Building a Variable Frequency Drive for a three-phase motor

Here are the power and driver boards that [Miceuz] designed to control a three-phase induction motor. This is his first time building such a setup and he learned a lot along the way. He admits it’s not an industrial quality driver, but it will work for motors that need 200 watts or less of power.

The motor control board uses an MC3PHAC driver IC and an IRAMS06UP60A handles the power side of things. The majority of the board design came from studying the recommended application schematics for these two parts. But that’s far from all that goes into the setup. Motor drivers always include levels of protection (the whole reason to have a driver in the first place) and that comes in several different forms. [Miceuz] made sure to add EMI, over voltage, and over current protection. He discusses all of these, sharing links that explain the concepts of each.

18 thoughts on “Building a Variable Frequency Drive for a three-phase motor

  1. I was asked to produce something like this over the summer for a small scale investigation into the effects of power line harmonics caused by using VFDs on large (15MW) electric compressors.
    Ended up buying a commercially available unit, wish id seen this first :(

  2. Excellent find! Not only useful for 3-phase mains motors, but VFDs are essentially the controllers used to run turbomolecular vacuum pumps! (albeit at lower voltages and much higher frequencies)

  3. Thanks for the writeup! This is chock full of helpful info for those (like me) who want to make something similar.

  4. I have never seen a 3 phase motor that uses less than 1 amp, or about 340ish watts? The smallest commercially available VFD that I have seen is 1/4 of a HP or so. They are available used or surplus for perhaps $30 or so on ebay and are fully featured industrial controllers. Awesome build though!

      1. well, we got our hands on several old soviet small induction motors for free, they are 1370RPM 180W.

        the setup theoretically can drive upto 500W – it’s IRAMS limit

        schematics are Eagle files

  5. I’ve been looking over these forever. This is probably the simplest I have found short of using a second 3 phase motor to generate the other leg. Great hack and thank you.

    1. I used to use a rotary phase converter on my lathe. Sucks too much power and the output is not as smooth as true three phase. I now use either VFDs or brushless servos on everything.

      For the price of commercial VFDs on the market is it hardly worth building your own. Especially if you want something reliable. Teco makes some cheap ones, but there is a lot better stuff out there with flux vector capabilities.

    1. Bigger IGBTs, more careful drivers and driver balancing, more capacitors, capacitor precharge and protection, more snubbering, higher bandwidth control loops, faster current measurement, de-sat protection… As I mentioned above, it gets hairy fast and that’s if you’re still interested in a straight V/Hz drive. If you want to do sensorless vector/flux vector/encoder control then you’re in for even more fun.

      This is a great project, and I grabbed a copy of it just to see how be built it, but don’t start playing with bigger currents until you’ve got a really good handle on what you’re playing with. VFDs can get unstable really fast and you end up with the IGBTs blowing, with the caps right after them. It’s loud as hell and if you head or hands are anywhere in the vicinity, you could get hurt really bad.

      1. Thanks for the cautions, Andrew.

        Do you have any advice, in addition to getting very familiar with the controller’s behavior before scaling things up? I’ve built 3-phase BLDC controllers, which were designed to drive small CNC mills (motors no larger than your hand), but nothing of this size or magnitude yet. Are there better protection schemes or precautionary measures you can recommend?

        That said, this project does indeed look very interesting, and I’m compelled to build & improve it. :)

  6. Steve-O-Rama, please drop me a note if you build/improve my build, i’ll have to build another version for 1kW motor used on a drill press – mic at hardcore.lt

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