The development of vehicle-to-grid technologies has been aided by the increased mobility of electric vehicles. Bidirectional power flow is made possible by vehicle-to-grid, or V2X, technology, which connects an electric vehicle’s battery to the other side. A specialized electric vehicle battery charger that enables bidirectional power transfer between the electric vehicle battery and the other side is necessary for the implementation of V2X technology. Typically, the main parts of an On Board charger are AC/DC with power factor correction (PFC) and DC/DC converter. In this paper, we focus on the second part which is the DC/DC converter, especially the bidirectional LLC resonant converter due to its high-performance efficiency. The resonant converter is controlled by varying the switching frequency; its formula can be extracted using the transfer function of the converter. A resonant DC/DC converter consists of 4 blocks the first one is the bridge composed of 4 switches its role is to generate a square wave signal, then a resonant tank (composed of Lm, Lr, and Cr), and after that, the signal is transferred to the second side via the transformer, which steps up or down the voltage, and then the switch bridge rectifier transforms AC voltage to DC allowing the bidirectional flow of power. This work aims to find the best compromise between resonant tank size and the control strategy of switching frequency.