# Design considerations for 3-phase AC-DC converter 60 vs 400 Hz

If I want to convert 400 Hz, three-phase, 200 VL-L to 28 VDC, how would I go about doing that compared to a conventional 60 Hz equivalent. In other words, what design considerations need to be taken in to account when a higher AC frequency is required for an AC-DC converter? I am looking at this TI paper as an example starting point, but I am not able to find examples for a 400 Hz equivalent.

https://www.ti.com/lit/ug/tiducj0g/tiducj0g.pdf?ts=1632215437004&ref_url=https%253A%252F%252Fwww.ti.com%252Ftool%252FTIDM-1000%253FHQS%253DTI-null-null-octopart-refdes-rd-null-wwe

• Very little. If you are using a line frequency transformer to do the downconversion, it can be made smaller due to higher frequency but if it's a one-off you can most probably get by with a 60 Hz rated one and just derate it a tiny bit from the increased core losses. Your link is to a Vienna rectifier, which is a quite different question. What power level are we talking about? Sep 21, 2021 at 15:45
• Looks like the output will need to be designed for 200Amps max at 28VDC. I'm looking for the highest efficiency and power factor as possible. Sep 21, 2021 at 15:54
• Darn! Would love to design that one. You can use either Vienna or three regular PFCs, one for each phase if you have a four wire system with ground and step down from your ~300 V to 28 V from there. Also, "as high as possible" is unfortunately not a good design criteria. I foresee lots of simplifications if you can live with high but not quite 0.999 PF. Sep 21, 2021 at 16:02
• No no! No need for any intermediate (line) frequency other than DC. You most probably can run a well designed Vienna made for 60 Hz at 400 Hz without issues. Sep 21, 2021 at 16:11
• Sorry no, just experience. If you simulate a normal single phase PFC and increase the line frequency, the inductor, transistor and diode won't really care and the capacitor is just unnecessarily large but does not hurt anything other than cost. Last time I did a (single phase) PFC, I tested it at 400 Hz in case someone used the product at some air field and also square wave in case of crappy inverter. No issues. Save for every so slightly lower PF at high line frequency, your PFC design is dimensioned by lowest frequency, output power and voltage span. Sep 21, 2021 at 16:46

The whole reason aviation uses 400 Hz instead of 60 Hz is transformers and motors.

A transformer of a particular power rating will take the same amount (mass) of copper or aluminum regardless of frequency.

However, frequency decides the mass of the iron core of the transformer.

Misusing a transformer core intended for the wrong frequency not only adds unnecessary mass, but it creates a thermal problem, as the transformer will heat up more. This thermal problem must be managed, and may require a significant derate of the transformer ( making the iron core even bigger).

However, switching power supplies "make up their own" exceedingly high frequency, allowing them to use small size components.

TRU (= Transformer rectifier unit) with a E-core and two bridges. Don´t forget Interphase transformer.

3500 VA has a weight of only 6 kg.

Use any 100V-240VAC input switching power supply with output that can be cranked up to 28V, and three phase input. If three-phase input is not affordable, add an external rectifier to the input of the switching supply.

Modern switching supplies rectify the input voltage and don't need AC input, and they don't care whether the input is 50Hz or 400Hz.

So, basically, you don't need to do anything special. Work as if you had regular 240VAC 3phase and had to use a switcher.

Now, mains transformers for 400Hz are much smaller than for 50/60Hz, so if you wanted a custom transformer followed by a rectifier, you certainly could order one, and it would be quite compact. There are good companies out there that will manufacture custom mains transformers in low quantities - usually you'll get more luck in Europe. The ones in US seem to want thousands of \$ to even talk to you.