Posted on 29 June 2019

Searching for the Golden Fleece

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By Werner Bresch, GvA

In the middle of January, I received a "call for help" from Bodo Arlt, who said that the author of the cover story for the March 2012 issue had deserted him. He asked me whether I might be able to help out. I would love to have written a fulsome and detailed technical article, for example writing about the developments for medium-voltage applications with bipolar and with BiMos semiconductors on which we are currently working. But to do this you need more time than the deadline for submitting the script allowed. So a discussion took place in which we jointly concluded that in our power electronics sector there is a lack of up-and-coming talent and this may have a very negative impact on technical expertise, economic growth and also social peace and harmony in our world. We also considered why it is not proving possible to inspire more talented young people to pursue a career in power electronics. One of the reasons may be that we "oldies“ do not communicate in sufficiently vivid terms what makes power electronics so fascinating!

Power Electronics 1

The first step is always the hardest!

Every month Bodo publishes its Power Systems and this means that every month "The Gallery“ appears on the first pages. I have now also been added there and a picture appears alongside my name. I must concede that I fit in well here, in the line-up of gentlemen with greying temples and sometimes slightly thinning hair. By contrast, you find far too few women and also far too few young men. This sheds a significant light on the next generation of talent in our industry.

When we interview graduates fresh out of universities of applied sciences and technical universities as potential applicants to join our development department, the interviews usually progress very well up to the point at which we start talking about our job profile. While we enthusiastically explain to applicants that we deliver customerspecific power electronics developments up to the high MW range and also work with kiloamperes and kilovolts, the applicants’ eyes light up and they look at us in amazement, incredulously and quizzically. The whole electronic equipment really is on a large scale with thick copper rails and this would certainly not fit on the laboratory bench, they then often ask. The whole thing really does make a racket and also makes other noises and, in the event of a fault, there is bound to be a big bang. Yes, this can happen, we then reply, but first comes the flash and then the bang and finally parts start flying around. This is what is known as a learning curve!

This is usually the point at which most applicants raise the white flag and give up. They say that all this involves too little electronics and too much mechanics and after all a high-tech job at a computer involving software development, for example, is much more interesting. By contrast, our field of work represents an archaic sledgehammer approach to doing things and is not very elegant.

And at first glance this statement does actually appear to have some truth to it. However, if you take a second look, unimagined opportunities are opening up with extraordinarily diverse career prospects in this field of power electronics.

Set theory

I now find myself in the "late autumn“ of my extremely interesting and varied working life. When I look back, I can only emphasise that I have never got bored in my domain. The work and assignments I have tackled have contributed a lot to my professional and personal development and given me a great deal of satisfaction. Over the years, I have developed my own "personal set theory“ on this.

In my view, to ensure that you can develop as a person in your work and deliver good results, you need the largest possible "cross section“ which is made up of three "subsets“.

I define subset 1 as being satisfaction with the assignment resulting from the challenge presented by the assignment you are given. In this regard, a role in the field of power electronics is hard to beat in terms of variety and diversity.

I define subset 2 as satisfaction with the working environment. Here too power electronics offers exceptional opportunities for professional and personal development.

Last but not least comes subset 3. This relates to aspects such as payment, career opportunities and future prospects working in the field of power electronics. Here too it should be stated that the prospects for the aspects mentioned above are better than excellent.

Even if individual subsets diverge from the cross-sectional optimum, in my case at least (and this is also true of many others I have met) I have never turned my back on power electronics. On the contrary. This field of study is so interesting, varied, diverse and exciting that it is almost as addictive as a drug. Once you have experienced one dose of it, you can never get away from it. I therefore declare myself guilty as charged! Yes, I am addicted! Addicted to power, addicted to power electronics!

Subset 1, playground for technology geeks

Some details about the terms of reference, challenge and diversity of the job were discussed earlier on. But what actually lies behind this can at best only be touched upon.

First of all, it should be clearly recognised that power electronics is not just confined to drive technology. Although drive technology itself is certainly very multifaceted. For example, there are DC drives with thyristor bridges, AC drives, in two-pulse inverters, three-pulse inverters, multilevel inverter circuit topologies. Power ranges of from 10s of watts up to hundreds of megawatts are achieved with these components. For example, we find power electronics as pulse-power switches in research facilities in kicker pulsers, in process facilities for metal processing and metal shaping in the multi-digit kV and kA range. We find power electronics as high-current rectifiers in electroplating facilities and welding facilities as well as high-voltage rectifiers in the range of several 100kV, e.g. in research facilities.

Power electronics are used for power generation and distribution. Wind turbines, photovoltaics, and h.v.d.c. transmission are mentioned here by way of example. Power electronics are used to improve the grid conditions in the form of thyristor power circuit-breakers for group compensation or also inverters in 2-pulse and 3-pulse configurations for active filters.

