Book recommendations about PWM motor control

In addition to looking for books, you may want to look for white papers on the web sites of microcontroller manufacturers. ADI, TI, and Freescale all make DSP chips with 3-phase PWM outputs that are optimized for driving motors -- you should find interesting material there.

If this is for a one-off application, you may find that you'll do better finding an off-the-shelf variable frequency drive rather than reinventing the wheel.

I don't think there is such thing as PWM algorithm - there might be PID algortithm with PWM output I guess. Anyway I belive you will not get away from PID in this case especially if it's big fan with long response time and inertion. You just won't be able to run it at constant speed either using PWM or by other means. Anyway coding PID is not a rocket science should give it a try.

So you are designing a Full 3 Phase AC Motor (variable Freq/Variabe Voltage) controller, or something a little simpler ?

Good suggestion - Also look at Infineon, they have some 8 bit uC with Motor control extensions, which may be all you need for a Fan Speed control.

-jg

If book you feel you need then I suggest:-

"Electrical Drives and Their Controls" by Richard M. Crowder Oxford Science Publications; ISBN 0-19-856565-8 Tim Wescott's suggestion of also searching out the white papers and application notes of device manufacturers is also a good one.

Try these ones:-

%oo 5pm at what frequency? How many poles?

Jerry

Whether you need a PID controller depends on what you're trying to do. An induction machine will give you about 500 RPM of slip; if you only need to be that close then you don't need the PID controller.

...

^Capital '5'. :-)

Jerry

-- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

I was thinking someone was going to ding me on pole count when I wrote that.

"About" 500RPM. So, anything from 0 to 750, or more. That should cover any number of poles.

For the PWM side of things check for SPRA524 application note on TI's site

Regarda

Mitja

PWM is for dc motor control. The average level gets applied to the motor. If you want to control the speed of an ac motor then you can use other methods.You could synthesis your own variable frequency AC but that's not PWM.

Hardy

Someone can correct me if I'm wrong.

As the speed of an AC motor approaches zero, you must somehow reduce the amplitude of the waveform to limit current draw. This likely would involve PWM modulation to generate a reduced amplitude sine wave.

The relation of motor voltage and rotation speed applies to all electric motors, but certain motors do not follow the input voltage alone.

If you have a shaded-pole induction AC motor, the motor creates the torque for running from the lag between the feed AC frequency and the rotation speed of the rotor.

When the lag grows, the motor quickly loses the torque and becomes essentially a shorted transformer.

The only way to safely control the rotation speed of an induction motor is to control the frequency and feed voltage synchronized to each other.

If you simply drop the input energy by clipping a part of the feed AC off, the motor quickly stalls when you're getting more than a couple of then of percent off the nominal speed.

Maybe the best way to control an induction motor is a DSP method, called rotor vector synthesis.

Dont waste your time, modern inverters use a vector control algorithm, but if you must IR "power train" development kits are available as well as a Fujitsu starter kit for inverters.

The book (whose details I have already posted) calls it "Full Vector Control" but is as you describe, controlling the applied voltage and the frequency of operation.

The following papers look interesting:-