Dynamic Modeling And Thermal Control Of PEM Fuel Cell Systems

As one of the most popular hydrogen energy development directions,proton exchange membrane fuel cell(PEMFC)has many advantages such as pollution-free and high energy conversion efficiency.They have been widely used in hybrid electric vehicles,mobile portable equipment,unmanned aerial vehicles and many other fields.Modeling of fuel cell system plays an important role in performance analysis,optimization design and control strategy development.There are two main streams of modeling approaches for fuel cells.One is system design and analysis oriented modeling approach,and the other is control design oriented modeling approach.The system design and analysis oriented models are usually distributed parameter models that are mathematically described by partial differential equations(PDEs).However,the PDE based models are not suitable for controller design due to their high complexity.For controller design purposes,lumped parameter models based on ordinary differential equations(ODEs)are commonly used.However,most lumped parameter models proposed so far suffer the drawback of being not precise enough for system design and analysis purposes.For both controller design and system analysis purpose,a dynamic scalable segmented model of PEM fuel cell systems with two-phase water flow is developed.With lumped parameter segmentation,the model can be scaled down with less segmentations for controller design and scaled up with more segmentations for system analysis.Based on the fuel cell model,a adaptive control strategy is developed for the thermal management.A battery model and DC-DC converter model are developed for the fuel cell-battery hybrid power system model,and a state-based energy management strategy is designed.The main contributions and innovations of this paper are summarized as follows:·Considering the coupling characteristic of internal multiple-domain physical subsystems,A lumped parameter dynamic model of the proton exchange membrane fuel cell(PEMFC)system with two-phase water flow is developed based on the reaction mechanism of fuel cell.The fuel cell system model includes air sources,orifices,the fuel cell and the electronic load,among which the fuel cell model covers the voltage subsystem,the thermal subsystem,the pressure dynamic subsystem and the two-phase water flow subsystem.With the ports connected to each other,physical variables such as pressure,flow rates,and temperature are equalized automatically.Therefore,it is not necessary to set many boundary conditions.Moreover,a new liquidation algorithm is proposed by introducing a stiffness term into the vapor pressure dynamics to simulate the two-phase water flow.Simulation and experimental results show that the model is effective·A lumped parameter dynamic scalable segmented model of the proton exchange membrane fuel cell(PEMFC)system is developed to predict the current density,temperature,pressure,and two-phase water flow distributions.Specifically,a single cell is divided into several interconnected segments that are connected according to flow field patterns with physical ports.Every segment is modeled with lumped parameters based on the ideal gas law,mass,and energy conservation principles.Compared to the existing mathematical modeling approaches,the physical modeling approach needs fewer boundary conditions.The main feature of the proposed model is the reconfigurations(different flow field patterns)and the flexibility(both scale up and scale down).Notably,the pattern reconfigurability and the segmentation scalability of the proposed model meet the requirements for both controller design and system analysis for fuel cells.In other words,we propose a unified modeling framework for both control design and system analysis.This modeling framework is applicable to the control problem of general PDE systems including but not limited to fuel cell systems.Simulation results show that the model can simulate both the steady state and dynamic operations well with two-phase water flow distribution.The reconfigurability(3 different cell designs)and the scalability(3×3 and 6×6 segmented models)of the proposed model is demonstrated through the simulations·To address the thermal management problem of fuel cell system cause by the dynamic load scenario,a adaptive thermal control strategy for regulating the stack temperature is proposed based on the water-cooled PEMFC model mentioned before.Firstly,a set of adaptation laws is designed to estimate the unknown parameters related to the gas flow rates in the flow fields.Secondly,considering that the stack temperature should be maintained in a certain range regardless of the dynamical changing current demand,a Barrier Lyapunov function is employed to construct a feedback error of the stack temperature.Particularly,a dynamic inversion tracking methodology is applied to design the non-affine input.A Lyapunov method based analysis demonstrates the stability and convergence of the closed-loop properties.Simulation results are provided to show that the proposed control strategy can satisfy all the control objectives and enhance the control performance compared to the proportional-integral controlled case.·A hybrid power system model is developed based on the fuel cell model mentioned before.A battery model and DC-DC converter model are developed.Each model is connected with the electrical physical ports,physical variables such as current and voltage are equalized automatically.Based on this hybrid power system model,an energy management strategy based on SOC of the battery and other states is proposed.Simulation results show that the proposed energy management strategy can satisfy all the control objectives during dynamic load scenario.