Capacitors for power electronic applications and innovations in the field

00:00:00: (mellow music)

00:00:01: - You're listening to the PCIM Podcast,

00:00:03: your podcast on power electronics.

00:00:07: - Hello, everybody, and welcome to the 13th episode

00:00:11: of PCIM Podcast, your Power Electronics Podcast,

00:00:14: powered by PCIM.

00:00:16: My name is Marco Jung, I'm a professor for eMobility

00:00:19: and electrical Infrastructure at

00:00:20: the Bonn-Rhein-Sieg University of Applied Science

00:00:22: at Sankt Augustin,

00:00:24: as well as head of department converters

00:00:26: and Electrical Drives at the Fraunhofer Institute

00:00:29: for Energy Economics and Energy System Technology at Kassel.

00:00:34: Both are located in Germany.

00:00:36: Additionally, I am the chairman

00:00:38: of the IEEE Joint IES IAS PELS German chapter,

00:00:43: IEEE PELS Region 8 Vice-Chair: Germany

00:00:46: and active member of several national

00:00:48: and international communities and committees.

00:00:52: And today our technical theme is capacitors

00:00:55: for power electronics, challenges and improvements.

00:01:00: And this I will discuss with Thomas Ebel

00:01:02: from the University of Southern Denmark.

00:01:04: Hello, Thomas, how are you?

00:01:07: - Hi, I'm fine, how are you?

00:01:12: - Fine as well.

00:01:13: So now, let's say the weather is not

00:01:15: so really nice in Germany right now,

00:01:18: but hopefully in Denmark it looks a little bit better.

00:01:22: - Yeah, we have blue sky

00:01:23: and I'm sitting here close to the Als Sund,

00:01:26: so close to the water

00:01:28: and we have blue sky and blue sea,

00:01:31: so I'm happy to participate here

00:01:35: in this podcast under these conditions.

00:01:39: - Fine.

00:01:41: Thomas, in the past you have had a rarity

00:01:44: of professional positions.

00:01:46: Can you give us a short introduction of your career?

00:01:50: - Yes, of course.

00:01:51: After my PhD in solid state chemistry

00:01:54: at the University of Münster in 1995,

00:01:59: I joined Siemens Matsushita Components in Germany,

00:02:03: which later became Epcos and it's now TDK,

00:02:06: as developing engineer for aluminum electric capacitors.

00:02:11: After some years I got promoted as R&D director

00:02:15: of that component at Epcos.

00:02:18: In 2001 I was delegated as R&D director, later as CTO,

00:02:24: to the Siemens partner company, Becromal,

00:02:27: which is now TDK Foil, located in Milano, Italy.

00:02:32: This company produced aluminum anode

00:02:35: and aluminum cathode foils

00:02:37: for aluminum electronic capacitors.

00:02:40: In 2008 I left the Siemens family

00:02:43: and joined FTCAP in Germany,

00:02:46: first as R&D director,

00:02:49: later as managing director and shareholder.

00:02:52: FTCAP is one of the few remaining

00:02:55: aluminum electric capacitor manufacturers in Europe.

00:02:58: In 2018 this company was taken over by Mersen

00:03:03: and I decided to leave and return back to academia.

00:03:07: The mission was to build up a new public

00:03:10: private partnership funded institution,

00:03:14: the Center for Industrial Electronics,

00:03:16: under the umbrella of the University of Southern Denmark

00:03:19: in Sønderborg, close to Flensburg,

00:03:22: where I still work right now.

00:03:25: I'm actually appointed as full professor

00:03:28: and head of center at SDU.

00:03:32: In the center we are right now 40 scientists

00:03:34: working mainly with power electronics.

00:03:37: In parallel I have established my own research group,

00:03:40: working with capacitors and related materials.

00:03:44: - Great.

00:03:45: So let us come a little bit more in our technical direction.

00:03:50: Capacitors are used today for various applications

00:03:54: such as energy storage or for filtering harmonics

00:03:57: or for other things.

00:03:59: In power electronics there are a wide

00:04:01: range of application scenarios,

00:04:04: so absorption of large amounts of energy

00:04:06: and the rapid discharge present significant challenges

00:04:11: regarding losses and aging.

00:04:14: There are new developments in high current

00:04:16: electrolytic capacitors.

00:04:18: Can you provide us with more insights?

00:04:22: - Yes, of course.

00:04:24: But before I come to this point,

00:04:26: I want just to describe generally

00:04:29: the capacitor technology used in power electronics.

00:04:33: In power electronics, very often film

00:04:35: and power capacitors are used

00:04:38: and this technology is mainly based on metalized

00:04:41: by actually orientated polypropylene films

00:04:43: which provide low ESR values, a high voltage strength

00:04:47: and a long lifetime.

