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Community.dialog

Issue 03-2016 I September

Issue 3-2016 | September

Community.dialog

Young Engineer Award/Power Electronics

Single-Event-Burnout due to cosmic radiation: Important failure mode of power semiconductors

Best Paper Award PCIM Asia/Power Electronics

The next generation high voltage package and IGBT/diode technologies

Young Engineer Award/Power Electronics

How to protect IGBTs against short circuits

PCIM Europe 2016

Visitor and exhibitor comments

Best Paper Award/Power Supply

Low power converter, how to achieve high performances?

PCIM Worldwide

Exhibition focusing on power electronics

Commentary

It’s all a matter of voltage

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Issue 03-2016 I September

being used for the electric machine could be simplified as well. At this point, I would also like to clear up a misunderstanding I was confron­ted with during a conversation with a battery manufacturer: Power electro­nics definitely had no influence on the decision to set the nominal battery voltage to 400 V.

“A nominal battery voltage of 400 V is not suitable for a fully electronic ve­hicle with an elec­tric drive power of 100 kW. In order to reduce transmission losses and the costs for components, the nomi­nal voltage should be considered to be raised to 800 V.” – Prof. Dr. Ing. Gerd Griepentrog, Institute for Pow­er Electronics and Control of Drives, TU Darmstadt

When the German Federal Government de­cided to subsidize the production of elec­tric vehicles this year, the whole nation was „electrified“ for a moment. Politics seemed to have given the necessary impetus to the industry. Taking into account the 12,000 new registrations in 2015, the ori­ginal objective of one million registered electric vehicles in Germany by 2020 ap­peared somewhat ambitious. Of course, the number of registrations has been gro­wing every year since 2010, which means that Germany’s fleet of electrical vehicles grows progressively. However, the situati­on in Asia looks a whole lot different. The Chinese automotive manufacturer BYD alo­ne is planning to sell 150,000 electric ve­hicles this year.

Faced with this situation, we have to ask and answer a rather technical question: Which battery voltage do these cars requi­re? As the nominal battery voltage of an electric vehicle determines the interme­diate circuit voltage of the inverter, it is highly important to start thinking about it. After cancellation of cell manufacturing in Germany a new industry is fortunately evol­ving that produces battery systems and integrates individual cells, cell balancing technology, cooling and battery manage­ment systems. Therefore, the meaning of the right battery voltage gains even greater significance. Today, most manufacturers use battery systems with a nominal voltage of 400 V (equivalent to 96 cells connected in series)

Commentary

It’s all a matter of voltage

to achieve a power between 90 and 150 kW. Discharge of the battery (“State of Char­ge“) reduces the voltage to 300 V. On the basis of this voltage, semiconductor ma­nufacturers produce IGBT systems with

„exotic“ blocking voltages of 650 V for the automotive industry. However, we have to ask ourselves if a nominal voltage of 400 V is the best choice from a system prospec­tive for electric vehicles.

At a voltage of 300 V and a power of 120 kW, the battery has to provide the in­verter with 400 ampere. This requires a Cu cross section of 185 mm2. Ambient temperatures of 60 °C demand an even larger cross section. Apart from restricted cable routing and a increased conduction losses within the semiconductors, the DC power switches are exposed to extreme stresses (lifting forces, short circuit cur­rent). The screw and plug contacts are faced with massive challenges, as well. Moreover, as their purpose is to reduce the transition losses to a minimum, they are also very complex and expensive. All these factors considered, would it be more reasonable to raise the nominal bat­tery voltage up to 800 V in order to optimi­ze the system? This would not exceed the upper limit of the low voltage area and, compared with 400 V, the clearance and creepage distances are not substantially higher. Furthermore, 1,200 V IGBT systems have proven their worth as a semiconductor technology for decades within industrial applications and the winding technology

Construction of the e-Golf: Motor and inverter in the front; lithium-ion battery in the back (Figure: © Volkswagen)

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Issue 03-2016 I September

Young Engineer Award/Power Electronics

Single-Event-Burnout due to cosmic radiation: Important failure mode of power semiconductors

A high reliability is a requirement in order to minimise the total costs of power con­verters for the use of renewable energy such as wind and photovoltaic power. Both reliability and lifetime have a direct influ­ence on the levelised cost of electricity which is relevant for investors and system operators.

