Fuel cell UPS system without bulky DC electrolytic capacitors

For the UPS using fuel cell as the backup power (Fuel Cell UPS), since the dynamics of fuel cell could not fulfill the requirements of the critical load, power management unit (PMU) is indispensable to fill the power gap at the time of load change or operation mode transfer. In this paper, a method utilizing the PMU to compensate low frequency ripple current on DC link is studied, which makes much smaller DC link capacitors become possible. With the method, bulky electrolytic capacitors can be replaced by film capacitors. Expectancy of the fuel cell UPS system will be increased. Linearized model of PMU circuit is derived. Since the DC operating point of inductor is zero. Conventional modeling method might become inaccuracy. This paper verifies the accuracy of the derived model by simulation. Both simulation and experiment result prove that proposed method for DC link ripple voltage suppression is effective.