Difference between revisions of "PID Control"

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This chapter describes the use of proportional integral derivative (PID) feedback for control systems design. We discuss the basic concepts behind PID control and the methods for choosing the PID gains.

Textbook Contents

• 1. Introduction
• 2. The PID Controller
• 3. PID Variations
• 4. PID Tuning (Ziegler Nichols)
• 5. Implementation
• 7. Exercises

Chapter Summary

This chapter describes the design and use of PID (proportional-integral-derivative) control:

1. The basic PID controller as the form

where  is the control signal and  is the control error. The control signal is thus a sum of three terms: a proportional term that is proportional to the error, an integral term that is proportional to the integral of the error, and a derivative term that is proportional to the derivative of the error.

2. Integral action guarantees that the process output agrees with the reference in steady state and provides an alternative to including a feedforward term for tracking a constant reference input. Integral action can be implemented using automatic reset, where the output of a proportional controller is fed back to its input through a low pass filter:

3. Derivative action provides a method for predictive action. The input-output relation of a controller with proportional and derivative action is

where  is the derivative time constant. The action of a controller with proportional and derivative action can be interpreted as if the control is made proportional to the \emph{predicted} process output, where the prediction is made by extrapolating the error  time units into the future using the tangent to the error curve.