C HAPTER 1 Introduction to control system

The basic ingredients of control system can be described by: Objectives of control or input. Control-system component. Results or outputs. The objective of the control system is to control the outputs in some prescribed manner by the inputs through the elements of the control system. 2

E XAMPLES OF C ONTROL S YSTEM A PPLICATION 1. Steering control of automobile: Controlled variables: direction of the front wheel (y), output of the system. Controlling variables: direction of the steering wheel (u), input of the system, actuating signal. Control system: steering mechanism and the dynamics of the entire vehicle. 3

E XAMPLES OF C ONTROL S YSTEM A PPLICATION 2. Speed control of automobile: Controlled variables: vehicle speed (y) Controlling variables: pressure exerted on the accelerator Control system: engine of the vehicle 4

The two previous systems might be used at the same time where we have: two inputs: steering wheel and accelerator two outputs: heading (movement direction) and speed. In this case, the two input and output variables are independent of each other (decoupled system). Multivariable systems: systems with more than one input and one output (MIMO). 5

S OME DEFINITIONS Process: the device, plant, or system under control. Actuator: the device that causes the process to provide the output, i.e. the device that provides the motive power to the process. Stable system: a dynamic system with a bounded system response to a bounded input 6

O PEN -L OOP C ONTROL S YSTEMS (N ONFEEDBACK S YSTEMS ) 7 These systems don’t contain feedback of the output (non feedback system), that is; the output quantity has no effect upon the input quantity.

They are economical, simple, but usually inaccurate. Controller might be as simple as an amplifier, mechanical linkages or in the sophisticated cases as a computer or microprocessor. This system is calibrated 8

E XAMPLE OF O PEN -L OOP C ONTROL S YSTEMS Electric washing machine: The amount of machine wash time is entirely determined by the judgment and estimation of the human operators. A true (sophisticated) automatic electric washing machine should have the means of checking the cleanliness of the clothes being washed continuously and turn itself off when the desired degree of cleanliness is reached. 9

C LOSED -L OOP C ONTROL S YSTEMS ( FEEDBACK S YSTEMS ) 10

In feedback systems, the controlled signal ( y ) is feedback and compared with the reference input ( r ), and an actuating signal ( u ) proportional to the difference of the input and the output ( r – y ) is sent to the system to correct this error These systems consist of the same parts of the open loop systems with the exception that a feed back from the output is compared with the reference input. 11

A DVANTAGES OF CLOSED LOOP SYSTEM More accuracy of the system is obtained (reduction of system error). Affect the gain of the system (increase/decrease). Improve stability of the system when applied properly. Reduce the effects of noise or external disturbances. Feedback might be unity or non-unity feedback Feedback might be positive or negative feedback. 12

E FFECTS OF FEEDBACK ON CONTROL SYSTEMS Let us consider that we have a feed forward transfer function (G) and a feedback transfer function (H), then if we consider. Open-loop case: Y (s) = R (s) G (s) G (s) =  input-output relationship 13