Actually I am looking for "unwrap" Matlab-like function in Modelica scope

http://www.mathworks.com/help/matlab/ref/unwrap.html

...
v_angle = atan2(v_beta, v_alpha);
unwrapped_angle = unwrap(v_angle);
der(v_freq) =  unwrapped_angle;
...

%Unwrap the signal xw(n)
xu = xw;
for i=2:length(xw)
difference = xw(i)-xw(i-1);
if difference > pi
xu(i:end) = xu(i:end) - 2*pi;
elseif difference < -pi
xu(i:end) = xu(i:end) + 2*pi;
end
end

I would prefer to do it "continually" but not on sampled signal batch as code snippet ...

Any idea how to do it under Modelica?

Thanks.

The only way you can access the previous value of something is by sampling/discrete events in Modelica.

I think you need to look for discontinuities in some way similar to:

algorithm

  v_angle = atan2(v_beta, v_alpha);

  if v_angle+n*pi > pi then

    n := n - 1;

  elsif v_angle+n*pi < -pi then

    n := n + 1;

  end when;

  unwrapped_angle := v_angle - 2*n*pi;

  der(v_freq) := unwrapped_angle;

I had another idea using a derivative that followed v_freq and tracked that instead, but I think the above is simpler. I didn't check if it is correct though.

Would be possible to use Modelica "previous()"  or "pre()" function. It seems those are related to discrete domain. Do they work on continuous domain as well?

They can only be applied to discrete signals.

Maybe delay() is the right function for you?

Maybe delay() is the right function for you?