# firing angle control of SCR

So I'm designing a Thyristor controlled reactor which is a connection of two SCRs in antiparallel and an inductor in series.I'm using a ZCD to find out the zero crossing point of the sine wave and from this point I'm inducing a delay up to which the SCR will remain in OFF state and then giving a pulse for a specified amount of time to turn the SCR on.The problem which I'm facing is that I want to trigger one SCR in positive half cycle and the other one in negative half cycle but as ZCD can't differentiate between the two I'm not able to trigger the SCRs alternatively.Anyone can help me with this?

Can you use a TRIAC? A TRIAC can be triggered in either direction with either a positive or negative trigger (4-quadrant operation).

Or, maybe you can trigger both SCRs every time, even though only one will be conducting?

Otherwise, if your ZCD can't tell you if the voltage is positive or negative (before or after the zero crossing) you may need another "detector" to determine positive or negative.

...When I did this a million years ago I didn't try to find the zero crossing (which is "difficult"). I found the point where the voltage crossed-above a certain positive voltage. From there, I calculated when the next two zero-crossings were coming.

Thanks alot for your suggestions and yeah even I was thinking of firing both the SCRs in each half cycle.I'll test this TCR with the artificial transmission line set up tomorrow for compensation.Hopefully,it should work.

Use a diode in series with the AC sine wave and hook it up the the analog port. If you get a zero crossing, and a reading on the analog port, you are in the positive half cycle.

Hello kkumarmohit,

I have been working on a similar project where I need to fire a TRIAC (BT139) after detecting the zero crossing of the AC Voltage. If possible please provide me with your sourcecode for arduino as a reference.

Thankyou!

Hi,
Have you used google phase control arduino

try here;

http://playground.arduino.cc/Main/ACPhaseControl

Tom.....

ayushmatic21:
If possible please provide me with your sourcecode for arduino as a reference.

Does that really mean "I have an assignment and I want to submit your code and pretend it is mine"? That's what it sounds like to me.