Fuji Electric Journal
Vol.75 No.8, 2002
Power Electronics Technology
Trends and Prospects
Hidetoshi Umida
1. Introduction
Power electronic devices have achieved higher performance
by using new technologies such as power transistors, IGBTs
(Insulated Gate Bipolar Transistors), and microprocessors.
In recent years, in response to the trend of IT (Information
Technology), FA (Factory Automation), and HA (Home
Automation), facilities management is becoming integrated in
factories, transportation systems, power systems, offices,
and stores, which are the traditional application area of
power electronic devices. At home, the number of electrical
appliances that include marks "IH" (Induction Heating) and
"Inverter" are increasing.
The basic functions of power electronics include the use of
electronics to control and transform electric energy in terms
of voltage, current, frequency, and waveform. The basic
functions also include the use of electronic control for
conversion to other forms of energy such as electromagnetic
energy, actuators, and high-frequency induction heating
(Figure 1). We can therefore expect power electronics to
play an increasingly important role in the accurate
management and control of electric energy at high speed in
the age of information.
This paper reports on the trends in power electronics and the
current state of research and development at Fuji Electric.
Fig.1. Essential technologies and power electronics products
Servo
Inverter for new
energy application
Motor
Inverter
UPS
Power system
compensator
High-frequency
application
Engineering
IT
Control
Various types
of power units
Electronic
circuit
Topology
Power
device
Cooling
Electromagnetics
Numerical
analysis
Structure
2. Current State and Issues of Power Electronics
Power electronic devices normally feature low losses
because the switching operations that they perform are
controlled by the on/off state of semiconductors. However,
because they can also cause electromagnetic interference
due to switching, it is necessary to maximize the advantages
of the devices while eliminating or minimizing their
disadvantages. Since the control technology is flexible and
wide in applications from high-speed control in the
generation of power with a high peak demand to operations
that save energy, appropriate operations can be adjusted to
the required conditions. It is therefore useful to have a clear
idea of the trend of technology for the improvement of
performance, functions and of the necessary benchmarks
while maintaining harmony with our surroundings, including
the environment, as seen from various points of view.
(1) Reduction of resource consumption and stress to the
environment
Roughly speaking, the size of current power electronics
equipment is about one-tenth that of 20 years ago and their
weight about one-fifth. In efforts to reduce the amount of
energy consumed and to reduce carbon dioxide levels,
attempts to save energy by reducing loss related to elements
and circuits and to use regenerative energy recovery have
been made. To continually maximize the effects of these
efforts, new technologies are needed to optimize system
operation beyond the partial optimization techniques, such
as the low-loss circuit systems and new power devices, and
the size and weight reduction provided by such techniques.
(2) Limiting noise and harmonics distortion
Circuits that suppress noise and harmonics distortion caused
by the switching of power devices and structures that block
the radiation of noise are important as means of preventing
failures and errors in other electronic equipment. In recent
years, steady progress has been made in the standardization
of EMC (Electromagnetic Compatibility). In the IEC
standard of the International Electrotechnical Commission, a
directive was issued to limit the terminal voltage noise
(conductive noise) in 150kHz - 30MHz to no more than the
preset value. In Japan, "The Guidelines for High-Voltage
Users" and the "Guidelines for Protective Measures against
Harmonics in Household Appliances and General-Purpose
Products" along with the IEC directive were established in
1994 to impose self-regulation. For domestic information
processing devices, self-regulation was imposed by the
VCCI (Voluntary Control Council for Information Processing
Equipment and Electronic Office Machines) to eliminate
radio interference caused by electromagnetic radiation.
The development of equipment that conform to the above
requirements and that are electromagnetically clean,
requires advanced circuits and structure technologies that
suppress power supply harmonics and terminal voltage
noise.
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Fuji Electric Journal
Vol.75 No.8, 2002
(3) Seeking new values
As information continues to gain greater importance, we can
expect more contributions from the creation of new
cutting-edge technologies, in which the control of electric
energy, motion and IT are closely integrated, by improving
the level of device performance.
