Speed Control of single phase induction motor using TRIAC

Speed control of an induction motor is enormously difficult unless you use the latest chips in a complex circuit.

Single phase is MUCH worse than three phase as well, owing to starting considerations.

The project is by no means trivial. At the very least, a full H bridge drive will likely be needed.

To properly control the speed of an induction motor, you have to change BOTH the voltage AND the frequency.

See

First make sure the motor is a PSC motor.

If you just need limited speed (eg. 2:1) control of a shaded-pole or PSC AC induction motor with a fan-type load (drag with little friction) the problem is trivial.

Best regards, Spehro Pefhany

Specify the type of motor, speed range desired and the application.

A small 1/20 hp shaded pole motor driving a light load like a fan would be a candidate for a simple triac control.

A 1 hp motor driving a large fan or heavy load would be a candidate for a variable frequency drive or a mechanical speed adjuster

Big difference in complexity. There might be some specialized IC's to make a VFD simple since there is a lot of call for it. When going to a VFD for speed control, there's a lot of incentive to use three phase because capacitor run/start motors don't take kindly to different frequencies and 3 ph does.

Thanks everybody for the help. Actually the project has been assigned to me by a very strict instructor of mine, so I can't tell her that its trivial or very hard etc etc. Also nothing else has been specified. As far as I understand I have to use TRIACs to design a variable voltage/frequency source, but thats the only thing I know. Can anyone suggest me a site or something from where I can get atleast a circuit diagram or the components to be used to design such a circuit.

No, you're supposed to use your textbooks and the library to figure it out for yourself.

That's why it's called "school". There isn't anybody to spoon-feed you the answers when you get out in real life.

Good Luck! Rich

Look up PSC motors and speed control. You don't need variable frequency and it won't help.

There's a basic treatment of the topic in a ST Micro applications note where they cover several triac topologies and problems they may have.

Thanks for the suggestion Rich but let me tell you that I wasn't demanding to be spoon fed. I was just asking for the right place to start with. Morever I had googled a lot before asking the question in this forum.

Thanks Mark, the document really helped me. That was the thing which I needed. Lots and lots of thanks again.

Also take a look at some thyristor triac scr databooks circa 1970's in your campus library if they have any, the application notes should have something.

The old GE SCR handbook and hobby book could be useful.