PWM control method for three-level LLC converter

Abstract

The invention discloses a PWM control method for a three-level LLC resonant converter. The LLC resonant converter at least comprises a first bridge arm which is connected with a plurality of switch tubes in series and coupled at the primary side of a transformer; the switch tubes comprise two outer tubes close to both ends of the first bridge arm and two inner tubes between the outer tubes; in the PWM mode, the duty ratio of the inner tube is maintained to be no less than the minimum duty ratio when the width modulation of duty ratio is carried out on the inner tube and the outer tube according to the gain demand; the minimum duty ratio is determined according to the requirement that the duration of delaying the turn-off of the inner tube can avoid the reverse resonance of resonance current after the outer tube is turned off. By maintaining the duty ratio of the inner tube to be no less than the minimum duty ratio, the resonance process of current of the primary side of the converter is changed, thereby avoiding generating the problem of the backward recovery of a body diode.

Description

technical field [0001] The invention relates to an LLC resonant converter, in particular to a PWM control method for a three-level LLC converter. Background technique [0002] The LLC resonant converter has been more and more widely used in the industry because of its simple structure and superior soft switching characteristics. In the case of high power and high power density, the three-level LLC resonant converter has gradually become the mainstream topology in the industry due to its advantages of low device stress, low switching loss, and high switching frequency. [0003] LLC resonant converter generally adjusts the gain of the converter by changing the operating frequency, so as to realize the stability and adjustment of the output voltage. In practical applications, considering the loss of power devices and the efficiency of the converter, the operating frequency of the converter cannot be increased without limit, and the frequency modulation range is limited to a ce...

AI Technical Summary

Problems solved by technology

[0009] Because the reverse recovery characteristics of the parasitic diode in the MOS tube are generally poor, the reverse recovery current flowing through the bridge arm is very large, and there is a large current change rate di / dt in the bridge arm, which is induced by the gate of the MOS tube. Spike voltage can cause MOS tube to be broken down

It can be seen that the three-level LLC converter controlled by PWM is not equal to the LLC converter controlled by PFM, nor is it different from the ordinary PWM converter. Design presents great difficulty

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