Resonant frequency tracking method for full bridge llc resonant converter

Abstract

The invention relates to a method for tracking the resonant frequency of a full-bridge LLC resonant converter, comprising: configuring the bottom layer of the controller, and triggering the controller to collect the secondary rectifier diode at the given leading time Δt before the switching tube is turned off Leading current value i D_off ; PI adjusts the switching frequency f of the full-bridge LLC resonant converter, and the leading current value i of the secondary rectifier diode D_off Control within the preset target range to achieve the LLC resonant frequency f r tracking. This method can realize the fast tracking of the resonant frequency, adjust the switching frequency to the left side of the resonant frequency point and close to the resonant frequency, so that the resonant converter can work in the optimal area, the full-bridge switch tube can realize zero-voltage turn-on, and the secondary rectifier diode has no Reverse recovery problem, thereby reducing system loss and improving system efficiency. At the same time, this method can effectively deal with the resonant frequency difference caused by the accuracy of the resonant device, device combination, line distribution parameters, etc., and the resonant frequency change caused by the attenuation of device parameters in batch products.

Description

technical field [0001] The invention belongs to the technical field of converters, and in particular relates to a method for tracking resonant frequency of a full-bridge LLC resonant converter. Background technique [0002] The existing full-bridge LLC resonant converter mainly has two control methods: PFM frequency conversion control and PWM fixed frequency phase shift control. No matter which control method is used, it is necessary to accurately determine the resonant frequency point of the LLC, and it is hoped that the resonant frequency is a fixed constant. For PWM fixed-frequency phase-shift control, it is necessary to set the switching frequency to the left of the resonant frequency point and close to the resonant frequency according to the determined resonant frequency point, so that the resonant converter can work in the optimal region. [0003] For batch products, the resonant frequency is generally controlled within an ideal range by improving the accuracy of reso...

AI Technical Summary

Problems solved by technology

However, the parameters of the resonant device will change during long-term use, especially the capacitance of the resonant capacitor will attenuate, coupled with the existence of stray inductance of the main circuit cable and copper row, the resonance frequency formula It can be seen that the actual resonant frequency of the converter may be higher than the ideal design value, or may be lower than the ideal design value

[0004] When the resonant frequency is lower than the switching frequency, there is a problem of reverse recovery of the secondary rectifier diode; when the resonant frequency is greater than the switching frequency, the secondary current intermittent time is longer, the output current ripple is larger, and the phase-shift control is relatively ineffective. Area

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