Ac Induction motor low cost H-Bridge circuit needed

"Michael Nikolaou" schreef in bericht news:f55bn8$1tve$ snipped-for-privacy@ulysses.noc.ntua.gr...

I doubt a motor like that to be suitable for variable speed. Startwinding and capacitor are designed to function at 50Hz (or 60Hz). Almost impossible to predict in general what happens at other frequencies. This type of motors often has a centifugal switch that switches off the startwinding before the motor reaches its nominal speed. At lower speeds that switch may stay on and the startwinding will be fried.

petrus bitbyter

Thanks Petrus for the answer

I show a lot of application notes that create this 90 degrees shift with a IGBT (6 actually) .So my conclusion is that the scheme works. Is there anoter single phase motor suitable for such applications ?.I show only microchip's application notes . Can you point me to a link with these motor types ?

Michael

The only single phase induction motor suitable for speed control I'm aware off is the permanent split capacitor type (PSC). A example of a variable frequency driver you found in Microchips AN967. So if you have another motor, you're out of luck. You'll have to do a lot of research to make a vfd for it... or find another motor. If you have to do so, you can as well go all the way and look for a three phase motor. The driver hardware will be the same. Maybe it's even cheaper to buy a driver then designing one of your own.

petrus bitbyter

if your motor has a centrifugal switch in it, I doubt very much you'll be able to control the speed properly.. You maybe able to rig up a special starting circuit to get it turning. This may work if you don't allow the motor to drop in RPM's to the point the switch engages on you. A permanent type capacitor motor you have a better chance with, with those, you make your self a 3 phase drive and remove the capacitor to let the drive do it for you.

On some motors, you can get to the wiring that hooks up the capacitor and the switch. If it that sort, you could bring the winding out and disconnect the capacitor etc. You would then have to provide the needed phase shifted current.

You have to be careful how you drive this part of the system. The capacitor winding can't take as large of a current and when the motor is running at full speed, it will have more voltage on it than the main winding.

You have to design the circuit that drives this winding so that it doesn't allow the current to flow out of it and back onto the power rails when you are going fast. This makes switching and snubbing tricky.

Have you done web searches? I would expect this to be in an app note someplace.

It's really a two phase motor with a cap to generate the second phase from single-phase AC, so you have some starting torque. The cap will only work for a relatively narrow range of frequencies, so you can't use it for what you want. You'll need to generate the starter winding voltage yourself, and you'll have to decide if you want to only generate it when the motor's going slow or generate it all the time.

Given that every single-phase motor will potentially have a different compromise between starter winding bulk and starting torque, and wear and tear and cost and a billion other factors, you may find getting the thing to work is quite a science project compared to getting a regular old 3-phase induction motor going -- with the 3-phase you can count on three identical windings that are electrically 120 degrees apart.