The present invention relates to the technical field of power generation, power transformation or power distribution, and provides a digital control method for achieving multi-step frequency modulation of an LLC resonant converter. The method is achieved by means of a system comprising a voltage sampling circuit (1), a control circuit (2) using a microcontroller as the core, and an isolation drive circuit (3). The method comprises: sampling an output voltage (Vout) value in each period; when an output voltage fluctuates caused by a change of an input voltage (VIN) or an output load, collecting a voltage value on a voltage dividing resistor by means of the voltage sampling circuit (1); by means of the control circuit (2) using the microcontroller as the core, comparing the output voltage sampling value with a set value, and then, calculating a frequency corresponding to a maximum gain or minimum gain value point and switching to the frequency point; and after eliminating output voltage (Vout) fluctuation caused by the change of the input voltage (VIN) or the output load, enabling the LLC converter to operate at the required switching frequency and performing PI regulation on the output voltage (Vout) according to the difference value between the output voltage and the set value so as to finally enable the output voltage (Vout) to be stable, thereby improving a dynamic response speed.
展开▼
