A three-switch structure for PEMFC and ultracapacitor hybrid in backup power

Proton exchange membrane fuel cell (PEMFC) has been widely studied and developed in recent years. PEMFC as a backup power source for the telecom industry uninterrupted power supply (UPS) is one of the applications which are popularized. Two obstacles are encountered when PEMFC applies to backup power: starting time delay and poor electrical dynamic response ability to rapid load change. The UPS is required to start instantly to take over the power supply when the grid power fails. Chemistry reaction controlled by mechanical equipments and the typical polarization characteristics lead the terminal voltage to vary with load. Ultracapacitor is widely popularized with its development and maturation, and its highlights such as high power density, long service time and free maintenance match PEMFC characteristics. This paper discussed a new method to overcome the obstacles on the base of a PEMFC backup power prototype which consists of lead-acid batteries and DC/DC converter. According to the telecom industry UPS electrical specifications, a three-switch structure which is controlled by finite state machine (FSM) is applied to hybrid the PEMFC and ultracapacitor. Much better performance is obtained in the PEMFC and ultracapacitor hybrid backup power with the application of three-switch structure.