High Currents Under Control Compact Vehicle Power ... - Semikron

ISSN: 1863-5598
ZKZ 64717
09-10
Electronics in Motion and Conversion September 2010

COVER STORY
High Currents Under Control
Compact Vehicle Power Systems
Users of power control equipment have used third-party systems for many years, because
they offer the benefits of reduced development costs, shorter time to market and ease of
meeting qualification standards. As specifications have become more demanding, it has
become necessary to use higher levels of integration, with much tighter control of all the
elements in the system.
By Paul Newman, Managing Director, Semikron UK Ltd
To meet the requirements for the broad automotive electronics market
– ranging from fork-lift trucks, to hybrid and electric vehicles, to
large agricultural and construction vehicles – Semikron has established
its Systems Group, to bring all the necessary expertise into
one organisation. The Group works closely with customers to develop
power systems, which are then marketed under the SKAI brand.
The second generation of fully integrated and tested SKAI systems
are now available.
The Systems Group has been formed to build on Semikron’s many
years of experience in these markets. The company has offered integrated
power electronics to its customers for almost 20 years. Initially
just combining power silicon and drivers in custom-designed enclosures,
these have evolved to become more highly integrated, now
including control electronics designed to be ready to accept software
to produce a complete system.
The SKAI vehicle power systems boast a high level of integration and
offer major advantages over comparable competitor systems. They
are developed in line with the latest automotive standards and system
qualification standards, allowing short time-to-market and lower
development costs. The SKAI systems are supplied as standard platforms
with low-voltage MOSFETS or high-voltage IGBTs as the silicon
base. SKAI systems can also be developed to meet individual
customer specifications. Semikron is a single-source supplier,
encompassing everything from feasibility and proof-of-principle studies,
to the development of optimum system architecture, to electrical
and mechanical simulations, end qualification and complete-system
series production.
Aux. power
CAN comm., external I/O
Enclosure IP67
One system, three types
The high-voltage SKAI 2 is available as a water-cooled 600/1200V
IGBT inverter system, and has been optimised for use in applications
such as full-electric cars, plug-in hybrid cars and electric buses. This
system is based on the established sintered, 100% solder-free
SKiM93 IGBT modules, features a polypropylene film DC-link capacitor,
driver electronics, a latest-generation DSP controller, EMC filters,
and current, voltage and temperature sensors, and is supplied in an
IP67 module case. Communication with the vehicle master controller
is via a CAN bus. These systems are designed for outputs of up to
150kW (Figures 1 and 2).
Figure 2: The high-voltage SKAI system is available as a liquidcooled
600/1200V IGBT inverter system, and has been optimised for
use in applications such as full-electric cars, plug-in hybrid cars and
electric buses.
DSP controller
Power supply
Gate driver
Protection
Power
input
terminals
DC-link
capacitor
V
Power section
• 3-phase IGBT inverter single/dual
• 3-phase MOSFET inverter single/dual
T
I
I
• DC-DC converter
I
• Battery charger
• Sensors I/T
• EMI filter
Current
Voltage
Temperature
Power
output
terminals
Heat sink
(Water inlet)
(Water outlet)
Figure 1: A typical SKAI system architecture
Figure 3: The low-voltage version is available as an air-cooled or liquid-cooled
50/100/150/200V MOSFETsingle and dual inverter system,
which is used in material handling and smaller vehicles.
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COVER STORY
The low-voltage version is available as an air-cooled or liquid-cooled
50/100/150/200V MOSFET single and dual inverter system, which is
used for material handling and smaller vehicles. These systems are
suitable for a motor output power of up to 40kW. They incorporate
many of the same features as the IGBT-based systems and therefore
offer the benefits to customers that they behave in the same way,
use the same core control system and I/O connections, and the
same system structure (Figure 3).
The third type of SKAI 2 platform is a multi-converter box. These systems
are also housed in liquid-cooled, IP67-protected cases and
communicate with the vehicle master controller via a CAN bus. The
signal interface features analogue and digital I/Os to allow for the
connection of a wide variety of sensors, such as temperature sensors
and resolver inputs. A typical multi-converter system would include a
three-phase 40kVA active front-end converter, a three-phase 20kVA
drive inverter, a three-phase 10kVA drive inverter, and a 14V/300A or
28V/165A DC/DC converter (Figures 4 and 5).
AD
Figure 4: Topology of a typical multi-converter system
Figure 5: The SKAI 2 highly integrated multi-converter system
All SKAI 2 modules are fully qualified using test techniques such as
highly-accelerated life testing (HALT) and end of component-life testing,
with full failure-mode effect analysis studies conducted at all critical
points of the design cycle, to ensure that they are in line with relevant
automotive standards. Thermal and electrical contact of the
power semiconductors is established by pressure contact technology,
which boasts extended service life and high load cycling capability.
The systems and semiconductor components are manufactured in
high-tech production processes that include end-of-line function tests
and, if required, 100% burn-in tests, ensuring a high degree of quality.
Novel technologies
There are many factors that affect the efficiency and reliability of
power systems.
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21

