ABSTRACT
This chapter introduces three-term PID controllers as a combination of P + I and P + D types and presents empirical rules for tuning three-term controllers. It describes the phase compensation, and the steps in a frequency response approach to compensator design. The chapter outlines some aspects of cascade and feed forward control. Compensators consist solely of the elements for altering system dynamics and are ofter built as required out of individual components. The steady-state performance of a system will usually be expressed in terms of the permissible error for particular types of input, most commonly step or ramp inputs. Testing and/or simulation would probably now be required to check performance, and if necessary slight modifications to parameters would need to be made. Suppose, that the proportional gain c an uncompensated system is chosen to give a suitable transient response, but that the value is too low for satisfactory steady-state performance.
