC
side output voltage waveforms without
excessive harmonic distortion and [highfrequency]
noise. "
According to the European Network
of Transmission System Operators for
Electricity
(ENTSO-E), MMC " is
be2.
Hitachi Energy, a joint venture firm officially launched in 2020 when Japanese technology
conglomerate Hitachi acquired a majority share in Swiss conglomerate ABB's Power Grids business,
says 70% of the world's 200-GW installed HVDC base is installed with its technology. This
includes half of all voltage-source converters (VSC) in the world. Courtesy: Hitachi Energy
previous converters, ushered in a new
HVDC capability (see sidebar) to switch
on and off many times to improve harmonic
performance, without being dependent
on synchronous machines in
the AC system for its operation.
The Evolving Technology Landscape
Currently, two main HVDC technologies
dominate the landscape: line-commutated
converters (LCC), also known as
current-source converters (CSC) using
thyristors, and VSC, using insulatedgate
bipolar transistors (IGBT). Experts
suggest that for long-distance and highcapacity
transmission links, CSC-HVDC
technology has both higher efficiency
and a higher power transfer capacity
than classical AC solutions. But for power
transmission from offshore power plants
or from other remote areas with limited
space, VSC-HVDC is the preferred technology
(Figure 2), owing to its smaller
footprint, and active and reactive power
control capabilities.
VSC's success over the past 10
years may point to a larger role on the
ever-more complex power systems
landscape, said Roger Rosenqvist, vice
president of business development for
Hitachi Energy's HVDC division in North
America. Combined with underground
transmission using polymer insulated cables
" there has been a scaling up of the
capacity of VSC, and today we can build
3,000-MW systems, " which has opened
up new opportunities, he said.
However, several other technologies
are also emerging to provide innovative
solutions to long-standing capability
gaps, such as modular multilevel con18
verters
(MMC), cascaded two-level converters
(CTL), and hybrid VSC-CSC links.
MMC, a technology first proposed in
2003, is a VSC converter that has two
forms: " half-bridge " and " full-bridge. "
MMC technology was commercially
deployed for the first time worldwide in
2018 as an upgraded control system in
an HVDC system in the Trans Bay Cable
(TBC) project (Figure 3), which includes a
53-mile HVDC submarine cable that runs
under San Francisco Bay.
The project was notably Siemens Energy's
first successful MMC converter
test for black-start capability using load
banks. " Practically speaking, each module
within an MMC is a discrete voltage
source with a local capacitor to define
its voltage step without creating ripple
voltage distortion across the converter's
coming the preferred power electronic
converter for converting between AC
and DC as it presents several benefits. "
Along with the ability to reverse the power
flow without reversing the polarity of
the DC voltages by DC current reversal,
MMC is modular and scalable, " making
it advantageous compared to other
VSC topologies, " ENTSO-E said. MMC
also has an inherent capability of storing
energy internally in the converter. " This
can benefit the system in which it is connected
and enables the drastic reduction
of operating losses of the converter stations
by avoiding the need for high frequency
switching of the semi-conductor
devices, " the grid organization noted.
Significant Applications for a Rapidly
Evolving Grid
HVDC's suitability to the rapidly changing
grid, meanwhile, is pegged to its many
advantages over classical AC solutions,
such as active power control, higher
transfer capacities, no reactive power,
longer possible transmission lengths,
and lower active power losses. According
to some experts, in some cases, it's
the only feasible technology.
Long-distance bulk power transmission,
with an added benefit of cost-effective
and efficient transmission, continues
to be HVDC's most shiny attribute. Sev3.
Siemens Energy in 2018 unveiled an upgraded control system for the San Francisco Trans
Bay Cable project, an HVDC transmission system with VSC technology realized in a modular
multi-level converter (MMC) topology. Courtesy: Siemens Energy
www.powermag.com
POWER | June 2022

http://www.powermag.com

POWER June 2022 Intl

Table of Contents for the Digital Edition of POWER June 2022 Intl