Even today, practical equipment with surprising levels of
performance, such as fast response IGBT type SVCs (Static
Var Compensator) that controls reactive power of several
tens of MVA, high-speed power supplies which provide
low-voltage and large currents to high-speed CPUs, and
servos that control precision mechanical equipment on the
order of nm, are being introduced one after the other.
3. Applied Power Electronic Technologies
The key elements required in power electronic equipment
are the power devices. As shown in Figure 2, controllable
power devices started with the thyristor. They have since
progressed to the bipolar transistor, Gate Turn-Off thyristor
(GTO) and lately to the IGBT. Because it is relatively easy
to make a high-voltage, large-capacity IGBT, the IGBT is
expected to replace the thyristor and GTO. It is also
important to develop IGBTs which have superior
characteristics to other power devices. The following
describes applied technologies for power devices.
Device capacity
Fig.2. Power device timeline
GTO
MVA
Thyristor
IGBT
Bipolar
transistor
1970
1980
is therefore not suitable for circuits to which reverse voltage
is applied, even though simple ones, such as a thyristor
rectifier. The newly developed reverse-blocking IGBT, with
its proprietary withstand voltage structure, succeeds in
having reverse withstand voltage without increasing the
forward voltage drop. When two reverse-blocking IGBTs
are connected in an antiparallel connection, a bidirectional
switch that is almost ideally fast and low in loss can be
realized (see Figure 4 in the paper "Applied Technology for
Reverse-Blocking IGBTs" in this special issue). A new
power device is a source for new applications. With the
advent of the reverse-blocking IGBT, we can expect new
developments in circuit systems, including AC-AC direct
conversion.
3.2 Sensing Technology within the Package
In a large-capacity power device in which multiple chips are
mounted, ensuring reliability is a major problem. Multiple
IGBT chips mounted in a package are designed so that the
load among them is balanced. The balancing is
accomplished by reducing differences in operating conditions
resulting from the structure and layout to a minimum.
However, when we attempted to check the load balancing
under more stringent conditions, it was not easy to measure
the current of each chip within a narrow package with high
electromagnetic fields, and a small, high-speed sensor with
the required precision was difficult to obtain. We therefore
developed a microsensor that could be incorporated into
pressure welding elements (see Figure 3) and succeeded in
observing minute differences in chip current without affecting
the elements. This procedure also verified that the load is
balanced normally in all areas. We think it is possible to use
this measuring technology to improve the performance and
reliability of large-capacity power devices.
MOSFET
Fig.3. Principle and appearance of the current sensor
1990
2000
Year
Small coil
cross-section
is
3.1 Applied Technologies for New Power Devices
Fuji Electric is currently working to develop two new devices,
the FS-IGBT (Field Stop IGBT) and reverse-blocking IGBT.
As the work on device development continues, applied
technologies are being developed, too.
(1) FS-IGBT
The FS-IGBT is a faster device compared with conventional
ones as well as it has a substantial reduced forward voltage
drop (see Figure 5 in the paper "Applied Technology for
Large-Capacity 6-in-1 IGBT Modules" in this special issue).
A slim-line package with a footprint one-half that of
conventional devices has been implemented by optimally
laying out IGBT chips that can take higher current densities
and input/output terminals. When we evaluated a prototype
inverter stack that includes a high-performance cooling fan,
the result we obtained showed a reduction in loss of about
20%. This result leads to a substantial miniaturization of
inverters and power supply equipment.
(2) Reverse-blocking IGBT
The reverse-blocking IGBT is an entirely new device with
reverse withstand voltage. Conventional IGBTs have no
reverse withstand voltage and are limited to opening and
closing in the forward direction only. The conventional IGBT
2
ip
Ro
v (t )
v (t )dt
Integrator
(a) Principle of the Rogowskii coil
(b) Appearance
Fuji Electric Journal
4. Technological Trends and Challenges
Figure 4 summarizes the relationships among the power
supply, drive fields and the essential technology for circuits,
control, and information. Because low noise, high power
factor, low harmonics, and high efficiency are the measures
of devices in the power supply field, the emphasis is on
circuit technology. In particular, if the capacity is small,
implementation with the minimum number of parts becomes
important.
