Control Of PEM Fuel Cell Systems For Efficiency And Durability

As one of the critical solutions of the vehicle energy system,hydrogen fuel cell engines have gradually stepped out of the laboratory and achieved small-scale commercial application verifica-tion.However,as the core part of the car,its efficiency and durability need to be further improved.In general,there are two feasible ways to improve the efficiency and service life of the fuel cell system.One is to improve the life-time and efficiency of the stack itself based on the development of new materials,catalysts,and other core components from the perspective of the fuel cell stack.The other is to maintain the fuel cell stack workers through effective integration and control means from the perspective of the fuel cell engine system Under the optimal conditions,the efficiency of the system can be improved based on ensuring the service life.Generally,a complete PEMFC system includes three main subsystems,the air supply subsys-tem,the hydrogen supply subsystem,and the temperature management subsystem.These subsys-tems work together to regulate the temperature,working pressure,and the flow rate of hydrogen and air for the PEMFC stack.In order to further optimize the adjustment of each param eter,first of all,we need to deeply understand the mechanism of fuel cell operation,to establish the rela-tionship between each operating parameter and the performance of the PEMFC stack,and then adjust the parameters to the optimal state by designing an active controller under different working conditions.Based on the above analysis,this paper starts from the mechanism model of the core components and key processes of the fuel cell engine,analyzes the regulation objectives of the op-erating parameters from the perspective of the system,and conducts in-depth research on the air intake,hydrogen supply,and temperature management processes of the fuel cell engine.The main work and contributions of this paper are summarized as follows:·For the air supply system,the control goal is to avoid oxygen starvation and reduce power consumption by tracking an optimal reference oxygen excess ratio.Specifically,an improved control oriented third order model of the air supply system is proposed with model identi-fication of the air compressor.The optimal reference oxygen excess ratio is obtained from experiments to maintain a maximum net power.Based on the air supply system model,a nonlinear controller is designed to track the optimal oxygen excess ratio.Lyapunov based technique is utilized to analyze the stability of the closed-loop system.Effectiveness of the proposed approach is illustrated by experimental results.·For the thermal management system,a model-based decoupling control method is proposed.Firstly,a coupled model of thermal management system is established based on the physi-cal structure of PEMFC engines.Then,in order to realize the simultaneous control of the inlet and outlet cooling water temperature of the PEMFC stack,a decoupling controller is proposed and its closed-loop stability is proved.Finally,based on the actual PEMFC engine platform,the effectiveness,accuracy and reliability of the proposed decoupling controller are tested.The experimental results show that with the proposed decoupling controller,the inlet and outlet temperatures of the PEMFC stack cooling water can be accurately controlled on-line.The temperature error range is less than 0.2? even under the dynamic current load conditions.·For the anode purge strategy,firstly,based on a typical topology of the hydrogen delivery sub-system,the water management of the anode loop is introduced to decouple the performance degradation caused by nitrogen accumulation from water flooding.For the purge strategy,an accurate and fast anode nitrogen concentration observer is established to determine the purge interval.Then,the purge duration is determined by the simulation analysis.Finally,the effectiveness and reliability of the proposed anode purge scheme are verified by testing a new and an aged commercial PEMFC stack.Experimental results show that the proposed anode purge strategy increases the hydrogen utilization rate of the actual PEMFC system to 99%(with considering the hydrogen crossover loss)and greatly prolongs the purge interval based on the real-time estimation of the anode nitrogen concentration.