Close Loop & Open Loop are 2 kinds of control mode in electric circuit.

The main difference between close loop and open loop is whether the control system has feedback or not.

In close loop system, there are mainly 2 kinds of control methods in thyristor rectifier filed, one is constant voltage (CV for short), another is constant current (CC for short). There is a voltage feedback in CV mode, current feedback in CC. Such a system can timely detect the output of the control, and reflect the detected information to the input through the feedback link, and adjust the input, so as to correct the control error and improve the control accuracy. Feedback technology is widely used in all kinds of systems that need precise control, especially in electronic control systems, such as gain control in various amplifying circuits, control of environment temperature, humidity, water level and pressure, position control and speed control of mechanical structure, etc. Therefore, people often feel that closed-loop control is complex, accurate and automatic, while open-loop control is relatively simple, rough and non-automatic. This kind of feeling often causes the beginner's misjudgment when analyzing the system, which needs special attention.