This paper deals with a combined system with fuel cell and supercapacitor to provide an electrical power to grid. The combined system many be a part of a microgrid. The generated power from fuel cell can be use as a boltage source, however, the response time to an abrupt load change is slow, therefore, the source can not provide high quality power. In order to compensate the poor response time characteristics a fast response energy sources such as flywheel or supercapacitor are combined with the fuel cell as a hybrid system. In this paper supercapacitor is used as the fast response source. The power flow of fuel cell is unidirectional, however, that of supercapacitor is bidirectional, and the charging and discharging of the supercapacitor is carried out through a bidirectional DC/DC converter. The operating principle of the bidirectional DC/DC converter is analysed in each mode of normal, charging, and discharging. A 3 kW bidirectional DC/DC converter is designed with the considerations of supercapacitor modeling, IGBT, MOSFET, transformer, reactor, etc. The converter is controlled with a proposed control method based on a phase shift PWM.
The main purpose of the control is to make the DC link voltage constant with 400 VDC. The DC link voltage can be changed with the load charge, however, the proposed control method guarantee the voltage almost constant.
Simulations are carried out with an abrupt load charge of 3 kW from 500 W and vice versa.
It is found that the DC link voltage overshoot at the instant of load change is 0.3 % ~ 0.6 % of the DC link voltage with the variation of DC link capacitor from 680 uF to 4700 uF.
It is expected that the good feature of the proposed scheme can be used as a fuel cell - supercapacitor hybrid system.