Advantages of current control system

The switching power supply using current mode control contains two kinds of negative feedback, voltage and current, forming a dual-loop control. When there is a disturbance in the input voltage or load, the system output end has a strong ability to suppress the disturbance. As long as the current in the loop changes slightly, it can automatically adjust without waiting for the output voltage to change, which is equivalent to having an output voltage differential feedback characteristic. Therefore, the advantages of the current mode control system are:

(1) Fast response;

(2) Automatic current limiting can be achieved;

(3) It is easy to achieve current sharing when connected in parallel;

(4) There is no conditional stability problem;

(5) The push-pull circuit can achieve flux balance in the magnetic core of the high-frequency transformer.

In addition to the current-controlled switching power supply, the active power factor correction device also belongs to the dual-loop control system. When the power factor PF≈1, it is referred to as the UPF (Unity Power Factor) correction device, which means "1 power factor". Moreover, its input current is close to sinusoidal in half a cycle and is in phase with the input voltage.

The main problem with using the state space average method to establish a transient model of an AC/DC or DC/DC switching converter is that the mathematical derivation process is complicated, especially for high-order circuits. For a dual-loop control system, establishing a state space average model is even more complicated. However, by using the Tellegen theorem in circuit theory and the concept of instantaneous power conservation, the relationship between the voltage and current of each branch in the main circuit of a current-controlled switching power supply is established, a small signal disturbance is applied, and high-order terms are ignored, and a low-frequency small signal model can be obtained. The modeling process is simple and convenient, avoiding complex mathematical derivation. This method is called the power conservation method.