Reverse current control method of synchronous boost converter for fuel cell using a mode boundary detector

This paper proposes the reverse current control method of the synchronous boost converter in hybrid system charging low voltage, high current energy to the battery from fuel cell. To achieve high efficiency, the diode in conventional boost converter is replaced by MOSFET to use the converter with synchronous method. When using the synchronous boost converter with MOSFET which is a bi-directional device, in discontinuous conduction mode (DCM), reverse current occurs because the secondary battery voltage is higher than the fuel cell voltage. Due to the long start-up time of the fuel cell, soft start method is required at the beginning where the reverse current can occur. Also, when charging the battery with constant current and constant voltage (CC/CV) charge method, DCM operation appears during CV mode. CCM and DCM are distinguished by the proposed mode boundary detector and the synchronous boost converter is controlled according to the determined mode. In DCM, the conventional boost converter with the diode is used, and the synchronous boost converter is used in CCM to prevent reverse current.