Control System Principles Flashcards

In a block diagram, the signal flow from the output back to the summing junction is called:

Answer: Feedback path

The feedback path carries the measured output (or processed output) back to the summing junction to be compared with the reference input.

For a unity-feedback system, the closed-loop transfer function T(s) = G(s)/[1+G(s)] has the sensitivity function S(s) equal to:

Answer: 1/[1+G(s)]

The sensitivity function S(s) = 1/[1+G(s)] quantifies how output changes in response to disturbances or plant perturbations.

Which statement about a minimum-phase system is correct?

Answer: All zeros are in the left-half plane

A minimum-phase system has all its zeros located in the left-half plane (open), giving the minimum possible phase lag for a given magnitude response.

State feedback control with full state feedback u = -Kx can place all closed-loop poles arbitrarily if and only if the system is:

Answer: Controllable

Arbitrary pole placement via state feedback is possible if and only if the system is completely controllable (the controllability matrix has full rank).

What is the bandwidth of a closed-loop system generally defined as?

Answer: The frequency at which the closed-loop magnitude drops to -3 dB below its DC value

Closed-loop bandwidth is defined as the frequency range over which the closed-loop magnitude stays within 3 dB of its low-frequency value.

In signal flow graphs, Mason's gain formula is used to find:

Answer: The overall transfer function from input to output

Mason's gain formula computes the overall transfer function by summing path gains weighted by cofactors of the signal flow graph determinant.

A PI controller introduces which of the following into the open-loop transfer function?

Answer: An additional pole at the origin and a zero in the LHP

A PI controller C(s) = Kp + Ki/s = (Kp·s + Ki)/s adds a pole at s=0 (integrator) and a zero at s = -Ki/Kp in the left-half plane.