In order to ensure high reliability through­out the entire operating time of a system the potential failure mechanisms of the used components have to be considered when developing the power conversion system. The expected failure rate is to be kept low by appropriate sizing and it has to be ensured that component failures caused by wear­out are not to be expected during the planned operating period of the system.

In this work the failure mode of single­ event­burnout induced by secondary cos­mic radiation particles that reach the earth surface was examined. Stress profiles for

photovoltaic central inverters with rated powers in the 800 kW region were gener­ated on the basis of simulations for several locations and different configurations of photovoltaic generators. Aside from invert­ers for the well­established 1.000 V sys­tems inverters for 1.500 V systems were also looked at. It is expected that in the future systems with maximum open circuit vol tages of 1.500 V will be more commonly used in order to reduce system costs of large PV systems. Additionally, the influ­ence of output power curtailments of PV parks on the voltage stress of the power semiconductors was considered on the basis of assumptions for the possible fre­quency of occurrence of such interven­tions.

As part of an ongoing research project accelerated measurement of the voltage dependent failure rate due to cosmic radi­ation of different Silicon and Silicon­Car­bide power semiconductors were conduct­ed. Using the simulated stress profiles and the measured voltage dependent failure rates the expected average failure rate due to cosmic radiation induced single­event­ burnout in the application was calculated for different scenarios.

The obtained results have shown that the use of 1.200 V semiconductors in inver­ters with maximum open­circuit voltage of 1.000 V, as well as the use of 1.700 V sem­iconductors in inverters with for 1.500 V

systems can be problematic for their reliability. It was shown that depending on the choice of semiconductor signif­icantly different failure rates can be expected due to the differences in ro­bustness of the different semiconduc­tors. Whether a certain power semicon­ductor is robust enough for a certain application or whether it is necessary to use devices of a higher voltage class or more complex multi­level topologies can only be decided for the individual case. For such a decision knowledge of the robustness of the considered de­vice as well as the expected voltage stress is required.

„Our investigation shows that it is important to deter­mine the robust­ness of the semi­conductors against cosmic radiation as well as the expected voltage stress accurately in order to evaluate the reliability of the components in the application.“ – Christian Felgemacher, University of Kassel, Germany

Fig. 1: Experimental setup for accelerated measurement of failure rate due to cosmic radiation

Fig. 2: Typical voltage dependency of failure rate of power semiconductors due to terrestrial cosmic radiation

Fig. 3:Exemplary voltage stress on a 1.000 /1.500 V PV inverter in different locations, not taking into account any external effects such as output power curtailment. (Figures: Universität Kassel)

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Issue 03-2016 I September

allel to the gate (Fig. 2). Thanks to the early short­circuit detection and the quick switch­off by means of the auxi­liary MOSFET, we can realize a short­circuit protection system that meets the requirements of modern high­performance IGBTs (Fig. 3).

„New protection systems must be developed in ac­cordance with the characteristics of modern power se­ mi conductors. 2D short­circuit detection is a new ap­proach that makes it possible to use IGBTs with a high desaturation cur­rent without having to make compro­mises in terms of short­circuit pro­tection.” – Dipl.­Phys. Stefan Hain, Institute for Energy Technology, Chair of Mechatronics, University of Bayreuth

The current trend towards the development of ever more powerful IGBTs requires ever more efficient short­circuit detection sys­tems. Of course, thinner chips and larger channel widths improve the voltage sweep. However, this also results in lower thermal capacities and a stronger desaturation cur­rent. These two parameters reduce the maximum short­circuit duration of a de­saturated IGBT. This is why some modern IGBTs cannot endure a long desaturation period without being damaged, which re­sults in many of these IGBTs being referred to as “not short­circuit proof“. However, it should rather be acknowledged that moni­toring the desaturation until the short­cir­cuit protection kicks in is not an appropri­ate approach to protect modern power semiconductors. Furthermore, it is impor­tant to recognize that new detection meth­ods like 2D detection are needed.

