This paper presents Dynamic Voltage Restorer (DVR) based on bidirectional full-bridge dc-dc converter to compensate severe voltage sag/swell problems in medium voltage system. Voltage swell causes the continuous rise at dc-link voltage of DVR which may damage the dc-link capacitors and solid-state devices, and increase the power losses. Unidirectional dc-dc converters based DVRs do not allow power flow from dc link of inverter to battery. This condition may damage the dc-link capacitors and solid-state devices, and increase the power losses. The main contribution of this study is that bidirectional dc-dc converter permits the DVR to prevent voltage rise at DC link capacitor under severe voltage swell conditions. In this topology, power can flow both from battery to multilevel inverter and vice versa. For this propose, a control algorithm based on Proportional-Integrator (PI) control is developed for bidirectional dc-dc converter. This algorithm can keep the DC link voltage constant during voltage sag/swell. The performance results of proposed topology and control method is verified with PSCAD/EMDTC.