Research on Soft Start Method for Buck-Boost Bi-directional DC-DC Converter of Fuel Cell Power System

The buck-boost bi-directional DC-DC converter is at double sources application in the proposed fuel cell power system-DC bus at high voltage port and battery at low voltage port. Due to complemented operation of switches in buck-boost bi-directional DC-DC converter, traditional soft start method will give rise to large inverse inductor current from the output source, and result in damage of devices. This paper proposes a novel soft start method-two-phase soft start method. By implementing soft start of both active switch and passive switch, two-phase soft start method can realize buck-boost bi-directional DC-DC converter soft start at double sources application, avoiding inverse inductor current. Two-phase soft start method applies to a series of bi-directional converter and can be extended to multi-level bi-directional converter. Experimental results of two-phase soft start and startup in fuel cell power system are finally given to verify the effectiveness of two-phase soft start method.