I am guessing you can get the same result by doing the followings:
- disable the fault and the breakers as mentioned in the example
- put 'open-input' analysis point at 'Vref' line
- put 'open-output' analysis point at 'Pa' line
- linearize it at a steady state point such as 0.99s (just before manual perturbation kicks in)
- in the linearization window, click on bode plot (and obtain 'linsys1')
- Note that the oscillation frequencies can be extracted by doing either:
imag(eig(linsys1.A))/2/pi
or
[wn zeta poles] = damp(linsys1);
imag(poles)/2/pi
