Mastering Power Modules The advantages over discrete solutions

Special Report – Powering Freight & Transportation
Special Report – Powering Freight & Transportation
Mastering Power Modules
The advantages over discrete solutions
With the strong upsurge in the need for power electronics in diverse applications such as solar,
wind, freight and logistics, industrial drives and UPS, system developers are becoming increasingly
aware that the selection of the power devices for these often remotely-sited applications is critical.
Such systems require the highest reliability and efficiency to minimize operating costs and build
industry integrity for the developer.
By Werner Obermaier, Head of Product Marketing, Power Modules & Hybrids,
Vincotech GmbH, Munich, Germany
T
here is much discussion over
what actually constitutes a Power
Module. A typical example of a
PIM Module for a drives application
(see figure 1) would contain, in a single
housing, a three-phase input rectifier, a
brake chopper, a three-phase inverter
plus the vital isolation material; the high
prevalent voltages and levels of thermal
stress are key to the ‘excellence factor’
encompassing the efficiency and most
importantly, the long-term reliability, of a
well designed PIM.
Power Modules have become the
most convenient way of building a cost
effective power supply system. Everything is optimized within the constraints
of the particular module manufacturer.
The designer can rest assured that the
module will do everything electrically
and mechanically that is specified, is
guaranteed to work to tight specifications such as EMI, efficiency, load cycling and reliability and it is virtually ‘offthe-shelf’ meaning that the all-important
time to market pressure is minimized.
Figure 4: Complete 12-cell Battery Monitoring Circuit with cell-balancing and protection circuitry.
useful features that simplify module
circuitry, such as an onboard 5V series
regulator, general-purpose ADC inputs,
and general purpose digital inputs and
outputs (GPIO). As an example, the
GPIO can be used as multiplexer controls to expand the two general purpose
ADC inputs to an eight-channel capacity. To ensure proper IC operation, an
open-drain output watchdog timer is
provided to indicate an idle period of
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communication.
Conclusion
After years of effort and steady progress, high energy battery systems will
soon be practical for everyday use, especially as part of the electric and hybrid
electric vehicle. The cost and complexity
of high-quality Lithium-Ion battery data
acquisition and cell-balancing controls
are greatly reduced with the advent of
the LTC6802 cell-monitoring platform.
This battery monitoring IC simplifies
the data acquisition task with a single
device, while improving intrinsic reliability and adding feature-rich functionality.
A well thought out design, including
plenty of protection mechanisms, provides robust operation in the unforgiving
environment of high-energy EV and HEV
systems.
www.linear.com
Power Systems Design Europe
October 2009
There is understandably a healthy
debate on the various arguments on the
topic of Module vs. Discrete component
structure. Cost inevitably seems to be
the driver in such arguments but then,
what is meant by cost? If we simply take
the sum of the costs of the individual
discrete parts plus the cost of putting
these parts together and shipping as
the system cost, then we are deluding ourselves. We need to consider the
impact of system reliability (load cycle
www.powersystemsdesign.com
/ temperature cycles). The last thing a
manufacturer wants in the field is an
installed base of ‘potential problems’. A
system that looks good on the balance
sheet and performs well in the lab, but
after being deployed for some time in
the field, suddenly fails. This escalates
the cost of the original calculation significantly and can destroy the credibility
that has been built by the manufacturer,
perhaps over decades.
There is also a high risk factor associated with developing a discrete solution.
It can be readily appreciated by any
designer that these projects never run
smoothly; there are the inevitable design
bugs to remedy requiring re-spins,
tough specifications to achieve and
regulations to adhere to and get verified.
All this takes up valuable time as well as
a significant financial burden.
With vital impact on system design,
the PCB layout needs to be given special
attention. Lead inductance and resistance play a great part in determining the
losses and heat generation, all of which
–unless skillfully compensated- can
impact detrimentally the reliability of the
system. Down time costs for an installation are painfully high and servicing faulty
units in the field is difficult, expensive
and in worst case, impossible. Reliability
is therefore a premium priority.
