Article - Efficiency in alternative power systems 01_00 | Nov 05, 2014 | PDF | 439 kb

SPECIAL REPORT : ALTERNATIVE ENERGY
POWER SYSTEMS DESIGN NOVEMBER
Efficiency in alternative
power systems
converter by power electronics.
Germany’s renewable power
generation in 2013 was about
135 billion kWh. Without power
electronics, 27 billion kWh would
have been lost.
What efficiency really means and why “good” isn’t good enough
By: Martin Schulz, Infineon Technologies
I
n October 1983, a recordbreaking wind generator
was taken into operation
and the world’s largest wind
energy converter called Growian
(artificial German abbreviation
meaning large scale wind power
plant) went live. The 3MW
machine can be considered
an example how the world has
changed since this happened.
Though it was an ingenious
design by the time, the power
harvested by an asynchronous
generator was transferred to
the grid by means of several
gearboxes and conversion
from variable frequency to
fixed frequency involved a
mechanical converter utilizing
rotating machines. Stacking five
mechanical systems resulted
in a conversion efficiency of
less than 80% and more than
600kW of losses were generated.
Today, harvesting, transferring,
storing and using electric energy
is one of the major challenges
industrialized nations face.
Though the scale changes from
Watt to MW, the task itself
remains the same
An issue in watts
40
Figure 1: Sketch of a supply grid integrating renewable power generation and
battery based energy storage.
Saving energy in a scale of
mobile phones in Germany
1W seems to be peanuts but
alone, charging one hour every
the number of devices within
day, the improvement due to
this range is enormous. A
semiconductors sums up to
mobile phone is one of these
146,000MWh per year.
applications. Using an USBport, a cell phone charges at 5V
A task in under one kilowatt
consuming 2.5W. Prior to the
Personal computers have made
era of high-voltage MOSFETs,
their way into almost every
the task would have been fulfilled house in Europe, starting with
using a transformer, a rectifier
the Commodore C64 in 1982.
and a linear regulator, leading to
It took until 2004 to start the
a system efficiency of about 50%.
80Plus initiative to foster power
supplies that feature at least
Today, compact switch-mode
80% efficiency. While most of
power supplies can do the same
these computers operate at a
task achieving 85% conversion
100W-level, high-power graphic
efficiency. With about 100 million cards and further accessories can
WWW.POWERSYSTEMSDESIGN.COM
2014
Figure 2: Three decades of power semiconductor development
boost the power consumption up energies. As any renewable
to 1000W.
power source is of fluctuating
nature, energy storage will be
Compared to the C64’s power
needed. Balancing between
supply based on transformer and
times of production and times
linear regulators, modern switch
of consumption will become a
mode power supplies feature a
key element to achieve stable
more complex structure but also
supplies with the availability
higher efficiency, lower weight
desired. The challenge for power
and volume and thus fewer
semiconductors now becomes
resources per Watt of output
obvious, taking a look to the
power. With 66 million privately
flow of energy as depicted in the
owned computers, power
scheme in Figure 1:
semiconductors contribute to
saving 10,000,000MWh per year
Energy, harvested from solar
in Germany alone. This quote
arrays or wind energy converters
would double if the average
is processed by power electronics
efficiency changed from 80% to
to be grid compliant. Comparing
90%
today’s wind converters to the
1983 Growian, efficiency grew by
A challenge in handling
roughly 20%. An average modern
megawatts
2MW wind power plant, operated
The German “Energiewende”
1000 full power hours per year,
is a project to eliminate the
has an additional energy harvest
need of nuclear power by 2020,
in a regime of 400,000kWh
substituting the centralized
due to efficiency improvement,
power plants using renewable
replacing the mechanical
Long-distance energy
transmission is most efficient
using High-Voltage DC lines
(HVDC) making AC/DC and
DC/AC conversion part of the
transfer. Storing energy in
batteries (4) again demands AC/
DC conversion while recovering
energy is a DC/AC path. Even
before the energy reaches the
end customer it passed power
electronics five times at least
and was converted seven times
if chemical conversion in the
batteries is taken into account.
Considering 95% conversion
efficiency for each state, 30%
of the initial energy would be
lost. Enhancing the situation in
regards of the power electronic
conversion systems can be done
on different but interacting
levels.
Technical improvements
To a certain extent, adapting
processes or introducing slight
changes to materials can
enhance existing technologies.
Power semiconductor switches,
IGBTs, benefit from thinner wafer
technology as this reduces the
switching losses. Changing the
cell design but remaining with
the same raw materials allows
optimization regarding forward
voltage. Increasing the junction
temperature without sacrificing
WWW.POWERSYSTEMSDESIGN.COM
41
SPECIAL REPORT : ALTERNATIVE ENERGY
POWER SYSTEMS DESIGN NOVEMBER
Efficiency in alternative
power systems
converter by power electronics.
