Single Phase Induction Motor Speed Control

Hi Guys,

Trying to put together a project for college. Already assembled main circuit with bridge rectifier and H-Bridge to drive the motor. Put together driver circuit with MC34151 driver IC I got, but stuck on coding part at the moment.

Tried searching internet for similar projects, as well as this forum but came up short. I have Arduino Mega and I am fairly inexperienced when it comes to using it. My understanding is that I need to use PWM pins, increase the frequency of the controller from default 490 and 980 Hz, and then do I control the frequency via manipulating delay?

Any input would be greatly appreciated. I included my main circuit as well as motor nameplate information.

Thank you!

pix.pdf (129 KB)

Can we guess you have tested your motor using square waves as power? Results?


No I have not, do not have means of doing that at the moment...

No I have not, do not have means of doing that at the moment...

Well, before you go very much further, don't you think it might be wise to see what the motor does when you use square waves instead of sine waves? Many AC motors will not run when powered from 12 VDC inverters that produce stepped square waves and yours will not be stepped. Get one and try it.

Is this a class project? What type of motor is it, there are many different AC motor types and they all behave differently. Why not post a schematic of your circuit, not a frizzy thing showing all power and ground connections. Data on the motor etc as well.

There’s a really good reason you didn’t find any existing projects. There aren’t any.

Do you know how a single phase ac induction motor manages to rotate when there is no rotational vector in a single phase supply? Better research that first. Hopefully you’ve studied that famous guy... what’s his name? Tes something or the other. Oh, right, Tesla.

If you have any doubts, rather than believe some unknown person on the Internet, call Marathon, give them the motor part number and ask them if you can run it on PWM. It should be a short, one word answer.

Hopefully you’ll quickly realize that a single phase motor wasn't such a good idea. If that’s the case, now is a good time to rethink your decision. There is a common motor design suited to PWM speed control. In fact, more of those motors are sold every day than single phase. If the professor selected the motor, you should ask for a refund - that is unless the course is to demonstrate how to destroy an otherwise perfectly good motor.

Maybe, just maybe, you might get lucky and you be able to control the motor speed, for a short time, assuming it’s unloaded. Put a load on it or run it below a certain speed and it’s game over. Quickly. Unfortunately, it will fail in a rather unspectacular fashion since it is a totally enclosed motor. No openings for the smoke to come out. What will be spectacular will be the IGBT’s blowing up. They’ll glow red for a second before that happens though. Watch closely, oh wait, no, don’t. They become shrapnel.

Finally, some (more) free advise. If you ever decide to test that power supply, better stand way back when you turn that on and make sure it’s fused! Do you have any idea of what the peak current in that diode bridge is going be? Hopefully there will be enough impedance in the feeder circuit that the bridge doesn’t go boom.

Can we guess you have tested your motor using square waves as power? Results?


No need to worry about this, its perfectly fine to use voltage PWM into any motor - the
inductance of the windings smooths the current waveform automatically. The only
tricky point is figuring out the best PWM frequency for a particular motor. Needs to be
high enough for smooth current waveform, but not so high that losses become an issue.
And of course the PWM drive input signal must be sinusoidal, conceptually like this:

analogWrite (pin, amplitude * sin (micros() * omega)) ;

Start with 8kHz to 20kHz as a reasonable value for PWM frequency.

But note that most single phase induction motors are not designed for speed control
by voltage variation alone, some will overheat and may catch fire if you try. V/f control is
most likely to work, so start with that scheme.

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