Simulink 6 Pulse Rectifier not working.

I'm trying to model a 6 Pulse Rectifier in Matlab Simulink but coming across some errors in the output voltage when the firing angle into the Pulse Generator exceeds 90 degrees. If my understanding of the system I've devised is correct, I thought the output voltage would decrease as the firing angle increased. This seems to occur between 0 and 90 degrees, however anything above this firing angle and the output voltage breaks down to what I didn't expect. Is this correct and if not, what in my model is causing this error?

Worth noting also is I didn't know how to generate the "wt" from the PLL so I just generated it from a repeating sequence. This may not be correct but I didn't see initially why it wouldn't be.

Any help or advice is much appreciated.

Ali.

[SEBASTIAN CHENNATTU]

hey I am facing a very similar issue too I have given a more detailed description kindly visit this link:

https://in.mathworks.com/matlabcentral/answers/416287-why-does-simulink-not-give-correct-results-with-load-inductance-for-3-phase-controlled-rectification

Answer 1

[Manan Mishra]

The output of the model is not correct even for firing angle between 0 and 90. There are two reasons why the model is not showing expected behavior:

1) The output of "Pulse Generator" block is not connected in the right order to the thyristors. The pulse ordering in the pulse train corresponds to the natural order of commutation of a three-phase thyristor bridge. This order is same as the order generally used for numbering of thyristors in a three-phase bridge, 1/3/5 for the upper half and 4/6/2 for the lower half. You need to connect the appropriate gate pulse to the corresponding thyristor. For more information on the output order of "Pulse Generator" block, refer the following link:

https://www.mathworks.com/help/physmod/sps/powersys/ref/pulsegeneratorthyristor.html

2) The snubber circuit parameters for each thyristor in the "Block Parameters" dialog box are not appropriate. The values given make it difficult for the thyristors to be switched at the right instant. If you are using this model just for the purpose of simulation, you can give very high values for these parameters to get the desired output. You can try "Rs = 1e+5 Ohms" and "Cs = inf" as an example.

[Alasdair Robertson]

Hi Manan,

Thanks for your help! I took your advice and developed my understanding on the 6 pulse rectifier further and realised that, with your corrections to my model, the voltage output with a firing angle from 0 to 60 degrees is correct. However, I am still under the impression that when the firing angle is set to 90 degrees the output voltage isn't correct.

From my research, the output of the rectifier at 90 degrees firing angle should be 0v average, with the positive to negative voltage output slant starting at wt = 150 degrees? This isn't the output I am receiving on the output of my matlab model, as what I am seeing in the output scope is just a couple of voltage spikes.

Any further assistance or advice towards this issue would be much appreciated. You may find the updated model attached as before.

Thanks again for your help,

Ali.