Research On Coordinated Control Strategy Of PEMFC Air Supply System For Rapid Response Demand

In recent years,the impact of the environmental pollution and the energy crisis has become increasingly serious.Proton exchange membrane fuel cells have become a research hotspot in automotive technology because of their low emissions,non-polluting and high energy conversion efficiency.The development of new energy vehicles represented by fuel cell electric vehicles has further promoted the research by government and companies.The output current changes frequently when the car travels,so proton exchange membrane fuel cell(PEMFC)system need to have a stable and rapid response.As an important part of the fuel cell system,PEMFC air supply system has a direct impact on the response of the output current.In this thesis,the characteristics of its main system components were studied.Combined with mechanism modeling and experimental modeling methods,PEMFC air supply system was modeled and simulated by doing research on its main system components.The simulation models were built to analyze its steady and dynamic characteristics.A feedback linearization control strategy was developed for the system characteristics.The air compressor and the back pressure valve were coordinatedly controlled to decouple the air mass flow and pressure to improve the dynamic performance of the system.The thesis first studied the current trend of PEMFC air supply system by accessing domestic and foreign literatures.While investigating fuel cell vehicle products,the thesis consulted the dynamic model of PEMFC air supply system,system control methods and experimental methods at home and abroad.Based on the steady-state characteristics,the working principle and structural composition of the fuel cell were analyzed.The three losses of the output voltage were analyzed.The PEMFC output voltage model was built.Based on the steady-state model,the steady-state effects of the oxygen excess ratio and the inlet pressure of the air supply system on the output voltage were analyzed.The model was simulated and experimentally verified.Based on the mechanism of the PEMFC air supply system,the characteristics of the main components such as air compressor,supply and return manifold,and back pressure valve in the system model were studied,and the air compressor model intake air temperature was corrected according to the thermodynamic principle;the air compressor and fuel cell were measured on the experimental platform,and the semi-mechanism and semi-empirical dynamic model was built by MATLAB/Simulink calculation software.For the air supply system,the dynamic performance indicators were defined and evaluated.The simulation of the system model was carried out under the PID control algorithm.The feasibility of the model was verified by comparison with the experimental results,which laid a foundation for the subsequent application of the control strategy.Based on the above model,the effects of the oxygen excess ratio and the inlet pressure on the dynamics of the system were analyzed.Aiming at the characteristics of nonlinearity and coupling,the feedback linearization method was proposed to control it.Theoretically,a system-based control algorithm was established to convert the nonlinear model into a linear model.At the same time,the air compressor and the back pressure valve were coordinated to decouple the intake flow rate and pressure to achieve a good adjustment of the dynamic performance index during the dynamic response process,which made the model control more stable and more responsive.By comparing with the simulation results under PID control,the fast response control of the feedback linearization to the system was verified.