This paper proposes a bi-directional isolated DC/DC converter for battery charger and discharger of electric vehicles controlled by a new phase-shift topology. The proposed DC/DC converter consists of two full-bridge inverters, an isolated transformer, and boost reactors. The converter provides bi-directional transmission, buck-boost conversion and zero-voltage switching, adjusting the phase-shift of two full bridge inverters continuously. A 400V-3.5kW experimental system provides stable bi-directional buck-boost conversion and seamless transition between charging and discharging modes. A maximum efficiency of 93.3% can be achieved for this experimental system.