.

 

What type of fan? Shaded pole motor?
Why are you not creating 3 speeds with one triac?
Are you hoping to get phase control with capacitors?
Max.

 

And there I was, looking for a rotary capacitor.

 

It's a ceiling fan.
I used triac based fan dimmer but it causes audible noise from fan at lower speed that's why i am building this capacitor based dimmer so i can get rid of that noise and can control it by microcontroller.

Another avenue to explore is to use a single triac with a zero crossing opto and use variable burst firing to obtain an average speed.
Max.

 

I tried that too, averaging, pulse skipping method, mosfet ,igbt.
I want to know why my circuit is making noise.
I am trying to replace rotary capacitor based fan dimmer using triac so i can control it by uc.

Not by Mosfet, by Triac.
Burst firing can be done with μp.
Max.

 

I am trying to replace rotary capacitor based fan dimmer using triac

I've never opened up a fan speed controller, but I'm having trouble imagining that it has a rotary (variable) capacitor in it. Is this a thing?

Separate from that, having both opto-TRIAC outputs fed from the same current source resistor might be the source of the chatter, since even when both opts's are on, the two opto-TRIACs come on at slightly different times. This changes the voltage drive and the amount of current available to fire the 2nd TRIAC.

Add another 470 ohm resistor ACR so each opto has its own source.

ak

 

Ya, i did that, detection of zero crossing and fire triac at every positive and negative cycle.

And what was the nature of the result?
Max.

 

You are going to get that in some degree by slowing a induction motor with triac, and they do not control at all with variable frequency.
You would be better off fitting a DC or BLDC motor for quiet operation at low rpm's.
Max.

 

I don't see anyway to resolve the humming issue when using Triacs at all, especially in the phase angle control mode.
Max.