Grid-connection Of Fuel-Cell Distributed Generation Systems

Renewable and green energy sources are currently exploited for sustainable development due to the world energy crisis and environmental deterioration. At present many energy experts and electric experts have recognized the super power combined with distributed generation as the main method which can protect environment, lower the consumption and improve the security and flexibility of the system. As there is a broad prospect of application about fuel cells as distributed generation systems, the reserch on the grid-connection of fuel cells attracts much attention.There are several kinds of fuel cells. PEMFC (Proton Exchange Membrane Fuel Cell) is widely used in distributed generation because of the lower working temperature, quick launch ability, high energy ratio and high power ratio. This paper first builds an experience model for the proton exchange membrane fuel cell according to its stack voltage characteristics, gas dynamic equation and dynamic characteristics. As the different situation of the circuit in the fuel cell grid-connected system, it can be divided into two parts:the ac and dc part.The dc side includes PEMFC and DC/DC converter. The BOOST transfer function could be deduced from the BOOST electric circuit principle, unified circuit model and model parameter. Two control strategies are considered for the dc side:control as a whole or control separately. Controller parameters are tuned by the IMC-PID method. Finally, the dc side model working under the two control structures are simulated in MATLAB/Simulink.The ac side includes DC/AC converter and LC filter. Whether the distributed generation system can be connected to the grid is directly related with the phase and frequency of the output voltage from the DC/AC converter and that from the grid. This paper first chooses a better control structure through simulations in MATLAB/Simulink, and then designs a circuit which can track phase automatically. Finally, combined with the control structure and controller parameters, better control strategy can be chosen from the waveform in the simulation.