Light load control method and device of LLC (Liquid Level Control) resonant converter

Abstract

The invention provides a light load control method and device of an LLC (Liquid Level Control) resonant converter, belongs to the field of power conversion, and solves the problem that soft switching environments of a zero-voltage switch and a zero-current switch are lost. The method comprises the following steps of: A, judging whether the device works at a light load state or not; B, when the device does not work at the light load state, carrying out frequency adjusting control mode; C, when the device works at the light load state, carrying out fixed frequency pulse width control mode; and D, outputting a control signal of a corresponding switching tube. The device comprises a controller, a frequency modulation module and a width modulation module, a current detection unit and a voltage detection unit, wherein the controller is connected with a feedback compensating error amplifier; the voltage detection unit is connected with the feedback compensating error amplifier; the current detection unit is connected with the controller; the controller is connected with a working module switching unit; the frequency modulation module and the width modulation module are respectively connected with the controller and the working mode switching unit; and the working module switching unit is connected with the switching tube. The device and the method realize optimization of the soft switching environments and resonance parameters in a full-load range.

Description

technical field [0001] The invention belongs to the field of power conversion, and relates to a light load control method and device of an LLC resonant converter. Background technique [0002] With the development of switching power supply technology, high efficiency and high power density have become the development trend. Therefore, the application of LLC resonant converter is born and becomes more and more extensive. The LLC resonant converter realizes the zero-voltage turn-on of the primary-side switch tube and the zero-current turn-off of the secondary-side rectifier tube in a wide frequency range. But as the load is reduced, in order to obtain the same DC gain, the LLC resonant converter needs to increase the switching frequency. The increase of switching frequency, on the one hand, increases the switching loss; on the other hand, it will also cause the current of the diode on the rectification side to be turned off when it does not return to zero, and the soft switc...

AI Technical Summary

Problems solved by technology

These solutions can reduce the loss at no-load or light load, but due to the addition of hardware in the main circuit, it will have a certain impact on the reliability of the circuit, and it is difficult to take into account the efficiency improvement at heavy load at the same time

[0004] Chinese patent literature discloses a control method and device for an LLC resonant converter with the application number 200910221471.4. The device judges the load state by inputting the conduction frequency of the switch tube, and then performs frequency conversion and width adjustment control according to the load state. To a certain extent The circuit loss is reduced, but the frequency conversion width adjustment control does not have any constraints, which will cause the loss of the soft switching environment of the switch tube zero-voltage switch and rectifier tube zero-current switch of the LLC resonant converter, thus making the voltage gain of the resonant cavity uncertain

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