The new 2D short­circuit detection method is capable of detecting a short circuit at the earliest possible point in time. This ap­proach takes advantage of the fact that a

Young Engineer Award/Power Electronics

How to protect IGBTs against short circuits

normal switching operation can be distin­guished from a short­circuit operation by monitoring the gate voltage and the di/dt behaviour of the semiconductor simultane­ously (Fig. 1). If the reference value for both measured parameters is exceeded at the same time, a short circuit has occurred and the IGBT can be protected in time by means of an adapted switch­off. When monitoring both parameters simultaneous­ly, a two­dimensional detection area oc­curs in the corresponding phase diagram. The approach is named after this detection area. The di/dt behaviour of the semicon­ductor causes a measurable drop in vol­tage at the parasitic inductance between the main and auxiliary emitter and the gate voltage can be measured directly at the terminal. For these two reasons, the imple­mentation of this method is quite simple and doesn’t require a connection to the high voltage side (unlike monitoring the de­saturation) or a particular chip design (un­like the current mirror). After the error has been recognized, the IGBT can be switched off by activating an auxiliary MOSFET par­

Fig. 1: Comparison of regular switching operations and short circuits by means of the 2D detection method

Fig. 2: Implementation of the 2D-short circuit detection method Fig. 3: Detection and elimination of a short circuit by means of 2D short-circuit detection (Figures: University of Bayreuth)

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Higher power integration and soft switch­ing behavior are major driving forces for next generation packages and chip­sets. With the previous chip­technologies like the enhanced planar SPT+ IGBT and the low leakage current and high temperature field shielded anode (FSA) Diode, stan­dards have been set in terms of robustness, current density and low losses. ABB’s lat­est enhanced trench or TSPT+ technology enables a significant reduction in V

ce(sat) of

600 mV for the same turn­off losses. This enables a 20% higher current carrying ca­pability for a given module footprint and a similar active area. TSPT+ uses an n­en­hancement layer encompassing the p­well regions and a striped architecture for the active Trench MOS Cell as shown in Fig. 1. This prevents that the p­well swallows holes and hence reduces the emitter­side carrier density. A controllable turn­on switching and reduced gate­charge in or­der to be compatible with existing IGBT gate­drive concepts is a key design factor.

As a companion diode for the TSPT+ IGBT we use a Field Charge Extraction (FCE) Di­ode with FSA front­side. Fig. 2 shows the

schematic cross­sections of the active area of the FSA diode. A high p+ doping forms the anode contact and a deep dif­fused p­buffer anode supports the electric field during blocking. In contrast to the uniform backside contact of the FSA diode, the cathode of the FCE diode consists of a two­dimensional lattice of p+ islands embedded in the high n+ cathode doping. During turn­off this pn­junction is forward biased and triggers an injection of holes from the p+ areas resulting in a limited ad­ditional supply of holes. This enables a soft reverse recovery by preventing the sudden depletion of the stored plasma.

The LinPak is a new generation high­power IGBT module featuring latest technologies such as ultrasonic welding of main termi­nals, bonded auxiliary connections for im­proved thermal cycling performance and a very low inductive package concept. The later allows for the first time the use of fast and low switching loss IGBTs and diodes in a high current package without the nega­tive effects such as inacceptable high tran­sient over­voltages. Fig. 3 shows the over­all inductance benefit of a LinPak solution

Best Paper Award PCIM Asia/Power Electronics

The next generation highvoltage package and IGBT/diode technologies

compared to a state of the art solution with 190 x 140 mm2 HiPak modules. An overall stray inductance reduction of a factor of five has been achieved. The record low overall inductance di­rectly translates in soft switching with low over­voltage, which is a key feature to our low voltage and low switching loss chip­sets like the fast 1700 V SPT++ IGBT.

“The new LinPak module enables to optimal use of the latest and future chip­sets like the SPT++ and TSPT+ IGBTs.” – Raffael Schnell, Global Pro­duct Manager Bi­MOS, Dr. Sven Matthias, Senior R&D Project Man­ager, ABB Switzer­land Ltd.

Fig. 3 Overall inductance benefit of a LinPak solution compared to a state of the art solution with 190 x 140 mm2 HiPak modules (Figures: ABB Switzerland Ltd.)

Fig. 1: Technology curve for TSPT+ and SPT+. Striped architecture for the active Trench MOS Cell

Fig. 2: Schematic cross-sections of the active area of the FSA diode

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The power supply system in an onboard aeronautical application represents an im­portant contribution to the recurring cost, global efficiency and the volume of the sys­tem. Moreover, power supplies are in­stalled in a harsh environment with a wide input voltage range and a confined area. In these conditions, power supply losses im­pact the converter volume and weight to prevent the system from overheating. Therefore, a gain in efficiency is the main purposes, since it has a significant impact on the reduction of weight and volume of the equipment.