00:04:49: Independence of AC or DC operation,

00:04:52: we can choose different metalizations,

00:04:54: for example aluminum or zinc or their alloys as well,

00:05:00: the related thickness of the films

00:05:02: which determine the voltage stability and the capacitance.

00:05:06: The thickness and the electrical constant

00:05:09: determine the capacitance.

00:05:11: Usually such capacitors are made of winding elements.

00:05:14: One can use one big winding element

00:05:17: or many winding elements in an array

00:05:20: to produce a, for example, a power capacitor.

00:05:24: And when you put them in series, it can ramp up the voltage.

00:05:27: Usually they are connected in big cans, on boxes,

00:05:32: and such device could become somewhat bulky

00:05:36: and larger capacitance voltage combinations.

00:05:40: If the voltage requirement is not so high,

00:05:43: for example, 450 volts,

00:05:46: aluminum electric capacitors are often used

00:05:48: because this technology provides very high capacitance

00:05:51: at the reasonable price.

00:05:53: And you were asking if we develop new high current voltage,

00:05:59: high current electric capacitors, and yes we do so.

00:06:03: And to get the ripple current up, mainly the ESR value

00:06:07: of such classical capacitors must be improved.

00:06:12: And we do this by using hybrid polymer

00:06:16: and purely polymer,

00:06:19: conducting polymer electrolytes for this application.

00:06:26: I worked on a new way to overcome the problem.

00:06:29: I'm using special conducting polymers

00:06:32: instead of liquid electrolytes

00:06:33: of aluminum electric capacitors to reduce the ESR

00:06:37: and increase the ripple current capability.

00:06:41: Recently we have realized

00:06:43: 1000 volt breakdown voltage in our lab

00:06:46: and the ESR values in average is a factor

00:06:49: of 10 smaller than those of classical electrolytes.

00:06:53: Means what can increase the ripple current load

00:06:55: by a factor of three.

00:06:57: You have asked for the power density outlook.

00:07:00: The power density will be increased accordingly

00:07:03: because the power density is independence of the voltage

00:07:07: at the current level.

00:07:10: We have also invented a flat back capacitor

00:07:13: which could be actively cooled.

00:07:15: It will lead to an even further ripple current enhancement.

00:07:20: - Okay, thank you.

00:07:22: So in recent years I have developed

00:07:24: many photovoltaic inverters or researched new concepts

00:07:28: and the key point has always been selection

00:07:31: of DC link capacitors

00:07:33: concerning the volume and first power density.

00:07:37: What are the current developments

00:07:38: regarding increased capacitor voltage and power density?

00:07:44: - Yeah, the power density, I explained it already before,

00:07:48: is mainly impacted by the ripple current load,

00:07:54: but of course you can also increase the voltage strengths.

00:07:59: And to increase the voltage strengths,

00:08:01: we did a lot of research

00:08:02: in understanding the fundamental

00:08:04: breakdown mechanisms of anodic oxide

00:08:07: and I have written several papers recently

00:08:11: about the fundamental understanding

00:08:12: of such breakdown voltage systems.

00:08:17: And we learned that beside defects

00:08:20: and the known tunneling current effect,

00:08:25: also the surface state of the oxide layer

00:08:28: plays an important reason.

00:08:31: And we figured out that the oxidation state

00:08:34: of the molecules lying on the surface of this anodic oxide

00:08:39: could impact the breakdown voltage.

00:08:42: It means if you have pieces organic materials

00:08:47: or inorganic materials

00:08:48: which can inject electrons into the oxide layer,

00:08:50: we observed the lower breakdown voltage.

00:08:54: And we have also discovered if you protect

00:08:57: such an oxide layer by a polymer

00:09:00: or in our case we are using conducting polymers,

00:09:04: we can decouple the ESR value from the breakdown phenomenon

00:09:08: and observed very low ESR values

00:09:11: with high breakdown voltages

00:09:15: which lead at the end to higher power densities.

00:09:19: - And what do you think when we will see

00:09:21: this kind of technology at the market?

00:09:27: - This is a good question.

00:09:29: Of course, we are having cooperations also

00:09:32: with capacitor manufacturers,

00:09:35: but I think it would take at least

00:09:36: five to 10 years till we have this technology

00:09:40: in the mass market.

00:09:41: Right now we are looking in the foundation

00:09:44: of a startup company and to accelerate this process,

00:09:50: but before let's say 2030,

00:09:54: I don't see this product in the market.

00:09:58: - So if you need a partner to test them,

00:10:00: please provide me some of them.

