Proportional-Integral (PI) Controllers

Proportional-Integral (PI) controllers are used in many industrial control applications. The main purpose of using Proportional and Integral (PI) in process system is to improve the steady-state accuracy of the system without affecting the stability of the system.

Proportional action responds quickly to the error deviation and the integral action will act slowly but offset or remove the steady-state error, i.e, it removes the difference between the setpoint value and actual process value in the plant over a period of time.

Choice of PI Controller

The choice of having PI controller in the process system when:

  1. The control system should not be required fast response.
  2. Systems consist of large disturbances and noise present during the operation of the process system.
  3. There is only capacitive or inductive energy storage element in the process system.
  4. There exist large transport delays in the process system.

In most of the plant control applications, PI or PID controllers are used. The derivative action speeds up the system response by adding a proportional to the rate of change of feedback error. This is consequently vulnerable to the noise in the error signals which can limit the derivative gain. Lager value of the derivative gains in the controller will lead to instability of the system and also requires higher values of the proportional and integral gains compared to gains required in PI controllers.

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