| As a renewable and clean energy source,hydrogen is considered to be the "ultimate energy source" of the 21 st century.Proton exchange membrane fuel cell(PEMFC)is a kind of power generation device that converts chemical energy in hydrogen fuel into electrical energy,which has the advantages of high power generation efficiency,no pollutant output,high operating stability and low noise compared with burning fossil energy.However,the fuel cell system still has the problems of high parasitic power and slow response.In order to maximize the net power output of the fuel cell system under the premise of safe and stable operation,and to improve its dynamic response performance,it is one of the effective ways to optimize the fuel cell system by analyzing and studying its output characteristics and then reasonably controlling each subsystem.In this paper,a 60 kW proton exchange membrane fuel cell system of a domestic brand is used as the research object,and a simulation model of the proton exchange membrane fuel cell system is established in MATLAB/Simulink environment based on its design parameters;the accuracy of the simulation model is verified by combining simulation and experiment,at the same time the steady-state and dynamic characteristics of the fuel cell system are analyzed;Based on the analysis of the results of the output characteristics,the control objectives of this paper are proposed,and suitable control methods are used to control the inlet gas flow,backpressure gas pressure and stack operating temperature according to the corresponding control requirements to achieve power and dynamic performance optimization,and to verify the effectiveness and robustness of the controller.The main tasks are as follows.(1)A simulation model of the fuel cell system is established by using the mechanistic method combined with data fitting,which mainly includes the reactor voltage output model,proton exchange membrane humidity model,cathode flow channel model,air compressor model,gas supply piping model,intercooler model,humidifier model,exhaust manifold model,backpressure valve model,and reactor operating temperature model,which can be used to investigate the internal components of the fuel cell system under dynamic operating conditions.The dynamic characteristics of material transfer,electrochemical reaction,heat transfer,water transfer,stack voltage output,and net power output of the system can be described.(2)A 100-kW fuel cell system performance test bench was used to test the steady-state and dynamic characteristics of the target fuel cell system,and the accuracy of the simulation model was verified by comparing the steady-state output and polarization curves of the system under different operating conditions.Through simulation analysis,the effects of stack operating temperature,proton exchange membrane humidity and cathode gas pressure on the three polarization phenomena and stack voltage output were explored.At the same time the effects of air compressor control voltage and backpressure valve opening on the operating parameters of the air supply system and the net power output of the system were investigated,and finally,the effects of cooling water flow on the operating temperature of the fuel cell were analyzed.It is concluded that the net power output of the system is the result of the game between the power output of the reactor and the parasitic power of the auxiliary components of the system,so there are optimal control parameters to maximize the net power output of the fuel cell system under different operating conditions.(3)According to the simulation results of the output characteristics of the system under dynamic conditions,the control following objective of maximizing the net power output is derived in this paper.The power consumption and inertia of the air compressor of the air supply system are the main factors affecting the net power and dynamic response characteristics of the fuel cell system.In order to facilitate the design of the controller,the simulation model is downscaled to a sixth-order air supply control model based on reasonable assumptions and simplifications after the analysis of air supply control requirements in this paper,and the accuracy of the control model is verified.(4)Based on the study of the effect of fuel cell operating temperature on performance output and operating stability,a PID control algorithm is used to control the cooling water flow rate to stabilize the stack temperature at the desired value.For the problem of coupling the inlet air flow and gas pressure in the air supply system,a feedback linearization controller and a sliding mode controller are used to control the air compressor and the backpressure valve to achieve the decoupling control of the inlet air flow and pressure,and the control effect and robustness of the controller are verified by simulation.Both controllers have better steady-state following effect and can achieve the purpose of optimizing the net power output of the system,but the feedback linearized control has smaller overshoot and faster regulation time,which can improve the dynamic response characteristics of the system and the overall control effect is better. |
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