Stability, Robustness and Performance
Stability: bounded inputs produce bounded outputs
Necessary and sufficient conditions: check for nonzero solutions around feedback loop.
Basic problem: positive feedback.
Performance: achieve desired response
Specify performance in terms of frequency response.
Main problems: disturbance rejection, command following.
Robustness: stability and performance in the presence of unknown dynamics
Check for stability in presence of uncertainty.
Need to check stability for a set of systems.
“Small gain theorem” gives tight conditions based on bounds of uncertainty operator.
No uncertainty No need for feedback