A T-type llc resonant converter and its control method

Abstract

The invention provides a T-type LLC resonant converter and a control method thereof. The DC input side is connected with two capacitors in series, a resonant cavity is connected through a T-type switching network, the resonant cavity is connected to the primary side of the transformer, and the secondary side of the transformer is connected to the rectifier circuit and the output Capacitor and load; by adding an auxiliary MOS tube, the Vin / 2 state can be inserted into the input voltage of the resonant cavity, the fundamental RMS value of the input voltage of the resonant cavity can be reduced, and a lower gain can be obtained at the same switching frequency; Within the switching frequency range, a wider gain range can be achieved; all MOS transistors on the primary side can be turned on at zero voltage, and the secondary diode can achieve ZCS in a wider range.

Description

technical field [0001] The invention relates to the field of power electronic converters, in particular to an LLC resonant converter and a control method thereof. Background technique [0002] LLC resonant converter has significant advantages such as high efficiency and high power density, so it has been widely used. The traditional LLC resonant converter adopts frequency modulation control (PFM), that is, the gain of the converter is controlled by controlling the switching frequency, and there is only one control degree of freedom for the switching frequency. After limiting the switching frequency range, the gain range of the converter is limited. The circuit structure and control method with unique control degrees of freedom limit the gain range of the LLC resonant converter. In order to achieve higher efficiency, the traditional LLC needs to increase the excitation inductance, thereby reducing the loss caused by the excitation current, but with the increase of the excit...

AI Technical Summary

Problems solved by technology

The circuit structure and control method with the only control degrees of freedom limit the gain range of the LLC resonant converter

In order to achieve higher efficiency, the traditional LLC needs to increase the excitation inductance, thereby reducing the loss caused by the excitation current, but with the increase of the excitation inductance, the range of switching frequency will become very wide, and the increase of switching frequency range will As a result, it is difficult to achieve the optimal design of the LLC transformer, the iron loss and copper loss of the transformer increase, and the efficiency decreases

In order to facilitate the design of LLC transformers, it is necessary to reduce the switching frequency range, which requires that the excitation inductance should not be too large, and the smaller excitation inductance will lead to an increase in the loss of the excitation current. Therefore, it is difficult for traditional LLC to realize the loss caused by the excitation current and the transformer The balance between design optimization

In addition, when the input voltage is greater than the rated voltage, in order to achieve a regulated output, the switching frequency of the converter needs to be greater than the resonant frequency. At this time, the secondary diode cannot achieve ZCS (zero current shutdown), and the turn-off loss cannot be avoided. This further limits the further improvement of the efficiency of the traditional LLC converter

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