In the drive field, on the other hand, the emphasis is on
operation and control––for example, energy-saving
operation, reduction of labor by tuning, and better
performance through state estimation and identification.
The series-parallel connection technology of the IGBT poses
a challenge in both the drive field and in power supply field
for increasing capacity.
The following explains how these essential technologies and
applications are being addressed.
Fig.4. Relationships among essential technologies and the
power supply and drive fields
Power supply field
High-performance
converter
Advance
control
se
sponse
labor
Less
High re
Main
Tuning
High-speed
control
Energy-saving
operation
tena
nce,
serv
ice
Worldwide
PFC
+
+
11 kW/400V DC
P
DC-DC
converter
N
(a) Circuit configuration
Large capacity
Control technology
High
respo
n
800V DC
T
Low s
high v urge,
oltage
Multilevel
converter
apa
rge c
La
Fig.6. Three-phase AC-DC power supply for worldwide use
S
Element seriesparallel connection
city
Fig.5. IC for switching power supply
Estimation/
identification
ss
Low lo
High rmance
perfo
Drive field
Soft
switching
se,
noi
Low loss
low wer
o
hp w
Hig tor, lo ics
c
fa rmon
ha
conversion circuit in principle that can capture all of these
features in a single system (Figure 6 shows the circuit
configuration and the device).
3ø 200V AC
or 400V AC
R
Circuit technology
Vol.75 No.8, 2002
(b) Device appearance
ol,
ontr
e
mc
yste ntrol, ervic
Computerization S lant co ance, s
p
n
te
main
4.1 Challenges in the Power Supply Field
4.1.1 Noise, harmonics, and loss reduction
Soft switching is a technology that attacks the given
problems by using the resonance of circuits. This
technology is particularly suitable for a small power supply
with high switching frequencies. One of the problems
entering public awareness recently is the reduction of power
consumption in the standby state. As a solution to this
problem, a top class technology for low power consumption
in the standby state that uses intermittent operation by burst
oscillation has been developed.
A high level of integration is effective for implementing a
small-capacity circuit with good reproducibility while
satisfying the complex requirements described above. Fuji
Electric has already brought to market ICs for power supply
switching. Figure 5 shows the IC.
A power supply with a rating of the several hundreds W to
several kW is in many cases used for server and
communications equipment. Such a power supply should
therefore feature high levels of precision and efficiency, a
high power factor, and low harmonics so that the system will
operate efficiently and stably. Fuji Electric has proposed the
system shown in Figure 1 of the paper "AC-AC Conversion
Circuit Technology" in this special issue as a superior
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Fuji Electric Journal
Vol.75 No.8, 2002
4.1.2 New applications
Some devices used in recent production facilities and
information processing require a very stable power supply
environment. If an instantaneous voltage drop occurs, the
damages, such as various problems and reduction in yield,
are serious. Also, a problem with the conventional UPS
(Uninterruptible Power Supply) is the rapid deterioration of
batteries caused by repeated charging and discharging of
the batteries if instantaneous voltage drops are frequent.
Fuji Electric has made commercially available equipment
that takes special measures for instantaneous voltage drops.
Figure 7 (b) shows the principle of operation.
Because a large capacitor is used as an energy storing
element instead of the batteries used in a UPS in Figure 7 (a),
the device has excellent reliability and does not require
maintenance for a long time. We think that the device will
contribute much to improve the quality of supplied power.
Fig.7. Comparison of basic configurations of UPS and
equipment providing proprietary measures for
instantaneous voltage drops
Power system
When biased
Converter
AC DC
Inverter
AC DC
Battery
The number of charging
and discharging times is Load
limited.
(a) UPS
Power system
When biased
Converter
AC DC
Large
capacitor
Inverter
AC DC
+
There is no limit on the
number of charging and
discharging times.
