Fuel Delivery Control For Vehicular Fuel Cell Power Systems

With the fast developments of society and technology,energy shortages and environmental pollution become key problems of the world.Therefore,hydrogen energy,with its abundant storage and high energy content,shows great potential to be one of the future sustainable energies.As one kind of hydrogen conversion plants,fuel cells become hot topics for researchers with high energy conversion efficiency and zero pollutant emission.Among that,Proton Exchange Membrane(PEM)fuel cells have special application prospects in transportation fields because of low operating temperature.However,considering the complex characteristics of the fuel cell systems,such as strong nonlinearity,multi-physical field coupling and interdisciplinary fusion,it is a little hard for fuel cells to achieve widely fluctuated car loads tracking caused by the various operating car modes,such as start,stop,low loads and idling.Consequently,adequate control strategies for the fuel cell systems are benefit in improving the performance,increasing the efficiency and prolonging the lifetime of the fuel cells.However,difficulties also exist in the controller design such as the nonlinearity and multi-physical of the fuel cells,and the widely fluctuated loads of the PEM fuel cells.This paper proposes a multi-input-multi-output(MIMO)nonlinear control strategy for fuel delivery in PEM fuel cell systems.Specifically,a control oriented dynamic model is developed for the fuel delivery system(FDS)including fuel supply,fuel delivery,electrochemical reaction,membrane permeation,anode bleeding and anode recirculation.Based on the model,studies on nitrogen permeation and accumulation are discussed with various current loads and recirculation ratios.On this basis,two contrastive control strategies are proposed to maintain adequate fuel supply and suitable anode hydrogen concentration using MIMO nonlinear state feedback control algorithm.Comparison and analysis are presented in the simulation results between these two control strategies.Moreover,hydrogen partial pressure estimations are developed in this paper considering the difficulty in measurements of manifold partial pressures.Combining the estimations and the state feedback control strategy,a MIMO nonlinear output feedback controller is proposed to improve the applicability of the controller.Lyapunov based stability analysis is carried out to analyze the proposed output feedback controller and the observers.Simulation results show the effectiveness of the proposed controller under various current demands.