Stability criteria and steady-state error

A general control system is made up of several interacting components: the plant to be controlled, the controller, the measurement systems, the actuators, etc. This is the reason why a control system may be very complex. Despite this, any closed-loop control system may be reduced to being represented by a single transfer function which relates the output to be controlled and the reference or the desired output. This closed-loop transfer function can be studied, as in Chap. 3. In the present chapter, the concept of block diagrams (see [1] for a historical perspective) is introduced to represent how a closed-loop control system is constituted and how to manipulate them to obtain the closed-loop transfer function is also explained.