A soft start control method for LLC full bridge converter based on variable duty cycle

Abstract

The invention discloses a soft start control method of LLC full-bridge converter based on variable duty cycle. The method is to control four MOSFETs on the primary side of the LLC full-bridge converter, as that signal of the upper and lower switch tube of the same bridge arm are complementary, at that same time, the duty cycle of the switch device is adjusted accord to the start-up time tr obtained according to the output voltage, so that the duty cycle of the driving signal of the switch device is gradually increased to a specified value according to a specified curve, so that the output voltage rises from 0 to a given voltage to reach a soft start. The method of the invention weakens the current impact in the start-up process of the traditional LLC full-bridge converter, reduces the output voltage overshoot, makes the circuit start more stable and reliable, and has higher engineering use value. The control method is reliable, the circuit is simple and easy to realize.

Description

technical field [0001] The invention relates to the technical field of soft start of an LLC full-bridge converter, in particular to a soft start control method for an LLC full-bridge converter based on a variable duty ratio. Background technique [0002] The LLC resonant converter is widely used in various fields due to its advantages of high working efficiency. However, during the start-up process of the circuit, the excessive current impact is a problem that cannot be ignored. On the one hand, when analyzing the bidirectional LLC resonant converter, it is assumed that the output filter capacitor is large enough to clamp the secondary voltage of the transformer when the diode is turned on. The output filter capacitor of the LLC resonant converter is charged (assuming that the capacitor has been fully discharged at startup), resulting in a large inrush current; on the other hand, due to the operation at the resonant frequency, the impedance of the resonant cavity in the LLC ...

AI Technical Summary

Problems solved by technology

[0002] LLC resonant converter has the advantages of high working efficiency and is widely used in various fields, but during the start-up process of the circuit, the excessive current impact is a problem that cannot be ignored

On the one hand, when analyzing the bidirectional LLC resonant converter, it is assumed that the output filter capacitor is large enough to clamp the secondary voltage of the transformer when the diode is turned on. The output filter capacitor of the LLC resonant converter is charged (assuming that the capacitor has been fully discharged at startup), resulting in a large inrush current; on the other hand, due to the operation at the resonant frequency, the impedance of the resonant cavity in the LLC resonant converter is very small, resulting in the resonant cavity generate a lot of current

Excessive impact circuit in the circuit can easily cause heat damage to power devices and affect the normal operation of the system

Images