p i d controller

MEHRAN UNIVERSITY OF ENGINEERING AND TECHNOLOGY JAMSHORO SINDH

PAKISTAN

SIR RAFIQUE AHMED JHATIAL

HAMMAMA SOHAIL11TE47

Submitted to:

Submitted by:

Presentation topic:

P-I-D CONTROLLER

Proportional Action(P-Action)

A Proportional Band that is too narrow causes hunting! The TC will than behave like an ON/OFF controller!

A correctly sized P-Band results in an Overshoot, followed by an Undershoot and than Stabilization, with a small offset near the Set Point.

With a (far) too large P-band the Set point temperature will never be reached!

Integral actionP+I -Action

When we add the “Integral Action” we can reduce the Offset to 0C, in a specified time.

The “Integral Action” will reduce the Offset completely, in the “Integral time”

Because the “Integral Action” “Resets” the Offset caused by the P-Action, the I action is in some books also called the “Reset Action”.

Integral control is a second form of feedback control.

A negative error will cause the signal to the system to decrease, while a positive error will cause the signal to increase.

I-only controllers are much slower in their response time than P only controllers.

This slower response time can be reduced by combining I-only control with another form, such as P or PD control.

I-only controls are often used when measured variables need to remain within a very narrow range and require fine-tuning control.

I-control correlates the controller output to the integral of the error.

Differential ActionP+ I+ D-Action

When we get a “Disturbance” in our process the PI controller responds “rather slow”

The D-Action looks at the speed of change.

It INCREASES the Output capacity of the TC VERY RAPIDLY

D-Action” we will have LESS Undershoot, LESS Overshoot and win valuable Time.

D-control is a form of feed forward control.

It functions to minimize the change of error, thus keeping the system at a consistent setting.

The primary benefit of D controllers is to resist change in the system.

Unlike proportional and integral controllers, derivative controllers do not guide the system to a steady state. Because of this property, D controllers must be coupled with P, I or PI controllers to properly control the system.

D-control correlates the controller output to the derivative of the error.

P I D Controller:•A proportional-integral-derivative controller (PID controller) is a generic control loop feedback mechanism (controller) widely used in industrial control systems.

•A PID controller calculates an "error" value as the difference between a measured process variable and a desired setpoint •The PID controller calculation algorithm involves three separate constant parameters, and is accordingly sometimes called three-term control: the proportional, the integral and derivative values

Proportional

P•P depends on the present error

Integral

I•I on the accumulation of past errors

Differential

D•D is a prediction of future errors, based on current rate of change

The Characteristics of P, I, and D Controllers

A proportional controller ( ) will have the effect of reducing the rise time and will reduce but never eliminate the steady-state error.

An integral control ( ) will have the effect of eliminating the steady-state error for a constant or step input, but it may make the transient response slower.

A derivative control ( ) will have the effect of increasing the stability of the system, reducing the overshoot, and improving the transient response.

In fact, changing one of these variables can change the effect of the other two.

With the PID controller we can set the P+I+D values so that we will not have any Over or undershoot and reach set point directly.

PID controller has all the necessary dynamics: fast reaction on change of the controller input (D mode), increase in control signal to lead error towards zero (I mode) and suitable action inside control error area to eliminate oscillations (P mode).

“This “combination”, of “Present + Past + Future”, makes it possible to control the application very well”

CL RESPONS

ESPEED OF

RESPONSE OVERSHOOT S-S ERROR

Kp Increase Increase Decrease

Ki Decrease Increase Eliminate

Kd Increase Decrease No Change

The effects of each of controller parameters Kp, Ki , Kd

 Advantages and disadvantages of controls

Typical uses of P, I, D, PI, and PID controllers