A charging device includes a first auxiliary bridge arm and a second auxiliary bridge arm. The first auxiliary bridge arm is connected between a first port and a second module. The second auxiliary bridge arm is connected between the first port and a third module. If the AC charging power is three-phase, the first module converts a first phase of the AC charging power, and the first auxiliary bridge arm and the second auxiliary bridge arm are disabled. Consequently, the second module converts a second phase of the AC charging power, and the third module converts a third phase of the AC charging power. If the AC charging power is single-phase, at least a first module is used to convert the AC charging power.