Load
(b) Equipment providing proprietary measures
for instantaneous voltage drops
4.2 Drive System Challenges
Presented here are the technologies for the inverter and
servo, the main applications in the motor drive field.
4.2.1 Inverter control technology
Inverters suitable for induction machines or permanent
magnet synchronous machines have been developed. With
regard to induction machines, vector control, speed
sensorless vector control, V/f control, and an enhanced type
of V/f control (that is, torque vector control) are already being
used in a wide range of motors, from specialized motors and
general-purpose motors to high-voltage motors. Fuji
Electric has an operational version of vector control and V/f
control for permanent magnet synchronous machine drives.
A V/f control that can be easily handled is appropriate for
energy-saving drives because high-efficiency control is
implemented. The V/f control achieves a control
performance that is comparable to the speed sensorless
vector control (see Figure 6 in the paper "Sensorless
Control Technology of Permanent Magnet Synchronous
Motors" in this special issue).
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4.2.2 New servo functions
Work on servo systems used for high-speed and
high-precision applications is focused on two areas. One
area is the performance improvement of the servo amplifier.
High-speed positioning and damping control are essential in
obtaining the best performance from machines in which a
servo is installed.
The other area is a support tool used for tuning when the
working machines are incorporated. The machine analysis
function incorporated in the tool can analyze the complex
machine oscillation modes that are to be used to tune the
system. Figure 8 shows an example of combining the servo
system and the support tool. Hitherto a long time was
needed for tuning if there were complex machine vibrations.
When the support tool is used, tuning of the vibration
suppression control are both quick and accurate. If the
identification accuracy of the machine transfer function is
improved in the future, automatic tuning of the servo may be
expected.
Fig.8. FALDIC-β and support system
Fuji Electric Journal
4.3 High Power Technology
In a large-capacity converter used for flicker compensation,
reactive power compensation, or driving of a large motor in a
power system, the required equipment capacity must be
implemented using series-parallel connections of power
devices. In the conventional series technology, a function
that balances the voltage among the thyristor, GTO, and
IGBT is implemented using a resistor or snubber circuit.
When this method is used, loss due to the resistor is large
and the balance can be maintained at a low carrier frequency
and switching speed. These restrictions prevent
miniaturization of the converters and hinder performance.
Fuji Electric has developed a new series technology that
could overcome these problems. The configuration is a
simple one in which balance cores are inserted for the gate
drive. Since the balance is maintained automatically by the
amplification of the IGBT, the technology has potential for
higher performance at high carrier frequencies. Figure 9
shows a basic configuration when a multiseries circuit is
applied to the inverter.
Fig.9. Basic configuration of multiseries circuits
DC voltage +
Vol.75 No.8, 2002
5. Conclusion
In this paper, we presented an overview of the current
research and development in power electronics. In the
future, we also intend to consolidate and improve our
technical expertise in response to various types of needs and
to quickly develop new technologies that will play a part in
solving environmental and energy problems.
References
(1)
(2)
(3)
(4)
Gekinozu, M. High-Efficiency Self-Oscillating Current
Resonant Converter. Electronic Technology. vol. 43, no. 5,
2001, pp. 22-25.
Miwa, K., Kuroki, K. Simulation Analysis Results and
Experiment Results of Rectifier Circuits for Worldwide Use.
Semiconductor Power Conversion SPC-00-78 Industrial
Electronics Application IEA-00-54 Joint Symposium. 2000,
pp. 23-28.
Igarashi, M. et al. Simple Power Factor Improved New
Section Resonant Converter. Semiconductor Power
Conversion Society SPC-00-19. 2000, pp. 37-42.
Itoh, J. et al. Higher Performance of V/f Control of Permanent
Magnet Synchronous Motors. Journal D of the Institute of
Electrical Engineers of Japan. vol. 122, no. 3, 2002, pp.
253-259.
Gate balance core
Gate drive
circuit
(upper arm)
Gate drive
circuit
(lower arm)
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