COVER STORY
To achieve maximum energy, cost and space efficiency, coupled with
high reliability, it is important to combine the best silicon, packaging,
layout, thermal performance and control in the design and manufacture
of power systems. This can often be difficult if the designer has
to depend on off-the-shelf parts. It is very important to be able to optimise
the selection of silicon and to be able to connect it as needed
for optimum performance in a system.
Many suppliers of systems focus on a single technology, such as
MOSFET or IGBT, or may concentrate on applications at a single
voltage. However, the wide variation in requirements of today’s systems
makes it important to be able to choose from the widest selection
of semiconductor technology to achieve the best match to the
application. It is also important for the design process to take into
account the many issues dependent on the semiconductor technology
and the relationships between them, to ensure that the hardware
is optimised for the application. As Semikron is a major manufacturer
of power semiconductors, it can push boundaries in areas such as
temperature and size. For example, the company produces very
large volumes of IGBT and MOSFET drivers, and from this expertise
has developed optimised application specific integrated circuits
(ASICs) to significantly reduce component count and increase reliability,
while reducing size dramatically.
Current developments in power electronics aim to achieve higher current
densities, system integration and greater reliability. At the same time,
there is more call for low-cost, standardized interfaces, as well as flexible
and modular product series. Semikron has set trends in this area by the
use of spring contacts for the auxiliary and load connections.
The reliability of classical module designs is not sufficient for many
developing applications in power electronics. For example, these
modules are limited in their capability to withstand passive temperature
cycles. It has therefore been necessary to develop new techniques,
which are capable of meeting the high-reliability requirements
of modern applications.
A major limitation of power module lifetime is the problem of solder
fatigue. In traditional constructions, this contributes to the end-of-life
failure of power modules, especially in the case of higher temperature
swings, which are predominant in most applications. Several
new technologies have been developed to eliminate all solder interfaces.
Each of these offers advantages compared with traditional
constructions, but in combination they offer significant benefits.
The most significant problem caused by higher temperatures and
larger swings of temperature is delamination of soldered joints. This
problem has been completely overcome in the latest SKAI systems
by using sinter technology to join the semiconductor chips to the
ceramic substrate instead of solder, meaning that higher operating
temperatures are possible with increased reliability. The sinter bond
is a thin silver layer that has a superior thermal resistance to a soldered
joint and contains far fewer, and smaller, voids. It is not subject
to the delamination that affects solder joints, resulting in a low thermal
resistance that remains low over many tens of thousands of
power cycles. The high melting point of silver also prevents premature
material fatigue.
Another issue raised by increased junction temperatures is the
fatigue of the wire bonds used to join the chips to the substrate. This
has been minimised by a number of changes to production techniques,
including changing the geometry of welded joints and the
introduction of novel stress-relief techniques.
SKAI 2 systems are offered with or without control software. If
required, Semikron will work with its customers to develop software
or the customer may prefer to use its own. This gives the customer
much more versatility and the capability to produce systems with its
own custom features.
SKAI 2 system in tractor application
The system is also integrated in tractors. An example:
A tractor manufacturer was developing an electric power supply system
for its upper power-class tractors, with the aim of reducing fuel
consumption and noise emissions. The development was also intended
to introduce the architecture needed for additional electric drive
applications in agricultural machinery.
Until now, secondary equipment in tractors has been connected to
the main drive mechanically via gears. This does not enable these
functions to operate at the optimum operating point, leading to poor
overall efficiency and consequently to increased fuel consumption
and pollutant emissions. The aim was therefore to disconnect the
secondary equipment from the main drive. For this purpose, a modified
generator connected to the main drive would be used to generate
electric power. This would then be electrically converted to
ensure optimum operation of the fan, air compressor, air conditioning
equipment and the 14V on-board power-supply.
A highly-integrated power electronics system from the multi-converter
system family was developed to meet the customer’s specifications.
The system comprises multiple converters used to control electric
current flow under harsh ambient conditions. Different operating
modes are possible, for example the system can be supplied with
electric power by way of a three-phase generator or an HVDC bus.
The system communicates with the vehicle master controller via a
CAN bus. The integrated semiconductor components come from the
tried and tested MiniSKiiP family (2nd generation). The signal interface
features analogue and digital I/Os to allow for the connection of
a wide variety of sensors, such as temperature sensors and resolver
inputs.
The new electric power supply system is the basis for the introduction
of ultra-precise, highly efficient electric drives for attachment and
trailer equipment, as well in final drive systems. The combination of
different technological solutions results in far lower fuel consumption
and reduced noise emissions, and ensures that future emissions limits
are met. All of the power transmission components were developed
or optimised in order to improve overall efficiency. In summary,
this constitutes a milestone on the path towards ultra-low consumption
in upper power class tractors, which are normally prone to high
consumption.
Integrated power systems
Many advances in the drive for higher integration of power systems
have been made. However, further advances in reliability, efficiency,
size and versatility will be needed to increase the market acceptance
of integrated power systems. By offering system-wide expertise in
one organisation, Semikron’s Systems Group is well placed to develop
higher levels of integration, improved cooling technologies, higher
silicon operating temperatures, higher performance from ASICs and
novel packaging techniques. New insulation systems, new methods
of silicon attach and, in time, the total removal of wire bonds, will all
improve efficiency and reliability still further.
www.semikron.com
22 Bodo´s Power Systems ® September 2010 www.bodospower.com