Open Loop and close loop control system ppt.pptx

Open loop And Close Loop Control System

1. Open Loop And Close Loop Control System Department:- ELECTRICAL ENGINEERING Name:- Amrit Singha Roll NO:- 27501621058 Semester:- 5Th Subject Name-:- Control System Subject Code:- PC EE 503

2. Open Loop System Definition: An open-loop system is a type of control system in which the output of the system depends on the input but the input or the controller is independent of the output of the system. These systems do not contain any feedback loop and thus are also known as non-feedback system.

3. Open Loop Description In the open-loop control system, a reference input is given to the system in order to get the desired output. But the achieved output is not considered by the system for further reference input. In this figure here represents the block diagram of an open-loop control system. Here as we can see that the system consists of two blocks, one is the controller while other is controlled process. Basically, according to the required output, an input is provided to the controller of the system. Depending on the achieved input, the controller generates the control signal which is fed to the processing unit. Thus according to the control signal, proper processing is performed and output is achieved. But as there is no feedback path present in the system, thus whether the achieved output is desired or not the input has nothing to do with it. So, this is the reason we say that in an open-loop system the input is independent of the output.

4. Example with Transfer Function We all are aware of the operation of a traffic light controller present at various road crossings. Basically the three signals generated by the controller is time-dependent. An internal timing is provided to the controller at the time of designing the system. So, when the traffic signal controller is installed at the crossing then each signal is displayed by the controller timely, independent of the rush present on any of the side. Basically relays are used to provide timing sequence to the system. In this figure clearly indicates that whatever output is achieved, the input will remain independent of it. We know transfer function is given as: When we separately consider the transfer function of each block then it will be given as: Thus the overall transfer function will be: So, the open-loop gain will be: The use of the open-loop control system indicates that the operator of the system is ready to consider some minimal deviation in the output from the expected value.

5. Open Loop Advantages And Disadvantages Advantages These systems possess simplicity in construction and ease of maintenance. Due to the lesser number of units, overall the system is economic. The output provided by the system shows stability. The operation is quite convenient. Disadvantages These systems require timely recalibration. The systems are more prone to errors. The changes in the desired output can be the result of internal or external disturbances.

6. Closed-Loop Control System Definition: A closed-loop control system is a type of control system in which the controlling action shows dependency on the generated output of the system. In simple words, in these systems, the output of the system controls the input applied to the system. The variation in input according to the output leads to produce more accurate system output. Thus controllability in the closed-loop system is achieved through the output generated by utilizing a feedback path. Now the controlling provided to the system can be either output independent or output dependent. This variation leads to give two different categories of control system. A system in which controlling action is independent of the generated system output is known as open-loop control system. While in a closed-loop system, the produced output controls the functioning of the system by the used of feedback

7. Transfer Function of Closed-Loop Control System Transfer function indicates the behaviour of the system as it is defined as the mathematical relation between the input and output of the system. The gain of the system defines the ratio of output to input. Thus we can say the output of the system is the product of transfer function and input. So, for the above-given system figure:, On substituting the value of E(s) in the 1st equation On transposing This is the transfer function of a closed-loop system with negative feedback. For a positive feedback system, it is given as: For a unity feedback system (i.,e H(s) = 0) with a high value of gain. The transfer function is unity.

8. Advantages: Closed loop control systems are more accurate even in the presence of non-linearities The sensitivity of the system may be made small to make the system more stable The closed loop systems are less affected by noise. Disadvantages: Closed loop control systems are costlier and complex The feedback in the closed loop system may lead to oscillatory response The feedback reduces the overall gain of the system Stability is the major problem in the closed loop system and more care is needed to design a stable closed loop system. Close Loop Advantages And Disadvantages

9. Comparison of Close Loop And Open Loop Control

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