Power Converter Design: Wide Input


Thread Starter


Hello there,

Working on a project where I need to implement a high efficiency (>98%) and low-cost converter for SOEC/SOFC. The system specifications are only just being set.

I know that my converter will have a wide voltage input range, about 20V to 400V. I'm also looking to use a boost (or buck-boost) isolated converter. I will decide later if it will need to be bidirectional or not.

What problems do you foresee when implementing a converter with this wide input range? Also, does anyone have any topology thoughts?
As far as I can see, this will be a very challenging task. One issue is related to input side - the input stage will oprate at high current (at 20V input) but it also must work at high voltage of 400V. Therefore, if you choose a single-stage converter, you might find yourself stuck with bulky supply that nobody wants. Therefore, you might try to use more flexible approach.
Another issue is control. Generally, control transfer function gain is directly proportional to the input voltage value. With extremely wide input range, the gain will vary significantly therefore you will either slow down your regulation (maybe beyond reasonable limits) or use some adaptive control method (usually nonlinear).
It is a question with many answers, including zero. It depends on power level and isolating transformer ratio. If the power level is low (below 30-50W), maybe you could try with flyback converter. Still, the problem of 20:1 input voltage range is what certainly will give you headaches, due to very wide duty ratio and possible very short driving impulses with high input voltage. Also, there is a family of quadratic boost converters which have much higher gain than regular boost. I am not very familiar with it but it is possible for you to find an interesting solution.


Do you know what the required output voltage is? You probably just need a buck converter.


As I said it is a SOEC/SOFC system, SOCs have high output currents, so the power capacity of my converter should be quite high, at least >3kW.

Furthermore, I would like to have an isolated topology.
3kW output with a 20V input? You said the input voltage range is 20-400V. Or did you mean 200-400V?

What is the o/p voltage required?
This project will be very hard.
400V at 7.5A to 20V at 150A You must use parts for 400V and 150A. The transistors are for a 60kw supply. I think the efficiency will suffer and the price will not be good.
Additional thoughts here ...

You need to convert the incoming AC to DC. So, convert that (using a MOSFET) to a high-frequency square wave and feed that to a high-current switching transformer. The windings should handle the minimum input peak and give the rated peak output. Good SMPS's have this.
That would create the HF square wave to be of a variable duty-cycle type. It would be with feedback, so then it can change the square wave’s pulse width in order to regulate the output.
Well, the transformer’s o/p should be set on the right course by a high speed/high current diode (or more). Then it would be filtered to get the right DC.