00:10:03: - Yes, definitely. (laughing)

00:10:05: No, no, this is for sure,

00:10:08: I think we are, right now

00:10:09: we have a small production line in our lab,

00:10:11: so we produce usually one to two capacitors a week,

00:10:16: and a lot of people are interested

00:10:19: and want to have components for testing

00:10:22: and a lot of tests are ongoing.

00:10:25: We also had some time ago an ECPE project

00:10:29: together with Fachhochschule Kiel

00:10:33: where we have tested the first

00:10:34: prototypes of these capacitors

00:10:36: and we could show and demonstrate that

00:10:39: the expected triple counts were really high

00:10:42: and the first advantage of

00:10:44: this device is that you can cool it

00:10:46: because it's a block of aluminum

00:10:48: and you can put it on a cooler

00:10:50: and when you design it in the proper way,

00:10:52: the thermal resistances are so small

00:10:55: that you can cool the residual losses easily away

00:10:59: and even higher, as I mentioned it also before,

00:11:02: even higher ripple current loads are possible.

00:11:06: - Great.

00:11:07: So let us have a look in another direction.

00:11:11: So new research and development are moving towards

00:11:14: printing capacitors.

00:11:16: What advantages does this technology offer

00:11:19: and what challenges need to be addressed?

00:11:23: - Our group has developed

00:11:25: a patented printed capacitor technology

00:11:28: by using special inks of polypropylene

00:11:33: and the embedding of nanoparticles into it.

00:11:38: And this technology could be an interesting pathway

00:11:42: for the further increase of integration of electronics

00:11:46: because this printing process itself

00:11:48: allows the increase of degree of freedom

00:11:52: and the arrangement of the components.

00:11:55: And it works like that that we just use this ink

00:12:00: as in a typical 3D printer,

00:12:03: and we found a way to print patterns on conducting.

00:12:09: So first you print a conductor on your PCB,

00:12:11: then you print your dielectric on the PCB,

00:12:14: do some special heat treatments

00:12:16: and then we can also create a so-called layer

00:12:18: by layer printing process,

00:12:20: which was also recently published in several papers,

00:12:23: and we also have patented it

00:12:25: and with this you can create completely new

00:12:28: electronic designs where you use capacitors

00:12:30: and this is then a classical film capacitor

00:12:32: with a quite high breakdown strength.

00:12:36: - So that's really interesting

00:12:38: and I think so in the future

00:12:41: maybe an enabler for a higher power density

00:12:47: for several applications.

00:12:50: So another technology I learned in the past

00:12:54: is hybrid polymer systems

00:12:56: and can hybrid polymer systems for instance,

00:13:00: be used in wind turbines

00:13:02: or photovoltaic inverters in the future

00:13:04: or is the voltage behavior still a significant hurdle?

00:13:09: - The thing is, when you use in the hybrid

00:13:11: polymer system you use still electrolyte

00:13:14: and the conducting polymer

00:13:16: and the capacitors on the market

00:13:17: are right now still quite small.

00:13:21: So the biggest ones are produced, as I know from Epcos, TDK,

00:13:26: which are actually based capacitor 18 diameter

00:13:30: and maybe 40 millimeter long or so.

00:13:33: And of course in the wind turbine

00:13:35: you need much, much bigger capacitors,

00:13:37: and therefore our idea to use stacked systems

00:13:41: could be advantage here because the stacking

00:13:45: of our electrodes allows some easy impregnation

00:13:48: of the single sheets and you can even increase the diameter.

00:13:53: So this could be principally a possibility.

00:13:55: So we produce in our lab 70 microFIT capacity,

00:13:59: which is of course still not big enough

00:14:01: compared to huge capacity needed for wind and PV.

00:14:06: But principally this could be feasible

00:14:08: because the impregnation of winding elements

00:14:12: with this polymer solution is not so trivial.

00:14:15: And the hybrid electrolyte is used

00:14:18: for improving leakage current and self healing capabilities

00:14:22: but we have proven with our techniques

00:14:25: that we don't need the electrolyte for that.

00:14:28: We have a special polymer, special additives,

00:14:31: which is also capable to do a similar job.

00:14:35: So right now these hybrid systems

00:14:37: are mainly used in automotive applications

00:14:39: where you can put many of those capacitors in parallel

00:14:45: and to reach a very high ripple current load

00:14:47: with these devices and they are very, very good.

00:14:51: But I can't see them right now, to be honest,

00:14:53: in wind and PV application.

00:14:57: - So maybe in the future.

00:15:00: So capacitors experience significant stress

00:15:04: as part of the EMC filter in inverters.

00:15:08: Current standards do not provide

00:15:10: application related testing.

00:15:12: Are improvements expected here

00:15:14: and how can reliability forecast be determined?