Germany’s renewable power
generation in 2013 was about
135 billion kWh. Without power
electronics, 27 billion kWh would
have been lost.
What efficiency really means and why “good” isn’t good enough
By: Martin Schulz, Infineon Technologies
I
n October 1983, a recordbreaking wind generator
was taken into operation
and the world’s largest wind
energy converter called Growian
(artificial German abbreviation
meaning large scale wind power
plant) went live. The 3MW
machine can be considered
an example how the world has
changed since this happened.
Though it was an ingenious
design by the time, the power
harvested by an asynchronous
generator was transferred to
the grid by means of several
gearboxes and conversion
from variable frequency to
fixed frequency involved a
mechanical converter utilizing
rotating machines. Stacking five
mechanical systems resulted
in a conversion efficiency of
less than 80% and more than
600kW of losses were generated.
Today, harvesting, transferring,
storing and using electric energy
is one of the major challenges
industrialized nations face.
Though the scale changes from
Watt to MW, the task itself
remains the same
An issue in watts
40
Figure 1: Sketch of a supply grid integrating renewable power generation and
battery based energy storage.
Saving energy in a scale of
mobile phones in Germany
1W seems to be peanuts but
alone, charging one hour every
the number of devices within
day, the improvement due to
this range is enormous. A
semiconductors sums up to
mobile phone is one of these
146,000MWh per year.
applications. Using an USBport, a cell phone charges at 5V
A task in under one kilowatt
consuming 2.5W. Prior to the
Personal computers have made
era of high-voltage MOSFETs,
their way into almost every
the task would have been fulfilled house in Europe, starting with
using a transformer, a rectifier
the Commodore C64 in 1982.
and a linear regulator, leading to
It took until 2004 to start the
a system efficiency of about 50%.
80Plus initiative to foster power
supplies that feature at least
Today, compact switch-mode
80% efficiency. While most of
power supplies can do the same
these computers operate at a
task achieving 85% conversion
100W-level, high-power graphic
efficiency. With about 100 million cards and further accessories can
WWW.POWERSYSTEMSDESIGN.COM
2014
Figure 2: Three decades of power semiconductor development
boost the power consumption up energies. As any renewable
to 1000W.
power source is of fluctuating
nature, energy storage will be
Compared to the C64’s power
needed. Balancing between
supply based on transformer and
times of production and times
linear regulators, modern switch
of consumption will become a
mode power supplies feature a
key element to achieve stable
more complex structure but also
supplies with the availability
higher efficiency, lower weight
desired. The challenge for power
and volume and thus fewer
semiconductors now becomes
resources per Watt of output
obvious, taking a look to the
power. With 66 million privately
flow of energy as depicted in the
owned computers, power
scheme in Figure 1:
semiconductors contribute to
saving 10,000,000MWh per year
Energy, harvested from solar
in Germany alone. This quote
arrays or wind energy converters
would double if the average
is processed by power electronics
efficiency changed from 80% to
to be grid compliant. Comparing
90%
today’s wind converters to the
1983 Growian, efficiency grew by
A challenge in handling
roughly 20%. An average modern
megawatts
2MW wind power plant, operated
The German “Energiewende”
1000 full power hours per year,
is a project to eliminate the
has an additional energy harvest
need of nuclear power by 2020,
in a regime of 400,000kWh
substituting the centralized
due to efficiency improvement,
power plants using renewable
replacing the mechanical
Long-distance energy
transmission is most efficient
using High-Voltage DC lines
(HVDC) making AC/DC and
DC/AC conversion part of the
transfer. Storing energy in
batteries (4) again demands AC/
DC conversion while recovering
energy is a DC/AC path. Even
before the energy reaches the
end customer it passed power
electronics five times at least
and was converted seven times
if chemical conversion in the
batteries is taken into account.
Considering 95% conversion
efficiency for each state, 30%
of the initial energy would be
lost. Enhancing the situation in
regards of the power electronic
conversion systems can be done
on different but interacting
levels.
Technical improvements
To a certain extent, adapting
processes or introducing slight
changes to materials can
enhance existing technologies.
Power semiconductor switches,
IGBTs, benefit from thinner wafer
technology as this reduces the
switching losses. Changing the
cell design but remaining with
the same raw materials allows
optimization regarding forward
voltage. Increasing the junction
temperature without sacrificing
WWW.POWERSYSTEMSDESIGN.COM
41
SPECIAL REPORT : ALTERNATIVE ENERGY
the PN-junction
dilemma.
