Feedback Control

Feedback Control

1. Feedback

   • The term feedback refers to a situation in which two (or more) dynamic system are connected together such that each system influnences the other and hence their dynamics are strongy coupled
   • A feeback wil be useful to maintain the output to a desired level to overcome any disturbances.

2. The error signal

   • The diference between the reference signal and the feedback output signal

3. Control system

   • A control system consits of subsytems and plant assembled for the purpose of obtaining a desired output with desired performance given a specified input.
   • Basic concerns of a control system
     • Stability
     • Tracking
     • Regulation
     • Sensitivity
     • Robustness
   • Good control system
     • Sytem must be stable at all times
       • Bounded inputs give rise to bounded outputs
     • The system output must track the command reference signal as closely as possible
     • The system output must be insensitive as possible to disturbance inputs, which are unknown.
     • These goals must be met or the dynamics of the physical system change over time

4. Disturbances

   • The disturbance is typically unknown but affects the output

5. Heading autopilot example

   • The error should be small
     • The heading output needs to be as close to the rference as possible (ideally zero)
   • Effect of disturbance on output should be small
     • The effects of wing gusts on heading should be small - ideally zero
   • Swift tracking response
     • The heading shoud respond quickly to changes in desired heading