What is a closed loop control system

Closed-loop control system is a type of control system that can feed part or all of the system output back to the output end of the system through certain methods and devices, and then compare the feedback information with the original input information. The comparison results are applied to the system for control to prevent the system from deviating from the predetermined target.

The operating environment of this tutorial: Windows 10 system, Dell G3 computer.

What is a closed-loop control system

A closed-loop control system is a type of control system. The specific content refers to: returning part or all of the output of the control system to the input end of the system through certain methods and devices, then comparing the feedback information with the original input information, and then applying the comparison results to the system for control. Prevent the system from deviating from its intended goals. Closed-loop control systems utilize negative feedback. That is, an automatic control system that consists of a signal forward path and a feedback path forming a closed loop, also known as a feedback control system.

Principle

An automatic control system based on the feedback principle. The so-called feedback principle is to control based on information about system output changes, that is, by comparing the deviation between the system behavior (output) and the expected behavior, and eliminating the deviation to obtain the expected system performance. In a feedback control system, there is both a signal forward path from input to output and a signal feedback path from output to input. The two form a closed loop. Therefore, the feedback control system is also called a closed-loop control system. Feedback control is the main form of automatic control. Most automatic control systems are feedback control systems. In engineering, the feedback control system that keeps the output consistent with the expected value during operation is often called an automatic adjustment system, and the feedback control system used to accurately follow or realize a certain process is called a servo system or a servo system.

Feedback control system consists of controller, controlled object and feedback channel. The comparison link is used to subtract the input and output to give a deviation signal. This link may be collectively called the regulator together with the controller in a specific system. Taking furnace temperature control as an example, the controlled object is the furnace; the output variable is the actual furnace temperature; the input variable is a given constant temperature, generally represented by voltage. The furnace temperature is measured with a thermocouple. The thermoelectromotive force representing the furnace temperature is compared with a given voltage. The difference voltage between the two is used to drive the corresponding actuator for control after power amplification.

Basic composition

The basic composition of a typical feedback control system can be represented by the block diagram shown in the figure.

The components that make up the system are divided according to their functions in the system. There are mainly the following types:

(1) Given components: given The amount of input corresponding to the desired output.

(2) Comparison element: To find the deviation between the input quantity and the feedback quantity, an integrated operational amplifier (referred to as integrated operational amplifier) ​​is often used to achieve this.

(3) Amplification components: Since the deviation signal is generally small and not enough to drive the load, amplification components are required, including voltage amplification and power amplification.

(4) Executive element: directly drives the controlled object to change the output. Commonly used ones include electric motors, regulating valves, hydraulic motors, etc.

(5) Measuring element: detects the controlled quantity and converts it into the required electrical signal. Commonly used in control systems include tachometer generators, photoelectric encoders, etc. for speed detection; rotary transformers, automatic machines, etc. for position and angle detection; transformers for current detection and thermocouples for temperature detection. wait. These detection devices generally convert the detected physical quantities into corresponding continuous or discrete voltage or current signals.

(6) Correction component: Also called compensation component, it is a component whose structure and parameters are easy to adjust. It is connected in the system in a series or feedback manner to complete the required computing functions to improve the performance of the system. According to their different positions in the system, they can be called series correction original elements and feedback correction elements respectively.

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