When I do frequency analysis on my feedback controlled system and the controller is really tightly tuned, I get a frequency response that looks like this:
Blue is excitation signal and green is system output signal. Does this mean that my system has nonlinear behavior? Or this just a condition that would be visible when hitting a zero or a pole?
Smaller frequencies work fine and produce a sine wave output that is easy to interpret. It is higher frequencies that end up looking like this.
Since I intend to use this to derive a bode plot, I'm also curious how do I interpret this data and what is the actual magnitude and phase on this plot for this frequency? It seems to me like it is fairly random. How would I go about sweeping frequencies and making a bode plot when many frequencies in this region look like this? FFT maybe on both signals? But how exactly?