Best way to resample the output of a Simulink simulation with variable time step into a signal with a fixed sample time

I have a simulation model that runs with a variable timestep:

(I don't want to change this)

For the purpose of system identification it would be convenient to have the output signals sampled at a regular frequency.

This seems to work:

y_resampled = resample(simOut.POW,simOut.POW.Time)

According to the documentation, this resamples the values, simOut.POW, by linear interpolation onto a vector of uniformly spaced instants with the same endpoints and number of samples as simOut.POW.Time.

Not sure if it is the right way to do it or if there is a better function to use.

Answer 1

[Ameer Hamza]

No, resample() samples the signal at vector specified by simOut.POW.Time. So, in this case, it is not doing anything. I suggest using interp1()

t_equally_spaces = min(simOut.POW.Time):0.01:max(simOut.POW.Time);
y_resamples = interp1(simOut.POW.Time, simOut.POW.Data, t_equally_spaces)

[Bill Tubbs]

Thanks. Getting a strange error with your method.

t_equally_spaced = min(simOut.POW.Time):0.01:max(simOut.POW.Time);
y_resampled = interp1(simOut.POW.Time, simOut.POW.Data, t_equally_spaced);

Error using interp1>reshapeAndSortXandV (line 424)

X and V must be of the same length.

Error in interp1 (line 93)

[X,V,orig_size_v] = reshapeAndSortXandV(varargin{1},varargin{2});

Any idea what the problem might be? Could it be due to the dimensions of simOut.POW.Data?

>> size(simOut.POW.Time)

ans =

5124 1

>> size(simOut.POW.Data)

ans =

1 1 5124

>> size(t_equally_spaced)

ans =

1 1600

[Bill Tubbs]

Confirmed. You may ignore above comment as it was simply a consequence of the dimensions of simOut.POW.Data. Not sure how they ended up this way but I corrected it this way:

y_data = reshape(simOut.POW.Data,[size(simOut.POW.Data,3),1]);

Thanks.

[Ameer Hamza]

Another easy solution is to use squeeze()

y_resamples = interp1(simOut.POW.Time, squeeze(simOut.POW.Data), t_equally_spaces)

[Bill Tubbs]

That is much better thanks.

[Ameer Hamza]

I am glad to be of help!!!