dsp.SineWave in Matlab function block not generating sine wave on the scope

When the plot function is called it generates the desired wave. However when a scope is used to observe this , constant values are rather observed. The same output is observed when the dispaly block is used - all values are generated at once even for a single step. What could I be doing wrongly here?

It also takes a long time to complete simulation when used in Simulink compared to Matlab.

See below the code.

function y = fcn()

sine1 = dsp.SineWave('Amplitude',1,'Frequency',60,'PhaseOffset',0,'SamplesPerFrame',1000,'OutputDataType','double');

y = sine1();

The idea is to later make the amplitude an argument(input) to the block so it can be varied.The application will be to make a closed loop control that uses over modulaton of SPWM..

Answer 1

[Abderrahim. B]

Hi!

Why do not you use sinWave block available in dsp system simulink library instead of writing a MATLAB function for that ? You will be able to change block parameters Check out the link below to learn about dsp system toolbox signal generation capabilities:

https://www.mathworks.com/help/dsp/referencelist.html?type=block&listtype=cat&category=sources&blocktype=all&capability=&s_tid=CRUX_lftnav

Hope this helps

[Andrew]

Hello Abderrahim. Thank you for your quick response and the suggestion.

As I mentioned earlier in the description, I wish to vary the amplitude of the sinewave based on the output voltage measured for the controller (closed loop) I am designing. The Matlab function allows me to include an input port so I can vary easily the parameters.

The sinewave block will not be helpful in my case. It will always be constant since it is not a block with parameters that can be specified by an input port.

I attempted using it for my open loop controller and it was kind of ok.

Is there a way to specify the parameters of the block as an input port? I see it has only an output port from the documentation.

[Abderrahim. B]

Hi Andrew,

There are control components in Simulink that you can use for this purpose. I build a small demo using slider to control sine wave amplitude (see picture attached).

Hope you find this reply helpful

[Andrew]

Hi Abderrahim.

Thank you for this suggestion..

The slider wouldn't be the appropriate block for this application.

I will keep checking for other alternatives.

[Sam Chak]

Hi Andrew,

Varying the amplitude of the sine wave is probably easier than you think.

This is the equation:

x(t) = Amp*[1*sin(2*pi*Freq*t)]

where you can define how the Amplitude should behave, perhaps as a function of time, t. For example, in the MATLAB Function block,

Amp = V/(1 + exp(- k*(t - t0))) + Offset.

Then, multiply Amp with the output of the Sine wave block.

[Andrew]

Thanks Sam.

Your solution gave a clue.

Using the Sinewave block from simulink & product block together with a constant/ varying input works.