1、 Overview of open loop / closed loop control

Closed loop control is a basic concept of cybernetics. It refers to a kind of control relationship in which the controlled output returns to the control input in a certain way and exerts control influence on the input. In cybernetics, closed-loop control usually refers to the feedback of output end to input through "side chain", so-called closed-loop control. The output feedback to the input and participate in the output re control, which is the purpose of closed-loop control, this purpose is achieved through feedback.

In the control system, the process of returning the output to the input through the appropriate detection device and comparing with the input is feedback.

If there is no feedback between the output and input of the system, that is, the output of the control system has no influence on the control of the system, such a system is called open-loop. Compared with the closed-loop control system, the control input of the system is not affected by the output. In open-loop control systems, there is no feedback path from the output to the input (see feedback control systems). Therefore, the open-loop control system is also called non feedback control system. Open loop control system is composed of controller and controlled object. The controller usually has the function of power amplification. Compared with the closed-loop control system, the structure of the open-loop control system is much simpler and more economical. Open loop control system is mainly used for enhanced system.

Open loop control system: a system that does not feedback the control results back to affect the current control.

2、 Open loop and closed loop control of frequency converter

Open loop: it refers to the inverter to control the quantity to be carried out, such as voltage, current, frequency, etc., to obtain the actual value of these parameters through the corresponding feedback current in the input and output, and then send the corresponding control unit through the feedback circuit and control circuit to compare with the target value, so as to make the final output automatically stable near the target value, so as to achieve accurate control. Open loop: there is no corresponding feedback circuit, as opposed to closed loop.

The open-loop control of frequency converter is that the frequency converter operates at fixed frequency according to the need, and cannot be adjusted according to the change of load. Closed loop control means that the frequency converter can change frequency according to the demand with the change of load to achieve the purpose of process requirements. Some sensors and meters may be used in the closed-loop control process.

3、 Difference between open loop control and closed loop control

The most important difference between open-loop control and closed-loop control is whether there is feedback and correction system. For a simple example, we use the control panel to set the output frequency of the frequency converter to reach 40Hz. Whether the output of the frequency converter is accurate or not can only be measured by professional instruments, then the conclusion can be drawn, which is open-loop control. If we use a professional instrument to give a feedback signal to the frequency converter, if the actual output frequency of the frequency converter does not reach 40Hz, then the instrument will feed back a result to the frequency converter, and the frequency converter will correct the deviation according to the feedback result to ensure that the frequency converter has been running at 40Hz, which is the closed-loop control.