Specifications and robustness

Question 1

When designing a controller, how do we decide between PD or PI?

Answer 1

PD adds phase at desired frequency
PI decreases phase at desired frequency
PI also reduces steady state error to

Question 2

What is meant by robust stability of a control system?

Answer 2

-despite possible uncertainty is the system stable?
-how much gain and phase can there be before the closed loop system is unstable?

Question 3

What is the effect of time delays on a system?

Answer 3

Phase lag of the delay reduces Phase margin
-in turn reduces the damping of the closed loop
-Large enough delays destabilise the closed-loop

Question 4

Why is it important to consider time delays in control design?

Answer 4

Delays occur in almost all real-world systems

Question 5

How do we express the time delay of a transfer function?

Answer 5

We multiply G(s) by e^(-Ts) where T is the length of delay