Automotive Power Electronics - Future Vehicles Drive Next - Semikron

p34-37 Feature Semikron 5/13/05 9:05 Page 34
AUTOMOTIVE POWER ELECTRONICS
Future Vehicles Drive Next
Generation of Power Modules
Power electronics plays an increasingly important role in the automotive industry. Hybrid electric drive technology
is now entering the mainstream market with hydrogen powered fuel cell vehicles still in research and
development. One of the clearest indications that the future of vehicle design is changing can be found in the
steady increase in the number of new hybrid models being offered in North America and Europe. This trend is
likely to increase the application of power modules in motor drives. John Mookken, Project Manager, SEMIKRON
Inc., Hudson NH, USA
FRANCAIS
L’électronique de puissance joue un rôle de plus en plus important dans
l’industrie automobile. La technologie d’entraînement à électricité hybride fait
désormais partie du marché de consommation courant tandis que les véhicules
fonctionnant au moyen de piles à combustible à hydrogène sont encore au stade
de la recherche et du développement. Une des plus claires indications que la
conception automobile est en train d’évoluer est l’augmentation constante du
nombre de nouveaux modèles hybrides étant commercialisés en Amérique du
Nord et en Europe. Cette tendance est susceptible d’augmenter l’application des
modules de puissance dans les entraînements de moteur. John
Mookken, Project Manager, SEMIKRON Inc., Hudson NH, USA
Two facts make the importance of
power electronics in future cars
a certainty. The first well-known
fact to consider is that DC motors are
unreliable and less efficient when compared
to AC types. An AC induction
motor has fewer parts, such as brushes
and commutators, which greatly improve
its reliability. AC motors are generally
smaller, less expensive and more efficient
compared to similarly rated DC motors.
It is also known that in the past, the cost
and complexity of AC drives have been
barriers to their acceptance in a number
of applications.
The second fact to consider is that
most hybrid electric vehicles (HEVs)
and most leading drive concepts for
future cars rely on the electric power
being stored in the DC form for a certain
length of time. This means, barring
any major technological breakthroughs
in DC motor design, power must be
converted from one form to another
several times on future cars, and that
virtually guarantees a bright future for
power electronics in the automotive
Figure 1 (right). Split hybrid or full
hybrid (above) a) is the most common
power train concept in current hybrid
cars. In hydrogen powered fuel cell
vehicle concepts (below) b) there are
no internal combustion engines
Die Leistungselektronik spielt eine zunehmend wichtigere Rolle in der
Automobilindustrie. Hybridantriebe gehen nun in den den
Massenmarkt, während mit Wasserstoff betriebene
Brennstoffzellenfahrzeuge noch immer in Forschung und Entwicklug
stecken. Einer der Klarsten Indikatoren für einen Wechsel in der
Automobilentwicklung ist die stetige Zunahme neuer Hybrid-Modelle in
Nordamerika und Europa. Dieser Trend wird die Anwendung von
Leistungsmodulen in Antrieben beschleunigen. John
Mookken, Project Manager, SEMIKRON Inc., Hudson NH,
USA
34 Power Electronics Europe Issue 4 2005
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industry. In current HEVs, electrical
energy is generated by the internal
combustion (IC) engine and stored in a
battery pack. This remains true whether
the powertrain design is a parallel, series
or the more common split hybrid design.
In future designs the fuel cell/battery
pack will likely replace the IC engine. In
either case, power must be converted
during charging, braking or coasting
(regeneration), and motoring. Power
converters and electric motors remain
the common denominator when comparing
different powertrain concepts
illustrated in Figure 1.
AUTOMOTIVE REQUIREMENTS
In today’s industrial applications
dominated $40 billion power electronics
market, modules are not produced
specifically for use in the automotive
industry. Industrial drives components
often cannot meet the reliability requirements
in the harsh automobile operating
environments and military grade components
are too costly for use in cars.
The market is now changing. With more
electrification in future cars and the
transition of the electric motors and
drives from R&D to production vehicles,
power module manufacturers are
recognizing the need to develop power
modules specifically designed to support
the near term and long term needs of
the auto industry. The race has begun
to produce an affordable module that
can meet the demanding performance,
reliability, cost and manufacturability
requirements set forth by the automobile
manufacturers.
In general, some of the key characteristics
for any new power module in
development or in production for
automotive traction applications can be
summarized as follows:
Integration – one can expect to see a
high degree of integration between the
power devices, bus work, heatsink, bus
capacitor, and gate drive/controller to
optimize overall performance. Performance
is measured in terms of output
power, size, weight, cost and manufacturability.
High temperature operation – the
ready source of circulating liquids
found in cars, like radiator coolant and
transmission fluids, make liquid cooling
of the power module on automobiles an
attractive option to improve module
performance. The challenge faced by
power module manufacturers is to
design power modules capable of being
cooled by engine coolant or lubricant
with inlet temperatures of 105ºC. For
power modules this translates to a wider
AUTOMOTIVE POWER ELECTRONICS
Figure 2 Above). The major sub-components that make up a 600 or 1200V IGBT
based SKAI power module (components shown in red can be substituted with
customer furnished parts)
Figure 3 (above). Modular design allows the SKAI module to be easily customised
for specific customers or applications
Issue 4 2005 Power Electronics Europe 35

p34-37 Feature Semikron 5/13/05 9:06 Page 36
AUTOMOTIVE POWER ELECTRONICS
Figure 4 (right).