Power electronics can be found in facilities for inductive welding, melting and hardening. Traction feed rectifiers, auxiliary generator sets, network interconnections, ripple control transmitters, UPS facilities, chargers, etc. Power electronics can be found everywhere. At this point, we should not forget to mention the huge new up-andcoming market: the electric car with all of its main and ancillary equipment such as battery chargers.

Power Electronics 2

As can easily be seen, a huge new interesting and varied field of activity is opening up here

In order to implement all of these power electronic systems, whole "arsenals“ of the power semiconductors differing in type and power data are available from various manufacturers. First and foremost, these are thyristors and diodes in all technological versions, MOSFETs and IGBTs as rapid turn-off MOS or BiMos power semiconductors as well as IGCTs and in certain limits also GTOs as turn-off bipolar power semiconductors for use at maximum power levels.

We thus now have all the ingredients in the form of applications and power semiconductors which are a prerequisite for the development of power electronics, apart from a specification. This transforms the requirements emerging from the application into a set of demands for the power electronics which are to be developed.

Naturally a wide range of different performance requirements are placed on the abovementioned power electronics, owing to their specific operating behaviour, and lifetime considerations and ambient conditions are also incorporated into this process. The interfaces for the control electronics, the main electrical connections, connections for liquid cooling for example and mechanical interfaces must be defined as clearly as possible.

In addition, requirements from sets of rules such as the DIN IEC must be considered. This is all taken into account in a specification which reflects the requirements placed on the power electronics an  describes them as completely and comprehensively as possible.

We can now start with the development. The interesting thing about this is that we are confronted with lots of interdisciplinary problems which need to be solved in order to develop reliable power electronics.

The suitable power semiconductor is quickly picked out and specified, as is the necessary cooling. This requires a precise thermal and thermodynamic consideration of the heat loss resulting from the load conditions defined in the specification. System simulation software which is suitable for power electronics can be very helpful here provided that the simulation parameters which are entered correctly reflect the conditions prevailing in the application. It proceeds slightly more laboriously of course also "manually“ with the aid of everything you have learned in your studies. Ohm, Kirchhof, Fourier, etc., come into play.

In the case of air-cooled power electronics, we are automatically confronted by flow-dynamic problems, but in the case of liquid cooling we also face electrochemical problems in the form of material compatibility in the water cycle and water treatment.

The power electronics must be able to mechanically withstand all of the current loads which occur, including short-circuit current loads. It must be possible to absorb the mechanical forces which occur here without any damage being caused. It is certain that mechanical size data will be defined in the specification and this must not be exceeded. Overcurrent protection devices, if necessary, may well require a large amount of space.

The same applies to voltage stress. The insulation coordinates in accordance with DIN IEC must be borne in mind here. Very particularly, this applies to developments in the medium-voltage or high-voltage range in relation to partial discharge resistance and the prevention of corona discharges. Any snubber circuits that may be required will be designed in accordance with the requirements which are defined in the specification.

All power electronics cause line-conducted interference which needs to be kept within the permitted limits by using suitable filters. The same applies to radiated emissions. Emission values must not exceed defined limit values. The power electronics themselves and the associated signal electronics such as driver boards, interfaces and CPUs must operate reliably even when there is interspersed stray radiation. Nevertheless, they work in a very dynamic environment with voltage edges of a few kV/us and rates of current increase of up to a few kA/us. This is achieved through suitable cable routing and suitable screening measures.

Up until now, we were dealing with the "macroelectronic“ sector. But power electronics does not just consist of metal and precious metal; there is also a need for "microelectronics“ in the form of driver boards for actuating the power components, interface boards as interface electronics between driver boards and CPUs, auxiliary voltage supplies, current, voltage and excess temperature sensors, etc. However, for these "miniature electronics“, the same set of requirements as specified previously applies when they are used in the field of power electronics.

With a little bit of luck and even more skill, the desired power electronics developed according to specification will then be mounted in the switchgear rack. The equipment is then "brought to life“ with the software which is suitable for the demands of the application. Functional trials, hot run tests, catastrophic failure tests and final qualitative tests demonstrate that the new power electronics are ready to be launched on the market.

The job of the development department would thus have come to a successful conclusion. And this is precisely the point in time at which the people involved in this development look back with satisfaction and state. Although it was hard work and stressful, it was a great deal of fun!

Subset 2, the satisfaction factor

As has already been alluded to, power electronics is a complex overall field which touches on lots of different specialist areas and subjects both in relation to the development work itself and the specific characteristics when the electronics are subsequently put into use. It is possible that, due to this complexity, my description may serve to put off rather than motivate people who may have been interested in a possible career in the power electronics sector. Such people should be reassured that they have simply experienced all the need to communicate on the subject that has built up as a result of more than thirty years of professional experience working in the field. It goes without saying that a newcomer to the industry cannot be expected to have this depth of knowledge. They will need to be introduced to the subject matter gradually step by step. This is also what happened to me over my professional career and even I still learn new things every single day. Over the years, very diverse problems are thrown up, both as far as the applications themselves are concerned and in relation to the electronic solutions to them, with the widest range of different characteristics of power semiconductors being used in them. You come into contact with experts from lots of different fields, learn about the technical problems presented there, and you get to work with people of different natures and from different cultures. Often a role in our field of power electronics involves trips to faraway countries in order to take a look at problems on the ground and come up with the right solution. The opportunities for development both professionally and personally are vast.

