Dynamic modeling and simulation of a small wind-fuel cell hybrid energy system

This paper describes dynamic modeling and simulation results of a small wind-fuel cell hybrid energy system. The system consists of a 400 W wind turbine, a proton exchange membrane fuel cell (PEMFC), ultracapacitors, an electrolyzer, and a power converter. The output fluctuation of the wind turbine due to wind speed variation is reduced using a fuel cell stack. The load is supplied from the wind turbine with a fuel cell working in parallel. Excess wind energy when available is converted to hydrogen using an electrolyzer for later use in the fuel cell. Ultracapacitors and a power converter unit are proposed to minimize voltage fluctuations in the system and generate AC voltage. Dynamic modeling of various components of this small isolated system is presented. Dynamic aspects of temperature variation and double layer capacitance of the fuel cell are also included. PID type controllers are used to control the fuel cell system. SIMULINK(TM) is used for the simulation of this highly nonlinear hybrid energy system. System dynamics are studied to determine the voltage variation throughout the system. Transient responses of the system to step changes in the load current and wind speed in a number of possible situations are presented. Analysis of simulation results and limitations of the wind-fuel cell hybrid energy system are discussed. The voltage variation at the output was found to be within the acceptable range. The proposed system does not need conventional battery storage. It may be used for off-grid power generation in remote communities. (C) 2004 Elsevier Ltd. All rights reserved.