One huge initial apparent cost saving
which can result in failures further down
the line is the use of a copper substrate.
Naturally, it looks an ideal and simple
Figure 1: Typical power module showing the vital electrical and thermal connections (a), and the robust, maintenance-free housing (b).
Figure 2: High quality, low inductance
electrical and thermal connections are
vital for high efficiency and field reliability.
45
SPS/ IPC/ DRIVES /
Figure 3: The layered construction of the PIM using highest quality materials (a), provides optimum long-term reliability with a
high load cycling capability (b).
choice due to its electrical and thermal
conductivity. The problem can appear
after field service and the normal inservice load and temperature cycling
(see Figure 3). The thermal expansion of
copper is not a good fit with silicon. A
much more reliable solution is achieved
with the use of ceramic. This is a solution that is initially more costly, but profoundly more reliable. One has to invest
up-front to save costs and integrity in
the longer term.
Apart from the electrical design, a vital
part of the overall product ‘persona’ is
the mechanical design and component
layout. Power systems generally operate
in extremes of the environment. Poor
ventilation and hostile physical
and environmental conditions are
generally the norm in industrial
drives and renewable energy installations such as solar or wind
power.
A great impact on system cost
is the assembly process. Discrete processes where soldering power semiconductors with
heatsinks attached needs to be
very precisely aligned requiring
specialized alignment tooling and
skilled operators in many cases
or individual heatsinks for each
semiconductor, using operators
of similarly high skill levels.
Vincotech has introduced its
new press fit technology to the
market and is now shipping
modules using this labour saving
46
technology. The modules featuring this
new pin technology are simply pressed in
rather than soldered into the PCB, thus
reducing PCB assembly time and costs.
The Vincotech press fit pin design is
well established in the automotive industry and provides a reliable and gas-tight
connection to the PCB. By eliminating
the necessity of a solder process for the
module, the customer reduces the PCB
assembly time and thereby the production costs. A higher production output
capacity is the direct consequence.
moved without damaging the PCB, thus
allowing for the reuse of the PCB with a
new module. Design flexibility is guaranteed by the elimination of the need
for soldering; the module can easily be
mounted on either side of the PCB at no
extra cost or effort.
Vincotech’s Press Fit Technology is
DIN and IEC compliant and available
upon request for all Vincotech proprietary module designs in pin-compatible
versions to the current portfolio.
Of course, there are many module
vendors in the marketplace and this
can be a tough call to make the right
selection. Most vendors are tied to their
own proprietary brand in the
choice of materials technology
and semiconductors. Naturally
it just would not be possible for
module-maker ‘A’ to select MOSFETs from semiconductor-maker
‘B’. Corporate rules would simply
not allow it. But does this result in
an optimum module? The answer
is of course, no. To get the best
of all worlds, one needs to go to
an independent source such as
Vincotech, where components
and assembly can be truly optimized or even customized. Never
has this been more important
than in the power generation field
where every percentage point in
efficiency, reliability and therefore
true cost of ownership adds to
Figure 4: Press fit technology utilizes new pin technol- the customer’s profitability.
ogy (a), which eases assembly to the PCB (b), reducwww.vincotech.com
ing time and cost of manufacturing.
Further advantages of press fit technology include reuse of the PCB and
design flexibility. The module can be re-
Power Systems Design Europe
October 2009
Electric
Automation
Systems and Components
Exhibition & Conference
24 – 26 Nov. 2009
Nuremberg
Experience electric automation
at its best!
Come and see it all!
Control Technology
IPCs
Drive Systems and Components
Human-Machine-Interface Devices
Industrial Communication
Industrial Software
Interface Technology
Electromechanical Components and Peripheral Equipment
Sensor Technology
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Special Report – Powering Freight & Transportation