SKiiP technology in SKAI
operating temperature range (-40 to
125ºC). Power devices will require
higher operating junction temperatures
(T j=175ºC), and higher temperature
ratings (150ºC) for packaging and
electronic components.
Flexibility – the term ‘flexibility’ in
this case encompasses the capability for
the module to be scalable, modular and
customizable. The present and near-term
continuous load for automotive traction
applications is between 10kW and
120kW. Just like IC engines in the past,
this figure is expected to rise over time.
Scalability allows the module output
power to be easily scaled up or down
without changing the module footprint.
Modularity allows the design to be
easily upgraded when new technology
becomes available and customizability
makes it easier to integrate customer
furnished materials into the existing
design.
Robustness – high reliability in the
harsh automotive environment is a re-
Table 1 (right).
Complete line of integrated
power modules for automotive
application
quirement for any automotive component.
However, traditionally power
modules have not had to meet the
under-the-hood temperature and vibration
requirements. Power modules used
in cars must be designed for the life of a
car, which is usually 100,000 miles
(160,000km) or 15 years. The new power
module designs will have to pass tougher
electrical, mechanical, EMI and environmental
tests.
Economical – one of the key characteristics
of the new power module that
is also in opposition to the other
characteristics listed above is affordability.
A reasonable price target for power
modules in automotive quantities is
estimated to be less than $6/kW for
the design to successfully penetrate the
automotive market.
SKAI ADVANCED INTEGRATION
MODULES
Incorporating most of the desirable
characteristics mentioned in the previ-
ous section into a new first generation
power module for the automotive industry
is SEMIKRON’s SKAI (SEMIKRON
Advanced Integration) module. It integrates
all the necessary hardware for a
drive into a single package and gives us
a glimpse into the future of power
modules.
The module integrates the power stage
with the liquid cooled heatsink, gate
drivers, controller, and protection logic
to provide a ready solution to the automotive
tier 1 suppliers. Figure 2 shows
the key components that make up the
SKAI module.
A high level of integration can be seen
between the AC and DC bus structure
on each of the baseplate less half-bridge
circuits (see Figure 4). Each Direct
Bonded Copper (DBC) AlN ceramic
substrate contains twelve 600V NPT or
1200V trench IGBTs, six matching
diodes and a positive coefficient thermistor
(PTC). The bus structures (AC
and DC) and the populated DBCs are
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all held together under more than 153kg/cm 2
of pressure using SEMIKRON’s SKiiP technology,
an unique and proprietary pressure
contact system. Tight integration of the
DC and AC bus bars on the DBC keeps
parasitics to a minimum. Bus filtering is
included with a 1mF metalised polypropylene
capacitor which is also closely integrated with
the bus bars. Two magneto resistive current
sensors are integrated with two of the three
AC bus bars which are attached to the
control board via flexible cables. The control
board interfaces with the DBCs via spring
pins and includes the power supply, gate
drives, DSP, communications hardware
(supports CAN/IEE485) and protection
circuitry.
The SKAI module is designed to operate
in the -40 to 85ºC temperature range. The
module is available on either liquid cooled
or air cooled heat sinks. Coolant inlet
temperatures are limited to 70ºC with higher
temperature operation possible with power
derating.
The modular nature of the SKAI
design allows the units to be easily
customized. Only minimal restrictions are
imposed in cases where the customer wants
to furnish the heatsink which could also be a
part of the customer’s system enclosure or
supply custom control boards with special
connectors or processor.
The SKiiP technology used in the SKAI
module was first introduced by SEMIKRON
in early 1992 in power modules. In addition
to simplifying module assembly, the pressure
system eliminates the large solder interfaces
typically seen between the DBC and the
module baseplate which greatly improves
reliability. The pressure system is shown to be
superior to traditional power modules by a
factor of 10 in power cycling tests. The use
of AlN substrate also improves reliability;
studies have shown that the module
lifetime can improved by a factor of 2 using
AlN rather than the less expensive Alumina
(Al 2O 3). The pressure system also reduces
the number of wire bonds in the power
module by using spring pins to contact the
gate and sensor connections from the DBCs
to the driver/control board. The use of
Ag plated spring pins have been shown to
be a highly reliable method for low current
control and sensor contacts for use in power
modules.
In addition to automotive applications
in hydrogen powered fuel cell vehicles,
SKAI modules are currently undergoing
field tests in applications as varied as
driving radiator fans and providing
auxiliary power on railroad locomotives
and agriculture vehicles, traction and
hydraulic pump motor drive on mining
vehicles and as traction drives on small
electric vehicles.
FUTURE DEVELOPMENTS
The second generation of the SKAI
module, which is under development, will
feature a wider operating and storage
temperature range. A more advanced
heatsink design has the potential to significantly
improve power density of the existing
SKAI module. Higher junction temperature
Si trench IGBTs, high temperature conductive
plastics or light weight metal enclosures,
new current sensor technologies and high
temperature capacitors are being developed
AUTOMOTIVE POWER ELECTRONICS
for FREE information enter 19
for the next generation. The new SKAI will
include a more capable controller such as
the TI 28xx series DSPs and triple sealed
automotive style connectors with more I/O
lines. The lure of high volumes in future
cars will continue to drive the power
module manufacturers to push the envelope
of performance and affordability of future
power modules. www.semikron.com
Enquiry No: 253
Issue 4 2005 Power Electronics Europe 37