A method for automatic tracking of resonant frequency of llc resonant converter

Abstract

The invention discloses an automatic tracking method for the resonant frequency of an LLC resonant converter. Aiming at the problem of the resonant frequency drift caused by the disturbance of the parameters of the resonant components during the fixed frequency control of the LLC resonant converter, the method of the invention detects that the primary side switch tube is turned off the t 1 time and turn-off time t 2 The absolute value of the secondary side current of the transformer is denoted as I s1 and I s2 , if I s1 =0, then the switching frequency is less than the resonant frequency, and now the switching frequency is improved, if I s2 greater than the set value I s ’, the switching frequency is greater than the resonance frequency, and the switching frequency is reduced at this time. When I s2 Greater than 0 and less than the set value I s ’ or I s1 >0 and I s2 =0, keep the switching frequency unchanged. Therefore, the real-time resonance frequency is automatically tracked, and the problems of voltage gain drift and efficiency reduction caused by resonance frequency drift are solved.

Description

technical field [0001] The invention relates to the technical field of switching power supplies, in particular to a method for automatically tracking the resonant frequency of an LLC resonant converter. Background technique [0002] Soft switching technology effectively improves the switching frequency and efficiency of the power supply. Among them, the LLC resonant converter, as a wide input range topology that can realize zero-voltage turn-on in the full load range without adding auxiliary circuits, has been widely used and studied. [0003] Due to the aging of resonant components, changes in the environment and operating points, the resonant frequency of the LLC resonant converter will drift. In the case of constant frequency control, it will affect the efficiency and gain characteristics of the LLC resonant converter, thereby affecting the stable operation of the system. There is an existing control method for tracking a resonance frequency based on a total harmonic dis...

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Problems solved by technology

However, the sine degree distortion of the resonant current in this algorithm is large under light load conditions, so the control method is difficult to be effective in the full load range; in addition, some scholars propose to use the idea of ​​predictive control to adjust the switching frequency according to the gain characteristics of the LLC resonant converter , so that the switching frequency automatically tracks the resonant frequency, but this method needs to collect two variables of input voltage and output voltage, which requires more hardware and higher cost

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