In order to solve these problems, a hybrid power system,which includes a PEMFC stack, two DC/DC converters anda lithium-ion battery pack, is designed in this paper. ThePEMFC provides the main power of the load demand andthe additional power demand is supplied by the battery. Apower coordinating algorithm using a virtual potential fieldconcept [9] is proposed to manage the power demand for thePEMFC and the battery pack to respond to the dynamicallychanged power load while maintaining the battery’s SOC. Asthe SOC of the battery cannot be measured directly, a nonlinear observer based on an inclusive equivalent circuit modelof the battery is utilized for the SOC estimation. Simulationsare done to validate the performance of the power management algorithm and experimental facility will be designed toverify it.This paper is organized in the following manner. In Section 2, the model of the PEMFC hybrid system is developed.Section 3 details the power management method of the hybrid system. Simulation results are provided in Section 4 andconclusions are given in Section 5.