00:15:20: - Well, I'm not a member of a relevant

00:15:22: technical committee anymore.

00:15:24: I was in the past,

00:15:26: but from my own experience being a member

00:15:28: in such a technical committee,

00:15:30: it took quite a while, a long time,

00:15:33: quite a while till new standards are in place.

00:15:37: This initiative should also come from the manufacturers.

00:15:40: For the automotive world, ZVEI

00:15:42: has developed an own testing standard

00:15:44: for big DC link capacitors.

00:15:47: This could be an idea also for this

00:15:49: EMC filter capacitor topic which you are mentioning here.

00:15:54: And the reliability thing is in fact a big issue

00:15:59: because I know from personal experience

00:16:01: that a lot of filter capacitors fail very often

00:16:05: due to humidity impact,

00:16:07: film capacitors are exposed to humidity start to deteriorate

00:16:11: under those conditions

00:16:12: and when they're grid connected, AC grid connected,

00:16:15: you have special effects,

00:16:17: you have electrochemical corrosion,

00:16:19: you could have chemical corrosion, have partial discharge

00:16:23: and all that lead to failures.

00:16:25: And here it is definitely, in my point of view,

00:16:27: a point where improvements could be developed.

00:16:32: - And can you tell us a little bit

00:16:34: which kind of improvements you expect

00:16:37: or have you some ideas in this direction?

00:16:41: - One idea could be using a better sealing system.

00:16:46: Means that shut off the impact humidity from the films

00:16:50: because they're very sensitive.

00:16:53: And then we also work right now on project

00:16:56: where we looked onto the metalization

00:16:59: because right now an AC application

00:17:02: usually think is used and those think

00:17:06: metalization have also issues,

00:17:08: and so we are looking right now

00:17:11: towards new kind of metalizations, which could be an idea,

00:17:15: but this is under-researched.

00:17:19: - So, and let's say a global question,

00:17:22: what further innovations can we expect in capacitors?

00:17:27: - Well, I think all manufacturers in the world

00:17:31: are working on improvements of their CV values

00:17:35: of aluminum electric capacitors.

00:17:37: It was always done in the past reducing ESR ESL values

00:17:42: by innovative constructions, innovative electrolytes,

00:17:46: better paper construction.

00:17:47: It was always ongoing and will ongoing,

00:17:52: so you will always see more compact smaller capacitors

00:17:56: in the field of electric capacitors.

00:17:59: Further, I see a trend that AI

00:18:03: is used for condition monitoring

00:18:06: and this will also allow to use capacitors

00:18:10: with these tools in situations

00:18:13: where you can get rid of safety margins of constructions

00:18:16: and this will also lead to higher power densities.

00:18:19: Also, it was always the case

00:18:21: that improvements in material properties,

00:18:24: purity of use materials, process control,

00:18:27: automation also will help further out as well.

00:18:31: Then I personally work on nanocomposite capacitors,

00:18:35: which could be also an interesting pathway.

00:18:38: We're right now developing new implementation techniques

00:18:41: for extrusion and 3D printing

00:18:43: and I want to mention a company

00:18:46: in the US, PolyCharge,

00:18:48: they work on a new film capacitor technology, NanoLam,

00:18:52: which is also promising in applying

00:18:55: those capacitors at high temperatures

00:18:57: and providing 10 times higher

00:18:59: energy densities using super thin.

00:19:02: So 750 nanometer thin polypropylene films.

00:19:06: So this is my vision.

00:19:09: I did not mention so much ceramic capacitors

00:19:12: because I'm not an expert in ceramic capacitors,

00:19:15: but I believe also in this field you will see in the future

00:19:18: new ceramics which provide better properties,

00:19:21: better switching and maybe also this problem

00:19:24: of the DC bias problem could be solved one day.

00:19:27: So I think a lot of things

00:19:29: are ongoing in the field of capacitors

00:19:31: and they're not passives,

00:19:33: they're in fact active research components.

00:19:38: - Yeah, thanks, Thomas.

00:19:40: So it's a nice experience for me to hear

00:19:42: and to learn that there are still research is ongoing

00:19:46: in this kind of capacitors and we will see in the future

00:19:49: I think a lot of improvements.

00:19:51: So I enjoyed our conversation.

00:19:53: Thank you.

00:19:54: - Thank you very much as well.

00:19:58: - To all the listeners, wherever you might be,

00:20:01: thank you very much for listening.

00:20:02: We hope you have enjoyed today's episode

00:20:05: and gained some valuable insights.

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00:20:30: Until then, have a great time.

00:20:33: (mellow music)

00:20:34: - We hope you enjoyed this edition of the PCIM Podcast.

00:20:36: Together we'll excel in power electronics.