Power Electronics 3

Over the years, as your wealth of experience grows, you become a valued technical dialogue partner, establish increasingly close links within the very tight-knit group of people in our industry, and you essentially become a "member of the family“, usually for life.

This does of course lead to a high degree of personal satisfaction.

Subset 3, where does the journey lead? Ultimately, every person must determine this for themselves and it will depend on people’s own personal inclinations and desires. Our industry has room to accommodate all personality structures from introvert to extrovert and it is multi-culturally liberal. Our field of activity stretches all around the world. This means that, with the appropriate training, everybody can find an area of activity that suits them, whether it be in development or marketing, or in sales or quality assurance or, or, or!

The future outlook regarding a job in the power electronics sector has never been as rosy as it is today. Our society has recognised that, for the sake of our children, we must reduce CO2 emissions when it comes to generating power. At the same time, we were forced to acknowledge after Fukushima that the unbridled use of nuclear power plants is probably not the answer to all of our problems.

On the other hand, it is clear that providing a secure and stable supply of electric power is an absolutely basic requirement for achieving healthy economic growth in the different economies around the world and ultimately for safeguarding social peace and harmony within society and within the international community.

The Government of the Federal Republic of Germany was therefore one of the first countries to decide that five nuclear power plants should be taken offline and that increasing focus should be placed on renewable energies. A decision such as this does of course have wide-reaching consequences as countless gigawatts of power which were previously fed centrally into the grid need to be replaced. Accomplishing this with large-scale power plants fired by fossil fuels as a substitute would be counterproductive.

Power Electronics 4

As things stand today in the world of technology, the only option is to generate increasing amounts of renewable energy. The result of this is that we will have a decentralised system of power production, but unfortunately this will rarely be where the electric power is actually required at any given time.

As a consequence, for generating power we will require many more, if not very many more, onshore and offshore wind turbines, pumped storage hydro power stations, hydraulic power stations, tidal power stations, photovoltaic installations, geothermal power stations or large-scale solar-thermal installations in the sunbelt around the earth. Large quantities of power electronics are required everywhere.

As the power generators mentioned previously feed power into the grid in a decentralised manner and are usually not located at the places where the electric power is needed, a power distribution system which is capable of handling this is required.

To transport and distribute the electric power, we require h.v.d.c. transmission routes, network interconnections, mains supply solutions, smart grids, passive and active filters, etc.

The networking of the power transmission routes will not just take place at a national level but also across national borders, certainly within continents and in the future also globally. This is because the sun is always shining somewhere on this earth.

Here too, power electronics will be required in very, very large quantities.

To be able to meet the CO2 emission limits of the future, to which many countries have already signed up, it will be absolutely imperative to replace vehicles which run on petrol and diesel with electric vehicles.

In the Federal Republic of Germany, the desire of the government is that within the next 10 years at least 1 million such vehicles should be on the roads. As well as the drive inverters, electric vehicles also require battery chargers.

Even if you assume that just five percent of all the vehicles on the world’s roads are going to be replaced, this means that another gigantic market for power electronics will emerge.

Up until now, we have spoken only about “ new” and “more” power electronics. But that does not tell the whole story. There are lots of electrical applications such as mediumvoltage drives which are still unregulated today. The excess energy is simply burnt off. Gigantic amounts of power simply blow up into the sky as heat loss, taking with it the CO2 which was just produced in order to generate this excess electric power. With new high-blocking semiconductors, it is now possible with an acceptable level of outlay to develop power electronics which provide the amount of electric power required for such motors in accordance with the actual load.

Many other examples of the ways in which power electronics are used could be listed, but we will leave it here. As it is easy to see, an almost infinite number of opportunities are opening up in the field of power electronics for people who decide to pursue a career in this sector. The same is true of the opportunities for personal and professional development on offer. You could almost conclude from this that we represent the future for this planet. We are the "saviours of the earth“. With the work we do, we are stopping global warming by reducing and preventing emissions of CO2. We are making this planet viable for the future lives of our children and our children’s children. We are rendering nuclear power plants that can explode with disastrous consequences redundant and preventing the homes of hundreds of thousands of people from suffering radioactive contamination.

And this is where it comes to an end, the search for the Golden Fleece. There is no need for an odyssey across the Mediterranean like the one that Jason once undertook with his Argonauts in a search for happiness and prosperity. The place where the Golden Fleece can be found is described here, you just need to bend down and grasp it.



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