Use the signal Processing Toolbox findpeaks function to count the peaks. The plotted signal does not appear to be noisy, so it will likely not be necessary to use other name-value pair arguments (such as 'MinPeakProminence') to define the peaks). (I have no idea if this works with Simulink, since I very rarely use Simulink.)
Just use:
t = ...; % Time Vector
s = ...; % Signal Vector
[pks,locs] = findpeaks(s);
NrPks = numel(pks)
.
