Ac Induction motor low cost H-Bridge circuit needed

Hi to newsgroup

I need to design a low cost variable speed motor control with a
microcontroller.As i understand PWM V/F conversion with an H-BRIDGE is used
The motor is single phase 300 Watt 220 Volt motor . It has two windings
one main and a secondary (start) with a capacitor .
Can anybody point me to a circuit with real component values so i can
evaluate costs and complexity.

Michael

 

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.

 

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.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html