Research On Decoupling And Optimal Control Strategy Of PEMFC Cathode Gas Supply System

As a clean and efficient hydrogen energy technology,proton exchange membrane fuel cell(PEMFC)is one of the solutions to achieve deep decarburization in transportation and other fields.In order to further develop and apply PEMFC,the optimization of its system-level energy consumption and the improvement of its dynamic response quality are yet to be studied in more depth.The cathode gas supply system is in charge of providing an appropriate amount of oxygen to the electrochemical reaction taking place in the stack.Among the many parameters of the cathode gas supply system,the oxygen excess ratio(OER)and cathode pressure have a significant effect on the performance of PEMFC.This paper proposes a cathode gas supply system control strategy that can effectively improve the net power of the system and optimize the dynamic response performance,focusing on the control problem of OER and cathode pressure.The specific research contents are summarized as follows:(1)Based on the working principle of PEMFC and the research status of cathode gas supply system modeling,the cathode gas supply system model and stack model are established by combining mechanism modeling method and empirical modeling method.According to the working characteristics of the auxiliary components in the cathode gas supply system,the mathematical models of air compressor,gas supply manifold,air cooler,humidifier and return manifold are established.In order to study the influence of various parameters on the performance of PEMFC system during operation,the stack model is further established.The stack model includes the output voltage model,the gas component dynamic model in the cathode and anode flow field and the membrane hydration model.The external characteristics of the model are verified and analyzed by simulation experiments.(2)Based on reasonable assumptions,the established complex model is simplified to a control-oriented model,and the operating characteristics of the cathode gas supply system are analyzed through this model.In order to improve the working performance of PEMFC system,the experimental results show that: firstly,the rapid and accurate response of air quality flow should be guaranteed,which can effectively avoid or slow down the phenomenon of gas shortage and oxygen excess;in the process of dynamic adjustment,it is necessary to suppress the overshoot of flow and pressure,otherwise it may lead to air compressor surge and reduce system efficiency;in order to avoid damage to the proton exchange membrane,the cathode pressure under steady state should be controlled within 2.5 bar;the coupling between flow control and pressure control further increases the control difficulty.(3)Aiming at the coupling problem of flow control and pressure control,a decoupling controller based on feedback linearization and sliding mode control is designed.The control target is determined according to the influence of OER and cathode pressure on the performance of PEMFC system.Firstly,the cathode gas supply system model is decoupled by feedback linearization method.Based on the linearization model,a sliding mode controller is designed to reduce the dependence of feedback linearization control on the nominal model and improve the robustness of the control system.A series of simulation experiments show that the decoupling controller has good transient performance and robustness.(4)The corresponding control scheme is designed to solve the problems of oxygen starvation,oxygen saturation and air compressor surge in the dynamic regulation process of PEMFC system under large load change.A load regulator is designed based on the interior point method,which can constrain the excess oxygen ratio within the set range by limiting the change of load current.An anti-surge controller based on fuzzy logic is designed,which can adjust the system control quantity in time to prevent surge when the working point exceeds the control line.The effectiveness of the proposed controller is verified by comparative experiments.The proposed controller can ensure the performance of the fuel cell under extreme conditions and provide a more stable output for the load.