Integrating large-scale renewable energy sources and electric vehicles into the power grid, Smart Charging and Vehicle-to-Grid of the electric vehicles play an important role for supply and demand matching in the power grid. Many control schemes have been proposed, and implementation of the smart charging and V2G to the electric vehicle charger is also an important issue. This paper proposes an off-board charger that realizes seamless charge and discharge control via the DC connector on the existing electric vehicle. A grid-friendly charging scheme is implemented to the V2G test system consisting of the off-board charger, an electric vehicle battery test-bed, and a smart interface controller with flexibility in software installation. Communication and control functions of each component are confirmed through fundamental experiments. A load frequency control function for the real-time digital power system simulator is tested on the proposed V2G test system.