I'm looking to design the power stage of a 3 Phase DC Motor Controller for use with the Emrax 268 motor. The maximum input battery voltage would be no higher than 300VDC and the maximum continuous current draw would be 180Amps (with a 360A 2 minute burst capability).

It's listed as a 3 phase sine wave driven motor, but I'm not sure if it needs to be a true sine wave or what waveform would be acceptable to drive it. If it needs to be a true sine wave, then how would I get that from an IGBT or MOSFET controlled output? Additionally, I'm not sure if I should go with IGBTs or MOSFETs. I have a contact at International Rectifier who could get me pretty much anything they make, so cost isn't necessarily a big deal.

This will likely become a part of my senior design project, but I'm a year out from that, so for right now I'm just doing some research and trying to get an idea of what I'll have to do. So any help or general tips when working with motor drives would be helpful!


  • \$\begingroup\$ Wow! Anything they make for free? That makes some really good stuff available to you. Be sure to appreciate this opportunity well. (and honestly; like don't use it to start your own store :) \$\endgroup\$
    – AaronD
    Apr 8, 2015 at 16:33
  • \$\begingroup\$ Well, I'm sure there will be some limitations, but after I mentioned what I was planning on making, they wanted their name on it as a sponsor. So he was very adamant about letting him know of anything we would need that they make so that he could get it to us. (And don't worry, I won't start a store with it!) \$\endgroup\$ Apr 8, 2015 at 16:39
  • \$\begingroup\$ I guess you'll need to create (aka, find online) and test a circuit to generate a fixed frequency sine wave of variable magnitude and configurable phase offset. Have 3 of these circuits, with 120 degree phase difference on each one. The output would then be fed into some serious high power gain stages as "voltage followers" to interface with and drive the Emrax motor. \$\endgroup\$
    – KyranF
    Apr 8, 2015 at 16:45
  • \$\begingroup\$ I guess a 3-phase (so, a full H bridge for each phase) H bridge setup with a direction control would be neat too \$\endgroup\$
    – KyranF
    Apr 8, 2015 at 16:46
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    \$\begingroup\$ That is a lot A LOT A LOT of energy... if you don't have any experience in this arena, you should maybe start with something that takes a few amps and work your way up. I have 10 years of design experience and if someone asked me to design this, I would probably say "no". \$\endgroup\$
    – Daniel
    Apr 8, 2015 at 16:57

1 Answer 1


As this is not yet homework but going to be, I'm not entirely sure how to answer. But as a Computer Engineering graduate with several years experience using industrial 480V Variable-Frequency-Drives (VFD's), I would advise you to read the manuals on a few of those. Try to get multiple models from multiple manufacturers and glean what you can about the inner workings.

There are some tricks that they use that may surprise you, one of which is how they produce an effectively sine output using the transistors as binary switches.

My advice for a general architecture would be to make a basic circuit that is pretty well bulletproof, but only when operated correctly, then do most of the work in software that both ensures correct operation and does the higher-level stuff like position/speed/acceleration control. And hang sensors all over it; for a prototype, it's better to not use a few than to wish you had more.

  • \$\begingroup\$ I have few contacts at Rockwell Automation, so I'll try to get some info from them (manuals as well) as they make some pretty big VFDs. Thanks! \$\endgroup\$ Apr 8, 2015 at 18:02
  • \$\begingroup\$ Your contacts at Rockwell/Allen-Bradley may prove me wrong on this, but their appearance to a consistent customer seems to indicate that the company itself is entirely software and support and that they outsource all of their hardware. Could be wrong though; I don't have the contacts that you do. And it doesn't invalidate the information that they give you either; I just wouldn't be surprised if they knew relatively little beyond their published documentation and support scripts compared to other brands. \$\endgroup\$
    – AaronD
    Apr 8, 2015 at 18:11
  • \$\begingroup\$ That's entirely possible, but from what I've heard from my dad (who's been a technician there for 20+ years) they still design almost all of their hardware. I'll have to ask him to ask around though to see if they still do the power stages themselves. \$\endgroup\$ Apr 8, 2015 at 18:15

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