Thyristor gate pulse triggering using Microcontroller...

[uv]

Hello Friends,

         I have doubt in thyrister controlling. I am using only single phase. in this only two back to back thyrister is connected. so only two gate pulse is required. my Qustion:

How to generate gate pusle:
[A] Using 2 Edge alined PWM
[B] using Timer and Generate pulse on Two Pin (GPIO)  
which is better and easiest way.

I am using freescale ColdFire V1 microcontroller.
I have done few programs on development board. without interfacing zero crossing detection its working ok. I can change (Edge Aligned) PWM duty cycle  as per feedback voltage. but when i introdused zero crossing (input capture Pin) at that time it does not work.

Please help me in this program. if you have any docdument please send me.
i do not have any ides on this.

[TurboBob]

have you worked out the voltage isolation issues yet?  Pulse transformer or optoisolator or other?

the way I do it is: 

    use an input capture to interrupt on the zero crossings,  use the delta readings to determine the incoming period.

    in the capture interupt set a timer interrupt to happen some time delay from the zero crossing for the start of your trigger pulse.

    in the trigger pulse interrupt,  set another timer interupt (can be the same timer) to occur when you want the pulse to turn off.

  software control of the trigger pulse will most likely be accurate enough,  and is more easily accomplished than trying to get a PWM channel to do what you want.

For the zero crossing,  you want to be sure you have good filtering and hysteresis,  as noise will trigger this otherwise.  This hysteresis and filtering can cause the zero crossing ISR to occur late and un even for the positive and negative half cycles depending on your circuitry.  Your software will need to handle this.

Good luck

Bob