What is PID 1

[Jigneshpadia2002]

What is PID ? Can anyone provide basic information on functioning of PID ?

Thanks in advance

 

[Skogsgurra]

This term is used and abused in most walks of control theory. The core thinking is that a controller makes a controlled value aka "actual value" follow a reference value aka setpoint.

The controller does so by amplifying the difference between actual value and setpoint. If actual value is too low, the controller increases its output to correct it. The gain that such a controller has is called a proportional gain. If the gain is, for instance, ten times - then the output is ten times the difference. The proportional gain gets a shorter name "P".

The fact that there has to be a remaining difference to keep controller output at the desired value is very often a problem. It makes the P controller steer the actual value close to, but not exctly to, the setpoint.
By introducing an integrating action that makes the controller output increase as long as there is any error at all, no matter how small, a PI (Proportional-Integrating) controller is created. The PI controller integrates the difference and adjusts its output to keep actual value exactly same as setpoint.

A PI controller is very often all you need. Most drive systems work very well with a PI controller for speed and a PI controller for torque. The output of the speed controller then is the setpoint for the torque controller.

But, there are situations where a PI controller simply doesn't react fast enough. It is then possible to antecipate deviations by taking the time derivative of the control difference. The controller will then be able to act forcefully to fast changes and this part of a controller is - of course - named Derivative action. So a combination of these three controller actions is a PID controller.



Gunnar Englund

http://www.gke.org

 

[Jigneshpadia2002]

Hi Gunnar, This is very useful. Thanks a lot for your valuable tips.

 

[jraef]

Want a good practical example?

The Cruise Control in your car is a PID controller. You set the speed you want (setpoint). It measures the speed the car is going (feedback) and adjusts the throttle to maintain that speed (proportional response output). If you go up a small hill, the car begins to slow down (error), so the controller increases the throttle (integral response to the size of error) until the setpoint is reached again (stasis). If the car is going up an steep hill, the speed drops faster than before, so the throttle response is greater (derivative of the rate of change).



"Our virtues and our failings are inseparable, like force and matter. When they separate, man is no more."
Nikola Tesla

 

[laundry]

Hello Jigneshpadia 2002
you asked what is PID.P=Proportional gain.this is the factor by which the speed error is multiplied in the speed loop algorithm to produce the proportional speed error correction term.Increasing this value increases both the system damping and transient speed response.but if takentoo far the drive will become unstable.
PID.I=Integral gain this is the factor by which the integral of the speed error is multiplied inthe speed loop algorithm to produce the integral speed error correction term.The integral speed error correction term ensures zero speed error during steady state load conditions, and by increasing its value results in a more rapid revovery after a transient disturbance ie sudden load change. if taken to high this will caus oscillatory conditions. PID.The derivative term,by adding derivetive value this willreduce any overshoot of your amplitude.