2.1 Introduction

In this chapter, I introduce a method for implementing a control system when a plant model does not exist or is too complex to be useful for design purposes. This technique is suitable for use with plants that are approximately linear, although it can also provide satisfactory results with nonlinear plants.

The structure considered here is called the PID controller. The PID controller's output signal consists of a sum of terms proportional to the error signal, as well as to the integral and derivative of the error signal hence, the name "PID." This is the most commonly used controller structure. By some estimates [1], 90 to 95 percent of all control problems are solved with PID control.

The input to a PID controller is the error signal created by subtracting the plant output from the reference input. The output of the PID controller is a weighted sum of the error signal and its integral and derivative. The designer determines a suitable weighting multiplier for each of the three terms by performing an iterative tuning procedure.

In this chapter, I describe iterative PID controller design techniques and show how they can be applied in practical situations.

2.2 Chapter Objectives

After reading this chapter, you should be able to

• describe when it is appropriate to apply PID controller design procedures;

• describe the structure and design parameters of a PID controller;

• describe when to use proportional-only, proportional plus derivative (PD), proportional plus integral (PI), and full PID controller structures;

• perform...