The Multi-functional Modular Multilevel Converter
Taking a revolutionary technology one step further
TU Delft has made an important
contribution to the ongoing
revolution in high & medium
voltage technology: researchers
have created the next generation
of Modular Multilevel Converters.
The concept is an improvement on
the German innovative converter
system M2C which is already
commercially available. The TU
Delft converters are called ‘M3C’
as they are not only ‘Modular’
and ‘Multilevel’ but also ‘Multifunctional’: they are not only
able to convert DC/AC , but also
- unlike M2C - DC/DC at high and
medium voltages. At low voltages
M3C offers the possibility to
individually manage the charge of
the cells in batteries.
Routinely plugging in our laptop or
cellphone to charge, not many of us
realise how radically our power system
has changed. Its complexity has greatly
increased, due to growing consumption,
new technology, a liberated electricity
market and the deployment of
renewable energy sources. Future
challenges include the electrification of
transportation, the rise of distributed
generation and the development of
smart grids. Needless to say there’s
a lot of innovation happening in the
world of power electronics and energy
conversion! New ideas and inventions
follow each other rapidly. Just a few
years after the release of M2C, a
revolutionary modular multilevel power
conversion system, TU Delft has applied
for a patent that significantly enhances
the functionality of the system: M3C.
M2C: a major step forward
M3C devices have all the advantages
of M2C. While conventional converters
are only capable of AC output voltage,
M2C/M3C is able to work as a power
converter that provides AC and DC
output voltages in the medium voltage
range. Due to the modularity of the
system, where identical converter
cells are switched sequentially, it
has high flexibility and versatility,
meaning it can cover a wide variety of
applications. As it is a transformerless
system that can easily handle high
voltages and need small filters, it is
more compact than existing systems,
saving space and money. It offers
very high efficiency and excellent
dynamic control of sinusoidal and other
voltage waveforms. Another important
advantage is the M2C/M3C’s high
reliability: the systems can continue to
operate even after some modules have
failed.
M3C’s extra benefit: DC/DC
The drawback of M2C is that it can
only convert DC/AC and vice versa; it
is not capable of modular multilevel
DC voltage conversion at high and
medium voltages. The limitation is
caused by the required energy balance
on the capacitors of the submodules.
TU Delft has found an elegant solution
to this problem by introducing a new
mechanism for independent submodule
energy balancing, resulting in the
world’s first Multi-functional Modular
Multilevel converter.
Possible applications range from DC/
DC step-up or step-down converters for
DC distribution grids (e.g. 600V/5kV),
HVDC-UHVDC DC/DC converters
(300kV/800kV, electrostatic systems
and battery cell energy management.
The TU Delft researchers intend to
start a R&D consortium to explore
the possibilities of a ‘power converter
building block’ enterprise for a large
range of potential products.
M3C’s advantages in a nutshell
• I mproves on M2C: able to convert
DC/DC
• Converts to any optional output in the
medium voltage range
• Highly flexible and versatile
• Transformerless
• Small filters are needed
• High efficiency
• Excellent waveforms
• High reliability method conserves
unique characteristics
M3C’s market potential
As M3C can be used in HVDC
systems, it has huge market potential,
considering the HVDC transmission
market is expected to at least double
within the next five years. The new
topology can be used for mains
applications such as network couplings,
but also for drives for compressors or
pumps. Examples of application areas
are ship drives, offshore wind farms,
the oil industry, railways and the steel
industry.
Ref. TU Delft OCT-12-030
TU Delft / Valorisation Centre
Mekelweg 2
2628 CD Delft
T: 015-2786751
www.patent.tudelft.nl