A power conversion system includes: a main battery configured to be recharged with power and to supply the recharged power to a motor, thereby supplying rotation force to a wheel of a vehicle; an auxiliary battery configured to recharge the main battery or to assist a power supply function of the main battery; and a power converter connected to auxiliary battery, the power converter comprising a bypass circuit and a buck converter. The buck converter includes a buck switch, and is configured to convert a voltage of the auxiliary battery into a voltage for recharging the main battery in accordance with an ON/OFF switching operation of the buck switch.