This study presents a novel bidirectional dc-dc buck-boost converter compatible with the flywheel energy storage system (FESS) and a robust control for bidirectional power flow, according to the single cycle average current control scheme and proportional-integral (PI) control theory. The proposed converter and its control are designed to adjust voltage to achieve current limiting start up and final speed keeping of the motor in charge mode and maintain a constant output voltage in the case that terminal voltage of the motor in the FESS drops continually in discharge mode. Simulation results demonstrate high performance of the converter in both steady-state and dynamic operations.