AC/DC conversion is to convert AC into DC, and AC/DC converter is a device to convert AC into DC. Its power flow can be bidirectional. The power flow from power supply to load is called rectification, and the power flow from load to power supply is called active inverter. AC/DC conversion can be divided into half-wave circuit and full-wave circuit according to the wiring mode of the circuit. According to the number of power phases, it can be divided into single, three-phase and multi-phase. According to the working quadrant of the circuit, it can be divided into one quadrant, two quadrant, three quadrant and four quadrant.