What is PID control

PID control

Basics of PID control

A PID controller is a control structure that tries to regulate a certain controlled variable (pressure, temperature, etc.) to a specified setpoint (PID setpoint). To do this, the controller needs information about the current status of the system in the form of a measured value (pressure sensor, temperature sensor, etc.). This signal is called PID feedback.

This control structure usually has three parts: P = proportional, I = integral and D = differential.



How is this regulated?

On the picture you can see that the PID feedback value is subtracted from the PID setpoint. The difference signal is generated from this. If the two values ​​are the same, no correction is necessary and the frequency converter will not change its frequency. If the PID setpoint is greater than the feedback value, the differential signal is positive and the frequency converter will increase its output frequency until the PID setpoint and the PID feedback value are equal. The frequency is therefore continuously adjusted as long as there is a difference between the PID setpoint and the PID feedback.

Simple example:
PID setpoint equal to PID feedback ==> no change in frequency on the converter
PID setpoint greater than PID feedback ==> increase the frequency at the converter
PID setpoint smaller than PID feedback ==> Reduction of the frequency at the converter

Effect of the individual parts of the PID control

P - portion:

The P component is the proportional component, which means that the effect only depends on the momentary difference between the PID setpoint and the PID feedback. However, the disadvantage is that the closer the setpoint and feedback approach, the smaller the correction is. This slows down the control behavior. In theory, the setpoint is never reached.

I - portion:

The I component can solve the problem of the P component not reaching the setpoint. The I component integrates the difference between the setpoint and the feedback. Even with small differences, after some time the correction signal becomes large enough to correct the error between the PID setpoint and the PID feedback.

D - share:

The D component solves another problem of the P controller. Since the correction signal can never be greater than the difference between the PID setpoint and the PID feedback, the D component can briefly amplify this difference and thus accelerate the controller's response. However, this is only recommended if the P and I components do not achieve good control behavior.

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