Paralleling IGBTs
still leads to a
forward voltage
across a PNjunction and thus
limits the benefit
in regards of
efficiency. Field
effect based
devices however
feature a channel
resistance and
paralleling n
devices results in
an improvement
of the overall
Figure 3: Built in efficiency, 20kVA converter with
resistance by
SiC-JFETs measuring 12.2cm x 6.2cm x 11.7cm and
a factor n-1.
weighing 1.7kg
Efficiency becomes
a question of how many devices
lifetime leads to higher power
are integrated, immediately
densities along with less material
used per kW installed. The diagram correlating it to money spent.
in Figure 2 summarizes recent and
A second approach leads to hybrid
ongoing developments in power
devices, combining silicon IGBTs
semiconductor technologies.
with SiC Schottky barrier diodes
as depicted in Figure 3. SiC diodes
Technological change
allow higher turn-on speed for the
Figure 2 also hints to the fact,
IGBT, reducing the turn-on losses;
that from a certain point on, a
the absence of a recovery charge
technological change is needed
eliminates the diode’s recovery
to overcome the drawbacks of
losses.
an existing technology. In case
of power semiconductors, wide
System development
band gap materials like Silicon
Today, the most widely used
Carbide (SiC) or Gallium Nitride
topology in power electronics
(GaN) are promising candidates
includes a three-phase inverter
to further improve efficiency. Two
based on a 2-level half-bridge
options arise from using these
as a basic building block.
new materials.
Depending on the application,
a change in topology may lead
First, a change from IGBTs being
to benefits regarding efficiency.
bipolar transistors towards field
Recently, solar inverters have
effect based devices overcomes
42
WWW.POWERSYSTEMSDESIGN.COM
SPECIAL REPORT : ALTERNATIVE ENERGY
seen a transition from twolevel to three-level designs.
The change was driven by the
efficiency gain that results from
using 650V semiconductors
instead of 1200V components.
Among others, the inherently
lower switching losses contribute
to the gain in efficiency.
In an approach to minimize
material content while
maximizing efficiency, Infineon
has successfully cooperated with
the University of Nottingham to
combine new technologies in a
different topology. The outcome
was a matrix converter that
was built using silicon carbide
JFETs. This 4-quadrant converter
achieved 97% efficiency at full
load and even higher values at
partial load (see Figure 3).
Good enough?
Efficiency in modern energy
conversion has massively grown
throughout the last decades.
Nevertheless, growing energy
demand along with harvesting
and storing renewable energies
makes further improvements in
this field a necessity. More and
more, electricity has to pass
semiconductors on its way from
generation to consumption,
making highly efficient
semiconductors a true gateway to
saving energy. Engineers will have
to strive to achieve even higher
efficiencies in future with a clear
target ahead. Less than “1” is
never good enough.
www.infineon.com
The IoT needs wireless charging
& energy harvesting
Traditionally devices were connected by wires to their power sources
By: Tony Armstrong, Linear Technology
T
he “Internet of
Things” (IoT), refers
to a growing trend
to connect not only
people and computers, but all
sorts of “things” to the Internet,
and therefore, each other. By way
of example, consider if you will
applications such as industrial
plants or large infrastructure
projects where connecting more
sensors (or actuators) in more
places can increase efficiency,
improve safety, and enable entirely
new business models.
Traditionally wires connected
devices and sensors to their power
sources. Now, rather than the
challenge and expense of running
cables all around a facility, it is
now possible to install reliable,
industrial-strength wireless
sensors that can operate for
years on a small battery, or even
harvest energy from sources such
as light, vibration or temperature
gradients. Furthermore, it is also
possible to use a combination of a
rechargeable battery and multiple
ambient energy sources too.
Moreover, due to intrinsic safety
concerns, some rechargeable
batteries cannot be charged by
wires but require being charged via
Figure 1: LTC3331 Energy Harvester & Battery Life Extender
wireless power transfer techniques. energy unit provided. Moreover,
systems incorporating energy
Energy harvesting & wireless
harvesting will typically be capable
power
of recharging after depletion,
State-of-the-art and off-thesomething that systems powered
shelf energy harvesting (EH)
by primary batteries cannot do.
technologies, for example in
vibration energy harvesting and
Nevertheless, most
indoor photovoltaic cells, yield
implementations will use an
power levels on the order of
ambient energy source as the
milliwatts under typical operating
primary power source, but will
conditions. While such power
supplement it with a battery that
levels may appear restrictive, the
can be switched in if the ambient
operation of harvesting elements
energy source goes away or is
over a number of years can
disrupted. This battery can be
mean that the technologies are
either be rechargeable or not and
broadly comparable to long-life
this choice is usually driven by
primary batteries, both in terms of
the end application itself. So it
energy provision and the cost per
follows that if the end deployment
WWW.POWERSYSTEMSDESIGN.COM
43
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