Converter system and control method thereof

A converter system, comprising:

• an AC source;
• a DC output, comprising a positive terminal and a negative terminal;
• a switching circuit, comprising a first switch, a second switch, a third switch, and a fourth switch, wherein the first switch and the second switch are electrically connected to the positive terminal of the DC output, and the third switch and the fourth switch are electrically connected to the negative terminal of the DC output, wherein the first switch and the third switch are electrically connected in series, and there is a first node between the first switch and the third switch, the second switch and the fourth switch are electrically connected in series, and there is a second node between the second switch and the fourth switch,
• a boost inductor, electrically connected to the second node;
• a grid inductor, electrically connected between the AC source and the boost inductor, wherein the AC source is electrically connected to the second node;
• a ZVS inductor and a ZVS capacitor electrically connected in series between the first node and the second node to form a ZVS branch;
• and
• a controller, configured to control the converter system to transit between a unipolar switching mode and a phase-shift switching mode, a bipolar switching mode and the phase-shift switching mode, or the unipolar switching mode and the bipolar switching mode according to a duty cycle of the switching circuit.