A soft-start control method for LLC full-bridge converter based on hybrid control

Abstract

The invention discloses a LLC full-bridge converter soft start control method based on hybrid control, which comprises the following steps: S1, sampling output voltage by a voltage dividing method, thereby obtaining output voltage rise time, namely start time; S2, sampling output voltage by a voltage dividing method; 2, carry out frequency reduction control on that bi-directional LLC converter during startup, wherein the working frequency fs of the converter is set to twice the nominal frequency fr during startup, fs is gradually reduced during startup, and fs=fr at the end of startup; S3, adjusting the duty ratio of the switching device over time according to the obtained output voltage rise time while S2 is in progress, so that the duty ratio of the driving signal of the switching devicegradually increases to a specified value according to a specified curve. S4, after the driving signal generated by the mixed control of S2 and S3 is amplified by the driving module, the driving signal acts on the switching transistor in the main topology, so that the output voltage rises slowly from 0 to a given voltage to reach the soft start. The invention reduces the current impulse in the starting process, improves the dynamic characteristics of the output voltage, and makes the starting process more stable and reliable.

Description

technical field [0001] The invention relates to the technical field of soft start of an LLC full-bridge converter, in particular to a hybrid control-based soft start control method for an LLC full-bridge converter. 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 resonant c...

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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 dynamic characteristics of the system

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