I am performing a simulation of a simple half wave rectifier using thyristor. I have applied the gate voltage with the help of resistor divider network .Can any one help me understand the method by which I can change the conduction angle without using any logic circuit or controller??

If you are trying “Phase Control" of SCR, you have to use phase sensing circuit for the control (no way out). Simple resistor divider voltage control does not work. Plus the Gate drive (trigger) must be "hard" enough, otherwise the SCR goes thru "Linear" region for longer time and it can be destructive.
I had used SCR long back (1978, 2000Amp water cooled, Siemens), now I use IGBT & Mosfets. But for certain application SCR is the best choice. The "Phase Control" method in AC line application generates poor Power Factor and higher Harmonics content, which is not welcome by Electricity Company. Nower days everybody wants Unity Power factor.

Mr. Amrit and Laurent thanks for your comments!! I was able to change the conduction angle with the help of resistor network. By changing the value of lower resistor,SCR is triggered at different voltages that means by changing the gate current we can control the conduction.Though this is not the best method but still it is simple to understand for starters.The problem with the circuit was that AC signal applied to the gate was not synchronized to the AC signal applied between anode and cathode , Hence kept a common AC signal for both gate and anode-cathode then proper results were achieved.

Mr.Laurent, thanks for sharing the document i will go through it and let you know if i have any further questions.

I can share the results if your interested!!