A PID controller an industry standard and most common closed loop control algorithm. Understanding how the PID controller operates is critical for successful tuning.

 

Any closed loop control system consists has target, actual and error values. The target is the desired value, the actual is the currently measured value and the error is the difference between the target and the actual value. Further more, each system has an actuator which is used to control the systems current state (e.g. wastegate solenoid, VVT solenoid etc).

 

A PID controller consists of three terms; a proportional term, an integral term and a derivative term. The Link PID system provides gains for each of these terms, increasing the individual term gains will increase their effect on the system. It is also important to realize that each term will have an effect on the process which will modify the effect of other terms.

 

Proportional Term

The proportional term makes a change to the actuator that is proportional to the error value.

 

Example

As the actual value moves closer to the target value the effect of the proportional term decreases.

 

Hint

Increase this value to increase rise time, increase it too much and the system will become unstable and oscillate.

 

Hint

Decrease this value to remove target overshoot.

 

Integral Term

The integral term makes a change to the actuator based on an accumulating error.

 

Example

A small offset between the actual value and the target value that will never be corrected by the proportional term alone.

 

Hint

Increase this value to increase the strength of offset correction, increase it too far and the system will become unstable and oscillate.

 

Derivative Term

The derivative term makes a change to the actuator based on the rate of change of error. The derivative term can be seen as a quick response to change.

 

Example

If the error is increasing rapidly the derivative term will make a change to the actuator to counteract this.

 

Hint

Increase this value to dampen the approach to a target, increase it too far and the system will become unstable and oscillate.