Choosing Drive Signals for System Identification? (I'm just learning a little about system identification so apologies in advance if this question is badly worded)

How do you go about choosing drive signals for system identification? I've seen PRBS signals used but it seems like that's going to work well for frequencies around the chip rate but not really low frequencies; I've also seen frequency sweeps.

If I have a SISO system that I know is close to a 2nd order linear system with poles in a certain range, and I can drive it with an arbitrary signal up to some amplitude A for up to some time length T, how do I pick a signal that would give me the best responses for determining the accuracy of the transfer function?

I tried googling for "system identification drive signals" but I don't see anything that pertains to my question.



edit: one particular type of SISO system I've dealt with is an (input=power dissipation, output=temperature) system for power semiconductor thermal behavior, and it seems very hard to model because there's usually a dominant pole at very low frequencies (&lt;1Hz) and the next one might be 100 times higher, so any high-frequency drive signals just get very heavily attenuated.
For linear systems, you can completely characterize the transfer function using its frequency response, so a frequency sweep would be one possible choice. However, you would need to ensure that at each test frequency, you allow time for the system's transient response to die out before measuring its steady-state amplitude/phase response.