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From: Otavio on 3 Jun 2010 14:49
Hello there

I'm new to Simulink and one of the first thing's i've done to explore it was trying to see the three-phase source waveform through the scope.

Such a pitty there's no way to post any picture here, like a printscreen, so you always have to describe the schemes using words, that can be pretty difficult depending on circuit's complexity. Fortunately in my case the circuit is very simple.

I got a three-phase source and used three voltage measurements, a ground reference, a scope and a MUX to see each phase waveform (phase-to-ground) in a single graph. The simulation was OK, but when I opened the scope to see the waveforms, what I saw was very far from sine waves! The signals were more similar to triangular waves. Not even the sinusoids obtained from our power companies are so ugly!

So, I believe there must be something wrong with my simulation settings, or maybe the scope settings. The three-phase source was kept with the same settings, except the voltage rms phase-to-phase, that I lowered to 460. So my question is.. What do I need to change in my settings in order to obtain sine waves more accurate on the scope?
From: Frank W. on 4 Jun 2010 04:02
Hello,
> I got a three-phase source and used three voltage measurements, a ground >reference, a scope and a MUX to see each phase waveform (phase-to-ground) in a >single graph. The simulation was OK, but when I opened the scope to see the >waveforms, what I saw was very far from sine waves! The signals were more similar to >triangular waves. Not even the sinusoids obtained from our power companies are so >ugly!
Every sinusoid becomes ugly when you sample it with a large sample time.
Concerning your simulation: try to set the maximum step size for the solver (Simulation>Configuration Parameters and then the Solver pane) to a value other than 'auto'. Of course, the entered value shoud be well below the sine waves cycle time.
Regards
Frank
From: Otavio on 4 Jun 2010 18:44
> Every sinusoid becomes ugly when you sample it with a large sample time.
> Concerning your simulation: try to set the maximum step size for the solver (Simulation>Configuration Parameters and then the Solver pane) to a value other than 'auto'. Of course, the entered value shoud be well below the sine waves cycle time.

Hmm, so this is the way you increase the sample rating! Thank you very much, I had no idea how this was done. It worked pretty well, now I could see "perfect" sine waves!

Regards,
Otavio
From: Frank W. on 5 Jun 2010 02:14
> Hmm, so this is the way you increase the sample rating!
Actually, it's not the sample rate. The rate could be set seperately in the scope block. With the mentioned settings for the solver you set the time when Simulink solves the equations which each blocks represents. The sampling rate of blocks is entirely different. It is the solver settings which determines the accuracy of your simulations.
I better should not have mentioned the sample rate in this context .
Frank
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