[SOLVED] Invertor for controling AC motors

[vishy71]

Hi

I have an AC motor which I wanna control it's speed with Invertor.this device gets analog voltage from 0 to 5v or 0 to 10v.Can I use PWM instead analoge voltage?without RC fillter.

thanks

 

[papunblg]

The ability to control the speed of the DC motor using PWM is one reason that DC motors are preferable over AC motors. Ac motor speed is dictated by the AC frequency of the voltage applied which is generally fixed.

---------- Post added at 01:53 ---------- Previous post was at 01:46 ----------

But there are AC drives that use PWM techniques for AC motors https://literature.rockwellautomation.com/idc/groups/literature/documents/wp/drives-wp002_-en-p.pdf

 

[Tahmid]

Hi

I have an AC motor which I wanna control it's speed with Invertor.this device gets analog voltage from 0 to 5v or 0 to 10v.Can I use PWM instead analoge voltage?without RC fillter.

thanks

Maybe you can't. It really depends on the inverter. But if you're going to use PWM, you might as well add the RC filter or a DAC. It won't hurt to add it and you can be sure it'll work as required. After all, all you need are a resistor and a capacitor (or inductor and capacitor).

---------- Post added at 18:40 ---------- Previous post was at 18:38 ----------

With PWM, you may have problems, since the output will be 5V for some time and 0 for the rest. And the inverter might detect the voltage as alternating 5V and 0V (and not the average voltage), you won't be able to control the motor.

 

[vishy71]

thanks.

but can you say what resistor and capacitor must be used?

I don't wanna use DAC.

 

[Tahmid]

You might use the tool here:
**broken link removed**

What frequency PWM are you using?

You can try with 10kΩ (or 1kΩ) and 0.1µF. Then you can use trial and error.

Hope this helps.
Tahmid.

 

[vishy71]

tanks.

I must use 270ohm and .1uf .

are you sure it will be answer?

 

[Tahmid]

Try it out and see. You can use trial and error to improve the output. One thing you can do is that, you can add a voltage follower (analogue buffer) at the output of the RC filter.

You haven't said what frequency you're using.

Hope this helps.
Tahmid.

 

[vishy71]

6000Hz or 8000Hz

how can I use voltage follower?

 

[Tahmid]

Check here:
https://www.google.com/search?hl=en...&um=1&ie=UTF-8&tbm=isch&source=og&sa=N&tab=wi
https://en.wikipedia.org/wiki/Opera...Voltage_follower_.28Unity_Buffer_Amplifier.29

Hope this helps.
Tahmid.

 

[vishy71]

I tried PWM without using any RC filter!

it works but you must connect a resistor between youre inverter ground and voltage pin because of noises which have voltages and they will effect on youre voltage and the motor will orbit in max speed.

thanks for youre helps.

 

[papunblg]

I tried PWM without using any RC filter!

it works but you must connect a resistor between youre inverter ground and voltage pin because of noises which have voltages and they will effect on youre voltage and the motor will orbit in max speed.

thanks for youre helps.

Hello Vishy71,
Please publish the circuit diagram.