Single-phase fully-controlled thyristor converter simulation using simulink

Hi!

I am trying to implement a simple single-phase fully-controlled thyristor converter using Simulink.

As load I have placed just an inductor, the firing angle is set to a=60 deg., f=50 Hz and the rms of the voltage source is 230 V. The output voltage is the one on the picture below,

How can I fix the part I have circled? The waveform is supposed to be repetitive, so there should be a negative part as in the next half-periods.

[ABHISEK BHUJABAL]

Value of gate pulse.

Answer 1

[Pavel Dey]

As far as I understood from your model is that you are using a pulse to trigger the gate and the input is a sine wave. However, at the beginning the thyrister is simply off since no pulse has yet been applied in the gate. So it wont be affected by the input signal. Hence, the output is simply unaffected by the input sine wave at the initial stage. Once the thyristor is turned on by pulse it provides output and stay turned on until it is reverse biased. Then the other thyristor is turned on. It goes on like this. It is nothing but just that none of the thyristor is turned on at the beginning. It cannot follow the downward signal because it is not at all active then.

If you simply make the firing angle 0, you will observe a rectified sine wave.

I hope that helps.

[Michail]

The operating principle as you describe it is correct. Unfortunately, setting the firing angle to zero is not the solution. The purpose is to implement a fully-controlled converter instead of just a rectifier. Through the firing angle of the thyristors we are supposed to be able to control the output DC voltage.

Answer 2

[Mohamed Hassanien]

Hi Michail,

Unfortunately I have a question for you instead of an answer :) , How did you transfer the firing angle ( 60 degree) to phase delay ( seconds ) so you can use it in the pulse generator ?

In my case I am using the same principle to get variable dc o/p ( 9 12 15 7 ) from 230 AC .. Also, I am using the equation : V(dc) = ((2*Vm)/ pi) * Cos(alpha) to get the alpha, but the problem that I don't know how to use it as phase delay ( seconds ) ?.

Appreciate your help.

[Michail]

Hello Mohamed,

Actually cos(α)=cos(ωt) => α=ωt => t = α/ω where ω=2πf (or 2π/T). If your delay angle is supposed to be 60 degrees (in rads 60*(π/180)) and your frequency 50Hz then your phase delay in seconds will be t=(60*(π/180))/(2π50) => t=0.0033s. Consider also that in single phase fully controlled converter the thyristors operate in couples every 180 degrees. So the delay for T1 and T3 will be t_a=(60*(π/180))/(2π50) while for T2 and T4 t_b=(240*(π/180))/(2π50).

Hope that helps.

KR, Michail

[Mohamed Hassanien]

Thank you very much for your kind replay for my question,

I actually tried to implement what you were saying on the next formula for the full wave rectifier : V(dc) = ((2*Vm)/ pi) * Cos(α)

By Applying the 60deg on this rule I suppose to get a 73.2 Vdc at time that you mentioned T1 & T4 = 0.0033s , T2 & T3 = 0.0133s as the arrangement below

But I get the volt in scope 2 as below :

do you have any idea why I don't get the 73v DC as the formula states ?

The question in another way, If I want to get a 12v output DC what angle should I use ?

[Michail]

Hello again Mohamed,

I think you miss an sqrt(2) in you formula. The average DC output of this fully controlled converter is Vdc = 0.9*Vs*cosα where Vs is the rms voltage of your source (230V). If you want your output to be 12V then your delay angle should be around 86.67 degrees. What you have to consider is the ripple in your output and how to eliminate it.

I suggest you to have a look in the literature. Mohan, Undeland and Robbins have authored a really great book.

KR, Michail

[Mohamed Hassanien]

Thank you Dear Michail for your kind help :). The book you suggested is really a good one.