This paper presents the control design of a bidirectional converter used to support a DC microgrid. The chosen topology for this purpose is the bidirectional buck-boost converter, for which its mathematical model is obtained. Next, a brief introduction of fractional order control is presented and the structure of a fractional order PID controller is shown. The tuning process of this controller is obtained by means of an arithmetic method whose parameters are set to control the bidirectional converter. In order to evaluate the performance of the converter and its fractional-order controller, this is simulated under different situations that represent different operating conditions, such as changes in battery voltage levels, climatic conditions, and uncertainty in the parameters. The simulation results of this controller are analyzed and compared with a classical PID. Finally, the conclusions are presented.