Lecture 8

Question 1

What is a compensator?

Answer 1

A component that is inserted into a control system to compensate for a deficient performance.

Question 2

What are the pros and cons of a open-loop system
(3, 3)?

Answer 2

pros:
- simple
-easy to maintain
- stable
cons:
- inaccurate
-unreliable
- changes from disturbances cannot be corrected

Question 3

What are some drawbacks with simple closed-loop controller and how can you fix it?

Answer 3

Oscillations in outputs which can be overcome using a more complex controller like a PID controller.

Question 4

What are the important closed-loop system terminologies (8) ?

Answer 4

• Process Variable: the parameter being controlled
• Sensor: used to measure and provide feedback
• The Set Point: the desired value for the process variable, like the desired temperature of a case
• Error: the different between the process variable and the set point
  -rise time: time to go from 100% to 90% of the final value
• overshoot: the maximum amount about the final value
• settling time: time to settle within a certain percentage of the final value
• steady-state error: the difference between the process variable and the target

Question 5

What is a PID controller?

Answer 5

a device that applies a correction based on Proportional, integral and derivative terms. it simplifies the sum of three parallel actions to generate a control output.

Question 6

What are the advantages of using a PID controller (4)?

Answer 6

• accurate
• eliminates steady-state error
• reduce overshoot and oscillations
• widely applicable

Question 7

What is a proportional controller?

Answer 7

provides a control input that is proportional to the error value

Question 8

What are the advantages of proportional controller(3)?

Answer 8

• simplicity
• fast response
• stabilization

Question 9

What are the limitations of the proportional controller(2)?

Answer 9

• steady-state error
• oscillations

Question 10

What is a proportional integral controller?

Answer 10

a feedback controller combining proportional and integral actions to correct errors in a system.

Question 11

What are the features of a PI controller(2)?

Answer 11

P: reacts to the current error.
I: reacts to the accumulation of past errors

Question 12

What does Integral control do?

Answer 12

eliminates the effect of disturbance at steady-state

Question 13

What are the advantages of proportional integral controller(3)?

Answer 13

• simplicity
• no steady-state error
• tracking

Question 14

What are the limitations of proportional integral controller(2)?

Answer 14

• slow response
• oscillations

Question 15

Important things to know about applying PI controllers (2)?

Answer 15

• pi controller needs tuning to eliminate steady-state error
• choosing low and high values for proportional and integral gains cause weak performance or instability

Question 16

What is derivative control (3)?

Answer 16

• proportional to the rate of change of the error signal
• introduces an element of prediction into the control action
• has a damping effect and reduces the oscillations caused by a large gain Kp and improves settling time.

Question 17

What are the affects of introduction a derivative control gain KD (3)?

Answer 17

• increase stability
• reduce overshoot
• improve the transient response

Question 18

What the uses cases for P, PI and PID?

Answer 18

P: when speed is more important the accuracy
PI: when steady-state accuracy is important
PID: high performance systems requiring stability

Question 19

What are the 5 steps to designing a PID controller?

Answer 19

1. obtain an open-loop response and determine what needs to be improved
2. add a proportional control to improve the rise time
3. add an integral control to eliminate steady-state error
4. if needed, add a derivative control to improve the overshoot.
5. adjust kp, ki, and kd until you obtain a desired overall response.