It is found from the discontinuous and continuous controller modes, that each mode has its own advantages and disadvantages.
In complex industrial processes most of these control modes do not fit the control requirements. It is both possible and expedient to combine several basic modes, thereby gaining the advantages of each mode.
In some cases, an added advantage is that the modes tend to eliminate some limitations they individually posses. The most commonly used composite controller modes are: Proportional-Integral (PI), Proportional- Derivative (PD) and Proportional- IntegralDerivative (PID) control modes