Question

Question 1 (a) Summarise P, Pl, and PID control actions by briefly mentioning at least one advantage and at least one disadvantage of each action. [10 marks]

Answer 1

Proportional controller: The control system is able to arrest the rise of the controlled variable and ultimately bring it to a rest at a new steady state value.

Advantages:

i) Fast response time

ii) Minimises fluctuation

Disadvantages:

i) Contains large offset

ii) Does not bring system to desired set point

Proportional Integral controller:

The addition of integral action in proportional control eliminates the offset, the controlled variable ultimately returns to the original value with more oscillatory behaviour.

Advantages:

I) contains small offset

ii) returns system to steady state

Disadvantages:

I) slow response time

Proportional-Integral-Derivative control:

The addition of derivative action to the PI action arrest the rise of controlled variable more quickly and it is returned rapidly to the original to the value with little or no oscillation.

Advantages:

i) Keeps system at consistent setting

ii) Controls process with rapidly changing outputs

Disadvantages:

i) Requires combined use with another controller.

ii) Not dependent on the process