A control system is a system of devices or set of devices, that manages, commands, directs or regulates the behavior of other device(s) or system(s) to achieve desire results. As the human civilization is being modernized day by day the demand of automation is increasing accordingly. Automation highly requires control of devices.
The block diagram is to represent a control system in diagram form. In other words practical representation of a control system is its block diagram. It is not always convenient to derive the entire transfer function of a complex control system in a single function. It is easier and better to derive transfer function of control element connected to the system, separately. The transfer function of each element is then represented by a block and they are then connected together with the path of signal flow. For simplifying a complex control system, block diagrams are used. Each element of the control system is represented with a block and the block is the symbolic representation of transfer function of that element. A complete control system can be represented with a required number of interconnected such blocks.
Requirements of a Good Control System
Accuracy : Accuracy is the measurement tolerance of the instrument and defines the limits of the errors made when the instrument is used in normal operating conditions. Accuracy can be improved by using feedback elements. To increase accuracy of any control system error detector should be present in control system.
Sensitivity : The parameters of control system are always changing with change in surrounding conditions, internal disturbance or any other parameters. This change can be expressed in terms of sensitivity. Any control system should be insensitive to such parameters but sensitive to input signals only.
Noise : An undesired input signal is known as noise. A good control system should be able to reduce the noise effect for better performance.
Stability : It is an important characteristic of control system. For the bounded input signal, the output must be bounded and if input is zero then output must be zero then such a control system is said to be stable system.
Follow the given steps to model a control system in Simulink.
1. Open Simulink.
2. Open the Library Browser.
3. Import the following blocks from the Library Browser onto the workspace: Step Input (Source), Sum Block, PID Controller, Gain Block, Transfer Function Block, Scope Block.
4. Connect all the blocks imported above as follows.
5. Change the value of the transfer function by double clicking on the transfer function block.
6. To change the value of the gain, double click on the gain block.
7. Add feedback to the given system as illustrated below.
8. Double click on the scope to view the output of the given control system.
9. In order to design a nonlinear control system, add a nonlinearity as shown below.
10. Double click on the dead zone block to manipulate its parameters.
11. View the output of the nonlinear system by double clicking on the scope. The output is shown below.
A linear and nonlinear control system were physically modelled in Simulink and their outputs were also observed.