Soft­switching is a reasonable technique to increase the switching frequency and limit the power losses. The selection of the topology should take into account three considerations:

• a low number of components, • an efficient control, which allows to

cover the wide input voltage range and • a soft­switching validity over a large

input voltage range.

Regarding all the considerations, the Fly­back Active­Clamp topology seems to be the best candidate which has a step­up and down transfer function and ZVS at the primary with only ones additional ca­pacitor and transistor.

A technological work is also done to further increase the power supply efficiency. The technologies which have been selected are the GaN transistors for its good switching performances and a planar transformer for its integration into the PCB. Also, the verti­cal integration of the converter which is actually on two stackable boards, one for the low frequency functions and the other one for the high frequency functions (Fig. 1), minimizes the footprint of the converter.

Those improvements lead to an increase of the converter efficiency (Fig. 2) up to 95% at 1 MHz. With the vertical integration, the module is more compact with a reduction of 60% of the surface compared to a single stage converter with the same schematic (Fig. 3).

Best Paper Award/Power Supply

Low power converter, how to achieve high performances ?

The new technologies will make a huge technological leap, especially in the systems where the power supply repre­sents a significant proportion of the equipment. The success of GaN tran­sistor highlights that the power elec­tronics is currently driving by the per­formance and reducing the parasitic elements is becoming the priority. Look­ ing forward into the future, the interest in 3D packaging and PCB integration will grow rapidly to provide a fully em­bedded power supply.

„Today, the emer­gence of new tech­ nologies is trans­forming the power supply toward an integrated system. However several technological issues need to be ad­dressed before having a Power Sup­ply in Package (PSiP) in aircraft ap­plications.“ – Nicolas Quentin, PhD Student Ampere Lab and Safran Group.

Fig . 1: Synoptic and breakdown of functions

Fig. 2: Power module and efficiency

Fig.3: : Prototypes comparison (Figures: Ampere Lab and Safran Group)

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„A great show, giving an insight into the development of the Power Market globally. A fantastic platform to meet customers suppliers and great for new business acqui­sition!“ – Aran Sharma, Sales Manager, Columbia Staver

„PCIM is the real unique meeting point for all power electronics professionals where information can be gathered quickly and up to date through highly skilled inter­faces.“ – Roberto Molteni, Technical Direc­tor, Gefran

„PCIM Europe is the very best show for po­wer electronics technology. It is great to see what is new and to catch up with all our customers and suppliers. I have been attending for 10 years and will continue to attend.“ – Hamish Laird, CTO, ELMG Digital Power

„PCIM successfully brings together power engineers to engage in the latest and finest Power Solutions in the industry.“ – Sam Taiwo, Distribution Manager, ROHM Semi­conductor

„I think PCIM Europe is the best show for the parts of the power electronics. I got the insight of how to design our product and what the direction of the development strategy.“ – Yongsung Jeon, Power Electro­nics Engineer, LG Electronics

PCIM Europe 2016

Visitor and exhibitor comments

„The PCIM Roadshow is a great opportunity to get an overview of new developments in the market of Power Semiconductors. For Plansee it is a good chance to meet customers, to talk to experts and provide support with our refractory materials.“ – Katja Rosenmüller, Manager Application Goup Power Semiconductors, Plansee

„PCIM is „the place to be“ to exhibit your products to the whole power electronics community, with great representation from participating companies: from technical to sales and executive levels.“ – Frederic Dupont, CEO, Exagan

„Vincotech has been an exhibitor at PCIM Europe for more than 15 years. For us PCIM Europe is the continent‘s leading trade fair and the venue where we present our new products to the market. We are looking forward to a renewed opportunity to do so in May 2017.“ – Eckart Seitter, SVP Sales & Marketing, Vincotech

„PCIM 2016 has been a success with growing customer audience and important customer meetings in the industrial & mass market segment.“ – Didier Dedeurwaerder, Corpo­rate Communications Manager, STMicro­electronics

„PCIM 2016 was an impressive exposition of high quality products.“ – Ercole Scampini, Quality Assurance, Kendeil

„Our first participation was straight in the bull‘s eye!“ – Thierry Vandereycken, Mana­ging Director, EME nv

As part fo the event, oustanding accomplishments have been awarded. From left to right Young Engineer Award Winners: Christian Felgemacher, University of Kassel, Germany, Christoph Marxgut, Helbling Technik, Germany, Stefan Hain, University of Bayreuth, GermanyBest Paper Award Winner: Nicolas Quentin,Sagem - Ampere Labs, France

This year’s PCIM Europe was a record-breaking event with more than 10,000 visitors from 67 different countries, with 436 exhibitors presenting their products, solutions and services on 21,500 m2.

