| With the increasingly serious energy crisis and environment pollution problems,the development and utilization of efficient and clean renewable energy has become the focus of the world,as an advanced clean energy technology,fuel cell technology has a hopeful prospect.Among them,Proton Exchange Membrane Fuel Cell(PEMFC)is successfully used in the fileds of transportation,protable power,distributed power station,aerospace and submarine with its low operating temperature,high power density,fast start-up characteristics and high generation efficiency.This dissertation is mainly focus on the modeling of fuel delivery system(FDS)with nitrogen accumulation,FDS control problems in the condition of uncertainty and nitrogen accumulation,study of observer for PEMFC system,optimization control of PEMFC air system based on observer and research on low frequency ripple mitigation of two-stage fuel cell generation system.The main research results are as follows:(1)When the hydrogen sub-system operates in the circulation exhaust mode,the phenomenon of nitrogen accumulation is analyzed and the model of FDS with nitrogen accumulation in the PEMFC anode is built,the FDS model includes the supply of hydrogen,mixed gas transmission,gas permeation through the membrane,electrochemical reaction of hydrogen,exhaust and circulation of mixed gas.It is the basis of FDS control study;(2)Due to the existence of parameter uncertainties in the fuel cell system,in order to satisfy the boundary of PEMFC output voltage and avoid the extreme phenomenon caused by random parameter boundaries determination,this dissertation analyses the parameter uncertainties on the PEMFC anode side combining the characteristics of PEMFC output voltage,and proposes a method based on Monte Carlo algorithm to renew the boundaries of anode parameters.Meanwhile,with parameter uncertainties on the PEMFC anode side added into the FDS model,the control of nitrogen content in FDS is implemented.Besides,combining with the NPID control and NMIMO control,a NPID+ASOSM robust control method is proposed,which makes the supply manifold pressure and the hydrogen content in the anode flow channel track the change of reference value accurately,the nitrogen in the supply manifold and anode channel maintain under 5%,and the PEMFC output voltage operate in the given boundary.The hydrogen concentration involved in electrochemical reaction of anode can be effectively increased and the generation efficiency of PEMFC can also be improved;(3)On the basis of the control-oriented sixth-order nonlinear dynamic PEMFC air subsystem model,a precise high order sliding mode(HOSM)observer is proposed,which can realize dynamic and real-time estimation of state variables(e.g.air mass in the supply manifold,oxygen mass and nitrogen mass in the cathode side,etc.),as a result,the OER is estimated,it can effectively solve the problem that the key control variable in the air subsystem cannot be obtained by the sensor,and it is beneficial to realize the closed loop control of the air subsystem.Besides,a RT-LAB semi-physical platform is set up,which runs in the hardware-in-the-loop mode,HOSM observer and traditional observer are compared on this platform,and the anti-interference ability and convergence property of HOSM observer are both verified after numerous tests;(4)In order to avoid oxygen starvation and improve the dynamic characteristics of the air subsystem,the estimation result of HOSM observer is used for air subsystem control,this dissertation proposes a feedback control structure TS?SM?STW based on super-twisting sliding mode algorithm to replace the traditional PID control,the Lyapunov function is used to prove the stability of the closed-loop system with sliding mode control.Moreover,in order to improve the dynamic characteristics,the fuzzy feedforward structure Fuzzy?FF is also proposed to replace the classical static feedforward FF.Meanwhile the combined oxygen excess ratio control method TS?SM?STW+Fuzzy?FF is compared with other nonlinear methods,the effectiveness of the proposed control method is verified;(5)The two stage three-phase PEMFC generation system will produce secondorder ripple at the fuel cell side when the three-phase load is unbalanced or under fault state,the generation,propagation mechanism and suppression methods of second-order ripple are derived and analyzed,and a theoretical analysis method of the ripple rejection gain for analyzing the low frequency ripple control capability is proposed.In addition,in order to prevent excessive low-frequency ripple current from damaging the electrode and electrolyte of the stack,realize the mitigation of low frequency ripple and improve the dynamic response performance of the load,this dissertation integrates the advantages and disadvantages of each ripple suppression method,and proposes a CMC+VLN+CFBRC control method,moreover,the effectiveness of the proposed method is verified through a semi-physical platform. |
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