Interview with Dr. Miaosen Shen

Featured Engineer

Dr. Miaosen Shen

Dr. Miaosen Shen - Senior Research Scientist, United Technologies Research Center

How did you get into power electronics and when did you start?

When I was an undergraduate student in department of electrical engineering, I talked to several professors before I choose my major focus. I was told that power electronics is one of areas that have lots of new research and development going on. Without knowing exactly what power electronics is, I started learning and working in this field. It has been 13 years, and I never regretted of making that choice.

What is power electronics?

Power electronics is using electronics means to control and convert electric power. It is widely used in everyone’s daily life, such as adaptor for your laptop, electronics ballast for fluorescent lamps, modern variable speed air conditioner, elevators, etc. It basically converts one form of electricity (say 60Hz 110V power from the wall) to another form that can be used directly (say 12V dc for battery charger). It has been broadened in recent decades to deal with larger systems that include many power electronics components, such as micro grid.

What are your favorite hardware tools that you use?

I use oscilloscopes a lot. I also use power analyzer and spectrum analyzer from time to time.

What are your favorite software tools that you use?

I used quite a few software tools in my work. To name a few, MATLAB for numerical analysis and system simulation, SABER and PSIM for circuit simulation, ORCAD for schematics and layout

What is the most memorable debugging experience you had?

When I was in graduate school, I built a 50kW inverter using IPM (intelligent power module), which has gate drives in it. When I was debugging the inverter, there was always shoot-through at high voltage and high current operation. However, when I was trying to figure out which gate was causing the shoot-through by connecting a probe to the gate signal pins, I never observed any problem with the gate signals. I scratched my head a lot until I observed that the shoot through was also gone when I connected probe to one of the gate signal pins. It turned out that the a few pF capacitor added to the gate signal pin by the probe actually solved the noise problem. As a result, I was able to solve the problem just adding a few 10pF capacitors to the gate signal pins.

What is on your bookshelf?

I don’t have a long list of books because research papers are the major resources in my work. However, I do have a list of good books I refer to every now and then, here are a few of them:

P. C. Krause, “Analysis of electric machinery”
A. E.Fitzgerald, C. Kingsley, S.D.Umans,” Electric Machinery”
D.W.Novotny, T.A.Lipo, “Vector control and dynamics of ac drives”,
W. Leonhard, “Control of electrical drives”
H.W. Ott, ”Noise reduction techniques in electronic systems”,
H.K.Khalil, “Nonlinear systems”
N.Mohan, T.M.Undeland, W.P.Robbins, “Power Electronics-converters, applications, and design”

What has been your favorite project?

In my previous job, we had a great team working on designing and building an integrated power-train for fuel cell vehicles, which includes a high power inverter (~200kW), a dc/dc converter, a motor, and a gearbox. We started with bare MOSFET and IGBT dia and built our own integrated power module, gate drives, and control. It was amazing to see all the pieces coming together and the power-train running in a fuel cell vehicle eventually.

It was a great project itself. It is even better when a group of engineers with very different backgrounds working together seamlessly. We had electrical engineers working on the converter/inverter design and firmware programming, control engineers working on motor control algorithm development, mechanical engineers working on structural/packaging and thermal design.

What are you currently working on?

I am currently working on EMI reduction techniques. With the development of semiconductor devices, the size and cost of power devices have been steadily going down in the recent years. However, there was not much progress being made in the passive components side, especially magnetic components. Modern power electronics systems have to pass rigorous EMI testing to meet various standards depending on their application. As a result, the passive components become the major size, weight, and cost contributor. In order to reduce the size, weight, and cost, we are looking at various techniques to reduce the EMI noise. Some of the methods we have been looking at include active EMI filters, PWM optimization to reduce EMI noise.

What would you like to work on in the future?

I would like to work on two different topics in the near future:

Power converter technologies: with the recent wide band-gap device development, such as SiC and GaN devices, very high frequency high temperature operation of power converters becomes possible. Plenty of opportunities exist to increase the power density and power conversion efficiency of the power converter, which is always desirable for varies industries.

The second area I would like to work on is power electronics system integration. In recent years, power electronics has been widely used in different applications. Besides the benefit of high efficiency and flexibility they brought to us, they created some problems, such as EMI and system stability issue. There are lots of opportunities to coordinate/control/optimize systems that consist of a series of power electronic components.