This was also the case for the conference, as 771 attendees visited PCIM Europe Conference to benefit of the comprehensive networking opportnities and to exchange knowledge.

Additionally, the forums and the poster-presentati-on were highly frequented.

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media, as well as corresponding reproduction and circulation, the right to electronic use, and publishing in all types of data networks and mediums. It also covers the transfer of the above­mentioned rights to third parties.

Contributions bearing the name or symbol of the author do not necessarily represent the opinion of the editors. No responsibility is accepted for unsolicited submissions.

ImprintCommunity.dialog

11. Jahrgang · ISSN: 1863­2416

Mesago PCIM GmbH, Rotebühlstr. 83–85, 70178 Stuttgart, Tel.: +49711­61946­0, Fax: +49711­61946­98, Mail: info@mesago.com, www.mesago.de · Local court: Stuttgart, HRB HRB 720222 · Director: Petra Haarburger, Martin Roschkowski · Vice president: Lisette Hausser · Editor: Holger Best (ViSdP), Tel.: +497251­724302, Mail: holger.best@bestmedienkonzepte.de · Reader Service: Caroline Lovell, Tel.: +49711­61946­26, Mail: caroline.lovell@mesago.com · Layout and Setting: JOY DESIGNS freude an guten Designs, Jennifer Dietmann, www.joy­designs.de · Publication frequency: 3 x per year

© Copyright: Mesago PCIM GmbH, 2016, Stuttgart.

Despite careful checks by the editorial team no responsibility can be taken for the accuracy of the publication. The newsletter and its con­tents are protected by copyright. Any usage outside of the copyright li­mitations requires the prior consent of Mesago PCIM GmbH. With the acceptance and publication of the script, the full and sole usage rights are transferred to Mesago PCIM GmbH without restrictions on region, time or content. This encompasses the publication in all types of print

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At PCIM Europe 2016 436 exhibitors and 93 represented companies presented themselves, which resulted in a five per­cent increase in comparison to last year. In particular, 10,053 visitors from 67 differ­ent countries praised the comprehensive overview of the complete power electro­nics industry as well as the first class net­working opportunities. Thereby, ninety four percent of all visitors would recommend PCIM Europe to their colleagues and would like to visit the exhibition in 2017 again.

Since 2002, PCIM Asia takes place annu­ally in Shanghai, China. This year 87 exhib­itors have met from 28 ­ 30 June 2016 on 5,600 square meter at the Shanghai World Expo Exhibition Center, China, to present their newest products and developments at Asia’s leading exhibition and confer­ence about power electronics and its appli­cations. During the three exhibition days, 5,492 visitors informed themselves about newest trends and developments within the industry. These are twelve percent more visitors as in 2015.

Here you may find a detailed analysis of PCIM Europe 2016 and of PCIM Asia 2016.

PCIM Worldwide

Exhibition Focusing on Power Electronics

The combination at the PCIM event of the user oriented conference and specialised exhibition is extraordinary. The excellent quality of the conference contributions, the high number of attendees from the in­dustry and the very good publication op­portunity in the IEEExplore, IET Inspec, Compendex and Scopus data base, are attributes which makes the PCIM Confer­ence an attractive platform for speakers to introduce their research and develop­ment results in first time publications.

With 771 attendees (fifty nine percent coming from abroad) and 295 presenta­tions PCIM Europe Conference 2016 con­firmed its high importance as international knowledge forum for the power electronics industry. The Call for Papers for PCIM Europe 2017 ends on 18 October 2016. Further information is online.

PCIM Asia Conference 2016 was able to register 358 attendees. With attractive keynote presentations, six sessions and two dialogue oriented poster sessions, the conference offered a comprehensive and versatile program for the Asian power electronics engineer. The Call for Papers for PCIM Asia 2017 ends on 16 November 2016. Further information is online.